Down by the riverside: Riparian edge effects on three monkey species in a fragmented Costa Rican forest

Rivers represent natural edges in forests, serving as transition zones between landscapes. Natural edge effects are important to study to understand how intrinsic habitat variations affect wildlife as well as the impact of human-induced forest fragmentation. We examined the influence of riparian and anthropogenic edge on mantled howler, white-faced capuchin, Central American spider monkeys, and vegetation structure at La Suerte Biological Research Station (abbreviated as LSBRS), Costa Rica. We predicted lower monkey encounter rate, tree species richness, and median dbh at both edge types compared to interior and that monkeys would show species-specific responses to edge based on size and diet. We expected large, folivorous–frugivorous howler monkeys and small, generalist capuchins would be found at increased density in forest edge, while large, frugivorous spider monkeys would be found at decreased density in forest edge. We conducted population and vegetation surveys along interior, riparian, and anthropogenic edge transects at LSBRS and used GLMM to compare vegetation and monkey encounter rate. Tree species richness and median dbh were higher in forest interior than anthropogenic edge zones. Although spider monkey encounter rate did not vary between forest edges and interior, howler monkeys were encountered at highest density in riparian edge, while capuchins were encountered at highest density in anthropogenic edge. Our results indicate that diverse forest edges have varying effects on biota. Vegetation was negatively affected by forest edges, while monkey species showed species-specific edge preferences. Our findings suggest that riparian zones should be prioritized for conservation in Neotropical forests.     

The influence of anthropogenic edge effects on primate populations and their habitat in a fragmented rainforest in Costa Rica

When a forest is fragmented, this increases the amount of forest edge relative to the interior. Edge effects can lead to loss of animal and plant species and decreased plant biomass near forest edges. We examined the influence of an anthropogenic forest edge comprising cattle pasture, coconut plantations, and human settlement on the mantled howler (Alouatta palliata), white-faced capuchin (Cebus capucinus), Central American spider monkey (Ateles geoffroyi), and plant populations at La Suerte Biological Research Station (LSBRS), Costa Rica. We predicted that there would be lower monkey encounter rate, mean tree species richness, and diameter at breast height (DBH) in forest edge versus interior, and that monkeys would show species-specific responses to edge based on diet, body size, and canopy height preferences. Specifically, we predicted that howler monkeys would show positive or neutral edge effects due to their flexible folivorous diet, large body size, and preference for high canopy, capuchins would show positive edge effects due to their diverse diet, small body size, and preference for low to middle canopy, and spider monkeys would show negative edge effects due their reliance on ripe fruit, large body size, and preference for high upper canopy. We conducted population and vegetation surveys along edge and interior transects at LSBRS. Contrary to predictions, total monkey encounter rate did not vary between the forest edge and forest interior. Furthermore, all three species showed neutral edge effects with no significant differences in encounter rate between forest edge and interior. Interior transects had significantly higher mean tree species richness than edge transects, and interior trees had greater DBH than edge trees, although this difference was not significant. These results suggest that forest edges negatively impact plant populations at La Suerte but that the monkeys are able to withstand these differences in vegetation.     

Edge influence on herbaceous plant species,diversity and soil properties in sparse oak forest fragments in Iran

