Using habitat models to determine conservation priorities for pond-breeding amphibians in a privately-owned landscape of northern Idaho, USA

As rural landscapes experience increasing levels of residential development, the persistence of species that rely on them will depend on informed planning and management decisions. An understanding of habitat requirements is essential for setting priorities and developing landscape-level plans for the survival of these species. In many temperate rural landscapes, artificially created ponds may be the only wetlands available for aquatic reproduction by amphibians. The introduction of non-native fish into these ponds reduces survival and prohibits successful reproduction of many native pond-breeding amphibians. We surveyed 105 randomly selected wetlands in a primarily privately-owned, rural landscape in north Idaho, USA, for pond-breeding amphibian larvae in 2004 and 2005. We used an information theoretic multimodel inference and an algorithmic (random forests) approach to model habitat for each species based on local and landscape characteristics. We also used a mail survey to quantify how landowners value fish in their wetlands and their plans for future wetland development and fish stocking. Sixty-seven percent of pond owners reported that fishing in their pond was at least slightly important to them and 36% of owners indicated that they were at least 50% likely to add fish to their ponds in the next 5-10 years. Landscape change predictions for this area indicate that forests will become more open due to thinning; habitat models indicated that this is likely to be detrimental to long-toed salamanders and beneficial to Pacific treefrogs. Habitat models also indicate that Columbia spotted frog breeding sites consist of wetlands on flat ground with high solar insolation and that this species is sensitive to nearby development, indicating that as this landscape becomes further developed, this species may require habitat protection for persistence.     

Assessing quality of clearcut habitats for amphibians: Effects on abundances versus vital rates in the southern toad (Bufo terrestris)

Forest clearcutting is a form of habitat alteration that drastically alters the landscape and may contribute to declines in amphibian populations. Indeed, many studies have documented decreases in amphibian abundances and species richness in clearcuts. The development of effective conservation strategies to reduce the effects of timber harvesting has been hindered by lack of knowledge of the mechanisms underlying these changes in abundance. To better understand the potentially negative consequences of forest clearcutting, we used field enclosures in forested and clearcut habitats to examine changes in the survival and growth of juvenile southern toads (Bufo terrestris) over a two-month period. We also conducted a comparative monitoring study using drift fences and pitfall traps in forests and clearcuts to determine the effect of clearcutting on the abundance of juvenile southern toads. We found no significant effect of habitat on the number of juvenile southern toads captured in forests or clearcuts. In contrast, the average survival of toads in clearcut enclosures was significantly reduced compared to that of toads in forested enclosures (17 ± 5% versus 61 ± 3%). Toads surviving in clearcuts were also significantly smaller than those surviving in forested enclosures (27.9 ± 0.1 mm versus 30.3 ± 0.8 mm SVL). Our results highlight the difficulty in interpreting abundance patterns as a sole metric for habitat comparison. Because there is much interest in studying the effects of habitat alteration on amphibian populations, we recommend that future studies place more emphasis on determining changes in vital rates of populations following habitat alteration.     

The importance of understanding spatial population structure when evaluating the effects of silviculture on spotted salamanders (Ambystoma maculatum)

Current silvicultural practices in the northeastern United States create diverse vegetation patterns and microclimates that provide a mosaic of terrestrial habitats for amphibian species. We inferred patterns of habitat use by the spotted salamander, Ambystoma maculatum, by studying colonization of four newly created breeding pools each surrounded by four different forest treatments: a control, partial cut, clearcut with coarse woody debris (CWD) removed, and clearcut with CWD retained. Created pools were rapidly colonized, indicating that breeding salamanders readily bred in new pools they encountered. This suggests that in our study area pool-specific philopatry and site fidelity may not be high and that particular pools may not define local breeding populations. In the experimental silvicultural treatments, juvenile salamanders preferred the control forest to the clearcuts, whereas adult salamanders showed no significant preferences among the treatments. Although silvicultural practices such as clearcutting may reduce juvenile movement between pools, inter-pool movement by adults that are more tolerant of habitat change may ameliorate this effect in our study area. If juveniles are the primary life-history stage dispersing between local populations (i.e., moving between more isolated groups of pools), however, there is potential for clearcutting to reduce the connectivity between local populations.     

