Forest Ecology and Management最新文献

Fire disturbances and atmospheric nitrogen (N) deposition can significantly soil nutrient dynamics and plant nutrient uptake, thereby influencing on biogeochemical cycles within forest ecosystems. Despite these known effects, the combined impact of burning and N addition on leaf nutrient characteristics and the underlying mechanisms remains largely unexplored, particularly within forest ecosystems. This study presents a three-year field experiment designed to assess the responses of leaf N and phosphorus (P) concentrations, N:P ratios, and nutrient resorption in six dominant species (comprising two tree species and four understory species) to burning and N addition in a coniferous-broadleaved mixed forest located within a subtropical-warm temperate transition zone in Central China. The findings revealed that burning did not affect N concentrations in either green or senesced leaves, nor did it influence N or P resorption across any of the tree or shrub species. However, it did increase P concentrations in green leaves and reduce N:P ratios in shrub species. N addition elevated the N concentrations and N:P ratio in green and/or senesced leaves (with the exception of Quercus acutissima Carruth.), without affecting N or P resorption. These results suggest that shrubs enhanced P uptake due to increased soil P availability but maintain consistent internal P cycling (i.e., nutrient resorption) following low-severity fires. Additionally, most shrub species exhibited lower N:P ratios compared to tree species post-burning, indicating distinct nutrient requirements and fire responses based on life form. This study provides essential insights, demonstrating that burning mitigates P limitation on plant growth in subtropical–warm temperate ecotonal forests. Furthermore, the differential responses of leaf nutrient traits and associated stoichiometry across diverse life forms to environmental disturbances may influence plant diversity and community composition within these forests.

Laminated Root Rot caused by the fungal pathogen Coniferiporia sulphurascens is a damaging disease within many Douglas-fir forests of the Pacific Northwest of North America. Management of these forests in a changing climate and fire regime will require changes to silvicultural practices. A long-term study (ca. 30 years) in Oregon, USA provides an opportunity to investigate the effects of thinning on disease dynamics in an area of historically high laminated root rot incidence. The effects of three thinning prescriptions on tree mortality caused by C. sulphurascens were compared on ca. 160 ha within the Siuslaw National Forest. Observations were compared with predictions from the Forest Vegetation Simulator and its Western Root Disease Model extension. No significant effect of thinning treatment on mortality (p = 0.981), or annual basal area increment (p = 0.372) was observed. In contrast to observations, the Forest Vegetation Simulator over estimated growth, while the Western Root Disease Model extension was consistent with field measurements. Thinning treatments appear to have minimal impacts on laminated root rot induced mortality but also do not result in the expected increase in growth rate typically associated with a thinning treatment.

Climate change-related extreme drought events already have a significant impact on the productivity and mortality of Central European forests. European beech (Fagus sylvatica ssp. sylvatica), one of the most important European broadleaved species, has responded to such drought periods with increasing mortality and reduced volume increment. This has raised concerns about its suitability and adaptive capacity in relation to future climatic conditions and motivated the search for alternative tree species that are suitable for assisted migration into European beech forests. One of the candidates is the Oriental beech species complex (F. sylvatica ssp. orientalis), whose range extends from the Balkan to Iran and, at least in some parts of its range, grows under a warmer and drier climate. In order to evaluate whether Oriental beech is more drought tolerant, we compared the radial growth response to droughts between 1920 and 2018 of a total of 138 European and 122 Oriental beeches growing under identical site conditions in eight different locations in Germany and France. The species identity of all analysed trees was verified by microsatellite analyses, and the origin of the introduced Oriental beech was traced to the Greater Caucasus (7 stands) and the Black Sea coast (1 stand). The drought responses of radial growth were quantified using the indices resistance, resilience, and recovery as suggested by Lloret et al. (2011) and growth recovery time (GRT) (Thurm et al., 2016) and used as response variables in generalized linear mixed effect models.

