Large projected increases in forest disturbance pose a major threat to future wood fiber supply and carbon sequestration in the cold-limited, Canadian boreal forest ecosystem. Given the large ...sensitivity of tree growth to temperature, warming-induced increases in forest productivity have the potential to reduce these threats, but research efforts to date have yielded contradictory results attributed to limited data availability, methodological biases, and regional variability in forest dynamics. Here, we apply a machine learning algorithm to an unprecedented network of over 1 million tree growth records (1958 to 2018) from 20,089 permanent sample plots distributed across both Canada and the United States, spanning a 16.5 °C climatic gradient. Fitted models were then used to project the near-term (2050 s time period) growth of the six most abundant tree species in the Canadian boreal forest. Our results reveal a large, positive effect of increasing thermal energy on tree growth for most of the target species, leading to 20.5 to 22.7% projected gains in growth with climate change under RCP 4.5 and 8.5. The magnitude of these gains, which peak in the colder and wetter regions of the boreal forest, suggests that warming-induced growth increases should no longer be considered marginal but may in fact significantly offset some of the negative impacts of projected increases in drought and wildfire on wood supply and carbon sequestration and have major implications on ecological forecasts and the global economy.
Summary
There is growing concern over rates of global species diversity loss and its implications on healthy ecosystem functioning. While positive relationships between tree species diversity and ...forest biomass production have been observed, forests are structurally complex, consisting of understorey vegetation layers that also contribute to ecosystem functioning as they often account for the majority of species richness. However, relationships between understorey vegetation diversity and function are largely unexplored. Further, few studies have simultaneously assessed how both overstorey and understory vegetation interact and contribute to overall ecosystem function.
By analysing Canada's National Forest Inventory data base using structural equation modelling, we explored the relationships between species richness and above‐ground biomass production across forest vegetation strata while accounting for potentially confounding factors, including climate, physical site characteristics and forest ageing.
We found positive relationships between species richness and biomass production across all forest vegetation layers, but the relationship was strongest for the overstorey layer. Species richness of the understorey tree, shrub and herb layers was positively related to overstorey species richness. However, overstorey biomass had a negative effect on the biomass production of all understorey layers.
Our results suggest that resource filtering by overstorey trees might have reduced the strength of the positive diversity–productivity relationships in the forest understorey, supporting previous hypotheses that the magnitude and direction of diversity–productivity relationships is context specific and dependent on the conditions of the surrounding environment. Further, heterogeneity in understory resources, as affected by the overstorey, may promote niche complementarity as the main mechanism driving diversity–productivity relationships in understorey vegetation.
Lay Summary
Reports of forest sensitivity to climate change are based largely on the study of overstory trees, which contribute significantly to forest growth and wood supply. However, juveniles in the ...understory are also critical to predict future forest dynamics and demographics, but their sensitivity to climate remains less known. In this study, we applied boosted regression tree analysis to compare the sensitivity of understory and overstory trees for the 10 most common tree species in eastern North America using growth information from an unprecedented network of nearly 1.5 million tree records from 20,174 widely distributed, permanent sample plots across Canada and the United States. Fitted models were then used to project the near‐term (2041–2070) growth for each canopy and tree species. We observed an overall positive effect of warming on tree growth for both canopies and most species, leading to an average of 7.8%–12.2% projected growth gains with climate change under RCP 4.5 and 8.5. The magnitude of these gains peaked in colder, northern areas for both canopies, while growth declines are projected for overstory trees in warmer, southern regions. Relative to overstory trees, understory tree growth was less positively affected by warming in northern regions, while displaying more positive responses in southern areas, likely driven by the buffering effect of the canopy from warming and climate extremes. Observed differences in climatic sensitivity between canopy positions underscore the importance of accounting for differential growth responses to climate between forest strata in future studies to improve ecological forecasts. Furthermore, latitudinal variation in the differential sensitivity of forest strata to climate reported here may help refine our comprehension of species range shift and changes in suitable habitat under climate change.
We compared tree growth response of different canopy strata to variations in climate across the boreal and temperate forests of North America using permanent sample plot networks. We observed an overall positive effect of warming on tree growth, but sensitivity to climate varied between overstory and understory canopy strata, likely driven by the buffering effects of the overstory canopy from warming and climate extremes. Our results underscore the importance of accounting for differential growth responses of forest strata to climate change in future studies to improve ecological forecasts and refine our comprehension of species range shift under global warming.