The impact of reed management on wildlife: A meta-analytical review of European studies

We reviewed European studies on the effect of reed management (harvesting, burning, mowing and grazing) on reedbed wildlife, and in addition, on the performance of re-growing reed (Phragmites australis). Our database consisted of 21 studies conducted on 10 plant species, 17 taxonomic groups of invertebrates and 11 bird species, and published between 1982 and 2006.We found that reed management modifies the structure of re-growing reed stands: reed stems were shorter and denser in managed sites than in unmanaged sites. However, harvesting does not have an impact on aboveground biomass. Plant species richness increased by 90% in managed stands in fresh water marshes, but not in saline water marshes.Overall, reed management had a significant negative impact on invertebrate community, but the duration of management was an important factor determining the magnitude of the effect. Short-term management (1-2 years) had no effect on invertebrates, whereas management for longer period significantly reduced invertebrate abundance. Reed harvesting and burning reduced abundance of passerine birds by about 60%. This was probably associated with food limitation as the numbers of butterflies, beetles and some spiders were reduced. Therefore, the optimal reed management regime to preserve number of birds and invertebrates in reedbeds could be a rotation of short-term management (1-2 years). However, the optimal interval between management applications should be established in future studies.     

Cost-effectiveness of silvicultural measures to increase substrate availability for red-listed wood-living organisms in Norway spruce forests

It is important that measures to maintain biodiversity are taken in a way that is cost-effective for the landowner. We analyzed the cost-effectiveness of silvicultural measures that aim at increasing the substrate availability for red-listed (species that are threatened, near threatened or where species probably are threatened but data is deficient) saproxylic (wood-inhabiting) organisms. We modelled stands of Norway spruce (Picea abies) in three regions of Sweden by using computer simulations and a database with substrate requirements of saproxylic beetles and cryptogams on the Swedish Red-List. Conclusions concerning cost-effectiveness of silvicultural measures depend on the extinction thresholds of the species they are intended to conserve; measures that generate only small amounts of coarse woody debris (CWD) may provide too little substrate to be useful for species with high extinction thresholds. In northern Sweden, forestland is relatively inexpensive, so a cost-effective strategy to increase the amount of spruce CWD was to set aside more forests as reserves. In central and southern Sweden, more emphasis should instead be given to increasing the amount of CWD in the managed forest. The regulations by the Forest Stewardship Council (FSC) could be made more cost-effective by prescribing creation of more high stumps and retention of larger amounts of naturally dying trees. Large-sized CWD, CWD from slow-growing trees, and CWD in late decay stages are substrate types that were particularly rare in managed forest in relation to unmanaged forests. Manual soil scarification and retention of living trees are measures that can increase the proportion of these underrepresented CWD types.     

Recovery of amphibian species richness and composition in a chronosequence of secondary forests,northeastern Costa Rica

In some tropical regions, following the abandonment of agriculture and pastures, secondary forests can recover plant species richness and forest structure (e.g. canopy cover, biomass); however, the importance of these secondary forests for fauna is not clear. Secondary forests can benefit fauna by providing suitable habitats, connecting forests fragments, and increasing gene flow. Previous studies of forest regeneration have showed different levels of amphibian recovery. In Puerto Rico, 1–5 years old secondary forests achieved similar amphibian species richness and composition in comparison with old-growth forests, while in Brazil secondary forests from 14 to 19 years of recovery only recovered 60% of the species of old-growth forests. We evaluated amphibian recovery in secondary forests in northeastern Costa Rica, by assessing amphibian recovery in 12 secondary forests that vary in age of recovery and in three old-growth forests using visual and acoustic surveys. Our sites varied in terms of their landscape (e.g. amount of surrounding forest) and forest characteristics (e.g. forest age, aboveground biomass, basal area, number of tree species, number of stems, leaf-litter depth), but there was no relationship between these characteristics and amphibian species richness or species composition. We found that amphibians are recovering rapidly in secondary forests in Costa Rica, and even young forests (10–16 years) had similar species richness and composition in comparison with old-growth forests. These forests are providing suitable microhabitats conditions for amphibians. In addition, this study highlights the importance of landscape characteristics. The abundance of amphibian species sources (e.g. forest patches) and connections between forests appear to be helping the species colonize these sites. Worldwide, the area of secondary forests is increasing, and our results show that these habitats are suitable for a diversity of amphibian species, suggesting that these forests can help reduce amphibian population and species decline.     

