Amount Of Plant Cover Research Articles

Desertification risk assessment in Turkey based on environmentally sensitive areas

Turkey's many and varied landscapes face the challenge of degradation and ultimately desertification due to soil problems that include organic matter deficiency, salinity-alkalinity, compaction and erosion and the loss of biological productivity. Yet, without fully accepted indicators for the monitoring and reporting of degradation, desertification cannot be definitively confirmed at the regional or national level. Environmentally Sensitive Areas Index (ESAI) was developed to identify areas vulnerable to the threat of desertification in the “MEDALUS” (Mediterranean Desertification and Land Use) model, which was chosen as the basis for the present study. Variables and thematic indicators such as climate, soil quality, land use, amount of plant cover and management are included in the ESAI. However, studies made at international scale are not sufficiently sensitive regarding data quality for calculations and modelling at the national scale. Therefore, aim of the present study was to i) create a modelling approach that can respond to national needs for monitoring and reporting on soil and land degradation by modifying the MEDALUS method, and ii) generate a national desertification map of Turkey by assessing environmentally sensitive areas (ESAs) at the national scale using this model. Results classified more than 60% (51.5 mil. ha) of the total area as fragile and critical, while only about 12% of the Turkey’ land was indicated as area non-affected by the desertification risk. In the determination of ESAI, the parametric and spatial models were re-designed according to data and impact value by using GIS software-supported geographical analysis. With that added-on facility, MEDALUS can be automatically re-run with updated data or the change-of-influence line, and thus the change of land quality can also be monitored.

Environmental factors associated with rodent infestations in Argentine poultry farms

1. Seasonal variations in rodent infestations were studied at poultry farms in central Argentina as well as the environmental factors associated with rodent infestations at poultry farms. 2. During the summer and winter of 1998 rodent infestation was monitored at 10 poultry farms by means of tracking stations, and 21 environmental variables were selected that a priori could be related with the extent of rodent infestation. 3. There was a higher rodent infestation in winter than in summer. 4. Species detected by rodent sightings at the poultry farms included Akodon azarae, Calomys spp. (C. laucha and possibly C. musculinus) and Mus musculus. 5. In summer, rodent infestation was positively associated with the perimeter of the farm, whereas there was an inverse relationship with the maintenance conditions of the sheds. In winter, rodent infestation was positively associated with the percentage of the borders of the farm covered with vegetation, and with the amount of plant cover, especially the amount of plant cover which was above 20 cm in height. 6. There was no significant relationship between rodent infestation and the time lag since the last application of rodenticide (first-generation anticoagulant) at the farms. 7. These results suggest that strategies for controlling rodents based solely on chemical methods may not be good enough for efficient rodent control. Farms which are properly managed, with a better control of vegetation growth at both the perimeter and within the internal area, in addition to a higher maintenance of sheds have appreciably lower rodent infestations.

On the evolution of group-living in the New World cursorial hystricognath rodents

We used the comparative method to examine the evolutionary causes of group-living in the New World cursorial hystricognath rodents. To do so, we used the available literature to collect information on behavioral (group size, burrow digging), ecological (amount of plant cover in the habitat), and life history (body mass, time to sexual maturity) variables, along with phylogenetic relationships of these rodents. We analyzed these variables in the context of three major hypotheses. A first explanation poses that rodents live in groups to reduce the energy needed in the construction of their burrows. A second hypothesis suggests that grouped rodents increase their ability to detect and escape from predators. A third possibility states that group-living is adopted by rodents to provide extra parental care to their offspring. Our comparative analysis revealed that across species variation of group size is, to some extent, influenced by body size, and by the habit of burrow digging. Thus, large sized rodent species that actively dig their own burrows form larger group sizes than small sized species that do not dig burrows. In contrast, across species variation of group size was not influenced by differences in the amount of plant cover in the habitat (an indirect measure of predatory risk), or by differences in the time to first reproduction (a measure of parental care given). Therefore, group-living among the New World histricognath rodents seems more linked to a strategy aimed to reduce their burrowing cost than to a strategy aimed to reduce their predatory risk, or to extend their parental investment.

