The Landscape Ecology of Tropical Secondary Forest in Montane Costa Rica

Multinomial logistic models of land use/land cover in montane Costa Rica and landscape pattern analysis showed that relative to agriculture, secondary forest occurred closer to old-growth forest, further from roads, in forest reserves, and at higher elevations. Collinearity between explanatory variables yielded simple multivariate models; proportion of surrounding old growth predicted secondary forest most accurately. An old-growth matrix [mean patch size (MPS) 24.5 ha], located mainly within protected areas, dominated elevations greater than 2500 m. A matrix of agriculture (MPS 23.5 ha), with smaller patches (approximately 9 ha) of secondary forest and old growth, dominated elevations from 1500 to 2500 m. Combining secondary forest with old growth decreased forest patch number and increased MPS from 7.3 to 37.1 ha. I concluded that: (a) secondary forest pattern is nonrandom, so ancillary data will aid its mapping with satellite imagery. The variables elevation, agriculture distance, road distance, and population density distinguished secondary forest from old growth with 74% accuracy; (b) socioeconomic and biological forces probably interact to create these secondary forest patterns; and (c) the strong association between secondary forest and old growth supports the concept that tropical forest recovery depends on the landscape structure of remnant forest. Received 16 February 1999; accepted 20 August 1999.     

The effect of land-use on the local distribution of palm species in an Andean rain forest fragment in northwestern Ecuador

The northern Andes is extremely rich in plant species, but this diversity is threatened by extensive deforestation. This study reports on how five palm species respond to human disturbance in an area of montane forest in Ecuador. The abundance of each species was determined in 250 40 × 30m plots, established in disturbed and undisturbed forest within an area of 3 × 3km and altitudes spanning 1248–1938m. Aiphanes erinacea (H. Karst.) H. Wendl. and to a lesser degree Geonoma undata Klotzsch were negatively affected by even moderate human disturbance, while Chamaedorea linearis (Ruiz & Pav.) Mart. and C. pinnatifrons (Jacq.) Oerst. benefitted from such disturbance and Prestoea acuminata (Willd.) H.E. Moore was unaffected given time enough to replenish its population after disturbance. At the scale of the plots, species richness was maximized in undisturbed forest. Aiphanes erinacea is endemic to northern Ecuador and southern Colombia and must be considered threatened by the extensive deforestation here. If the behaviour of these palms is representative of Andean rain forest plans in general, the negative effect of moderate anthropogenic disturbance on plant biodiversity at scales of 1km2 might be negligible. Thus, biologically sustainable logging could be possible.     

Tree species richness in primary and old secondary tropical forest in Singapore

If secondary succession can accumulate species rapidly, then tropical secondary forests may have an important role to play in the conservation of biodiversity. Data on the floristic composition of forest stands in the Central Catchment Nature Reserve, Singapore, have been analysed to investigate the diversity of approximately 100-year-old tropical secondary forest. Classification using TWINSPAN indicated that three floristic communities could be recognized from 59 0.2 ha plots enumerated for trees >30 cm gbh. These were two types of secondary forest, both dominated by Rhodamnia cinerea (Myrtaceae), and dryland primary forest. The secondary forest was developed on land abandoned after use for agriculture at the end of the 19th century. The 16 primary forest plots contained a total of 340 species, more than the 281 recorded from the 43 plots of the two secondary forest types combined. The mean species number per plot in the more diverse of the two secondary forests was only about 60% of the primary forest. Thus the secondary forest, despite a century or so for colonization by species and the presence of contiguous primary forest, was still significantly less diverse than primary forest areas. It is concluded that secondary forest cannot be assumed to accrete biodiversity rapidly in the tropics, and may not be of direct value in conservation. However, other indirect roles, such as providing resources for native animals, and buffering and protecting primary forest fragments may make the protection of secondary forest worthwhile.     

