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1.
A study was carried out in the Lama forest reserve of Benin to characterize the habitat of Afzelia africana Sm., an endangered multipurpose tree species (found in African humid, dry forests and woodlands), in order to define a sustainable management strategy for its conservation. An estimation of species density was done on 100 square plots of 1 ha each, while tree height and dbh of all the species were measured on subplots of 50 m × 30 m within the 1 ha plots. The regenerations of A. africana (dbh < 10 cm) were counted in the diagonal quadrats of the principal plots. Presence–absence data of the species was subjected to multidimensional scaling and results showed four vegetation communities including: young fallow, old fallow, typical dense forest and degraded dense forest. Significant differences were noted between the four communities with respect to dendrometric parameters of the species. High values of these parameters were noted for the species in typical dense forest (5.2 stems/ha, 66.7 cm, 17.9 m, 7.9 m2/ha and 38.8% for the tree-density, the mean diameter, the mean height, basal area and basal area contribution of the species, respectively) whereas the lowest values were obtained for the old preforest fallow as far as the mean diameter (59.7 cm), the mean height (15.7 m) and the basal area contribution (27.7%) of the species were concerned. In general, the basal area of A. africana in the over vegetation types was less than 3 m2/ha. No A. africana tree was found in the young preforest fallow while more than 80% of A. africana trees were found in the typical dense forest community. Stem diameter and height structures of the species in all the four communities showed a left dissymmetric Gaussian shape and were well adjusted to Weibull distribution.  相似文献   

2.
To assess the effects of clearcutting on snowshoe hare (Lepus americanus) relative abundance, we surveyed pellets in 1 m2 circular plots and, vegetation and browse surveys in 4.5 m2 circular plots among four different aged clearcut (30, 20, 10, 5 years post-harvest) and mature forests (>150 years old) in central Labrador, Canada. Data were modelled at three grain sizes: transect (4400 m2), plot (314 m2) and subplot scales (4.5 m2). Betula papyrifera, distance from mature forest edge, tree and herb cover as well as remotely sensed forest inventory data were used as predictors for hare pellets. We found pellet abundance was 5 and 37 times greater (new and old pellets, respectively) in clearcut stands 30 years old than the next highest in 20 year old cuts. There were few hare pellets in the remaining stand ages. B. papyrifera was the most proportionately used browse species and most important of our fine-detailed vegetation in predicting hare pellets. The coarse-detailed, forest inventory and topographic data better predicted hare pellets than the fine-detailed vegetation data.  相似文献   

3.
We demonstrate a method for evaluating the appropriate number of samples required to estimate plant species richness in different forest types within a forested landscape. In each of 36 plots (0.1 ha each) from 5 forest types (deciduous broad-leaved secondary forest and 4 categories of coniferous plantation classified according to stand age) in central Japan, 40 quadrats of 1 × 1 m were set in a regular pattern; the total number of quadrats in each forest type ranged from 200 to 400. In each plot, the number of observed species in 40 quadrats ranged from 60 to 80% of the number of species estimated by the rarefaction method for each forest type. Sampling 30 quadrats detected approximately 90% of the observed species in each plot that were detected using 40 quadrats. In specific functional groups (i.e., tall trees and weed species), the ratios of both tall trees and weed species to all species were at equilibrium for 30 or more quadrats. For fewer than 30 quadrats these ratios were highly variable. No significant differences were found among forest types in the ratio of the observed number of species in each plot to the estimated number of species calculated using the rarefaction method, and in sampling efficiency estimated by use of non-parametric estimators. We concluded that the number of samples does not need to be changed according to forest type or plantation stand age in the studied landscape, and that the method used to evaluate the number of samples could be useful.  相似文献   

