Subtropical Montane Forest Research Articles

High precipitation causes large fluxes of dissolved organic carbon and nitrogen in a subtropical montane Chamaecyparis forest in Taiwan

Fluxes of dissolved organic carbon (DOC) and nitrogen (DON) may play an important role for losses of C and N from the soils of forest ecosystems, especially under conditions of high precipitation. We studied DOC and DON fluxes and concentrations in relation to precipitation intensity in a subtropical montane Chamaecyparisobtusa var. formosana forest in Taiwan. Our objective was, to quantify DOC and DON fluxes and to understand the role of high precipitation for DOC and DON export in this ecosystem. From 2005 to 2008 we sampled bulk precipitation, throughfall, forest floor percolates and seepage (60 cm) and analyzed DOC, DON and mineral N concentrations. Average DOC fluxes in the soil were extremely high (962 and 478 kg C ha−1 year−1 in forest floor percolates and seepage, respectively) while DON fluxes were similar to other (sub)tropical ecosystems (16 and 8 kg N ha−1 year−1, respectively). Total N fluxes in the soil were dominated by DON. Dissolved organic C and N concentrations in forest floor percolates were independent of the water flux. No dilution effect was visible. Instead, the pool size of potentially soluble DOC and DON was variable as indicated by different DOC and DON concentrations in forest floor percolates at similar precipitation amounts. Therefore, we hypothesized, that these pools are not likely to be depleted in the long term. The relationship between water fluxes in bulk precipitation and DOC and DON fluxes in forest floor percolates was positive (DOC r = 0.908, DON r = 0.842, respectively, Spearman rank correlation). We concluded, that precipitation is an important driver for DOC and DON losses from this subtropical montane forest and that these DOC losses play an important role in the soil C cycle of this ecosystem. Moreover, we found that the linear relationship between bulk precipitation and DOC and DON fluxes in forest floor percolates of temperate ecosystems does not hold when incorporating additional data on these fluxes from (subtropical) ecosystems.

Geochemical characterization of placic horizons in subtropical montane forest soils, northeastern Taiwan

Well‐developed placic horizons have been found in subalpine forest soils with large clay contents in Taiwan. We investigated their formation processes in five profiles in a subalpine ecosystem of northeastern Taiwan, using scanning electron microscopy (SEM), energy‐dispersive spectrometry (EDS), electron probe microanalysis (EPMA), differential X‐ray diffraction (DXRD) and chemical extractions. The placic horizons, ranging from 3‐ to 17‐mm thick, always occurred above argillic horizons with abrupt changes in pH and texture between the two horizons. When fully developed, the placic horizons were clearly differentiated between upper and lower sub‐horizons. EDS and chemical extractions revealed that the cementing materials in both were predominantly inorganic Fe oxides. However, contents of aluminosilicates and organically complexed Fe and Al were greater in the lower than in the upper placic sub‐horizon. Results of EPMA indicated that interstitial fine materials in the upper placic sub‐horizon were composed mainly of Fe oxides, whereas Fe oxides were codominant with illuvial clay in the lower sub‐horizon. These analyses identified the migration of Fe and clay as major formation processes in both sub‐horizons. We hypothesize that there is a pedogenic sequence that starts with clay illuviation, followed by podzolization. The resultant textural and permeability differentiation reinforces the tendency to profile episaturation that is already inherent from the heavy rainfall and clayey surface soils. Topsoil Fe is therefore reduced and mobilized, and then illuviated with clay and organically complexed Fe/Al to initiate the lower placic sub‐horizon. The poor permeability of this layer reinforces the moisture conditions in the surface soils, and the further reduction, illuviation and deposition of inorganic Fe to form the upper placic sub‐horizon.