热带森林树种多度和丰富度空间分布特征研究

用巴拿马50 hm2森林动态监测样地内直径≥1 cm的树种资料,分析了该样地树种多度(个体数)和丰富度(物种数)及其方差和变异系数在6个取样尺度(5 m×5 m,10 m×10 m,20 m×20 m,25 m×25 m,50 m×50 m,100 m×100 m)的变化规律.结果显示:(1)由于多度的可加性,不同取样尺度在样地内树种多度的变化表现出一致性;随取样尺度的增加,多度方差呈线性增加,而变异系数呈线性减小.(2)丰富度随取样尺度的变化较为复杂,随取样尺度的增加,丰富度方差呈非线性变化,在取样尺度为25 m×25 m时方差最大;变异系数随取样尺度的增加而呈线性减小.研究表明,大尺度的多度值可以由小尺度的多度值通过外推法估计,而丰富度却不能,在生物多样性的保护和管理中不能简单地从一个取样尺度的生物丰富度推测另一个取样尺度丰富度.     

西双版纳片断热带雨林30多年来植物种类组成及种群结构的变化

通过对西双版纳景洪曼仰广的“龙山”片断热带雨雨林30年前后植物区系组成和样方调查资料的对比研究,探讨了30年来该“龙山”片断热带雨林植物区系组成、生活型及群落生态成分和乔木树种的种群变化规律。在植物区系组成上,已确认有种子植物7科53属55种从该片断雨林中消失。在消失的这55种植物中,属于群落顶级成分的有18种,属于耐阴的林下和层间植物有30种,喜阳种类有2种,广生态幅的随遇种有5种。初步得出该龙山热带雨林随着30多年的片断化,8．8％的科,26．8％的属和22．4％的种类消失或被后来的成分替换了。在生活型及群落生态成分变化上,群落中小高位芽及一年生植物相对增加,阳性植物明显增加,阴生（耐阴）植物明显减少,亦即雨林固有成分减少,非雨林成分增加。在乔木树种的种群变化上,过去该片断雨林的优势成份,绝大多数现在仍存在,多数仍在优势种之列,少数优势种衰退了,少数变得更优势。首先消失的种类,或为先锋树种（短命）或为种群数量很少的树种。     

西双版纳热带季节雨林土壤氮含量对乔木树种多样性的影响?

大气氮沉降或人类活动导致生态系统氮输入增加,可能会提高土壤氮含量水平,促进优势种的生长和减少环境异质性,从而使物种共存的生态位减少,群落物种多样性降低。为研究土壤氮含量的增加对森林群落乔木树种多样性的影响,本研究在西双版纳热带季节雨林随机设置了14个1 ha的样方,对各样方土壤总氮( TN)含量、乔木树种丰富度以及西双版纳热带季节雨林20 ha动态监测样地中各样方乔木树种及建群种望天树( Parashorea chinensis)生物量进行了调查。结果表明：土壤氮含量与乔木树种丰富度具有显著负相关而与群落及建群种望天树生物量具有显著正相关。我们推测其机制可能是：土壤氮含量增加促进了建群种望天树等的生长及群落生物量的积累,减少树种共存的生态位,由于竞争排斥等原因而导致群落树种丰富度降低。因此,减少生态系统人为氮输入,对于保护西双版纳热带季节雨林乔木树种多样性具有重要意义。     

Cross-Scale Responses of Biodiversity to Hurricane and Anthropogenic Disturbance in a Tropical Forest