4.
Heterogeneity of forest stand structure often results from repeated small disturbances, but structural variation also arises in a stand that has regenerated after a single large stand-replacing disturbance. We explored the structural variation within a subalpine Abies forest in Japan that regenerated after a large typhoon in 1959. In 2004, four 50 × 50 m plots were established at two sites in the regenerated forest. To characterize local stand structure within each plot, we determined the stem density, stand basal area, mean diameter at breast height (DBH), and coefficient of variation (CV) of DBH in 10 × 10 m subplots. We analyzed the spatial distribution pattern of the trees in each subplot using the L(t) function and categorized the distributions as clumped or non-clumped. The analysis revealed marked variation among subplots in the stand’s structural characteristics. Although the spatial distribution patterns of the trees in all plots were clumped, 11 of 50 subplots at one site and 39 of 50 subplots at the other site were non-clumped. Subplots with a clumped distribution pattern generally had a smaller basal area, smaller mean DBH, and greater CV of DBH than subplots with the same density but a non-clumped pattern. These results illustrated the spatial heterogeneity of forest structure that can arise in Abies forest that has experienced a large disturbance, probably because of the different densities and distribution of saplings surviving the disturbance and the different forest growth dynamics that result.  相似文献   

5.
In the Okavango Delta information on the riparian woodland vegetation community composition and distribution is generally lacking. Past studies in the Delta were mainly focused on the quantitative classification of seasonal floodplain herbaceous vegetation communities. The aim of this study was to determine riparian woodland vegetation communities in the Okavango Delta. Vegetation sampling was conducted in 20?m × 50?m randomly placed plots. The plots were placed along a gradient from the main water body to the drier fringe of the riparian zone. Plant species present in each plot were recorded with their estimated percentage cover using the Braun–Blanquet cover abundance scale. Hierarchical cluster analysis was used to determine vegetation communities. Indicator species analysis was used to calculate indicator values for species groups defined from the cluster analysis. Plant species and diversity were determined for each vegetation cluster. Multi-response permutation procedures (MRPP) were used to determine significance of differences between communities. The Kruskal–Wallis test was used to compare species diversity and richness between vegetation communities. Four vegetation communities were identified: Croton megalobotrys– Hyphaene petersiana, Vachellia erioloba–Diospyros lycioides, Syzygium cordatum–Phoenix reclinata and Garcinia livingstonei–Senegalia nigrescens. In this classification, the Syzygium cordatum–Phoenix reclinata and Garcinia livingstonei–Senegalia nigrescens plant communities are found in frequently flooded regions, whereas the Croton megalobotrys–Hyphaene petersiana and Vachellia erioloba–Diospyros lycioides are in occasionally flooded regions. Total number of species was highest in the Garcinia livingstonei–Senegalia nigrescens and lowest in the Syzygium cordatum–Phoenix reclinata vegetation communities. The MRPP showed that there was significant (p < 0.05) differences between vegetation communities. Species diversity and richness were significantly (p < 0.05) higher in the Garcinia livingstonei–Senegalia nigrescens vegetation community. This study provided an inventory of riparian woodland plant communities, which can be used as a vital monitoring tool of vegetation change in the Okavango Delta.  相似文献   

6.
The effects of removing aboveground vegetation on survival and growth of Hondo spruce (Picea jezoensis var. hondoensis) saplings were examined in a dense dwarf bamboo (Sasa nipponica) field inside a deer-proof fence built in a degraded sub-alpine forest on Mt Ohdaigahara, central Japan. All bamboo culms were removed within a radius of 1 m from each sapling in a plot of 0.6 ha (removal plot), whereas no culms were removed in two control plots of 0.1 ha. We measured the height, crown depth, and main shoot elongation over 1 year for all spruce saplings, culm height and cover ratios of dwarf bamboo growing around each spruce sapling, and the light levels above each sapling. Removal of dwarf bamboo regulated the culm height and bamboo coverage until the following summer such that light conditions improved. The mortality of saplings smaller than the average culm height was lower in the removal plot (0.89%) than in a control plot (5.9%). After bamboo removal, sapling height growth was reduced with increasing bamboo cover in the previous year. Complete removal of the aboveground portions of covering bamboo improved sapling survival while regulating elongation growth, possibly because of the sudden increase in light intensity. Thus, controlling the extent of dwarf bamboo removal might be necessary to facilitate the growth of spruce saplings to restore the forest.  相似文献   

7.
The aim of this inventory (acronym: INFOCARB) was to measure the organic carbon stored in the forest ecosystems of the Trento region (Provincia Autonoma di Trento, Northern Italy) in both above- and belowground pools, according to the Kyoto protocol and IPCC requirements. A total of 150 forest sampling points were selected on the entire regional area (6206 km2) with a statistical sampling approach, based on the timber volume as a proxy variable for a stratified sampling. Each sampling point was located with a GPS receiver and a 600 m2 circular plot was delimited around each point. Inside the plots, the biomass of trees, shrubs and herbaceous vegetation was measured, while litter was collected in systematically placed subplots. Topsoil (down to 30 cm depth) was sampled with the excavation method on three systematically located pits, to determine the organic carbon content, the bulk density and the volume occupied by stones and roots.  相似文献   

