Life zone

Abstract: This study describes the distributional patterns of Costa Rican and Panamanian species of Bignoniaceae. These species tend to be wide-ranging but restricted to certain climatic zones. Abundance and ecological importance of Bignoniaceae are greatest in dry areas, but species diversity is generally constant in lowland dry, moist and wet forest habitats. About 20 of the 80 Costa Rican/Panamanian species occur at any suitable site. A comparison of pollination strategies with species distributions suggests unique pollination niches for the strictly sympatric species. In any given area only one (uncommonly two) species with a given pollination strategy is in flower at any one time. THE FAMILY BIGNONIACEAE is especially appropriate for ecological studies. It includes many of the poorly known but characteristic tropical forest vines, as well as important canopy trees. In Panama and Costa Rica more species of liana (here defined as woody vines) belong to the Bignoniaceae than to any other plant family. The family is well-represented in many different tropical habitats. Species have large ranges, and their occurrences in a particular community seem to be more a function of ecological conditions than of the vagaries of dispersal. Moreover, the large number of vegetatively similar species of Bignoniaceae which often occur together has led to difficulty in the explanation of their occurrences in terms of adaptive strategies, thus making the family a fitting test case for such current theories 'of non-adaptive evolution as that of Federov (1966). The first objective of this paper is to document two distribution patterns with direct taxonomic significance for the Bignoniaceae of Costa Rica and Panama: 1) In many genera, closely related species which appear sympatric and doubtfully separable in the herbarium have distinct ecological requirements and are specifically distinct. 2) Within their ecological limits most species of Bignoniaceae are wideranging. The wide disjunctions in known distribution, which have led to taxonomic splitting of many of these species, are mostly collecting artifacts, since understanding the ecology of such species makes possible the accurate prediction of their occurrence in geographically intermediate areas. The second objective of this paper is to consider the distributional patterns of Bignoniaceae as a function of community ecology. Analysis of the distribution, conceived as a taxonomic exercise, reveals three patterns of significance. First, the ecological importance of this family is greater in drier environments; second, most species of the family have well-defined habitats; and third, the number of species of Bignoniaceae in dry, moist, and wet forest habitats is nearly constant at about 20 species. The final objective concerns the previously published data on flowering strategies, or pollination niches (Gentry 1974c), which are correlated with distributional data to suggest within-habitat niche specificity. Throughout this study I have followed the Holdridge et al. (1971) life zone system of environmental classification. In the absence of adequate climatic data, the life zone maps of the various Latin American countries provide the best means for comparing the macroenvironments of different sites. Moreover, the distributions shown by many Costa Rican and Panamanian Bignoniaceae correlate well with Holdridge life zones. While there are some unresolved problems with the Holdridge model (see Myers 1969), and I would disagree with certain boundary lines (e.g., between the tropical moist and premontane wet forests in the Pipeline Road area of the Canal Zone) on the life zone map of Panama (Tosi 1970), the use of this system makes possible accurate predictions for Bignoniaceae distribution. Although many species of Bignoniaceae have sufficient ecological amplitude to occur in more than one life zone, the life zone system provides the most useful ecological categorization for the tropical environment. SAMPLING SITES AND METHODS As a quantitative baseline for ecological evaluation of Bignoniaceae distribution, seven sites representing five different life zones were selected for intensive study. On each site plots 2 m wide and 50 m long were surveyed for all plant species over 1 inch (2.54 cm) dbh (diameter at breast height) as well as for all younger individuals of Bignoniaceae. These BIOTROPICA 8(2): 117-131 1976 117 This content downloaded from 157.55.39.212 on Thu, 09 Jun 2016 05:58:35 UTC All use subject to http://about.jstor.org/terms plots were laid out by running a linear 50-meter transect line through the forest from a randomly selected point in a predetermined direction (usually perpendicular or parallel to a trail or stream) and recording all plants within 1 m of it on either side. Individuals falling partly within the transect area were included only if more than half of their basal stem diameter fell within it. All vines were included which were rooted in the transect area even though many of them also crossed the forest floor for long distances outside the plot. All vines or lianas which arose from a single above-ground origin were included as a single individual with its recorded diameter being that of its thickest stem. If aboveground or ground-level physical connections between lianas could not be discovered, they were treated as separate entities, even though in some cases they had at one time obviously been branches of a single parent plant. In all other instances the point at which a plant left the ground determined its inclusion or exclusion from the plot. Although approximate dbh (measured at the level of a transect line with both ends at 1.37 m above ground level) was generally used to determine diameters, multiple shoots from a single base were classed as one plant for density determinations. A few plants were also included which had been cut off below the transect level but which had shoots less than 1 inch thick reaching that level; these plants were accorded the diameter of the basal stump. Each plant was tabulated as to species, habit, and diameter, and for every transect each species present was summarized as to the number and diameters of individuals present. Ten such plots were made for a total sample area of 1000 square meters per area for three sites in the Canal Zone: Albrook Forest (fig. 1,C), Madden Forest (fig. 1,M), and Pipeline Road (fig. 1,P). Eight such plots were made in upland forest and, = Tropical and Premontane Dry Forest A1 jj ' rvppl = Tropical and Premontane LUali1LJ Moist Forest = Tropical and Premontane Wet Forest =Montane and Lower Montane FIGUE 1. S orest FIGURE 1. Schematized life zone map of Panama (below) and Costa Rica (above) x intensive study sites.

Abstract: Tibetan Plateau with the average altitude of about 5000m is one of very important regions in the world, because its natural conditions are very severe and much vulnerable to changes in climate. Therefore it is expected that changes in climate and consequent biomes on this region may play a role of pilot and/or pioneer in monitoring the global environmental degradation due to intensive human activity. In this paper, the responses of biomes on the Tibetan Plateau to the global climate change induced by doubled CO2 were studied using improved Holdridge life zone classification system, vertical vegetation belt system, permafrost model, and NPP model. The global climate changes will cause the considerable changes in the vertical distribution of vegetation, permafrost zone, and NPP-values on the Tibetan Plateau. It was expected that the increment in annual mean temperature by 4 °C and annual precipitation by 10% under doubled CO2 condition would accerelate the speed of desertification which is spreading on this area mainly due to the intensive mass land use at present.