查看更多>>摘要：? 2022 Elsevier B.V.Bracken (Pteridum arachnoideum) is an invasive fern species that slows or inhibits forest regeneration over vast areas worldwide, affecting biodiversity, ecosystem functions and productivity. To overcome arrested succession, effective restoration interventions are necessary. We examined the effects of planting pioneer shrubs on establishment success in mid- to late-successional tree species transplants, and their combined effects on bracken dominance in abandoned pastures of former cloud forest in Mexico. We hypothesised that the rapid development of nurse shrubs will reduce bracken growth and facilitate mid- to late-successional tree species establishment. We analysed the effects of planting cuttings of the shrubs Tithonia diversifolia and Sambucus nigra on bracken and on the seedling performance of Juglans pyriformis, Quercus insignis, Meliosma alba and Tapirira mexicana, in three sites under four treatments: (1) trees without shrubs, (2) trees with T. diversifolia, (3) trees with S. nigra, and (4) trees with both T. diversifolia and S. nigra. Increased transplant performance was expected under mixed shrub species, compared to single shrub species plantings, due to complementarity in the use of resources (niche separation). After two years, plantings with shrubs and trees reduced bracken cover by >60% and bracken live rhizome biomass by >50%. Shrubs effects were species-specific, reflecting a complex combination of facilitation and competition mechanisms. In comparison to the trees without shrubs, survival of M. alba and Q. insignis significantly increased with T. diversifolia, T. mexicana survival decreased with S. nigra and J. piriformis survival decreased with T. diversifolia and the mixture. The results support the use of cuttings of T. diversifolia or S. nigra separately, rather than in combination, and the inclusion of mid- to late-successional trees, to assist recovery of degraded cloud forest areas where succession has been stalled by bracken. An integrated management approach that considers synergistic factors causing plant mortality in bracken sites needs to be addressed.
查看更多>>摘要：? 2022 Elsevier B.V.Bamboo species are cultivated for different purposes around the world, mainly because they adapt easily to environmental changes. However, their aggressive growth strategies and competitive superiority make bamboos opportunistic, allowing for rapid colonization. The aim of this study was to evaluate the effect of bamboo management methods on the structure and composition of seed rain. We evaluated seed rain in riparian areas with and without bamboo dominance. In the area dominated by bamboo we evaluated: control (no interventions), chemical management, and mechanical management treatments. The area without bamboo dominance is a seasonal semi-deciduous forest remnant, considered a reference ecosystem. The control treatment showed a lower abundance of seed rain than the other treatments. The chemical treatment presented greater total abundance due to the overabundance of the morphospecies Mikania sp.; however, the species richness did not differ from the control treatment. Moreover, the chemical treatment showed low seed input with biotic dispersal, differing from the mechanical and reference treatments. Seed abundance for both dispersal mechanisms (biotic and abiotic) was similar between the mechanical and reference treatments. We concluded that the bamboo management methods favored the increase in seed rain. The bamboo mechanical management treatment facilitated seed dispersal and provided a significant increase in terms of richness and abundance in relation to the control treatment. Despite not showing a significant increase in richness, the chemical management treatment promoted a significant increase in seed abundance in relation to the control treatment.
