Frog call intensities and sound propagation in the South American temperate forest region

Sound pressure levels and the spectral structure of the advertisement calls of five species of frogs from the South American temperate austral forest were analyzed. Males of Eupsophus emiliopugini, Batrachyla antartandica and B. leptopus call from the ground in bogs, while males of Hylorina sylvatica and Pleurodema thaul call from the water surface in marshes. Calling males of the species from bogs and marshes spaced at average distances that were shorter and longer than 2 m, respectively. The properties of these habitats for sound propagation were evaluated by broadcasting pure tones, broadband noise and tape-recorded advertisement calls of the three species from bogs and of H. sylvatica. Excess attenuation and spectral degradation were higher for calls broadcast in bogs than in the marsh. The calls of B.␣antartandica and B. leptopus, with dominant frequencies of about 2 kHz, were more affected than those of E.␣emiliopugini and H. sylvatica, with dominant frequencies below 1.5 kHz. These results show the lack of an optimal relationship between properties of habitats for sound transmission and the spectral structure of these anuran calls. Body size imposes an important constraint on call spectra and propagation, which frogs counteract by distribution patterns and auditory capabilities. Received: 18 April 1997 / Accepted after revision: 15 February 1998     

Bird metacommunities in temperate South American forest: vegetation structure, area, and climate effects

Spatial structure in metacommunities and their relationships to environmental gradients have been linked to opposing theories of community assembly. In particular, while the species sorting hypothesis predicts strong environmental influences, the neutral theory, the mass effect, and the patch dynamics frameworks all predict differing degrees of spatial structure resulting from dispersal and competition limitations. Here we study the relative influence of environmental gradients and spatial structure in bird assemblages of the Chilean temperate forest. We carried out bird and vegetation surveys in South American temperate forests at 147 points located in nine different protected areas in central Chile, and collected meteorological and productivity data for these localities. Species composition dissimilarities between sites were calculated, as well as three indices of bird local diversity: observed species richness, Chao estimate of richness, and Shannon diversity. A stepwise multiple regression and partial regression analyses were used to select a small number of environmental factors that predicted bird species diversity. Although diversity indices were spatially autocorrelated, environmental factors were sufficient to account for this autocorrelation. Moreover, community dissimilarities were not significantly related to distance between sites. We then tested a multivariate hypothesis about climate, vegetation, and avian diversity interactions using a structural equation modeling (SEM) approach. The SEM showed that climate and area of fragments have important indirect effects on avian diversity, mediated through changes in vegetation structure. Given the scale of this study, the metacommunity framework provides useful insights into the mechanisms driving bird assemblages in this region. Taken together, the weak spatial structure of community composition and diversity, as well as the strong environmental effects on bird diversity, support the interpretation that species sorting has a predominant role in structuring avian assemblages in the region.     

Biogeochemistry of a temperate forest nitrogen gradient

Wide natural gradients of soil nitrogen (N) can be used to examine fundamental relationships between plant-soil-microbial N cycling and hydrologic N loss, and to test N-saturation theory as a general framework for understanding ecosystem N dynamics. We characterized plant production, N uptake and return in litterfall, soil gross and net N mineralization rates, and hydrologic N losses of nine Douglas-fir (Pseudotsuga menziesii) forests across a wide soil N gradient in the Oregon Coast Range (U.S.A.). Surface mineral soil N (0-10 cm) ranged nearly three-fold from 0.29% to 0.78% N, and in contrast to predictions of N-saturation theory, was linearly related to 10-fold variation in net N mineralization, from 8 to 82 kg N.ha(-1) x yr(-1). Net N mineralization was unrelated to soil C:N, soil texture, precipitation, and temperature differences among sites. Net nitrification was negatively related to soil pH, and accounted for <20% of net N mineralization at low-N sites, increasing to 85-100% of net N mineralization at intermediate- and high-N sites. The ratio of net: gross N mineralization and nitrification increased along the gradient, indicating progressive saturation of microbial N demands at high soil N. Aboveground N uptake by plants increased asymptotically with net N mineralization to a peak of approximately 35 kg N.ha(-1) x yr(-1). Aboveground net primary production per unit net N mineralization varied inversely with soil N, suggesting progressive saturation of plant N demands at high soil N. Hydrologic N losses were dominated by dissolved organic N at low-N sites, with increased nitrate loss causing a shift to dominance by nitrate at high-N sites, particularly where net nitrification exceeded plant N demands. With the exception of N mineralization patterns, our results broadly support the application of the N-saturation model developed from studies of anthropogenic N deposition to understand N cycling and saturation of plant and microbial sinks along natural soil N gradients. This convergence of behavior in unpolluted and polluted forest N cycles suggests that where future reductions in deposition to polluted sites do occur, symptoms of N saturation are most likely to persist where soil N content remains elevated.     