Soil phosphorus and disturbance influence liana communities in a subtropical montane forest

Questions: What are the effects of soil, topography, treefall gaps, tree species composition, and tree density on liana species composition and total liana abundance? Location: A 6-ha permanent plot in a subtropical montane forest in northwest Argentina. Methods: Multiple regressions were used to quantify associations of liana species composition and total liana abundance with edaphic, disturbance and tree community variables. Gradients in liana and tree species composition were quantified using principal components analysis (PCA). Results: Liana species composition was correlated most strongly with soil phosphorus concentration (R2=0.55). Total liana aanased with phosphorus and the density of recent treefall gaps (R2=0.60). Conclusions: In our study area, liana composition and abundance are most strongly correlated with features of the physical environment, rather than host tree characteristics. Our results support the hypothesis that recent increases in liana abundance in mature tropical forests may be related to increased rates of gap formation.

Neither Biased Sex Ratio nor Spatial Segregation of the Sexes in the Subtropical Dioecious Tree Eurycorymbus cavaleriei (Sapindaceae)

Knowledge of sex ratio and spatial distribution of males and females of dioecious species is both of evolutionary interest and of crucial importance for biological conservation. Eurycorymbus cavaleriei, the only species in the genus Eurycorymbus (Sapindaceae), is a dioecious tree endemic to subtropical montane forest in South China. Sex ratios were investigated in 15 natural populations for the two defined ages (young and old). Spatial distribution of males and females was further studied in six large populations occurring in different habitats (fragmented and continuous). The study revealed a slight trend of male-biased sex ratio in both ages of E. cavaleriei, but sex ratio of most populations (13 out of 15) did not display statistically significant deviation from equality. All of the four significantly male-biased populations in the young class shifted to equality or even female-biased. The Ripley's K analysis of the distribution of males with respect to females suggested that individuals of the opposite sexes were more randomly distributed rather than spatially structured. These results suggest that the male-biased sex ratio in E. cavaleriei may result from the precocity of males and habitat heterogeneity. The sex ratio and the sex spatial distribution pattern are unlikely to constitute a serious threat to the survival of the species.

Nest Selection by Cavity‐nesting Birds in Subtropical Montane Forests of the Andes: Implications for Sustainable Forest Management

ABSTRACTDevelopment of sustainable forestry has been hampered in tropical countries by a scarcity of research on the ecological effects of logging. We focused on cavity‐nesting birds, a group known to be sensitive to logging. Cavities used for nesting were not a random subset of all available suitable cavities. Birds selected cavities that were relatively high above the ground, had smaller entrances, and were excavated by woodpeckers. The use of tree species was also not random: Calycophyllum multiflorum, Blepharocalyx gigantea, and Podocarpus parlatorei were disproportionately important. Cavity nests were also more likely to be found in areas with trees with high mean diameter at breast height. This study emphasizes the need to maintain some unlogged forest patches within logging areas and retain certain species of trees. This study has implications for forest management in Argentina, where a new law mandates the sustainable use of forest resources and where many landowners are interested in forest certification.

Ancestry and divergence of subtropical montane forest isolates: molecular biogeography of the genus Abies (Pinaceae) in southern México and Guatemala

The genus Abies has a complex history in southern México and Guatemala. In this region, four closely related species, Abies flinckii, A. guatemalensis, A. hickelii, and A. religiosa, are distributed in fragmented and isolated montane populations. Range-wide genetic variation was investigated across species using cytoplasmic DNA markers with contrasted inheritance. Variation at two maternally inherited mitochondrial DNA markers was low. All species shared two of the nine mitotypes detected, while the remaining seven mitochondrial DNA types were restricted to a few isolated stands. Mitochondrial genetic differentiation across taxa was high (G(ST) = 0.933), it was not related to the taxonomic identity (amova; P > 0.05) of the populations, and it was not phylogeographically structured (G(ST) approximately N(ST)). In contrast, variation at three paternally inherited chloroplast DNA microsatellites was high. Chloroplast genetic differentiation was lower (G(ST) = 0.402; R(ST) = 0.547) than for mitochondrial DNA, but it was significantly related to taxonomy (amova; P < 0.001), and exhibited a significant phylogeographical structure (G(ST) < R(ST)). Different analyses of population structure indicated that A. flinckii was the most divergent taxon, while the remaining three species formed a relatively homogeneous group. However, a small number of the populations of these three taxa, all located at the limits of their respective ranges or in the Transverse Volcanic Belt, diverged from this main cluster. These trends suggest that the Mesoamerican Abies share a recent common ancestor and that their divergence and speciation is mainly driven by genetic drift and isolation during the warm interglacial periods.