Detecting fragmentation of cover in desert grasslands using line intercept

Changes in the amount or spatial distribution of grass plants are thought to be indicative of the stability of desert grasslands. This study assessed, through simulation, the sensitivity of statistical properties for distance between plants (fetch length), measured with a line intercept transect, to changes in the spatial distribution and amount of plant cover. Monitoring plots, 30 X 30 m, were simulated for 1, 2.5, 5, 10 and 15% grass cover with random and fragmented spatial distribution. Fetch lengths were measured on 2 randomly placed 30 m transects. In addition to the median and interquartile range, the asymmetry of the sampling distributions was measured with a ratio [(maximum-median)/(median-minimum)] that would identify the presence of at least 1 large open space. The accuracy of the fetch length method was confirmed by the similarity of its sampling distribution to that for the well known random point-to-plant sampling procedure. In both the fetch length and the point-to-plant measures, the median and interquartile range increased with decreasing cover for random and fragmented distribution. The asymmetry estimate increased sharply with increasing cover for the fragmented distribution but asymmetry was nearly constant with increasing cover for the random distribution. The results suggest that the evaluation of changes over time at a monitoring site could use fetch lengths measured along a line intercept transect to detect changes in both absolute and spatial arrangement of cover.

Detecting Fragmentation of Cover in Desert Grasslands Using Line Intercept

Changes in the amount or spatial distribution of grass plants are thought to be indicative of the stability of desert grasslands. This study assessed, through simulation, the sensitivity of statistical properties for distance between plants (fetch length), measured with a line intercept transect, to changes in the spatial distribution and amount of plant cover. Monitoring plots, 30 X 30 m, were simulated for 1, 2.5, 5, 10 and 15% grass cover with random and fragmented spatial distribution. Fetch lengths were measured on 2 randomly placed 30 m transects. In addition to the median and interquartile range, the asymmetry of the sampling distributions was measured with a ratio [(maximum-median)/(median-minimum)] that would identify the presence of at least 1 large open space. The accuracy of the fetch length method was confirmed by the similarity of its sampling distribution to that for the well known random point-to-plant sampling procedure. In both the fetch length and the point-to-plant measures, the median and interquartile range increased with decreasing cover for random and fragmented distribution. The asymmetry estimate increased sharply with increasing cover for the fragmented distribution but asymmetry was nearly constant with increasing cover for the random distribution. The results suggest that the evaluation of changes over time at a monitoring site could use fetch lengths measured along a line intercept transect to detect changes in both absolute and spatial arrangement of cover. DOI:10.2458/azu_jrm_v54i1_kuehl

Rapidly assessing the 1997 drought in Papua New Guinea using composite AVHRR imagery

During 1997 Papua New Guinea (PNG) experienced an intense drought. Emergency famine relief operations provided many subsistence agricultural communities with food, water and health provisions during the height of the drought. The locations of relief operations were based on a rapid and spatially explicit extensive field survey conducted at the height of the drought for all PNG. We have tested the utility of composite Advanced Very High Resolution Radiometer (AVHRR) data to assist in a rapid assessment of drought conditions in PNG. Composited data were used to provide a means to overcome the frequent cloudy conditions that exist in PNG. To assess the drought we divided land surface temperatures (T s) by the Normalized Difference Vegetation Index (NDVI). The ratio (T s/NDVI) increases during times of drought. This is due to the increase in T s associated with more net radiation being partitioned into the sensible heat flux and the decrease in NDVI associated with decreasing amounts of plant cover. A time series of T s/NDVI is a rapid indicator of the drought at the country and province level. We calculated the integral under the T s

Factors influencing macroinvertebrate colonization of seasonal wetlands: responses to emergent plant cover

1. We conducted field experiments to examine factors influencing macroinvertebrate colonization of seasonally flooded marshes. Few macroinvertebrate species were found aestivating in soils within non‐flooded wetlands indicating that most taxa colonize these marshes from other flooded habitats. 2. We manipulated amounts of salt grass (Distichlisspicata) to examine how emergent plant cover affects aerial colonization by macroinvertebrates. Areas mowed 3 weeks before flooding had low plant cover, areas mowed 5 and 9 weeks before flooding had medium and high plant cover, respectively, and non‐mowed control areas had the most plant cover. Macroinvertebrate numbers and biomass were generally higher in mowed treatment areas than in control areas, but overall diversity was generally higher in high plant cover and control areas than in low plant cover areas. 3. Mosquitoes (Culicidae), brine flies (Ephydridae) and hover flies (Syrphidae) were positively correlated with amount of plant cover, and waterboatmen (Corixidae), midges (Chironomidae) and water scavenger beetles (Hydrophilidae) were negatively correlated with plant cover. Species assemblages changed seasonally among treatment areas because these taxa colonize wetlands at different times in the year. 4. These results demonstrate that invertebrate communities may be different within plant stands with heterogeneous amounts of emergent cover, and management practices that alter the structure of wetland vegetation can influence macroinvertebrate communities colonizing seasonal marshes.

