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Different Land Uses (different + land_use)
Selected AbstractsRecovery of a Subtropical Dry Forest After Abandonment of Different Land Uses,BIOTROPICA, Issue 3 2006Sandra Molina Colón ABSTRACT We studied the ecological characteristics of 45,50-yr-old subtropical dry forest stands in Puerto Rico that were growing on sites that had been deforested and used intensively for up to 128 yr. The study took place in the Guánica Commonwealth Forest. Our objective was to assess the long-term effects of previous land use on this forest,i.e., its species composition, structure, and functioning. Previous land-use types included houses, farmlands, and charcoal pits. Stands with these land uses were compared with a nearby mature forest stand. The speed and path of forest recovery after deforestation and land-use abandonment depended on the conditions of the land. Study areas where land uses had removed the forest canopy and altered soil conditions (houses and farmlands) required a longer time to recover and had a different species composition than study areas where land uses retained a forest canopy (charcoal pits). Different forest attributes recovered at different rates. Crown area index, stem density, and litterfall rate recovered faster than stemwood and root, biomass, tree height, and basal area. Where previous land uses removed the canopy, Leucaena leucocephala, a naturalized alien pioneer species, dominated the regrowth. Native species dominated abandoned charcoal pits and mature forest. The change in species composition, including the invasion of alien species, appears to be the most significant long-term effect of human use and modification of the landscape. RESUMEN Estudiamos las características ecológicas de rodales de un bosque seco subtropical en Puerto Rico que tenían 45-50 años de recuperación después de haber sido usados intensamente durante 128 años. El estudio se realizó en el Bosque Estatal de Guánica. Nuestro objetivo fue el de evaluar los efectos a largo plazo de los distintos tipos de usos del terreno en la composición de especies, la estructura y el funcionamiento. Los usos de terreno en el pasado incluyeron viviendas, terrenos agrícolas y carboneras. Estos rodales fueron comparados con un rodal de bosque maduro en un área cercana. La rápidez de recuperación y la manera en cómo sucede depende de las condiciones del terreno después de ser abandonado. Las áreas de estudio en las que se había removido el dosel y alterado las condiciones del suelo (casas y terrenos agrícolas) necesitaron más tiempo para recuperarse y reflejaron una composición de suelo diferente a las áreas de estudio donde el dosel se mantuvo (carboneras). Los diferentes atributos forestales se recuperaban a ritmos diferentes. El índice del área foliar de la copa, la densidad de tallos y la caída de hojarasca se recuperaron más rápido que la biomasa de tallos y raíces, la altura de los árboles y el área basal. La especie pionera naturalizada, Leucaena leucocephala (Lam.) de Wit-Fabaceae, fue la especie dominante en los bosques donde se habia removido el dosel. Las especies nativas dominaban las carboneras abandonadas y el bosque maduro. El cambio en la composición de especies e incluso la invasión de especies foráneas, parece ser el efecto a largo plazo más significativo del uso humano y de la modificación del paisaje. [source] Effect of land use on some soil properties related to the risk of loss of soil phosphorusLAND DEGRADATION AND DEVELOPMENT, Issue 1 2008F. Troitiño Abstract Although land use clearly modifies soil properties, the intensity of the modifications depends on the management procedures and also on the soil properties themselves. To enable construction of models that describe soil nutrient losses, extensive databases corresponding to soils under different land use must be made available. Analysis of 404 samples of soils (from Galicia, NW Spain), under different types of use revealed that most of the soil properties underwent changes in the following order: forest use (least modified) - grassland - arable (most modified). Decreases in the contents of organic matter, extractable oxides and P-adsorption capacity followed the same order, as did increases in the contents of available P (total, inorganic and organic), P desorbed with distilled water, and degree of P saturation. In general, in all of the soils, independently of their use, the amount of P desorbed (whether total P, molybdate reactive P or particulate P) was more closely related to the degree of P saturation than to the levels of P extracted with bicarbonate. Copyright © 2007 John Wiley & Sons, Ltd. [source] Evaluation of the PESERA model in two contrasting environmentsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2009F. Licciardello Abstract The performance of the Pan-European Soil Erosion Risk Assessment (PESERA) model was evaluated by comparison with existing soil erosion data collected in plots under different land uses and climate conditions in Europe. In order to identify the most important sources of error, the PESERA model was evaluated by comparing model output with measured values as well as by assessing the effect of the various model components on prediction accuracy through a multistep approach. First, the performance of the hydrological and erosion components of PESERA was evaluated separately by comparing both runoff and soil loss predictions with measured values. In order to assess the performance of the vegetation growth component of PESERA, the predictions of the model based on observed values of vegetation ground cover were also compared with predictions based on the simulated vegetation cover values. Finally, in order to evaluate the sediment transport model, predicted