森林干扰生态研究

陆地上80％的生态系统都已受到了来自人类和自然的各种干扰,森林生态系统也不例外．在各种干扰作用下,尤其是人类不合理的干扰导致世界范围内的森林退化／衰退已成为一个十分严峻的事实,因此,以维持、恢复森林生态系统固有的多种功能为基础,实现高效、稳定、可持续就成为经营森林生态系统的总目标．随着干扰的加剧,近年来生态学界更加关注的是“受干扰”生态系统的研究．干扰对森林生态系统主要生态过程的影响以及森林生态系统对干扰的响应等问题,已成为森林生态研究领域的国际前沿与热点．因此,系统地研究干扰条件下森林生态系统的生态过程,并在此基础上确立干扰森林的经营理论与技术,对中国天然林资源保护等林业工程实施及国家生态安全建设具有重要的科学和现实意义．本文在广泛收集国内外有关森林干扰研究结果的基础上,总结了森林干扰的基本概念,分析了干扰与森林经营的关系,探讨了森林干扰研究领域所涉及的内容和关注的基础问题,提出了森林干扰生态研究的主要内容与方向,对今后干扰森林生态研究和中国天然林保护等林业工程建设具有参考价值．     

Dynamics of seedling populations and tree species coexistence in a forest: a simulation study

Theoretically, temporal variation of reproduction promotes species coexistence of sessile and polycarpic organisms when the reproduction is synchronized within species but independent among species. Monopoly of vacant sites and high relative population growth rate of minor species in the absence of propagules of other species is the essence of this mechanism. The mechanism is expected to work in forests, but persistent populations of seedlings may affect the promotion of coexistence. Using a tree-based simulation model of forest dynamics, it was demonstrated that the number of coexisting tree species was sensitively affected by the seedling establishment rate. The coexistence was not enhanced by temporal variation of reproduction when seedling establishment rate was low. This is because the reproducing minor species fail to monopolize vacant sites and allow the establishment of seedlings of other species in later years. High mortality of established seedlings under shade also suppressed coexistence. This is likely to be the result of a reduced storage effect of the population of seedlings. A forest structure and dynamics pattern that appears when tree species coexistence is promoted by fluctuating reproduction was searched for, and the number of coexisting species was varied by manipulating the seedling establishment rate. No distinct difference other than the species number itself was found between species-rich and species-poor forests. For example, the seedling population size varied, reflecting the temporal variation of reproduction, irrespective of the seedling establishment rate. Further strategy development is needed to validate the proposed mechanisms of species coexistence.     

The effects of stand structure on ground-floor bryophyte assemblages in temperate mixed forests

The effect of tree species composition, stand structure characteristics and substrate availability on ground-floor bryophyte assemblages was studied in mixed deciduous forests of Western Hungary. Species composition, species richness and cover of bryophytes occurring on the soil and logs were analysed as dependent variables. The whole assemblage and functional groups defined on the basis of substrate preference were investigated separately. Substrate availability (open soil, logs) was the most prominent factor in determining species composition, cover and diversity positively, while the litter of deciduous trees had a negative effect on the occurrence of forest floor bryophytes. Besides, bryophyte species richness increased with tree species and stand structural diversity, and for specialist epiphytic and epixylic species log volume was essential. Sapling density and light heterogeneity were influential on bryophyte cover, especially for the dominant terricolous species. Many variables of the forest floor bryophyte community can be estimated efficiently by examining stand structure in the studied region. Selective cutting increasing tree species diversity, stand structural heterogeneity and dead wood volume can maintain higher bryophyte diversity in this region than the shelter-wood system producing even-aged, monodominant, structurally homogenous stands.     

Tree species richness complementarity, disturbance and fragmentation in a Mexican tropical montane cloud forest

Tropical montane cloud forest exhibits great heterogeneity in speciescomposition and structure over short geographic distances. In central Veracruz,Mexico, the conservation priority of seven cloud forest fragments was assessedby considering differences in woody plant species richness and complementarityof species among sites, forest structure, tree mortality, and timber andfirewood extraction as indicators of anthropogenic disturbance. Densities oftrees 5 cm dbh (360–1700 trees/ha) weredifferent among the sites, but basal area (35.3–89.3m²/ha) did not differ among fragments. The number of dead trees rangedfrom 10–30 to 170–200 trees/ha. The fragments'species composition was different but complementary. The Morisita–Hornindex indicated low similarity between fragments. A non-parametric estimator ofspecies richness indicated that more sampling effort would be necessary tocomplete the inventory (15 additional trees and two understory shrub species).Unfortunately, most of the fragments are threatened with deforestation. The numberof cut trees was similar among sites (0–15 cut trees/0.1 ha).Sites with immediate need for conservation were close to settlements, with highnumbers of cut trees and no legal protection. The selected sites represent thevariety of situations that exist in the region. Given the high complementarityobserved between fragments, a regional conservation approach will be required topreserve the last repositories of part of the tremendous biodiversity of theonce continuous forest in this region.     

