Structure Of Forest Ecosystems Research Articles

Patterns and variability in seedling carbon assimilation: implications for tree recruitment under climate change.

Predicting future forests' structure and functioning is a critical goal for ecologists, thus information on seedling recruitment will be crucial in determining the composition and structure of future forest ecosystems. In particular, seedlings' photosynthetic response to a changing environment will be a key component determining whether particular species establish enough individuals to maintain populations, as growth is a major determinant of survival. We quantified photosynthetic responses of sugar maple (Acer saccharum Marsh.), pignut hickory (Carya glabra Mill.), northern red oak (Quercus rubra L.) and eastern black oak (Quercus velutina Lam.) seedlings to environmental conditions including light habitat, temperature, soil moisture and vapor pressure deficit (VPD) using extensive in situ gas exchange measurements spanning an entire growing season. We estimated the parameters in a hierarchical Bayesian version of the Farquhar model of photosynthesis, additionally informed by soil moisture and VPD, and found that maximum Rubisco carboxylation (V(cmax)) and electron transport (J(max)) rates showed significant seasonal variation, but not the peaked patterns observed in studies of adult trees. Vapor pressure deficit and soil moisture limited J(max) and V(cmax) for all four species. Predictions indicate large declines in summer carbon assimilation rates under a 3 °C increase in mean annual temperature projected by climate models, while spring and fall assimilation rates may increase. Our model predicts decreases in summer assimilation rates in gap habitats with at least 90% probability, and with 20-99.9% probability in understory habitats depending on species. Predictions also show 70% probability of increases in fall and 52% probability in spring in understory habitats. All species were impacted, but our findings suggest that oak species may be favored in northeastern North America under projected increases in temperature due to superior assimilation rates under these conditions, though as growing seasons become longer, the effects of climate change on seedling photosynthesis may be complex.

우리나라 삼림의 변화와 전망

The changes in the area and standing crop of forests and the understory vegetation structure of various plantations were investigated by literature survey to predict the changes in the structure of forest ecosystems of the Korean Peninsula in the future. The greater part of forest was severely destroyed in 1950's in the Korean Peninsula. The forest standing crop has been dramatically increasing since the nationwide plantation was actively performed in 1970's and 1980's in the Republic of Korea. The area of forest was incessantly decreased at the rate of 5,500ha yr-1. The results of regression analysis on the changes in forest standing crop of the Republic of Korea showed that the forest might approach to the maturity stage in around 2150. It was predicted that the potential natural vegetation of Quercus mongorica, Fraxinus rhynchophyllus, Prunus sargentii, etc. would establish in the plantations of Larix leptolepsis, Pinus koraiensis and Robinia pseudoacacia in the future.

Dynamics of spectral brightness of the species/age structure for groups of forest types on Landsat satellite images

The articles presents the results from studying the dependence upon the spectral characteristics of a Landsat 5/TM multispectral high-resolution space image and the species/age structure of forest ecosystems. The parameters that affect the variability of the spectral brightness of forest ecosystems on space images are described for green-moss (hilocominosa), various-grass (larioherbosa), large-grass (magnoherbosa) and sphagnous (sphagnosa) groups of forest types in the Angara taiga region of Eastern Siberia. The trends of dynamics of spectral brightness are revealed for the groups of forest types, depending on the age and share of coniferous species in the structure of forest stands based on the ecological and dynamic analysis of forests, which grow in identical vegetation conditions.

Broadleaf and conifer tree responses to long-term enhanced UV-B radiation in outdoor experiments: a review

Trees as a perennial growth form require time to evolve the complex response to enhanced ultraviolet-B radiation (UV-B), and this might lead to slow but important changes in forest ecosystem structure and function. Long-term outdoor experiments on trees however are few in number. The available published results suggest that broadleaf and conifer trees may show different response strategies to enhanced UV-Bradiation. The long-term outdoor experiments indicate species- and season-specific differential responses in tree secondary metabolism, photosynthesis, water relations, and growth and development.

Disturbance legacies increase the resilience of forest ecosystem structure, composition, and functioning.