Considering only the average radial growth response to severe and extreme drought events, both the different Lloret indices and the GRT did not show prominent difference between Oriental and European beech. However, the mixed model analyses, which also included interaction terms, revealed interspecific differences in drought tolerance, depending on the intensity and timing of the drought. In extreme summer drought years, values of resistance predicted by the mixed-effect models were significantly higher in Oriental beech than in European beech, whereas its resilience was only slightly better than in European beech, regardless of drought intensities. In contrast, Oriental beech was much more susceptible to spring drought with significantly weaker growth recovery and distinctly longer growth recovery times.

Based on these results, Oriental beech provenances from the Caucasus do not appear to be sufficiently more drought tolerant than European beech to justify an assisted migration approach to adapt Central European forests to climate change. To analyse the drought tolerance of Oriental beech more comprehensively, introduced trees representing other genetic clusters need to be analysed, as well as the effects of repeated drought events on growth and mortality.

Numerous factors influence the frequency and intensity of forest fires. Forest fire damage and recovery are influenced by the species composition of the forests. This study assessed forest fire damage vulnerability and forest fire resistance according to the species composition of the forest stand (i.e., the proportion of needle leaf trees (NTs) versus broadleaved trees (BTs) within the forest stand). Following a forest fire event in South Korea, fire damage severity was determined by comparing the pre- and post-event normalized burn ratio obtained from Sentinel-2 imagery. In addition, using 3 m PlanetScope images, we were able to quantify (1) the species composition between NTs and BTs within 30 m of Sentinel-2 pixels and (2) the extent of fire damage and recovery based on changes in phenological timing events and the vegetation index. The results showed that the NT-dominated forest stands underwent more fire damage than the BT-dominated stands, and the differences increased with increasing fire severity. In NT-dominated forest stands, an increase in BT proportion led to a decrease in fire damage, whereas in BT-dominated forest stands, no such correlations were observed. Furthermore, the NT-dominated stands showed more delayed phenological events at the beginning and end of the growing season than the BT-dominated stands, implying slow post-fire recovery in the NT-dominated stands. Our results showed differences in fire damage vulnerability and recovery depending on species composition and demonstrated that the increased fire resistance of BT could improve the fire resistance of a forest stand. These results suggest that considering tree species biodiversity is critical for restoring fire-damaged areas, particularly in the context of climate change, where wildfire frequency is expected to increase.

Nutrient limitation of forest growth, especially nitrogen (N) deficiency, is widespread in the boreal region. N fertilisation has thus become a common silvicultural practice in Fennoscandian Norway spruce stands, but to what extent phosphorus (P) is co-limiting productivity and how initial basal area affects the growth response to N addition remains unresolved. To address these questions, two experiments were established in mid-rotation Norway spruce stands in southern Sweden where decades of high atmospheric N deposition have reduced the severity of N-limitation. In a P experiment initiated in 2011, we tested P addition alone (two applications of 200 kg P ha⁻¹) and in a second study also starting in 2011 (NP experiment), a single dose of N was administered alone (200 kg ha⁻¹ in thinned and unthinned stands, hereafter called N and N-unthinned treatments) and in combination with P (N+P = one-time 200 kg N ha⁻¹, two applications of 200 kg P ha⁻¹ in thinned stands). P addition alone increased PAI (periodic annual increment) significantly by 21 % during the first, moister assessment period up to 2014 and by 18 % in the drier 2015–2019 period, resulting in a 10 % increase in final stem volume yield. In the NP experiment, significant PAI increases under favourable meteorological conditions up to 2014 occurred in all fertilisation treatments. The strongest effects were seen in the N-unthinned treatment while no significant additive effect resulted from the joint addition of N and P (N: +20 %, N-unthinned: +38 %, N+P: +23 %). In the drier 2015–2019 period, only the N+P treatment caused significantly greater PAI (+29 %). Final stem volume yield in the NP experiment significantly increased by 10 %, 39 % and 16 % in the N, N-unthinned and N+P plots, respectively. In both experiments, foliar P and thus P/N rose drastically in response to P addition alone or in combination with N. Minor increases in leaf area index (LAI) only occurred in P-containing treatments. Our findings indicate that Norway spruce productivity in southern Sweden is constrained to a similar extent by both N and P. Sustainable nutrient management in Norway spruce growing regions with high N loading (like southern Sweden) should prioritise P over N supply.