The width of riparian habitats for understory birds in an Amazonian forest

Riparian habitats are important for the maintenance of regional biodiversity. Many studies have compared bird distributions between riparian and non-riparian habitats but have not established how wide riparian habitats used by birds are, as measured by distance from the nearest stream. We investigated the distribution of understory birds along gradients of distance from streams, soil clay content, and slope in a central Amazonian forest, by mist-netting birds three times in 45 plots. We used nonmetric multidimensional scaling (NMDS) to reduce the dimensionality of species quantitative (abundance) and qualitative (presence-absence) composition to one multivariate axis. Estimates of the width of riparian habitats as indicated by understory birds depended on the community attribute considered, measuring 90 m for species quantitative composition and 140 m for species qualitative composition. Species distributions were correlated with clay content but were independent of slope, while distance from streams was positively correlated with clay content but independent of slope. Clay content affects plant species composition, which in turn, may influence bird species composition. However, distribution patterns of birds in relation to distance from streams are consistent among studies carried out in many different temperate and tropical regions, indicating an effect of distance from streams itself. Protection of riparian habitats is one of the most widely used conservation strategies, and Brazilian environmental legislation mandates the protection of a 30 m wide strip of riparian vegetation on either side of small streams. We show that the protected strip should be much wider and recommend strategies to place other forms of land protection contiguous with riparian areas so that Brazilian environmental legislation better fulfills its role of protecting biodiversity associated with riparian habitats.     

Self-organization of tropical seasonal rain forest in southwest China

How to measure development of ecosystems is both a theoretical and practical question in ecology. Species richness and biomass accumulation are familiar figures of merit, but they cannot be instant watched. Self-organization is a tacit character. However, methods to measure the degree of self-organization of ecosystem are problematic. To this end Lin et al. (2009) have devised indicators of energy capture and dissipation so that self-organization defined via maximum energy dissipation can be quantified easily. Here the method is used to analyze long-term data (2004-2006) of a tropical seasonal rain forest included in the ChinaFLUX program. Three years of average self-organization values were clearly separated by seasonal variation. Reflection and long wave radiation are the main two pathways of energy loss. For tropical seasonal rain forest studied, long wave radiation contributed most to energy loss, and was negatively correlated with energy capture ability (Rn/DR). The nocturnal difference between canopy and air temperatures had a strong negative correlation with the long wave radiation loss ratio. However, the long wave radiation loss ratio was slightly lower than the reflection loss ratio in rainy season, when values were very low. Precipitation and wind had significant impact on energy dissipation ability in the hot dry season, but the correlation coefficients between precipitation and wind with thermal response numbers (TRNs) were very low. The results indicated that the self-organization estimation system based on “maximum energy dissipation theory” is applicable for tropical forest.     

The impact of fragmentation and density regulation on forest succession in the Atlantic rain forest

The Atlantic Rain Forest, an important biodiversity hot spot, has faced severe habitat loss since the last century which has resulted in a highly fragmented landscape with a large number of small forest patches (<100 ha). For conservation planning it is essential to understand how current and future forest regeneration depends on ecological processes, fragment size and the connection to the regional seed pool. We have investigated the following questions by applying the forest growth simulation model FORMIND to the situation of the Atlantic Forest in the state of São Paulo, SE Brazil: (1) which set of parameters describing the local regeneration and level of density regulation can reproduce the biomass distribution and stem density of an old growth forest in a reserve? (2) Which additional processes apart from those describing the dynamics of an old growth forest, drive forest succession of small isolated fragments? (3) Which role does external seed input play during succession? Therefore, more than 300 tree species have been classified into nine plant functional types (PFTs), which are characterized by maximum potential height and shade tolerance. We differentiate between two seed dispersal modes: (i) local dispersal, i.e. all seedlings originated from fertile trees within the simulated area and (ii) external seed rain. Local seed dispersal has been parameterized following the pattern oriented approach, using biomass estimates of old growth forest. We have found that moderate density regulation is essential to achieve coexistence for a broad range of regeneration parameters. Considering the expected uncertainty and variability in the regeneration processes it is important that the forest dynamics are robust to variations in the regeneration parameters. Furthermore, edge effects such as increased mortality at the border and external seed rain have been necessary to reproduce the patterns for small isolated fragments. Overall, simulated biomass is much lower in the fragments compared to the continuous forest, whereas shade tolerant species are affected most strongly by fragmentation. Our simulations can supplement empirical studies by extrapolating local knowledge on edge effects of fragments to larger temporal and spatial scales. In particular our results show the importance of external seed rain and therefore highlight the importance of structural connectivity between regenerating fragments and mature forest stands.     

