Forest Ecology and Management最新文献

Climate change-induced windfalls and droughts exacerbate bark beetle outbreaks, severely impacting forest ecosystems. Despite extensive research on bark beetle infestation patterns, the question regarding the optimal spatial grid (SG) size for analyzing this phenomenon remains unresolved. The protective potential of natural forest complexity against bark beetles has been underestimated. We used remotely sensed data to fit Generalized Linear Models and structural equation models to explore the direct and environment-mediated effects of mixed forest cover (MFC) on Norway spruce forest infestation in central Europe. We assessed the effectiveness of various spatial grids (from 100 m to 1 km) for studying infestation by Ips typographus. We found a strong non-linear decline in infestation with increasing MFC across different spatial scales. The relationship between infestation and temperature was positive, while elevation had a negative effect on infestation, with higher infestation rates observed below 900 m. Direct effects of environmental predictors on infestation were significant at SGs of 100 m, 300 m, 400 m, and 500 m, but insignificant at 200 m and 1000 m SGs. Slope positively influenced infestation at 300 m and 400 m SGs. MFC exhibited significant indirect effects on infestation mediated by elevation, temperature, potential evapotranspiration, slope, and heat load index. Landscape variables played a significant role in the models at high-resolution spatial grids, whereas climate variables were influential in models at lower spatial grids of infestation data. We argue that mixed forest facilitates cooling, preserves water, enriches symbiotic fungal community, alleviating tree drought stress and mitigating infestation risk. Broad-leave trees’ non-host volatiles presumably disrupt olfactory signals, impeding beetles’ ability to locate host trees effectively. Our results underscore the potential of increasing mixed forest cover as a self-sustainable silvicultural measure for forest protection against I. typographus and for mitigating the effects of climate change.

A recent paper by Karpov et al. (2024) discusses forest disturbances on Kunashir Island due to windstorms and bark beetle outbreaks. The study uses medium-resolution satellite data, which we argue is conceptually flawed for analyzing windthrows and spruce dieback in mixed forests of the study area. The results significantly underestimate disturbed areas by over 50 %. Here we highlight the methodological shortcomings of the Karpov et al. (2024) study and caution against using medium-resolution data for forest disturbance detection in mixed forests. Such underestimations can provide an extremely imprecise baseline for disturbance impacts under climate change, potentially misguiding projections of impacts on forest ecology and management.

Douglas fir is a largely introduced species in Europe and is often presented as a promising alternative to more drought-sensitive species. However, the observed and predicted increase in drought frequency and intensity could undermine its ability to cope with drought. This study aims to investigate the radial growth response of Douglas fir to drought in its climatic optimum in Europe, considering a number of drought characteristics (in terms of timing during the growing season, intensity, and consecutive occurrence), site conditions (average climatic water balance, maximal extractable soil water), and stand densities. Using growth data from 360 trees sampled across 24 sites in Wallonia (Belgium), we fitted linear mixed models to investigate the influence of drought, site, and stand characteristics on three commonly used resilience indices, as well as on an integrated index comparing observed resilience with a theoretical full resilience reference. On average, radial growth was reduced during droughts regardless of drought characteristics and site conditions. Trees always recovered to some extent, but not always to full resilience. Drought characteristics had a stronger influence on drought response than site and stand characteristics. Under the most intense droughts, trees were less resistant and less resilient to early droughts than to late droughts. Higher intensity and consecutive droughts increased the negative impact of a drought on resistance and resilience. Resistance was slightly higher on sites that were wetter and had higher maximal extractable soil water. In contrast, resilience to non-consecutive droughts was higher on drier sites. Finally, we did not detect any significant impact of stand density on Douglas fir growth response. The integrated index showed that Douglas fir has the best chance to be completely resilient to droughts when droughts are later, not very intense, and not consecutive and when trees are located on more water-limited sites. In conclusion, Douglas fir radial growth may not be as drought-resilient as expected. It is therefore advisable to avoid an overreliance on this species, and increase species diversity to strenghten forest stability. In this context, future research avenues could involve the comparison of drought response of Douglas fir with other species.

