Tree species composition and rain forest-environment relationships in the middle Caquetá area,Colombia, NW Amazonia

As part of an integrated forest vegetation and soil survey, tree species composition (DBH 10 cm) was recorded in 95 plots of 0.1 ha, distributed over the principal physiographic units in the middle Caquetá area, Colombian Amazonia. A total of 1077 tree species was found, classified into 271 genera and 60 families. Leguminosae and Sapotaceae show high familial importance values in all physiographic units. Lauraceae, Chrysobalanaceae, Moraceae, and Lecythidaceae are more important on well drained (flood plain or upland) soils, while Palmae, Guttiferae, Bombacaceae, and Apocynaceae are more important in swamps and on podzolised (white sand'rs) soils. Plots on well drained soils show a lower degree of dominance than plots in swamps or on podzolised (white sand) soils. The composition of the most dominant species in the plots changes continuously. Most species (59%) are only recorded in one plot. Individual plot pairs generally show a low overlap of about 2–5 tree species, resulting in Jaccard coefficients below 20%.complementary to a previous forest classification based on TWINSPAN analyses, detrended and canonical correspondence analyses were carried out, using CANOCO 3.1. Despite of a low amount of tree species variance explained (only 6.2% by the first two canonical axes), meaningful patterns of tree species composition were recognised. These are most strongly related to drainage, flooding, humus forms, and soil nutrient status. Forest types are well separated in the CCA ordination diagram. The most frequently found tree species are listed according to their preference with respect to drainage, flooding, and soil nutrient status.Tree species composition in the well drained upland forests was analysed separately. In view of the model explaining high NW Amazonian tree species diversity on the basis of dense community packing and high beta diversity along soil gradients, the canonical analysis here focused on the effect of soils. By means of partial canonical ordination it was found that patterns of tree species composition depended significantly on soil properties, even though the edaphic component explains only a small fraction of the tree species variance. The results show that the well drained uplands of the middle Caquetá area are covered by a complex of two intergrading tree species assemblages. The first assemblage (community of Goupia glabra-Clathrotropis macrocarpa) is associated to some-what less poor, clayey soils developed in Andean origin deposits or Tertiary sediments from the Pebas formation. The second assemblage (community of Swartzia schomburgkii-Clathrotropis macrocarpa) shows affinities to very poor, loamy soils developed in parent materials derived from the Guiana shield. This simple dichotomous pattern of geology, soils, and forest types is incompatible with concepts of high soil heterogeneity and associated beta diversity controlling tree species diversity in well drained uplands of NW Amazonia. The gradient length of tree species in the detrended correspondence analysis was low (3.7 SD), also suggesting a low beta diversity.     

Small Canopy Gaps Influence Plant Distributions in the Rain Forest Understory1

This study tested three hypotheses regarding how plants respond to the spatial heterogeneity in light availability in the rain forest understory: (1) understory plants occur preferentially in the lighter parts of the understory; (2) under–story palms are more shade tolerant than other understory plants; (3) rain forest plants differ in their ontogenetic response to understory light conditions. The study was carried out in old–growth rain forest in the Yasuní National Park, Amazonian Ecuador. The hypotheses were tested by comparing the distributions of 20 plant species (1454 individuals) over microsites with differing degrees of exposure to canopy gaps to the background distribution of these microsites in the forest. The gap exposure of a given microsite was described by an index based on the number and size of gaps in the canopy to which the site was exposed. Two plant height classes were studied: 0.80–2.49 and 2.50–5 m. The first and third hypotheses were accepted, while the second hypothesis was rejected. The results for the individual species corresponded well with what is known from earlier studies about the ecology of these species or close relatives, suggesting that the patterns observed can be generalized for Neotropical rain forests. Notably, the most abundant species in the study represent several different life history strategies. Thus, abundance in the rain forest understory can be achieved by several different strategies. This suggests that niche differentiation in terms of response to small changes in understory light conditions may be an important factor in the maintenance of the high local plant species richness of tropical rain forests.     

车八岭山地常绿阔叶林冰灾后土壤节肢动物群落的多样性

2008年初车八岭山地常绿阔叶林受到中国南方80年一遇的冰灾的重创。为了揭示灾后林冠开度的梯度对土壤节肢动物多样性与分布的影响, 在受冰灾影响的车八岭山地常绿阔叶林设置2 ha固定样地, 按照冠层受损程度选取17个20 m×20 m的样方, 用半球面影像技术获取林冠开度, 并分凋落物层、0–10 cm和10–20 cm的矿质土层采集凋落物及土壤样品, 分析土壤节肢动物多样性。利用双向聚类分析(two-way cluster analysis)对凋落物层的土壤节肢动物和样地进行聚类, 以典范对应分析(canonical correspondence analysis)研究冠层开度、土壤有机质、电导率以及自然含水量与0–10 cm表土层土壤节肢动物的关系。结果表明土壤节肢动物的多度、丰富度和多样性随土壤层的加深而下降, 具有明显的表聚性; 林冠开度与凋落物层的土壤节肢动物类群数量呈负相关; 甲螨亚目、中气门亚目和前气门亚目动物对光照的适应范围广; 膜翅目、鞘翅目幼虫、综合纲和伪蝎目动物具有明显的避光性; 土壤节肢动物类群的分布与林冠开度、土壤自然含水量、电导率和有机质关系密切。因此可以推论, 冰灾对车八岭山地常绿阔叶林冠层的破坏及土壤因子的变化会进一步影响土壤节肢动物群落的组成和分布。本项研究还表明, 土壤节肢动物群落能有效地表征它们所栖息的生态系统的特点, 可用于监测冰灾后森林恢复和演替动态。而双向聚类分析和典范对应分析对于揭示土壤节肢动物的空间异质性及其与环境因子的相互关系具有理想的效果。     

