Mixed-species versus monocultures in plantation forestry: Development, benefits, ecosystem services and perspectives for the future

'How to adapt forests?'-Exploring the role of leaf trait diversity for long-term forest biomass under new climate normals

Forests, critical components of global ecosystems, face unprecedented challenges due to climate change. This study investigates the influence of functional diversity-as a component of biodiversity-to enhance long-term biomass of European forests in the context of changing climatic conditions. Using the next-generation flexible trait-based vegetation model, LPJmL-FIT, we explored the impact of functional diversity on long-term forest biomass under three different climate change scenarios (video abstract: https://www.pik-potsdam.de/~billing/video/2023/video_abstract_billing_et_al_LPJmLFIT.mp4). Four model set-ups were tested with varying degrees of functional diversity and best-suited functional traits. Our results show that functional diversity positively influences long-term forest biomass, particularly when climate warming is low (RCP2.6). Under these conditions, high-diversity simulations led to an approximately 18.2% increase in biomass compared to low-diversity experiments. However, as climate change intensity increased, the benefits of functional diversity diminished (RCP8.5). A Bayesian multilevel analysis revealed that both full leaf trait diversity and diversity of plant functional types contributed significantly to biomass enhancement under low warming scenarios in our model simulations. Under strong climate change, the presence of a mixture of different functional groups (e.g. summergreen and evergreen broad-leaved trees) was found more beneficial than the diversity of leaf traits within a functional group (e.g. broad-leaved summergreen trees). Ultimately, this research challenges the notion that planting only the most productive and climate-suited trees guarantees the highest future biomass and carbon sequestration. We underscore the importance of high functional diversity and the potential benefits of fostering a mixture of tree functional types to enhance long-term forest biomass in the face of climate change.

Leaf nutrient traits of planted forests demonstrate a heightened sensitivity to environmental changes compared to natural forests

Leaf nutrient content (nitrogen, phosphorus) and their stoichiometric ratio (N/P) as key functional traits can reflect plant survival strategies and predict ecosystem productivity responses to environmental changes. Previous research on leaf nutrient traits has primarily focused on the species level with limited spatial scale, making it challenging to quantify the variability and influencing factors of forest leaf nutrient traits on a macro scale. This study, based on field surveys and literature collected from 2005 to 2020 on 384 planted forests and 541 natural forests in China, investigates the differences in leaf nutrient traits between forest types (planted forests, natural forests) and their driving factors. Results show that leaf nutrient traits (leaf nitrogen content (LN), leaf phosphorus content (LP), and leaf N/P ratio) of planted forests are significantly higher than those of natural forests (P< 0.05). The impact of climatic and soil factors on the variability of leaf nutrient traits in planted forests is greater than that in natural forests. With increasing forest age, natural forests significantly increase in leaf nitrogen and phosphorus content, with a significant decrease in N/P ratio (P< 0.05). Climatic factors are key environmental factors dominating the spatial variability of leaf nutrient traits. They not only directly affect leaf nutrient traits of planted and natural forest communities but also indirectly through regulation of soil nutrients and stand factors, with their direct effects being more significant than their indirect effects.

The influence of stand composition and season on canopy structure and understory light environment in different subtropical montane Pinus massoniana forests

Canopy structure and understory light have important effects on forest productivity and the growth and distribution of the understory. However, the effects of stand composition and season on canopy structure and understory light environment (ULE) in the subtropical mountain Pinus massoniana forest system are poorly understood. In this study, the natural secondary P. massoniana-Castanopsis eyrei mixed forest (MF) and P. massoniana plantation forest (PF) were investigated. The study utilized Gap Light Analyzer 2.0 software to process photographs, extracting two key canopy parameters, canopy openness (CO) and leaf area index (LAI). Additionally, data on the transmitted direct (Tdir), diffuse (Tdif), and total (Ttot) radiation in the light environment were obtained. Seasonal variations in canopy structure, the ULE, and spatial heterogeneity were analyzed in the two P. massoniana forest stands. The results showed highly significant (P < 0.01) differences in canopy structure and ULE indices among different P. massoniana forest types and seasons. CO and ULE indices (Tdir, Tdif, and Ttot) were significantly lower in the MF than in the PF, while LAI was notably higher in the MF than in the PF. CO was lower in summer than in winter, and both LAI and ULE indices were markedly higher in summer than in winter. In addition, canopy structure and ULE indices varied significantly among different types of P. massoniana stands. The LAI heterogeneity was lower in the MF than in the PF, and Tdir heterogeneity was higher in summer than in winter. Meanwhile, canopy structure and ULE indices were predominantly influenced by structural factors, with spatial correlations at the 10 m scale. Our results revealed that forest type and season were important factors affecting canopy structure, ULE characteristics, and heterogeneity of P. massoniana forests in subtropical mountains.

Mixing with native broadleaf trees modified soil microbial communities of Cunninghamia lanceolata monocultures in South China

Mixing with different broadleaf trees into the monocultures of Cunninghamia lanceolata is widely adopted as an efficient transformation of the pure C. lanceolata forest. However, it is unclear how native broad-leaved trees influence the belowground ecological environment of the pure C. lanceolata culture plantation in nutrient-poor soil of South China. Herein, we aimed to investigate how a long-time mixing with native broadleaf trees shape soil microbial community of the pure C. lanceolata forest across different soil depth (0-20 cm and 20-40 cm) and to clarify relationships between the modified soil microbial community and those affected soil chemical properties. Using high-throughput sequencing technology, microbial compositions from the mixed C. lanceolata-broadleaf forest and the pure C. lanceolata forest were analyzed. Network analysis was utilized to investigate correlations among microorganisms, and network robustness was assessed by calculating network natural connectivity. Results demonstrated that the content of soil microbial biomass carbon and nitrogen, total phosphorus and pH in mixed forest stand were significantly higher than those in pure forest stand, except for available phosphorus in topsoil (0-20 cm). Simultaneously, the mixed C. lanceolata-broadleaf forest has a more homogeneous bacterial and fungal communities across different soil depth compared with the pure C. lanceolata forest, wherein the mixed forest recruited more diverse bacterial community in subsoil (20-40 cm) and reduced the diversity of fungal community in topsoil. Meanwhile, the mixed forest showed higher bacterial community stability while the pure forest showed higher fungal community stability. Moreover, bacterial communities showed significant correlations with various soil chemical indicators, whereas fungal communities exhibited correlations with only TP and pH. Therefore, the mixed C. lanceolata-broadleaf forest rely on their recruiting bacterial community to enhance and maintain the higher nutrient status of soil while the pure C. lanceolata forest rely on some specific fungi to satisfy their phosphorus requirement for survive strategy.

Nitrogen addition affected the root competition in Cunninghamia lanceolata-Phoebe chekiangensis mixed plantation

Little is known about below-ground competition in mixed-species plantations under increasing nitrogen (N) deposition. This study aims to determine the effects of N addition on root competition in coniferous and broad-leaved species mixed plantations. A pot experiment was conducted using the coniferous species Cunninghamia lanceolata and the broad-leaved species Phoebe chekiangensis planted in mixed plantations with different competition intensities under N addition (0 or 45 kg N ha-1 yr-1). Biomass allocation, root morphology, root growth level, and competitive ability were determined after five months of treatment. Our findings indicated that root interactions in mixed plantations did not influence biomass allocation in either C. lanceolata or P. chekiangensis but promoted growth in C. lanceolata when no N was added. However, N addition decreased biomass accumulation in both species in the mixed plantation and had a negative effect on the root growth of C. lanceolata due to intensified competition. Addition of N increased the relative importance of root predatory competition in P. chekiangensis, and increased the allelopathic competitive advantage in C. lanceolata. This suggests that N addition causes a shift in the root competitive strategy from tolerance to competition. Overall, these findings highlight the significant impact that the addition of N can have on plant interactions in mixed plantations. Our results provide implications for the mechanisms of root competition in response to increasing atmospheric N deposition in mixed plantations.