查看更多>>摘要：? 2021Although it is well-established that macroinvertebrates are an integral part of a healthy stream ecosystem, studies designed to inform forest harvest best management practices for sustainability of macroinvertebrate communities in small streams have been limited. Current riparian management practices for headwater streams generally focus on providing adequate wood supply, reducing debris flows and transport of sediment, and maintaining water quality in larger streams that contain fish. Here we studied the effects of contemporary forest harvest practices on benthic macroinvertebrate density and community composition in 12 small headwater streams as part of the Trask River Watershed Study. To account for seasonal and year-to-year variability in macroinvertebrate densities, we sampled each site at the same time of year for six years before and four years after harvest. Three watersheds were clearcut with variable riparian buffers, three were clearcut with 12 m riparian buffers, and one was thinned with 15 m buffers. Five adjacent watersheds were not treated and were studied as reference sites. All sites had approximately 50 yr old conifer and alder forests, which had revegetated following fires and harvest in prior decades. In these steep mountain streams, benthic macroinvertebrate density and community composition were generally similar across watersheds prior to harvest. Collectors were the most abundant functional feeding group, followed by shredders; scrapers were the least abundant. After harvest, in two of the three clearcut watersheds with variable buffers, the total benthic density and percentage of collectors increased, primarily due to greater numbers of Chironomidae. We also observed more abundant emergence post-harvest at these two watersheds. In the third clearcut watershed with a variable buffer and in the three clearcut watersheds with uniform 12 m riparian buffers, we did not see changes in density or functional feeding groups after harvest. We explored the spatial and temporal aspects of the data using both non-parametric and parametric statistical methods. High variability swamped the treatment effect when watersheds were grouped by riparian treatment for the repeated measure analyses, while NMDS showed a significant shift post-harvest for the watersheds with variable buffers. In the clearcut watersheds with uniform buffers, macroinvertebrates densities and community composition did not shift. At two of the clearcut watersheds with variable buffers, we observed increased density for the first two years after harvest, and chironomids comprised up to 80% of the abundance in samples. In the subsequent years, we documented mixed responses for two watersheds. It was invaluable to have multiple pre- and post-harvest sampling periods in both harvested and reference watersheds in order to better identify site specific responses to treatment and to separate background variability from responses to harvest. We show that retention of riparian vegetation on headwater streams during clearcut harvesting minimized changes in total macroinvertebrate densities and community composition. Small buffers may be key to maintenance of diverse stream invertebrate communities in headwaters.
查看更多>>摘要：? 2022 The AuthorsThe damage to trees that is caused by ungulate species is a natural result of their presence in ecosystems. High densities of ungulates may have a negative effect on biodiversity and the regeneration and survival of trees. The aim of this study was to identify the factors that affect the probability of the occurrence of damage in forest stands as a result of the presence of European bison (Bison bonasus). We collected data on the presence of European bison in given locations in winter and spring of 2020; this data also concerned damage to trees, forest stand characteristics, and densities of other ungulates. European bison was the most important debarking agent. Within the home range of the European bison, 344 forest stands were damaged, which represented 43.5% of all stands. The most frequent damage was bark stripping, 35.9%. The most important factors in terms of bark damage were canopy cover, dominating tree species, dominating tree age, and distance to a feeder. More debarking occurred in stands with open canopies, and coniferous species were more likely to be damaged than broadleaved species. Frequency of damage in forest stands with dominating Norway spruce was higher than 0.5, whereas for forest stands with silver fir and Scots pine it was over 0.4. Other coniferous species also presented a relatively high proportion of damage (0.38). The results of our study indicate a need for rational damage-prevention measures in the ranges of other free-living wisent populations that live in managed forests.
查看更多>>摘要：? 2022 Elsevier B.V.It is important to guarantee the property of biological compatibility when estimating tree biomass of the total and components for carbon accounting under global climate change. The issue was successfully considered in traditional nonlinear regression models, but not for machine learning methods. A new method for approaching the compatibility of tree biomass estimation in ANN (Artificial Neural Network) was developed by using the multi-task loss function, which had the desire features of minimizing residuals and approaching biomass compatibility. The method was tested by two tree species biomass dataset and showed the desired feature. Leave-one-out validation results showed that comparing ANN model with simultaneously fitting 7 outputs (stem, bark, branch, leaf, crown, trunk, aboveground) and classical loss function, the RMSE of aboveground estimation (AGB) and the mean absolute relative difference between AGB and the sum of component biomass estimations from the model developed by our new method decreased from 166.864 (kg) to 154.860 (kg) and from 4.757% to 0.071%, respectively for Abies nephrolepis dataset, and from 49.18 (kg) to 33.060 (kg) and from 5.314% to 0.636%, respectively for Acer mono dataset. It provided a trade-off solution for the error accumulation and the compatibility among components and the total estimations when using ANN for tree biomass modelling, and was useful for carbon accounting using machine learning methods.