Landscape context and microenvironment influences on liana communities within treefall gaps

AbstractQuestions:How do gap aspect, openness, age and gap density in the surroundings affect diversity and composition of lianas within treefall gaps? Are the variation patterns in liana communities within treefall gaps associated with their climbing mechanisms?Location:Subtropical montane forests in northwestern Argentina.Methods:We used ordination analyses (NMDS) and multiple regressions to describe liana communities (species and climbing groups, stems ≥ 1 cm) in 35 gaps located in a 6‐ha plot and to assess relationships with aspect, canopy and subcanopy openness, age and density of recent (three to eight years old) and old (&gt; 8 years old) gaps.Results:Treefall gaps segregated in the ordination diagrams based on their liana species and climbing mechanisms composition: gaps surrounded by a higher density of recent gaps showed higher densities of lianas species using tendrils, spines/hooks and voluble stems. Liana density and richness (independent of stem density) were also positively associated with the density of recent gaps in the surroundings, and negatively associated to gap age. The number of liana species corrected per area was negatively associated to gap aspect and subcanopy openness, and absolute number of liana species was positively associated to gap canopy openness.Conclusions:This study integrates the analysis of different factors influencing liana communities within treefall gaps, and shows that spatial context of gap density (a variable largely neglected in previous studies) is particularly important on lianas composition and diversity, probably by increasing propagule input and the availability of small trellises for support.

Tree life histories in a montane subtropical forest: species differ independently by shade‐tolerance, turnover rate and substrate preference

Summary 1. To investigate life-history differentiation and an objective functional classification of tree species we analysed the demography of 29 species in subtropical montane forests in north-western Argentina. 2. We computed 13 growth, demographic, abundance and distribution variables based on: (i) two 5-year re-measurements of stems ≥ 10 cm diameter at breast height (d.b.h.) in 8 ha of old growth forest and 4 ha of secondary forest; (ii) assessments of tree crown illumination; and (iii) sapling counts under shade and on landslides. 3. We assessed the potential confounding effects of stem size and crown illumination on absolute stem diameter growth rate for the 24 most abundant species. As diameter increased, one species showed significant increases in growth rate and five showed significant reductions. Seventeen species grew significantly faster with increased exposure to light and we controlled for this confounding effect in the computation of diameter growth rates for subsequent analyses. 4. A principal component analysis resulted in three meaningful and interpretable axes of demographic variation across species. The first axis (interpreted as shade tolerance) indicates that trees of species with inherently high growth rates tend to have wellexposed crowns at 10‐30 cm d.b.h., have high density of trees in secondary forest and are less tolerant of shade. 5. The second axis (turnover) shows that in old-growth forest short-lived species, with high mortality rates, size-class distributions with a steep negative slope and low dominance, persist due to high rates of recruitment (to ≥ 10 cm d.b.h.). 6. The third axis indicates that species that colonize landslides have lower tree recruitment rates and greater growth variability in secondary forest, reflecting spatio/ temporal differences in species’ recruitment linked to differences in their substrate requirements for regeneration. 7. Maximum height and diameter are correlated with the first and second axes, indicating that higher rates of both growth and survival permit some species to attain large size. 8. All three demographic axes depict separate trade-offs that confer competitive advantage to each ‘demographic type’ under contrasting ecological conditions (of light availability, disturbance frequency and disturbance intensity), thus underpinning species’ coexistence in dynamic forest landscapes.