Pollarded oak woodlands have been historically managed by people to produce firewood and timber. Pruning cessation and climate warming could contribute to their decline, especially in southern Europe under ongoing aridification. Widespread pollarding abandonment could make oaks more responsive to drought stress and increase between-site growth synchrony. To fill this research gap, we compared the basal area increment (BAI) trends and the responses of growth indices to climate variables and a drought index of formerly pollarded oak stands (five stands of Quercus faginea, one stand of Q. humilis) located in northern and eastern Spain. Radial growth indices were correlated with monthly climate variables (mean maximum and minimum temperatures, precipitation) and a multiscalar drought index. BAI was also projected based on recent trends to forecast stands viability in the 21st century. Major growth suppressions (MGS), which were attributed to pollarding, were reconstructed using dendrochronology. Wet-cool conditions from prior winter to current early summer improved oak growth. Year-to-year growth synchrony has increased since 1850 as summer conditions became more arid, but BAI did not significantly decline in four out of the six study sites. Synchrony among sites regarding MGS was low indicating a high spatial variability in oak pollarding. The strongest BAI decline was observed in La Guarguera site, where growth cessation was forecasted in the mid-21st century. In contrast, BAI data suggested strong growth improvement in sites Campillo de Dueñas and Valsalobre, which were pollarded in the 1960–1970s. These findings confirm that pollarding is a suitable management tool to keep vigorous old oak stands under more arid climate conditions.

Drought induced great tree growth declines and high mortality, leading to high uncertainty in carbon storage estimation. The influences of droughts on tree growth had been extensively explored, however, how to predict tree growth during drought years to reduce uncertainty in carbon storage prediction is still challenging. We utilized a combined approach of random forest importance assessment and the "VSURF" package in R software to optimize the variable selection, and then used the selected variables in random forest and multiple linear regression (MLR) method to predict the tree growth based on 132 monthly climate variables and tree-ring network consisting of 1198 Larix gmelinii var. principis-rupprechtii trees from 48 sites. Forty-three out of 132 variables were selected if the random forest importance assessment was only used to selected climate variable, however, twelve important variables were identified by optimized variable selection, which further improve model efficiency with the least variables. The comparison between random forest and MLR showed that the predictions of the random forest model showed a better fit with the observed tree-ring values than MLR from 1989 to 2018. The predicted growth of L. gmelinii var. principis-rupprechtii is better in dense sites compared to sparse sites. During summer drought years, random forest performs well to predict tree growth in densely distributed sites. Our results highlighted the usage of optimized variable selection method combined with the random forest model to predict drought-year growth over the dense sites. Our study is crucial to predict drought-year carbon sink of planted larch forests under different climate changes scenarios in the future.

Increasing wildfire activity has spurred an increasing push for the application of prescribed fire to reduce wildfire risk while simultaneously acting as a surrogate for fire’s historical role as a fundamental ecosystem process. However, prescribed fires are often ignited using uniform ignitions to maintain operational control and there are concerns that they may not be able to replicate the landscape heterogeneity, particularly patterns in unburned patches, generated by historical fires. Fire refugia, unburned areas within fire perimeters, play an integral role in determining post-fire recovery and community structure. We assess patterns in fire refugia across 443 large (>200 ha) wildfire and prescribed fire perimeters using remotely sensed fire severity data in longleaf pine (Pinus palustris) savannas of the Florida Panhandle. Contrary to concerns, large prescribed fires had a significantly greater proportion of unburned area than wildfires, driven by larger refugia patch sizes. Drier conditions promoted smaller and more numerous fire refugia patches. Our study demonstrates differences in wildfires versus prescribed fire outcomes on landscape structure, with implications for future longleaf pine savanna management.

Solar radiation is a major driver of forest ecosystems and affects the hydrological cycle and energy balance. The vitality of trees strongly depends on the amount of light input to individual trees, and successful forest regeneration demands a certain level of solar radiation. Therefore, characterization of the light regime inside a plant canopy (i.e., quantification and timing of light penetration) is of particular importance. Because these parameters greatly depend on the 3D structure of the forest canopy, Light Detection and Ranging (LiDAR) systems provide suitable technology for solving this task. In this study, an algorithm was developed to estimate the amount of potential solar radiation reaching the forest floor from a point cloud collected in a temperate mixed forest located in Lanzenkirchen (Lower Austria) using terrestrial LiDAR. The path length through the canopy was calculated for 40 forest inventory plots as the distance between the first and last canopy hit along a sun ray, that is, for each day during the vegetation period at an hourly resolution. This distance was easily derived from the z-coordinates of the point cloud after transforming the latter into a coordinate system in which the z-axis ran parallel to the sun rays. Applying Beer’s law, the amount of solar radiation on the forest floor was expressed as a function of the solar radiation above the canopy and the path length through the canopy. To validate the results, we used two sets of reference data: (1) hemispherical photographs taken at the same plots, using a camera on a self-levelling mount, which were processed with the HemiView software, and (2) data from a Solariscope survey. Both the Solariscope and HemiView software calculate below-canopy radiation as a percentage of above-canopy radiation, joining direct and diffuse radiation (Total Site Factor, TSF). The TSF values obtained from our modeling procedure were consistent with the Solariscope ($\mathrm{R²}=0.61$) and HemiView ($\mathrm{R²}=0.71$) results for the entire growing season. Because modern LiDAR-based forest inventories provide all the necessary data for our light modeling approach (the point cloud, the geographical position, and a record of the occurring tree species) without additional requirements, together with the easy applicability of the algorithm, this tool is a promising asset for ecological and silvicultural activities.