伊朗稀疏橡木林片段对草本植物物种多样性和土壤特性的边缘影响 温带和热带森林中的森林边缘现象已经得到了很好的研究,但在稀疏的橡木林片段中的相关研究却较为缺乏。本文研究了稀疏橡木林片段对植物物种多样性和土壤特性的边缘影响。本研究沿着伊朗克尔曼沙赫省3个小型(<10 ha)和3个大型(>10 ha)橡木林片段的3个横断面收集了从边缘到内部的相 关数据,测量了0(森林边缘)、25、50、100和150 m处的草本植物(高度<0.5 m)和土壤特性。使用香农指数量化了物种多样性,使用稀疏标准化方法比较了两个大小不同片段中的物种丰富度,并应用了非度量多维测度排序研究了物种组成的变化。通过随机化测试估算了边缘影响的距离,并利用Tukey HSD事后检验法的广义线性混合模型评估了距边缘距离和片段大小对多样性和土壤特性的影响。研究结果表明,大小片段边缘具有较高的物种丰富度、多样性和均匀度,而大片段边缘的土壤氮和有机碳含量则较内部更低(边缘50 m范围内的变化最大)。大小片段的物种组成、土壤有机碳和氮总量都存在显 著差异。本研究关于这些稀疏森林对草本植物和土壤特性产生显著边缘影响的发现,对于边缘研究,尤其是边缘和草本植物的相关研究具有重大贡献。     

Primate population densities in three nutrient-poor amazonian terra firme forests of south-eastern Colombia

We censused primate populations at three non-hunted 'terra firme' forests of south-eastern Colombian Amazonia. The aggregate biomass densities of diurnal primates at all sites were amongst the lowest recorded for any non-hunted forest in western Amazonia and elsewhere in the Neotropics. Densities of red howler monkeys were low, as is typical in Amazonian terra firme forests far removed from white-water rivers, and densities of woolly monkeys were 1.5-3.5 times lower than those estimated for this species in central-western Brazilian Amazonia. Densities of small to mid-sized primates except for brown capuchins (Cebus apella) and white-faced capuchins (Cebus albifrons) were similar to those of other oligotrophic Amazonian forest sites. Our results are in agreement with other studies showing that terra firme forests of lowland Amazonia typically sustain a low biomass density of primates and other mid-sized to large vertebrates. Large reserves are therefore required to assure the viability of primate populations in oligotrophic systems. Given the escalating negative impacts of human habitat disturbance and hunting in Colombian Amazonia, we urge that a baseline sampling protocol to quantify the abundance and distribution of the harvest-sensitive vertebrate fauna be established within protected areas and the large indigenous reserves so that conservation efforts can be defined and implemented.     

Breeding Birds in Riparian and Upland Dry Forests of the Cascade Range

ABSTRACT We quantified breeding bird abundance, diversity, and indicator species in riparian and upland dry forests along 6 third- to fourth-order streams on the east slope of the Cascade Range, Washington, USA. Upland dry forest on southerly aspects was dominated by open ponderosa pine (Pinus ponderosa) and dry Douglas-fir (Pseudotsuga menziesii) plant associations. Upland mesic forest on northerly aspects was dominated by closed-canopy Douglas-fir or dry grand fir (Abies grandis) plant associations. Riparian overstory vegetation was dominated by black cottonwood (Populus trichocarpa) plant associations with a prominent hardwood tree and shrub component. We quantified bird assemblages, diversity, and abundance from parallel point transects on riparian and adjacent dry and mesic upslope forests. We detected 80 bird species from >12,000 point-transect observations during 1998–1999. Eighteen species accounted for 75% of all detections. Species richness and evenness were similar in all 3 forest types, with approximately 35 species and high evenness (0.85) in each forest type. Bird species assemblages differed among dry, mesic, and riparian forest types, with the greatest differences between riparian and both dry and mesic upland forests. Riparian forest had the greatest number (9) of strong characteristic, or indictor, species among the 3 forest types. Upland mesic forest was characterized by 7 indicator species. Upland dry forest had 4 indicator species. Our results indicate that current standards and guidelines for riparian buffers zones would allow for avian refuge and corridor functions along these streams. Forest managers could use our indicator species to predict and monitor shifts in upland forest species composition from thinning and prescribed burning practices that are used to reduce fuels in uplands and to reduce continuity of fire effects between riparian and upland zones.     

