Fragmentation drives tropical forest fragments to early successional states: A modelling study for Brazilian Atlantic forests

Land use leads to massive habitat destruction and fragmentation in tropical forests. Despite its global dimensions the effects of fragmentation on ecosystem dynamics are not well understood due to the complexity of the problem. We present a simulation analysis performed by the individual-based model FORMIND. The model was applied to the Brazilian Atlantic Forest, one of the world's biodiversity hot spots, at the Plateau of São Paulo. This study investigates the long-term effects of fragmentation processes on structure and dynamics of different sized remnant tropical forest fragments (1-100 ha) at community and plant functional type (PFT) level. We disentangle the interplay of single effects of different key fragmentation processes (edge mortality, increased mortality of large trees, local seed loss and external seed rain) using simulation experiments in a full factorial design.Our analysis reveals that particularly small forest fragments below 25 ha suffer substantial structural changes, biomass and biodiversity loss in the long term. At community level biomass is reduced up to 60%. Two thirds of the mid- and late-successional species groups, especially shade-tolerant (late successional climax) species groups are prone of extinction in small fragments. The shade-tolerant species groups were most strongly affected; its tree number was reduced more than 60% mainly by increased edge mortality. This process proved to be the most powerful of those investigated, explaining alone more than 80% of the changes observed for this group. External seed rain was able to compensate approximately 30% of the observed fragmentation effects for shade-tolerant species.Our results suggest that tropical forest fragments will suffer strong structural changes in the long term, leading to tree species impoverishment. They may reach a new equilibrium with a substantially reduced subset of the initial species pool, and are driven towards an earlier successional state. The natural regeneration potential of a landscape scattered with forest fragments appears to be limited, as external seed rain is not able to fully compensate for the observed fragmentation-induced changes. Our findings suggest basic recommendations for the management of fragmented tropical forest landscapes.     

Effects of Artificial Roosts for Frugivorous Bats on Seed Dispersal in a Neotropical Forest Pasture Mosaic

Abstract:  In the Neotropics ongoing deforestation is producing open and heavily fragmented landscapes dominated by agriculture, mostly plantations and cattle pastures. After some time agriculture often becomes uneconomical and land is abandoned. Subsequent habitat regeneration may be slow because seed inputs are restricted by a lack of incentives—such as suitable roost sites—for seed dispersers to enter deforested areas. Increasing environmental awareness has fostered growing efforts to promote reforestation. Practical and cost-efficient methods for kick-starting forest regeneration are, however, lacking. We investigated whether artificial bat roosts for frugivorous bat species can attract these key seed dispersers to deforested areas, thereby increasing seed rain. We installed artificial bat roosts in a forest-pasture mosaic in the Costa Rican Atlantic lowlands and monitored bat colonization and seed dispersal. Colonization occurred within a few weeks of installation, and 10 species of bats occupied the artificial roosts. Five species of frugivorous or nectarivorous bats colonized artificial roosts permanently in both primary habitat and in deforested areas, in numbers similar to those found in natural roosts. Seed input around artificial roosts increased significantly. Sixty-nine different seed types, mostly of early-successional plant species, were transported by bats to artificial roosts in disturbed habitats. The installation of artificial bat roosts thus successfully attracted frugivorous bats and increased seed inputs into degraded sites. This method is likely to speed up early-vegetation succession, which in turn will attract additional seed dispersers, such as birds, and provide a microhabitat for seeds of mid- and late-successional plants. As well as supporting natural forest regeneration and bat conservation, this cost-efficient method can also increase environmental awareness among landowners.     