Disturbances are key drivers of forest ecosystem dynamics, and forests are well adapted to their natural disturbance regimes. However, as a result of climate change, disturbance frequency is expected to increase in the future in many regions. It is not yet clear how such changes might affect forest ecosystems, and which mechanisms contribute to (current and future) disturbance resilience. We studied a 6364-ha landscape in the western Cascades of Oregon, USA, to investigate how patches of remnant old-growth trees (as one important class of biological legacies) affect the resilience of forest ecosystems to disturbance. Using the spatially explicit, individual-based, forest landscape model iLand, we analyzed the effect of three different levels of remnant patches (0%, 12%, and 24% of the landscape) on 500-year recovery trajectories after a large, high-severity wildfire. In addition, we evaluated how three different levels of fire frequency modulate the effects of initial legacies. We found that remnant live trees enhanced the recovery of total ecosystem carbon (TEC) stocks after disturbance, increased structural complexity of forest canopies, and facilitated the recolonization of late-seral species (LSS). Legacy effects were most persistent for indicators of species composition (still significant 500 years after disturbance), while TEC (i.e., a measure of ecosystem functioning) was least affected, with no significant differences among legacy scenarios after 236 years. Compounding disturbances were found to dampen legacy effects on all indicators, and higher initial legacy levels resulted in elevated fire severity in the second half of the study period. Overall, disturbance frequency had a stronger effect on ecosystem properties than the initial level of remnant old-growth trees. A doubling of the historically observed fire frequency to a mean fire return interval of 131 years reduced TEC by 10.5% and lowered the presence of LSS on the landscape by 18.1% on average, demonstrating that an increase in disturbance frequency (a potential climate change effect) may considerably alter the structure, composition, and functioning of forest landscapes. Our results indicate that live tree legacies are an important component of disturbance resilience, underlining the potential of retention forestry to address challenges in ecosystem management.

Формирование лесных фитоценозов правобережья реки Волги

The coastal forests, presented by valuable deciduous and coniferous forests, grow in the northeastern and eastern parts of the Volga region of the Republic of Tatarstan, skirting the high right bank of the Volga River. They contribute to the maintenance of biological diversity in nature. The study of the formation of coastal forest phytocenoses, their species diversity and the modern state is now urgent work, and development activities for the conservation of natural habitats of plants, improve the sustainability of forest ecosystems are perspective direction. According to research of the forests of the right bank of the river Volga, we present the structure of coastal forest ecosystems. The association of forest ecosystems to the various elements of the relief was installed. The types of soil and litter were presented. The estimation of α-diversity of vascular herbaceous plants and ß-diversity of the studied forest ecosystems were reported. The largest number of species of vascular plants in coastal forests are: oak plant communities; a second group includes birch plants, pine and willow; the third group - the lime and larch; the fourth group - maple plant communitie. The ß-diversity index (Whittaker’s index) of plants in the studied forests varies between 2.2-6.8. The Jaccard coefficient of floristic similarity between forest ecosystems varies from 0.01 to 0.30, which confirms the diversity of generated by coastal forest ecosystems. The greatest diversity of plants was found in forests of ash and mixed grass, mixed grass willow, oak and lime-grove, maple, ash and mixed grass larches, birch wood. The forestry activities in coastal areas should be aimed at creating productive, sustainable forest ecosystems with a rich biodiversity of flora and fauna.

Sap-feeding insects on forest trees along latitudinal gradients in northern Europe: a climate-driven patterns.

Knowledge of the latitudinal patterns in biotic interactions, and especially in herbivory, is crucial for understanding the mechanisms that govern ecosystem functioning and for predicting their responses to climate change. We used sap-feeding insects as a model group to test the hypotheses that the strength of plant-herbivore interactions in boreal forests decreases with latitude and that this latitudinal pattern is driven primarily by midsummer temperatures. We used a replicated sampling design and quantitatively collected and identified all sap-feeding insects from four species of forest trees along five latitudinal gradients (750-1300km in length, ten sites in each gradient) in northern Europe (59 to 70°N and 10 to 60°E) during 2008-2011. Similar decreases in diversity of sap-feeding insects with latitude were observed in all gradients during all study years. The sap-feeder load (i.e. insect biomass per unit of foliar biomass) decreased with latitude in typical summers, but increased in an exceptionally hot summer and was independent of latitude during a warm summer. Analysis of combined data from all sites and years revealed dome-shaped relationships between the loads of sap-feeders and midsummer temperatures, peaking at 17°C in Picea abies, at 19.5°C in Pinus sylvestris and Betula pubescens and at 22°C in B. pendula. From these relationships, we predict that the losses of forest trees to sap-feeders will increase by 0-45% of the current level in southern boreal forests and by 65-210% in subarctic forests with a 1°C increase in summer temperatures. The observed relationships between temperatures and the loads of sap-feeders differ between the coniferous and deciduous tree species. We conclude that climate warming will not only increase plant losses to sap-feeding insects, especially in subarctic forests, but can also alter plant-plant interactions, thereby affecting both the productivity and the structure of future forest ecosystems.

