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1.
Simulation of vegetation dynamics and management strategies on south Texas, semi-arid rangeland 总被引:1,自引:0,他引:1
In this paper, we describe a model designed to simulate seasonal dynamics of warm and cool season grasses and forbs, as well as the dynamics of woody plant succession through five seral stages, in each of nine different plant communities on the Rob and Bessie Welder Wildlife Refuge. The Welder Wildlife Refuge (WWR) is located in the Gulf Coastal Prairies and Marshes ecoregion of Texas. The model utilizes and integrates data from a wide array of research projects that have occurred in south Texas and WWR. It is designed to investigate the effects of alternative livestock grazing programs and brush control practices, with particular emphasis on prescribed burning, the preferred treatment for brush on the WWR. We evaluated the model by simulating changes in the plant communities under historical (1974-2000) temperature, rainfall, livestock grazing rotation, and brush control regimes, and comparing simulation results to field data on herbaceous biomass and brush canopy cover collected on the WWR over the same period. We then used the model to simulate the effects of 13 alternative management schemes, under each of four weather regimes, over the next 25 years. We found that over the simulation period, years 1974-2000, the model does well in simulating the magnitude and seasonality of herbaceous biomass production and changes in percent brush canopy cover on the WWR. It also does well in simulating the effects of variations in cattle stocking rates, grazing rotation programs, and brush control regimes on plant communities, thus providing insight into the combined effects of temperature, precipitation, cattle stocking rates, grazing rotation programs, and brush control on the overall productivity and state of woody plant succession on the WWR. Simulation of alternative management schemes suggests that brush canopy removal differs little between summer and winter prescribed burn treatments when precipitation remains near the long-term average, but during periods of low precipitation canopy removal is greater under winter prescribed burning. The model provides a useful tool to assist refuge personnel with developing long-term brush management and livestock grazing strategies. 相似文献
2.
Use and knowledge of fuelwood in three rural caatinga (dryland) communities in NE Brazil 总被引:1,自引:0,他引:1
I. M. M. Sá e Silva L. C. Marangon N. Hanazaki U. P. Albuquerque 《Environment, Development and Sustainability》2009,11(4):833-851
The woody species known, used, and preferred as fuelwood were examined in three rural communities within the county of Soledade,
Paraíba State, NE Brazil. Ethnobotanical information was collected using semi-structured interviews with more than 90% of
the local households (55 adult residents; 31 women, and 24 males). The interviewees cited 36 plant species as fuelwoods, distributed
among 30 genera and 15 families, in addition to two unidentified plants. The plant families represented by the largest numbers
of species were Euphorbiaceae, Anacardiaceae, Mimosaceae, Caesalpiniaceae, Sapotaceae, and Fabaceae. The species Caesalpinia pyramidalis Tul. (“catingueira”) was cited with the greatest frequency in all three communities. Within the communities we found significant
differences on the number of plants cited and actually used (p < 0.05), indicating that the residents knew more fuelwood species than they effectively harvest. The different distances
from the communities to the urban centers were not related to differences on the use or the size of the stocks of fuelwood.
Additionally, the study revealed that the communities examined still maintain a significant knowledge of the use of energy-providing
plants in spite of the widespread use of liquefied petroleum gas (LPG).
Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue. 相似文献
3.
The study focuses on evaluating factors that farmers consider relevant in adopting cassava production in five semi-arid zone
of West African countries. The study is based on primary data randomly collected as part of collaborative study of cassava
in semiarid zones of Africa (COSCASSA) village level survey from five West African countries namely: Nigeria, Ghana, Chad,
Niger and Burkina Faso. This study models effects of farm, farmer and technology specific factors on the decision of semi
arid farmers to adopt cassava into their farming system. By way of threshold decision models—Probit and Logit models, the
estimation of each country and the pooled data adoption models reveal different adoption models for the countries considered.
For each country, different variables appeared as major adoption shifters. Comparatively, the adoption models for Nigeria
and whole region appear to have the highest significance variables, being seven in number. This is followed by Chad (6), Ghana
(4), and Burkina Faso and Niger with three each. For the variables considered, distance to nearby urban market appears a major
adoption shifter in all the country, except for Niger. This is closely followed by contact with extension, variety, pest/disease
resistance and livestock feeds, which appear significant in four of the countries. Membership of cooperative societies appears
as the least adoption predictor, which is only significant in Chad republic. The study therefore recognizes the importance
of varietial characteristics and farmers’ characteristics in acceptance of cassava as a major root tuber crop in the semi
arid region of West Africa.
Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue. 相似文献
4.