Two Novel Plant-Growth-Promoting Lelliottia amnigena Isolates from Euphorbia prostrata Aiton Enhance the Overall Productivity of Wheat and Tomato

Euphorbiaceae is a highly diverse family of plants ranging from trees to ground-dwelling minute plants. Many of these have multi-faceted attributes like ornamental, medicinal, industrial, and food-relevant values. In addition, they have been regarded as keystone resources for investigating plant-specific resilience mechanisms that grant them the dexterity to withstand harsh climates. In the present study, we isolated two co-culturable bacterial endophytes, EP1-AS and EP1-BM, from the stem internodal segments of the prostate spurge, Euphorbia prostrata, a plant member of the succulent family Euphorbiaceae. We characterized them using morphological, biochemical, and molecular techniques which revealed them as novel strains of Enterobacteriaceae, Lelliotia amnigena. Both the isolates significantly were qualified during the assaying of their plant growth promotion potentials. BM formed fast-growing swarms while AS showed growth as rounded colonies over nutrient agar. We validated the PGP effects of AS and BM isolates through in vitro and ex vitro seed-priming treatments with wheat and tomato, both of which resulted in significantly enhanced seed germination and morphometric and physiological plant growth profiles. In extended field trials, both AS and BM could remarkably also exhibit productive yields in wheat grain and tomato fruit harvests. This is probably the first-ever study in the context of PGPB endophytes in Euphorbia prostrata. We discuss our results in the context of promising agribiotechnology translations of the endophyte community associated with the otherwise neglected ground-dwelling spurges of Euphorbiaceae.

Sharp decline in future productivity of tropical reforestation above 29°C mean annual temperature

Tropical reforestation is among the most powerful tools for carbon sequestration. Yet, climate change impacts on productivity are often not accounted for when estimating its mitigation potential. Using the process-based forest growth model 3-PGmix, we analyzed future productivity of tropical reforestation in Central America. Around 29°C mean annual temperature, productivity sharply and consistently declined (-11% per 1°C of warming) across all tropical lowland climate zones and five tree species spanning a wide range of ecological characteristics. Under a high-emission scenario (SSP3-7.0), productivity of dry tropical reforestation nearly halved and tropical moist and rain forest sites showed moderate losses around 10% by the end of the century. Under SSP2-4.5, tropical moist and rain forest sites were resilient and tropical dry forest sites showed moderate losses (-17%). Increased vapor pressure deficit, caused by increasing temperatures, was the main driver of growth decline. Thus, to continue following high-emission pathways could reduce the effectiveness of reforestation as climate action tool.

Integrated metagenomics and metabolomics analysis reveals changes in the microbiome and metabolites in the rhizosphere soil of Fritillaria unibracteata

Fritillaria unibracteata (FU) is a renowned herb in China that requires strict growth conditions in its cultivation process. During this process, the soil microorganisms and their metabolites may directly affect the growth and development of FU, for example, the pathogen infection and sipeimine production. However, few systematic studies have reported the changes in the microbiome and metabolites during FU cultivation thus far. In this work, we simultaneously used metagenomics and metabolomics technology to monitor the changes in microbial communities and metabolites in the rhizosphere of FU during its cultivation for one, two, and three years. Moreover, the interaction between microorganisms and metabolites was investigated by co-occurrence network analysis. The results showed that the microbial composition between the three cultivation-year groups was significantly different (2020-2022). The dominant genera changed from Pseudomonas and Botrytis in CC1 to Mycolicibacterium and Pseudogymnoascus in CC3. The relative abundances of beneficial microorganisms decreased, while the relative abundances of harmful microorganisms showed an increasing trend. The metabolomics results showed that significant changes of the of metabolite composition were observed in the rhizosphere soil, and the relative abundances of some beneficial metabolites showed a decreasing trend. In this study, we discussed the changes in the microbiome and metabolites during the three-year cultivation of FU and revealed the relationship between microorganisms and metabolites. This work provides a reference for the efficient and sustainable cultivation of FU.

Transitional forestry in New Zealand: re-evaluating the design and management of forest systems through the lens of forest purpose

Forestry management worldwide has become increasingly effective at obtaining high timber yields from productive forests. In New Zealand, a focus on improving an increasingly successful and largely Pinus radiata plantation forestry model over the last 150 years has resulted in some of the most productive timber forests in the temperate zone. In contrast to this success, the full range of forested landscapes across New Zealand, including native forests, are impacted by an array of pressures from introduced pests, diseases, and a changing climate, presenting a collective risk of losses in biological, social and economic value. As the national government policies incentivise reforestation and afforestation, the social acceptability of some forms of newly planted forests is also being challenged. Here, we review relevant literature in the area of integrated forest landscape management to optimise forests as nature-based solutions, presenting 'transitional forestry' as a model design and management paradigm appropriate to a range of forest types, where forest purpose is placed at the heart of decision making. We use New Zealand as a case study region, describing how this purpose-led transitional forestry model can benefit a cross section of forest types, from industrialised forest plantations to dedicated conservation forests and a range of multiple-purpose forests in between. Transitional forestry is an ongoing multi-decade process of change from current 'business-as-usual' forest management to future systems of forest management, embedded across a continuum of forest types. This holistic framework incorporates elements to enhance efficiencies of timber production, improve overall forest landscape resilience, and reduce some potential negative environmental impacts of commercial plantation forestry, while allowing the ecosystem functioning of commercial and non-commercial forests to be maximised, with increased public and biodiversity conservation value. Implementation of transitional forestry addresses tensions that arise between meeting climate mitigation targets and improving biodiversity criteria through afforestation, alongside increasing demand for forest biomass feedstocks to meet the demands of near-term bioenergy and bioeconomy goals. As ambitious government international targets are set for reforestation and afforestation using both native and exotic species, there is an increasing opportunity to make such transitions via integrated thinking that optimises forest values across a continuum of forest types, while embracing the diversity of ways in which such targets can be reached.

Climatic drought impacts on key ecosystem services of a low mountain region in Germany

The frequency of extreme weather events has increased in the latest years in Europe. The recent consecutive droughts caused severe damage in many sectors and underlined the demand for adaptation. There is a need for a better understanding of the response of ecosystems to climate change and the consequences for key ecosystem services, such as water supply and carbon sequestration, at a local and regional scale. This paper aims to support decision-making for climate adaptation in a low-mountainous region of central Germany. We analysed the temperature and precipitation trends and drought conditions. The response of two key services (surface water provision and carbon sequestration) to droughts is estimated using an ecosystem service model. The spatially averaged water yield, net ecosystem productivity (NEP), and soil moisture are assessed and compared for the five worst droughts with long-term averages to identify the vulnerable areas and ecosystems. The temperature increased on seasonal and annual scales, while precipitation decreased in some areas in summer and increased in winter and annually. The standardised precipitation-evapotranspiration index (SPEI) showed worsening drought conditions, especially after the late 1980s. Droughts caused a reduction of water yield by 54%, NEP by 18%, and upper zone soil moisture by 13%. The impacts varied spatially, with the central region being worst affected, while the southern part was relatively more resilient. Adaptation is urgently needed to reduce drought risks and enhance climate resilience. Adaptive measures can include amending crop rotations, introducing more drought-tolerant varieties, upgrading agriculture and food industry technology, increasing mixed forests, and reducing non-native tree species.