Abstract In studies of biodiversity, considerations of scale—the spatial or temporal domain to which data provide inference—are important because of the non-arithmetic manner in which species richness increases with area (and total abundance) and because fine-scale mechanisms (for example, recruitment, growth, and mortality of species) can interact with broad scale patterns (for example, habitat patch configuration) to influence dynamics in space and time. The key to understanding these dynamics is to consider patterns of environmental heterogeneity, including patterns produced by natural and anthropogenic disturbance. We studied how spatial variation in three aspects of biodiversity of terrestrial gastropods (species richness, species diversity, and nestedness) on the 16-ha Luquillo Forest Dynamics Plot (LFDP) in a tropical forest of Puerto Rico was affected by disturbance caused by Hurricanes Hugo and Georges, as well as by patterns of historic land use. Hurricane-induced changes in spatial organization of species richness differed from those for species diversity. The gamma components of species richness changed after the hurricanes and were significantly different between Hurricanes Hugo and Georges. Alpha and two beta components of species richness, one related to turnover among sites within areas of similar land use and one related to variation among areas of different land use, varied randomly over time after both hurricanes. In contrast, gamma components of species diversity decreased in indistinguishable manners after both hurricanes, whereas the rates of change in the alpha component of species diversity differed between hurricanes. Beta components of diversity related to turnover among sites declined after both hurricanes in a consistent fashion. Those related to turnover among areas with different historic land uses varied stochastically. The immediate effect of hurricanes was to reduce nestedness of gastropod assemblages. Thereafter, nestedness increased during post-hurricane secondary succession, and did so in the same way, regardless of patterns of historic land use. The rates of change in degree of nestedness during secondary succession were different after each hurricane as a result of differences in the severity and extent of the hurricane-induced damage. Our analyses quantified temporal changes in the spatial organization of biodiversity of gastropod assemblages during forest recovery from hurricane-induced damage in areas that had experienced different patterns of historic human land use, and documented the dependence of biodiversity on spatial scale. We hypothesize that cross-scale interactions, likely those between the local demographics of species at the fine scale and the landscape configuration of patches at the broad scale, play a dominant role in affecting critical transfer processes, such as dispersal, and its interrelationship with aspects of biodiversity. Cross-scale interactions have significant implications for the conservation of biodiversity, as the greatest threats to biodiversity arise from habitat modification and fragmentation associated with disturbance arising from human activities.     

Vascular Epiphytes on Isolated Pasture Trees Along a Rainfall Gradient in the Lowlands of Panama

Secondary habitats are increasing in importance in tropical countries due to ongoing destruction of pristine vegetation. In spite of the magnitude of current changes, our understanding of their effects on nontrees (e.g., nonvascular or vascular epiphytes) is still very patchy, particularly in lowland habitats. Here, we report a study with isolated pasture trees in southwest Panama. The >800 studied trees, which belonged to >100 different species, harbored almost 27,000 epiphytes of 83 species. Orchidaceae was the most species‐rich family, with almost 60 percent of all species, while Bromeliaceae were most abundant. A rainfall gradient in the study region from ca 1000 to >3000 mm explained more of the variation in species abundance and richness than host characteristics (e.g., species identity, tree size). The unexpectedly large number of epiphytes in these pastures still represents a substantial change relative to a natural setting, which is suggested by a comparison with a forest inventory under similar climatic conditions. In pastures, species richness was lower as deduced from individual‐based rarefaction curves, a larger proportion of species and individuals showed crassulacean acid metabolism, and the relationship of epiphyte abundance/species richness and tree diameter was much less steep. Even the already reduced diversity, however, may be only transient in secondary habitats—the long‐term persistence of epiphyte populations in pastures is an open question and has to be addressed by repeated monitoring to fully evaluate the significance of pasture trees for the conservation of vascular epiphytes in tropical lowlands.     

Characterization of changes in land cover and carbon storage in Northeastern China: An analysis based on Landsat TM data

We use Landsat TM time series data for the years of 1991/1992, 1995/1996 and 1999/2000 to characterize land-cover change in northeast China. With the information on land-cover change and the density of vegetation and soil carbon, we assess the potential effect of land-cover change on vegetation and soil carbon in this region. Our results show a large decrease of 2.76(104km2 in forest area and a rapid increase of 2.32(104km2 in urban area. Land-cover changes in northeast China have resulted in a potential maximum loss of 273.2 Tg C for the period of 1991-2000, with a net loss of 95.7 Tg C in vegetation and 177.5Tg C in soil. . The conversion of forests into other land-cover types could have potentially resulted in a loss of 254.6 Tg C for the study period, accounting for 68.8% of the total potential carbon loss in the northeast China. To quantify the net effect of land-cover change on carbon storage will require accounting for vegetation regrowth and soil processes. Our results also imply that forest protectionand reforestation are of critical importance to carbon sequestration in China.     