Lemurs and the Regeneration of Dry Deciduous Forest in Madagascar

Abstract: We sought to assess the role of lemurs for seed dispersal in the dry deciduous forest of western Madagascar and the possible consequences of the demise of lemurs for forest regeneration. Forest regeneration was studied in eight plots in two large blocks of primary forest and in seven fragments of primary forest (1 plot per fragment). In 4 of the 15 study plots, the abundance of saplings was negatively and significantly correlated ( p < 0.05) with the abundance of mature individuals of the same tree species. In another 10 study plots there were negative correlations, although these were not significant on the community level. Second-order statistics were significant with p < 0.001 and indicated that seed dispersal away from the parent trees was important for successful establishment of saplings. Apart from possibly the bush pig ( Potamochoerus larvatus ), only one vertebrate species of the dry forest, the brown lemur ( Eulemur fulvus ), ingested seeds> 11 mm long and passed them through its digestive tract unharmed. These results for lemurs were based on direct observations and fecal analyses. To evaluate the role of E. fulvus , we compared regeneration in forest plots with and without E. fulvus . In forest fragments without E. fulvus , fewer lemur-dispersed tree species regenerated than would be expected based on the presence of mature tree species that are lemur-dispersed ( p < 0.05). No such effect was seen in primary forests with E. fulvus or for trees whose seeds can also be dispersed by other vertebrates. Thus, regeneration of the dry deciduous forest of western Madagascar with the complete set of primary forest tree species seems to depend upon the presence of E. fulvus .     

Tropical forest restoration: tree islands as recruitment foci in degraded lands of Honduras.

Tropical forest recovery in pastures is slowed by a number of biotic and abiotic factors, including a lack of adequate seed dispersal and harsh microclimatic extremes. Accordingly, methods to accelerate forest recovery must address multiple impediments. Here, we evaluated the ability of "tree islands" to serve as "recruitment foci" in a two-year study at three sites in northern Honduras. Islands of three sizes (64, 16, and 4 m2) and at two distances to secondary forest (20 and 50 m) were created by planting 2 m tall vegetative stakes of two native species: Gliricidia sepium (Fabaceae) and Bursera simaruba (Burseraceae), each in monoculture. Open-pasture "islands" of equal sizes served as controls. Tree islands reduced temperature and light (PAR) extremes as compared to open pasture, creating a microenvironment more favorable to seedling establishment. Seed-dispersing birds (quantified at one site only) showed an overwhelming preference for islands; 160 visits were recorded to islands compared with one visit to open pasture. Additionally, frugivores visited large islands more often, and for longer time periods, than small islands, thereby increasing the likelihood of a dispersal event there. In total, 144 140 seeds belonging to 186 species were collected in islands; more than 80% were grasses. Tree islands increased zoochorous tree seed rain; seed density and species richness were greater in tree islands than in open pasture, and large islands had greater seed density than smaller islands (Gliricidia only), suggesting that they are more effective for restoration. Distance to forest did not affect seed rain. A total of 543 seedlings and 41 species established in islands; > 85% were zoochorous. Seedling density did not differ among treatments (mean 0.2 seedlings/m2 for islands vs. 0.1 seedlings/m2 for pasture), although an increasing trend in tree islands over the course of two years suggests that seedling recruitment is accelerated there. Lastly, similar seedling densities were censused in the 1 m perimeter surrounding islands, suggesting that islands can expand outward into pasture. Planting vegetative stakes to create tree islands in pastures accelerates forest recovery by overcoming a number of impediments, and presents a simple, broadly applicable alternative for facilitating forest regeneration in abandoned pastures.     

Long-term CO2 enrichment of a forest ecosystem: implications for forest regeneration and succession.

The composition and successional status of a forest affect carbon storage and net ecosystem productivity, yet it remains unclear whether elevated atmospheric carbon dioxide (CO2) will impact rates and trajectories of forest succession. We examined how CO2 enrichment (+200 microL CO2/L air differential) affects forest succession through growth and survivorship of tree seedlings, as part of the Duke Forest free-air CO2 enrichment (FACE) experiment in North Carolina, USA. We planted 2352 seedlings of 14 species in the low light forest understory and determined effects of elevated CO2 on individual plant growth, survival, and total sample biomass accumulation, an integrator of plant growth and survivorship over time, for six years. We used a hierarchical Bayes framework to accommodate the uncertainty associated with the availability of light and the variability in growth among individual plants. We found that most species did not exhibit strong responses to CO2. Ulmus alata (+21%), Quercus alba (+9.5%), and nitrogen-fixing Robinia pseudoacacia (+230%) exhibited greater mean annual relative growth rates under elevated CO2 than under ambient conditions. The effects of CO2 were small relative to variability within populations; however, some species grew better under low light conditions when exposed to elevated CO2 than they did under ambient conditions. These species include shade-intolerant Liriodendron tulipifera and Liquidambar styraciflua, intermediate-tolerant Quercus velutina, and shade-tolerant Acer barbatum, A. rubrum, Prunus serotina, Ulmus alata, and Cercis canadensis. Contrary to our expectation, shade-intolerant trees did not survive better with CO2 enrichment, and population-scale responses to CO2 were influenced by survival probabilities in low light. CO2 enrichment did not increase rates of sample biomass accumulation for most species, but it did stimulate biomass growth of shade-tolerant taxa, particularly Acer barbatum and Ulmus alata. Our data suggest a small CO2 fertilization effect on tree productivity, and the possibility of reduced carbon accumulation rates relative to today's forests due to changes in species composition.     

