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Patch Scale (patch + scale)

Distribution by Scientific Domains

Life Sciences	40%
Earth and Environmental Science	40%

Selected Abstracts

The role of vegetation patterns in structuring runoff and sediment fluxes in drylands

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2005
Juan Puigdefábregas
Abstract The dynamics of vegetation-driven spatial heterogeneity (VDSH) and its function in structuring runoff and sediment fluxes have received increased attention from both geomorphological and ecological perspectives, particularly in arid regions with sparse vegetation cover. This paper reviews the recent findings in this area obtained from field evidence and numerical simulation experiments, and outlines their implications for soil erosion assessment. VDSH is often observed at two scales, individual plant clumps and stands of clumps. At the patch scale, the local outcomes of vegetated patches on soil erodibility and hydraulic soil properties are well established. They involve greater water storage capacity as well as increased organic carbon and nutrient inputs. These effects operate together with an enhanced capacity for the interception of water and windborne resources, and an increased biological activity that accelerates breakdown of plant litter and nutrient turnover rates. This suite of relationships, which often involve positive feedback mechanisms, creates vegetated patches that are increasingly different from nearby bare ground areas. By this way a mosaic builds up with bare ground and vegetated patches coupled together, respectively, as sources and sinks of water, sediments and nutrients. At the stand scale within-storm temporal variability of rainfall intensity controls reinfiltration of overland flow and its decay with slope length. At moderate rainfall intensity, this factor interacts with the spatial structure of VDSH and the mechanism of overland flow generation. Reinfiltration is greater in small-grained VDSH and topsoil saturation excess overland flow. Available information shows that VDSH structures of sources and sinks of water and sediments evolve dynamically with hillslope fluxes and tune their spatial configurations to them. Rainfall simulation experiments in large plots show that coarsening VDSH leads to significantly greater erosion rates even under heavy rainfall intensity because of the flow concentration and its velocity increase. Copyright © 2005 John Wiley & Sons, Ltd. [source]

The effects of an underwater fish observation technique on stream macroinvertebrates at two spatial scales

ECOLOGY OF FRESHWATER FISH, Issue 3 2000
J. T. Petty
Abstract , We examined the effects of snorkeling, a commonly used fish observation technique, on the distribution and abundance of benthic macroinvertebrates at both the reach (i.e., 10 m) and patch scale (i.e.,< 1 m) within a southern Appalachian stream (North Carolina, USA). At the reach scale, we quantified increases in macroinvertebrate drift rates associated with snorkeling and used these values to calculate the percentage of the macrobenthos that drifted out of snorkeled reaches. We also used a simple decay model of macroinvertebrate drift to quantify patch scale effects of snorkeling. The model incorporated size specific macroinvertebrate settling rates to estimate the total number of benthic macroinvertebrates that entered the drift in response to snorkeling disturbance. We found that snorkeling consistently produced significant increases in the number of drifting macroinvertebrates. Nevertheless, these increases comprised a very small percentage (<1%) of the total number of organisms in the benthos, suggesting that snorkeling probably did not strongly affect macroinvertebrate assemblages at either the reach or patch scale. However, our analyses also indicated that snorkeling had a disproportionate effect on the drift of small ephemeropterans (4,5% entered the drift in response to snorkeling) relative to other macroinvertebrate taxa. Consequently, the microdistribution of early instar mayflies may have been altered within snorkeled reaches. We conclude that snorkeling related disturbance to the benthos should have a minimal effect on the behavior and distribution of most stream fishes at either the reach or patch scale. However, because snorkeling had a substantial effect on the drift of small mayflies, snorkeling may influence the behavior of fishes that depend on early instar mayflies as a primary food resource., [source]

Effects of invasive woody plants on avian nest site selection and nesting success in shrublands