查看更多>>摘要：? 2022 Elsevier B.V.In a changing world, riparian forests are coming under more and more stress from biotic threats. This impacts all stages from saplings to older trees. One of the most dominant biotic threats are alien species and eruptive pest species. Sustainable silvicultural methods are required to reduce the risk of such biotic threats. We investigated the influence of climate, site, tree, and silvicultural characteristics on leaf damage by insect pests or fungal pathogens, herbaceous alien plant species, browsing, and the abundance of native tree saplings. Transects across the Danube-Mura-Drava biosphere reserve from Austria in the northwest to Serbia in the southeast, each containing 7–8 plots, were established to assess tree and site characteristics, regeneration, as well as fungal and insect leaf damage. We found that the horizontal stand structure affected insect leaf damage in different ways. Insect leaf damage was positively correlated with fungal leaf damage and tree height, and negatively correlated with intensity of forest management (from natural forests to coppice/plantations), temperature and precipitation during the vegetation season. Fungal leaf damage was negatively associated with intensity of forest management, and negatively with public ownership and tree species richness. Browsing was positively influenced by the number of saplings. The abundance of alien herbaceous plant species was negatively associated with distance to the watercourse, mean tree height, mean temperature of the vegetative period (MTVP), competition level, and the number of trees per layer, and positively associated with the DBH.
查看更多>>摘要：? 2022Tree volume equations including branches are scarce in forestry literature, especially in diverse tropical forests, where the variability in tree shapes hampers the development of overall volume descriptions. We present species-composite cumulative volume profile models that describe the volume contained up to a given height in the trunks and crowns of tropical trees. We use terrestrial laser scanning (TLS) and quantitative structure models to estimate the trunk and crown volume of 177 trees (49 species) in a lowland tropical forest in the Barro Colorado Island in Panamá. These models were fitted using multilevel mixed-effects models recognizing the diversity of architectures in tropical trees. We found that (1) the rate at which volume accumulated with height was much higher and variable in the whole tree (trunk + branches) than only in the trunk; (2) the variability in the rate of volume accumulation was three times higher in the trunk and nine times higher in the whole tree across individuals within species than between species; and (3) parameters describing the rate of volume accumulation significantly depended on the height of attachment of the lowest branch, but not on the tree size. The resulting equations can be used to estimate the proportion of volume contained up to any height in tropical trees.
Elias F.Ferreira J.Nascimento R.O.Maria Moraes de Seixas M....
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查看更多>>摘要：? 2022 The AuthorsSecondary forests (SFs) growing on previously cleared land could be a low-cost climate change mitigation strategy due to their potential to sequester CO2. However, given widespread changes in climate and land-use in the Amazon in the past 20 years, it is not clear whether current rates of carbon uptake by SFs reflect estimates based on dividing the carbon stock by the estimated age of the forest. This is important, as differences between methodological approaches could lead to important discrepancies in estimates of carbon accumulation. Furthermore, we know little about how carbon uptake rates of secondary forests vary across some of the most deforested regions of the Amazon, where reforestation actions are most needed. Here, we compare the rates of carbon accumulation estimated over the lifetime of a stand (by stand age) with the contemporary rates estimated by recensus data, based on 28 permanent SFs plots distributed across four regions. Then, we compare how carbon uptakes rates vary across regions and how they compare to previous studies. The average rates of contemporary (1.23 ± 0.57 Mg C ha?1 yr?1) and lifetime (1.14 ± 0.63 Mg C ha?1 yr?1) carbon accumulation were strongly correlated (r = 0.78) and similar between regions. Overall, our carbon accumulation rates were much lower than other estimates of Amazonian SFs, which suggests that regions with the greatest opportunities for large-scale implementation of SFs have some of the slowest rates of carbon accumulation. Contrary to predictions from chronosequence analysis, the lack of difference between lifetime and contemporary rates of carbon accumulation suggests forests are maintaining a consistent rate of growth in the first decades after abandonment. These results—combined with the high rates of ongoing environmental change - highlight the importance of continuing to monitor the rate of carbon accumulation in secondary forests. This is necessary to support the implementation and monitoring of large-scale passive restoration in the highly-deforested Amazon.