天然林林龄的模拟估算及案例

林龄是森林生态系统的一个重要特征,具有生态学意义.但是目前生态学调查中对天然林林龄的估算方法有一定缺陷.在特定的环境条件下,森林有着相应的演替过程.已有林窗研究表明.长白山森林是按照一定次序演替,森林的径级结构也是有规律可循的.由于总是缺乏足够的长期系统观测数据,因此作者采用数值模拟作为替代方法.应用校正过的林窗模型模拟0～600 a的森林演替序列,比较对长白山原始天然林的采样的结果,发现目前的林龄最接近400 a.这个估测结果可以从本地区历史资料记载得到印证.     

Population maintenance of the short-lived shrub Sambucus in a deciduous forest

This study quantitatively clarifies the life history of a shrub, Sambucus racemosa ssp. sieboldiana, in an old-growth forest, the Ogawa Forest Reserve, Japan, by a demographic approach using a projection matrix model that incorporates interactions between demographic parameters and canopy height dynamics. S. racemosa is a common deciduous shrub in central Japan and is known to grow predominantly at forest edges or roadsides. This indicates that it is a highly light-demanding species, and occurrence in gaps in old-growth stands suggests its "fugitive," gap-dependent life history in old-growth forests. We found that one distinctive feature of this species was that its seedlings can survive well in shaded conditions by alternating stems every year like perennial herb species. Matrix model analyses demonstrated that S. racemosa can continuously regenerate under the present disturbance regime of this forest and is highly adaptable to the structural dynamics of the old-growth forest. The maturity of S. racemosa shrubs depends on their size, and nearly all (>90%) of the mature (reproducing) individuals were found in gaps or near gaps. But wide seed dispersal by birds and the ability to form both seed banks and seedling banks, the latter of which has been regarded as a common characteristic of shade-tolerant climax species, probably increase the species' chances to encounter canopy gaps. Dynamic-canopied matrix models showed that the greatest elasticity is with shaded seedling survival. The frequent stem alternation of shaded seedlings often makes the growth rate negative, but the survival rate of seedlings in low light awaiting new gap creation is remarkably high (0.93 yr(-1)). The lower survival rate of the larger individuals and smaller minimum size to start reproduction than other canopy or subcanopy shade-tolerant species indicate that S. racemosa has the potential to reproduce before the closure of the encountered gaps and to complete its life history rapidly.     

Seed predation by Neotropical rain forest mammals increases diversity in seedling recruitment

Seed dispersal and seedling recruitment (the transition of seeds to seedlings) set the spatiotemporal distribution of new individuals in plant communities. Many terrestrial rain forest mammals consume post-dispersal seeds and seedlings, often inflicting density-dependent mortality. In part because of density-dependent mortality, diversity often increases during seedling recruitment, making it a critical stage for species coexistence. We determined how mammalian predators, adult tree abundance, and seed mass interact to affect seedling recruitment in a western Amazonian rain forest. We used exclosures that were selectively permeable to three size classes of mammals: mice and spiny rats (weighing <1 kg), medium-sized rodents (1-12 kg), and large mammals (20-200 kg). Into each exclosure, we placed seeds of 13 tree species and one canopy liana, which varied by an order of magnitude in adult abundance and seed mass. We followed the fates of the seeds and resulting seedlings for at least 17 months. We assessed the effect of each mammalian size class on seed survival, seedling survival and growth, and the density and diversity of the seedlings that survived to the end of the experiment. Surprisingly, large mammals had no detectable effect at any stage of seedling recruitment. In contrast, small- and medium-sized mammals significantly reduced seed survival, seedling survival, and seedling density. Furthermore, predation by small mammals increased species richness on a per-stem basis. This increase in diversity resulted from their disproportionately intense predation on common species and large-seeded species. Small mammals thereby generated a rare-species advantage in seedling recruitment, the critical ingredient for frequency dependence. Predation by small (and to a lesser extent, medium-sized) mammals on seeds and seedlings significantly increases tree species diversity in tropical forests. This is the first long-term study to dissect the effects of various mammalian predators on the recruitment of a diverse set of tree species.     

