查看更多>>摘要：In northern hardwood stands of the northeastern USA and southeastern Canada, the abundance and occurrence of American beech (Fagus grandifolia Ehrh) regeneration have increased substantially over the past decades, to the detriment of other deciduous species such as sugar maple (Acer saccharum Marshall) and yellow birch (Betula alleghaniensis Britton). To promote the regeneration of these declining species, we established an experimental study near Que ' bec City (Quebec, Canada) to compare the effects of various partial cutting treatments and mechanical control of understory American beech. The design comprises 4 randomized complete blocks, each containing an uncut control, a hybrid single-tree and group selection cutting (SC), two intensities of continuous cover irregular shelterwood (CCIS) and an extended irregular shelterwood (EIS). American beech regeneration, which dominated the sapling layer before cutting, was removed with brush saws in gaps created in the SC and CCIS treatments as well as in the entire understory of the EIS treatment. In addition, gaps and the EIS understory were scarified to favor yellow birch regeneration, and 12 exclosures were built to prevent cervid browsing in CCIS gaps and in entire understory of the EIS treatment. Ten years after cutting, yellow birch regeneration was more abundant in gaps and in the EIS treatment than in the uncut control. These results confirm that increasing the understory light level, eliminating American beech saplings and scarifying the soil can successfully favor yellow birch establishment. However, preferential browsing of yellow birch outside exclosures maintained the overall dominance of American beech in the long term. Thus, under these conditions, damage from repetitive browsing outweighed the positive effects of actions aimed at promoting the regeneration of yellow birch. In the end, despite abundant seed availability, sugar maple remained only a minor component of the regeneration.
Wright, James R.Matthews, Stephen N.Pinchot, Cornelia C.Tonra, Christopher M....
9页
查看更多>>摘要：Nut-bearing trees such as oaks (Quercus genus) and American chestnut (Castanea dentata, hereafter: chestnut) rely on scatter-hoarding animals for seed dispersal. With the pursuit of blight-resistant chestnuts for eventual reintroduction into eastern hardwood forests of the United States, it becomes important to understand how foraging preferences of avian seed-hoarders will influence chestnut dispersal in oak-dominated forests. Using six seed selection trials over three years and two "seasons " (early fall and late fall), we assess the relative seed preferences - when gathering seeds for hoarding or consumption - of five species of avian seed dispersers in southeast Ohio. In each trial, we presented an equal number of chestnuts and two species of common acorns, black (Q. velutina) and white oak (Q. alba), to wild birds on feeding platforms monitored by cameras. We used Bayesian discrete choice models to determine preferences of each species, and estimate the influence of natural variation in background mast availability (i.e., different years and seasons). Blue Jays (Cyanocitta cristata) showed a consistent preference for the seeds of black oak over chestnut over white oak, and the strength of preference for black oak increased in late season when acorns were scarce. Other species showed variable preferences, with White-breasted Nuthatch (Sitta carolinensis) the only species to prefer chestnuts over both acorns, though sample size was small (n = 26 selections). Our results suggest chestnuts are used by a host of avian seed-hoarders that may facilitate dispersal of chestnut, particularly in years of black oak mast failure.
Nieves, Jennifer M.Ward, Jeffrey S.Royo, Alejandro A.McDill, Marc E....
7页
查看更多>>摘要：Stump sprouting is a widespread phenomenon in North American hardwood tree species following logging or severe crown damage from natural disturbances such as fire, wind, or insect attack. However, other than the effects of species and tree size, factors that influence the probability of sprouting are not well understood. Data from harvested stands in Pennsylvania and Connecticut, USA, were used to evaluate the effects of several variables on stump sprouting frequencies measured within the first year after cutting for several oak and other hardwood species. After adjusting for species and diameter of the "parent " tree (ortet), clearcut harvests were found to result in a higher frequency of sprouted stumps than shelterwood harvests or crop tree releases. In addition, the probability of sprouting was higher for trees in the Ridge and Valley province of Pennsylvania vs. the Appalachian Plateaus, and in general it was higher on dry vs. moist sites. After accounting for all measured variables, there remained statistically significant stand-to-stand differences in sprouting frequency that arose from unknown causes. Results should temper expectations of stump sprout contributions to regeneration stocking that are based on simple models derived from a small number of stands or a limited geographic area. On the stand-level basis at which most managers work, the actual contribution of sprouts to future stand development may vary widely from modeled expectations.