Fire survival of lowland tropical rain forest trees in relation to stem diameter and topographic position

The objective of this study was to relate patterns in forest structure, tree species diversity, and tree species composition to stem diameters and topography in unburned, once burned and twice burned lowland dipterocarp rain forests in East Kalimantan, Indonesia. To do this four unburned old growth forests were compared with three forests that burned once (1997/1998) and three forests that burned twice (1982/1983 and 1997/1998). Fire resulted in a strong reduction of climax tree density which was negatively related to tree diameter. However, a disproportionate reduction in small diameter understorey climax tree species occurred only after repeated fires. Climax tree species in both burned forest types were most common in swamps, river valleys and on lower slopes, while their density was much lower on places higher along hillsides. In unburned forest the opposite was observed, with climax tree density increasing steadily from swamp and river valleys to upper slopes and ridges. In contrast to climax trees, pioneer trees were abundant throughout the burned forest, with highest numbers on hill sides and ridges. Our results indicate that both diameter and topographic position of trees strongly affect their fire survival chances in tropical lowland forests.     

Tree diversity in primary forest and different land use systems in Central Sulawesi,Indonesia

We studied the tree communities in primary forest and three different land use systems (forest gardens, ca. 5-year-old secondary forests, cacao plantations) at 900–1200 m elevation in the environs of Lore Lindu National Park, Central Sulawesi. The primary forests had ca. 150 tree species 10 cm diameter at breast height (dbh) per hectare, which is unusually high for forests at this elevation in southeast Asia. Basal area in the primary forest was 140 m² ha^–1, one of the highest values ever recorded in tropical forests worldwide. Tree species richness declined gradually from primary forest to forest gardens, secondary forests, and cacao plantations. This decline was paralleled by shifts in tree family composition, with Lauraceae, Meliaceae, and Euphorbiaceae being predominant in primary forests, Euphorbiaceae, Rubiaceae and Myristicaeae dominating in the forest gardens and Euphorbiaceae, Urticaceae, and Ulmaceae in the secondary forests. Cacao plantations were composed almost exclusively of cacao trees and two species of legume shade trees. Forest gardens further differed from primary forests by a much lower density of understorey trees, while secondary forests had fewer species of commercial interest. Comparative studies of birds and butterflies demonstrated parallel declines of species richness, showing the importance of trees in structuring tropical forest habitats and in providing resources.     

Seed-deposition and recruitment patterns of Clusia species in a disturbed tropical montane forest in Bolivia

Spatial patterns of seed dispersal and recruitment of fleshy-fruited plants in tropical forests are supposed to be driven by the activity of animal seed dispersers, but the spatial patterns of seed dispersal, seedlings and saplings have rarely been analyzed simultaneously. We studied seed deposition and recruitment patterns of three Clusia species in a tropical montane forest of the Bolivian Andes and tested whether these patterns changed between habitat types (forest edge vs. forest interior), distance to the fruiting tree and consecutive recruitment stages of the seedlings. We recorded the number of seeds deposited in seed traps to assess the local seed-deposition pattern and the abundance and distribution of seedlings and saplings to evaluate the spatial pattern of recruitment. More seeds were removed and deposited at the forest edge than in the interior. The number of deposited seeds decreased with distance from the fruiting tree and was spatially clustered in both habitat types. The density of 1-yr-old seedlings and saplings was higher at forest edges, whereas the density of 2-yr-old seedlings was similar in both habitat types. While seedlings were almost randomly distributed, seeds and saplings were spatially clustered in both habitat types. Our findings demonstrate systematic changes in spatial patterns of recruits across the plant regeneration cycle and suggest that the differential effects of biotic and abiotic factors determine plant recruitment at the edges and in the interior of tropical montane forests. These differences in the spatial distribution of individuals across recruitment stages may have strong effects on plant community dynamics and influence plant species coexistence in disturbed tropical forests.     