Responses of New Zealand forest birds to management of introduced mammals

Over the past 1000 years New Zealand has lost 40–50% of its bird species, and over half of these extinctions are attributable to predation by introduced mammals. Populations of many extant forest bird species continue to be depredated by mammals, especially rats, possums, and mustelids. The management history of New Zealand's forests over the past 50 years presents a unique opportunity because a varied program of mammalian predator control has created a replicated management experiment. We conducted a meta-analysis of population-level responses of forest birds to different levels of mammal control recorded across New Zealand. We collected data from 32 uniquely treated sites and 20 extant bird species representing a total of 247 population responses to 3 intensities of invasive mammal control (zero, low, and high). The treatments varied from eradication of invasive mammals via ground-based techniques to periodic suppression of mammals via aerially sown toxin. We modeled population-level responses of birds according to key life history attributes to determine the biological processes that influence species’ responses to management. Large endemic species, such as the Kaka (Nestor meridionalis) and New Zealand Pigeon (Hemiphaga novaeseelandiae), responded positively at the population level to mammal control in 61 of 77 cases for species ≥20 g compared with 31 positive responses from 78 cases for species <20 g. The Fantail (Rhipidura fuliginosa) and Grey Warbler (Gerygone igata), both shallow endemic species, and 4 nonendemic species (Blackbird [Turdus merula], Chaffinch [Fringilla coelebs], Dunnock [Prunella modularis], and Silvereye [Zosterops lateralis]) that arrived in New Zealand in the last 200 years tended to have slight negative or neutral responses to mammal control (59 of 77 cases). Our results suggest that large, deeply endemic forest birds, especially cavity nesters, are most at risk of further decline in the absence of mammal control and, conversely suggest that 6 species apparently tolerate the presence of invasive mammals and may be sensitive to competition from larger endemic birds.     

Identifying climate change refugia for South American biodiversity

Refugia-based conservation offers long-term effectiveness and minimize uncertainty on strategies for climate change adaptation. We used distribution modelling to identify climate change refugia for 617 terrestrial mammals and to quantify the role of protected areas (PAs) in providing refugia across South America. To do so, we compared species potential distribution across different scenarios of climate change, highlighting those regions likely to retain suitable climatic conditions by year 2090, and explored the proportion of refugia inside PAs. Moist tropical forests in high-elevation areas with complex topography concentrated the highest local diversity of species refugia, although regionally important refugia centers occurred elsewhere. Andean–Amazon forests contained climate change refugia for more than half of the continental species’ pool and for up to 87 species locally (17 × 17 km² grid cell). The highlands of the southern Atlantic Forest also included megadiverse refugia for up to 76 species per cell. Almost half of the species that may find refugia in the Atlantic Forest will do so in a single region—the Serra do Mar and Serra do Espinhaço. Most of the refugia we identified, however, were not in PAs, which may contain <6% of the total area of climate change refugia, leaving 129–237 species with no refugia inside the territorial limits of PAs of any kind. Our results reveal a dismal scenario for the level of refugia protection in some of the most biodiverse regions of the world. Nonetheless, because refugia tend to be in high-elevation, topographically complex, and remote areas, with lower anthropogenic pressure, formally protecting them may require a comparatively modest investment.     