Structure of nematode communities in forest soils of southern British Columbia: relationships to nitrogen mineralization and effects of clearcut harvesting and fertilization

The effects of clearcut harvesting and fertilization of clearcuts on the structure of nematode communities were assessed at three sites in the southern interior of British Columbia. The Shannon-Weaver and Simpson indices of diversity were greater in clearcuts than in forests. The diversity of the bacterivorous and fungivorous trophic groups were not significantly different between clearcuts and forests, whereas the diversity of omnivorous and predacious nematodes was lower in clearcuts than in forests. The nematode maturity index (MI) was lower in clearcuts than in forests. Several ratios describing the prevalence of enrichment opportunists (the absolute abundance of Rhabditida, the relative abundance of Rhabditida, and the ratio of Aphelenchida/fungivorous nematodes) were greater in clearcuts than in forests. Nematode diversity tended to be lower in fertilizer treatments than in controls within clearcuts, but the effects were not consistent across sample dates. The MI was lower in fertilizer treatments than in controls. All ratios representing the relative abundance of enrichment opportunists were greater in fertilizer treatments than in controls. The MI was negatively correlated with N mineralization in data sets representing forests and fertilized and non-fertilized plots within clearcuts. None of the diversity indices were correlated with N mineralization. The absolute abundance of Rhabditida and the relative abundance of Rhabditida were both consistently positively correlated with N mineralization in the data set representing fertilized and non-fertilized plots within clearcuts, and the absolute abundance of Rhabditida was positively correlated with N mineralization in forests.     

Population recovery following differential harvesting of Allium tricoccum Ait. in the southern Appalachians

Over 100 native herbaceous forest perennials are harvested in the United States. Management of these populations for continued survival requires information on the long-term effects of varied harvesting levels on populations of forest perennials. Allium tricoccum Ait. is a species that is harvested throughout its range for its edible bulb. We examined the recovery of A. tricoccum populations over a 5-year period following experimental harvests of different intensity to predict the number of years required to return to pre-harvest levels and to establish guidelines for sustainable harvesting. Our harvest treatments included removal of 0, 25, 50, 75, and 100% of plants within experimental plots. Treatments were repeated at three sites. Population recovery was monitored for 4 years at two sites and 7 years at one site. We found a relationship between the level of harvest and the negative impacts on populations of A. tricoccum, with limited population recovery in the 4 years following harvesting. We projected recovery times as a function of harvest level using a population projection model. Deterministic projections of recovery time ranged from 148 years for a 95% harvest to 2.5 years for a 5% harvest. Incorporating stochasticity into our projections increased the uncertainty in our estimates of recovery time. For example the recovery time from a 5% harvest ranged from 1 to 89 years (95% confidence limit). Based on our results, a 10% harvest once every 10 years would, on average, be a sustainable level of harvest for A. tricoccum in southern Appalachian forests.     