Regeneration niche partitioning in neotropical pioneers: effects of gap size,seasonal drought and herbivory on growth and survival

Adaptive trade-offs underlie the specialisation that permits habitat partitioning in species rich plant communities. We investigated the influence of the trade-offs that determine differences in growth and survival among six species of neotropical pioneer trees in gaps in semideciduous forest in Panama. Seedlings of Miconia argentea, Cecropia insignis, Luehea seemannii, Trema micrantha, Ochroma pyramidale and Croton bilbergianus were planted into artificial small (25 m²), medium (64 m²) and large (225 m²) gaps in secondary forest in the Barro Colorado Nature Monument. Trema and Ochroma suffered 50% mortality across all gap sizes, while Cecropia had high mortality only during the dry season and in the small gaps, and Miconia and Croton suffered low to zero mortality across all environments. The highest growth rates in large gaps were attained by Cecropia seedlings and in the smaller gaps by Miconia seedlings, although there were indications that Trema and Ochroma required gaps that were larger than any used in this study. Variation in growth and mortality could not be attributed to differences in foliar herbivore damage. Instead, there was strong evidence of a trade-off between maximum growth in the wet season and the ability to survive seasonal drought, particularly in small gaps. We conclude that variation in allocation in response to multiple limiting resources may be as important as allocation to growth and defence in determining the habitat preferences of neotropical pioneers.     

Reviewing the strength of evidence of biodiversity indicators for forest ecosystems in Europe

With a growing number of forest biodiversity indicators being applied in forest policy documents and even more being suggested by the scientific community, there is a need to evaluate, review and critically assess the strength of evidence for individual indicators, their interrelationships and potential overlaps and gaps. Biodiversity indicators proposed for forest ecosystems in Europe were reviewed with the overarching aim of providing advice on strategic selection and combination of indictors. The objectives were to (1) establish interrelationships between indicators and their indicandum (i.e. the indicated aspect of biodiversity); (2) assess the strength of scientific evidence for individual indicators; and (3) identify a set of indicators with confirmed validity for further scientific testing and inclusion in long-term reporting and decision-making regarding forest biodiversity. Ten indicator groups and 83 individual indicators were identified with application from stand scale up to landscape scale in 142 eligible scientific papers. In 62 of the 142 studies no statistical correlations between indicator(s) and indicandum were performed and 42 (out of the 62) did not even present a clear indicandum. In the remaining 80 studies, 412 correlations between indicator and indicandum were identified. However, only six correlations were assessed as being supported by strong evidence, i.e. three or more studies found statistical correlation between the indicator and indicandum, and no studies reported contradictory results. For the species richness relationships, there was strong evidence for positive correlations between deadwood volume and wood-living fungal species richness; deadwood volume and saproxylic beetle species richness; deadwood diversity and saproxylic beetle species richness; age of canopy trees and epiphytic lichen species richness. There was strong evidence for a negative correlation between tree canopy cover and spider species richness. Concerning species composition-related correlation, there was strong evidence that the species composition of epiphytic lichens changed with the age of canopy trees. These results imply that the validity of most indicators on which monitoring and conservation planning are based are weakly scientifically supported and that further validation of current biodiversity indicators for forest ecosystems is needed.     

Plant species diversity in abandoned coppice forests in a temperate deciduous forest area of central Japan

We investigated plant species diversity as it related to stand structure and landscape parameters in abandoned coppice forests in a temperate, deciduous forest area of central Japan, where Fagus crenata was originally dominant. The species occurring in the study plots were classified into habitat types based on a statistical analysis of their occurrence bias in particular habitats (e.g., primary forest, coniferous plantation) in the landscape studied. The relationships between stand structure, which reflected the gradient of management, and forest floor plant species diversity (H and J) and richness (number of species per unit area) were not significant. However, these factors did influence the forest floor plant composition of the different types of habitat. According to the multiple regression analysis, species diversity and the richness of forest floor plants was affected by landscape parameters rather than by stand structure. For trees, species richness was mainly affected by the relative dominance of F. crenata, which is one of the stand structure parameters that decreases with intensive management. This is probably because many of the tree species that are characteristic of coppice forests increase after F. crenata have been eliminated by management; these species are not dominant in the original forest, where they are suppressed by F. crenata, the shade-tolerant dominant species. The species diversity (H and J) of trees was positively correlated with some landscape parameters, including the road density around the study plot, which may be associated with the intensity of management activity. The number of disturbance-tolerant species increased with increasing road density. Stand structure mainly affected disturbance-intolerant forest floor plant species and disturbance-tolerant tree species. Thus, the species diversity responses differed between forest floor plants and trees. The impact of forest management on species diversity was more prominent for forest floor plants.     