Effects of Pioneer Tree Species Hyperabundance on Forest Fragments in Northeastern Brazil

Abstract: Despite many studies on fragmentation of tropical forests, the extent to which plant and animal communities are altered in small, isolated forest fragments remains obscure if not controversial. We examined the hypothesis that fragmentation alters the relative abundance of tree species with different vegetative and reproductive traits. In a fragmented landscape (670 km²) of the Atlantic Forest of northeastern Brazil, we categorized 4056 trees of 182 species by leafing pattern, reproductive phenology, and morphology of seeds and fruit. We calculated relative abundance of traits in 50 1‐ha plots in three types of forest configurations: forest edges, small forest fragments (3.4–83.6 ha), and interior of the largest forest fragment (3500 ha, old growth). Although evergreen species were the most abundant across all configurations, forest edges and small fragments had more deciduous and semideciduous species than interior forest. Edges lacked supra‐annual flowering and fruiting species and had more species and stems with drupes and small seeds than small forest fragments and forest interior areas. In an ordination of species similarity and life‐history traits, the three types of configurations formed clearly segregated clusters. Furthermore, the differences in the taxonomic and functional (i.e., trait‐based) composition of tree assemblages we documented were driven primarily by the higher abundance of pioneer species in the forest edge and small forest fragments. Our work provides strong evidence that long‐term transitions in phenology and seed and fruit morphology of tree functional groups are occurring in fragmented tropical forests. Our results also suggest that edge‐induced shifts in tree assemblages of tropical forests can be larger than previously documented.     

Ecological consequences of forest elephant declines for Afrotropical forests

Poaching is rapidly extirpating African forest elephants (Loxodonta cyclotis) from most of their historical range, leaving vast areas of elephant‐free tropical forest. Elephants are ecological engineers that create and maintain forest habitat; thus, their loss will have large consequences for the composition and structure of Afrotropical forests. Through a comprehensive literature review, we evaluated the roles of forest elephants in seed dispersal, nutrient recycling, and herbivory and physical damage to predict the cascading ecological effects of their population declines. Loss of seed dispersal by elephants will favor tree species dispersed abiotically and by smaller dispersal agents, and tree species composition will depend on the downstream effects of changes in elephant nutrient cycling and browsing. Loss of trampling and herbivory of seedlings and saplings will result in high tree density with release from browsing pressures. Diminished seed dispersal by elephants and high stem density are likely to reduce the recruitment of large trees and thus increase homogeneity of forest structure and decrease carbon stocks. The loss of ecological services by forest elephants likely means Central African forests will be more like Neotropical forests, from which megafauna were extirpated thousands of years ago. Without intervention, as much as 96% of Central African forests will have modified species composition and structure as elephants are compressed into remaining protected areas. Stopping elephant poaching is an urgent first step to mitigating these effects, but long‐term conservation will require land‐use planning that incorporates elephant habitat into forested landscapes that are being rapidly transformed by industrial agriculture and logging.     

Responses of Seed‐Dispersing Birds to Amount of Rainforest in the Landscape around Fragments

Habitat loss and fragmentation alter the composition of bird assemblages in rainforest. Because birds are major seed dispersers in rainforests, fragmentation‐induced changes to frugivorous bird assemblages are also likely to alter the ecological processes of seed dispersal and forest regeneration, but the specific nature of these changes is poorly understood. We assessed the influence of fragment size and landscape forest cover on the abundance, species composition, and functional properties of the avian seed disperser community in an extensively cleared, former rainforest landscape of subtropical Australia. Bird surveys of fixed time and area in 25 rainforest fragments (1–139 ha in size across a 1800 km² region) provided bird assemblage data which were coupled with prior knowledge of bird species’ particular roles in seed dispersal to give measurements of seven different attributes of the seed disperser assemblage. We used multimodel regression to assess how patch size and surrounding forest cover (within 200 m, 1000 m, and 5000 m radii) influenced variation in the abundance of individual bird species and of functional groups based on bird species’ responses to fragmentation and their roles in seed dispersal. Surrounding forest cover, specifically rainforest cover, generally had a greater effect on frugivorous bird assemblages than fragment size. Amount of rainforest cover within 200 m of fragments was the main factor positively associated with abundances of frugivorous birds that are both fragmentation sensitive and important seed dispersers. Our results suggest a high proportion of local rainforest cover is required for the persistence of seed‐dispersing birds and the maintenance of seed dispersal processes. Thus, even small rainforest fragments can function as important parts of habitat networks for seed‐dispersing birds, whether or not they are physically connected by vegetation. Respuestas de Aves Dispersoras de Semillas al Incremento de Selvas en el Paisaje Alrededor de Fragmentos     