Tropical montane forest ecotones: climate gradients, natural disturbance, and vegetation zonation in the Cordillera Central, Dominican Republic

AbstractAim We examined relationships between climate–disturbance gradients and patterns of vegetation zonation and ecotones on a subtropical mountain range.Location The study was conducted on the windward slopes of the Cordillera Central, Dominican Republic, where cloud forest appears to shift in a narrow ecotone to monodominant forest of Pinus occidentalis.Methods Climate, disturbance and vegetation data were collected over the elevation range 1100–3100 m and in 50 paired plots along the ecotone. Aerial photographs were georeferenced to a high‐resolution digital elevation model in order to enable the analysis of landscape‐scale patterns of the ecotone.Results A Shipley–Keddy test detected discrete compositional ecotones at 2200 and 2500 m; the distributions of tree species at lower elevations were continuous. The elevation of the ecotone determined with aerial photographs was fairly consistent, namely ± 164 m (SD) over its 124‐km length, but it exhibited significant landscape variation, occurring at a lower elevation in a partially leeward, western zone. The ecotone also occurred significantly lower on ridges than it did in drainage gullies. Ecotone forest structure and composition differed markedly between paired plots. In pine paired plots, the canopy height was 1.7 times higher and the basal area of non‐pine species was 6 times lower than in the cloud forest directly below. Fire evidence was ubiquitous in the pine forest but rare in the abutting cloud forest. Mesoclimate changed discontinuously around the elevation of the ecotone: humidity and cloud formation decreased markedly, and frost frequency increased exponentially.Main conclusions The discreteness of the ecotone was produced primarily by fire. The elevational consistency of the ecotone, however, resulted from the overarching influence of mesoclimate on the elevational patterns of fire occurrence. Declining temperature and precipitation combine with the trade‐wind inversion to create a narrow zone where high‐elevation fires extinguish, enabling fire‐sensitive and fire‐tolerant taxa to abut. Once established, mesotopography and contrasting vegetation physiognomy probably reinforce this boundary through feedbacks on microenvironment and fire likelihood. The prominence of the pine in this study – and of temperate and fire‐tolerant taxa in subtropical montane forests in general – highlights the importance of climate‐disturbance–biogeography interactions in ecotone formation, particularly where fire mediates a dynamic between climate and vegetation.

Breeding Biology of Passerines in a Subtropical Montane Forest in Northwestern Argentina

Abstract The breeding ecology of south temperate bird species is less widely known than that of north temperate species, yet because they comprise a large portion of the world's avian diversity, knowledge of their breeding ecology can contribute to a more comprehensive understanding of the geographic diversity of avian reproductive traits and life history strategies. We provide the first detailed examination of the reproductive strategies of 18 forest passerines of subtropical, northwestern Argentina. Mean clutch sizes were smaller and egg mass was greater than for north temperate birds, but differed among species and nest types, with cavity-nesters having larger clutches than species with open-cup and enclosed nests. Across all species, the average breeding season duration was 50 days; thus, the common perception that southern species have smaller clutch sizes because of longer breeding seasons is not supported in this community. Daily nest predation rates were influenced by nest type, cavity nests suffering the least from predation, as found in north temperate systems. Only females incubated eggs in all but one species, whereas both parents fed and cared for nestlings in all species. Mean nest attentiveness was low compared to north temperate passerines. Mean hourly nestling feeding rates differed among species and were negatively related to nest predation risk. In short, coexisting species in this subtropical forest varied in their life history strategies, in part correlated with variation in nest predation risk, but also differing from north temperate species.

Decline of the Tucumán parrot Amazona tucumana in Argentina: present status and conservation needs

The Tucumán parrot Amazona tucumana is a rare, Near Threatened species on CITES Appendix I with a restricted range in the tropical and subtropical montane forests of Argentina and Bolivia. We assessed the conservation status of the species in Argentina based on a detailed review of available information and an extensive survey throughout its range. A total of 6,015 individuals were detected in 14 sites, eight of which are new localities. The total number recorded in this study represents less than a third of the number exported from Argentina between 1985 and 1989 (18,641), indicating a significant reduction in population size. Research needs to be extended to additional sites, especially in Bolivia, to assess further the global status of the species, and high priority given to the creation of state and private reserves for the species.