Aboveground and belowground effects of single-tree removals in New Zealand rain forest

There has been considerable recent interest in how human-induced species loss affects community and ecosystem properties. These effects are particularly apparent when a commercially valuable species is harvested from an ecosystem, such as occurs through single-tree harvesting or selective logging of desired timber species in natural forests. In New Zealand mixed-species rain forests, single-tree harvesting of the emergent gymnosperm Dacrydium cupressinum, or rimu, has been widespread. This harvesting has been contentious in part because of possible ecological impacts of Dacrydium removal on the remainder of the forest, but many of these effects remain unexplored. We identified an area where an unintended 40-year "removal experiment" had been set up that involved selective extraction of individual Dacrydium trees. We measured aboveground and belowground variables at set distances from both individual live trees and stumps of trees harvested 40 years ago. Live trees had effects both above and below ground by affecting diversity and cover of several components of the vegetation (usually negatively), promoting soil C sequestration, enhancing ratios of soil C:P and N:P, and affecting community structure of soil microflora. These effects extended to 8 m from the tree base and were likely caused by poor-quality litter and humus produced by the trees. Measurements for the stumps revealed strong legacy effects of prior presence of trees on some properties (e.g., cover by understory herbs and ferns, soil C sequestration, soil C:P and N:P ratios), but not others (e.g., soil fungal biomass, soil N concentration). These results suggest that the legacy of prior presence of Dacrydium may remain for several decades or centuries, and certainly well over 40 years. They also demonstrate that, while large Dacrydium individuals (and their removal) may have important effects in their immediate proximity, within a forest, these effects should only be important in localized patches containing high densities of large trees. Finally, this study emphasizes that deliberate extraction of a particular tree species from a forest can exert influences both above and below ground if the removed species has a different functional role than that of the other plant species present.     

The importance of protected areas for the forest and endemic avifauna of Sulawesi (Indonesia).

Protected areas are critical for the conservation of residual tropical forest biodiversity, yet many of these are being deforested by humans both within and outside of their administrative boundaries. Therefore, it is critical to document the significance of protected areas for conserving tropical biodiversity, particularly in mega-diverse Southeast Asia. We evaluated the importance of protected areas (national parks [NP], nature reserves [NR], and wildlife reserves [WR]) in preserving avifaunal diversity, particularly the endemic and forest species, on the island of Sulawesi. This island has one of the highest numbers of endemic avifauna genera (12) globally and is also experiencing heavy deforestation. Rarefaction analyses and species estimators showed that parks and reserves consistently recorded higher number of forest, endemic, and endemic forest bird species, in addition to larger population densities, than in their surrounding human-modified areas across eight protected areas (Gunung Manembo-nembo WR, Tangkoko-Batu Angus and Dua Saudara NR, Gunung Ambang NR, Bogani Nani Wartabone NP, Gunung Tinombala NR, Gunung Sojol NR, Lore Lindu NP, and Rawa Aopa Watumohai NP). This implies that protecting natural forests must remain as one of the fundamental conservation strategies in Sulawesi. Two small reserves (Gunung Manembo-nembo WR and Tangkoko-Batu Angus and Dua Saudara NR), however, had high number of forest and endemic bird species both within and outside their boundaries, suggesting the importance of buffer areas for augmenting small reserves so as to improve their conservation value. Ordination analyses revealed the differential response of bird species to different environmental factors (e.g., native tree cover), highlighting the significance of forested habitats with dense native vegetation cover for effective conservation of forest dependent and endemic avifauna. In addition, the distinctiveness in bird species composition among protected areas highlights the importance of establishing a reserve network across major altitudinal zones so as to achieve maximum complementarity for the conservation of Sulawesi's unique avifauna.     

Tree species control rates of free-living nitrogen fixation in a tropical rain forest

Tropical rain forests represent some of the most diverse ecosystems on earth, yet mechanistic links between tree species identity and ecosystem function in these forests remains poorly understood. Here, using free-living nitrogen (N) fixation as a model, we explore the idea that interspecies variation in canopy nutrient concentrations may drive significant local-scale variation in biogeochemical processes. Biological N fixation is the largest "natural" source of newly available N to terrestrial ecosystems, and estimates suggest the highest such inputs occur in tropical ecosystems. While patterns of and controls over N fixation in these systems remain poorly known, the data we do have suggest that chemical differences among tree species canopies could affect free-living N fixation rates. In a diverse lowland rain forest in Costa Rica, we established a series of vertical, canopy-to-soil profiles for six common canopy tree species, and we measured free-living N fixation rates and multiple aspects of chemistry of live canopy leaves, senesced canopy leaves, bulk leaf litter, and soil for eight individuals of each tree species. Free-living N fixation rates varied significantly among tree species for all four components, and independent of species identity, rates of N fixation ranged by orders of magnitude along the vertical profile. Our data suggest that variations in phosphorus (P) concentration drove a significant fraction of the observed species-specific variation in free-living N fixation rates within each layer of the vertical profile. Furthermore, our data suggest significant links between canopy and forest floor nutrient concentrations; canopy P was correlated with bulk leaf litter P below individual tree crowns. Thus, canopy chemistry may affect a suite of ecosystem processes not only within the canopy itself, but at and beneath the forest floor as well.     