Tree recovery and seed dispersal by birds: Comparing forest, agroforestry and abandoned agroforestry in coastal Ecuador

We used a highly replicated study to examine vegetation characteristics between patches of intervened forest, abandoned agroforestry systems with coffee and actively managed agroforestry systems with coffee in a tropical landscape. In all habitats, plant structural characteristics, individual abundance, species richness and composition were recorded for the three plant size classes: adult trees, saplings and seedlings. Furthermore, bird species richness and composition, and seeds dispersed by birds were recorded. Tree abundance was higher in forest habitats while saplings and seedlings were more abundant in abandoned coffee sites. Although species richness of adult trees was similar in the three habitats, species richness of saplings and seedlings was much higher in forest and abandoned coffee than in managed coffee sites. However, in spite of their relatively low species richness, managed coffee sites are an important refuge for tree species common to the almost disappeared mature forest in the area. Floristic similarity for adult trees was relatively low between land use types, but clearly higher for seedlings, indicating homogenizing processes at the landscape level. More than half of the saplings and seedling were not represented by adults in the canopy layer, suggesting the importance of seed dispersal by birds between habitats. Our results show that each of the studied ecosystems plays a unique and complementary role as seed source and as habitat for tree recovery and tree diversity.     

Patterns in the structure of grassland butterfly communities along a gradient of human disturbance: further analysis based on the generalist/specialist concept

Kitahara and Fujii, in 1994, analyzed the butterfly communities along a gradient of human disturbance by applying the generalist/specialist concept. Butterfly species were classified into generalist or specialist species based on their voltinism (seasonal time dimension) and potential larval resource breadth (food dimension). The community structure and species composition showed the systematic changes along the gradient. To verify the generality of those trends, we monitored five grassland butterfly communities with varying degrees of human disturbance twice a month during 1985 by the line transect method at the foot of Mt. Fuji, central Japan, and analyzed their structure in a manner similar to that employed by Kitahara and Fujii. Most results were consistent with the patterns recognized by Kitahara and Fujii. The route (community) order based on increasing human disturbance was strongly and negatively correlated with butterfly species richness but with neither butterfly species diversity (H′) nor evenness (J′). Also, the degree of human disturbance was significantly and negatively correlated with the number of specialist species, but not with that of generalists, in a community. Butterfly species richness was more strongly correlated with the number of specialist species than with that of generalists. Our analyses also showed that the generalist species were distributed more widely over the communities than were the specialists. However, in contrast to the trend revealed by Kitahara and Fujii, there was no significant difference in the population densities and in the spatial population variability between the two species groups. As a whole, our analyses confirmed the consistency of most community patterns detected by Kitahara and Fujii. The causes of the inconsistencies in some patterns were thought to be mainly the present habitat conditions with a relatively short growing season at high altitudes. Received: October 19, 1999 / Accepted: June 5, 2000     

The effects of forest disturbance on diversity of tropical soil nematodes

We provide the first account of the effects of forest disturbance on species richness of nematodes in tropical forest soils, from 24 sites along gradients of disturbance and regeneration in the Mbalmayo Forest Reserve, Cameroon. Species richness was very high. Samples of 200 nematodes from individual soil cores contained a maximum of 89 and an average of 61 species; in total we recorded 431 species and approximately 194 genera. The model of Siemann et al. (1996), predicting that species richness scales as the number of individuals I ^0.5, underestimates nematode diversity 4–6 fold in these samples. Over 90% of specimens cannot be assigned to known species. Although nematode species richness declined with forest disturbance, statistically significant effects were detectable only under the most extreme conditions (active slash-and-burn agriculture and complete mechanical forest clearance) and even here remained at 40% of the richness of near primary sites. Impacts on trophic structure were also small, and there were no significant changes in the maturity index (MI) (Bongers 1990) with disturbance (mean MI across all treatments was very high, at 3.58). In the light of this study, the problems of completing reliable all-taxon inventories in tropical forests are briefly discussed. Received: 22 July 1996 / Accepted: 3 April 1997     

Using structural sustainability for forest health monitoring and triage: Case study of a mountain pine beetle (Dendroctonus ponderosae)-impacted landscape

Heavy disturbance-induced mortality can negatively impact forest biota, functions, and services by drastically altering the forest structures that create stable environmental conditions. Disturbance impacts on forest structure can be assessed using structural sustainability⿿the degree of balance between living and dead portions of a tree population⿿s size-class distribution⿿which is the basis of baseline mortality analysis. This analysis uses a conditionally calibrated reference level (i.e., baseline mortality) against which to detect significant mortality deviations without need for historical references. Recently, a structural sustainability index was developed by parameterizing results of this analysis to allow spatial and temporal comparisons within or among forested landscapes. The utility of this index as a tool for forest health monitoring programs and triage decisions has not been examined. Here, we investigated this utility by retrospectively analyzing the structural sustainability of a mountain pine beetle (Dendroctonus ponderosae)-impacted, lodgepole pine (Pinus contorta)-dominated landscape annually from 2000 to 2006 as well as among watersheds. We show that temporal patterns of structural sustainability at the landscape-level reflect accumulating beetle-induced mortality as well as beetle-lodgepole pine ecology. At the watershed-level, this sustainability spatially varied with 2006 beetle-induced mortality. Further, structural sustainability satisfies key criteria for effective indicators of ecosystem change. We conclude that structural sustainability is a viable tool upon which to base or supplement forest health monitoring and triage programs, and could potentially increase the efficacy of such programs under current and future climate change-associated disturbance patterns.     

