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991.
Joseph J. O'Brien Steven F. Oberbauer David B. Clark Deborah A. Clark 《Biotropica》2008,40(2):151-159
The relationship between phenology and tree stem diameter increment is largely unexplored in tropical species, especially in wet tropical forests. To explore links between these phenomena, we measured stem diameter increment and phenology of ten canopy tree species from a range of functional types in the Atlantic lowlands of Costa Rica to test for seasonal and interannual patterns. We measured stem diameter increment using band dendrometers and visually assessed leaf and reproductive phenology monthly from 1997 to 2000. We categorized the species into groups based on patterns of leaf exchange and reproduction. Species were either deciduous with synchronous or asynchronous leaf drop, or evergreen with continuous or seasonal leaf flushing. Flowering occurred supra-annually, annually, or continuously. Of the ten species studied, four species, Cecropia insignis, Dipteryx panamensis, Lecythis ampla, and Simarouba amara , had consistent seasonal stem diameter increment patterns in both years. Dipteryx panamensis and L. ampla were deciduous with synchronized leaf drop . Cecropia insignis was evergreen and produced new leaves continuously. Simarouba amara , also evergreen, exchanged leaves over a brief period once a year. We tested whether stem diameter increment was correlated to phenology using logistic regression. Leaflessness significantly explained patterns in stem diameter increment but reproductive phenology did not. Deciduous trees were 2.6–9.3 times more likely to grow less than average the month following leaffall than in months when trees had full crowns. 相似文献
992.
Philipp Wagner Jörn Köhler reas Schmitz Wolfgang Böhme 《Journal of Biogeography》2008,35(8):1349-1361
Aim The Kakamega Forest, western Kenya, has been biogeographically assigned to both lowland and montane forest biomes, or has even been considered to be unique. Most frequently it has been linked with the Guineo‐Congolian rain forest block. The present paper aims to test six alternative hypotheses of the zoogeographical relationships between this forest remnant and other African forests using reptiles as a model group. Reptiles are relatively slow dispersers, compared with flying organisms (Aves and Odonata) on which former hypotheses have been based, and may thus result in a more conservative biogeographical analysis. Location Kakamega Forest, Kenya, Sub‐Saharan Africa. Methods The reptile diversity of Kakamega Forest was evaluated by field surveys and data from literature resources. Faunal comparisons of Kakamega Forest with 16 other African forests were conducted by the use of the ‘coefficient of biogeographic resemblance’ using the reptile communities as zoogeographic indicators. Parsimony Analysis of Endemism and Neighbour Joining Analysis of Endemism were used to generate relationship trees based on an occurrence matrix with paup *. Results The analysis clearly supports the hypothesis that the Kakamega Forest is the easternmost fragment of the Guineo‐Congolian rain forest belt, and thus more closely related to the forests of that Central–West African complex than to any forest further east, such as the Kenyan coastal forests. Many Kenyan reptile species occur exclusively in the Kakamega Forest and its associated forest fragments. Main conclusions The Kakamega Forest is the only remnant of the Guineo‐Congolian rain forest in the general area. We assume that the low degree of resemblance identified for the Guineo‐Congolian forest and the East African coastal forest reflect the long history of isolation of the two forest types from each other. Kenyan coastal forests may have been historically connected through forest ‘bridges’ of the southern highlands with the Congo forest belt, allowing reptile species to migrate between them. The probability of a second ‘bridge’ located in the region of southern Tanzanian inselbergs is discussed. Although not particularly rich in reptile species, the area should be considered of high national priority for conservation measures. 相似文献
993.
Aim The aims of this paper are to reconstruct the vegetation and fire history over the past 2000 years in a well‐preserved rain‐forest area, to understand interactions between climate, fire, and vegetation, and to predict how rain forest responds to global warming and increased intensity of human activity. Location Xishuangbanna, south‐west China, 21–22° N, 101–102° E. Methods Phytolith (plant opal silica bodies) morphotypes, assemblages, and indices were used to reconstruct palaeovegetation and palaeoclimate changes in detail. Micro‐charcoal particles found in phytolith slides, together with burnt phytoliths and highly weathered bulliform cells, were employed to reconstruct a record of past fire occurrence. A survey of field sediments, lithology, and 14C dating were also employed. Results Phytoliths were divided into 11 groups and classified into 33 well‐described morphotypes according to their shape under light microscopy and their presumed anatomical origins and ecological significance. The phytolith assemblages were divided into six significant zones that reveal a complete history of vegetation changes corresponding to climate variation and fire occurrence. Phytolith assemblages and indices show that the palaeoclimate in the study area is characterized by the alternation of warm–wet and cool–dry conditions. Phytolith and charcoal records reveal that 12 fire episodes occurred. Comparison of burnt phytoliths with an aridity index (Iph) shows that fire episodes have a strong relationship with drought events. Main conclusions Our results indicate that fire occurrence in the tropical rain forest of Xishuangbanna is predominantly under the control of natural climate variability (drought events). Nearly every fire episode is coupled with a climatic event and has triggered vegetation composition changes marked by a pronounced expansion of grasses. This indicates that drought interacts with fire to exert a strong influence on the ecological dynamics of the rain forest. However, the impact of human activity in recent centuries is also significant. Our results are important for understanding the interactions between climate, fire, and vegetation, and for predicting how rain forest responds to global warming and increased human activity. 相似文献
994.