Biomass and its allocation of Chinese forest ecosystems

Forest biomass and its allocation have long been considered important in forest ecosystem structure and function. However, discrete forest biomass data and its allocation to various forest components must be standardized to explore many ecological questions, e.g., plant allometric scaling laws, biomass allocation theory, and terrestrial carbon cycling. Currently, available data sets focus either on regions other than China, or studies in China are spatially and/or temporally limited, e.g., specific habitats and/or time periods. Therefore, the applicability of conclusions to world or China forests might be problematic. Consequently, in the present study, published studies (during the 1978–2008 period) on biomass and its allocations in China's forests (excluding Hong Kong, Macao, and Taiwan) were collected and critically reviewed, and a comprehensive forest biomass data set of China was developed. The data set included the following biomass data: tree overstory components (stems, branches, leaves, and roots, among all other plant material), the understory vegetation (saplings, shrubs, herbs, and mosses), woody liana vegetation, and the necromass components of dead organic matter (litterfall, suspended branches, and dead trees). Moreover, associated information was also included, i.e., geographical location, climate, soil fertility, stand description, sampling regime (the dimension and sample size of plots), and biomass measurement methods. The data set included 1607 entries for 348 study sites, which exhibited a broad spatial distribution, and covered broad climatic gradients (−5.1°C to 23.8°C in mean annual temperature and 223–2515 mm in mean annual precipitation). Our data set can be used to verify the accuracy of models used to budget China's forest carbon dynamics, and also provides an opportunity to further elucidate and confirm general principles and patterns in ecology. Finally, the data set is freely available for noncommercial scientific applications.

Lethal control of an apex predator has unintended cascading effects on forest mammal assemblages

Disruption to species-interaction networks caused by irruptions of herbivores and mesopredators following extirpation of apex predators is a global driver of ecosystem reorganization and biodiversity loss. Most studies of apex predators' ecological roles focus on effects arising from their interactions with herbivores or mesopredators in isolation, but rarely consider how the effects of herbivores and mesopredators interact. Here, we provide evidence that multiple cascade pathways induced by lethal control of an apex predator, the dingo, drive unintended shifts in forest ecosystem structure. We compared mammal assemblages and understorey structure at seven sites in southern Australia. Each site comprised an area where dingoes were poisoned and an area without control. The effects of dingo control on mammals scaled with body size. Activity of herbivorous macropods, arboreal mammals and a mesopredator, the red fox, were greater, but understorey vegetation sparser and abundances of small mammals lower, where dingoes were controlled. Structural equation modelling suggested that both predation by foxes and depletion of understorey vegetation by macropods were related to small mammal decline at poisoned sites. Our study suggests that apex predators' suppressive effects on herbivores and mesopredators occur simultaneously and should be considered in tandem in order to appreciate the extent of apex predators' indirect effects.

Influence of prior distributions and random effects on count regression models: implications for estimating standing dead tree abundance

The presence and abundance of standing dead trees (SDTs) in forests is typically characterized by an excess number of zeros and high variation. The variability inherent in SDT data naturally leads to the assessment of novel quantitative methods to represent SDT populations and their role in contributing to forest ecosystem structure. This analysis assessed the performance of count regression methods fit with Bayesian mixed-effects models that estimate SDTs (all dead trees with a diameter at breast height \({\ge }12.7\hbox { cm}\) found on plots 0.07-ha in size) on over 17,000 forest inventory plots across the US Lake States (Michigan, Minnesota, and Wisconsin). Random effects models that used the independent variables basal area, mean annual temperature, and plot ownership (i.e., publicly- or privately-owned) as fixed effects and forest type as a random effect outperformed a method which used fixed-effects, alone. Standard and zero-inflated negative binomial models were effective in accounting for overdispersion present in the data (variance/mean ratio for SDT counts was 72.6), whereas Poisson count models were not. Random effects were calibrated on a new population of SDTs. Employing informative prior distributions from the developed model led to improved estimates of SDT abundance by reducing root mean square error by seven percent. This analysis highlights an approach that uses existing models for representing population averages while calibrating their local random effects with new data to arrive at improved estimates of SDTs across the region.

