Showing papers on "Biodiversity published in 1978"

Forest vegetation of the colorado front range: patterns of species diversity*

Abstract: Plant species diversity patterns of the Rocky Mountain forests were found to be at variance with patterns reported from other regions. The most centrally located forests in terms of elevation, site moisture and successional status were found to have the lowest diversity. In contrast, the peripheral and environmentally more severe sites were found to have relatively high diversity. In particular, the forest-grassland transition and the low elevation riparian forests have species diversity values as high as any yet reported from western North America. When diversity was examined in terms of variation across elevation or moisture gradients, varying results were obtained due to the interaction of these factors. The failure of previous studies to converge on generalizations about plant diversity reflects, in part, the failure of most investigators to view diversity in a regional context of variation across several interacting gradients. Diversity was seen to vary inversely with the degree of development of the forest canopy. The interaction of different components of the forest community is one reason for the failure of general patterns of plant species diversity to emerge from previous studies. A potentially rich herb community can be greatly suppressed by a single species tree stratum. Among the most successful work to date on species diversity is that on birds, a distinct albeit large and functional group. It is unlikely that similar success could have been achieved through work on all animal species simultaneously. This suggests the need to examine plant species diversity, not in terms of total diversity, but in terms of component functional groups, perhaps guilds, growing under similar microclimatic conditions and subject to similar competitive pressures.

Plant species diversity and ecological districts of the Sinai desert

Abstract: Lists of vascular plant species for each of the 12 ecological districts of Sinai were prepared. In all 78,000 observations on altogether 812 species were analyzed. The number of districts where each species occurred was also counted. Linear regressions were calculated for the log-transformed values of species/area, species/altitude and multiple regression of species on both area and altitude. The regression of species on area for the 12 ecological districts of Sinai gave the equation: log S = 1.0309+0.3 log A The value of z=0.3 is higher than 0.222—the measured overall value for the continents and higher than the values for the Sahara, California mainland, the British Isles, and the Netherlands. However, it is lower than the values for the Galapagos Archipelago and the California Islands. The number of species supported in districts characterized by fissured limestone, gravel plains, chalk, marl, sandstones, sands or fissured magmatic and metamorphic rocks is close to the regression of species on area, whereas large outcrops of smooth-faced rocks are relatively richer in total number of species as well as in stenotople species. It is suggested that the high gamma diversity of Sinai as compared with other parts of the world is primarily due to its environmental heterogeneity. Sinai being a meeting place of three phytogeographical regions and to past climatic changes. The effect of smooth-faced rock outcrops as conducive to providing refugia must also be taken into account.