Detrimental effects of peat mining on amphibian abundance and species richness in bogs

Peat bogs of eastern North America are increasingly being mined for peat, which results in the extensive draining of these systems. First, I quantified the effects of peat mining on amphibian species richness and abundance in bog remnants adjacent to mining activity and unmined bogs. I then investigated amphibian occurrence patterns in bog remnants relative to the distance to the mined edge, after accounting for microhabitat and distance to landscape elements. The response of amphibians to peat mining varied across taxa. For instance, amphibian species richness, total amphibian captures (all spp. combined), as well as those of green frogs (Rana clamitans) were greater in unmined bogs than in bog remnants. Wood frogs (Rana sylvatica) were most abundant in unmined bogs in areas far from bog ponds, as well as in unmined bogs in areas near shrub patches. After accounting for microhabitat and landscape variables, American toads (Bufo americanus) in bog remnants were most abundant close to mined edges, whereas the other species did not respond to the proximity of mined edges. Peat mining negatively impacts amphibians occurring in bog remnants. The response of amphibians to peat mining is similar to the one of birds and plants, but differs with small mammals. Maintaining a complex mosaic of bog ponds, shrub and forest patches might help mitigate peat mining effects on amphibian patterns of abundance.     

The genetic structure of coastal giant salamanders (Dicamptodon tenebrosus) in a managed forest

The salamander, Dicamptodon tenebrosus, is threatened by habitat loss and fragmentation associated with forest harvest activities. We used three microsatellite loci and 38 amplified fragment length polymorphisms (AFLPs) to quantify population structure and indirectly evaluate the impacts of forest harvesting on this species. We sampled two old growth sites, three second growth sites and three recently clearcut sites in British Columbia, Canada. Microsatellite allelic richness and the percentage of polymorphic AFLPs were positively correlated with the age of forest stands. Similarly, heterozygosity estimated from both marker types was positively correlated with stand age. Population subdivision (F_st) estimated among forested sites using microsatellite and AFLP markers was 0.033 and 0.095, respectively. Lower genetic variation and heterozygosity in recent clearcuts suggest that clearcut logging may be associated with local population declines. Our genetic findings are consistent with previous studies that report lower salamander densities in recently clearcut sites.     

A multi-taxa assessment of nestedness patterns across a multiple-use Amazonian forest landscape

Understanding how biodiversity is partitioned among alternative land-uses is an important first step for developing effective conservation plans in multiple-use landscapes. Here, we analysed nestedness patterns of species composition for nine different taxonomic groups [dung beetles, fruit-feeding butterflies, orchid bees, scavenger flies, leaf-litter amphibians, lizards, bats, birds and woody plants (trees and lianas)] in a multiple-use forestry landscape in the Brazilian Amazon containing primary, secondary and Eucalyptus plantation forests. A formal nestedness analysis was performed to investigate whether species-poor land-uses were comprised of a subset of species from more diverse forests, and the extent to which this pattern varied among taxa. At the landscape-scale the species-by-sites matrices were significantly nested for all nine taxonomic groups when both sites and species were sorted to maximally pack the species/occurrence matrix and, except for orchid bees when sorted by land-use intensity (primary forest to Eucalyptus plantation). Different patterns emerged when we conducted pairwise analyses of nestedness between the three forest types: (a) most of the taxonomic groups were nested in accordance with increased land-use intensity; (b) neither orchid bees nor leaf-litter amphibians from secondary forest made up a significant nested subset of primary forest species, although species found in Eucalyptus plantation sites were nested within secondary forest communities; and (c) lizards from Eucalyptus plantations were not a nested subset of either primary or secondary forest. Our findings emphasize the complex nature of patterns of species occupancy in tropical multiple-use forestry landscapes, and illustrate that there may be no easy solutions to questions regarding the conservation value of secondary and exotic plantation forests.     

Effects of increased salinity and an introduced predator on lowland amphibians in Southern China: Species identity matters