monthly erosion rates were also calculated using observed values of runoff and vegetation cover instead of simulated values. Moreover, in order to investigate the capability of PESERA to reproduce seasonal trends, the observed and simulated monthly runoff and erosion values were aggregated at different temporal scale and we investigated at what extend the model prediction error could be reduced by output aggregation. PESERA showed promise to predict annual average spatial variability quite well. In its present form, short-term temporal variations are not well captured probably due to various reasons. The multistep approach showed that this is not only due to unrealistic simulation of cover and runoff, being erosion prediction also an important source of error. Although variability between the investigated land uses and climate conditions is well captured, absolute rates are strongly underestimated. A calibration procedure, focused on a soil erodibility factor, is proposed to reduce the significant underestimation of soil erosion rates. Copyright © 2009 John Wiley & Sons, Ltd. [source] Organophosphorus pesticides in storm-water runoff from southern California (USA)ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2004Kenneth Schiff Abstract Large quantities of the organophosphorus (OP) pesticides diazinon and chlorpyrifos are applied to California (USA) watersheds every year, but few data are available on the sources of OP pesticides in urban watersheds. The goal of this study was to characterize diazinon and chlorpyrifos concentrations from different land uses indicative of source categories in urban southern California watersheds. This characterization included analysis of 128 runoff samples from eight different land uses over five storm events. Diazinon was consistently detected (93% of samples) during this study, whereas chlorpyrifos was not consistently detected (12% of samples). The mixed agricultural land use had the highest flow weighted mean (FWM) concentration of diazinon (4,076 ng/L), which exceeded the next-highest land-use categories (commercial and residential) by one to two orders of magnitude (324,99 ng/L, respectively). Open space had the lowest concentration of diazinon (<20 ng/L). Concentrations of diazinon at replicate land-use sites and during replicate storm events at the same site were highly variable. The difference in diazinon FWM concentrations among replicate sites ranged from 1.5-fold to 45-fold. The difference in diazinon FWM concentrations among storms at the same site ranged from 1.25-fold to 30-fold. Part of this variability is a response to the temporal patterns observed within a storm event. The majority of land-use site-events had peak concentrations before peak flow indicating a first-flush effect, but this was not always a predictable temporal trend. The first-flush effect was rarely evident in terms of mass loadings because flows can range orders of magnitude during a single event in highly impervious urban watersheds. Flow variability thus overwhelms the variability in diazinon concentrations attributable to the first-flush effect. [source] Factors controlling the partitioning of pyrene to dissolved organic matter extracted from different soilsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2005B. Marschner Summary The mobility of hydrophobic organic compounds (HOCs) in soils can be influenced by the presence of dissolved organic matter (DOM). While numerous studies have determined interactions of HOCs with humic and fulvic acids, only few data exist on the partitioning of HOCs to natural, non-fractionated DOM as it occurs in soil solutions. In this study, DOM was extracted from 17 soil samples with a broad range of chemical and physical properties, originating from different land uses. The partition coefficients of pyrene to DOM were determined in all soil extracts and for two commercial humic acids using the fluorescence quenching method. For the soil extracts, log KDOC values ranged from 3.2 to 4.5 litres kg,1. For the Aldrich and Fluka humic acids, log KDOC was 4.98 and 4.96 litres kg,1, respectively, thus indicating that they are not representative for soil DOM. After excluding these two values, the statistical analysis of the data showed a significant negative correlation between log KDOC and pH. This was also shown for one sample where the pH was adjusted to values ranging from 3 to 9. A multiple regression analysis suggested that ultraviolet absorbance at 280 nm (an indicator for aromaticity) and the E4:E6 ratio (an indicator for molecular weight) had additional effects on log KDOC. The results indicate that the partitioning of pyrene to DOM is reduced at alkaline pH, probably due to the increased polarity of the organic macromolecules resulting from the deprotonation of functional groups. Only within a narrow pH range was the KDOC of pyrene mainly related to the aromaticity of DOM. [source] Land use affects the relationship between species diversity and productivity at the local scale in a semi-arid steppe ecosystemFUNCTIONAL ECOLOGY, Issue 5 2006Z. ZHOU Summary 1The accelerating extinction rate of plant species and its effect on ecosystem functioning is a hotly debated topic in ecological research. Most research projects concerning the relationship between species diversity and productivity have been conducted in artificial plant communities, with only a few in natural ecosystems. In this study we examined the relationship between species diversity and above-ground net primary productivity (ANPP) over two consecutive growth seasons (2004 and 2005) in a semi-arid steppe ecosystem of northern China, that were subjected to different land uses. 2Land use affected the relationship between species diversity and ANPP in this semi-arid steppe ecosystem. Exclusion of grazing without or with biomass removal by mowing increased ANPP, species richness and species diversity compared with free grazing; the effect was reflected mainly as enhanced importance of the perennial forbs functional group in terms of their relative contributions to ANPP, plant cover and plant abundance. 