Quantifying the Effect Size of Management Actions on Aboveground Carbon Stocks in Forest Plantations

Purpose of the Review

Improved forest management is a promising avenue for climate change mitigation. However, we lack synthetic understanding of how different management actions impact aboveground carbon stocks, particularly at scales relevant for designing and implementing forest-based climate solutions. Here, we quantitatively assess and review the impacts of three common practices-application of inorganic NPK fertilizer, interplanting with N-fixing species, and thinning-on aboveground carbon stocks in plantation forests.

Recent Findings

Site-level empirical studies show both positive and negative effects of inorganic fertilization, interplanting, and thinning on aboveground carbon stocks in plantation forests. Recent findings and the results of our analysis suggest that these effects are heavily moderated by factors such as species selection, precipitation, time since practice, soil moisture regime, and previous land use. Interplanting of N-fixing crops initially has no effect on carbon storage in main tree crops, but the effect becomes positive in older stands. Conversely, the application of NPK fertilizers increases aboveground carbon stocks, though the effect lessens with time. Moreover, increases in aboveground carbon stocks may be partially or completely offset by emissions from the application of inorganic fertilizer. Thinning results in a strong reduction of aboveground carbon stocks, though the effect lessens with time.

Summary

Management practices tend to have strong directional effects on aboveground carbon stocks in plantation forests but are moderated by site-specific management, climatic, and edaphic factors. The effect sizes quantified in our meta-analysis can serve as benchmarks for the design and scoping of improved forest management projects as forest-based climate solutions. Overall, management actions can enhance the climate mitigation potential of plantation forests, if performed with sufficient attention to the nuances of local conditions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40725-023-00182-5.

Sustainability in Wood Products: A New Perspective for Handling Natural Diversity

Wood is a renewable resource with excellent qualities and the potential to become a key element of a future bioeconomy. The increasing environmental awareness and drive to achieve sustainability is leading to a resurgence of research on wood materials. Nevertheless, the global climate changes and associated consequences will soon challenge the wood-value chains in several regions (e.g., central Europe). To cope with these challenges, it is necessary to rethink the current practice of wood sourcing and transformation. The goal of this review is to address the intrinsic natural diversity of wood, from its origin to its technological consequences for the present and future manufacturing of wood products. So far, industrial processes have been optimized to repress the variability of wood properties, enabling more efficient processing and production of reliable products. However, the need to preserve biodiversity and the impact of climate change on forests call for new wood processing techniques and green chemistry protocols for wood modification as enabling factors necessary for managing a more diverse wood provision in the future. This article discusses the past developments that have resulted in the current wood value chains and provides a perspective about how natural variability could be turned into an asset for making truly sustainable wood products. After briefly introducing the chemical and structural complexity of wood, the methods conventionally adopted for industrial homogenization and modification of wood are discussed in relation to their evolution toward increased sustainability. Finally, a perspective is given on technological potentials of machine learning techniques and of novel functional wood materials. Here the main message is that through a combination of sustainable forestry, adherence to green chemistry principles and adapted processes based on machine learning, the wood industry could not only overcome current challenges but also thrive in the near future despite the awaiting challenges.

Rubber expansion and age-class mapping in the state of Tripura (India) 1990-2021 using multi-year and multi-sensor data

The present study focuses on the spread of rubber monoculture in the state of Tripura during past three decades (1990-2021) in the northeast region of India which is known for its rich biodiversity, shifting cultivation, and extensive forest dynamics. Earth observation (EO) data of seven time periods from Landsat missions (1990, 1995, 2000, 2004, and 2009) and Sentinel-2 (2016 and 2021) were the main source for mapping and were supplemented with MODIS-EVI temporal spectral profiles, GEDI-derived vegetation heights (2019), and Google Earth high-resolution historical images for additional cues to support discrimination, mapping, and accuracy assessment. The methodology for rubber used its unique phenology from spectral-temporal profile and multi-year comparison of patches and their dynamics for age-class mapping. The results indicate that in the state of Tripura (geographic area 1.08 Mha), the area under rubber increased from 0.3% in 1990 to 8.9% of the geographic area in 2021. The overall classification accuracy for the maps created for the years 1990, 1995, 2000, 2004, 2009, 2016, and 2021 was 84.2%, 83.9%, 84.8%, 88.0%, 86.0%, 86.7%, and 89.5%, respectively. New areas under rubber originated from various land cover classes including open forests, shifting cultivation lands, and scrub. Recent expansion has resulted in 84.3% of rubber plantations under the 10-year age class. Implications of this transformation of the natural landscape, biodiversity and biomass, and carbon pool assessment are discussed.

Fifteen essential science advances needed for effective restoration of the world's forest landscapes

There has never been a more pressing and opportune time for science and practice to collaborate towards restoration of the world's forests. Multiple uncertainties remain for achieving successful, long-term forest landscape restoration (FLR). In this article, we use expert knowledge and literature review to identify knowledge gaps that need closing to advance restoration practice, as an introduction to a landmark theme issue on FLR and the UN Decade on Ecosystem Restoration. Aligned with an Adaptive Management Cycle for FLR, we identify 15 essential science advances required to facilitate FLR success for nature and people. They highlight that the greatest science challenges lie in the conceptualization, planning and assessment stages of restoration, which require an evidence base for why, where and how to restore, at realistic scales. FLR and underlying sciences are complex, requiring spatially explicit approaches across disciplines and sectors, considering multiple objectives, drivers and trade-offs critical for decision-making and financing. The developing tropics are a priority region, where scientists must work with stakeholders across the Adaptive Management Cycle. Clearly communicated scientific evidence for action at the outset of restoration planning will enable donors, decision makers and implementers to develop informed objectives, realistic targets and processes for accountability. This article paves the way for 19 further articles in this theme issue, with author contributions from across the world. This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.

Leaf and tree water-use efficiencies of Populus deltoides × P. nigra in mixed forest and agroforestry plantations

In a global context where water will become a scarce resource under temperate latitudes, managing tree plantations with species associations, i.e., forest mixture or agroforestry, could play a major role in optimizing the sustainable use of this resource. Conceptual frameworks in community ecology suggest that, in mixed plantations, environmental resources such as water may be more efficiently used for carbon acquisition and tree growth thanks to niche complementarity among species. To test the hypotheses behind these conceptual frameworks, we estimated water-use efficiency (WUE) for poplar trees grown in a monoculture, in association with alder trees (forest mixture) and in association with clover leys (agroforestry) in an experimental plantation located in northeastern France. Water-use efficiency was estimated (i) at leaf level through gas exchange measurements and analysis of carbon isotope composition, (ii) at wood level through carbon isotope composition and (iii) at tree level with sap flow sensors and growth increment data. We hypothesized that species interactions would increase WUE of poplars in mixtures due to a reduction in competition and/or facilitation effects due to the presence of the N2-fixing species in mixtures. Poplar trees in both mixture types showed higher WUE than those in the monoculture. The differences we found in WUE between the monoculture and the agroforestry treatment were associated to differences in stomatal conductance and light-saturated net CO2 assimilation rate (at the leaf level) and transpiration (at the tree level), while the differences between the monoculture and the forest mixture were more likely due to differences in stomatal conductance at the leaf level and both transpiration and biomass accumulation at the tree level. Moreover, the more WUE was integrated in time (instantaneous gas exchanges < leaf life span < seasonal wood core < whole tree), the more the differences among treatments were marked.