Distribution of carabid beetles (Coleoptera: Carabidae) across a forest-grassland ecotone in southwestern China

This paper studied the occurrence of carabid beetles (Coleoptera: Carabidae) in the forest edge, the adjacent forest interior, and the surrounding grassland in southwestern China. Beetles were collected with pitfall traps along five replicated transects. Forest species rarely penetrated into the grassland from the forest interior, and the grassland specialists were not found in the forest interior. The forest edge hosted additional species from the adjacent grassland that increased its overall species richness. Nearly all forest species (23 of 24 species) and grassland species (13 of 15 species) can be found in the forest edge. Carabids of the forest edge were more similar to those of the forest interior than to those of the grassland by ordination and cluster analysis. Based on the specificity and fidelity, carabids can be distinguished into five species groups: habitat generalists, grassland-associated species, forest generalists, forest specialists, and edge-associated species. Multiple linear regression analysis showed that canopy cover and/or shrub cover were the most important factors in determining the richness, abundance, and diversity of carabids. The forest edge may serve as a transition zone for dispersal and re-colonization of carabid beetles from adjacent habitats and therefore is important for natural conservation.     

Lemur responses to edge effects in the Vohibola III classified forest, Madagascar

Forest edges are dynamic zones characterized by the penetration (to varying depths and intensities) of conditions from the surrounding environment (matrix) into the forest interior. Although edge effects influence many tropical organisms, they have not been studied directly in primates. Edge effects are particularly relevant to lemurs because of the highly fragmented forest landscapes found in Madagascar. In this study, data are presented regarding how the densities of six lemur species (Avahi laniger, Cheirogaleus major, Eulemur rubriventer, Hapalemur griseus griseus, Microcebus rufus, and Propithecus diadema edwardsi) varied between six 500-m interior transects and six 500-m edge transects in the Vohibola III Classified Forest in SE Madagascar. Diurnal (n = 433) and nocturnal (n = 128) lemur surveys were conducted during June-October 2003 and May-November 2004. A. laniger, E. rubriventer, and H. g. griseus exhibited a neutral edge response (no differences in densities between habitats). M. rufus and P. d. edwardsi had a positive edge response (higher densities in edge habitats), which may be related to edge-related variations in food abundance and quality. Positive edge responses by M. rufus and P. d. edwardsi may ultimately be detrimental due to edge-related anthropogenic factors (e.g., hunting by local people). The negative edge response exhibited by C. major (lower densities in edge habitats) may result from heightened ambient temperatures that inhibit torpor in edge habitats.     

Ground nest predation might not be higher along edges of Neotropical forest remnants surrounded by pastures: evidence from the Brazilian Atlantic forest

Several studies indicate that nest predation is higher along edges than in habitat interiors mainly due generalist predators arising from or proliferating in the surrounding matrix. Recent reviews demonstrate however that this is far from universal, in part because studies are strongly biased in temperate regions. Far fewer are known from the Neotropics and just a handful of studies have been carried out in the biologically-rich but severely fragmented Atlantic Forest of Brazil. Here we tested the influence of edge proximity on ground nest predation in a large (21,787 ha) Atlantic forest reserve. The experiment was carried out using chicken and quail eggs in 12 transects with 500 m in length, half of which parallel to internal edges (dirt roads) and half parallel to external edges (forest/pasture). Nest predation was significantly higher in wet season (42.7%), when no difference was found between edge and forest interior, than in dry season (16.5%), when nest predation was higher in forest interior (400 m). Within seasons, the difference between internal and external edges and the association between edge distance and edge type were not significant. Results suggest that ground nest predation in large protected areas of the Atlantic forest is mainly caused by forest dwellers rather than by species inhabiting the surrounding grassland-dominated landscape, mirroring recent findings in other tropical areas.     