COMPOSIÇÃO FLORÍSTICA DA FLORESTA OMBRÓFILA MISTA MONTANA DO PARQUE MUNICIPAL DO BARIGÜI, CURITIBA, PR

Realizou-se o levantamento florístico das espécies vasculares (exceto epífitas) de um fragmento de Floresta Ombrófila Mista Montana localizado no Parque Municipal do Barigüi, município de Curitiba, PR. Foram registradas 390 espécies, 226 gêneros e 99 famílias, entre pteridófitas, gimnospermas e angiospermas. Dentre as pteridófitas, destacaram-se como as mais ricas Dryopteridaceae (oito) e Blechnaceae (seis); e dentre as angiospermas, Asteraceae (30), Solanaceae (25), Myrtaceae (25) e Poaceae (17). As gimnospermas foram representadas por somente duas famílias, Araucariaceae e Podocarpaceae, cada uma delas com uma espécie. Foram listadas 141 espécies arbóreas, 129 herbáceas, 67 arbustivas, 50 trepadeiras e três hemiepífitas. A floresta, apesar de situada dentro de uma zona urbana, sujeita à intensa interferência antrópica, apresentou elevada riqueza específica.

Liana–host tree associations in a subtropical montane forest of north-western Argentina

In a subtropical montane forest of north-western Argentina (27 ◦ S, 1000 m elevation), we analysed the effect of crown illumination, trunk diameter, foliar phenology and tree species identity as determinants of liana-host tree associations, as well as the spatial pattern of liana abundance in a 6-ha permanent plot. We recorded 2346 liana individuals ≥ 2 cm and 2320 trees ≥ 10 cm dbh. Sixty-five per cent of the trees hosted at least one liana stem. Large and well-lit trees were more likely to support lianas and supported more liana abundance than small and shaded trees. Yet, when trees were standardized by their size (liana basal area/tree basal area ratio), lianas were more abundant in smaller and less-exposed trees. Foliar phenology and tree species identity showed no association with the frequency of liana colonization and their abundance. Overall, tree features played a minor or even neutral role in structuring the liana community within this forest. Instead, lianas showed a positive autocorrelation at spatial scales up to 40 m. This suggests that lianas might be mostly structured by light- and dispersal-related factors such as those involving canopy access or canopy disturbances, with a negligible effect of host species identity and foliar phenology.

Precipitation variability and landslide occurrence in a subtropical mountain ecosystem of NW Argentina

Landslides are common on the steep slopes of the subtropical montane forests in Northwestern (NW) Argentina (Yungas). Instrumental and tree-ring records from this region indicate that rainfall has increased during the second half of the 20th century and there has also been an increase in landslide events. We used dendroecological techniques to date the occurrence of landslides during the past 50 years and examine the relationships with regional precipitation trends. Alnus acuminata H.B.K. is the dominant species in the upper montane forest and colonizes the bare areas exposed by landslides. Landslide dating was based on the identification of suppression-release patterns in ring-width series from trees growing along the landslide scarps, in combination with age determination of trees growing on the landslide failure or depositional surfaces. We cored A. acuminata in three areas that span the latitudinal range of the montane forest in NW Argentina: Los Sosa (27°S), Hualinchay (26°S) and Yala (24°S). The results show that landslide occurrence (and therefore probability) is more frequent during summers with abundant rainfall. As General Circulation Models for subtropical South America predict an increase in summer precipitation during the 21st century, increased precipitation could induce changes in landslide regime that would lead to important environmental changes in these montane ecosystems.

Providing artificial nest platforms for Cabot's tragopan Tragopan caboti (Aves: Galliformes): a useful conservation tool?