Effects of Tree Composition and Soil Depth on Structure and Functionality of Belowground Microbial Communities in Temperate European Forests

Depending on their tree species composition, forests recruit different soil microbial communities. Likewise, the vertical nutrient gradient along soil profiles impacts these communities and their activities. In forest soils, bacteria and fungi commonly compete, coexist, and interact, which is challenging for understanding the complex mechanisms behind microbial structuring. Using amplicon sequencing, we analyzed bacterial and fungal diversity in relation to forest composition and soil depth. Moreover, employing random forest models, we identified microbial indicator taxa of forest plots composed of either deciduous or evergreen trees, or their mixtures, as well as of three soil depths. We expected that forest composition and soil depth affect bacterial and fungal diversity and community structure differently. Indeed, relative abundances of microbial communities changed more across soil depths than in relation to forest composition. The microbial Shannon diversity was particularly affected by soil depth and by the proportion of evergreen trees. Our results also reflected that bacterial communities are primarily shaped by soil depth, while fungi were influenced by forest tree species composition. An increasing proportion of evergreen trees did not provoke differences in main bacterial metabolic functions, e.g., carbon fixation, degradation, or photosynthesis. However, significant responses related to specialized bacterial metabolisms were detected. Saprotrophic, arbuscular mycorrhizal, and plant pathogenic fungi were related to the proportion of evergreen trees, particularly in topsoil. Prominent microbial indicator taxa in the deciduous forests were characterized to be r-strategists, whereas K-strategists dominated evergreen plots. Considering simultaneously forest composition and soil depth to unravel differences in microbial communities, metabolic pathways and functional guilds have the potential to enlighten mechanisms that maintain forest soil functionality and provide resistance against disturbances.

Effects of Plantation Type and Soil Depth on Microbial Community Structure and Nutrient Cycling Function

Declining soil quality and microecological imbalances were evaluated in larch plantations in this study. One potential solution to this problem is the cultivation of mixed coniferous and broad-leaved plantations. However, it is unclear whether and how soil microbial community structure and nutrient cycling function would be affected by mixed plantations and soil depths. In this study, we used high-throughput sequencing technology to investigate bacterial 16S and fungal ITS regions for comparisons of soil microbial diversity among plantation types (a Larix gmelinii pure plantation, a Fraxinus mandshurica pure plantation, a Larix–Fraxinus mixed plantation within the Larix row, the Fraxinus row, and between the Larix and Fraxinus rows) and soil depths (0–10, 10–20, and 20–40 cm). These data were used to evaluate variations in microbial communities and nutrient cycling function with the determining environmental factors. Our results indicated that bacteria had a stronger spatial dependence than did fungi, while plantation types significantly affected the fungal community. The relative abundance of Gaiellaceae, as well as bacterial ligninolysis, nitrate ammonification, and nitrite ammonification functions significantly increased with increasing soil depth. Compared with other plantations, the relative abundance of Inocybaceae was significantly higher in the Larix plantation. Distance-based redundancy analysis (db-RDA) showed that Gaiellaceae and Inocybaceae abundances were positively correlated with ammonium nitrogen content, available phosphorus content, and phosphatase activity. Our findings indicate that variations in soil available phosphorus are closely related to the relative abundances of Gaiellaceae at different soil depths and Inocybaceae in different plantation types. Mixed plantations might change the availability of soil phosphorus by controlling the relative abundance of Inocybaceae. We recommend that fungal community changes be considered in the sustainable management of mixed plantations.

Diversity regained: Precautionary approaches to COVID-19 as a phenomenon of the total environment

As COVID-19 emerged as a phenomenon of the total environment, and despite the intertwined and complex relationships that make humanity an organic part of the Bio- and Geospheres, the majority of our responses to it have been corrective in character, with few or no consideration for unintended consequences which bring about further vulnerability to unanticipated global events. Tackling COVID-19 entails a systemic and precautionary approach to human-nature relations, which we frame as regaining diversity in the Geo-, Bio-, and Anthropospheres. Its implementation requires nothing short of an overhaul in the way we interact with and build knowledge from natural and social environments. Hence, we discuss the urgency of shifting from current to precautionary approaches to COVID-19 and look, through the lens of diversity, at the anticipated benefits in four systems crucially affecting and affected by the pandemic: health, land, knowledge and innovation. Our reflections offer a glimpse of the sort of changes needed, from pursuing planetary health and creating more harmonious forms of land use to providing a multi-level platform for other ways of knowing/understanding and turning innovation into a source of global public goods. These exemplary initiatives introduce and solidify systemic thinking in policymaking and move priorities from reaction-based strategies to precautionary frameworks.

Does Agroforestry Correlate with the Sustainability of Agricultural Landscapes? Evidence from China’s Nationally Important Agricultural Heritage Systems

Compared with industrial monoculture, agroforestry has been perceived as a more sustainable approach to landscape management that provides various landscape-specific benefits. However, little is known about agroforestry’s influence on the comprehensive sustainability of agricultural landscapes. This study focused on the importance of agroforestry and its influence on landscape sustainability, using 118 China National Important Agricultural Heritage Systems (China-NIAHS) as cases. In each China-NIAHS, we evaluated the importance of agroforestry and the landscape’s comprehensive sustainability and explored their correlation. The findings indicate that agroforestry is important in most China-NIAHS. Agroforestry’s importance is strongly correlated with most sustainability indicators, including biodiversity, income diversity, resource utilization, hydrogeological preservation, and water regulation. Based on the findings, we discuss the role of agroforestry in promoting sustainability and provide suggestions for sustainable management and policymaking for agricultural landscapes on a national scale.

In Situ Synthesis of Fe3O4 Nanoparticles and Wood Composite Properties of Three Tropical Species

Magnetic wood is a composite material that achieves harmony between both woody and magnetic functions through the active addition of magnetic characteristics to the wood itself. In addition to showing magnetic characteristics, magnetic wood offers low specific gravity, humidity control and acoustic absorption ability. It has potential for broad applications in the fields of electromagnetic wave absorption, electromagnetic interference shielding, furniture, etc. This work reports on the synthesis of Fe3O4 nanoparticles (NPs) in wood from three tropical species (Pinus oocarpa, Vochysia ferruginea and Vochysia guatemalensis) using a solution of iron (III) hexahydrate and iron (II) chloride tetrahydrate with a molar ratio of 1.6:1 at a concentration of 1.2 mol/L ferric chlorate under 700 kPa pressure for 2 h. Afterward, the wood samples were impregnated with an ammonia solution with three different immersion times. The treated wood (wood composites) was evaluated for the weight gain percentage (WPG), density, ash content and Fe3O4 content by the Fourier transform infrared spectroscopy (FTIR) spectrum, X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). The results show that the species P. oocarpa had the lowest values of WPG, and its density decreased in relation to the untreated wood, with lower ash and Fe3O4 NP content. The XRD and some FTIR signals associated with changes in the wood component showed small differences from the untreated wood. Fe3O4 NPs presented nanoparticles with the smallest diameter of (approx. 7.3 to 8.5 nm), and its saturation magnetization (Ms) parameters were the lowest. On the other hand, V. guatemalensis was the species with the best Ms values, but the wood composite had the lowest density. In relation to the different immersion times, the magnetic properties were not statistically affected. Finally, the magnetization values of the studied species were lower than those of the pure Fe3O4 nanoparticles, since the species only have a certain amount of these nanoparticles (NPs), and this was reflected proportionally in the magnetization of saturation.