Leaf traits are good predictors of plant performance across 53 rain forest species

We compared the leaf traits and plant performance of 53 co-occurring tree species in a semi-evergreen tropical moist forest community. The species differed in all leaf traits analyzed: leaf life span varied 11-fold among species, specific leaf area 5-fold, mass-based nitrogen 3-fold, mass-based assimilation rate 13-fold, mass-based respiration rate 15-fold, stomatal conductance 8-fold, and photosynthetic water use efficiency 4-fold. Photosynthetic traits were strongly coordinated, and specific leaf area predicted mass-based rates of assimilation and respiration; leaf life span predicted many other leaf characteristics. Leaf traits were closely associated with growth, survival, and light requirement of the species. Leaf investment strategies varied on a continuum trading off short-term carbon gain against long-term leaf persistence that, in turn, is linked to variation in whole-plant growth and survival. Leaf traits were good predictors of plant performance, both in gaps and in the forest understory. High growth in gaps is promoted by cheap, short-lived, and physiologically active leaves. High survival in the forest understory is enhanced by the formation of long-lived well protected leaves that reduce biomass loss by herbivory, mechanical disturbance, or leaf turnover. Leaf traits underlay this growth-survival trade-off; species with short-lived, physiologically active leaves have high growth but low survival. This continuum in leaf traits, through its effect on plant performance, in turn gives rise to a continuum in species' light requirements.     

Diversity pattern and spatial scale: a study of a tropical rain forest of Malaysia

Scale is emerging as one of the critical problems in ecology because our perception of most ecological variables and processes depends upon the scale at which the variables are measured. A conclusion obtained at one scale may not be valid at another scale without sufficient knowledge of the scaling effect, which is also a source of misinterpretation for many ecological problems, such as the design of reserves in conservation biology.This paper attempts to study empirically how scaling may affect the spatial patterns of diversity (tree density, richness and Shannon diversity) that we may perceive in tropical forests, using as a test-case a 50 ha forest plot in Malaysia. The effect of scale on measurements of diversity patterns, the occurrence of rare species, the fractal dimension of diversity patterns, the spatial structure and the nearest-neighbour autocorrelation of diversity are addressed. The response of a variable to scale depends on the way it is measured and the way it is distributed in space.We conclude that, in general, the effect of scaling on measures of biological diversity is non-linear; heterogeneity increases with the size of the sampling units, and fine-scale information is lost at a broad scale. Our results should lead to a better understanding of how ecological variables and processes change over scale.     

Mechanisms of moisture stress in a mid-latitude temperate forest: Implications for feedforward and feedback controls from an irrigation experiment

While it is well established that stomata close during moisture stress, strong correlations among environmental (e.g., vapor pressure deficit, soil moisture, air temperature, radiation) and internal (e.g., leaf water potential, sap flow, root-shoot signaling) variables obscure the identification of causal mechanisms from field experiments. Models of stomatal control fitted to field data therefore suffer from ambiguous parameter identification, with multiple acceptable (i.e., nearly optimal) model structures emphasizing different moisture status indicators and different processes. In an effort to minimize these correlations and improve parameter and process identification, we conducted an irrigation experiment on red maples (Acer rubrum L.) at Harvard Forest (summers of 2005 and 2006). Control and irrigated trees experienced similar radiative and boundary layer forcings, but different soil moisture status, and thus presumably different diurnal cycles of internal leaf water potential. Measured soil moisture and atmospheric forcing were used to drive a transient tree hydraulic model that incorporated a Jarvis-type leaf conductance in a Penman–Monteith framework with a Cowan-type (resistance and capacitance) tree hydraulic representation. The leaf conductance model included dependence on both leaf matric potential, Ψ_L (so-called feedback control) and on vapor pressure deficit, D (so-called feedforward control). Model parameters were estimated by minimizing the error between predicted and measured sap flow. The whole-tree irrigation treatment had the effect of elevating measured transpiration during summer dry-downs, demonstrating the limiting effect that subsurface resistance may have on transpiration during these times of moisture stress. From the best fitted model, we infer that during dry downs, moisture stress manifests itself in an increase of soil resistance with a resulting decrease in Ψ_L, leading to both feedforward and feedback controls in the control trees, but only feedforward control for the irrigated set. Increases in the sum-of-squares error when individual model components were disabled allow us to reject the following three null hypotheses: (1) the f(D) stress is statistically insignificant (p = 0.01); (2) the f(Ψ_L) stress is statistically insignificant (p = 0.07); and (3) plant storage capacitance is independent of moisture status (p = 0.07).     