Fresh water, a fundamental element of all estuarine ecosystems, is South Africa’s most limited natural resource. Recent projections
indicate that by the year 2020 the country will be utilizing all its exploitable freshwater sources. Steeply increasing demands
by a rapidly growing population on this limited commodity have already resulted in a severe reduction of water supplies to
natural users such as estuaries-this trend is predicted to increase in the future. Concurrent with excesive water abstraction,
poor land husbandry (e.g. soil erosion) in many catchment basins and pollution (e.g. salinization) in return flows have led
to a serious deterioration in water quality. In contrast, a review of estuarine responses to varying flow regimes stresses
the strong dependence of local systems on riverine fresh water inputs of adequate quantity and quality. Freshwater dependence
is i.a. expressed in: flooding events that scour accumulated sediments, riverine nutrient input to drive estuarine phyto-
and zooplankton production, axial salinity gradients that increase habitat and species diversity, and maintenance of open
tidal inlets that prevent salinity and temperature extremes and facilitate larval exchange, fish migrations and tidal flushing
of salt marshes. Thus, estuarine conservation will have to encompass management of rivers and watersheds and play an increasingly
political role in decision processes concerning water allocations among ‘human’ and ‘natural’ users. 相似文献
5.
Fresh water, a fundamental element of all estuarine ecosystems, is South Africa’s most limited natural resource. Recent projections
indicate that by the year 2020 the country will be utilizing all its exploitable freshwater sources. Steeply increasing demands
by a rapidly growing population on this limited commodity have already resulted in a severe reduction of water supplies to
natural users such as estuaries — this trend is predicted to increase in the future. Concurrent with excessive water abstraction,
poor land husbandry (e.g. soil erosion) in many catchment basins and pollution (e.g. salinization) in return flows have led
to a serious deterioration in water quality. In contrast, a review of estuarine responses to varying flow regimes stresses
the strong dependence of local systems on riverine fresh water inputs of adequate quantity and quality. Freshwater dependence
is i.a. expressed in: flooding events that scour accumulated sediments, riverine nutrient input to drive estuarine phyto-
and zooplankton production, axial salinity gradients that increase habitat and species diversity, and maintenance of open
tidal inlets that prevent salinity and temperature extremes and facilitate larval exchange, fish migrations and tidal flushing
of salt marshes. Thus, estuarine conservation will have to encompass management of rivers and watersheds and play an increasingly
political role in decision processes concerning water allocations among ‘human’ and ‘natural’ users. 相似文献
6.
Wenming Dong Jiamin Wan Tetsu K. Tokunag Benjamin Gilbert Kenneth H. Williams 《环境科学学报(英文版)》2017,29(7):24-32
In order to understand the transport and humification processes of dissolved organic matter(DOM) within sediments of a semi-arid floodplain at Rifle,Colorado,fluorescence excitation–emission matrix(EEM) spectroscopy,humification index(HIX) and specific UV absorbance(SUVA) at 254 nm were applied for characterizing depth and seasonal variations of DOM composition.Results revealed that late spring snowmelt leached relatively fresh DOM from plant residue and soil organic matter down into the deeper vadose zone(VZ).More humified DOM is preferentially adsorbed by upper VZ sediments,while non-or lesshumified DOM was transported into the deeper VZ.Interestingly,DOM at all depths undergoes rapid biological humification process evidenced by the products of microbial by-product-like(i.e.,tyrosine-like and tryptophan-like) matter in late spring and early summer,particularly in the deeper VZ,resulting in more humified DOM(e.g.,fulvic-acid-like and humic-acid-like substances) at the end of year.This indicates that DOM transport is dominated by spring snowmelt,and DOM humification is controlled by microbial degradation,with seasonal variations.It is expected that these relatively simple spectroscopic measurements(e.g.,EEM spectroscopy,HIX and SUVA) applied to depth-and temporally-distributed pore-water samples can provide useful insights into transport and humification of DOM in other subsurface environments as well. 相似文献
7.
The potential purification of an horizontal subsurface flow constructed wetlands (HSSFCW) treating greywater in a Moroccan primary school was investigated according to the monitoring of water quality parameters over a period of 100 days through two simultaneous stages: first, an internal three dimensional grid of sampling ports; secondly, an entry and exit. The calibration of the relaxed TIS concentration model based on tank in series hydraulic assumption with experimental data gave the frequency distribution profiles of K-rate constant values for the three parameters: BOD5, COD and TN, whose maximum values are respectively 50 m/yr, 70 m/yr, and 42 m/yr. The HSSFCW system has higher K-rate coefficient for all the three parameters at the bottom layer compared with the surface layer, with increasing K-rates over length. The analysis of bacteriological and chemical results has shown that the HSSFCW could not completely remove all pollutants (especially TN and TP), but it could be used successfully to upgrade the quality of greywater to an acceptable level. However, we predict that there will be an increase in removal efficiencies with time bearing in mind that the system is newly implemented. 相似文献
8.