Cabot's tragopan Tragopan caboti, a pheasant that inhabits subtropical montane forests in south-east China, is categorized as Vulnerable on the IUCN Red List. Nesting in trees, it routinely makes use of natural platforms and the old nests of other species, both of which may sometimes be in short supply. This study was designed to test how much use would be made of artificial nest platforms, and to identify factors influencing their occupation. Basketry platforms made of bamboo were erected in parts of Wuyanling National Nature Reserve, Zhejiang Province, China. The tragopans used 16 platforms (8%) in 2002 and 12 (5%) in the following year. A census of the population in spring suggested that a high proportion of the females (41% in 2002, 36% in 2003) in the study area made use of the platforms. There were significant preferences for platforms in mixed conifer/broadleaf forest, as opposed to pure stands, as well as for sites on the upper part of hill slopes. Principal component scores were used to represent variation in 11 variables measured at each platform site. Binary logistic regressions employing these scores as predictors for each year separately did not reveal a consistent model for distinguishing used from unused platforms, although short distances to the forest edge were associated with use in both years. These nest platforms are cheap and easy to erect, and may have the potential to halt or reverse a perceived downward population trend for this species across the whole of its fragmented range. Further trials are therefore advocated.

Natural regeneration of subtropical montane forest after clearing fern thickets in the Dominican Republic

Tropical forests can recover after anthropogenic disturbances of light to moderate intensity (Aide et al. 1995, 1996, 2000; Uhl 1987, Uhl et al. 1988); however, severe disturbances (e.g. compaction or loss of soil) often result in conditions that prevent forest recovery. These degraded sites are often dominated by grasses (Aide &amp; Cavelier 1994, Cabin et al. 2002, Cavelier et al. 1998, Uhl et al. 1988) and ferns (Cohen et al. 1995, García et al. 1994, Slocum et al. 2000, Walker &amp; Boneta 1995) that can impose barriers for tree regeneration and arrest the succession process. Important barriers for tree regeneration include: (1) competition with grasses and ferns for soil moisture, nutrients and light (Aide &amp; Cavelier 1994, Guimarães-Vieira et al. 1994, Holl et al. 2000, Nepstad et al. 1996, Russell et al. 1998, Walker 1994, Zimmerman et al. 2000), and (2) dispersal limitation given that grasses and fernlands offer few resources that attract seed dispersers (Guevara &amp; Laborde 1993, Holl et al. 2000, McDonnell &amp; Stiles 1983, Slocum &amp; Horvitz 2000, Zimmerman et al. 2000).

Shrew opossums (Paucituberculata: Caenolestes) from the Huancabamba region of east Andean Peru.

Shrew opossums of the genus Caenolestes are restricted to the northern Andes and include four species: C. fuliginosus, C. convelatus, C. caniventer and C. condorensis (Albuja and Patterson 1996). Caenolestes fuliginosus is a highland species of the paramos of central Ecuador, Colombia and western Venezuela, but the remaining three species occur in sub-tropical montane forests at lower elevations (Albuja and Patterson 1996). Caenolestes convelatus and C. caniventer are known from the western slopes of the Andes, the former from Colombia and northern Ecuador and the latter from southern Ecuador and northern Peru (Bublitz 1987), while the recently described Caenolestes condorensis is currently known only from the isolated Cordillera del Condor along the eastern slopes of the Andes in southern Ecuador (Albuja and Patterson 1996). The first records of Caenolestes from Peru were collected in the Departamento de Piura (Barkley and Whitaker 1984) and were originally reported as C. fuliginosus but later were later identified as C. caniventer (Albuja and Patterson 1996). The Departamento de Piura lies just north of the Huancabamba Depression, a region defined by the arid valley of the Rio Chamaya and adjacent low elevation passes (Fig. 1). Many species of Andean bird reach their southernmost distributional limit at the Huancabamba Depression (Parker et al. 1985), and it has been postulated that the region might also serve as a barrier to the southward dispersal of Caenolestes (Vivar et al. 1997). However, these same authors also cautioned that the Huancabamba region remains poorly surveyed for mammals and that what may appear to be a pattern may in fact be the result of inadequate sampling. In this paper we present additional data on the distribution of Caenolestes from localities in Peru north and south of the Huancabamba Depression.