查看更多>>摘要：? 2022Warming temperatures and drought are leading to unprecedented irruptions of forest insects worldwide. Altered climatic regimes have the potential to allow native forest insects to express novel behaviors and expand in latitude and elevation beyond their hypothesized thermal tolerances. Yet, disentangling the drivers of novel behaviors and range expansions is difficult due to cross-scalar interactions that dictate forest insect population dynamics. We investigated the irruptive dynamics of western balsam bark beetle (Dryocoetes confusus Swaine), which undergoes intermittent, long-lasting, but low-severity outbreaks in subalpine fir (Abies lasiocarpa Hook) forests. We compiled data from 1998 to 2019 across British Columbia, Canada, at 1 and 16 km2 resolutions to describe the spatiotemporal structure of beetle outbreaks, predict the landscape susceptibility to outbreaks, explain when outbreaks occur based on bioclimatic drivers, explore whether beetle populations exhibit self-driving growth, and determine whether the extent of outbreaks has increased. Overall, we found that outbreaks occur in discrete clusters and are synchronous at distances of 10–25 km. Further, we found that landscape susceptibility to beetle outbreaks was best explained by latitude*elevation (i.e., the product of latitude [m] and elevation [m] Z-standardized) and volume of fir (m3/ha; >17.5 cm size class; >100 yrs.) both within 8 km and each pixel. Meanwhile, a longer growing season, increased growing degree day accumulation, and drought best explained when outbreaks occurred. Further, we did not find evidence to suggest that beetle populations exhibit self-driving population growth. Finally, we found that the extent of beetle outbreaks has increased over the last 20 years and that increases in landscape susceptibility primarily occurred at higher latitude*elevations and were best explained by an increase in the mean growing season and degree day accumulation. In other words, abnormally warm temperatures have facilitated a northward and upward expansion of western balsam bark beetle. Collectively, these results serve as the first quantification of the spatiotemporal dynamics of this understudied insect and support previous modeling efforts to investigate the multi-scale drivers of western balsam bark beetle outbreaks. We propose that future work should identify specific supercooling points, the relationship between temperature and development rate, and how the relatively high within-stand variability in age and size class of subalpine fir affect the irruptive dynamics of this understudied bark beetle.
查看更多>>摘要：? 2022 Elsevier B.V.Although important for both restoration and conservation provisions, little is known of the multispecific tree interactions involved in secondary spruce-broadleaf stands undergoing natural conversion from conifer monospecific plantations. We aimed to identify signals of such interactions in a partially converted, 60-year-old stand located in the Eastern Carpathians (northern Romania) and composed of sycamore, ash, maple, and wych elm (hereinafter, SAE), beech and remnant spruce trees. The position and size of all standing tree species individuals at least 1.50 m tall were measured within a 1.5 ha plot. Bivariate spatial pattern analysis, hierarchical Strauss models, and generalised linear squares regression were used for estimating tree neighbourhood interaction and interference. At fine scales, the beech sapling distribution was closely described through opposite models of attraction or inhibition with respect to spruce and SAE trees, respectively. The repulsion detected within the 3 m neighbourhood between SAE and spruce trees translated also in a significant inhibition process. This was in accordance with the negative effect of the nearest spruce on SAE tree growth. The significant segregation and spatial dissociation between beech and SAE trees was very likely related to the negative effect of neighbouring beech veterans on SAE tree diameter. Negative effects on spruce tree growth were only detected through interference with the nearest beech tree. In the given context of site conditions and stand development stage, the observed spatial interdependence and interference patterns were probably determined, to a large extent, by the intense interspecific competition for below-ground resources and light. The remnant spruce trees can act as both growth promoter and inhibitor in relation to the neighbouring beech and SAE trees, respectively. The spruce trees slow down the natural conversion to a mixed SAE stand by contributing to beech dominance, but that will eventually lead through negative feedback to the gradual exclusion of spruce.
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