Parental distance and plant density dependence of seedling leaf turnover and survival was examined to investigate predictions of the Janzen–Connell hypothesis. The focal study species, Shorea ...macroptera is a canopy tree species in a lowland rain forest in peninsular Malaysia. We found that the peak of the distribution of plants shifted from 3–6 m to 6–9 m during the course of the change from seedling to sapling stage. The leaf demography of the seedlings was influenced by their distance from the adult tree and also by the seedling density. Although significant density-and distance dependence in leaf production was not detected, seedling leaf loss decreased with distance from the parent tree and with seedling density. Similarly, leaf damage was not found to be distance-or density-dependent, but net leaf gain of seedlings increased with distance from the parent tree. Although no significant distance-or densitydependence was evident in terms of leaf damage, significant distance dependence of the net leaf gain was found. Thus, we concluded that positive distance dependence in the leaf turnover of seedlings may gradually contribute to a shift in the distribution pattern of the progeny through reductions in growth and survivorship.
Fully mapped tree census plots of large area, 25 to 52 hectares, have now been completed at six different sites in tropical forests, including dry deciduous to wet evergreen forest on two continents. ...One of the main goals of these plots has been to evaluate spatial patterns in tropical tree populations. Here the degree of aggregation in the distribution of 1768 tree species is examined based on the average density of conspecific trees in circular neighborhoods around each tree. When all individuals larger than 1 centimeter in stem diameter were included, nearly every species was more aggregated than a random distribution. Considering only larger trees (≥ 10 centimeters in diameter), the pattern persisted, with most species being more aggregated than random. Rare species were more aggregated than common species. All six forests were very similar in all the particulars of these results.
The authors compared tropical rain forest canopy structure and tree species composition in two forests southeast of Kuala Lumpur, Malaysia: a primary forest and a regenerating forest that was ...selectively logged in 1958. For each of the forests, the study plots were set out and all trees of ≥1
cm in DBH (diameter at breast height) were mapped and measured. Canopy heights were measured in the two study plots based upon aerial triangulation using aerial photographs taken over the forests in 1997. Using this data, digital elevation models of the canopy were then constructed. The mean canopy height was greater in the primary forest (27.4
m versus 24.8
m), as was the variance in height and the number of emergent canopy trees >40
m height. The mean canopy surface area in the primary forest was nearly 1.5 times the value in the regenerating forest, and the mean crown size of canopy layer trees in the primary forest was more than twice that in the regenerating forest. The species diversity index (Fisher’s
α) differed for the two forests, indicating that tree species diversity had been affected by the logging. Both forests had the same five families with the greatest stem density (stems
ha
−1), but the 50 most abundant species, in terms of both stem density and basal area, differed greatly between the two forests. Stem densities and basal areas were similar, but the number of stems per hectare and the basal areas of medium-sized trees (10–30
cm in DBH) were distinctly higher in the regenerating forest. These results suggest that average basal area and stem density in the regenerating forest that had been selectively logged 41 years earlier had recovered to levels similar to those in the primary forest; however, the regenerating forest had a more monotonic canopy structure comprised of medium-sized trees growing at high density. These findings also imply that structural development takes a long time to manifest in a regenerating forest as a result of the time taken for the development of emergent and canopy trees and the formation of gaps; structural development might also be delayed by the high density of medium-sized trees in the canopy layer.
Dynamics of the Pasoh forest in Peninsular Malaysia were assessed by drawing a comparison with a forest in Panama, Central America, whose dynamics have been thoroughly described. Census plots of 50 ...ha were established at both sites using standard methods. Tree mortality at Pasoh over an eight-year interval was 1.46% yr−1 for all stems greater than or equal to 10 mm diameter at breast height (dbh), and 1.48% yr−1 for stems greater than or equal to 100 mm dbh. Comparable figures at the Barro Colorado Island site in Panama (BCI) were 2.55% and 2.03%. Growth and recruitment rates were likewise considerably higher at BCI than at Pasoh. For example, in all trees 500 to 700 mm in dbh, mean BCI growth over the period 1985 to 1995 was 6 mm yr−1, whereas mean Pasoh growth was about 3.5 mm yr−1. Examining growth and mortality rates for individual species showed that the difference between the forests can be attributed to a few light-demanding pioneer species at BCI, which have very high growth and mortality; Pasoh is essentially lacking this guild. The bulk of the species in the two forests are shade-tolerant and have very similar mortality, growth and recruitment. The Pasoh forest is more stable than BCI's in another way as well: few of its tree populations changed much over the eight-year census interval. In contrast, at BCI, over 10% of the species had populations increasing or decreasing at a rate of > 0.05 yr−1 (compared to just 2% of the species at Pasoh). The faster species turnover at BCI can probably be attributed to severe droughts that have plagued the forest periodically over the past 30 years; Pasoh has not suffered such extreme events recently. The dearth of pioneer species at Pasoh is associated with low-nutrient soil and slow litter breakdown, but the exact mechanisms behind this association remain poorly understood.
The relationship between species diversity and sampled area is fundamental to ecology. Traditionally, theories of the species–area relationship have been dominated by random-placement models. Such ...models were used to formulate the canonical theory of species–area curves and species abundances. In this paper, however, armed with a detailed data set from a moist tropical forest, we investigate the validity of random placement and suggest improved models based upon spatial aggregation. By accounting for intraspecific, small-scale aggregation, we develop a cluster model which reproduces empirical species–area curves with high fidelity. We find that inter-specific aggregation patterns, on the other hand, do not affect the species–area curves significantly. We demonstrate that the tendency for a tree species to aggregate, as well as its average clump size, is not significantly correlated with the species' abundance. In addition, we investigate hierarchical clumping and the extent to which aggregation is driven by topography. We conclude that small-scale phenomena such as dispersal and gap recruitment determine individual tree placement more than adaptation to larger-scale topography.
