Deciduous

Abstract: 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.

Abstract: 1 Possible patterns in nutrient resorption efficiency (% of the leaf nutrient pool resorbed) from senescing leaves of perennials were examined at both the intra- and the interspecific level. Most of the data used originated from studies with evergreen and deciduous shrubs and trees. 2 Combining all data, mean nutrient resorption efficiency was 50% for N (n = 287) and 52% for P (n = 226). N resorption efficiency of evergreen shrubs and trees (47%) was significantly lower than in deciduous shrubs and trees (54%), whereas P resorption efficiency did not differ significantly between these growth-forms (51 and 50%, respectively). Although nutrient resorption is an important nutrient conservation mechanism at the species level, it does not differ strongly between growth-forms. 3 Mean N and P concentrations in leaves of deciduous shrubs and trees were about 60% higher than in evergreen species. There were only small differences in mean resorption efficiency and nutrient concentrations in leaf litter of deciduous species were therefore much higher than in evergreens. This implies that, in comparison with deciduous species, the low nutrient concentrations in mature leaves of evergreens contribute far more to nutrient conservation than does nutrient resorption. 4 Relations between leaf nutrient status and leaf nutrient resorption were absent or very weak. Assuming that leaf nutrient status reflects nutrient availability, this implies that nutrient resorption is only weakly controlled by nutrient availability. 5 At the intraspecific level, nutrient resorption was not very responsive to increased nutrient availability. There was no response in 63% of the experiments analysed (covering 60 spp.), whereas in 32% there was a decrease in N resorption in response to increased nutrient availability. For P (37 species analysed) there was no response in 57% of the cases and in 35% of the cases P resorption decreased upon enhanced nutrient supply. Evergreen shrubs and trees showed especially low responsiveness. 6 This review shows that there are no clear nutritional controls on nutrient resorption efficiency. Future research should focus on the biochemical basis of variation in nutrient resorption efficiency and on the factors, other than nutrient availability, that control nutrient resorption efficiency.

Abstract: Lack of information on ecological characteristics of species across different continents hinders development of general world-scale quantitative vegetation dynamic models. We constructed common scales of shade, drought, and waterlogging tolerance for 806 North American, European/West Asian, and East Asian temperate shrubs and trees representing about 40% of the extant natural Northern Hemisphere species pool. These scales were used to test the hypotheses that shade tolerance is negatively related to drought and waterlogging tolerances, and that these correlations vary among continents and plant functional types. We observed significant negative correlations among shade and drought tolerance rankings for all data pooled, and separately for every continent and plant functional type, except for evergreen angiosperms. Another significant trade-off was found for drought and waterlogging tolerance for all continents, and for evergreen and deciduous angiosperms, but not for gymnosperms. For all data pooled, for Europe and East Asia, and for evergreen and deciduous angiosperms, shade tolerance was also negatively associated with waterlogging tolerance. Quantile regressions revealed that the negative relationship between shade and drought tolerance was significant for species growing in deep to moderate shade and that the negative relationship between shade and waterlogging tolerance was significant for species growing in moderate shade to high light, explaining why all relationships between different tolerances were negative according to general regression analyses. Phylogenetic signal in the tolerance to any one of the three environmental factors studied was significant but low, with only 21-24% of cladogram nodes exhibiting significant conservatism. The inverse relationships between different tolerances were significant in phylogenetically independent analyses both for the overall pool of species and for two multispecies genera (Pinus and Quercus) for which reliable molecular phylogenies were available. Only 2.6-10.3% of the species were relatively tolerant to two environmental stresses simultaneously (tolerance value � 3), and only three species were tolerant to all three stresses, supporting the existence of functional trade-offs in adjusting to multiple environmental limitations. These trade-offs represent a constraint for niche differentiation, reducing the diversity of plant responses to the many combinations of irradiance and water supply that are found in natural ecosystems.