Approximately 30% of amphibian species are threatened due to a variety of factors affecting their habitats and physiology, yet contributions that interactions among factors make to population declines are not well-explored. Two factors, introduced mosquitofish (Gambusia affinis) and increased salinity, may coincide in lowland habitats used by breeding amphibians. Mosquitofish have been introduced worldwide and can be significant predators of amphibian larvae. Salinization of wetlands is an increasing problem globally due to (1) application of road deicing salts in temperate regions, (2) irrigation practices associated with intensive agriculture, and (3) saltwater intrusion due to sea-level rise. We investigated the effects of mosquitofish (G. affinis) and increasing salinity on five species of lowland wetland-breeding amphibians from southern China. We exposed anuran hatchlings to four salinity levels and two fish treatments and all combinations of the two factors in a series of experiments. Four of the species were susceptible to predation by mosquitofish, two were sensitive to increased salinity at concentrations >6% seawater, and one was tolerant of both increased salinity and mosquitofish. We found no interaction between the predator and increased salinity. Salinization and mosquitofish represent significant threats to lowland amphibians in this region and, coupled with the ongoing loss and degradation of lowland wetlands, portend a bleak future for lowland amphibian populations in the region.     

Magnitude of the US trade in amphibians and presence of Batrachochytrium dendrobatidis and ranavirus infection in imported North American bullfrogs (Rana catesbeiana)

Amphibians are globally threatened by anthropogenic habitat loss, the wildlife trade and emerging diseases. Previous authors have hypothesized that the spread of the amphibian disease chytridiomycosis (Batrachochytrium dendrobatidis) and amphibian ranaviruses are associated with the international trade in live amphibians. The North American bullfrog (Rana catesbeiana) is thought to be a carrier of these pathogens, is globally traded as a live commodity, and is sold live in US markets. We obtained importation data for all live amphibians, and parts thereof, into three major US ports of entry (Los Angeles, San Francisco and New York) from 2000 to 2005. Importation of live amphibians into these ports totaled almost 28 million individuals over this 6-year period. We collected samples from freshly-imported market frogs and found infection with both pathogens in all three cities and all seasons, with an overall infection prevalence of 62% (306/493) and 8.5% (50/588) for B. dendrobatidis and ranaviruses, respectively, by PCR. This study definitively identifies these two important pathogens in recently imported live market frogs and suggests that the amphibian trade can contribute to introductions of these pathogens into new regions. It provides support for the recent listing of B. dendrobatidis and ranaviral diseases by the OIE, and provides evidence for measures to be taken to eradicate these pathogens from the trade.     

Factors related to the distribution and prevalence of the fungal pathogen Batrachochytrium dendrobatidis in Rana cascadae and other amphibians in the Klamath Mountains

The fungal pathogen Batrachochytrium dendrobatidis (Bd), which causes the disease chytridiomycosis, has been associated with declines and extinctions of montane amphibians worldwide. To gain insight into factors affecting its distribution and prevalence we focus on the amphibian community of the Klamath Mountains in northwest California. The Cascades frog (Rana cascadae), one of the most common amphibians in these mountains, experienced increased mortality as a result of Bd exposure in laboratory trials and has experienced recent, dramatic declines in other parts of California. We surveyed 112 sites in the Klamaths, all of which supported R. cascadae between 1999 and 2002, for amphibians and Bd to (1) determine the distribution of Bd, (2) evaluate changes in the distribution of R. cascadae, and (3) assess associations between potential biotic and abiotic drivers and Bd infection. Bd was widely distributed in the Klamath Mountains – we detected the pathogen at 64% of sites. R. cascadae was found at 79% of sites, and was often infected with Bd. These results suggest that Bd has not caused dramatic declines in R. cascadae in the Klamaths in recent years. Subadult R. cascadae had a higher Bd prevalence than other R. cascadae life stages (subadults: 36%, adults: 25%, metamorphs: 4%, larvae: 1%), and while the probability of infection decreased over the season for adults, it did not for subadults, suggesting that subadults may be more vulnerable to chytridiomycosis than other R. cascadae life stages. Bd prevalence in R. cascadae was highest early in the season at high-elevation sites, which may indicate that populations inhabiting high elevation sites may have a greater risk of being affected by chytridiomycosis. Three other common amphibian species also tested positive for Bd: Pacific chorus frog (Pseudacris regilla), western toad (Anaxyrus boreas), and rough-skinned newt (Taricha granulosa).     