查看更多>>摘要：Natural regeneration of forests is the most cost-effective and most technically straightforward strategy to mitigate climate change. Natural forests account for 71% of China's forested area, but their carbon stocks and sequestration potentials remain unclear. Here, we compiled data from 762 natural forest sites across China and found that natural forests had a carbon stock of 9.40 +/- 1.45 Pg C in 2010. When naturally regenerated to the over-mature stage, existing natural forests can additionally sequestrate 8.67 +/- 6.93 Pg C in the next two centuries, accounting for 48% of the carbon carrying capacity of the natural forest ecosystem in China, i.e. 18.07 +/- 6.78 Pg C. Future carbon sequestration potential in natural forests is dominated by the tree layer at 6.88 +/- 6.87 Pg, followed by the shrub layer at 1.02 +/- 0.55 Pg, floor layer at 0.72 +/- 0.74 Pg and herb layer at 0.05 +/- 0.10 Pg. The natural forests are expected to achieve 70% of their future carbon sequestration potential by 2100. We also note that assisted regeneration via tree planting can play a significant role in natural forest restoration, as the carbon densities of natural and planted forests are rarely significantly different at the same age under 60 years old. Therefore, the preservation and expansion of natural forests is the key strategy for achieving long-term carbon sequestration.
Vanderwel, Mark C.Shovon, Tanvir AhmedSprott, AdamGagnon, Daniel...
10页
查看更多>>摘要：Advances in unmanned aerial vehicle (UAV) technology have opened new opportunities for measuring canopy mortality processes through high-resolution aerial imagery. Unlike traditional plot-based sampling, UAVs can easily survey areas several hectares in size that encompass hundreds of canopy trees. The resulting imagery provides extensive data on the number and locations of dead trees (snags), which can be related to neighbourhood conditions and environmental factors that vary among stands. Here, we used a UAV to measure the relative proportions of live and dead canopy trees in stands varying in soil moisture across a mixed forest landscape. Crowns of live trees and snags were first segmented and classified to species from high-resolution canopy imagery. We then modeled whether crowns of each species were alive or dead as a function of tree height, neighbourhood competition, soil moisture, and the relative abundance of conspecifics. Short lodgepole pine (Pinus contorta var. latifolia) trees were more likely to be dead when surrounded by a tall canopy in sites with greater soil moisture, reflecting effects of competition on this shade-intolerant species. Trembling aspen (Populus tremuloides) was more likely to be alive when surrounded by tall neighbours, perhaps because this clonal species can benefit from facilitation through root connections with neighbouring aspen stems. There was a higher frequency of white spruce (Picea glauca) snags in sites where it had a high relative abundance, suggesting strong effects of intraspecific competition for this species. Soil moisture did not appear to have a direct effect on the snag frequency of any of these species, despite pronounced niche partitioning along an elevation-driven moisture gradient. Our models explained 39% and 33% of the variation in white spruce and lodgepole pine snag frequency, respectively, but did not have much predictive power for trembling aspen or total snag frequency. Our results reflect the important role of competition in determining tree mortality, but also indicate that stochastic or unexplained processes account for considerable variation in snag frequency among stands. As UAV technology becomes more widely used by ecologists, it may enable a better understanding of how biotic and abiotic processes produce local variation in canopy mortality.
Green, David S.Facka, Aaron N.Smith, Kevin P.Matthews, Sean M....
9页
查看更多>>摘要：Understanding the role of landscapes managed for timber production in the conservation of forest-obligate species is a priority for preserving ecological integrity and fostering socioeconomic wellbeing. The forest characteristics generally associated with the survival, reproduction, and persistence of forest-obligate species (e.g., large-diameter trees, standing dead trees, understory vegetation, downed logs) are often believed to be at odds with timber production. One such species is the fisher (Pekania pennanti), a mesocarnivoran (member of the order Carnivora) associated with mature forest characteristics whose range has decreased substantially since the mid1800s. Fishers exemplify the perceived conflict between forest-obligate species and timber production because they generally require areas exhibiting complex forest structure including multiple canopy layers, old trees and standing dead trees with cavities, logs, and understory vegetation that provide sufficient prey, escape cover, and structures to support reproduction and parturition. Consequently, understanding if fishers can persist in landscapes managed for timber production can provide a critical test of the compatibility among forest-obligate species and forest management. We reintroduced 40 fishers (24 females, 16 males) between November 2009 and December 2011 onto a landscape managed for timber production to establish a new fisher population and to evaluate the viability of fisher populations on a forest managed for timber production. We studied this reintroduced population of fishers for 8 years following the reintroduction using annual live-captures and year-round tracking with radio telemetry. Using population modeling with spatial capture-recapture methods, we estimated this population of fishers to be growing during the 7-year study period. The density of the reintroduced fisher population in 2017 (10.8 fishers/100 km2) was within the reported range of fisher densities across the western United States. The reintroduction of fishers to previously occupied portions of their range is an important component of fisher conservation and will play a role in the recovery of the species in western portions of the fisher's range. Our results suggest that forests managed for timber production with landscape conditions similar to our study area may be important for future fisher reintroductions and species recovery.