Woody Species Diversity, Community Structure, and Regeneration Capacity in Central Ethiopian Urban Forest Patches

Land cover change in Addis Ababa, Ethiopia’s capital, is driven by recurring drought and the economic problems of society-initiated afforestation. The goal of this study was to learn about the state of woody species regeneration in Yeka’s urban forest patches. Thirty plots (20 m × 20 m in size) were sampled to identify plants for this purpose. All wooden trees with a height greater than 1.3 m in each plot were identified, enumerated, and their diameter were measured. Acacia decurrens was determined to be the predominant species, with an importance value index (IVI) of 161.09, followed by Acacia melanoxlon (IVI = 44.69). The bootstrapping PERMANOVA test was used to show how the species in the community overlapped. The result reveals that dissimilarity is low (p > 0.05), which is supported by the assumption of multivariate dispersion homogeneity. The area’s generalized linear model (GLM) showed all species statistically significant for characteristics associated with closure year and presence of mature trees and the entire closure year. Two of the twenty tree species, i.e., Acacia decurrens and Acacia melanoxylon were found in nearly equal numbers in all three growth stages as well as having strong regenerating potential. The rapid expansion of exotic Acacia spp. necessitates careful attention to their regeneration. To reinforce and improve ecosystem services, conservation and restoration efforts should encourage the regeneration of native plant species.

Ecological Stoichiometry in Pinus massoniana L. Plantation: Increasing Nutrient Limitation in a 48-Year Chronosequence

Stoichiometric ratios of carbon (C), nitrogen (N), and phosphorus (P) are considered indicators of nutrient status and ultimate ecosystem health. A detailed investigation of these elements in the leaves, branches, forest layer vegetation and soil, depending on stand age, was carried out. We investigated the effects of stand age (9-, 18-, 28-, and 48-year) on the aboveground plant parts (leaf, branch, herb, shrub, plant litter) and belowground pools (soil, roots) of P. massoniana plantations. The CNP stoichiometry of trees was affected by stand age. Mean N content in the aboveground parts in the nine-yr stand was greater than the other stands (18-, 28-, 48-yr), which decreased with increasing stand age. As stands aged, the nutrient demands of the plantations increased as well as their N:P ratios in soil. C content in the soil ranged from 30 to 105, the total N was 0.06 to 1.6, and the total P content ranged from 3.3–6.4 g kg−1. Soil C, N and P contents were greatly influenced by both stand age and soil depth, because surface soil sequester C and N more actively compared to deeper horizons, and more nutrients are released to the topsoil by the plant litter layer. Similarly, the ratios of other layers had a similar pattern as CNP because more nutrients were taken up by the plantations, decreasing nutrient supply in the deeper soil horizons. The green leaves N:P ratios (16) indicate limited growth of P. massoniana, as the range for global nutrient limitation for woody plants oscillated between 14–16, indicating N and P limitation. Young stands were observed to have greater P content and P resorption efficiency (56.9%–67.3%), with lower C:P and N:P ratios (704.4; 14.8). We conclude that with stand development, the nutrient demands of the plantations also increase, and soil N:P stoichiometry shows that these improve soil quality.

The Functional Structure of Tropical Plant Communities and Soil Properties Enhance Ecosystem Functioning and Multifunctionality in Different Ecosystems in Ghana

Plant functional traits are useful in tracking changes in the environment, and play an important role in determining ecosystem functioning. The relationship between plant functional traits and ecosystem functioning remains unclear, although there is growing evidence on this relationship. In this study, we tested whether the functional structure of vegetation has significant effects on the provision of ecosystem services. We analysed plant trait composition (specific leaf area, leaf carbon and nitrogen ratio, isotopic carbon fraction, stem dry matter content, seed mass and plant height), soil parameters (nutrients, pH, bulk density) and proxies of ecosystem services (carbon stock, decomposition rate, invertebrate activity) in twenty-four plots in three tropical ecosystems (active restored and natural forests and an agroforestry system) in Ghana. For each plot, we measured above-ground biomass, decomposition rates of leaves and invertebrate activity as proxies for the provision of ecosystem services to evaluate (i) whether there were differences in functional composition and soil properties and their magnitude between ecosystem types. We further aimed to (ii) determine whether the functional structure and/or soil parameters drove ecosystem functions and multifunctionality in the three ecosystem types. For functional composition, both the leaf economic spectrum and seed mass dimension clearly separated the ecosystem types. The natural forest was more dominated by acquisitive plants than the other two ecosystem types, while the non-natural forests (agroforest and restored forest) showed higher variation in the functional space. The natural forest had higher values of soil properties than the restored forest and the agroforestry system, with the differences between the restored and agroforestry systems driven by bulk density. Levels of ecosystem service proxies and multifunctionality were positively related to the functional richness of forest plots and were mainly explained by the differences in site conditions. Our study demonstrated the effects of functional forest structure on ecosystem services in different forest ecosystems located in the semi-deciduous forest zone of Ghana.

Afforestation of Transformed Savanna and Resulting Land Cover Change: A Case Study of Zaria (Nigeria)

This paper presents the effects of actions aiming at tree planting, and thus protection of the land belonging to Ahmadu Bello University (ABU) in Zaria (Nigeria) from erosion. This area is located within the northern limits of the Guinea savanna belt, which has been considerably transformed primarily for agricultural purposes. For years this area has been subjected to the destructive surface and gully erosion processes, which were documented both by field work and the analysis of high-resolution images presented by Google Earth. Land erosion leads to the silting of an impounding reservoir (Kubanni)—the primary water source for the university campus and the basis for its existence. Since 2000, the university has been actively involved in tree-planting efforts in the campus vicinity, executed mainly through the establishment of small plantations ranging in area from approximately 1 ha to 56 ha. Today, these measures have brought tangible effects such as increment of tree-planted expanses, as evidenced in the multitemporal analysis of the Landsat 7 ETM+ and Landsat 8 OLI satellite images. The increasing planted area protects both the soil and the reservoir. A marked stand increment (almost doubled) has been recorded, which is evident from the satellite imageries, and is presented on the land-use map produced with GIS technique for this project.

Response of Poplar Leaf Transcriptome to Changed Management and Environmental Conditions in Pure and Mixed with Black Locust Stands

Mixed cropping in short rotation coppice can be an alternative to monocultures. To design optimized mixtures, field trials are needed. Poplar, as an economically important and fast-growing species, and black locust, as a nitrogen-fixing species, are promising candidates for such studies. RNA sequencing (RNA-seq) was used to monitor effects of mixed and pure cultivations on the gene expression of poplar along with growth measurements during 2017 and 2018. Both biomass production and leaf transcriptomes revealed a strong competition pressure of black locust and the abiotic environment on poplar trees. Gene expression differed between the two study sites and pure and mixed stands. Shading effects from black locust caused the downregulation of photosynthesis and upregulation of shade avoidance genes in mixed stands in 2017. As a result of higher light availability after cutting black locust, plant organ development genes were upregulated in mixed stands in 2018. Drought conditions during the summer of 2018 and competition for water between the two species caused the upregulation of drought stress response genes in mixed stands and at the unfavorable growing site. Further investigations are required to discover the mechanisms of interspecific competition and to develop stand designs, which could increase the success and productivity of mixed plantations.