Growth strategies of main trees and forest architecture of aFagus-Magnolia forest in Florida, USA

Growth strategies of six species of trees are compared and used to analyze forest architecture. They included the overstory speciesFagus grandifolia, Magnolia grandiflora, Pinus glabra andLiquidambar styraciflua, and the understory speciesOstrya virginiana andIlex opaca. The six species were abundant in Woodyard Hammock, an old-growth forest in northern Florida, USA. Height, stem diameter, crown projection and radial growth were measured in trees between 5 and 35 m tall. Three different, but non-exclusive, growth strategies were identified for the tree species: survival (Fagus grandifolia, Magnolia grandiflora, Ilex opaca), occupy open space (Fagus grandifolia, Ostrya virginiana, Ilex opaca), and reach above competitors (Liquidambar styraciflua, Pinus glabra). In two transects (0.42 ha) and one quadrat (1 ha), heights of dominant trees were used to distinguish different phases of forest development, which were mapped. In the quadrat, juvenile canopy trees in the undergrowth were mapped. The combination of presence of different developmental phases, presence of juveniles in the undergrowth, growth strategies of main tree species, and disturbance regime was used to assess forest development in the near future.Fagus grandifolia is predicted to become the main dominant species, but the frequent hurricanes open the forest canopy and provide opportunities for understory species (Ostrya virginiana andIlex opaca), and light-demanding overstory species (Liquidambar styraciflua andPinus glabra).     

A role-type model (rope) and its application in assessing climate change impacts on forest landscapes

Gap-phase replacement is a general phenomenon found in forest ecosystems, worldwide. Different tree species can be expected to produce different sizes of gaps when they die. Species also vary in their regeneration success in gaps of different sizes. In this paper, the gap-phase interactions among tree species in a forest stand are simulated by a role-type stand model called ROPE. By incorporation of environmental effects on tree height, ROPE can simulate forest composition and stand leaf area under different climate conditions. The model was developed for forest ecosystems in northeastern China and was used to simulate the forest landscape structures under current climate conditions and under four climate change scenarios for greenhouse gas related warming. These scenarios were obtained from general circulation models developed by different atmospheric research centers. Korean pinebroadleaf mixed forest and larch forest are the major stand types in the study area under present conditions. Under the four climate change scenarios, Korean pine-broadleaf mixed forest would be expected to occur only on the higher parts of large mountains. Larch forest only would be found north of the study area. Broadleaf forest would become the dominant vegetation over the study area. Use of the Kappa statistic to test for similarity in spatial maps, indicates that each climate change scenario would result in a significant change of forest distributions.Supported by The United States National Science Foundation Grant BSR-8702333 to University of Virginia.     

Conservation of temperate forest birds in Chile: implications from the study of an isolated forest relict

We characterize the bird assemblage of an isolated relict temperaterainforest (Santa Inés) in terms of its structure, composition anddynamics. The relict character and long-term isolation of this forest remnant,immersed in a matrix of semiarid scrub, provide a natural experiment to assessthe consequences of long-term isolation and forest area reduction for temperatebird species. Bird surveys were conducted in a forest fragment and thesurrounding scrub matrix between April 1999 (austral autumn) and October 2000(austral spring) on a seasonal basis. Within the forest fragment wedistinguished two microhabitat types: creeks and areas far from creeks (i.e.slopes). A total of 36 species were recorded in the study site, of which 21were inside the relict forest. Highest bird abundance and richness wererecorded during winter and spring, and these were always higher in creek plotsrather than slope plots. Comparisons between this assemblage and thosedistributed in the continuous temperate forest (located more than 900km southwards) indicate that this bird assemblage shares moresimilarities, with regard to bird species composition, to southern temperateforest localities and to other relict forests, than to nearer scrub habitats.However, there are eight species, endemic to temperate forests in southern SouthAmerica, missing from our system. In this regard, our analyses indicate thatthese eight endemic species should be of great conservation concern and willlikely be the ones that will go extinct first if the fragmentation of thetemperate forest continues.