In response to the combined impacts of the climate and biodiversity crises, as well as for timber security and increased recreational access to green spaces, there is a global drive to increase tree cover. In the UK, an estimated 1.5 million ha of afforestation are required to meet its carbon net-zero emissions targets (Committee on Climate Change, 2018). Despite the potential benefits, careful consideration must be given to the impacts of woodland creation on species adapted to open habitats. To investigate potential risks and mitigation for the IUCN Near Threatened Eurasian curlew Numenius arquata, a national spatially extensive field-scale dataset was used to investigate the relationships between curlew presence during the breeding season and a range of forest and landscape variables at two different spatial scales (0.5 km and 1 km). Variables included forest extent and configuration, and interaction between forests and extent of semi-natural open habitats, moorland management and topography. At both spatial scales, a negative relationship existed between extent of forest and the probability of curlew presence, and at 1 km, between probability of presence and the number of forest patches. However, these negative patterns depended on landscape context and were reduced where there was a greater quantity of semi-natural open habitat, such as moorland or rough grassland, and moorland management present. Overall, the findings emphasise the need to consider the impacts of woodland creation projects on species adapted to open habitats. However, the results suggest that these impacts can be influenced by landscape. These results could help inform decisions regarding the appropriateness of woodland creation in different landscapes and possible mitigation measures that could be applied against the risks created by afforestation.

Windthrow is a disturbance in south-eastern Australian forests which significantly re-arranges forest and fuel structure by removing canopy trees. The implications for fuel dynamics and fire behaviour remains unquantified, making it a concern for fire managers. This study quantifies changes to forest and fuel structure caused by windthrow of varying severity, and uses this data to consider potential implications for fire behaviour. Thirty sites were established across dry eucalypt forests in south-eastern Australia ∼2 years after a severe windstorm resulted in extensive areas of windthrow. Ten sites were selected within each of unimpacted, low and high severity windthrow areas. Fine fuels were assessed using visual estimates of height, cover and percent dead across various fuel strata (surface; near-surface; elevated; bark) to develop fuel hazard scores using established protocols. Coarse fuels (fallen branches, logs) were assessed using a line-intercept survey. Fuel data were used to calculate expected fire behaviour (rate of spread, flame height, total heat output and residence time) across windthrow severity. The trends in both fine and coarse fuels were largely reflective of the forest structural changes induced by windthrow. Surface fuel (i.e. dead litter on the forest floor) decreased in depth and cover, while near-surface fuels increased in cover, height and proportion of dead with increasing windthrow severity. This reflects a reduction in litter inputs from reduced canopy cover, and an increase in the abundance of grasses and fallen canopy debris. Elevated fuels (i.e., shrubs) were unchanged across windthrown and unimpacted sites;bark fuel decreased with increasing windthrow severity, reflecting a reduction in standing basal area at severely impacted sites. Coarse fuel loads substantially increased with windthrow severity: high severity sites had ∼300 Mg/ha of coarse fuel loads compared to ∼20 Mg/ha at unimpacted sites. The changes in fine and coarse fuels resulted in a 1.2-fold increase in predicted flame height and a 17-fold increase in total heat output and residence time in high severity windthrow sites compared with unimpacted sites. Our research shows that windthrow produces complex and contrasting patterns in fine and coarse fuel loads, and the increase in near-surface and coarse fuels confers greater potential fire intensity via increased flame height, total heat output and residence time. Windthrow represents a conundrum for fire managers who are required to balance the reduction in fire risk while also retaining the important habitat resource fallen logs represent.