8.
This article compares three methods for forest resource estimation based on remote sensing features extracted from Airborne laser scanning and CIR orthophotos. The estimation was made exemplarily for the total stem volume of trees for a given area, measured in cubic metres per hectare [m3 ha−1] (as one of the most important quantitative parameters to characterise a forest stand). The following methods were compared: Regression Analysis (RA), k-NN (nearest neighbour) method and a method that utilises regional yield tables, referred to as the yield table method (YT-method). The estimation of stem volume was examined in a mixed forest in Southern Germany using 300 circular inventory plots, each with a size of 452 m2. Remote sensing features relating to vegetation height and structures were extracted and used as input variables in the different approaches. The accuracy of the estimation was analysed using scatter plots and quantified using absolute and relative root mean square errors (RMSE). The comparison was made for all plots, as well as for averaged plot values located within forest stands that have the same age class. On “plot level” the RMSE yielded 79.79 m3 ha−1 (RA), 81.93 m3 ha−1 (k-NN) and 81.78 m3 ha−1 (YT-method) and for the averaged values 35.75 m3 ha−1 (RA), 35.06 m3 ha−1 (k-NN) and 42.98 m3 ha−1 (YT-method). Advantages and disadvantages, as well as requirements, of the methods are discussed.  相似文献   

9.

The weighted k - nearest neighbour (kNN) method was used for estimating stem volume (m3 ha?1) and basal area (m2 ha?1) on a compartment level (average 19 ha) by combining satellite image data with measurements from Swedish National Forest (NFI) inventory plots. In the kNN method each estimation location (target plot) is assigned a value that is an average, which is weighted, of the attribute data from the k closest reference plots (NFI plots). The distance between target and reference plot was measured on different scales, which were transforms of spectral values and/or ancillary data. The standard error (assuming bias with no trend) of stem volume estimates in the compartments was 36% using only spectral data. This estimation accuracy improved to 17% if site index, age of the forest and mean tree height (ancillary data) were known for the compartments. Low volumes were overestimated and high volumes underestimated. This bias was reduced if ancillary data were added but was also dependent on the transform of the original scales.  相似文献   

10.
Diversity, density and species composition of naturally regenerated woody plants under Eucalyptus grandis plantation and the adjacent natural forest were investigated and compared. Twenty plots, with an area of 20 m × 20 m for each, were established in both of E. grandis plantation and adjacent natural forest, independently. In each plot, species name, abundance, diameter and height were recorded. Numbers of seedling were collected in five sub-plots (4 m2) within each major plot. A total of 46 species in the plantation, and 52 species in the natural forest, which belongs to 36 families were recorded. The diversity of species (H′) is 2.19 in the plantation and 2.74 in the natural forest. The density of understory woody plant was 3842 stems/ha in the plantation and 4122 stems/ha in the natural forest. The densities of seedlings in the natural forest and the plantation were 8101 stems/ha and 4151 stems/ha, respectively. High similarity of woody species composition was found between the natural forest and the plantation. The E. grandis plantation was found favoring the regeneration and growth of Millitia ferruginia and Coffea arabica in a much better way than other underneath woody species.  相似文献   