Grasslands as movement barriers for a forest-associated salamander: Migration behavior of adult and juvenile salamanders at a distinct habitat edge

The persistence of amphibian populations in fragmented landscapes requires dispersal and recolonization of habitat patches after local extinction. These processes entail individuals crossing habitat edges. Edge permeability integrates the behavior of individuals with the vegetative structure of the habitat edge and may influence the dispersal rates between habitat patches. We used drift fences, radio telemetry, and an experimental displacement to examine the movement behavior of juvenile and adult spotted salamanders (Ambystoma maculatum) at a pond located in continuous forest and a pond located on a distinct forest-grassland edge. At the pond on the habitat edge, adult salamanders migrated to and from the forested side of the pond. Resident adults with transmitters migrated to forested habitat without approaching the habitat edge. Displaced adults with transmitters halted emigration movements when they approached the habitat edge. None of the radio-tagged adults were observed more than a few meters into the grassland. Recently metamorphosed juveniles exiting the grassland side of the pond changed their direction of movement and migrated into the forested habitat. We conclude that salamanders oriented movements with respect to features in the terrestrial habitat, detected the habitat edge, and behaviorally avoided the grassland. Exploring the permeability of habitat edges will improve our understanding of dispersal within fragmented landscapes and enhance efforts to conserve regional populations of amphibians.     

Soil and detrital carbon dynamics following forest cutting in the Southern Appalachians

Summary Soil-system CO₂ efflux and detrital C pools were measured in three hardwood watersheds in the Southern Appalachians, USA. On two of the watersheds (hereafter referred to as clearcuts), forests were cut via clearcut logging methods and allowed to naturally regenerate; logging residue was removed on one clearcut and was left in place on the other. The third watershed was an uncut reference watershed. There was no statistically significant difference in CO₂ efflux between the two types of residue treatments on the clearcuts; however, CO₂ effluxes from the clearcuts were 33% less than effluxes from the uncut watershed. Lower CO₂ effluxes on the two clearcuts were associated with higher soil temperatures, smaller live-root masses, and larger forest-floor masses. No long-term (5–8 years) changes in soil C pools were apparent following forest cutting. Therefore, reductions in CO₂ efflux on the clearcuts appear to be due both to fewer live roots and to slower rates of forest-floor decomposition. Cutting of these forests followed by regeneration does not appear to result in large net C transfers to the atmosphere, as has been generally assumed.     

Effects of forest management on carabid beetles in Belgium: implications for biodiversity conservation

We sampled the carabid beetles in 22 forests managed by six different silvicultural systems, defined by treatment and tree species composition: even-aged conifer, even-aged beech, even-aged oak, uneven-aged conifer, uneven-aged beech and group mixed (beech + conifer). In each of these forests, we placed pitfall traps in young, medium-aged and mature stands (3 stages). We evaluated the effect of treatment, tree species composition, silvicultural system, stage and habitat type (silvicultural system + stage) on indicators of community conservation value and ecological structure. The species composition and the ecological structure of carabid beetles of the managed stands were then compared to that of nine unmanaged stands (without tree exploitation). In the managed forests, species richness was highest in large young stands (3-10 years old) and in forests managed by even-aged systems (with large clear-cuts), mainly due to eurytopic and opportunist carabid species with high dispersal abilities. Oak and beech, uneven-aged, and mature stands were mainly inhabited by typical forest species, and even-aged conifer stands mainly by ubiquitous species. Several typical forest species recorded in unmanaged stands were lacking from the managed forests. Large scale clear-cutting allows open-habitat species to enter the forest, which increases the species richness at a landscape level but can disfavour typical forest species by competition. Long rotations should be implemented and more areas left unmanaged in Belgium, in order to help typical forest species to re-colonise managed forests.     