Diversity and composition of Arctiidae moth ensembles along a successional gradient in the Ecuadorian Andes

Andean montane rain forests are among the most species‐rich terrestrial habitats. Little is known about their insect communities and how these respond to anthropogenic habitat alteration. We investigated exceptionally speciose ensembles of nocturnal tiger moths (Arctiidae) at 15 anthropogenically disturbed sites, which together depict a gradient of forest recovery and six closed‐forest understorey sites in southern Ecuador. At weak light traps we sampled 9211 arctiids, representing 287 species. Arctiid abundance and diversity were highest at advanced succession sites, where secondary scrub or young forest had re‐established, followed by early succession sites, and were lowest, but still high, in mature forest understorey. The proportion of rare species showed the reverse pattern. We ordinated moth samples by non‐metric multidimensional scaling using the chord‐normalized expected species shared index (CNESS) index at various levels of the sample size parameter m. A distinct segregation of arctiid ensembles at succession sites from those in mature forest consistently emerged only at high m‐values. Segregation between ensembles of early vs. late succession stages was also clear at high m values only, and was rather weak. Rare species were responsible for much of the faunal difference along the succession gradient, whereas many common arctiid species occurred in all sites. Matrix correlation tests as well as exploration of relationships between ordination axes and environmental variables revealed the degree of habitat openness, and to a lesser extent, elevation, as best predictors of faunal dissimilarity. Faunal differences were not related to geographical distances between sampling sites. Our results suggest that many of the more common tiger moths of Neotropical montane forests have a substantial recolonization potential at the small spatial scale of our study and accordingly occur also in landscape mosaics surrounding nature reserves. These species contribute to the unexpectedly high diversity of arctiid ensembles at disturbed sites, whereas the proportion of rare species declines outside mature forest.     

The Effect of Phosphorus Availability on Decomposition Dynamics in a Seasonal Lowland Amazonian Forest

Once the weathering of parent material ceases to supply significant inputs of phosphorus (P), vegetation depends largely on the decomposition of litter and soil organic matter and the associated mineralization of organic P forms to provide an adequate supply of this essential nutrient. At the same time, the decomposition of litter is often characterized by the immobilization of nutrients, suggesting that nutrient availability is a limiting factor for this process. Immobilization temporally decouples nutrient mineralization from decomposition and may play an important role in nutrient retention in low-nutrient ecosystems. In this study, we used a common substrate to study the effects of native soil P availability as well as artificially elevated P availability on litter decomposition rates in a lowland Amazonian rain forest on highly weathered soils. Although both available and total soil P pools varied almost three fold across treatments, there was no significant difference in decomposition rates among treatments. Decomposition was rapid in all treatments, with approximately 50% of the mass lost over the 11-month study period. Carbon (C) and nitrogen (N) remaining and C:N ratios were the most effective predictors of amount of mass remaining at each time point in all treatments. Fertilized treatments showed significant amounts of P immobilization (P < 0.001). By the final collection point, the remaining litter contained a quantity equivalent to two-thirds of the initial P and N, even though only half of the original mass remained. In these soils, immobilization of nutrients in the microbial biomass, late in the decomposition process, effectively prevents the loss of essential nutrients through leaching or occlusion in the mineral soil.     