3Many mechanisms regulate the relationship between species diversity and productivity. Differential effects of anthropogenic activities on biodiversity and ecosystem functioning greatly complicate the analysis of such relationships. On grazing-exclusion sites the relationship between ANPP and species richness can be best described as an exponential growth function (R2 = 0·99, P < 0·001, n = 24); whereas on the free-grazing site the relationship takes the form of exponential decay (R2 = 0·96, P < 0·001, n = 24). Our study concludes that the mode and severity of disturbance are important factors for interpreting the relationship between species diversity and productivity in semi-arid steppe ecosystems. [source] Net regional ecosystem CO2 exchange from airborne and ground-based eddy covariance, land-use maps and weather observationsGLOBAL CHANGE BIOLOGY, Issue 3 2007F. MIGLIETTA Abstract Measurements of regional net ecosystem exchange (NEE) were made over a period of 21 days in summer 2002 in the South-Central part of the Netherlands and extrapolated to an area of 13 000 km2 using a combination of flux measurements made by a Sky Arrow ERA research aircraft, half-hourly eddy covariance data from four towers, half-hourly weather data recorded by three weather stations and detailed information on regional land use. The combination of this type of information allowed to estimate the net contribution of the terrestrial ecosystems to the overall regional carbon flux and to map dynamically the temporal and spatial variability of the fluxes. A regional carbon budget was calculated for the study period and the contributions of the different land uses to the overall regional flux, were assessed. Ecosystems were, overall, a small source of carbon to the atmosphere equivalent to to 0.23±0.025 g C m,2 day,1. When considered separately, arable and grasslands were a source of, respectively, 0.68±0.022 and 1.28±0.026 g C m,2 day,1. Evergreen and deciduous forests were instead a sink of ,1.42±0.015 g C m,2 day,1. During the study period, forests offset approximately 3.5% of anthropogenic carbon emission estimates obtained from inventory data. Lacking of a robust validation, NEE values obtained with this method were compared with independent state of art estimates of the regional carbon balance that were obtained by applying a semi-empirical model of NEE driven by MODIS satellite fAPAR data. The comparison showed an acceptable matching for the carbon balance of forest that was a sink in both cases, while a much larger difference for arable and grassland was found. Those ecosystems were a sink for satellite-based estimates while they were a source for the combined aircraft and tower estimates. Possible causes of such differences are discussed and partly addressed. The importance of new methods for determining carbon balance at the regional scale, is outlined. [source] Long-term land-cover changes in the Belgian Ardennes (1775,1929): model-based reconstruction vs. historical mapsGLOBAL CHANGE BIOLOGY, Issue 7 2002C. C. Petit Abstract Understanding long-term human-environment interactions requires historical reconstruction of past land-cover changes. The objective of this study is to reconstruct past land-use and land-cover changes in a rural municipality of the Belgian Ardennes over the last 250 years. Two approaches were compared. The first approach produced backward projections based on a mechanistic model which computes the demand for different land uses under the assumption of an equilibrium between the production and consumption of resources. The second approach involved using a series of historical maps to extract directly land-use areas. A stochastic Markov chain model was also used to project backward missing land-cover data in the time series. The consistency between the results obtained with the different approaches suggests that land-use area can be successfully reconstructed on the basis of the mechanistic model, under conditions of a subsistence farming system and a closed economy. Land-use/cover changes in the Belgian Ardennes from 1775 to 1929 were more driven by the interventionist measures of the Belgian government and by technological progress than by the ,pressure' of the growing population and livestock. Thanks to agricultural intensification, a decrease in land under human use was supporting increasing human and livestock populations from 1846 to 1880. Reforestation has accelerated since the mid-19th century. This case study illustrates the highly dynamic and non-linear character of land-use change trajectories over long time periods and their strong interactions with the history of societies. [source] Effects of Land Use on Ground Water Quality in the Anoka Sand Plain Aquifer of MinnesotaGROUND WATER, Issue 4 2003Michael D. Trojan We began a study, in 1996, to compare ground water quality under irrigated and nonirrigated agriculture, sewered and nonsewered residential developments, industrial, and nondeveloped land uses. Twenty-three monitoring wells were completed in the upper meter of an unconfined sand aquifer. Between 1997 and 2000, sampling occurred quarterly for major ions, trace inorganic chemicals, volatile organic compounds (VOCs), herbicides, and herbicide degradates. On single occasions, we collected samples for polynuclear aromatic hydrocarbons (PAHs), perchlorate, and coliform bacteria. We observed significant differences in water chemistry