Trade-offs between carbon stocks and biodiversity in European temperate forests

The inclusion of improved forest management in strategic forest planning and its impact on timber harvests, carbon and biodiversity conservation

In forestry, although the so-called nature-based climate solutions have usually been focused on the calculation of carbon captured in new afforestation projects, it should be noted that the increase in carbon associated with improvements in their management (Improved Forest Management) can also be computed. This type of carbon is not usually integrated into strategic forest planning models, nor has its possible degree of conflict with other regulation ecosystemic services, like biodiversity conservation, been verified. In this research, those two issues have been approached by calculating a baseline in an emblematic forest with an extensive forestry history. For this purpose, we have designed two scenarios, i.e., one linked to its current management (Business As Usual, BAU) and another justified by the inclusion of Improved Forest Management (IFM). The results reveal a notable conflict between the carbon captured and the values of the indicators used to measure biodiversity. In order to reach a compromise between both scenarios, a multi-criteria model has been proposed that could be more attractive than the above ones. In addition, the carbon profit credits in the first ten years have been computed under the IFM scenario; the latter could be, a priori, an object of transaction in a voluntary carbon market. In conclusion, our model generates feasible solutions that allow the integration of IFM into strategic planning. Besides, those solutions show interesting tradeoffs between carbon and biodiversity. This discord must be distinguished by the current state of the forest and its expected growth, as well as their influence on the values associated with provision ecosystem services, such as the present net value associated with timber harvests.

Environmental and social impacts of carbon sequestration

Climate change requires major mitigation efforts, mainly emission reduction. Carbon sequestration and avoided deforestation are complementary mitigation strategies that can promote nature conservation and local development but may also have undesirable impacts. We reviewed 246 articles citing impacts, risks, or concerns from carbon projects, and 78 others related to this topic. Most of the impacts cited focus on biodiversity, especially in afforestation projects, and on social effects related to avoided deforestation projects. Concerns were raised about project effectiveness, the permanence of carbon stored, and leakage. Recommendations include accounting for uncertainty, assessing both mitigation and contribution to climate change, defining permanence, creating contingency plans, promoting local projects, proposing alternative livelihoods, ensuring a fair distribution of benefits, combining timber production and carbon sequestration, ensuring sustainable development and minimizing leakage. A holistic approach that combines carbon sequestration, nature conservation, and poverty alleviation must be applied. The potential occurrence of negative impacts does not invalidate carbon projects but makes it advisable to conduct proper environmental impact assessments, considering direct and indirect impacts, minimizing the negative effects while maximizing the positive ones, and weighing the trade-offs between them to guide decision-making. Public participation and transparency are essential. Integr Environ Assess Manag 2024;00:1-27. © 2024 SETAC.

Declining Radial Growth in Major Western Carpathian Tree Species: Insights from Three Decades of Temperate Forest Monitoring

This study investigates the radial growth response of five key European forest tree species, i.e., Fagus sylvatica, Picea abies, Abies alba, Quercus petraea, and Pinus sylvestris, to dry years in the West Carpathians, Slovakia. Utilizing data from ICP Forests Level I plots, we identified species-specific growth declines, particularly in Pinus sylvestris and Fagus sylvatica, with milder radial growth declines for Quercus petraea and Picea abies. Abies alba exhibited a growth peak in the mid-2000s, followed by a decline in the end of the observed period. Elevation emerged as the only significant environmental predictor, explaining 3.5% of growth variability during dry periods, suggesting a potential mitigating effect. The scope of this study was limited by the complex interplay of ecological factors that influence tree growth, which vary across the ICP Forests Level I monitoring sites. Nonetheless, our findings enhance the understanding of species-specific growth responses and offer insights for the climate-smart management of temperate forests under changing conditions.

Carbon-biodiversity relationships in a highly diverse subtropical forest

Carbon-focused climate mitigation strategies are becoming increasingly important in forests. However, with ongoing biodiversity declines we require better knowledge of how much such strategies account for biodiversity. We particularly lack information across multiple trophic levels and on established forests, where the interplay between carbon stocks, stand age, and tree diversity might influence carbon-biodiversity relationships. Using a large dataset (>4600 heterotrophic species of 23 taxonomic groups) from secondary, subtropical forests, we tested how multitrophic diversity and diversity within trophic groups relate to aboveground, belowground, and total carbon stocks at different levels of tree species richness and stand age. Our study revealed that aboveground carbon, the key component of climate-based management, was largely unrelated to multitrophic diversity. By contrast, total carbon stocks-that is, including belowground carbon-emerged as a significant predictor of multitrophic diversity. Relationships were nonlinear and strongest for lower trophic levels, but nonsignificant for higher trophic level diversity. Tree species richness and stand age moderated these relationships, suggesting long-term regeneration of forests may be particularly effective in reconciling carbon and biodiversity targets. Our findings highlight that biodiversity benefits of climate-oriented management need to be evaluated carefully, and only maximizing aboveground carbon may fail to account for biodiversity conservation requirements.