Species Mixing Proportion and Aridity Influence in the Height–Diameter Relationship for Different Species Mixtures in Mediterranean Forests

Estimating tree height is essential for modelling and managing both pure and mixed forest stands. Although height–diameter (H–D) relationships have been traditionally fitted for pure stands, attention must be paid when analyzing this relationship behavior in stands composed of more than one species. The present context of global change makes also necessary to analyze how this relationship is influenced by climate conditions. This study tends to cope these gaps, by fitting new H–D models for 13 different Mediterranean species in mixed forest stands under different mixing proportions along an aridity gradient in Spain. Using Spanish National Forest Inventory data, a total of 14 height–diameter equations were initially fitted in order to select the best base models for each pair species-mixture. Then, the best models were expanded including species proportion by area (mi) and the De Martonne Aridity Index (M). A general trend was found for coniferous species, with taller trees for the same diameter size in pure than in mixed stands, being this trend inverse for broadleaved species. Regarding aridity influence on H–D relationships, humid conditions seem to beneficiate tree height for almost all the analyzed species and species mixtures. These results may have a relevant importance for Mediterranean coppice stands, suggesting that introducing conifers in broadleaves forests could enhance height for coppice species. However, this practice only should be carried out in places with a low probability of drought. Models presented in our study can be used to predict height both in different pure and mixed forests at different spatio-temporal scales to take better sustainable management decisions under future climate change scenarios.

Degradation of White Birch Shelterbelts by the Attack of White-Spotted Longicorn Beetles in Central Hokkaido, Northern Japan

A widespread decline of white birch (Betula platyphylla var. japonica) shelterbelts was observed in central Hokkaido, Japan. Many exit holes bored by white-spotted longicorn beetles (Anoplophora malasiaca) were found at the base of the trunks of trees in these stands. The present study aims to evaluate the effects of infestation on the degradation, and demonstrates whether the number of exit holes (Nholes) can be used as an index of the decline of trees. We selected 35 healthy appearing stands and 16 degraded stands in the study area. A generalized linear mixed model with zero inflation revealed that Nholes of standing dead trees tended to be greater than that of living trees, and the tree vigor decreased with increasing Nholes. These results implied that the degradation of the shelterbelts was caused by the beetle. We also found size-dependent mortality, i.e., only a few larvae can cause the death of smaller trees, but not larger trees. Furthermore, evaluation of the degradation at the stand level (Nholes) using a logistic regression analysis revealed that the degradation at the stand level could be predicted by Nholes. Our findings can be used as a useful index marker for diagnosing white birch shelterbelts.

The Effects of a Megafire on Ecosystem Services and the Pace of Landscape Recovery

(1) Background: Megafires have affected several regions in the world (e.g., Australia, California), including, in 2017, the central and south-central zones of Chile. These areas represent real laboratories to monitor the impacts on the sustainability of landscapes and their recovery after fires. The present research examines the modification of dynamics and the provision of ecosystem services by a megafire in a Mediterranean landscape in central Chile, combining remote sensing technologies and ecosystem service assessments. (2) Methods: Land cover and spectral indices (NBRI, BAIS-2, NDVI, and EVI) were measured using Sentinel-2 imagery, while the provision of ecosystem services was evaluated using an expert-based matrix. (3) Results: The megafire affected forest plantations, formerly the dominant land cover, as well as other ecosystems, e.g., native forests. After five years, the landscape is dominated by exotic shrublands and grasslands. (4) Conclusions: The megafire caused a loss of 50% of the landscape’s capacity to supply ecosystem services. Given that native forests are the best provider of ecosystem services in this landscape, restoration is a key to recovering landscape sustainability.

Water Availability Controls the Biomass Increment of Melia dubia in South India

Farmland tree cultivation is considered an important option for enhancing wood production. In South India, the native leaf-deciduous tree species Melia dubia is popular for short-rotation plantations. Across a rainfall gradient from 420 to 2170 mm year–1, we studied 186 farmland woodlots between one and nine years in age. The objectives were to identify the main factors controlling aboveground biomass (AGB) and growth rates. A power-law growth model predicts an average stand-level AGB of 93.8 Mg ha–1 for nine-year-old woodlots. The resulting average annual AGB increment over the length of the rotation cycle is 10.4 Mg ha–1 year–1, which falls within the range reported for other tropical tree plantations. When expressing the parameters of the growth model as functions of management, climate and soil variables, it explains 65% of the variance in AGB. The results indicate that water availability is the main driver of the growth of M. dubia. Compared to the effects of water availability, the effects of soil nutrients are 26% to 60% smaller. We conclude that because of its high biomass accumulation rates in farm forestry, M. dubia is a promising candidate for short-rotation plantations in South India and beyond.

Chemodiversity of Soil Dissolved Organic Matter and Its Association With Soil Microbial Communities Along a Chronosequence of Chinese Fir Monoculture Plantations

The total dissolved organic matter (DOM) content of soil changes after vegetation transformation, but the diversity of the underlying chemical composition has not been explored in detail. Characterizing the molecular diversity of DOM and its fate enables a better understanding of the soil quality of monoculture forest plantations. This study characterized the chemodiversity of soil DOM, assessed the variation of the soil microbial community composition, and identified specific linkages between DOM molecules and microbial community composition in soil samples from a 100-year chronosequence of Chinese fir monoculture plantations. With increasing plantation age, soil total carbon and dissolved organic carbon first decreased and then increased, while soil nutrients, such as available potassium and phosphorus and total nitrogen, potassium, and phosphorus, increased significantly. Lignin/carboxylic-rich alicyclic molecule (CRAM)-like structures accounted for the largest proportion of DOM, while aliphatic/proteins and carbohydrates showed a decreasing trend along the chronosequence. DOM high in H/C (such as lipids and aliphatic/proteins) degraded preferentially, while low-H/C DOM (such as lignin/CRAM-like structures and tannins) showed recalcitrance during stand development. Soil bacterial richness and diversity increased significantly as stand age increased, while soil fungal diversity tended to increase during early stand development and then decrease. The soil microbial community had a complex connectivity and strong interaction with DOM during stand development. Most bacterial phyla, such as Acidobacteria, Chloroflexi, and Firmicutes, were very significantly and positively correlated with DOM molecules. However, Verrucomicrobia and almost all fungi, such as Basidiomycota and Ascomycota, were significantly negatively correlated with DOM molecules. Overall, the community of soil microorganisms interacted closely with the compositional variability of DOM in the monoculture plantations investigated, both by producing and consuming DOM. This suggests that DOM is not intrinsically recalcitrant but instead persists in soils as a result of simultaneous consumption, transformation, and formation by soil microorganisms with extended stand ages of Chinese fir plantations.

Impacts of ecological restoration on public perceptions of cultural ecosystem services

Although ecological restoration has increased the stability and diversity of regional ecosystem services, its effects on public perceptions of cultural ecosystem services (CESs) remain unclear. Therefore, this study conducted a questionnaire survey of 455 interviewees in Ansai County on the Loess Plateau and combined the structural equation model (SEM) to explore the characteristics and influencing factors of public perceptions of CESs. Moreover, we also calculated landscape importance to quantify the impact of landscape features on CESs. The results showed that ecological restoration increased the overall public perceptions of CESs. Regarding the different types of CESs, the public most strongly perceived esthetic services but had the lowest perception of cultural heritage after ecological restoration. Regarding demographic characteristics, gender and age were the most important factors affecting public perceptions. Men were more likely to perceive CESs than women, while older interviewees had higher perceptions of the value of physical and mental health services, education and science than young interviewees. In addition, forestlands were perceived as playing more important roles than other landscape types in providing CESs. This study demonstrates that ecological restoration will improve public perceptions of CESs. Managers should incorporate public perceptions of CESs into the formulation of ecological management policies.

