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991.
Faith R.?KearnsEmail author N. Maggi?Kelly James L.?Carter Vincent H.?Resh 《Landscape Ecology》2005,20(1):113-125
Freshwater research and management efforts could be greatly enhanced by a better understanding of the relationship between landscape-scale factors and water quality indicators. This is particularly true in urban areas, where land transformation impacts stream systems at a variety of scales. Despite advances in landscape quantification methods, several studies attempting to elucidate the relationship between land use/land cover (LULC) and water quality have resulted in mixed conclusions. However, these studies have largely relied on compositional landscape metrics. For urban and urbanizing watersheds in particular, the use of metrics that capture spatial pattern may further aid in distinguishing the effects of various urban growth patterns, as well as exploring the interplay between environmental and socioeconomic variables. However, to be truly useful for freshwater applications, pattern metrics must be optimized based on characteristic watershed properties and common water quality point sampling methods. Using a freely available LULC data set for the Santa Clara Basin, California, USA, we quantified landscape composition and configuration for subwatershed areas upstream of individual sampling sites, reducing the number of metrics based on: (1) sensitivity to changes in extent and (2) redundancy, as determined by a multivariate factor analysis. The first two factors, interpreted as (1) patch density and distribution and (2) patch shape and landscape subdivision, explained approximately 85% of the variation in the data set, and are highly reflective of the heterogeneous urban development pattern found in the study area. Although offering slightly less explanatory power, compositional metrics can provide important contextual information. 相似文献
992.
Florent?MouillotEmail author Jean-Pierre?Ratte Richard?Joffre David?Mouillot and ?Serge Rambal 《Landscape Ecology》2005,20(1):101-112
Two hundred years of landscape changes were studied on a 3,760 ha area of central Corsica (France) representing a typical Mediterranean environment. Different historical sources, including an accurate land-cover map from 1774 and statistics on land cover from 1848 and 1913, were used. Three additional maps (1960, 1975 and 1990) were drawn, and a complete fire history from 1957 to 1997 was created. Forests expanded slowly by a border effect. Forest expansion was more rapid in unburnt sites (0.59% per year) than in burnt sites (0.23% per year), mostly because the initial amount of forests was greater. Because of the border effect, the combination of past landscape pattern and short distance colonization abilities of forest species may have allowed the shrublands to persist in some places after land abandonment. This persistence may explain the pattern of fire in the landscape, since shrubland burn more readily than forests. 相似文献
993.
Maria C.S.?NunesEmail author Maria J.?Vasconcelos José M.C.?Pereira Nairanjana?Dasgupta Richard J.?Alldredge Francisco C.?Rego 《Landscape Ecology》2005,20(6):661-673
The purpose of this study is to investigate if, or under what conditions, fires select given land cover types for burning.
If fires burn unselectively then the land cover composition (the proportional area of various land cover types) of individual
fires should approximate the land cover composition available in their neighborhood. In this study we test this hypothesis
by performing statistical analyses of a data set consisting of paired vectors with the proportions of land cover types present
in burned areas and in their respective surroundings. The statistical methods employed (a permutation technique and the Cmax statistic) are commonly used in resource selection studies where data is subject to a unit-sum constraint. The results of
the analysis of 506 fires that burned in Portugal in 1991 indicate that fires are selective, with small fires exhibiting stronger
land cover preferences than large fires. According to the results of a multiple comparison analysis performed for small fires,
there is a marked preference for shrubland followed by other forest cover types, while agriculture is clearly avoided. A similar
analysis is performed to test if fire selectivity is related to the ecological region where it occurs. The results obtained
in this study contribute to the discussion on the relative importance of fuels as a drivers of fire spread. 相似文献
994.
It is reasonable to assume that there is a relationship between the spatial distribution of forest fuels and fire hazards.
Therefore, if fire risk is to be included into numerical forest planning, the spatial distribution of risky and non-risky
forest stands should be taken into account. The present study combines a stand-level fire risk model and landscape level optimization
to solve forest planning problems in which the fire risk plays an important role. The key point of the method was to calculate
forest level fire resistance metrics from stand level indices and use these metrics as objective variables in numerical optimization.
This study shows that maximizing different landscape metrics produces very different landscape configurations with respect
to the spatial arrangement of resistant and risky stands. The landscapes obtained by maximizing different metrics were tested
with a fire spread simulator. These tests suggested that the mean fire resistance of the landscape, which is a non-spatial
metric, is the most important factor affecting the burned area. However, spatial landscape metrics that decrease the continuity
of fire resistance in the landscape can significantly improve the fire resistance of the landscape when used as additional
objective variables. 相似文献
995.
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997.
In animal systems, several methods exist for the direct delivery of nucleic acids and proteins into cells for functional analysis.
Until recently, these methods have not been applied to plant systems. Now, however, several preliminary reports suggest that
both nucleic acids and proteins can also be delivered into plant cells by very simple, direct application. This promises to
open the way for high-throughput screening for gene function in a range of plant species. 相似文献
998.
Background
Eukaryotic organisms are defined by the presence of a nucleus, which encloses the chromosomal DNA, and is characterized by its DNA content (C-value). Complex eukaryotic organisms contain organs and tissues that comprise interspersions of different cell types, within which polysomaty, endoreduplication, and cell cycle arrest is frequently observed. Little is known about the distribution of C-values across different cell types within these organs and tissues. 相似文献999.
Since the first report of wheat transformation by Agrobacterium tumefaciens in 1997, various factors that influence T-DNA delivery and regeneration in tissue culture have been further investigated
and modified. This paper reviews the current methodology literature describing Agrobacterium transformation of wheat and provides a complete protocol that we have developed and used to produce over one hundred transgenic
lines in both spring and winter wheat varieties. 相似文献
1000.
Guillemette?Garry Alberto?Salas Gregory?A.?ForbesEmail author Wilmer?Perez Magnolia?Santa?Cruz Rebecca?J.?Nelson 《European journal of plant pathology / European Foundation for Plant Pathology》2005,113(1):71-81
To determine whether populations of Phytophthora infestans attacking wild and cultivated potatoes in the highlands of Peru are specialized on their hosts of origin, we characterized
isolates using several neutral markers, metalaxyl resistance and for aggressiveness in a detached leaf assay. One hundred
and fifty-three isolates were collected from the northern and central highlands of Peru from different potato cultivars (both
modern and native cultivars) and from different species of wild, tuber-bearing potatoes. All the isolates analyzed belonged
to one of four clonal lineages that had been described previously in Peru: EC-1, US-1, PE-3 and PE-7. The EC-1 lineage (n = 133) was dominant and present in similar frequencies on wild and cultivated potatoes. PE-3 (n = 14) was found primarily on cultivated potatoes, with only one isolate coming from a wild host. US-1 (n = 2) and PE-7 (n = 4) were rare; all but one (PE-7) occurred on wild potatoes. Isolates from the EC-1 lineage from modern cultivars were compared
in three separate detached leaf inoculation assays with EC-1 isolates from the wild potato species S. sogarandinum, S. bill-hookerii or S. huancabambense, respectively. No significant interactions between isolate type (from wild or cultivated potato) and host type (wild or cultivated)
were measured for any assay. It appears that the pathogen genotypes in the EC-1 lineage indiscriminately attack both wild
and cultivated tuber-bearing solanaceous hosts in Peru, and breeders should be able to select for resistance using the common
EC-1 lineage. 相似文献