Disturbance regimes are changing in forests across the world in response to global climate change. Despite the profound impacts of disturbances on ecosystem services and biodiversity, assessments of ...disturbances at the global scale remain scarce. Here, we analyzed natural disturbances in boreal and temperate forest ecosystems for the period 2001–2014, aiming to 1) quantify their within‐ and between‐biome variation and 2) compare the climate sensitivity of disturbances across biomes. We studied 103 unmanaged forest landscapes with a total land area of 28.2 × 106 ha, distributed across five continents. A consistent and comprehensive quantification of disturbances was derived by combining satellite‐based disturbance maps with local expert knowledge of disturbance agents. We used Gaussian finite mixture models to identify clusters of landscapes with similar disturbance activity as indicated by the percent forest area disturbed as well as the size, edge density and perimeter–area‐ratio of disturbed patches. The climate sensitivity of disturbances was analyzed using Bayesian generalized linear mixed effect models and a globally consistent climate dataset. Within‐biome variation in natural disturbances was high in both boreal and temperate biomes, and disturbance patterns did not vary systematically with latitude or biome. The emergent clusters of disturbance activity in the boreal zone were similar to those in the temperate zone, but boreal landscapes were more likely to experience high disturbance activity than their temperate counterparts. Across both biomes high disturbance activity was particularly associated with wildfire, and was consistently linked to years with warmer and drier than average conditions. Natural disturbances are a key driver of variability in boreal and temperate forest ecosystems, with high similarity in the disturbance patterns between both biomes. The universally high climate sensitivity of disturbances across boreal and temperate ecosystems indicates that future climate change could substantially increase disturbance activity.
Increasing soil carbon and nitrogen storage can help mitigate climate change and sustain soil fertility
. A large number of biodiversity-manipulation experiments collectively suggest that high plant ...diversity increases soil carbon and nitrogen stocks
. It remains debated, however, whether such conclusions hold in natural ecosystems
. Here we analyse Canada's National Forest Inventory (NFI) database with the help of structural equation modelling (SEM) to explore the relationship between tree diversity and soil carbon and nitrogen accumulation in natural forests. We find that greater tree diversity is associated with higher soil carbon and nitrogen accumulation, validating inferences from biodiversity-manipulation experiments. Specifically, on a decadal scale, increasing species evenness from its minimum to maximum value increases soil carbon and nitrogen in the organic horizon by 30% and 42%, whereas increasing functional diversity enhances soil carbon and nitrogen in the mineral horizon by 32% and 50%, respectively. Our results highlight that conserving and promoting functionally diverse forests could promote soil carbon and nitrogen storage, enhancing both carbon sink capacity and soil nitrogen fertility.
Abstract
Climate warming has the potential to influence forest composition and species recruitment over the course of the 21st century. Although many of these impacts are expected to occur during the ...growing season, important life history events, like seed dormancy release, may be affected during the winter. For seeds of balsam fir (Abies balsamea (L.) Mill.) to germinate, they require a lengthy cold stratification period to break seed dormancy, which may not be experienced under warmer winters. Moreover, within Atlantic Canada, balsam fir populations experience very different climates. Dissimilarities among the genetics of these balsam fir populations and adaptations to their local environments may engender variations in population response to winter warming. In this study, we selected three balsam fir seedlots each from four different seed origin zones within Atlantic Canada and subjected them to simulated winter warming in outdoor seed plots that were heated to ≈ 6°C above the ambient temperature from December to April. Contrary to our hypotheses, germination success of the heated balsam fir seeds did not significantly decrease relative to the controls, and there was no interaction between warming and seed origin zone. Seedlots of some seed origin zones exhibited variable responses to warming, suggesting that dormancy levels substantially differ among populations from similar climates. This diversity in phenotype expression within balsam fir populations may improve this species resilience under future climate change.
1. Understanding the impact of forest harvesting is critical to sustainable forest management, yet there remains much uncertainty regarding how harvesting affects soil carbon (C), nitrogen (N) and ...phosphorus (P) dynamics. 2. Here, we conducted a global meta-analysis of 808 observations from 49 studies to test the effects of harvesting on the stocks and concentrations of soil C, N and and C:N:P ratios relative to uncut control stands. 3. With all harvesting intensities combined, C stock was unaffected by harvesting in either the forest floor or mineral soil, while harvesting reduced forest floor C, N and P and C:N ratio, increased the mineral soil C and C:N ratio, but reduced mineral soil N stock. The impacts of harvesting on forest floor C and N stocks, C:P and N:P and mineral soil C and N changed from no effects by partial, stem-only and whole-tree harvesting (WTH) to significantly negative effects by the harvesting coupled with fire. Stem-only and WTH similarly reduced forest floor P. The negative effects of harvesting were most pronounced in conifer stands. Soil C, N and C:N decreased with time since harvesting, but soil P did not, resulting in an increase in forest floor N:P. 4. Synthesis and applications. Our findings highlight the importance of harvest intensity and rotation length on long-term soil nutrient availability when managing forests. Furthermore, the lag in the recovery of phosphorus concentration following harvesting may indicate a decoupling of the phosphorus cycle from those of carbon and nitrogen, and a potential concern in managed forests.