Historical climate modelling predicts patterns of current biodiversity in the Brazilian Atlantic forest 总被引:3,自引:0,他引:3
Aim We aim to propose validated, spatially explicit hypotheses for the late Quaternary distribution of the Brazilian Atlantic forest, and thereby provide a framework for integrating analyses of species and genetic diversity in the region. Location The Atlantic forest, stretching along the Brazilian coast. Methods We model the spatial range of the forest under three climatic scenarios (current climate, 6000 and 21,000 years ago) with BIOCLIM and MAXENT. Historically stable areas or refugia are identified as the set of grid cells for which forest presence is inferred in all models and time projections. To validate inferred refugia, we test whether our models are matched by the current distribution of the forest and by fossil pollen data. We then investigate whether the location of inferred forest refugia is consistent with current patterns of species endemism and existing phylogeographical data. Results Forest models agree with pollen records and predict a large area of historical forest stability in the central corridor (Bahia), as well as a smaller refuge (Pernambuco) along the Brazilian coast, matching current centres of endemism in multiple taxa and mtDNA diversity patterns in a subset of the species examined. Less historical stability is predicted in coastal areas south of the Doce river, which agrees with most phylogeographical studies in that region. Yet some widely distributed taxa show high endemism in the southern Atlantic forest. This may be due to limitations of the modelling approach, differences in ecology and dispersal capability, historical processes not contemplated by the current study or inadequacy of the available test data sets. Main conclusions Palaeoclimatic models predict the presence of historical forest refugia in the Atlantic rain forest and suggest spatial variation in persistence of forests through the Pleistocene, predicting patterns of biodiversity in several local taxa. The results point to the need for further studies to document genetic and species endemism in the relatively poorly known and highly impacted areas of Atlantic rain forests of north‐eastern Brazil. 相似文献
995.
Gentile Francesco Ficetola Dario Furlani Giorgio Colombo Fiorenza De Bernardi 《Biodiversity and Conservation》2008,17(9):2185-2195
Secondary forests constitute a growing portion of forested areas worldwide. They might have a substantial role for the conservation
of biodiversity in tropical areas, but there is little information on their potential to support forest species and the recovery
of faunal communities. We studied two forest frogs (Eleutherodactylus diastema and E. fitzingeri) in an area of Costa Rica composed of a mosaic of primary forest, young secondary forest and pasture, and we compared the
density of calling males in areas with different forest alteration. Autoregressive models were used to compensate for potentially
undesired effects of spatial autocorrelation and pseudoreplication. Both species were most abundant in riparian, primary forest.
However, E. fitzingeri was also abundant in riparian secondary forests, and its density far from the river was similar in primary and secondary
forest, suggesting that river proximity can influence the recovery of secondary forest for amphibians. Conversely, the density
of E. diastema was similar in secondary forest and pasture, stressing interspecific differences for recovery rate. These frogs have a keystone
role in nutrient cycling and food webs, and their prompt recovery might represent an important step for the functional recovery
of forests. Nevertheless, the strong interspecific differences stress the complexity of these processes. 相似文献
996.
Lucia Acebey Amira Apaza Rosy de Michel Stephan Beck Valérie Jullian Grace Ruiz Alberto Gimenez Séverine Chevalley Michel Sauvain 《Biodiversity and Conservation》2008,17(8):1853-1859
Developing countries with a rich biodiversity want to control the use of this natural patrimony, especially in the research
of natural compounds of pharmaceutical interest. Here we present the organization of six permanent plots in a mountain tropical
forest on the east side of the Andean Cordillera in Bolivia, and their role in the discovery of plants with antiplasmodial
or antileishmanial activities. Permanent plots are widely used in ecological survey, but rarely in bioprospecting. This set-up
allows Bolivian authorities to control the bioprospecting, and facilitates further chemical studies on the bioactive plants.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Lucia Acebey and Amira Apaza have contributed equally to this work. 相似文献
997.