Assessing strategies to reconcile agriculture and bird conservation in the temperate grasslands of South America

Globally, agriculture is the greatest source of threat to biodiversity, through both ongoing conversion of natural habitat and intensification of existing farmland. Land sparing and land sharing have been suggested as alternative approaches to reconcile this threat with the need for land to produce food. To examine which approach holds most promise for grassland species, we examined how bird population densities changed with farm yield (production per unit area) in the Campos of Brazil and Uruguay. We obtained information on biodiversity and crop yields from 24 sites that differed in agricultural yield. Density–yield functions were fitted for 121 bird species to describe the response of population densities to increasing farm yield, measured in terms of both food energy and profit. We categorized individual species according to how their population changed across the yield gradient as being positively or negatively affected by farming and according to whether the species’ total population size was greater under land‐sparing, land‐sharing, or an intermediate strategy. Irrespective of the yield, most species were negatively affected by farming. Increasing yields reduced densities of approximately 80% of bird species. We estimated land sparing would result in larger populations than other sorts of strategies for 67% to 70% of negatively affected species, given current production levels, including three threatened species. This suggests that increasing yields in some areas while reducing grazing to low levels elsewhere may be the best option for bird conservation in these grasslands. Implementing such an approach would require conservation and production policies to be explicitly linked to support yield increases in farmed areas and concurrently guarantee that larger areas of lightly grazed natural grasslands are set aside for conservation.     

多形态多水平氮添加对温带森林土壤根系呼吸和微生物呼吸的影响

为阐明不同水平、不同形态的氮添加对土壤总呼吸、土壤微生物呼吸、根系呼吸的影响及微生物机制,本研究以温带森林土壤为研究对象,开展多形态(硝态氮(NaNO_3)、铵态氮((NH_4)_2SO_4)和混合态氮(NH_4NO_3))多水平(50 kg N·ha~(-1)·a~(-1)和150 kg N·ha~(-1)·a~(-1))的增氮控制实验.在施氮后的第7—9年,利用静态箱-气相色谱法研究土壤呼吸组分和磷脂脂肪酸方法研究微生物群落丰度和群落结构的改变.结果表明,氮添加显著提高了土壤硝态氮和铵态氮含量,而土壤pH平均降低0.85个单位.在施氮后的第7—9年,氮添加将会减弱土壤呼吸活动,高水平的氮添加效应强于低水平氮添加;就形态来说,(NH_4)_2SO_4起到促进效应,而NH_4NO_3则逐渐由促进效应转变成抑制效应,例如在2019年(施肥后第9年),高水平的(NH_4)_2SO_4施加分别提高土壤总呼吸和微生物呼吸的34.06%和37.95%,而高水平NH_4NO_3添加则分别抑制了土壤总呼吸和微生物呼吸的27.62%和31.70%.而高水平的(NH_4)_2SO_4添加对根系呼吸有促进作用,而高水平的NH_4NO_3则有抑制效应.微生物呼吸和细菌、真菌显著正相关,和真菌/细菌比值也呈正相关.总之,土壤呼吸各组分对氮添加的响应受氮素形态和水平的控制,特定森林土壤碳排放量对土壤氮基质响应具有多阶段性,微生物呼吸的降低反映了土壤有机质分解速度的降低,这有可能会进而促进土壤碳的积累,达到氮促碳汇的效果.     