Giant panda-focused conservation has limited value in maintaining biodiversity and carbon sequestration

Biodiversity and climate are interconnected through carbon. Drivers of climate change and biodiversity loss interact in complex ways to produce outcomes that may be synergistic, and biodiversity loss and climate change reinforce each other. Prioritizing the conservation of flagship and umbrella species is often used as a surrogate strategy for broader conservation goals, but it is unclear whether these efforts truly benefit biodiversity and carbon stocks. Conservation of the giant panda offers a paradigm to test these assumptions. Here, using the benchmark estimates of ecosystem carbon stocks and species richness, we investigated the relationships among the giant panda, biodiversity, and carbon stocks and assessed the implications of giant panda conservation for biodiversity and carbon-focused conservation efforts. We found that giant panda density and species richness were significantly positively correlated, while no correlation was found between giant panda density and soil carbon or total carbon density. The established nature reserves protect 26 % of the giant panda conservation region, but these areas contain <21 % of the ranges of other species and <21 % of total carbon stocks. More seriously, giant panda habitats are still facing high risks of habitat fragmentation. Habitat fragmentation is negatively correlated with giant panda density, species richness, and total carbon density. The ongoing giant panda habitat fragmentation is likely to cause an additional 12.24 Tg C of carbon emissions over 30 years. Thus, giant panda-focused conservation efforts have effectively prevented giant panda extinction but have been less effective in maintaining biodiversity and high‑carbon ecosystems. It is urgent for China to contribute to the development of an effective and representative national park system that integrates climate change issues into national biodiversity strategies and vice versa in dealing with the dual environmental challenges of biodiversity loss and climate change under a post-2020 framework.

Carbonated tiger-high above-ground biomass carbon stock in protected areas and corridors and its observed negative relationship with tiger population density and occupancy in the Terai Arc Landscape, Nepal

Healthy natural forests maintain and/or enhances carbon stock while also providing potential habitat and an array of services to wildlife including large carnivores such as the tiger. This study is the first of its kind in assessing relationships between above-ground biomass carbon stock, tiger density and occupancy probability and its status in protected areas, corridors, and forest connectivity blocks. The dataset used to assess the relationship were: (1) Converged posterior tiger density estimates from camera trap data derived from Bayesian- Spatially Explicit Capture-Recapture model from Chitwan National Park; (2) Site wise probability of tiger occupancy estimated across the Terai Arc Landscape and (3) Habitat wise above-ground biomass carbon stock estimated across the Terai Arc Landscape. Carbon stock maps were derived based on eight habitat classes and conservation units linking satellite (Landsat 7 ETM+) images and field collected sampling data. A significant negative relationship (r = -0.20, p<0.01) was observed between above-ground biomass carbon stock and tiger density in Chitwan National Park and with tiger occupancy (r = -0.24, p = 0.023) in the landscape. Within protected areas, we found highest mean above-ground biomass carbon stock in high density mixed forest (~223 tC/ha) and low in degraded scrubland (~73.2 tC/ha). Similarly, we found: (1) highest tiger density ~ 0.06 individuals per 0.33 km2 in the riverine forest and lowest estimates (~0.00) in degraded scrubland; and (2) predictive tiger density of 0.0135 individuals per 0.33 km2 is equivalent to mean total of 43.7 tC/ha in Chitwan National Park. Comparatively, we found similar above-ground biomass carbon stock among corridors, large forest connectivity blocks (~117 tC/ha), and within in tiger bearing protected areas (~119 tC/ha). Carbon conservation through forest restoration particularly in riverine habitats (forest and grassland) and low transitional state forests (degraded scrubland) provides immense opportunities to generate win-win solutions, sequester more carbon and maintain habitat integrity for tigers and other large predators.

Natural disturbance regimes as a guide for sustainable forest management in Europe

In Europe, forest management has controlled forest dynamics to sustain commodity production over multiple centuries. Yet over-regulation for growth and yield diminishes resilience to environmental stress as well as threatens biodiversity, leading to increasing forest susceptibility to an array of disturbances. These trends have stimulated interest in alternative management systems, including natural dynamics silviculture (NDS). NDS aims to emulate natural disturbance dynamics at stand and landscape scales through silvicultural manipulations of forest structure and landscape patterns. We adapted a "Comparability Index" (CI) to assess convergence/divergence between natural disturbances and forest management effects. We extended the original CI concept based on disturbance size and frequency by adding the residual structure of canopy trees after a disturbance as a third dimension. We populated the model by compiling data on natural disturbance dynamics and management from 13 countries in Europe, covering four major forest types (i.e., spruce, beech, oak, and pine-dominated forests). We found that natural disturbances are highly variable in size, frequency, and residual structure, but European forest management fails to encompass this complexity. Silviculture in Europe is skewed toward even-aged systems, used predominately (72.9% of management) across the countries assessed. The residual structure proved crucial in the comparison of natural disturbances and silvicultural systems. CI indicated the highest congruence between uneven-aged silvicultural systems and key natural disturbance attributes. Even so, uneven-aged practices emulated only a portion of the complexity associated with natural disturbance effects. The remaining silvicultural systems perform poorly in terms of retention compared to tree survivorship after natural disturbances. We suggest that NDS can enrich Europe's portfolio of management systems, for example where wood production is not the primary objective. NDS is especially relevant to forests managed for habitat quality, risk reduction, and a variety of ecosystem services. We suggest a holistic approach integrating NDS with more conventional practices.