11.
Vegetation and birds were inventoried on the same plot before and after a severe windstorm in 1999 disturbed a mature black spruce (Picea mariana)–jack pine (Pinus banksiana) forest in northern Minnesota. Following the storm, another plot was established in an adjacent portion of the forest that was salvage-logged. Birds were inventoried on both plots through 2002. The original unsalvaged plot was prescribed-burned in 2004, but vegetation was surveyed through 2003, and through 2005 on the salvaged plot. We examined the effects of wind disturbance by comparing the pre-storm bird and vegetation communities with those developing afterwards through 2002 and 2003, respectively, and the effects of salvage logging by comparing vegetation and the bird community on the unsalvaged plot with those in the salvaged area. Wind reduced the canopy of the forest by over 90% with a temporary increase in the shrub layer, mostly resulting from tip-ups. Several plant species, including jack pine and beaked hazel (Corylus americana), appeared temporarily in the ground layer (<1 m height), but did not persist through 2003. Quaking aspen (Populus tremuloides) root sprouts were abundant in 2001, but decreased dramatically by 2003. Delayed mortality of tipped trees resulted in reduction of the shrub layer to pre-storm levels, and release of advanced regeneration black spruce and balsam fir (Abies balsamea). Bird species using the forest changed from dominance by canopy-foraging species to ground-brush foraging species, with an overall increase in bird diversity. Salvage logging resulted in significant reduction in coarse woody debris, and successful recruitment of jack pine seedlings. Quaking aspen sprouts were nearly 30 times more abundant in the salvage-logged area compared to the unsalvaged control. Ruderal species, especially red raspberry (Rubus ideaus), fringed bindweed (Polygonum cilinode), and several sedges (Carex spp.), were significantly more abundant after salvage logging. The bird community, on the other hand, was greatly diminished by salvage logging, with a reduction in diversity, density, and overall richness of species.  相似文献   

12.
通过对江苏大丰麋鹿保护区Ⅰ、Ⅱ放养区内麋鹿粪堆频率分布的系统抽样调查,发现半野生麋鹿在秋、冬季粪堆呈聚集型分布,分布型服从负二项分布、奈曼A型分布和Thomas分布,其中以负二项分布拟合程度最好。造成粪堆聚集分布的主要原因是环境因素的影响,与麋鹿的习性关系不大。在放养区主要生境类型草地和林地中,粪堆均服从负二项分布。粪堆密度林地大于草地,但粪堆聚集指数草地却高于林地。粪堆的聚集强度与鹿群在该生境中的活动类型有关,当麋鹿粪堆在单一生境内服从负二项分布时,粪堆聚集指数与鹿群对该生境的休息利用率之间存在着明显的相关关系(r=0.988,P<0.05)。粪堆频数调查显示,秋、冬季大丰麋鹿对林地的利用率高于草地。  相似文献   

13.
The aim of this study was to develop a method for segment-based forest inventory and determine whether segment-level inventories can be used in forest management planning. The study area covered 76 ha located in two different aerial photographs in eastern Finland. The study area was segmented into 220 segments with the aid of aerial photographs and the segment-level forest characteristics were assessed in the field using relascope sample plots and a field computer which displayed the aerial photographs, segment borders and surveyor's location on the screen. The segment estimates were calculated as weighted averages of k nearest neighbours (kNN) for the segments and the sample plots. The estimates were tested with a cross-validation technique. The averages and the standard deviations of the spectral values of aerial images extracted for the segments and the sample plots were used in the kNN estimation. The relative root mean square error of the mean volume was 58.1% (bias –6.4%) at the segment level and 57.9% (bias –0.9%) at the sample plot level. The segment-based approach studied here needs further research and improvement before it can be applied to forest management planning.  相似文献   

14.
Abstract

An airborne laser scanning (ALS) dominant height model was developed based on data from a national scanning survey with the aim of developing a digital terrain model (DTM) for Denmark. Data obtained in the ongoing Danish national forest inventory (NFI) were used as reference data. The data comprised a total of 2072 measurements of dominant height on NFI sample plots inventoried in 2006–2007 and their corresponding ALS data. The dominant height model included four variables derived from the ALS point cloud distribution. The variables were related to canopy height, canopy density and species composition on individual plots. The RMSE of the final model was 2.25 m and the model explained 93.9% of the variation (R 2). The model was successful in predicting dominant height across a wide range of forest tree species, stand heights, stand densities, canopy cover and growing conditions. The study demonstrated how low-density ALS data obtained in a survey not specifically aimed at forest applications may be used for obtaining biophysical forest properties such as dominant height, thereby reducing the overall forest inventory costs.  相似文献   