Primates Decline Rapidly in Unprotected Forests: Evidence from a Monitoring Program with Data Constraints

Growing threats to primates in tropical forests make robust and long-term population abundance assessments increasingly important for conservation. Concomitantly, monitoring becomes particularly relevant in countries with primate habitat. Yet monitoring schemes in these countries often suffer from logistic constraints and/or poor rigor in data collection, and a lack of consideration of sources of bias in analysis. To address the need for feasible monitoring schemes and flexible analytical tools for robust trend estimates, we analyzed data collected by local technicians on abundance of three species of arboreal monkey in the Udzungwa Mountains of Tanzania (two Colobus species and one Cercopithecus), an area of international importance for primate endemism and conservation. We counted primate social groups along eight line transects in two forest blocks in the area, one protected and one unprotected, over a span of 11 years. We applied a recently proposed open metapopulation model to estimate abundance trends while controlling for confounding effects of observer, site, and season. Primate populations were stable in the protected forest, while the colobines, including the endemic Udzungwa red colobus, declined severely in the unprotected forest. Targeted hunting pressure at this second site is the most plausible explanation for the trend observed. The unexplained variability in detection probability among transects was greater than the variability due to observers, indicating consistency in data collection among observers. There were no significant differences in both primate abundance and detectability between wet and dry seasons, supporting the choice of sampling during the dry season only based on minimizing practical constraints. Results show that simple monitoring routines implemented by trained local technicians can effectively detect changes in primate populations in tropical countries. The hierarchical Bayesian model formulation adopted provides a flexible tool to determine temporal trends with full account for any imbalance in the data set and for imperfect detection.     

Environment heterogeneity and seasonal effects in ground-dwelling ant (Hymenoptera: Formicidae) assemblages in the Parque Estadual do Rio Doce, MG, Brazil

This work aimed to explore the response of ant species assemblage to contrasting types of forests in a semideciduous stationary rainforest, in the Parque Estadual do Rio Doce, South Eastern Brazil. We compared antropomorphic borders of this park and natural ecotones, such as lake margins continuous with forests, as well as preserved forests far from ecotones. We investigated whether ground-dwelling ant species richness, abundance and composition would change according to forest types and ecotones. We expected greater species richness in interior tall forest, compared with low forest or ecotone habitats. In addition, we tested the effect of climate seasonality on ant assemblages found in each studied vegetation type. Each forest type was surveyed based on a minimum transect sampling unit of 150 m long summing up 30 pit-falls per unit. Two sampling events, one in dry season (September of 2001) and another in the rainy season (January of 2002) were performed. For both seasons, tall forest presented greater total number of ant species, however lower mean ant species and abundance per trap than other forest types, thus corroborating the prediction that ecotones might present high alpha diversity. Mean species richness and abundance did not differ between interior low forest and lake edge, or between these habitats and reserve border. In general, species composition were not clearly defined by forest types. Results here found suggest that species loss or community dominance by generalist species, eventually due to deforestation, is probably a much greater problem than previously thought. However, to understand patterns of insect species diversity and distribution in tropical ecosystem should be taken in account much more comprehensive, spatially explicit sampling designs.     

Changes in Nothofagus pumilio forest biodiversity during the forest management cycle. 2. Birds

Human activities, such as logging, modify the forest structure and the microenvironments of the original Nothofagus forests. The aims of this work were to evaluate changes in the diversity and relative abundance of birds and to analyze their trophic relationships with insect and plant communities along the Nothofagus pumilio forest management cycle. Data was collected using a point sampling method along transects located in different forest structures during the summer season, by direct (sight) and indirect (hearing) recognition following sunrise. Bird diversity and abundance significantly varied along the forest management cycle. Seven new species appeared after harvest, but the total number did not vary by the end of the forest management cycle, and there was no significant loss of species. Bird abundance was directly related to the insect abundance and plant biomass. Relationship between groups (lower plants, monocotyledons and dicotyledonous) is also discussed. Major studies in bird ecology are necessary to develop new silvicultural alternatives based on the more sensitive species to harvest. Forest management strategies and mitigation alternatives must be incorporated into forest planning in order to maintain the original structure of bird communities and the equilibrium with other forest species.     