Ecological thresholds under atmospheric nitrogen deposition for 1200 herbaceous species and 24 communities across the United States

Nitrogen (N) emissions and atmospheric deposition have increased significantly during the last century and become a stressor for many N-sensitive plant species. Understanding individual and community herbaceous plant species thresholds to atmospheric N deposition can inform emissions reduction policy. Here, we present results using Threshold Indicator Taxa Analysis (TITAN) applied to more than 1200 unique plant species and 24 vegetation communities (i.e., alliances) across the United States (US) to assess vulnerability to N deposition. Alliance-level thresholds (change points) for species decreasing in abundance along the gradient ranged from 1.8 to 14.3 kg N ha^─1  year^─1 and tended to be lower in the west than the east, which suggests that eastern communities, where N deposition has been historically higher, may have already lost many sensitive species. For the species that were present in more than one alliance, over half had a variable response to the N deposition gradient, suggesting that local factors affect vulnerability. Significant progress has been made during the past 30 years to reduce N emissions, which has reduced the percentage of plots at risk to N deposition from 72% to 35%. Nevertheless, over a third of plots remain at risk, and an average reduction of N deposition of 20% would protect half of the plots where N deposition exceeds community thresholds. Furthermore, the alliance- and species-level change points determined in this study may be used to inform N critical loads.

Natural disturbance impacts on trade-offs and co-benefits of forest biodiversity and carbon

With accelerating environmental change, understanding forest disturbance impacts on trade-offs between biodiversity and carbon dynamics is of high socio-economic importance. Most studies, however, have assessed immediate or short-term effects of disturbance, while long-term impacts remain poorly understood. Using a tree-ring-based approach, we analysed the effect of 250 years of disturbances on present-day biodiversity indicators and carbon dynamics in primary forests. Disturbance legacies spanning centuries shaped contemporary forest co-benefits and trade-offs, with contrasting, local-scale effects. Disturbances enhanced carbon sequestration, reaching maximum rates within a comparatively narrow post-disturbance window (up to 50 years). Concurrently, disturbance diminished aboveground carbon storage, which gradually returned to peak levels over centuries. Temporal patterns in biodiversity potential were bimodal; the first maximum coincided with the short-term post-disturbance carbon sequestration peak, and the second occurred during periods of maximum carbon storage in complex old-growth forest. Despite fluctuating local-scale trade-offs, forest biodiversity and carbon storage remained stable across the broader study region, and our data support a positive relationship between carbon stocks and biodiversity potential. These findings underscore the interdependencies of forest processes, and highlight the necessity of large-scale conservation programmes to effectively promote both biodiversity and long-term carbon storage, particularly given the accelerating global biodiversity and climate crises.

Evaluating nature-based solutions for climate mitigation and conservation requires comprehensive carbon accounting

Nature-based solutions (NbS) can address climate change, biodiversity loss, human well-being and their interactions in an integrated way. A major barrier to achieving this is the lack of comprehensiveness in current carbon accounting which has focused on flows rather than stocks of carbon and led to perverse outcomes. We propose a new comprehensive approach to carbon accounting based on the whole carbon cycle, covering both stocks and flows, and linking changes due to human activities with responses in the biosphere and atmosphere. We identify enhancements to accounting, namely; inclusion of all carbon reservoirs, changes in their condition and stability, disaggregated flows, and coverage of all land areas. This comprehensive approach recognises that both carbon stocks (as storage) and carbon flows (as sequestration) contribute to the ecosystem service of global climate regulation. In contrast, current ecosystem services measurement and accounting commonly use only carbon sequestration measured as net flows, while greenhouse gas inventories use flows from sources to sinks. This flow-based accounting has incentivised planting and maintaining young forests with high carbon uptake rates, resulting, perversely, in failing to reveal the greater mitigation benefit from protecting larger, more stable and resilient carbon stocks in natural forests. We demonstrate the benefits of carbon storage and sequestration for climate mitigation, in theory as ecosystem services within an ecosystem accounting framework, and in practice using field data that reveals differences in results between accounting for stocks or flows. Our proposed holistic and comprehensive carbon accounting makes transparent the benefits, trade-offs and shortcomings of NbS actions for climate mitigation and sustainability outcomes. Adopting this approach is imperative for revision of ecosystem accounting systems under the System of Environmental-Economic Accounting and contributing to evidence-based decision-making for international conventions on climate (UNFCCC), biodiversity (CBD) and sustainability (SDGs).

