Temperature And Betula Disribution On The Holy — страница 3

trees. Also birch trees grow in areas that other trees occupy and this could either help or hinder the growth of Betula on either side of the range, or inter-specific competition between trees. Another possible reason for Betula densities to change is herbivory. Wilsey (1998) describes the effects that herbivorous insects and fungi have on leaf asymmetry by increasing it, which would increase productivity of the leaves of the trees (Betula). While discussing some of the certain biotic factors, abiotic factors must also be considered for possible reasons of birch tree densities. A study on hurricane disturbance on a forest was done in the Harvard Forest in north-central Massachusetts, and it was found that after this massive disturbance, there is a reorganization of biomass and

openings into the forest canopy (Cooper-Ellis et al. 1999). In this experiment, disturbance had little effect on composition of the forest, but does lead to a possible explanation for the densities differences of Betula. Possibly the irregular growth of Betula on the Holyoke range can be contributed to the, or the lack of a major disturbance (i.e. hurricane) in the area. With the combination of both biotic and abiotic factors, it is best explained by Claus (1999): ??Compositions and structure of a community are shaped by both abiotic factor and interaction among organisms.?? Figure Legend Fig 1. Mean basal area (cm2 m-2) of adult Betula species on Holyoke range Fig 2. Frequency of adult Betula species on the Holyoke range Betula Betula Betula Betula lenta lutea papyrifera

populifolia Adults North side 110.9 (10.7) 4.7 (3.4) 2.3 (1.3) 5.5 (2.9) South side .8 (.8) 0.0 (0.0) 0.0 (0.0) 0.0 (0.0) Table 1. Mean adult densities (ind ha-1) and standard error in parerthses. Betula species on the Holyoke Range, Massachusetts. (Sept 20 and Sept 27, 2000) 1. Elias, T. E. 1980 The Complete Trees of North America, Outdoor Life/Nature Books New York, USA 2. Livingston, R. B. 1982. Microclimates and Vegetation of the Holyoke Range, Dept of Biology, University of Massachusetts 3. Cooper-Ellis, .S, Foster D. R., Carlton, D., Lezberg, A., 1999. Forest response to catastrophic wind: results from an experimental hurricane, Ecology 4. Wilsey, B. J. 1998 Leaf fluctuating asymmetry increase with hybridization and elevation in tree line birches, Ecology 5. Holzapfel, C.,

Mahall, B., 1999 Bidirection facilitation and interference between shrubs and annuals in the Mojave Desert, Ecology