Plant flammability research has proven pivotal in comprehending the contribution of vegetation to the flammability of forest ecosystems. Yet, the relationship between many leaf chemical traits and plant flammability is poorly understood. While terpenes and some leaf nutrients in plants have been extensively studied for their role in flammability, a wide array of other secondary metabolites remain unexplored in this context. Here, we present the volatile secondary metabolites composition of fresh leaves from nine dominant species from central Chile, both native and exotic, and determine whether there is variability within and among species in chemical composition and flammability. Moreover, we investigate how these compounds influence various leaf flammability traits. The Chilean Mediterranean ecosystem emerges as a useful study site given its unique endemic flora, increased frequency of forest fires, proliferation of invasive plants and extensive land conversion that favors the spread of fire-prone exotic species, and significant scarcity of phytochemical research dedicated to this ecosystem. A total of 118 volatile chemical compounds were quantified, belonging to over ten groups of volatile secondary metabolites. Terpenes, ketones, and hydrocarbons comprised 75 % of these compounds, and each species displayed a unique phytochemical profile. Surprisingly, some native species (Citronella mucronata, Cryptocarya alba) exhibited equivalent or higher leaf flammability than the well-known flammable exotics Eucalyptus globulus and Pinus radiata, respectively. Leaf flammability was best explained by the concentration of aldehydes, ketones, green leaf volatiles, and aromatic compounds. Interestingly, terpenes as well as moisture content were not significantly correlated with flammability. In conclusion, our results highlight the importance of considering a broader range of phytochemicals, beyond terpenes, to fully understand leaf flammability among species. Consequently, a deeper understanding -within and across ecosystems- of the influence exerted by diverse groups of phytochemicals on flammability is an urgent need for forest management planning in an increasingly flammable world.

Lightning is the primary natural ignition source for wildfires. However, in certain ecosystems, anthropogenic fires predominate and account for the majority of fire incidents. In many countries, the prevailing perception holds that wildfires are overwhelmingly human-caused. While statistically accurate when pooling data from across the country, this perspective leads to a misconception that wildfires are not a natural component of ecosystems. This generalization requires a critical examination of regional variability in lightning-induced wildfires (LIWs). As a case study, we examined the spatial distribution of LIWs in Türkiye using national wildfire data between 2002 and 2022. We considered three main wildfire causes: human-caused, lightning-induced, and unknown-origin. We investigated the distribution of fire occurrences and burned areas to demonstrate the spatial variability of LIWs and human-caused fires (HCFs) across Türkiye at the regional and local forest management unit levels. We found considerable regional and local disparities in the incidence of LIWs across Türkiye. We also observed a higher incidence of LIWs in areas with higher lightning densities, especially in the mountainous regions of western and northern Anatolia, including southwestern and northwestern Anatolia. In certain years, the proportion of LIWs exceeds 45 % in some regional units and 75 % in many local units. However, LIWs burned significantly smaller areas than HCFs. The most populated regions primarily experienced HCFs, while in several other regions, including less-populated or forest-rich ones, lightning was a major source of wildfires. Seasonal trends also emerged, showing an increased prevalence of LIWs, with a peak during the fire season and a relatively higher percentage during seasonal transitions. Despite the increasing human activity, LIWs have remained a significant cause of wildfires in several regions in the country. Our results on the significant spatial variability in LIWs challenge the traditional belief that human activities are the primary ignition sources for wildfires across Türkiye and downplay lightning as an ignition source. Our findings suggest that a one-size-fits-all fire management strategy which has led to wildfire suppression policies for the past century is suboptimal for countries where lightning is a significant source of wildfires. Therefore, an ecologically sound and economically efficient wildfire management policy must account for regional variability in the causes of wildfires. Accordingly, we recommend a reassessment of blanket fire suppression strategy in several countries such as Türkiye, advocating for more selective suppression practices that consider the role of naturally occurring wildfires.