Predicting Species Diversity in Tropical Forests Plotkin, Joshua B.; Potts, Matthew D.; Yu, Douglas W. ...
Proceedings of the National Academy of Sciences - PNAS,
09/2000, Letnik:
97, Številka:
20
Journal Article
Recenzirano
Odprti dostop
A fundamental question in ecology is how many species occur within a given area. Despite the complexity and diversity of different ecosystems, there exists a surprisingly simple, approximate answer: ...the number of species is proportional to the size of the area raised to some exponent. The exponent often turns out to be roughly 1/4. This power law can be derived from assumptions about the relative abundances of species or from notions of self-similarity. Here we analyze the largest existing data set of location-mapped species: over one million, individually identified trees from five tropical forests on three continents. Although the power law is a reasonable, zeroth-order approximation of our data, we find consistent deviations from it on all spatial scales. Furthermore, tropical forests are not self-similar at areas ≤ 50 hectares. We develop an extended model of the species-area relationship, which enables us to predict large-scale species diversity from small-scale data samples more accurately than any other available method.
We estimated the total aboveground tree biomass (TAGB) in an old-growth primary forest and in a regenerating forest that had been selectively logged in 1958, both within the tropical rainforest of ...the Pasoh Forest Reserve in Peninsular Malaysia. This was achieved by comparing aerial photographs with data obtained previously from destructive sampling in the same area. Aerial photographs were taken above the primary and logged forest plots in 1997. The heights of the canopy-forming trees were estimated in both plots by means of aerial triangulation and were regressed against the diameter at breast height (DBH) of the corresponding trees measured during ground surveys. The resulting allometric relationship between tree height and DBH let us estimate TAGB: in the primary forest, TAGB was 310
Mg
ha
−1, which was ca. 10–12% smaller than the value estimated by means of destructive sampling conducted in the 1970s. The estimated TAGB of the logged forest was 274
Mg
ha
−1, which was significantly smaller than that of the primary forest (
P < 0.05). We also measured canopy surface height in a 2.5
m grid system. We found that the mean canopy surface height (MCH) in every 20
m × 20
m subplot (0.04
ha) was significantly (
P < 0.0001) correlated with TAGB for that subplot. This suggests that the spatial variation of TAGB can be estimated using MCH values obtained from such a grid system, and that biomass levels can potentially be estimated by means of satellite remote sensing on larger scales, even for very dense tropical forests. We also found that digital reflectance values from Landsat Thematic Mapper (TM) images differed significantly between the logged and primary forests, and hypothesize that these differences relate to structural differences in the canopy surface. However, TAGB in both plots was poorly correlated with the Landsat reflectance values, suggesting the necessity of using an active remote-sensing sensor or a laser profiling system that can quantify changes in the forest's vertical structure or volume to estimate biomass and its variation in dense evergreen forests.
Species-accumulation curves for woody plants were calculated in three tropical forests, based on fully mapped 50-ha plots in wet, old-growth forest in Peninsular Malaysia, in moist, old-growth forest ...in central Panama, and in dry, previously logged forest in southern India. A total of 610 000 stems were identified to species and mapped to < 1 m accuracy. Mean species number and stem number were calculated in quadrats as small as $5m \times 5 m$ to as large as $1000 m \times 500 m$, for a variety of stem sizes above 10 mm in diameter. Species-area curves were generated by plotting species number as a function of quadrat size; species-individual curves were generated from the same data, but using stem number as the independent variable rather than area. 2 Species-area curves had different forms for stems of different diameters, but species-individual curves were nearly independent of diameter class. With $< 10^4$ stems, species-individual curves were concave downward on log-log plots, with curves from different forests diverging, but beyond about $10^4$ stems, the log-log curves became nearly linear, with all three sites having a similar slope. This indicates an asymptotic difference in richness between forests: the Malaysian site had 2.7 times as many species as Panama, which in turn was 3.3 times as rich as India. 3 Other details of the species-accumulation relationship were remarkably similar between the three sites. Rectangular quadrats had 5-27% more species than square quadrats of the same area, with longer and narrower quadrats increasingly diverse. Random samples of stems drawn from the entire 50 ha had 10-30% more species than square quadrats with the same number of stems. At both Pasoh and BCI, but not Mudumalai, species richness was slightly higher among intermediate-sized stems (50-100 mm in diameter) than in either smaller or larger sizes. These patterns reflect aggregated distributions of individual species, plus weak density-dependent forces that tend to smooth the species abundance distribution and `loosen' aggregations as stems grow. 4 The results provide support for the view that within each tree community, many species have their abundance and distribution guided more by random drift than deterministic interactions. The drift model predicts that the species-accumulation curve will have a declining slope on a log-log plot, reaching a slope of 0.1 in about 50 ha. No other model of community structure can make such a precise prediction. 5 The results demonstrate that diversity studies based on different stem diameters can be compared by sampling identical numbers of stems. Moreover, they indicate that stem counts < 1000 in tropical forests will underestimate the percentage difference in species richness between two diverse sites. Fortunately, standard diversity indices (Fisher's $\alpha$, Shannon-Wiener) captured diversity differences in small stem samples more effectively than raw species richness, but both were sample size dependent. Two nonparametric richness estimators (Chao, jackknife) performed poorly, greatly underestimating true species richness.
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