Resprouting as a persistence strategy of tropical forest trees: relations with carbohydrate storage and shade tolerance

Resprouting is an important persistence strategy for woody species and represents a dominant pathway of regeneration in many plant communities, with potentially large consequences for vegetation dynamics, community composition, and species coexistence. Most of our knowledge of resprouting strategies comes from fire-prone systems, but this cannot be readily applied to other systems where disturbances are less intense. In this study we evaluated sapling responses to stem snapping for 49 moist-forest species and 36 dry-forest species from two Bolivian tropical forests. To this end we compared in a field experiment the survival and height growth of clipped and control saplings for a two-year period, and related this to the shade tolerance, carbohydrate reserves, and the morphological traits (wood density, leaf size) of the species. Nearly all saplings resprouted readily after stem damage, although dry-forest species realized, on average, a better survival and growth after stem damage compared to moist-forest species. Shade-tolerant species were better at resprouting than light-demanding species in moist forest. This resprouting ability is an important prerequisite for successful regeneration in the shaded understory, where saplings frequently suffer damage from falling debris. Survival after stem damage was, surprisingly, only modestly related to stem reserves, and much more strongly related to wood density, possibly because a high wood density enables plants to resist fungi and pathogens and to reduce stem decay. Correlations between sampling performance and functional traits were similar for the two forest types, and for phylogenetically independent contrasts and for cross-species analyses. The consistency of these results suggests that tropical forest species face similar trade-offs in different sites and converge on similar sets of solutions. A high resprouting ability, as well as investments in stem defense and storage reserves, form part of a suite of co-evolved traits that underlies the growth-survival trade-off, and contributes to light gradient partitioning and species coexistence. These links with shade tolerance are important in the moist evergreen forest, which casts a deep, more persistent shade, but tend to diminish in dry deciduous forest where light is a less limiting resource.     

Effects of Patch Size and Type of Coffee Matrix on Ithomiine Butterfly Diversity and Dispersal in Cloud-Forest Fragments

Abstract: Determining the permeability of different types of landscape matrices to animal movement is essential for conserving populations in fragmented landscapes. We evaluated the effects of habitat patch size and matrix type on diversity, isolation, and dispersal of ithomiine butterflies in forest fragments surrounded by coffee agroecosystems in the Colombian Andes. Because ithomiines prefer a shaded understory, we expected the highest diversity and abundance in large fragments surrounded by shade coffee and the lowest in small fragments surrounded by sun coffee. We also thought shade coffee would favor butterfly dispersal and immigration into forest patches. We marked 9675 butterflies of 39 species in 12 forest patches over a year. Microclimate conditions were more similar to the forest interior in the shade‐coffee matrix than in the sun‐coffee matrix, but patch size and matrix type did not affect species richness and abundance in forest fragments. Furthermore, age structure and temporal recruitment patterns of the butterfly community were similar in all fragments, independent of patch size or matrix type. There were no differences in the numbers of butterflies flying in the matrices at two distances from the forest patch, but their behavior differed. Flight in the sun‐coffee matrix was rapid and directional, whereas butterflies in shade‐coffee matrix flew slowly. Seven out of 130 recaptured butterflies immigrated into patches in the shade‐coffee matrix, and one immigrated into a patch surrounded by sun coffee. Although the shade‐coffee matrix facilitated movement in the landscape, sun‐coffee matrix was not impermeable to butterflies. Ithomiines exhibited behavioral plasticity in habitat use and high mobility. These traits favor their persistence in heterogeneous landscapes, opening opportunities for their conservation. Understanding the dynamics and resource requirements of different organisms in rural landscapes is critical for identifying management options that address both animals’ and farmers’ needs.     