•Species diversity effects on tree growth varied during forest succession.•Mid-succession, with increased functional diversity, exhibited stronger diversity effects.•Tree species showed ...individualistic responses to successional changes in diversity.•Individual tree size influence on species diversity effects was highly variable.
Although major advances have demonstrated that species diversity has a general positive effect on forest ecosystem productivity, some studies report negligible or even negative effects, highlighting remaining uncertainty in our knowledge of the ecological mechanisms that influence diversity–productivity relationships. In particular, ecological succession is postulated to drive temporal shifts in the strength and direction of diversity–productivity relationships, but few studies have explicitly tested this hypothesis because long-term succession data (from forest initiation to eventual climax) are rare.
Using a detailed, replicated chronosequence (space-for-time substitution) study design of 53 natural forest stands (ages 8 to 210 years) in the boreal forests of central Canada, we investigated the relationship between neighbourhood species diversity and tree growth of five dominant boreal tree species, covering entire, long-term secondary successional sequences following stand-replacing wildfire.
We found compelling evidence that the strength of the relationship between species diversity and tree growth changes over the course of secondary succession, following a general “hump-shaped” pattern, with mid-succession stages of higher functional diversity exhibiting the strongest growth–diversity relationships. However, tree species exhibited individualistic responses to succession-driven changes in species diversity, with broadleaf species (e.g., Populus tremuloides) generally showing negative responses, whereas conifers (e.g., Pinus banksiana) responded more favorably to higher neighbourhood diversity. Furthermore, our results show the effect of individual tree size on the relationship between species diversity and tree growth to be highly variable, contradicting the hypothesis that larger trees benefit more from complementarity due to size-asymmetric competitive ability. These results contribute to disentangling the mechanisms that link species diversity to forest growth and function, which is important to sustainable forest management planning and for predicting the consequences of global biodiversity loss, especially for the boreal forest, which plays a critical role in controlling global carbon flux and climate.
Many studies project future bird ranges by relying on correlative species distribution models. Such models do not usually represent important processes explicitly related to climate change and ...harvesting, which limits their potential for predicting and understanding the future of boreal bird assemblages at the landscape scale. In this study, we attempted to assess the cumulative and specific impacts of both harvesting and climate-induced changes on wildfires and stand-level processes (e.g., reproduction, growth) in the boreal forest of eastern Canada. The projected changes in these landscape- and stand-scale processes (referred to as "drivers of change") were then assessed for their impacts on future habitats and potential productivity of black-backed woodpecker (BBWO; Picoides arcticus), a focal species representative of deadwood and old-growth biodiversity in eastern Canada. Forest attributes were simulated using a forest landscape model, LANDIS-II, and were used to infer future landscape suitability to BBWO under three anthropogenic climate forcing scenarios (RCP 2.6, RCP 4.5 and RCP 8.5), compared to the historical baseline. We found climate change is likely to be detrimental for BBWO, with up to 92% decline in potential productivity under the worst-case climate forcing scenario (RCP 8.5). However, large declines were also projected under baseline climate, underlining the importance of harvest in determining future BBWO productivity. Present-day harvesting practices were the single most important cause of declining areas of old-growth coniferous forest, and hence appeared as the single most important driver of future BBWO productivity, regardless of the climate scenario. Climate-induced increases in fire activity would further promote young, deciduous stands at the expense of old-growth coniferous stands. This suggests that the biodiversity associated with deadwood and old-growth boreal forests may be greatly altered by the cumulative impacts of natural and anthropogenic disturbances under a changing climate. Management adaptations, including reduced harvesting levels and strategies to promote coniferous species content, may help mitigate these cumulative impacts.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Quantum-Guided Molecular Mechanics (Q2MM) can be used to derive transition state force fields (TSFFs) that allow the fast and accurate predictions of stereoselectivity for a wide range of catalytic ...enantioselective reactions. The basic ideas behind the derivation of TSFFs using Q2MM are discussed and the steps involved in obtaining a TSFF using the Q2MM code, publically available at github.com/q2mm, are shown. The applicability for a range of reactions, including several non-standard applications of Q2MM, is demonstrated. Future developments of the method are also discussed.
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