Soil‐mediated effects of invasive ungulates on native tree seedlings

Summary Invasive browsing ungulates can have strong impacts on the structure and composition of forest ecosystems, particularly where ungulates are not native ecosystem components as in New Zealand. Ungulate impacts on plant communities have been considered mostly from an above‐ground perspective. However, understanding below‐ground effects of these invasive herbivores is critical as they may drive feedbacks to above‐ground ecosystem components. We measured growth responses of seedlings of five common tree species in a greenhouse experiment in soils collected from 26 plots fenced to exclude invasive ungulates for at least 17 years and from paired, unfenced control plots. We then further investigated soil‐mediated effects of ungulates on one tree species, Melicytus ramiflorus, by partitioning these effects into soil abiotic and biotic components, as well as measuring arbuscular mycorrhizal fungal (AMF) root infection. Biomass of seedlings of all five species was greater in soils from within exclosures, although this was only significant for two species. These soil‐mediated effects were partially driven by changes in physical and chemical soil properties; soil bulk densities were lower inside exclosures than in controls. Effects of invasive ungulates on seedling biomass of M. ramiflorus were positively related to effects on per cent AMF root infection. The biomass of M. ramiflorus seedlings was positively related to the AMF infection of its roots, which in turn was related to greater organic matter content and lower bulk density of soils from within exclosures. Results for M. ramiflorus indicated that soil‐mediated effects of ungulates on seedling biomass were of abiotic origin, but were mediated by the biotic soil component, that is, through effects on AMF. Synthesis. Invasive herbivores may potentially impact on plant performance and community structure not only directly but also indirectly through influencing soil abiotic and biotic properties. Our results show that shifts in plant–soil interactions and feedbacks represent important but understudied pathways by which invasive ungulates can have wide‐ranging impacts on forest ecosystems. Future studies should consider the importance of soil‐mediated effects of invasive ungulates relative to direct effects of herbivory.

Analisi dendrometrica e naturalistica speditiva a fini pianificatori forestali. Un caso di studio e di concreta applicazione sul campo

The Romagna Coast is a very human made area of Northern Italy. It appears as a mosaic in which every single tile is represented by a different landscape unit. However, this territory is rich also in ecological systems with relevant natural value. There is an 80 kilometers long woodland strip which runs in North-South direction over the Provinces of Ravenna, Ferrara and Forli-Cesena.These woodlands are mostly of human origin and made up by Maritime Pine (Pinus pinaster Ait.). Despite of their origin, now they are rich in biodiversity, especially in relation to the botanical composition richness and they represent a very big ecological corridor, which includes and keeps in connection many Natural Protected Areas.Thirteen of these Areas are classified as “State Nature Reserves”. Here the forest management has been directed for decades by appropriate forest plans. These plans are now undergoing a review and upgrade process. The first step of this process has been to get useful data in order to describe the forest ecosystem structure. The current study reports on the activities done in this first step. A speedy investigation method, based on specific forest mensuration and nature evaluation analysis, has been applied here. This made it possible to get reliable data in a short time and at small cost.

