Afforestation using a range of tree species, in New Zealand: New Forest trial series establishment, site description, and initial data

Global climate change and shift towards a bio-economy has heightened the need to design sustainable forestry systems that balance economic, environmental and social benefits. In New Zealand, production forests are dominated by planted Pinus radiata, which makes up 90 % of the planted forest area. There is very little data driven evidence in New Zealand to support diversifying across a range of tree species and what timber and non-timber benefits may be gained by diversifying tree species in New Zealand's production forests. The New Zealand New Forest Trial Series (NFTS) was designed and established in 2013 on marginal pastoral land to address the knowledge gap for how afforesting land with different trees species, both exotic and indigenous to New Zealand, across a climate range can deliver to both timber and non-timber benefits. These trials were planted with Cupressocyparis ovensii, Eucalyptus fastigata, Fraxinus excelsior, Nothofagus fusca (plus Leptospermum scoparium), Pinus radiata, Podocarpus totara and Sequoia sempervirens plus a control with no planting to monitor natural succession. The Before-After-Control-Impact (BACI) experiment design has collected pre-planting data describing the present vegetation and a range of soil properties, presented in this paper. This will allow the comparative monitoring of the changes that will occur through planting the various tree species on marginal land in different environments through time. With time the long-term trials will deliver data evidence on tree species survival when planted into marginal pastoral land, tree productivity and the flow of economic, environmental and social benefits from the new plantings. This knowledge will strengthen New Zealand's forestry sector confidence to make informed decisions to diversify tree species with changing climatic and social challenges.

Partner or perish: tree microbiomes and climate change

Understanding the complex relationships between plants, their microbiomes, and environmental changes is crucial for improving growth and survival, especially for long-lived tree species. Trees, like other plants, maintain close associations with a multitude of microorganisms on and within their tissues, forming a 'holobiont'. However, a comprehensive framework for detailed tree-microbiome dynamics, and the implications for climate adaptation, is currently lacking. This review identifies gaps in the existing literature, emphasizing the need for more research to explore the coevolution of the holobiont and the full extent of climate change impact on tree growth and survival. Advancing our knowledge of plant-microbial interactions presents opportunities to enhance tree adaptability and mitigate adverse impacts of climate changes on trees.

How much anthropogenic carbon fixation do we need?

Carbon dioxide (CO2) emissions resulting from human activities are the primary driver of global warming. The reduction of emissions is the key solution to limit global warming, although it is likely that some level of anthropogenic CO2 emissions will remain unavoidable. Therefore, it is crucial to determine the amount of carbon fixation necessary to achieve net zero CO2 emissions and the extent of anthropogenic carbon fixation required to meet this target. According to the RCP2.6 scenario, which aligns with the criteria outlined in the Paris Agreement to keep global warming below 1.5 °C, we have calculated that anthropogenic activity must achieve 1.5 gigatons (Gt) of CO2 to reach net zero CO2 emissions by 2050. This figure will significantly increase if emissions are not reduced by 2050. However, estimating the additional anthropogenic fixation required becomes challenging due to potential disruptions to natural fixation. Therefore, we strongly recommend conducting further research on the stability of natural carbon fixation processes to establish meaningful goals for anthropogenic carbon fixation.

Long-term plant diversity increases soil extractable organic carbon and nitrogen contents in a subtropical forest

Plant diversity is one of the various factors influencing ecosystem functions such as soil carbon (C) and nitrogen (N) stocks. Soil extractable organic carbon (EOC) and nitrogen (EON) contents are active fractions in soil organic matter, but little is known about the impact of variations in long-term plant diversity on soil EOC and EON contents in forest ecosystems. Utilizing the Biodiversity-Ecosystem Functioning Experiment China platform, we selected long-term plant diversity level treatments, distinguished the functional types of evergreen and deciduous plants, and explored their effects on soil EOC and EON contents. The results showed that soil EOC and EON contents increased significantly with greater plant diversity, which is mainly attributed to proportional increases in complementary effects. After distinguishing plant functional types, we did not find the strong complementary effects at the mixed planting of evergreen and deciduous tree species. Within two-species planting mixtures, evergreen tree species can increase soil EON compared to deciduous tree species. Cyclobalanopsis have a strong carbon and nitrogen storage capacity, suggesting that increasing the plant diversity and the proportion of Cyclobalanopsis planting in forest management will promote carbon and nitrogen accumulation in forest soil. These findings enhance our understanding of long-term forest C and N cycling processes and also provide theoretical support for managing forest soil C sinks.