Linear edge effects on liana and tree communities in two tropical forest ecosystems in Ghana

The study determined linear edge effects on liana and tree community assemblages in moist semi-deciduous (Afram Headwaters Forest Reserve) and upland evergreen (Tano Offin Forest Reserve) forests in Ghana. Fifteen plots (20 × 20 m²) were randomly set up at each habitat in the forests: edge habitat (0–40 m) and interior habitat (≥500 m). Lianas (diameter at 1.30 m from rooting base ≥1 cm) and trees (diameter at breast height, dbh ≥5 cm) were identified and enumerated in the plots. In the forest ecosystems, liana and tree species composition differed significantly between the two habitats. Liana and tree diversity did not differ significantly between edge and interior habitats. Nevertheless, edge habitat in moist semi-deciduous forest supported significantly higher liana abundance and basal area than its interior habitat, whereas edge habitat in upland evergreen forest harboured significantly lower liana basal area than its corresponding interior habitat. Edge habitat in moist semi-deciduous and upland evergreen forests had significantly lower tree abundance and basal area, respectively, than interior habitat. The results suggest that overall, linear edge effects on liana and tree assemblages were more pronounced in moist semi-deciduous forest than upland evergreen forest. Lianas exhibited dominance over trees in edge habitat within moist semi-deciduous forest, implying that they can have serious implications on tree diversity and ecosystem functioning in the forest. As our study is the first of its kind in the tropics with respect to edge type and forest ecosystems studied, our findings can contribute towards edge theory development.     

Density Estimation of the Endangered Udzungwa Red Colobus (Procolobus gordonorum) and Other Arboreal Primates in the Udzungwa Mountains Using Systematic Distance Sampling

Estimates of population density and abundance are essential for the assessment of nonhuman primate conservation status, especially in view of increasing threats. We undertook the most extensive systematic primate survey yet of the Udzungwa Mountains of Tanzania, an outstanding region for primate endemism and conservation in Africa. We used distance sampling to survey three arboreal monkey species, including the endangered and endemic Udzungwa red colobus (Procolobus gordonorum). Overall, we encountered 306 primate clusters over 287 km walked along 162 line transects. We found the lowest cluster densities for both red colobus and Angolan colobus (Colobus angolensis; 0.8 clusters/km²) in the least protected forest (Uzungwa Scarp Forest Reserve, US), while we found the highest densities (3.2 and 2.6 clusters/km² for red colobus; 3.2 and 2.7 clusters/km²for Angolan colobus) in two large and protected forests in the national park. Unexpectedly, Magombera, a small forest surrounded by plantations, had the highest densities of red colobus (5.0 clusters/km²), most likely a saturation effect due to the rapid shrinking of the forest. In contrast, Sykes’ monkey (Cercopithecus mitis monoides/moloneyi) had more similar densities across forests (3.1–6.6 clusters/km²), including US, suggesting greater resilience to disturbance in this species. For the endemic red colobus monkey, we estimated an abundance of 45–50,000 individuals across all forests, representing ca. 80% of the global population. Though this is a relatively high abundance, the increasing threats in some of the Udzungwa forests are of continued concern for the long-term survival of red colobus and other primates in the area.     

Contribution of peeling host for epiphyte abundance in two tropical dry forests in the “El Cielo Biosphere Reserve”, Mexico