beneath different land uses. Concentrations of several trace inorganic chemicals were greatest under sewered urban areas. VOC detection frequencies were 100% in commercial areas, 52% in sewered residential areas, and <10% for other land uses. Median nitrate concentrations were greatest under irrigated agriculture (15,350 ,g/L) and nonsewered residential areas (6080 ,g/L). Herbicides and degradates of acetanilide and triazine herbicides were detected in 86% of samples from irrigated agricultural areas, 68% of samples from nonirrigated areas, and <10% of samples from other land uses. Degradates accounted for 96% of the reported herbicide mass. We did not observe seasonal differences in water chemistry, but observed trends in water chemistry when land use changes occurred. Our results show land use is the dominant factor affecting shallow ground water quality. Trend monitoring programs should focus on areas where land use is changing, while resource managers and planners must consider potential impacts of land use changes on ground water quality. [source] Assessing the impacts of fire on the vegetation resources that are available to the local communities of the seasonal wetlands of the Okavango, Botswana, in the context of different land uses and key government policiesAFRICAN JOURNAL OF ECOLOGY, Issue 2009Budzanani Tacheba Abstract The Okavango wetlands in north western Botswana are the most fire-prone environment in Botswana. Most of these fires are anthropogenic. The fires in this environment are thought to impact the environment negatively and therefore practices that are associated with extensive use of fire have been strongly criticized. Despite this, there has been little work done to understand how these fires impact the wetlands environment and its dynamics, especially the vegetation resources that are used by the local communities in the wetlands. The objective of the study was to identify fire spatial and temporal trends in relation to settlement distribution, through the use of remote sensing, socio-economic and phytosociological surveys. The fire history results show that geographically there has not been any significant change in vegetation structure and that in fact fires may have promoted biodiversity. The results of analysis show an overall variance on vegetation structure of 23% whereas the rest are unaccounted for. There is a strong association between settlements, ethnicities, literacy and fire occurrences. The most fire-prone areas are inhabited by communities that have used fire in the past for various resource use practices. [source] Sensitivity of different taxonomic levels of soil Gamasina to land use and anthropogenic disturbancesAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 2 2010José Camilo Bedano 1The effect of taxonomic level on the sensitivity of bioindicators has been widely investigated in aquatic ecosystems and, to a lesser extent, in terrestrial ecosystems. However, no studies have been conducted on the sensitivity of the different taxonomic levels of soil mites, especially Gamasina, to human activities. 2The present study aimed to assess the sensitivity of different taxonomic levels of soil Gamasina mites to anthropogenic disturbances in Europe and Argentina. We arranged the data from previous projects in a hierarchical system and conducted a study to identify the critical taxonomical levels that had the highest discriminative potential between sites (Europe and Argentina) or management types (forests, grasslands, fallows, succession, recultivation and agricultural sites). 3For the Gamasina community, geographical location was by far more important than the influence of any land use type. The analysis including only the European sites demonstrated that communities belonging to sites subjected to different land uses were also significantly different. 4The species data set provided a clearer separation of sites according to both the geographical and the land-use gradients than the genus and family data sets. The genus and, to a lesser extent, the family approach may be sufficient to elucidate the influence of great geographical differences and also of certain land uses (e.g. grasslands from the forests and arable sites). 5Species presence/absence data provided valuable information in our analyses, although the use of quantitative data yielded a clearer separation of sites. [source] Effect of Cloud Cover on UVB Exposure Under Tree Canopies: Will Climate Change Affect UVB Exposure?PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2006Richard H. Grant ABSTRACT The effect of cloud cover on the amount of solar UV radiation that reaches pedestrians under tree cover was evaluated with a three-dimensional canopy radiation transport model. The spatial distribution of UVB irradiance at the base of a regular array of spherical tree crowns was modeled under the full range of sky conditions. The spatial mean relative irradiance (I), and erythemal irradiance of the entire below-canopy domain and the spatial mean relative irradiance and erythemal irradiance in the shaded regions of the domain were determined for solar zenith angles from 15° to 60°. The erythemal UV irradiance under skies with 50% or less cloud cover was not remarkably different from that under clear skies. In the shade, the actual irradiance was greater under partly cloudy than under clear skies. The mean ultraviolet protection factor for tree canopies under skies with 50% or less cloud cover was nearly equivalent to that for clear sky days. Regression equations of spatially averaged Ir. as a function of cloud cover fraction, solar zenith angle and canopy cover were used to predict the variation in erythemal irradiance in different land uses across Baltimore, MD. [source] | |||||||||||||