共查询到4条相似文献,搜索用时 0 毫秒
1.
Elk, fire and climate have influenced aspen populations in the Rocky Mountains, but mostly subjective studies have characterized
these factors. A broad-scale perspective may shed new light on the status of aspen in the region. We collected field measurements
of aspen (Populus tremuloides Michx.) patches encountered within 36 randomly located belt transects in 340 km2 of Rocky Mountain National Park, Colorado, to quantify the aspen population. Aspen covered 5.6% of the area in the transects,
much more than expected based on previously collected remotely sensed data. The distribution and structure of aspen patches
were highly heterogeneous throughout the study area. Of the 123 aspen patches encountered in the 238 ha surveyed, all but
one showed signs of elk browsing or had conifer species mixed with the aspen stems. No significant difference occurred in
aspen basal area, density, regeneration, browsing of regeneration and patch size, between areas of concentrated elk use (elk
winter range) and areas of dispersed elk use (elk summer range). Two-thirds of the aspen patches were mixed with conifer species.
We concluded that the population of aspen in our study area is highly variable in structure and that, at a landscape-scale,
evidence of elk browsing is widespread but evidence of aspen decline is not.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
We evaluated the effects of aspen patch area and orientation (relative to North and an elevational gradient) on the early
breeding season abundance and species richness of migratory and resident birds in the northern ungulate winter range of the
Yellowstone ecosystem, USA. Using an information-theoretic model selection approach, we found patch area and basal area of
aspen to be the most important covariates for long distance migrants, and patch orientation relative to elevational gradient
the most important covariate for residents/short-distance migrants. Basal area of live aspen and aspen snags was marginally
important for both migratory strategies, likely because aspen snags are an important habitat for most cavity-nesting species.
Landscape ecological theory postulates passive interception of dispersing or migrating organisms by patches of suitable habitat.
Our results suggest that residents/short-distance migrants are intercepted by patches that are oriented perpendicular to the
elevational gradient of our study region resulting in greater abundances and species richness in those patches. However, long-distance
migrants appear to use aspen patches without regard to orientation, but rather to patch area. 相似文献
3.
Tania Schoennagel Monica G. Turner Daniel M. Kashian Andrew Fall 《Landscape Ecology》2006,21(8):1281-1296
A probabilistic spatial model was created based on empirical data to examine the influence of different fire regimes on stand
structure of lodgepole pine (Pinus contorta var. latifolia) forests across a >500,000-ha landscape in Yellowstone National Park, Wyoming, USA. We asked how variation in the frequency
of large fire events affects (1) the mean and annual variability of age and tree density (defined by postfire sapling density
and subsequent stand density) of lodgepole pine stands and (2) the spatial pattern of stand age and density across the landscape.
The model incorporates spatial and temporal variation in fire and serotiny in predicting postfire sapling densities of lodgepole
pine. Empirical self-thinning and in-filling curves alter initital postfire sapling densities over decades to centuries. In
response to a six-fold increase in the probability of large fires (0.003 to 0.018 year−1), mean stand age declined from 291 to 121 years. Mean stand density did not increase appreciably at high elevations (1,029
to 1,249 stems ha−1) where serotiny was low and postfire sapling density was relatively low (1,252 to 2,203 stems ha−1). At low elevations, where prefire serotiny and postfire lodgepole pine density are high, mean stand densities increased
from 2,807 to 7,664 stems ha−1. Spatially, the patterns of stand age became more simplified across the landscape, yet patterns of stand density became more
complex. In response to more frequent stand replacing fires, very high annual variability in postfire sapling density is expected,
with higher means and greater variation in stand density across lodgepole pine landscapes, especially in the few decades following
large fires. 相似文献
4.
Data collected across timber harvest boundaries on nine sites within the Redwood National and State Park management area in California, USA, were used to estimate the effective size of old-growth coast redwood preserves. Fourteen variables related to stand structure and composition, wildlife habitat, and physical environment were significantly correlated to distance from the timber harvest boundary using multiple regression analysis. A maximum depth of edge influence of 200 m was determined for variables exhibiting a significant correlation to the distance from the harvest edge. A spatial analysis using ArcView indicated that 53% of the old growth preserved within the study area was influenced by edge conditions, leaving 47% as effective old-growth.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献