Modelling forest–savanna mosaic dynamics in man-influenced environments: effects of fire,climate and soil heterogeneity

Forests and savannas are the major ecotypes in humid tropical regions. Under present climatic conditions, forest is in a phase of natural expansion over savanna, but traditional human activities, especially fires, have strongly influenced the succession. We here present a new model, FORSAT, dedicated to the forest–savanna mosaic on a landscape scale and based on stochastic modelling of key processes (fire and succession cycle) and consistent with common field data. The model is validated by comparison between the qualitative emergent behaviour of the model and results of biogeographical field studies. Three types of forest succession are shown: progression of the forest edge, formation and coalescence of clumps in savanna and global afforestation of savanna. The parameters (frequency of savanna fires, climate and soil fertility) appear to have comparable effects and there is a sharp threshold between a forest edge progression scenario and the cluster formation one. Moreover, pioneer seed dispersal pattern and recruitment are determinant: peaked curves near a seed source and far dispersal combine to increase the fitness of the pioneers.     

Potentials and limitations of using large-scale forest inventory data for evaluating forest succession models

Forest gap models have been applied widely to examine forest development under natural conditions and to investigate the effect of climate change on forest succession. Due to the complexity and parameter requirements of such models a rigorous evaluation is required to build confidence in the simulation results. However, appropriate data for model assessment are scarce at the large spatial and temporal scales of successional dynamics. In this study, we explore a data source for the evaluation of forest gap models that has been used only little in the past, i.e., large-scale National Forest Inventory data. The key objectives of this study were (a) to examine the potentials and limitations of using large-scale forest inventory data for evaluating the performance of forest gap models and (b) to test two particular models as case studies to derive recommendations for their future improvement.     

Design and validation of a spatially explicit simulation model for bottomland hardwood forests

Species composition in forests depends on the interaction of species traits and species availability. Yet many forest simulation models focus only on interactions of adult trees and saplings, ignoring how species become members of the community. We modify a published forest model for bottomland hardwood forests (program SWAMP [Phipps, R.L., 1979. Simulation of wetlands forest vegetation dynamics. Ecol. Modell. 7, 257–288]) to make it spatially explicit and incorporate explicit seed production and dispersal algorithms. The resulting individual-based, spatially explicit forest simulator (YAFSIM) combines mechanistic seed dispersal with growth and mortality of trees to track forest dynamics over time. We describe the structure of the model and test its validity for dynamics in small bottomland hardwood patches in the Mississippi Alluvial Valley. Dynamics of species composition and basal areas of trees predicted by Yazoo Forest Simulator (YAFSIM) were similar to those of natural second- and old-growth bottomland forests. However, diversity of simulated forest patches declined over time largely because of random dynamics acting on small, isolated populations.     

Mediation of area and edge effects in forest fragments by adjacent land use

Habitat loss, fragmentation, and degradation have pervasive detrimental effects on tropical forest biodiversity, but the role of the surrounding land use (i.e., matrix) in determining the severity of these impacts remains poorly understood. We surveyed bird species across an interior-edge-matrix gradient to assess the effects of matrix type on biodiversity at 49 different sites with varying levels of landscape fragmentation in the Brazilian Atlantic Forest—a highly threatened biodiversity hotspot. Both area and edge effects were more pronounced in forest patches bordering pasture matrix, whereas patches bordering Eucalyptus plantation maintained compositionally similar bird communities between the edge and the interior and exhibited reduced effects of patch size. These results suggest the type of matrix in which forest fragments are situated can explain a substantial amount of the widely reported variability in biodiversity responses to forest loss and fragmentation.     

Simulating dynamics of managed monsoon evergreen broad-leaved forest in south China

The forest succession model FORDYN is developed based on TREEDEV model. TREEDEV is a process-based tree growth model, that calculates tree growth based on carbon and nitrogen balance, and is calculated using on the photo-production of leaves, respiration, nitrogen content of all organisms and that in soil, and other losses due to respiration, litter and renewal of stems, branches, leaves and roots. In the FORDYN model succession is divided into three phases called early, middle and late succession, and the transition between these three succession phases is distinguished by a difference in leaf area index. As a verification of the model we used the characteristics and available data of a monsoon evergreen broad-leaved forest in Dinghushan Biosphere Reserve (DHS-BR). The model was validated with natural forest data. In addition, a sensitivity analysis was performed in which 30 independent variables were varied and analyzed in connection with their influence on 16 dependent variables describing forest conditions. The simulation results describe the changes in total biomass, carbon and nitrogen change in plant–litter–soil system of an undisturbed monsoon evergreen broad-leaved forest during succession. We compared these findings with simulation in which different logging management strategies were used. The results show that having a longer logging cycle, delaying the first logging time and a smaller logging fraction the scenario can contribute to a sustainable forest development, while still having a positive economic yield.     