Multiple ecological drivers, along with forest age, determine the species composition of boreal forest ecosystems. However, the role of age in successional changes in forests cannot be understood without taking site conditions, the disturbance regime and forest structure into account. In this study, we ask two research questions: 1. What is the relationship between forest age and overall species composition in older near-natural spruce forests, i.e. forests of age beyond harvest maturity? 2. Do species associated with different forest habitats respond similarly to variation in forest age? Data were collected in 257 Norway spruce dominated 0.25 ha plots from three study areas in Southeastern and Central Norway. Species inventories were conducted for lichens and bryophytes on trees and rocks, vascular plants on the forest floor, and for deadwood-associated bryophytes and polypore fungi. Although NMDS ordination analyses of the total species composition identified a main axis related to the age of the oldest trees in two of the study areas, variation partitioning analyses showed that age explained a small fraction of variation of the species composition compared to site conditions, logging history, forest structure, and differences between the sites in all habitats. The unique variation explained by forest age species was, however, significant for all habitats. The fraction of variation in species composition explained by forest age was the largest for lichens and bryophytes on trees, and for deadwood-associated bryophytes and polypore fungi. Our results suggest that practical mapping of near-natural forests for management purposes inventories should include site conditions, forest structure and between site differences in addition to forest age.

Afforestation programs as a strategy to address the climate crisis are on the rise worldwide. Although concerns exist about the effects of afforesting treeless habitats on their biodiversity and ecosystem services, potential impacts on areas beyond afforestation boundaries have been largely overlooked. Cork oak (Quercus suber) woodlands in southern Spain are regarded as a successful example of sustainability. However, the afforestation of their neighbouring treeless habitats may compromise their productivity through indirect effects that are not fully understood. Using a multi-method approach, we studied the effects of the afforestation of Mediterranean heathland (herriza) areas with pine tree species on the productivity of neighbouring cork oak woodlands downslope over a 37-year period. The differences in Normalized Difference Vegetation Index (NDVI) and Basal Area Increment (BAI) between cork oak woodlands below open herriza and below afforested herriza became apparent approximately ten years after pine afforestation. Specifically, NDVI was significantly reduced in cork oak stands below afforested herriza areas for the remaining years, while a substantial decrease in BAI of cork oak trees was also associated with afforested herriza areas upslope. Moreover, the NDVI and BAI trends of cork oak stands below afforested herriza reached the minimum levels of the time series following an extreme drought event. Our results reveal that the ecological impacts of afforestation of naturally treeless habitats can expand beyond the plantation area. We propose that the restoration of treeless habitats, such as the herriza, in areas where pine plantations are no longer productive, may enhance their ecological services, particularly in the context of climate change. Therefore, afforestation programs worldwide should carefully consider the trade-offs between carbon mitigation and other ecosystem services at the landscape scale.

Aims

Many empirical studies have found neutral or positive effects of forestry on plant alpha diversity in temperate deciduous forests, reflecting a positive effect of soil and canopy disturbances caused by forestry operations. The level to which this positive response to artificial disturbances mimics processes in natural forest ecosystems is less clear; hence, the systemic effects of forest management on ground floral communities remain obscure.

Location

Temperate Europe, Denmark.

Methods

We studied communities of ground-dwelling bryophytes and vascular plants in 400 plots distributed across 40 beech stands across four classes of forest management intensity – long unmanaged, recently unmanaged, near-to-nature managed, and shelterwood managed – while recording the incidence of a diverse array of microhabitats related to hydrology, canopy closure and soil disturbance.

Results

Microhabitat availability differed considerably among forest management classes as a response to management. Overall, forest management had a significant positive effect on the plot-level alpha diversity of both vascular plants and bryophytes. In contrast, beta diversity and total ecospace decreased with forest management intensity. Litter accumulation simultaneously decreased alpha diversity in both groups, while light availability, soil exposure and presence of wetlands respectively, were crucial for vascular plant and bryophyte richness. Forestry-created canopy gaps had a similar effect on alpha diversity as natural tree-fall gaps but supported a different set of species, mainly ubiquitous generalists.

Conclusions

Even if plant alpha diversity was lower in unmanaged forest stands, this did not significantly affect gamma diversity across the sampled stands, suggesting that plant richness needs to be considered at a relevant scale when evaluating forest management impact on biodiversity. These scaling issues seem to reflect fundamental differences in disturbance dynamics in managed and unmanaged forest ecosystems, which are typically not well accounted for in monitoring and research. A better understanding of disturbance dynamics in forest ecosystems and their spatial impact on biodiversity is needed to guide ecological restoration and management for biodiversity in production forest.