Tree–Crop Ecological and Physiological Interactions Within Climate Change Contexts: A Mini-Review

The effects of climate change are increasingly noticed worldwide, and crops are likely to be impacted in direct and indirect ways. Thus, it is urgent to adopt pliable strategies to reduce and/or mitigate possible adverse effects to meet the growing demand for sustainable and resilient food production. Monoculture cropping is globally the most common production system. However, adaptation to ongoing climate change, namely, to more extreme environmental conditions, has renewed the interest in other practices such as agroforestry, agroecology, and permaculture. This article provides an overview of ecological and physiological interactions between trees and crops in Mediterranean agroforestry systems and compares them with those from monocultures. The advantages and disadvantages of both systems are explored. The added value of modeling in understanding the complexity of interactions within agroforestry systems, supporting decision-making under current and future weather conditions, is also pinpointed. Several interactions between trees and crops might occur in agroforestry systems, leading to mutual positive and/or negative effects on growth, physiology, and yield. In this sense, selecting the most suitable combination of tree/crop species in mixtures may be best be indicated by complementary traits, which are crucial to maximizing trade-offs, improving productivity, ecosystem services, and environmental sustainability.

Assessment of the Role of PAL in Lignin Accumulation in Wheat (Tríticum aestívum L.) at the Early Stage of Ontogenesis

The current study evaluates the role of phenylalanine ammonia-lyase (PAL) and the associated metabolic complex in the accumulation of lignin in common wheat plants (Tríticum aestívum L.) at the early stages of ontogenesis. The data analysis was performed using plant samples that had reached Phases 4 and 5 on the Feekes scale—these phases are characterized by a transition to the formation of axial (stem) structures in cereal plants. We have shown that the substrate stimulation of PAL with key substrates, such as L-phenylalanine and L-tyrosine, leads to a significant increase in lignin by an average of 20% in experimental plants compared to control plants. In addition, the presence of these compounds in the nutrient medium led to an increase in the number of gene transcripts associated with lignin synthesis (PAL6, C4H1, 4CL1, C3H1). Inhibition was the main tool of the study. Potential competitive inhibitors of PAL were used: the optical isomer of L-phenylalanine—D-phenylalanine—and the hydroxylamine equivalent of phenylalanine—O-Benzylhydroxylamine. As a result, plants incubated on a medium supplemented with O-Benzylhydroxylamine were characterized by reduced PAL activity (almost one third). The lignin content of the cell wall in plants treated with O-Benzylhydroxylamine was almost halved. In contrast, D-phenylalanine did not lead to significant changes in the lignin-associated metabolic complex, and its effect was similar to that of specific substrates.

Site-Effects Dominate the Plant Availability of Nutrients under Salix Species during the First Cutting Cycle

Fast-growing willows (Salix spp.) provide alternative sources of renewable energy generation, but need an adequate nutrient availability in the soil for high biomass production. In general, species mixtures can be more nutrient-efficient than pure cultures, but this is scarcely known for Salix spp. Therefore, this study evaluates the nutrient availability and P mobilization under two willow species, Salixdasyclados var. ‘Loden’ and S. schwerinii × viminalis var. ‘Tora’, grown as pure and mixed cultures at non-fertilized former arable sites in Germany (Stagnic Cambisol) and Sweden (Vertic Cambisol). The plant availability of potassium (K), magnesium (Mg) and phosphorus (P) and soil phosphatase activities in the topsoil were measured in spring of the year of planting (initial) and under 4 years-old stocks (one year after the first 3-year cutting cycle). The initial plant availability of the nutrients significantly differed between the sites and the two sampling dates at both sites. The plant availability of K and Mg was optimal to high at both sites and sampling dates, but rather low for P (after 4 years ≤5 mg P 100 g−1 soil). The plant-available P and K content in soil significantly decreased within the 4 years of willow growth at both sites. The acid and alkaline phosphatase activity in the soil of the German site (Rostock) was significantly lower after 4 years of willow growth, but differed not significantly between the two sampling dates at the Swedish site (Uppsala). Higher activity of acid phosphatase compared to alkaline phosphatase was recorded in the soils at both test sites based on the site-specific soil pH (<7). The slight decrease of plant availability of P after 4 years of Salix growth in pure culture differed not significantly between the different species. Mixed growth did not decrease the plant availability of P within this period, although no significant difference in the biomass production of pure and mixed growth was observed. This was valid at both sites, and therefore, seems independent of the site-specific differences in soil and climate conditions. The general validity of the assumptions should be tested also for other species mixtures and soil conditions in the future before site-adapted growth designs can be recommended in biomass production of Salix.

Drought and Nitrogen Application Modulate the Morphological and Physiological Responses of Dalbergia odorifera to Different Niche Neighbors

Mixed stands can be more productive if growth facilitation via niche segregation occurs. Dalbergia odorifera T. Chen, a tropical tree species endemic to Hainan Island with great economic values, belongs to the family Leguminosae. However, selecting mixed species with suitable ecological niches to efficiently construct mixed forests of D. odorifera in the context of abiotic stress [drought, nitrogen (N) deposition] remained obscure. In the present study, the target plant D. odorifera was planted with the same species D. odorifera, heterogeneous but the same family Delonix regia and non-Leguminous Family Swietenia mahagoni in the root interaction and isolated models under two watering regimes [100% and 30% field capacity (FC)] and two N applications (application, non-application), respectively. Principle component analysis based on the performances of growth, phenotype, and physiology was performed to identify the main factors affected by the treatments and the most discriminatory effects of water, N level, and species interaction models. Both comprehensive evaluation values and comprehensive index values were calculated to evaluate the influences of different niche neighbors on D. odorifera. Results showed that D. odorifera was benefited from S. mahagoni but inhibited from D. odorifera in all treatments under root system interaction. Drought stress aggravated the inhibitory effects on D. odorifera from D. odorifera. N application stimulated the promoted effects on D. odorifera from S. mahagoni but enhanced competition intensity of D. odorifera from D. regia under the 100% FC condition. N application alleviated the inhibitory effect of drought stress on D. odorifera from D. odorifera and S. mahagoni. Furthermore, the responses of D. odorifera to different niche neighbors were dominated by belowground interaction rather than the negligible aboveground one. Therefore, the feasibility of niche segregation as the criterion for selecting neighbors to construct D. odorifera mixed stands was confirmed. In addition, water level and N application could alter responses of D. odorifera to different niche neighbors under the root system interaction. Appropriate N application could alleviate the inhibitory effect of drought stress on D. odorifera in its mixed forests. A mixture with S. mahagoni under appropriate N application could be the optimal planting model.

Disentangling the Relationship between Tree Biomass Yield and Tree Diversity in Mediterranean Mixed Forests

Tree biomass and the diversity relationship in mixed forest have an impact on forest ecosystem services provisions. Tree biomass yield is driven by several aspects such as species identity, site condition, stand density, tree age and tree diversity expressed as species mingling and structural diversity. By comparing diverse degrees of tree mixtures in natural forests, we can gain insight into the ecosystem services provision level and dynamic. Two monitoring sites in the Castilian Northern Plateau (Spain) have been analyzed to disentangle the relationships between biodiversity levels and tree biomass yield. Two permanent one hectare (ha) squared plots were established at Llano de San Marugán and Valdepoza. In each plot, all individual trees were measured (diameter and height), georeferenced and its species identity defined. Tree species in the two sites were Pinus sylvestris, Pinus nigra, Pinus pinea, Quercus pyrenaica, Quercus ilex, Quercus faginea and Juniperus thurifera. From these datasets, ten diversity indices that fall in three categories (species richness indices, species compositional/mingling indices and vertical structural indices) were used as predictor variables to fit several candidate models. By merging the trees by site (without considering the species identity) selected models include individual tree basal area as an explanatory variable combining by addition or interaction with diversity indices. When species are analyzed independently, structural diversity impacts on biomass yield in combination (additive or multiplicative) with tree size is negative for Pinus nigra and positive for the other species.