Patch Occupancy and Potential Metapopulation Dynamics of Three Forest Mammals in Fragmented Afromontane Forest in South Africa

Abstract: We investigated the persistence of three medium-sized (2–9 kg), rare forest mammals in the fragmented mist-belt Podocarpus forests of the midlands of KwaZulu-Natal Province, South Africa. We recorded patch occupancy of blue duiker (   Philantomba monticola ), tree hyrax (   Dendrohyrax arboreus ), and samango monkey ( Cercopithecus mitis labiatus ) in 199 forest patches. Their rarity is ascribed to the fragmentation and destruction of their forest habitat. Incidence functions, derived from presence and absence data, were formulated as generalized linear models, and environmental effects were included in the fitted logistic models. The small and mostly solitary hyrax and duiker persisted in smaller patches than the large and social monkey. Although this result follows expectations based on relative home-range sizes of each species, the incidence probability of the samango monkey was invariant with increasing isolation, whereas a gradual decrease with increasing isolation was observed for the hyrax and duiker. Group dynamics may inhibit dispersal and increase the isolation effect in social species such as samango monkeys. A mainland-island metapopulation model adequately describes patterns of patch occupancy by the hyrax and duiker, but the monkeys' poor dispersal ability and obvious area-dependent extirpation suggest that they exist in transient, nonequilibrium (declining) metapopulations. Through identification of large forest patches for careful protection and management, the survival of all three species—especially the monkey—could be prolonged. Because no functional metapopulation may exist for the monkey, however, this is an emergency measure. For the duiker and hyrax, larger patches should form part of a network of smaller and closer patches in a natural matrix.     

地形因子对暖温带森林群落物种丰富度-地上生物量关系的影响

地形因子是森林群落物种丰富度与生产力的重要影响因素,可以修正物种丰富度-生产力两者之间的关系。为了厘清地形因子对物种丰富度-生产力关系的修正效应,以东灵山暖温带天然次生林为研究对象,基于20 hm2样地DEM地图,提取海拔、坡度、坡向、凹凸度等地形因子,用GLM模型探讨了地形因子对群落丰富度与地上生物量的影响。结果表明,群落地上生物量与物种丰富度分别受不同地形因子的影响,群落地上生物量受Ea、El2、El3、Co34个因子的显著影响（P〈0.05）,而物种丰富度则受Sl、El、El2、El34个因子的显著作用（P〈0.05）,两者受海拔相关因子的影响最大,分别解释了两者3.99%和11.09%的变异。地形因子修正了物种丰富度-地上生物量之间的单峰曲线关系,使其朝着单调与直线化趋势变化。以后在探讨森林群落物种丰富度-生产力关系时,地形因子的修正作用应该受到重视。     

Background levels of heavy metals in plants of different taxonomic groups from a montane rain forest in Sri Lanka

An undisturbed natural reserve area iocated in a tropical montane rain forest at about 1800 m altitude in Sri Lanka served as a study site to investigate and assess the natural background concentration levels of As, Cd, Co, Cu, Ni, Pb and Zn in plants representing different taxonomic groups (divisions) in the plant kingdom. The plants selected were: the lichen,Usnea barbata (old man's beard);Pogonatum sp. (a moss);Lycopodium selago (epiphytic lycopod);Polypodium lanceolatum (epiphytic fern);Bulbophyllum elliae (epiphytic orchid) andActinodaphne ambigua (dicotyledonous large tree). Degree of homogeneity with respect to Cd, Cu, Pb and Zn in homogenised materials of all samples were within acceptable limits, whereasPogonatum sp. showed the highest degree of homogeneity for Pb. In addition to confirming extremely low levels of heavy metals in all plant species, the survey also found that generally the primitive plants,Usnea andPogonatum appear to have a greater tendency to accumulate As, Cd, Co and Pb; in particular,U. barbata appears to be an efficient accumulator for those heavy metals, suggesting its potential use in environmental studies.Actinodaphne ambigua was found to have a specific accumulating ability for nickel. Surface cleaning of theA. ambigua leaves resulted in a substantial decrease in the foliar contents of Cd, Ni, Pb and Zn. Variations in heavy metal contents observed in different plant genera are discussed in terms of their habits and place of growth in the forest. It is anticipated that the background levels presented in this paper from a remote, unpolluted tropical ecosystem will provide useful reference data for comparative environmental studies.