Eutrophication and Sedimentation Patterns in Complete Exploitation of Water Resources Scenarios: An Example from Northwestern Semi-arid Mexico 总被引:1,自引:0,他引:1
Sánchez-Carrillo S Alatorre LC Sánchez-Andrés R Garatuza-Payán J 《Environmental monitoring and assessment》2007,132(1-3):377-393
Water requirements to supply human needs lead water stakeholders to store more water during surplus periods to fulfil the
demand during – not only – scarcity periods. At the reservoirs, mostly those in semi-arid regions, water level then fluctuates
extremely between rises and downward during one single year. Besides of water management implications, changes on physical,
chemical and biological dynamics of these drawdown and refilling are little known yet. This paper shows the results, throughout
a year, on solids, nutrients (N and P), chlorophyll-a, and sedimentation changes on the dynamics, when the former policy was applied in a reservoir from the semi-arid Northwestern
Mexico. Water level sinusoidal trend impinged changes on thermal stratification and mixing, modifying nutrient cycling and
primary producer responses. According to nitrogen and phosphorus concentration as well as chlorophyll-a, reservoir was mesotrophic, becoming hypertrophic during drawdown. Nutrient concentrations were high (1.22 ± 0.70 and 0.14 ± 0.12 mg
P l−1), increasing phosphorus and lowering N:P significantly throughout the study period, although no intensive agricultural, no
urban development, neither industrial activities take place in the watershed. This suggests nutrient recycling complex mechanisms,
including nutrient release from the sediment–water interface as the main nutrient pathway when shallowness, at the same time
as mineralization, increases. Outflows controlled nitrogen and phosphorus availability on the ecosystem while organic matter
depended on river inflows. As on other subtropical aquatic ecosystems, nitrogen limited primary productivity (Spearman correlation
R = 0.75) but chlorophyll-a seasonal pattern showed an irregular trend, prompting other no-nutrient related limitants. Shallowness induced a homogeneous
temporal pattern on water quality. This observed temporal variability was mainly explained statistically by changes on solids
(mineral and organic), chlorophyll-a and flows (62.3%). Annual sedimentation rates of total solids ranged from 11.73 to 16.29 kg m−2 year−1 with organic matter comprising around 30%. N:P ratio on sedimentation rates were as high as could be expected in a resuspension
dominated ecosystem, and spatially inverse related with N:P ratio on bottom sediments. Distance from river inlet into the
reservoir reveals a marked spatial heterogeneity on solid and nitrogen sedimentation, showing the system dependence on river
inflows and supporting resuspension as the main phosphorus pathway. Accretion rates (2.19 ± 0.40 cm year−1) were not related to hydrological variability but decreased with the distance to the river input. Total sediment accumulation
(9,895 tons km−2 year−1) denotes siltation as other serious environmental problem in reservoirs but possibly not related with operational procedures. 相似文献
9.
Irene Iniesta-Arandia David García del Amo Ana Paula García-Nieto Concepción Pi?eiro Carlos Montes Berta Martín-López 《Ambio》2015,44(4):285-296
Local ecological knowledge (LEK) has been found to be one of the main bridges to manage biocultural diversity. We analyzed the factors affecting LEK maintenance and transmission in a Mediterranean watershed. We used a mixed methods approach to evaluate the agricultural LEK in three different dimensions: biological, soil and water management, and forecasting. We found that the main factors for its maintenance were the respondent''s time living in the area and the social relationships established among farmers, which involved partner collaboration and farmer information exchanges. Protected areas also played a key role for maintaining the LEK associated with soil and water management. Finally, we found that outmigration and mechanization were the most important indirect drivers of change underlying LEK erosion. We suggest that environmental policies should focus on promoting this experiential knowledge, considering both intergenerational renewal and the gendered aspects of this knowledge.
Electronic supplementary material
The online version of this article (doi:10.1007/s13280-014-0556-1) contains supplementary material, which is available to authorized users. 相似文献10.
Mark Thompson Jan Vlok Mathieu Rouget M. T. Hoffman Andrew Balmford R. M. Cowling 《Environmental management》2009,43(4):585-596
Improved techniques for measuring and monitoring the state of biodiversity are required for reporting on national obligations
to international and regional conservation institutions. Measuring the extent of grazing-related degradation in semi-arid
ecosystems has proved difficult. Here we present an accurate and cost-effective method for doing this, and apply it in a South
African semi-arid region that forms part of a globally significant biodiversity hotspot. We grouped structurally and functionally
similar vegetation units, which were expert-mapped at the 1:50,000 scale, into four habitat types, and developed habitat-specific
degradation models. We quantified degradation into three categories, using differences between dry and wet season values of
the Normalized Difference Vegetation Index (NDVI) for the three succulent karoo habitats, and the difference between maximum
and mean NDVI values for the subtropical thicket habitat. Field evaluation revealed an accuracy of 86%. Overall, degradation
was high: 24% of the study area was modeled as severely degraded, and only 9% as intact. Levels of degradation were highest
for bottomland habitats that were most exposed to grazing impacts. In sharp contrast to our methods, a widely used, broad-scale
and snapshot assessment of land cover in South Africa was only 33% accurate, and it considerably underestimated the extent
of severely degraded habitat in the study area. While our approach requires a multidisciplinary team, and in particular expert
knowledge on the characteristics and spatial delimitation of vegetation types, it is repeatable, rapid, and relatively inexpensive.
Consequently, it holds great promise for monitoring and evaluation programs in semi-arid ecosystems, in Africa, and beyond. 相似文献