Spatial and temporal dynamics of forest canopy gaps following selective logging in the eastern Amazon

Selective logging is a dominant form of land use in the Amazon basin and throughout the humid tropics, yet little is known about the spatial variability of forest canopy gap formation and closure following timber harvests. We established chronosequences of large‐area (14–158 ha) selective logging sites spanning a 3.5‐year period of forest regeneration and two distinct harvest methods: conventional logging (CL) and reduced‐impact logging (RIL). Our goals were to: (1) determine the spatial characteristics of canopy gap fraction immediately following selective logging in the eastern Amazon; (2) determine the degree and rate of canopy closure in early years following harvest among the major landscape features associated with logging – tree falls, roads, skid trails and log decks; and (3) quantify spatial and temporal differences in canopy opening and closure in high‐ and low‐damage harvests (CL vs. RIL). Across a wide range of harvest intensities (2.6–6.4 felled trees ha^?1), the majority of ground damage occurred as skid trails (4–12%), whereas log decks and roads were only a small contributor to the total ground damage (<2%). Despite similar timber harvest intensities, CL resulted in more ground damage than RIL. Neither the number of log decks nor their individual or total area was correlated with the number of trees removed or intensity of tree harvesting (trees ha^?1). The area of skids was well correlated with the ground area damaged (m²) per tree felled. In recently logged forest (0.5 years postharvest), gap fractions were highest in log decks (mean RIL=0.83, CL=0.99) and lowest in tree‐fall areas (RIL: 0.26, CL: 0.41). However, the small surface area of log decks made their contribution to the total area‐integrated forest gap fraction minor. In contrast, tree falls accounted for more than two‐thirds of the area disturbed, but the canopy gaps associated with felled trees were much smaller than for log decks, roads and skids. Canopy openings decreased in size with distance from each felled tree crown. At 0.5 years postharvest, the area initially affected by the felling of each tree was approximately 100 m in radius for CL and 50 m for RIL. Initial decreases in gap fraction during the first 1.5 years of regrowth diminished in subsequent years. Throughout the 3.5‐year period of forest recovery, tree‐fall gap fractions remained higher in CL than in RIL treatments, but canopy gap closure rates were higher in CL than in RIL areas. During the observed recovery period, the canopy gap area affected by harvesting decreased in radius around each felled tree from 100 to 40 m in CL, and from 50 to 10 m in RIL. The results suggest that the full spatial and temporal dynamics of canopy gap fraction must be understood and monitored to predict the effects of selective logging on regional energy balance and climate regimes, biogeochemical processes including carbon cycling, and plant and faunal population dynamics. This paper also shows that remote sensing of log decks alone will not provide an accurate assessment of total forest area impacted by selective logging, nor will it be closely correlated to damage levels and canopy gap closure rates.     

Pattern and Performance of Understory Bamboos (Chusquea spp.) under Different Canopy Closures in Old-Growth Oak Forests in Costa Rica1

The effect of canopy closure on spatial and morphological patterns of three understory Chusquea species was studied in pristine upper montane oak forests. Plots with either Chusquea talamancenis Widmer & L.G. Clark or C. tomentosa Widmer & L.G. Clark were set out in gaps, under intermediate tree canopy and under closed canopy. The third species Chusquea foliosa L.G. Clark was only found in gap and intermediate canopy sites in the study area. Clumps of all bamboo species tend to be few and large under open conditions and numerous and small under more shady conditions. The larger size of clumps in gaps is reflected in the number of culms per clump, the diameter of the culms and, as a consequence, clump basal area, clump crown area, and biomass (index of plant volume) compared to intermediate and closed canopy. The smaller clump density in gaps compared to closed canopy implies that there is more intraspecific competition and density dependent mortality (self-thinning effect) when a bamboo species is dominant under favourable light conditions. Parameters of performance like culm length, number of nodes per culm, number and length of primary branches, and number of branch nodes seem not to be affected by the light regime, unlike total number of branches, total branch length, and the branching pattern. Species differ in their response to the light environment: C. tomentosa and C. foliosa have a higher degree of morphological plasticity than C. talamancensis, which in turn, appears to be more shade tolerant. No difference between species has been found regarding their contribution to vegetation, parameters reflecting abundance per unit area (site clump area, site crown area and site index of clump volume) were similar for all three species.     