Scale-Dependent Relationships between Treefalls and Species Richness in a Neotropical Montane Forest

Recent community studies found no relationship between treefall regime and species richness at the scale of individual treefalls. Here, spatial patterns of trees >5 cm diameter and treefalls (mostly dated by using dendroecological techniques) were described in 6 ha of subtropical montane forest in northwest Argentina, to explore the relationships between treefalls and tree community composition at different spatial scales. Time since gap formation showed spatial autocorrelation at spatial scales smaller than 5000 m2 (Moran's I coefficient). Point pattern analysis (Ripley's K function) showed that very recent treefalls (1990–1997) are spatially associated with previous treefalls (1978–1987) at scales of 1000–5000 m2. At the scale of individual treefalls (100–400 m2), species richness was uncorrelated with treefall regime, and shade-tolerant and light-demanding species were not discriminated in a multidimensional scaling ordination analysis. However, correlation between treefalls and species richness, and the discrimination of regeneration groups, increased abruptly at the scales of treefall aggregations. In agreement with previous studies, this study suggests that isolated treefalls have little effect on species composition and diversity, probably due to recruitment limitation. Instead, this study shows that at scales >1000 m2, treefall regime is a good predictor of species richness and composition of regeneration groups. This may be because treefall aggregations and gap expansion increase the probability of new nearby treefalls being colonized by light-demanding species. These results emphasize the importance of scale and spatial dynamics of disturbances and species dispersal in the study of canopy disturbances and their effects on community composition and diversity.

SCALE-DEPENDENT RELATIONSHIPS BETWEEN TREEFALLS AND SPECIES RICHNESS IN A NEOTROPICAL MONTANE FOREST

Recent community studies found no relationship between treefall regime and species richness at the scale of individual treefalls. Here, spatial patterns of trees >5 cm diameter and treefalls (mostly dated by using dendroecological techniques) were described in 6 ha of subtropical montane forest in northwest Argentina, to explore the relationships between treefalls and tree community composition at different spatial scales. Time since gap formation showed spatial autocorrelation at spatial scales smaller than 5000 m2 (Moran's I coefficient). Point pattern analysis (Ripley's K function) showed that very recent treefalls (1990–1997) are spatially associated with previous treefalls (1978–1987) at scales of 1000–5000 m2. At the scale of individual treefalls (100–400 m2), species richness was uncorrelated with treefall regime, and shade-tolerant and light-demanding species were not discriminated in a multidimensional scaling ordination analysis. However, correlation between treefalls and species richness, and the discrimination of regeneration groups, increased abruptly at the scales of treefall aggregations. In agreement with previous studies, this study suggests that isolated treefalls have little effect on species composition and diversity, probably due to recruitment limitation. Instead, this study shows that at scales >1000 m2, treefall regime is a good predictor of species richness and composition of regeneration groups. This may be because treefall aggregations and gap expansion increase the probability of new nearby treefalls being colonized by light-demanding species. These results emphasize the importance of scale and spatial dynamics of disturbances and species dispersal in the study of canopy disturbances and their effects on community composition and diversity.

Anurans of a subtropical montane forest in northwestern Argentina: ecological survey and a proposed list of species of conservation concern

The species composition, reproductive ecology, and patterns of activitywere determined for an anuran assemblage of an area of subtropical montaneforest in northwest Argentina. Twenty-four species were recorded at ParqueNacional Calilegua, Province of Jujuy. This study reflects a 75% increase in thenumber of species reported in previous surveys. Most species inhabiting the parkare mainly from adjacent Chacoan regions and only six taxa are known to beendemic from montane forest areas. Most species are aquatic breeders, and theabsence of many forest reproductive modes is noticeable. Although baselineinformation to compare former community composition was lacking, comparisonsbased on museum specimens revealed no evidence of local population extinctions.Immediate intensive monitoring is needed to quantitatively address amphibianpopulation fluctuations and to examine the effectiveness of present-day montaneforest protection. Although long-term population monitoring and documentation ofspecies declines is lacking, I propose a list of seven species of conservationconcern in order to assist and promote future monitoring programs.