15.
对肯尼亚东南部泰塔(Taita)山区的3片破碎的森林进行了树种生物多样性评估,比较外来的松树、柏树、桉树人工林的物种多样性以及外来树种森林和本土森林物种多样性。研究地点为Ngangao(120 hm2)、Chawia(86 hm2)和Mbololo(185 hm2)。采用Y型设计设立32个样区,包含65个小样区。按树种记录每个小样区胸高直径5cm和5cm以上的幼树,同时也记录了各树木的更新情况(幼苗和树苗)。用 Shannon-weiner指数计算了物种的多样性和均匀度。导处的 Shannon指数被进一步转化成有效的数值,用于展示物种多样性的差别幅度。为了评估物种多样性的差别,进行单因素方差分析,为了分离均值,分别用Tukey HSD法和Duncan检测法验证偶数和奇数样品。采用Jaccard相似指数评估物种的类似性。共有58个树种的林木密度变化在每公顷10到2000棵树之间。森林类型和立地之间的物种多样性存在显著差异。本地森林的物种多样性比外来树种森林高;Chawia立地的物种多样性比Nganga和Mbololo立地高,且更新的树种数量也比其他2个立地多,包括野柠檬木(Xymalos monospora)、黑皮密花木(Rapanea melanophloeos)、和(几内亚蒲桃(Syzygium guineense),这些树种具有低干扰属性。这些发现说明,本地森林物种多样性比较高,正如热带地区所预期。Chawia立地的物种多样性高说明此地经历干扰比其他2个立地大。在Chawia地区发现有低干扰树种更新,说明有长期土壤种子库的存在。在Nganga和Mbololo地区发现的外来树种样地上的更新较差情况,可能是缺少种子库所致,因为很多人工林是造在裸地上(如Nganga地区),或者是因为某些树种固有的生理特性(相生相克)抑制了其他树种的更新。  相似文献   

16.
广西森林资源连续清查角规样地体系评价   总被引:3,自引:0,他引:3  
广西森林资源连续清查(以下简称"广西连清)"角规样地体系,是我国唯一的以点抽样理论为基础,以固定角规样地为监测载体的省(区)级森林资源连续清查体系。广西连清第7次复查,除了增设的方形样地调查以外,还对原有的角规样地进行了复查,因此本文得以用同时进行调查的方形样地调查结果作为参照对象,对角规样地体系的优点和存在的问题进行定性和定量相结合的综合分析评价。分析评价结果表明,与方形样地比较,角规样地除了具有显著的隐蔽性外,外业工作量只相当于方形样地的53%,两套体系的活立木蓄积量差异仅为3.16%,角规样地和方形样地体系总蓄积量抽样精度分别为94.47%与94.57%,均达到国家森林资源连续清查技术规定要求(≥90%)。角规样地复位率大于规定的98%,样木复位率远大于规定的95%,达97%以上,能满足林木蓄积生长量和消耗量监测的要求。角规样地体系的不足主要是由于漏测木和进测木的存在,导致森林资源的现状估计值偏低,且动态估计精度明显低于方形样地体系。  相似文献   

17.
The complex mix of economic and ecological objectives facing today's forest managers necessitates the development of growth models with a capacity for simulating a wide range of forest conditions while producing outputs useful for economic analyses. We calibrated the gap model ZELIG to simulate stand-level forest development in the Oregon Coast Range as part of a landscape-scale assessment of different forest management strategies. Our goal was to incorporate the predictive ability of an empirical model with the flexibility of a forest succession model. We emphasized the development of commercial-aged stands of Douglas-fir, the dominant tree species in the study area and primary source of timber. In addition, we judged that the ecological approach of ZELIG would be robust to the variety of other forest conditions and practices encountered in the Coast Range, including mixed-species stands, small-scale gap formation, innovative silvicultural methods, and reserve areas where forests grow unmanaged for long periods of time. We parameterized the model to distinguish forest development among two ecoregions, three forest types and two site productivity classes using three data sources: chronosequences of forest inventory data, long-term research data, and simulations from an empirical growth-and-yield model. The calibrated model was tested with independent, long-term measurements from 11 Douglas-fir plots (6 unthinned, 5 thinned), 3 spruce-hemlock plots, and 1 red alder plot. ZELIG closely approximated developmental trajectories of basal area and large trees in the Douglas-fir plots. Differences between simulated and observed conifer basal area for these plots ranged from −2.6 to 2.4 m2/ha; differences in the number of trees/ha ≥50 cm dbh ranged from −8.8 to 7.3 tph. Achieving these results required the use of a diameter-growth multiplier, suggesting some underlying constraints on tree growth such as the temperature response function. ZELIG also tended to overestimate regeneration of shade-tolerant trees and underestimate total tree density (i.e., higher rates of tree mortality). However, comparisons with the chronosequences of forest inventory data indicated that the simulated data are within the range of variability observed in the Coast Range. Further exploration and improvement of ZELIG is warranted in three key areas: (1) modeling rapid rates of conifer tree growth without the need for a diameter-growth multiplier; (2) understanding and remedying rates of tree mortality that were higher than those observed in the independent data; and (3) improving the tree regeneration module to account for competition with understory vegetation.  相似文献   