中国南方3种主要人工林生物量和生产力的动态变化

Forests form the main body of terrestrial ecosystems and play an important role in mitigating global climate change through carbon dioxide sequestration in forest biomass. Biomass and productivity are essential characteristics of forestecosystem structure and function,and knowledge of both are essential for the study of carbon sink function and carbon sequestration. Cunninghamia lanceolata,Pinus massoniana,and Eucalyptus urophylla × Eucalyptus grandis are the primary plantation trees used in southern China,accounting for 90% of the plantation area in ten southern provinces. However,few studies have analyzed the dynamics of forest biomass and productivity of these forest types. Forty-five 20 m × 50 m research plots were established and analyzed using three dominant plantation species( C lanceolata,P. massoniana,E. urophylla ×E. grandis) in southern China with the goal of improving our understanding the vertical structure of each community,the distribution of biomass to the various organs,and gaining a better understanding of forest biomass and productivity of differently aged stands. Each plantation type was studied using five age classes: young,middle-aged,near-mature,mature,and over-mature forest,with three replicates of each. Regression models relating tree biomass to diameter at breast height( DBH 1.3 m) were developed to estimate tree biomass. Other biomass components were sampled in quadrats within the same forty-five research plots: shrubs( three 4 m2quadrats),herbs( three 1 m2quadrats),and litterfall( three 1 m2quadrats). This method was used for estimating biomass,productivity,and biomass allocation rates to various organs in the three main plantations types; we also analyzed the relationships between stand age and biomass productivity to determine the biomass allocation rates to various organs. Results showed that a significant relationship exists between stand biomass and stand productivity of the three main plantation types as they relate to stand age,with a high degree of fitting in growth models. The total biomass of C. lanceolata,P. massoniana,and E. urophylla × E.grandis plantations increased with stand age and the biomass of mature forest was 192.30,191.53,105.77 Mg /ha,respectively. Living biomass made up 95.76%—98.39%,75.01%—99.14%,85.60%—97.61% of these three plantation types,respectively. Most of the biomass of the three main plantation types was concentrated in the tree layer and biomass increased with stand age for all three types. The biomass of other layers accounted for only a small percentage of total biomass,and generally litterfall herb shrub biomass. The trunk biomass occupied the greatest proportion of the tree layer; for C. lanceolata,P. massoniana,and E.urophylla × E. grandis truck biomass made up 54. 89%—75. 97%,49. 93%—83. 10%,and 51. 07%—98. 48% of total biomass,respectively,and trunk biomass increased with stand age. Root biomass made up the second largest percent of tree biomass and the percentages of both branch and leaf biomass were lower than root biomass and decreased with stand age.Shrub branches made up the majority of shrub biomass; both the above-and belowground biomass allocation of herbs did not exhibit an obvious trend or pattern of change. Compared with other forest types,the total biomass of C. lanceolata plantations and P. massoniana plantations were both greater than most and the total biomass of E. urophylla × E. grandis was lower than most,but the level of productivity of all three plantation types was high,or 12.37,8.98,21.10 Mg hm-2a-1,respectively. All three are fast growing forest tree species with higher photosynthetic efficiency and potential carbon sequestration than other forest plantation species in South China.

Can thinning alleviate negative effects of fertilization on boreal forest floor vegetation?

Society’s increased interest in renewable energy and materials put pressure on forest biomass production. Intensive fertilization of young Norway spruce (Picea abies) forest has a considerable potential to increase the production of tree biomass, but there are concerns about negative side-effects on forest ecosystem structure and function. Fertilization of young forest has a strong negative impact on light availability below the tree canopy and reduces the abundance of the forest floor vegetation. The silvicultural practice of thinning has been shown to affect composition and diversity of forest floor vegetation, and it has been proposed, but rarely tested, that the effects of fertilization are interdependent on the type of thinning performed. Here we present responses on the forest floor vegetation following 25years of fertilization and eighth years after thinning (removing 30% or 60% of the tree basal area) in a Norway spruce forest in northern Sweden. Fertilization without thinning led to a considerable reduction in abundance of most forest floor plants. It did not affect species richness but resulted in an increased evenness. Thinning reduced the fertilization effects so that the total abundance of the vegetation was comparable to the unfertilized control plots. A considerable change in species composition had, however, taken place. Thinning favored early-successional species and pteridophytes on the account of dwarf-shrubs. Thinning also increased species richness and functional richness, while none, or negative effects were seen on evenness and functional evenness, respectively. A comparison with data from the National Forest Inventory revealed that the type of vegetation generated by fertilization, without or in combination with thinning, is a type of vegetation very uncommon in Swedish boreal forests. First, we conclude that the effects of fertilization on forest floor vegetation in young stands of Norway spruce are largely dependent on thinning regime. Secondly, fertilization will, independently of thinning, lead to considerable changes in the vegetation, including a functional shift from dwarf-shrubs with ericoid mycorrhiza to ferns and grasses with arbuscular mycorrhiza, resulting in a functional type of vegetation that is rare in this part of the boreal forest biome. Finally, in contrast to what previously has been suggested for unfertilized forests, thinning of fertilized forests may not promote late-successional species.