Accelerator trial series in Pinus radiata stands in New Zealand: Trial establishment, site description and initial soil, forest floor and tree data

Interest in establishing biological-based economies has created increasing and rapidly moving demand for wood and fibre from production forests. Meeting the global demand for timber supply will require investment and development across all components of the supply chain but will ultimately rely on the ability of the forestry sector to increase productivity without compromising the sustainability of plantation management. To address this issue in the context of New Zealand forestry, a trial series was established from 2015 to 2018 to accelerate plantation forest growth by exploring current and future limitations to timber productivity, then altering management practices to overcome these limits. The six sites in this Accelerator trial series were planted with a mix of 12 different types of Pinus radiata D. Don stock expressing various traits related to tree growth, health and wood quality. The planting stock included ten clones, a hybrid and a seed lot representing a widely planted tree stock used throughout New Zealand. At each trial site a range of treatments were applied, including a control. The treatments were designed to address the specific current and predicted limitations to productivity at each location, with consideration for environmental sustainability and impacts on wood quality. Additional site-specific treatments will be implemented across the approximately 30-year life span of each trial. Here we present data describing both the pre-harvest and time zero state of at each trial site. These data provide a baseline that will enable treatment responses to be holistically understood as the trial series matures. This comparison will determine if current tree productivity has been enhanced, and if improvements in site characteristics may also benefit future rotations. The Accelerator trials represent an ambitious research goal that will take planted forest productivity to a new level of enhanced long-term forest productivity without compromising the sustainable management of future forests.

Rethinking experiments that explore multiple global change factors

Our current capacity to predict the responses of ecosystem functions under global change factors is limited. We propose new and more efficient approaches to experimental design and modeling that utilize interactions between ecosystem functions to improve our understanding of their sensitivity to global change factors.

Reducing plant-derived ethylene concentrations increases the resistance of temperate grassland to drought

Model predictions indicate that extreme drought events will occur more frequently by the end of this century, with major implications for terrestrial ecosystem functions such as plant productivity and soil respiration. Previous studies have shown that drought-induced ethylene produced by plants is a key factor affecting plant growth and development, but the impact of drought-induced ethylene on ecosystem functions in natural settings has not yet been tested. Here, we reduced the amount of plant-derived ethylene concentrations by adding the ethylene inhibitor aminoethoxyvinylglycine (AVG), and investigated in situ plant productivity, soil respiration and ethylene concentrations for two years in a semi-arid temperate grassland in Inner Mongolia, China. Drought significantly reduced plant productivity and soil respiration, but the application of AVG reduced ethylene concentrations and significantly increased aboveground plant productivity and soil respiration, effectively enhancing resistance to drought. The reason for this could be that AVG application increased the activity of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and abundance of the acdS gene (the key gene for ACC deaminase), facilitating reduced ACC concentrations in the plant tissue and reduced in planta ethylene synthesis. In addition, there was a significant correlation between soil ACC deaminase activity and plant productivity. Given the global distribution of arid and semi-arid areas, and the expected increases in the frequency and intensity of drought stress, this is a significant concern. These results provide novel evidence of the impact of drought-induced plant ethylene production on ecosystem functions in semi-arid temperate grassland ecosystems.

Incorporation of NPP into forest CH4 efflux models

Forest soils are the largest atmospheric methane (CH₄) sinks in terrestrial ecosystems, but models simulating this uptake have considerable uncertainties. Soil organic matter derived from aboveground vegetation net primary productivity (NPP) significantly influences CH₄ uptake; therefore, we propose that the incorporation of NPP into global CH₄ uptake models will greatly improve model predictions.

Manipulation of soil methane oxidation under drought stress

Drought events are predicted to occur more frequently, but comprehensive knowledge of their effects on methane (CH₄) oxidation by soil methanotrophs in upland ecosystems remains elusive. Here, we put forward a new conceptual model in which drought influences soil CH₄ oxidation through a direct pathway (i.e., positive effects of soil CH₄ oxidation via increasing soil aeration) and through an indirect pathway (i.e., negative effects of in planta ethylene (C₂H₄) production on soil CH₄ oxidation). Through measuring soil CH₄ efflux along a gradient of drought stress, we found that drought increases soil CH₄ oxidation, as the former outweighs the latter on soil CH₄ oxidation, based on a mesocosm experiment employing distinct levels of watering and a long-term drought field trial created by rainfall exclusion in a subtropical evergreen forest. Moreover, we used aminoethoxyvinylglycine (AVG), a C₂H₄ biosynthesis inhibitor, to reduce in planta C₂H₄ production under drought, and found that reducing in planta C₂H₄ production increased soil CH₄ oxidation under drought. To confirm these findings, we found that inoculation of plant growth-promoting rhizobacteria containing the 1-aminocyclopropane-1-carboxylate deaminase alleviated the negative effects of drought-induced in planta C₂H₄, thus increasing soil CH₄ oxidation rates. All these results provide strong evidence for the hypothesis that in planta C₂H₄ production inhibits soil CH₄ oxidation under drought. To our knowledge, this is the first study to manipulate the negative feedback between C₂H₄ production and CH₄ oxidation under drought stress. Given the current widespread extent of arid and semiarid regions in the world, combined with the projected increased frequency of drought stress in future climate scenarios, we provide a reliable means for increasing soil CH₄ oxidation in the context of global warming.