Genetic Diversity of a Tropical Tree Species,Shorea leprosula Miq. (Dipterocarpaceae), in Malaysia: Implications for Conservation of Genetic Resources and Tree Improvement1

Genetic diversity and population genetic structure of Shorea leprosula was investigated using seven natural populations distributed throughout Peninsular Malaysia and one natural population from Borneo. The mean population and species level genetic diversity were exceptionally high (H_e= 0.369 ± 0.025 and 0.406 ± 0.070, respectively). Heterozygosity varied among populations, ranging from 0.326 to 0.400, with the highest values found in the populations from central Peninsular Malaysia. Correlations among ecological factors (longitude, latitude, and annual rainfall) were not significant (P > 0.05), indicating that these ecological variables were not responsible for the observed genetic differences among populations. The Bangi adult population exhibited a higher level of observed heterozygosity but lower fixation indices in comparison to its seedling population. All other seedling populations also showed positive fixation indices (f), indicating a general excess of homozygotes. This also may suggest selection against homozygotes between the seedling and adult stages. A low level of population differentiation was detected (G_ST= 0.117 with the Lambir population and GST= 0.085 without the Lambir population). Furthermore, gene flow (N_m) between populations was not significantly correlated with geographical distances for the populations within Peninsular Malaysia. Cluster analysis also did not reflect geographical proximity and gave little insight into the genetic relatedness of the populations. This may indicate that the populations sampled are part of a continuous population with fragmentation having occurred in the recent past.     

Patterns of Clonal Diversity in Dicranopteris linearis on Mauna Loa,Hawaii1

The clonal mat-forming fern, Dicranopteris linearis (N. L. Burm.) Underw., dominates vast areas of rainforests on the windward slopes of Mauna Loa Volcano on the island of Hawai'i. Because clone size has important ecological and evolutionary consequences in such a dominant species, we used isozyme analysis to investigate clone size and other aspects of genetic diversity and reproduction over a broad range of environmental conditions on primary successional sites (pahoehoe lava substrates). Isozyme analysis provided a measure of the upper limit of clonal size in this interdigitating clonal species. Each 0.5-ha primary successional site on Mauna Loa was comprised of a minimum of two to four clones. Genetic diversity in Dicranopteris was low; of 32 putative loci investigated, only 4 were polymorphic, with 2 or 3 alleles/locus. Over the 17 study locations on Mauna Loa and Kilauea Volcanoes, we identified nine multilocus genotypes based on unique combinations of allozymes. Seven of the nine genotypes were heterozygous for at least one locus, evidence of an intergametophytic mating system. Highly dispersible spores, coupled with intergametophytic mating should promote higher genetic diversity. We propose that the following factors contributed to low genetic diversity: founder effects; extreme isolation from mainland gene pools; high potential for mating among different gametophytes produced from the same sporophyte; relatively low numbers of safe sites for gametophyte establishment over space and time; and long-term reliance on vegetative growth. Leaf phenotypes were associated with genotype, but also with environmental conditions. Enough variability within a genotype existed to support the current treatment of Hawaiian Dicranopteris as one species. Vegetative growth was the primary means by which Dicranopteris covered the landscape. Nevertheless, spore production, gametophyte establishment, and sexual reproduction were absolutely essential for colonization of the few favorable microsites available on pahoehoe lava substrates of Mauna Loa following lava eruptions, dieback, and similar landscape-level disturbances.     

生长光强对4种热带雨林树苗光合机构的影响

于雾凉季研究了西双版纳热带雨林 4种植物幼苗对光抑制及光破坏的防御。发现不同光强下生长的玉蕊和滇南红厚壳日间光抑制均较团花树和滇南插柚紫重 ,在中光强下还发生了长期光抑制。中光强下生长的团花树和滇南插柚紫叶绿素含量降低 ,光合能力升高 ,同时增加热耗散量 ,维持光能平衡 ,避免了光破坏的发生。中光强下玉蕊和滇南红厚壳减少光能吸收、提高热耗散的同时 ,发生了光系统II光化学量子产量长期下调。中光强下生长的 4种植物叶片的类胡罗卜素的绝对含量并不高 ,但单位叶绿素的类胡罗卜素含量显著升高 ,相对保护作用增强。先锋树种团花树类胡罗卜素含量低于另 3种植物 ,这与其较低的热耗散速率相一致 ,光合能力的提高对其光破坏的防御有重要的作用