查看更多>>摘要：Gap-based silvicultural systems are of particular interest in secondary forest management because gaps are associated with regeneration and tree species diversity. However, whether using a range of gap sizes to influence tree regeneration is effective remains unclear. In this study, gaps of different sizes were created to determine their effects on tree regeneration and growth in a secondary Pinus massoniana Lamb. forest in Hunan Province, China. A robustly designed experiment was used with over nine years of repeated measurements. Seedling densities were highest in small gaps, and seedling diversity increased with increasing gap size. Sapling densities and diversity were highest in medium gaps. Within medium and large gaps, saplings were heterogeneously distributed along gradients from opening to closed forest canopy, suggesting gap partitioning of saplings. Emergence rates of three dominant species (Pinus massoniana Lamb, Schima superba Gardn. et Champ., and Cyclobalanopsis glauca (Thunb.) Oerst.) were roughly equal in medium gaps. Regeneration of P. massoniana and C. glauca was spatially diverse as gap sized increased. However, there was little evidence of S. superba divergence within and among gaps, which indicated differential tolerance to shade. A nonlinear mixed-effects model was used to detect effects of microenvironmental variables on diameter-biomass relations. The model suggested that gaps combined with solar radiation, soil moisture, and soil temperature had various effects on sapling biomass accumulation. For saplings with the same basal diameter, estimated average aboveground biomass of S. superba and C. glauca was highest in medium gaps, whereas that of P. massoniana was highest in large gaps. The study suggests that tree regeneration and growth requirements are often not met with a single gap size alone. In practice, a single tree/group selection with medium gaps hybrid approach may be required in subtropical secondary forests to increase regeneration and ecosystem resilience, while also considering other factors such as microenvironmental variables, shade tolerance, and others.
Bloin, PierrickMazerolle, Marc J.Hebert, Christian
12页
查看更多>>摘要：Deadwood left on site after logging can be colonized by many saproxylic insects including xylophagous species that can damage the wood. This study aims to estimate the risks resulting from the storage of logs at the edge of balsam fir-white birch stands. We used taxonomic richness, as well as visitation and colonization rates of saproxylic insects to determine how their use of freshly cut logs varies with the seasonal availability of logs and the tree species. During the summer of 2019, balsam fir, black spruce, and paper birch logs were experimentally cut at three different periods and were placed in four harvested sites located in the Foret Montmorency experimental forest in eastern Quebec, Canada. Visitation and colonization rates were assessed using trunk-window traps and log dissection, respectively. A total of 854 saproxylic insects belonging to 53 genera were captured over the three months of sampling. The logs were colonized by xylophagous species within one month after tree death. These xylophagous insects belonged mainly to the species Urocerus prob. albicornis, and Monochamus prob. scutellatus. Colonization rates of logs by Monochamus prob. scutellatus were higher from mid-July to mid-September than earlier during the season. These xylophagous species also responded to tree species, with higher abundance on conifers than on white birch both in terms of visitation and colonization rates. Furthermore, there was no evidence of colonization on paper birch. Our results suggest that a prompt harvesting of conifer logs between mid July and mid-September on harvested sites will minimize damage to freshly cut logs.
查看更多>>摘要：Microclimate acts as a strong filter on species performance in restored and regenerating forests, particularly in seasonally dry tropical forests (SDTF). Yet few studies have measured microclimate patterns across succession in SDTF. Furthermore, although dynamic vegetation models simulate microclimate, evaluation of these simulated variables with field observations has been relatively uncommon. Here, we investigated the seasonal patterns of soil temperature and soil water in naturally regenerated and planted successional vegetation in SDTF in Costa Rica and Puerto Rico, using complementary approaches of intensive field observations and simulation modeling with the Ecosystem Demography model. We found that plots representing later successional stages were wetter on average, but only during the dry season. During the wet season, mean soil water did not differ across vegetation types, but open, early successional vegetation experienced more frequent extreme wet and dry con-ditions than older forest and plantations. Soil temperature tended to decline with forest structure, and later successional vegetation also experienced less extreme daily temperature fluctuations. Basal area and leaf area index were the best predictors of differences in soil water and temperature across plots. Model simulations were consistent with observations of wet season soil temperature and soil water, but the model failed to reproduce dry season soil moisture dynamics, suggesting that further work is needed to reduce model biases in microclimate variables. Collectively, our results imply that common assumptions about how microclimates influence succes-sional processes in SDTF should be revisited.
查看更多>>摘要：Climate change will cause a range shift in tree species, which will create challenges for forest management, utilization and preservation in the future; hence, it is worthy of more attention, especially at the regional scale. Here, we selected 56 common cultured tree species in southern China and employed a comprehensive habitat suitability model to analyse the changes in the potential planting areas of these species at baseline and in different future climate change scenarios. The results indicated that climatic variable changes, especially a change in the mean diurnal temperature range greater than +/- 0.25 degrees C, will cause a decrease in the distribution area of most tree species in southern China. With the projected temperature rise, the number of species with habitat loss and the rate of distribution area loss will increase significantly. In the most intense warming scenarios, 22 tree species will lose more than 50% of their potential distribution area compared with that in the baseline condition. Additionally, increasing temperatures are expected to cause species diversity loss in the study area. This phenomenon will generate an increase in wood gaps, environmental degradation and the risk of alien species invasion. Mountainous areas in southern China may provide a refuge for tree species in the context of global warming. In future planting initiatives and forest management strategies, the range shifts and distribution area loss for tree species should be fully considered.
NSTL
Elsevier