18.
Multivariate analyses were applied to forest canopy and understory data collected in 70 forest stands in the Mid-Boreal Upland Ecoregion in Saskatchewan. Random sampling of various types of forest focused on vegetation strata shown elsewhere to be of importance to woodland caribou (Rangifer tarandus caribou Gmelin). Cluster analyses revealed seven community types based on summer vegetation, and six community types when considering vegetation present during winter. Ordination by nonmetric multidimensional scaling suggested that two of the seven summer communities be combined, and that six community types be recognized in each season. Stands dominated by Populus tremuloides Michx. were all placed in one community type as were those dominated by Picea glauca (Moench) Voss. Young stands of Pinus banksiana Lamb. were placed in one community type, while the division of older stands was related to degree of canopy closure. The primary division among Picea mariana (Mill.) B.S.P. dominated stands was also based on the degree of canopy closure. Canonical correspondence analysis revealed strong relationships between the vegetation communities and data on canopy characteristics contained in the provincial forest inventory. In general, the techniques we employ provide a framework for objectively deriving vegetation communities relevant to wildlife species, and measuring their correspondence with readily available forest cover data. Specifically, we describe community types available to woodland caribou in our study area and their relationship to the provincial forest inventory.  相似文献   

19.
The emergence of Norway spruce seedlings on different types of germination sites in uneven-aged Norway spruce dominated stands four years after selection harvesting was studied. The data were collected from 20 stands in southern Finland. In each stand, ground cover was measured from a set of 64 one square metre subplots on a permanent experimental plot of 1600?m2. Correlation analysis, direct comparison of subplots with and without seedlings and mixed-effects models were used to estimate the influence of ground and tree cover on seedling occurrence. Grass cover, dwarf shrub cover, cover of certain moss species and close vicinity of trees decreased the occurrence probability and number of seedlings, while greater stand and local basal area around the subplots increased the seedling number. The cover of vegetation free surfaces, usually considered as good germination sites, was rather low. Variation in seedling emergence between plots was high. We concluded that spruce regeneration was slightly more abundant in stands with greater overall stand density and local density within a stand in postharvest conditions.  相似文献   

20.
Dry afromontane forests are among the most poorly managed and endangered ecosystems.Therefore,we assessed the composition,diversity,and conservation status of woody plant species of the Debre Libanos church forests and surrounding forest lands in Oromiya Regional National State,central Ethiopia in 62 nested circular sample plots spaced 200 m apart along two transect lines.Large circular plots 314 m~2 were used to sample trees with DBH of at least 10 cm,and subplots of 28.26 m~2 were laid in each main plot were used to assess saplings and shrubs;a small subplot of 3.14 m~2 was used to assess seedlings.In total,70 woody plant species belonging to 62 genera and 43 families were recorded.Of these,59,28 and 32 were in the church,government and private forest types,respectively.The most dominant families were Fabaceae and Verbenaceae,each represented by five species.In the forests considered,trees accounted for 61%,and shrubs with diameter at breast height(DBH) of 1-10 cm accounted for ca.33%.Among growth forms of woody species,shrubs and seedlings,followed by trees constituted much of the density of woody species in all the three ownership types of forests.The church forest had the most species(59) and highest Shannon(3.12) and Simpson(0.92) species diversity indices,and the government and private forests had a nearly similar total number of species and Shannon and Simpson species diversity indices.Most of the species with higher importance value indices(IVI) were indigenous in origin within the church forest(Juniperus procera=82),government forest(J.procera=66) and private forest(Acacia abyssinica=84).The composition,diversity,and population structure of woody species in the church forest were significantly higher than in the other forest lands.However,interventions of the government and private sectors to conserve forest systems in the areas,particularly the government-owned forest and specific species such as Olea europaea need active enrichment plantings due to their limited natural regeneration.Without improved management interventions,livelihood income diversification and ecosystem services obtained from the forest will not be sustainable.  相似文献   

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