The effect of harvesting biofuel and woodland restoration on biodiversity is debated. To evaluate the effects of partial cutting
on more organism groups, we used pairwise experimental and undisturbed control stands in a large landscape. On average 26%
of the basal area including 50–95% of the understorey was harvested at each of 15 oak-rich forest sites. Our earlier results
of partial cutting suggested a positive short-term effect for vascular plants and beetles and no or minor negative effects
for fungi. Here we analyse the response of mycetophilids (Diptera: Sciaroidea excl. Sciaridae), a neglected but species-rich
insect group that was strongly disfavoured by clear-cutting in previous studies. Increased deadwood (slash) caused increase
in the number of individuals of mycetophilids associated with wood or wood fungi. The rarefaction species numbers of mycetophilids
declined after the treatment, but the absolute number of species was not affected. Our results indicate that a 25% harvest
can be compatible with conservation of vascular plants, fungi, saproxylic and herbivorous beetles and mycetophilids in temperate
hardwood stands of the type studied. However, more studies are needed to determine what level(s) of stand thinning can be
tolerated by different taxa in landscapes with small fragmented conservation stands. 相似文献
998.
The impact of human disturbance on colonisation dynamics of vascular epiphytes is poorly known. We studied abundance, diversity
and floristic composition of epiphyte seedling establishing on isolated and adjacent forest trees in a tropical montane landscape.
All vascular epiphytes were removed from plots on the trunk bases of Piptocoma discolor. Newly established epiphyte seedlings were recorded after 2 years, and their survival after another year. Seedling density,
total richness at family and genus level, and the number of families and genera per plot were significantly reduced on isolated
trees relative to forest trees. Seedling assemblages on trunks of forest trees were dominated by hygrophytic understorey ferns,
those on isolated trees by xerotolerant canopy taxa. Colonisation probability on isolated trees was significantly higher for
plots closer to forest but not for plots with greater canopy or bryophyte cover. Seedling mortality on isolated trees was
significantly higher for mesophytic than for xerotolerant taxa. Our results show that altered recruitment can explain the
long-term impoverishment of post-juvenile epiphyte assemblages on isolated remnant trees. We attribute these changes to a
combination of dispersal constraints and the harsher microclimate documented by measurements of temperature and humidity.
Although isolated trees in anthropogenic landscapes are considered key structures for the maintenance of forest biodiversity
in many aspects, our results show that their value for the conservation of epiphytes can be limited. We suggest that abiotic
seedling requirements will increasingly constitute a bottleneck for the persistence of vascular epiphytes in the face of ongoing
habitat alteration and atmospheric warming. 相似文献
999.
1000.
油松水源保护林人工诱导更新与定向恢复机理 总被引:3,自引:0,他引:3
以油松水源保护林为对象,进行人工诱导更新与定向恢复机理研究。结果表明,在郁闭林分内油松更新苗密度平均为5 375株.hm-2,更新苗年龄为1~2年,而在人工Gap“效应岛”样地内,更新苗密度平均为17 062.5株.hm-2,其中1~2年、3~4年、5~6年生更新苗分别占73.44%,13.97%和12.59%;生长季光照强度在0、1.5和2.0 m三个不同高度梯度上,在Gap内部的平均值分别为289.0×100、542.0×100和589.0×100 lux,在对照林分内分别为139.0×100、146.0×100和246.0×100lux;从夏季观测到的空气温度平均值日变化分析,在白天Gap内的温度高于郁闭林分内部,温差可差2~3℃,在夜间Gap内的温度低于郁闭林分内,温差可差0.5~1℃;在白天6:00~11:00,人工Gap“效应岛”内空气湿度明显低于郁闭林分内,在其它时间段大致相当;对于同一层次土壤而言,Gap内的土壤温度明显高于郁闭林分内且变化幅度大,在0、10和20 cm三个梯度上Gap与郁闭林分相比土壤温度最大差值分别可达10、5和2℃;0~10、10~20和20~30 cm三个层次平均土壤含水量在Gap内分别为16.9%1、5.1%和12.3%,在郁闭林分内分别为14.6%、12.5%和9.9%。总体上比较二者的光照强度、空气温度、空气湿度、土壤温度、土壤水分等有显著差异,因此人工Gap“效应岛”的创建是诱导其内部微环境因子变化的基础,也是油松水源保护林定向恢复更新的机理之所在。 相似文献