National series of long-term intensive harvesting trials in Pinus radiata stands in New Zealand: Initial biomass, carbon and nutrient pool data

Global interest in addressing knowledge gaps relating to the effect of forest harvest intensity on soil fertility and long-term site productivity has resulted in the installation of numerous experiments, including Long-Term Site Productivity (LTSP) trials. To explore this issue in the context of the New Zealand planted forest estate, six LTSP sites were established from 1985 to 1994 across differing climate and soil conditions, then subjected to varying levels of organic matter removal during the harvest of the trees. Here we present data describing live above ground, forest floor and mineral soil carbon and nutrient pools immediately prior to, and following, harvesting at each site. Harvest residue management practices employed included the removal of stem only, whole tree, whole tree plus forest floor, whole tree plus forest floor and topsoil, and the addition of double harvest slash material. The data provides an understanding of biomass, carbon and nutrient pools at harvest and the impact of different harvest removal treatments on these pools. With the maturation of the trees at the LTSP sites, the data acquires even greater future value by enabling changes in soil properties to be quantified and correlated to variations in the biological properties at the site, including site productivity and critical microbial parameters. Overall, these data sets comprise a foundation for New Zealand to address the question – can the productivity of intensively managed planted Pinus radiata be maintained or enhanced through the judicious management of organic matter and nutrient pools over successive growing and harvesting cycles?

Effects of climate change on the delivery of soil-mediated ecosystem services within the primary sector in temperate ecosystems: a review and New Zealand case study

Future human well-being under climate change depends on the ongoing delivery of food, fibre and wood from the land-based primary sector. The ability to deliver these provisioning services depends on soil-based ecosystem services (e.g. carbon, nutrient and water cycling and storage), yet we lack an in-depth understanding of the likely response of soil-based ecosystem services to climate change. We review the current knowledge on this topic for temperate ecosystems, focusing on mechanisms that are likely to underpin differences in climate change responses between four primary sector systems: cropping, intensive grazing, extensive grazing and plantation forestry. We then illustrate how our findings can be applied to assess service delivery under climate change in a specific region, using New Zealand as an example system. Differences in the climate change responses of carbon and nutrient-related services between systems will largely be driven by whether they are reliant on externally added or internally cycled nutrients, the extent to which plant communities could influence responses, and variation in vulnerability to erosion. The ability of soils to regulate water under climate change will mostly be driven by changes in rainfall, but can be influenced by different primary sector systems' vulnerability to soil water repellency and differences in evapotranspiration rates. These changes in regulating services resulted in different potentials for increased biomass production across systems, with intensively managed systems being the most likely to benefit from climate change. Quantitative prediction of net effects of climate change on soil ecosystem services remains a challenge, in part due to knowledge gaps, but also due to the complex interactions between different aspects of climate change. Despite this challenge, it is critical to gain the information required to make such predictions as robust as possible given the fundamental role of soils in supporting human well-being.

The right tree for the job? perceptions of species suitability for the provision of ecosystem services

Stakeholders in plantation forestry are increasingly aware of the importance of the ecosystem services and non-market values associated with forests. In New Zealand, there is significant interest in establishing species other than Pinus radiata D. Don (the dominant plantation species) in the belief that alternative species are better suited to deliver these services. Significant risk is associated with this position as there is little objective data to support these views. To identify which species were likely to be planted to deliver ecosystem services, a survey was distributed to examine stakeholder perceptions. Stakeholders were asked which of 15 tree attributes contributed to the provision of five ecosystem services (amenity value, bioenergy production, carbon capture, the diversity of native habitat, and erosion control/water quality) and to identify which of 22 candidate tree species possessed those attributes. These data were combined to identify the species perceived most suitable for the delivery of each ecosystem service. Sequoia sempervirens (D.Don) Endl. closely matched the stakeholder derived ideotypes associated with all five ecosystem services. Comparisons to data from growth, physiological and ecological studies demonstrated that many of the opinions held by stakeholders were inaccurate, leading to erroneous assumptions regarding the suitability of most candidate species. Stakeholder perceptions substantially influence tree species selection, and plantations established on the basis of inaccurate opinions are unlikely to deliver the desired outcomes. Attitudinal surveys associated with engagement campaigns are essential to improve stakeholder knowledge, advancing the development of fit-for-purpose forest management that provides the required ecosystem services.

Methane oxidation needs less stressed plants

Methane oxidation rates in soil are liable to be reduced by plant stress responses to climate change. Stressed plants exude ethylene into soil, which inhibits methane oxidation when present in the soil atmosphere. Here we discuss opportunities to use 1-aminocyclopropane-1-carboxylate deaminase to manage methane oxidation by regulating plant stress responses.