几种不同更新的森林群落碳储量结构特征分析

森林更新是维持和扩大森林资源的主要途径,也是森林结构调整、森林可持续经营和构建多功能高效的森林生态系统的过程。在安徽南部的岭南林场,选择了马尾松（Pinus massoniana Lamb）人工林（MP）、杉木（Cunninghamia lanceolata）人工林（CF）、阔叶混交天然次生林（MB）和针阔混交人工次生林（MN）等4种具有典型代表性的森林群落类型,研究了不同更新方式形成的森林群落的碳储量结构特征。结果表明：（1）针阔混交次生林树干生物量密度最大,为（67.32±56.57）mg.hm-2,杉木人工林生物量密度最小,为（43.79±9.13）mg.hm-2,而马尾松树干生物量所占比例最大,为（64.04±1.49）%。阔叶混交次生林碳储量最高,为（126.47±90.75）mg.hm-2;（2）4种群落类型中,阔叶混交林与马尾松群落碳密度最大,分别为95.67和98.21mg.hm-2,杉木群落碳密度最小,为55.41 mg.hm-2。阔叶混交林中的灌木层生物量碳密度最大,为（17.438±24.627）mg hm-2,马尾松林的草本层和枯落层生物量碳密度最高,分别为（1.326±0.431）、（5.517±2.846）mg.hm-2;（3）阔叶混交林群落的地下碳储量最高,为（10.5±9.8）mg.hm-2,群落地下碳储量从大到小的顺序是阔叶混交林〉针阔混交林〉杉木林〉马尾松林。相应的群落地上碳储量从大到小的顺序是阔叶混交林〉针阔混交林〉马尾松林〉杉木林。杉木林根茎比（R/S）最大,为0.21±0.01,杉木林群落中的灌木层根茎比（R/S）最大,为1.61±0.11;（4）在阔叶混交林中,株数密度与乔木层、草本层的碳比例正相关。在杉木林群落中,平均胸径、株数密度与乔木层碳所占比例成负相关。除杉木林群落外,灌木层碳含量之比与胸径及密度等调查因子都呈负相关。     

Modelling succession of Eastern Canadian mixedwood forest

The succession of a mixed species stand of the Acadian Forest was simulated by adopting an approach taken by Botkin et al. (1972) (JABOWA) and later modified by Shugart and West (1977) (FORET). The model simulates the dynamic aspects of successional behaviour of the stand by projecting the current stage of vegetation composition (size of each individual of each species present on a 1/12 ha plot) with an element of randomness. The growth of each tree is modeled as a function of its size (represented by its diameter at breast height (dbh), height and leaf area index), the climate, the tree's tolerance to shade and the competition for available resources and space. Stand aboveground biomass (metric ton/ha), leaf area index, number of trees/ha and species composition of the stand were simulated under seven different conditions: (a) normal treatment, (b) increasing biomass maximum 30%, (c) decreasing biomass maximum 30%, (d) increasing degree-days 30%, (e) decreasing degree-days 30%, (f) increasing light extinction coefficient 30% and (g) decreasing light extinction coefficient 30%. Under the first set of conditions (normal treatment), the aboveground biomass reached a maximum value during the first hundred years, decreased during the second, and remained stable for the rest of the 500-year simulation period. The leaf area showed a similar pattern. The total number of trees/ha decreased sharply during the first fifty years and reached a stable value by the end of the first hundred years. Successional patterns and species competitive abilities were interpreted from the accumulated biomass of each species over the simulation period under the different treatments.Species composition of the stand under the normal treatment showed dominance of deciduous species at early stages of succession, with conifer species being increased and becoming dominant at the end of the simulation period. When the climate was raised 30% (warmer) over the average, the deciduous species continued their dominance over the course of the simulation period. Other simulated species dynamics also appeared to follow what is known about their successional behaviour in the field.