Host traits partly determine the abundance and species richness of epiphytes in tropical forests. It has been proposed that older trees with rough bark and evergreens often house more individuals and more epiphytic species than those with thin, smooth, and peeling bark, which harbor few epiphytes. We hypothesize (i) that epiphytes are more abundant and species-rich in the more shaded forest, which is related to bark roughness, and (ii) that epiphytes are distributed in the middle of the host, where microenvironmental conditions are more favorable to survival. We evaluated abundance, species richness, and vertical distribution of epiphytes in two tropical dry forests, according to the deciduousness and basal area of the trees. Moreover, we selected the most abundant epiphytes to test whether their distribution is related to a specific bark type and examine their vertical distribution in two dry forests. We distinguished a high abundance and species richness of epiphytes in the deciduous forest, although basal area and host species richness were higher in the semi-deciduous forest. In both forests, we found a positive relationship between epiphyte abundance and basal area. Higher abundance of epiphytes was related to the predominance of Tillandsia schiedeana, a drought-adapted species, in both forests. Unexpectedly, epiphytes abundantly colonized Bursera simaruba, a host with peeling bark and a very branched crown, where small individuals of T. schiedeana colonized abundantly toward the top of the crown. Our results show the importance of the tropical dry forest, particularly, B. simaruba, in maintaining epiphyte diversity in terms of T. schiedeana colonization.     

Long-term dynamics of wild primate populations across forests with contrasting protection in Tanzania

Anthropogenic activities driving tropical forests' loss imperil global biodiversity and provision of ecosystem services. In this context, systematic monitoring programs evaluating wildlife trends are essential. Non-human primates are relevant conservation targets since they represent vital components of tropical forests by serving as pollinators and seed dispersers. Here, we present primate group counts data collected over 19 years in a primate hotspot in Tanzania. We analyzed data with a hierarchical dynamic model accounting for imperfect detection that estimates local group abundance and temporal rates of change, to assess whether habitat protection explained trends of the arboreal and diurnal Peters' Angola colobus (Colobus angolensis palliatus), Udzungwa red colobus (Piliocolobus gordonorum), and Tanzania Sykes' monkey (Cercopithecus mitis subsp. moloneyi). We targeted populations occurring in two forest blocks with contrasting protection regimes, with one block impacted by targeted poaching of the two Colobus species. We found that these latter species were much less abundant in the more human impacted forest, underwent a rapid decline, and subsequently remained at low abundance and without signs of recovery once this forest was granted greater protection. Instead, Sykes' abundance did not differ between forests, and improved protection was associated with a slight increase in abundance. Age class composition for social groups of both Colobus species differed between forests, indicating altered births and survivorship rates in the impacted forest. Results suggest that targeted hunting can prevent recovery for several years and even after increased habitat protection. Our approach appears valuable to monitor population dynamics over the long term, highlighting species-specific variations in both vulnerability to anthropogenic disturbance and recovery patterns in primate populations.     

Ant (Hymenoptera: Formicidae) diversity and community composition along sharp urban forest edges

The effects of forest edge on ant species richness and community composition were examined within an urbanized area of northeast Ohio. The ground-dwelling ant fauna was inventoried in three deciduous forest fragments that have resulted from human disturbance. We surveyed ants via leaf-litter extraction along 150 m transects positioned perpendicular to the forest edge. We collected 4,670 individuals from 14 genera and 29 species. Samples closest to the forest edge contained more species and accumulated species at a higher rate than did samples located in the forest interior. Our rarefied and expected richness estimates revealed a decline of species richness from edge to forest interior. The higher ant richness at the forest edge was due mostly to the presence of species characteristic of the neighboring open habitats. Although most of the typical forest ant species were represented equally at the edge and at the forest interior, a few responded to the presence of edges with changes in their relative abundance and frequency of occurrence. Forest edges had a higher proportion of opportunistic species and a lower proportion of cryptic ants, whereas interior locations exhibited a more even distribution among ant functional groups. In addition, we documented a community composition shift between the edge and the forest interior. Consistent with previous findings, we suggest that the edge effects are most pronounced within 25 m of the forest edge, which may have implications for the overall conservation of forest-dwelling fauna.     