Long-term effects of experimental forest harvesting on abundance and reproductive demography of terrestrial salamanders

Both observational and experimental studies have documented drastic reductions in salamanders after forest harvesting. Yet, the amount of time until salamander populations rebound and the factors limiting recovery after harvesting are unknown. We compared the effects of six oak regeneration practices to a control, representing a disturbance gradient from no treatment to silvicultural clearcut, on the relative abundance and reproductive demography of terrestrial salamanders through 13-years post-harvest. Following the experimental disturbance, relative abundance of terrestrial salamanders in treatments that opened the canopy were significantly and persistently lower than in either untreated control stands or midstory herbicide treatments. In general, this trend persisted through 9-13 years after treatment. Changes to demography of commonly captured salamanders varied by species, but Plethodon cinereus had a greater proportion of juveniles in unharvested treatments 7-13-years post-harvest, and Desmognathus ochrophaeus had a greater proportion of juveniles and a greater number of eggs/female in unharvested treatments 1-6-years post-harvest. Population modeling of P. cinereus indicated that adult survival had the greatest elasticity of the vital rates. Further, >60 years may be needed before P. cinereus reduced by the observed decline could reach pre-harvest levels of abundance. Of the treatments with canopy disturbance, the group selection harvest had the greatest abundances of salamanders 7-13-years post-harvest, but when coupled with future stand entries, the volume of wood fiber extracted, costs of harvesting, reduced sprouting of oaks, and soil disturbances, this method may not have the best balance of ecological and economic sustainability in central Appalachian hardwood forest.     

Understory herb assemblages 25 and 60 years after clearcutting of a northern hardwood forest, USA

The abundance of understory herbs in 25- and 60-year old clearcuts was compared to adjacent old secondary stands to infer how herb assemblages change in space and time following clearcutting of secondary forest. Herb densities and environmental conditions were sampled along 100 m transects crossing the clearcut/old secondary forest boundary, at three sites with 25-year old clearcuts and three sites with 60-year old clearcuts. At the 25-year sites, species densities of the 23 most frequent species were compared between clearcuts and adjacent old secondary forest to classify species into response groups. Species were classed as “insensitive” if there was little or no difference in density (seven species), “sensitive” if densities were lower in the clearcuts (six species), “enhanced” if densities were higher in clearcuts (four species), and “edge-enhanced” if densities were highest near clearcut edges (six species). Densities of two of the six sensitive species declined significantly with distance from the edge into the clearcut. Further, when regression results for all 23 species were combined, the mean slope of density vs. distance was significantly negative, indicating an overall trend to lower density with distance into the clearcuts. Most species classed as sensitive at 25 years did not show similar sensitivity at the 60-year sites; only one species had lower density in 60-year clearcuts than adjacent old secondary stands. Overall, there were substantial residual effects of clearcutting on herb assemblages within 50 m of the historical edge at 25-year sites, but not at 60-year sites. This difference may be due to different logging practices at the two historical times, as well as the difference in time for recovery since logging.     

The amphibian chytrid fungus along an altitudinal transect before the first reported declines in Costa Rica

Amphibian populations have declined and disappeared in protected and apparently undisturbed areas around the world, especially in montane areas of the tropics. The amphibian chytrid fungus, Batrachochytrium dendrobatidis has been implicated in many of these declines. In Costa Rica most declines occurred in the highlands. We examined an amphibian collection made in Braulio Carrillo National Park in 1986 for the amphibian chytrid fungus B. dendrobatidis, prior to the well documented amphibian declines in Monteverde, along an altitudinal transect from 100 to 2600 m elev. Skin from the pelvic patch of 202 specimens corresponding to 30 species was examined histologically to determine whether the disease was present in the highlands of the park before amphibian populations declined. For comparison, in 2002 we collected and examined 18 specimens of seven species of Eleutherodactylus and Craugastor from two other lowland Caribbean sites. The chytrid fungus was present in almost all altitudes in 1986, including lower areas. The pathogen was also found in both species that later declined and in species that did not do so. We detected chytrid fungus on amphibians collected at almost all altitudes in 1986, including those sampled at 280 m. B. dendrobatidis was abundant in frogs collected in the 2002 survey, and seems to be endemic in most of Costa Rica. More retrospective museum surveys are needed in order to determine whether it can be found in the area before 1986.