Changes of forest stand dynamics in Europe. Facts from long-term observational plots and their relevance for forest ecology and management

Nearly one and a half centuries ago, far-sighted Central European forest scientists established a network of long-term observational plots, many of them being under observation up to the present day. Especially the untreated plots reveal significant anthropogenic impacts on the structure and dynamics of forest ecosystems. Based on 14 observational plots, this study shows that tree size and stand parameters of oak (sessile oak, Quercus petraea (MATT.) LIEBL. and pedunculate oak, Quercus robur L.) presently develop much faster than in the past, which is highly relevant for forestry in Central Europe. Thus, certain threshold sizes are reached decades earlier compared with the past. Due to the accelerated stand development, stem numbers per unit area are presently lower than at the same stand age in the past, while at the same time, stand density is higher. As we can show, also the level of the tree growth rate vs. tree size allometry increased significantly. These changes have major consequences for forest ecology and management, forest modeling, and eco-monitoring.

The potential effects of climate change on the distribution and productivity of Cunninghamia lanceolata in China

Climate changes may have immediate implications for forest productivity and may produce dramatic shifts in tree species distributions in the future. Quantifying these implications is significant for both scientists and managers. Cunninghamia lanceolata is an important coniferous timber species due to its fast growth and wide distribution in China. This paper proposes a methodology aiming at enhancing the distribution and productivity of C. lanceolata against a background of climate change. First, we simulated the potential distributions and establishment probabilities of C. lanceolata based on a species distribution model. Second, a process-based model, the PnET-II model, was calibrated and its parameterization of water balance improved. Finally, the improved PnET-II model was used to simulate the net primary productivity (NPP) of C. lanceolata. The simulated NPP and potential distribution were combined to produce an integrated indicator, the estimated total NPP, which serves to comprehensively characterize the productivity of the forest under climate change. The results of the analysis showed that (1) the distribution of C. lanceolata will increase in central China, but the mean probability of establishment will decrease in the 2050s; (2) the PnET-II model was improved, calibrated, and successfully validated for the simulation of the NPP of C. lanceolata in China; and (3) all scenarios predicted a reduction in total NPP in the 2050s, with a markedly lower reduction under the a2 scenario than under the b2 scenario. The changes in NPP suggested that forest productivity will show a large decrease in southern China and a mild increase in central China. All of these findings could improve our understanding of the impact of climate change on forest ecosystem structure and function and could provide a basis for policy-makers to apply adaptive measures and overcome the unfavorable influences of climate change.

Microclimate in forests with varying leaf area index and soil moisture: potential implications for seedling establishment in a changing climate

SummaryForest microclimate is crucial for the growth and survival of tree seedlings and understorey vegetation. This high ecological relevance contrasts with the poor functional and quantitative understanding of how the properties of forest ecosystems influence forest microclimate.In a long‐term (1998–2011) trial, we investigated how temporal patterns of microclimate below sparse and dense forest canopy related to those of nearby open areas and how this relationship was influenced by soil moisture and seasonality. Air temperature (T), vapour pressure deficit (VPD), soil matrix potential and leaf area index (LAI) were measured in a unique set‐up of below‐canopy and open‐area meteorological stations at eleven distinct forest ecosystems, characteristic of subalpine and temperate climate zones. Data from these plots were analysed for the moderating capacity of the canopy, that is, the differences between below‐canopy and open‐area microclimate, with respect to (i) long‐term means, (ii) dynamics within homogeneous moist‐ vs. dry‐soil periods and (iii) diurnal patterns.The long‐term mean moderating capacity of the canopy was up to 3.3 °C for dailyTmaxand 0.52 kPa for daily VPDmax, of which soil moisture status alone accounted for up to 1.2 °C (Tmax) and 0.21 kPa (VPDmax). Below dense canopy (LAI > 4), the moderating capacity was generally higher when soils were dry and increased during dry‐soil periods, particularly in spring and somewhat less in summer. The opposite pattern was found below sparse canopy (LAI < 4). At the diurnal level, moderating capacity below dense canopy was strongest in mid‐afternoon and during dry‐soil conditions, whereas peak moderation below sparse canopy occurred in mid‐morning and during moist‐soil conditions.Synthesis. Our results suggest a threshold canopy density, which is probably linked to site‐specific water availability, below which the moderating capacity of forest ecosystems switches from supportive to unsupportive for seedling establishment. Under supportive moderating capacity, we understand a stronger mitigation during physiologically most demanding conditions for plant growth. Such a threshold canopy density sheds new light on forest resilience to climate change. Climate change may alter forest canopy density in a way that precludes successful establishment of tree species and ultimately changes forest ecosystem structure and functioning.