Biodiversity response to forest management intensity, carbon stocks and net primary production in temperate montane forests

Managed forests are a key component of strategies aimed at tackling the climate and biodiversity crises. Tapping this potential requires a better understanding of the complex, simultaneous effects of forest management on biodiversity, carbon stocks and productivity. Here, we used data of 135 one-hectare plots from southwestern Germany to disentangle the relative influence of gradients of management intensity, carbon stocks and forest productivity on different components of forest biodiversity (birds, bats, insects, plants) and tree-related microhabitats. We tested whether the composition of taxonomic groups varies gradually or abruptly along these gradients. The richness of taxonomic groups was rather insensitive to management intensity, carbon stocks and forest productivity. Despite the low explanatory power of the main predictor variables, forest management had the greatest relative influence on richness of insects and tree-related microhabitats, while carbon stocks influenced richness of bats, birds, vascular plants and pooled taxa. Species composition changed relatively abruptly along the management intensity gradient, while changes along carbon and productivity gradients were more gradual. We conclude that moderate increases in forest management intensity and carbon stocks, within the range of variation observed in our study system, might be compatible with biodiversity and climate mitigation objectives in managed forests.

Can nature conservation and wood production be reconciled in managed forests? A review of driving factors for integrated forest management in Europe

Integrated forest management (IFM) can help reconcile critical trade-offs between goals in forest management, such as nature conservation and biomass production. The challenge of IFM is dealing with these trade-offs at the level of practical forest management, such as striving for compromises between biomass extraction and habitat retention. This paper reviews some of the driving factors that influence the integration of nature conservation into forest management. The review was conducted in three steps - a literature review, an expert workshop and an expert-based cooperative analysis. Of 38 driving factors identified, three were prioritised by more of the participants than any of the others: two are socio-cultural factors, identity (how people identify with forest) as well as outreach and education, and one is economic - competitiveness in forest value chains. These driving factors correspond to what are considered in the literature as enablers for IFM. The results reveal that targeted, group-oriented, adaptive and innovative policy designs are needed to integrate nature conservation into forest management. Further, the results reveal that a "one-size-fits-all" governance approach would be ineffective, implying that policy instruments need to consider contextually specific driving factors. Understanding the main driving factors and their overall directions can help to better manage trade-offs between biodiversity conservation and biomass production in European forests.

Carbon sequestration and biodiversity co-benefits of preserving forests in the western United States

Forest carbon sequestration via forest preservation can be a viable climate change mitigation strategy. Here, we identify forests in the western conterminous United States with high potential carbon sequestration and low vulnerability to future drought and fire, as simulated using the Community Land Model and two high carbon emission scenario (RCP 8.5) climate models. High-productivity, low-vulnerability forests have the potential to sequester up to 5,450 Tg CO₂ equivalent (1,485 Tg C) by 2099, which is up to 20% of the global mitigation potential previously identified for all temperate and boreal forests, or up to ~6 yr of current regional fossil fuel emissions. Additionally, these forests currently have high above- and belowground carbon density, high tree species richness, and a high proportion of critical habitat for endangered vertebrate species, indicating a strong potential to support biodiversity into the future and promote ecosystem resilience to climate change. We stress that some forest lands have low carbon sequestration potential but high biodiversity, underscoring the need to consider multiple criteria when designing a land preservation portfolio. Our work demonstrates how process models and ecological criteria can be used to prioritize landscape preservation for mitigating greenhouse gas emissions and preserving biodiversity in a rapidly changing climate.

Radar vision in the mapping of forest biodiversity from space

Recent progress in remote sensing provides much-needed, large-scale spatio-temporal information on habitat structures important for biodiversity conservation. Here we examine the potential of a newly launched satellite-borne radar system (Sentinel-1) to map the biodiversity of twelve taxa across five temperate forest regions in central Europe. We show that the sensitivity of radar to habitat structure is similar to that of airborne laser scanning (ALS), the current gold standard in the measurement of forest structure. Our models of different facets of biodiversity reveal that radar performs as well as ALS; median R² over twelve taxa by ALS and radar are 0.51 and 0.57 respectively for the first non-metric multidimensional scaling axes representing assemblage composition. We further demonstrate the promising predictive ability of radar-derived data with external validation based on the species composition of birds and saproxylic beetles. Establishing new area-wide biodiversity monitoring by remote sensing will require the coupling of radar data to stratified and standardized collected local species data.