Primate Group Size and Abundance in the Caatinga Dry Forest, Northeastern Brazil

The Caatinga dry forest poses a series of ecological challenges for mammals in general and primates in particular. The erratic rainfall pattern impacts on plant diversity and phenological patterns; from year to year there is marked variability in fruit production and failure to fruit is common. The harshness apparently accounts for the impoverished mammalian fauna. However, data on primate abundance, distribution, and possible environmental effects on primate density are lacking in this type of dry forest. I censused the primate community in 3 habitats of the Serra da Capivara National Park, Piaui, NE Brazil, over a total distance of 318 km. Overall, the abundance of primates in the Caatinga dry forest is very low as a consequence of low abundance of food resources both in space and time. Alouatta caraya (predominantly folivorous) occurs at extremely low density, and during the dry season are apparently confined to canyon areas, where trees retain their leaves. Callithrix jacchus has morphological feeding specializations for gum-eating, and gum is an important resource during food bottleneck periods. Nonetheless, Callithrix jacchus occurs at comparatively low densities. Group sizes for howlers and marmosets in the Caatinga are significantly smaller than in other forest types. Contrarily, Cebus apella libidinosus had an average group size within the range reported for Amazonian and Atlantic forests. Researchers consider the generalized diet of capuchins as the explanation for their similar abundance in different habitats, indicating relative independence from ecological constraints. However, I suggest that capuchin foraging style and cognitive abilities are important factors accounting for their unreduced group size and density even under extreme conditions.     

Dung beetle assemblages in primary forest and disturbed habitats in a tropical dry forest landscape in western Mexico

Dung beetles (Scarabaeinae) are conspicuous components in most terrestrial ecosystems, performing important ecological functions and services. Being sensitive to several types of disturbance, they have been successfully used as indicators of habitat change. Dung beetle communities in tropical rainforests have been well studied, but considerably less information is available for tropical dry forests. In this study I sampled dung beetles in two undisturbed habitats, deciduous forest and semideciduous forest, and two disturbed habitats, secondary forest and open area habitat, in the Chamela-Cuixmala region of western Mexico. Dung beetle species with high indicator value for each habitat were identified. Beetle abundance, observed species richness and estimated species richness were similar in the three forest habitats, but significantly lower in the open area habitat. A more detailed analysis of species-specific abundances in the three forest habitats revealed some differences. Transects of one of the undisturbed habitats, the deciduous forest, were more similar to the non-adjacent transects of disturbed secondary forest, than to the adjacent undisturbed semideciduous forest transects. Unlike studies in other tropical sites that have found a decrease in equitability in Scarabaeinae assemblages between undisturbed forest and disturbed habitat (particularly open habitats), in the Chamela-Cuixmala region all four habitats showed similar low equitability in community structure, with two or three very dominant species.     

Diversity,composition, and structure of tropical dry forests in Central America

Tropical dry forests have been reduced to less than 0.1% of their original expanse on the Pacific side of Central America and are considered by some to be the most endangered ecosystem in the lowland tropics. Plots 1000 m² were established in seven tropical dry forests in Costa Rica and Nicaragua in order to compare levels of species richness to other Neotropical dry forest sites and to identify environmental variables associated with species richness and abundance. A total of 204 species and 1484 individuals 2.5 cm were encountered. Santa Rosa National Park was the richest site with the highest family (33), genera (69), and species (75) diversity of all sites. Species richness and forest structure were significantly different between sites. Fabaceae was the dominant tree and shrub family at most sites, but no species was repeatably dominant based on number of stems in all fragments of tropical dry forest. Central American dry forests had similar species richness when compared to other Neotropical forests. There was no correlation between forest cover within reserves, or precipitation and plant species richness. There was a significant correlation between anthropogenic disturbance (intensity and frequency of fire, wood collection, grazing) and total species richness, tree and shrub species richness, and liana abundance. These results suggest controlling levels on anthropogenic disturbance within reserves should be a high priority for resource managers in Central America. Further research in forest fragments which examine individual and a combination of disturbance agents would help clarify the importance of anthropogenic disturbance on species richness and abundance.