Assessing changes in species distribution from sequential large-scale forest inventories

It is assumed that global change is already affecting the composition, structure and distribution of forest ecosystems; however, detailed evidences of altitudinal and latitudinal shifts are still scarce. To develop a method based on National Forest Inventory (NFI) to assess spatio-temporal changes in species distributions. We develop an approach based on universal kriging to compare species distribution models from the different NFI cycles and regardless of the differences in the sampling schemes used. Furthermore, a confidence interval approach is used to assess significant changes in species distribution. The approach is applied to some of the southernmost populations of Pinus sylvestris and Fagus sylvatica in the Western Pyrenees over the last 40 years. An increase of the presence of the two species in the region was observed. Scots pine distribution has shifted about 1.5 km northwards over recent decades, whereas the European beech has extended its distribution southwards by about 2 km. Furthermore, the optimum altitude for both species has risen by about 200 m. As a result, the zone in which the two species coexist has been enlarged. This approach provides a useful tool to compare NFI data from different sampling schemes, quantifying and testing significant shifts in tree species distribution over recent decades across geographical gradients.

Effects of introduced insects and diseases on forest ecosystems in the Catskill Mountains of New York

Repeated invasions of non-native insects and pathogens have altered the structure and function of forest ecosystems in the Catskill Mountains of New York State, and will continue to do so in the future. Gypsy moth, beech bark disease, and hemlock woolly adelgid are among the insects and diseases currently established in the Catskills that are having significant effects on forests. Many others, including emerald ash borer, Asian long-horned beetle, Phytophthora ramorum, and Sirex wood wasp, are either very recently established in the Catskills or have been found elsewhere in North America and threaten to spread to this region. Short-term disturbances associated with these pests include reduction of productivity, tree decline and mortality, disruption of nutrient cycles, and reduction of seed production. Longer-term impacts are associated with shifts in tree species composition that alter productivity, nutrient cycling, and biodiversity. Catskill forests at mid to high elevations, such as the New York State Forest Preserve lands, are dominated by sugar maple and are particularly vulnerable to pests that use maple as a host, including the Asian long-horned beetle. The simultaneous effects of multiple invading insects and pathogens, and their interactions with changing climate and air pollution regimes, make it very difficult to predict the future composition of Catskill forests.

Deadwood Density of Five Boreal Tree Species in Relation to Field-Assigned Decay Class

Aboveground deadwood, consisting of downed woody debris (DWD), snags, and stumps, is an important component of boreal forest ecosystem structure. Accurate deadwood density estimates are essential for evaluating ecosystem biomass and carbon stocks. The objective of this study was to examine the relationships between deadwood density, tree species, and decay status, identified in the field by morphological characteristics. We sampled DWD, snags, and stumps of trembling aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh.), jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana [Mill.] B.S.P.), and balsam fir (Abies balsamea [L.] Mill.) in the boreal forest of central Canada. A total of 240 samples (99 DWD, 94 snags, and 47 stumps) were collected. Decay class and tree species explained >80% of the variation in wood density of all deadwood types. Wood density decreased consistently from the lowest to the highest decay class. Tree species identity was also important in determining the relationships between wood density and field-assigned decay class for snags and stumps, but not for DWD, probably because of the five-class system used for DWD, rather than the three-class system used for snags and stumps. These results indicate that decay class and tree species are adequate predictors of deadwood density.