ANIMAL CONSERVATION, Issue 3 2010
S. Schlossberg
Abstract Exotic, invasive plants are a growing conservation problem. Birds frequently use invasive plants as nest substrates, but effects of invasives on avian nesting success have been equivocal in past studies. In 2004 and 2005, we assessed effects of invasive woody plants on avian nest-site selection and nesting success in western Massachusetts shrublands. At the nest scale, we tested the effects of invasive versus native substrates on nesting success as well as differences among individual invasive species. At the patch scale, we tested effects of invasive prevalence on nesting success in natives and invasives. We found that, as a whole, shrubland birds preferred invasive substrates. Of two species sufficiently abundant for individual analysis, gray catbirds Dumetella carolinensis preferred invasive substrates, but chestnut-sided warblers Dendroica pensylvanica showed no preference for natives or invasives. At the nest scale, nests of gray catbirds placed in invasive substrates were more successful than those in natives. Chestnut-sided warblers and all species combined, however, had equal nest success in invasives and natives. We found no differences in nest success for nests in different species of invasive substrates or in invasive substrates with and without thorns. At the scale of the patch, nest success in invasive substrates increased with the prevalence of invasives on a site. Nest success in native plants did not change with invasive prevalence. We attribute this finding to the tendency for thickets of invasive plants to be larger on sites with more invasive cover. These findings illustrate the complex interaction of different factors that can determine how invasive plants affect avian nesting success. We conclude that control of invasive woody plants should be neutral for most shrubland birds. [source]

Effects of pioneer shrubs on the recruitment of the fleshy-fruited tree Olea europaea ssp. cuspidata in Afromontane savanna

APPLIED VEGETATION SCIENCE, Issue 1 2006
Raf Aerts
Abstract Question: Is seedling recruitment of a fleshy-fruited tree in degraded Afromontane savanna dependent on shelter from pioneer shrubs, and is shelter availability related to shrub traits? Location: Degraded montane savanna in northern Ethiopia (13°36,N, 39°21,E). Method: Nurse plants of Olea europaea ssp. cuspidata seedlings were recorded using T-square plotless sampling and clustered according to shrub traits, using Ward's method after Principal Components Analysis. Facilitation was further examined through experimental planting and Kaplan-Meier survival analysis. Results: Both in grazed and protected areas, Olea recruits were found exclusively under shrubs, primarily under Euclea racemosa although Acacia etbaica was more abundant. Olea recruitment is distributed randomly at landscape scale, but depends on shelter at patch scale. Shelter ability is related to shrub shape and species identity. Dense multi-stemmed shrubs with a wide base and crown on a mulch-rich mound are key recruitment foci. Euclea shrubs have these favoured traits and probably act as preferential perching sites for avian seed dispersers. Soil and organic matter accumulation under Euclea shrubs may also create favourable conditions for Olea germination and survival. Experimentally planted seedlings had a better chance for survival under Euclea. Conclusions:Olea regeneration is probably subject to both passive (disperser-mediated) and active facilitation. Small changes of shrub traits can alter the suitability of a patch for Olea recruitment. Protection of shrubs can increase facilitation for seedlings, while pruning may reduce competition for saplings and thus enhance forest succession. Planting of raised Olea seedlings under Euclea shrubs in years with a good rainy season may further assist forest restoration. [source]

Spatial distribution of canine faeces in Buenos Aires suburbs: implications for public health

AREA, Issue 3 2009
Mayra Milkovic
Canine faecal contamination contributes to environmental degradation and increases the exposure of humans , mainly children , to helminth infections. We studied the magnitude and spatial distribution of faecal contamination on the pavements of two neighbourhoods representative of Buenos Aires suburbs. The pavements of a low-income neighbourhood (LIN) and a middle-income neighbourhood (MIN) were selected at random. Field maps including all substrates and objects observed on each pavement were drawn, viewed from above, on millimetre paper at 1:100 scale. Data were then loaded into a geographic information system (GIS) Arc View 3.1 with a digitiser board. The spatial distribution of faeces and its association with substrates or standing elements were analysed at three scales: substrate, pavement and neighbourhood. Permeable substrate cover was higher in LIN (75%) than in MIN (35%). The faeces were not homogeneously distributed on the substrates. In both neighbourhoods, the substrates with >50 per cent grass cover showed a significantly higher proportion of faeces than those with <50 per cent grass cover, bare soil and tile. At pavement scale, the number of faeces on pavements was not related to either the number of trees, posts and domiciled dogs in the block, or with the number of faeces and percentage cover of each substrate. At patch scale, substrate patches with faeces were larger than those without faeces. Patches with faeces did not differ in shape between neighbourhoods and were more regularly shaped than patches without faeces. The spatial distribution of faeces relative to each other was almost random, even when analysed in relation to trees or standing objects. Strategies for the sustainable control of this problem are suggested. [source]