Simulating the Effects of Intensifying Silviculture on Desired Species Yields across a Broad Environmental Gradient

In the past two decades, forest management has undergone major paradigm shifts that are challenging the current forest modelling architecture. New silvicultural systems, guidelines for natural disturbance emulation, a desire to enhance structural complexity, major advances in successional theory, and climate change have all highlighted the limitations of current empirical models in covering this range of conditions. Mechanistic models, which focus on modelling underlying ecological processes rather than specific forest conditions, have the potential to meet these new paradigm shifts in a consistent framework, thereby streamlining the planning process. Here we use the NEBIE (a silvicultural intervention scale that classifies management intensities as natural, extensive, basic, intensive, and elite) plot network, from across Ontario, Canada, to examine the applicability of a mechanistic model, ZELIG-CFS (a version of the ZELIG tree growth model developed by the Canadian Forest Service), to simulate yields and species compositions. As silvicultural intensity increased, overall yield generally increased. Species compositions met the desired outcomes when specific silvicultural treatments were implemented and otherwise generally moved from more shade-intolerant to more shade-tolerant species through time. Our results indicated that a mechanistic model can simulate complex stands across a range of forest types and silvicultural systems while accounting for climate change. Finally, we highlight the need to improve the modelling of regeneration processes in ZELIG-CFS to better represent regeneration dynamics in plantations. While fine-tuning is needed, mechanistic models present an option to incorporate adaptive complexity into modelling forest management outcomes.

N supply mediates the radiative balance of N2 O emissions and CO2 sequestration driven by N-fixing vs. non-fixing trees

Forests are a significant CO₂ sink. However, CO₂ sequestration in forests is radiatively offset by emissions of nitrous oxide (N₂ O), a potent greenhouse gas, from forest soils. Reforestation, an important strategy for mitigating climate change, has focused on maximizing CO₂ sequestration in plant biomass without integrating N₂ O emissions from soils. Although nitrogen (N)-fixing trees are often recommended for reforestation because of their rapid growth on N-poor soil, they can stimulate significant N₂ O emissions from soils. Here, we first used a field experiment to show that a N-fixing tree (Robinia pseudoacacia) initially mitigated climate change more than a non-fixing tree (Betula nigra). We then used our field data to parameterize a theoretical model to investigate these effects over time. Under lower N supply, N-fixers continued to mitigate climate change more than non-fixers by overcoming N limitation of plant growth. However, under higher N supply, N-fixers ultimately mitigated climate change less than non-fixers by enriching soil N and stimulating N₂ O emissions from soils. These results have implications for reforestation, suggesting that N-fixing trees are more effective at mitigating climate change at lower N supply, whereas non-fixing trees are more effective at mitigating climate change at higher N supply.

Nitrogen-fixing trees increase soil nitrous oxide emissions: a meta-analysis

Nitrogen-fixing trees are an important nitrogen source to terrestrial ecosystems. While they can fuel primary production and drive carbon dioxide sequestration, they can also potentially stimulate soil emissions of nitrous oxide, a potent greenhouse gas. However, studies on the influence of nitrogen-fixing trees on soil nitrous oxide emissions have not been quantitatively synthesized. Here, we show in a meta-analysis that nitrogen-fixing trees more than double soil nitrous oxide emissions relative to non-fixing trees and soils. If planted in reforestation projects at the global scale, nitrogen-fixing trees could increase global soil nitrous oxide emissions from natural terrestrial ecosystems by up to 4.1%, offsetting climate change mitigation via reforestation by up to 4.4%.

Role of Mixed-Species Stands in Attenuating the Vulnerability of Boreal Forests to Climate Change and Insect Epidemics

We investigated whether stand species mixture can attenuate the vulnerability of eastern Canada's boreal forests to climate change and insect epidemics. For this, we focused on two dominant boreal species, black spruce [Picea mariana (Mill.) BSP] and trembling aspen (Populus tremuloides Michx.), in stands dominated by black spruce or trembling aspen ("pure stands"), and mixed stands (M) composed of both species within a 36 km² study area in the Nord-du-Québec region. For each species in each stand composition type, we tested climate-growth relations and assessed the impacts on growth by recorded insect epidemics of a black spruce defoliator, the spruce budworm (SBW) [Choristoneura fumiferana (Clem.)], and a trembling aspen defoliator, the forest tent caterpillar (FTC; Malacosoma disstria Hübn.). We implemented linear models in a Bayesian framework to explain baseline and long-term trends in tree growth for each species according to stand composition type and to differentiate the influences of climate and insect epidemics on tree growth. Overall, we found climate vulnerability was lower for black spruce in mixed stands than in pure stands, while trembling aspen was less sensitive to climate than spruce, and aspen did not present differences in responses based on stand mixture. We did not find any reduction of vulnerability for mixed stands to insect epidemics in the host species, but the non-host species in mixed stands could respond positively to epidemics affecting the host species, thus contributing to stabilize ecosystem-scale growth over time. Our findings partially support boreal forest management strategies including stand species mixture to foster forests that are resilient to climate change and insect epidemics.

The Timber Footprint of the German Bioeconomy—State of the Art and Past Development

The article gives a comprehensive overview of the roundwood equivalents (RE) consumed in the German bioeconomy from Germany and abroad between 1995 and 2015, i.e., the Timber Footprint of final Consumption (TFPcon). The calculation is based on an adapted version of Exiobase 3.4. The sustainability of roundwood procurement for the TFPcon is assessed. A systematic embedding of the tree compartments considered in the TFP in the context of national forest inventories and material flow analysis is presented. The results show that, in 2015, the total volume of the TFPcon of Germany is 90 Mm3 (slightly above the 1995 level) and is composed of 61% coniferous and 39% non-coniferous wood. Germany is strongly dependent on roundwood sourced from abroad and thus was a net importer of RE in 2015. Among the 17 countries with the largest supply of RE for the TFPcon, around one third very likely include large shares of roundwood procured from deforestation or clear-cutting. The self-sufficiency rate in 2015 was only 76%. It would be possible to increase domestic roundwood production by 8–41% (mainly in the hardwood sector) without exceeding the sustainability limits as defined in the WEHAM scenarios.

The Who or the How? Species vs. Ecosystem Function Priorities in Conservation Ecology

Current conservation strategies are targeted at preserving species, without explicitly aiming at the maintenance of ecosystem functions. In a physically highly connected world, the unintentional relocation of terrestrial, marine, and microbial life is therefore unavoidable and has been an integral part of human evolution for thousands of years. Here, we challenge the default perception often shared among conservation ecologists that preserving native species at all costs and reducing the number of exotic species and their abundance is the only way to conservation and restoration success. While this strategy is valuable in cases where exotic species disrupt ecological function, there are examples where exotic species have similar functional traits to the threatened or extinct native species and can in fact help maintain the overall or target function of an ecosystem. In the race to cope with global environmental change, we argue that ecosystem function and ecosystem services need to be viewed not only through a taxonomic lens, but increasingly also through a functional, trait-based one.