Colonization of gaps produced by death of bamboo clumps in a semideciduous mesophytic forest in south-eastern Brazil

The study was carried out in 16 gaps produced by bamboo clump death (Merostachys riedeliana Rupr. ex Doell) in a semideciduous mesophytic forest in the Santa Genebra County Reserve (22°4945 S and 47°0633 W), Campinas, SP, south-eastern Brazil. All shrub and tree individuals in the gap with height 0.50 m were sampled. The floristic similarity among the colonizing vegetation in these gaps and in gaps produced by treefall was assessed by the Jaccard similarity index and cluster analysis. The colonization process of these gaps was found to be similar to that in gaps formed by treefall, but this colonization only began after the bamboo clump death. The gap area varied from 35 m² to 454 m², but small gaps predominated. In the set of gaps, 3677 individuals were sampled belonging to 40 families, 83 genera and 114 species. The families with the greatest species richness in the gaps were Myrtaceae (10), Euphorbiaceae (9) and Solanaceae and Rubiaceae (8 each). The species with the greatest number of individuals in the gaps were the pioneers Celis tala Gillies ex Planchon and Croton priscus Muell. Arg. and the shade-tolerant shrubs Actinostemon klotschii (Muell. Arg.) Pax, Polygala klotzschii Chod., Psychotria hastisepala Muell. Arg. and Galipea multiflora Engl. Late secondary species predominated because of the greater number of small gaps. The gaps formed by bamboo clump death contributed to the successional and structural organization of the forest, creating suitable environments for colonization by shrub and tree species of the different successional groups.     

Bat assemblage structure in two dry forests of Colombia: Composition, species richness, and relative abundance

We studied the composition, species richness, and relative abundance of bat assemblages in the Colombian dry forests of Chicamocha and Patía. In Chicamocha, 11 bats of the family Phyllostomidae were captured with mist-nets, corresponding to 85–100% of the potential phyllostomids species in the area. Two bats of the family Vespertilionidae were also captured in Chicamocha. In Patía, 12 species were captured with mist-nets, all Phyllostomidae, representing 72–100% of the estimated total number of species in the zone. Minor differences in number of species and composition were detected among sampling periods in Chicamocha. The most common species in this dry forest were Glossophaga longirostris and Sturnira lilium. In Patía, notable differences in the number of species and composition were observed among sampling periods, and the most common species were Artibeus jamaicensis, Carollia perspicillata and Phyllostomus discolor. Arid-zone dwelling bats were absent in Patía and we suggest that this absence may be associated with the isolation of Patía from other northern dry zones of Colombia since Quaternary times. There was also low abundance of bats in Patía, which appears to be related to human disturbance. The most abundant phyllostomid bat species in the two dry forests studied are those that include fruit and/or nectar-pollen from columnar cacti as an important proportion of their diets.     

Tree species distribution in canopy gaps and mature forest in an area of cloud forest of the Ibitipoca Range,south-eastern Brazil

The tree community of both canopy gaps and mature forest was surveyed in a 5 ha plot of cloud forest in the Ibitipoca Range, south-eastern Brazil, aiming at: (a) comparing the tree community structure of canopy gaps with that of three strata of the mature forest, and (b) relating the tree community structure of canopy gaps with environmental and biotic variables. All saplings of canopy trees with 1–5 m of height established in 31 canopy gaps found within the plot were identified and measured. Mature forest trees with dbh 3 cm were sampled in four 40×40 quadrats laid on the four soil sites recognised in the local soil catena. All surveyed trees were identified, measured and distributed into three forest strata: understorey (<5 m of height), sub-canopy (5.1–15 m) and canopy (15.1–30 m). The following variables were obtained for each gap: mode of formation, age, soil site, slope grade, size, canopy openness and abundance of bamboos and lianas. A detrended correspondence analysis indicated that the tree community structure of gaps in all soil sites was more similar to that of the mature forest understorey, suggesting that the bank of immatures plays an important role in rebuilding the forest canopy and that gap phases may be important for understorey shade-tolerant species. There was evidence of gap-dependence for establishment for only one canopy tree species. Both canonical correspondence analysis and correlation analysis demonstrated for a number of tree species that the distribution of their saplings in canopy gaps was significantly correlated with two variables: soil site and canopy openness. The future forest structure at each gap is probably highly influenced by both the present structure of the adjacent mature forest and the gap creation event.     

“El Niño” events recorded in dry-forest species of the lowlands of northwest Peru

The northwest coast of Peru (5°S, 80°W) is very sensitive to and impacted by the climate phenomenon El Niño-Southern Oscillation (ENSO). Though mainly desert, this warm, dry region contains an equatorial dry forest. We report the first dendrochronological studies from this region and identify several species that have dendrochronological potential. Short ring-width chronologies of Palo Santo (Bursera graveolens) show a well-developed response to the ENSO signal over the last 50 years and good inter-site correlations. Preliminary isotopic studies in Algarrobo (Prosopis sp.) also show evidence of the 1997–98 El Niño event. ENSO events have a strong effect on the variability in the growth of several species and thereby on the economy of rural communities where the wood is used for housing, cooking, furniture, tools, fodder and medicinal uses. The extensive use of wood in archeological sites also offers the possibility of ultimately developing longer records for some of these species.