Factors influencing macroinvertebrate colonization of seasonal wetlands: responses to emergent plant cover

1. We conducted field experiments to examine factors influencing macroinvertebrate colonization of seasonally flooded marshes. Few macroinvertebrate species were found aestivating in soils within non-flooded wetlands indicating that most taxa colonize these marshes from other flooded habitats. 2. We manipulated amounts of salt grass (Distichlisspicata) to examine how emergent plant cover affects aerial colonization by macroinvertebrates. Areas mowed 3 weeks before flooding had low plant cover, areas mowed 5 and 9 weeks before flooding had medium and high plant cover, respectively, and non-mowed control areas had the most plant cover. Macroinvertebrate numbers and biomass were generally higher in mowed treatment areas than in control areas, but overall diversity was generally higher in high plant cover and control areas than in low plant cover areas. 3. Mosquitoes (Culicidae), brine flies (Ephydridae) and hover flies (Syrphidae) were positively correlated with amount of plant cover, and waterboatmen (Corixidae), midges (Chironomidae) and water scavenger beetles (Hydrophilidae) were negatively correlated with plant cover. Species assemblages changed seasonally among treatment areas because these taxa colonize wetlands at different times in the year. 4. These results demonstrate that invertebrate communities may be different within plant stands with heterogeneous amounts of emergent cover, and management practices that alter the structure of wetland vegetation can influence macroinvertebrate communities colonizing seasonal marshes.

The Potential of Some Mechanical Treatments for Rehabilitating Arid Rangelands I. Within-Site Effects and Economic Returns.

Attempts to rehabilitate degraded arid rangelands do not always succeed, and we perceived a need for some simple ecological indicators which would help determine whether mechanical intervention was likely to be useful. In this first of two papers, we largely focus on the effect of pitting and opposed discing, although we consider ripping and exclosure briefly, at 26 locations in central Australia. Pits and furrows successfully trapped erosion products and supported more basal cover and a greater number of plants than inter-furrow mounds or untreated areas. In addition, a number of soil variables were altered by the treatments. However, economic returns were unlikely to exceed outlays in most of the cases we considered. The best returns are predicted where degradation is minor, where livestock are of high quality and where landholders collect their own seed. Exclusion of grazing in the initial stages will enhance the amount of plant cover.

Modeling moisture movement in revegetating waste heaps: 1. Development of a finite element model for liquid and vapor transport

A management concern with waste dumps is the movement of Ieachate into local groundwater systems. This paper presents a model to predict the saturated‐unsaturated flow of water within such waste dumps. The model predicts moisture movement when the surface of the dump is bare and when it has revegetated. For the bare state, the evaporation rate is related to a number of complex processes, including atmospheric transport, radiation balance, and subsurface water supply in either liquid or vapor forms. Transpiration from the revegetated heap is related to the leaf area index and rooting depth, both of which change as plants grow. Mechanisms influencing vapor transport are considered in some detail, and a nonequilibrium approach employed to explain combined liquid and vapor movement. The mathematical problem consists of solving a system of coupled, nonlinear, partial differential equations which are related dynamically to the surface boundary conditions. The boundary conditions are determined by a combination of meteorological variables as well as the type and amount of plant cover. A moving node finite element method is presented which has the capability of automatically relocating nodes to areas of numerical difficulty. This method is validated through comparison with a proven solution to the unsaturated flow equation. The next paper in this series presents the application of the model to oil shale waste dumps.

Species and plant community distribution in a Mojave-Great Basin desert transition

Multivariate analyses were used to describe the vegetation characteristics of a transition from lowelevation Mojave desert to higher-elevation Great Basin desert. Vegetation data used were from Plutonium Valley in the Nevada Test Site. Data from forty nine releves were analyzed with two classifications (two-day indicator analysis or TWINSPAN and unweighted paried group cluster analysis or CLUSTER). Three ordinations, reciprocal averaging (RA), detrended reciprocal averaging (DCA) and non-metric multidimensional scaling (MNDS), were also used. A rotational correlation analysis was used to determine the vector direction of environmental gradients that correlate best with ordination results. Only token correspondence was found between multivariate classes generated by TWINSPAN and CLUSTER, and seven classes (plant communities) identified from field reconnaissance. The latter seven communities were based on differences in dominant species. Distribution of the vegetation was related more to beta diversity than alpha diversity. Individual species were much less diagnostic than the amount of plant cover, groups or guilds of species or differences in elevation and steepness of slope. Because of the high beta diversity the NMDS ordination gave results with the greatest ease of interpretation.

Resource Partitioning in Two Coexisting Sunfish: Pumpkinseed (Lepomis gibbosus) and Northern Longear Sunfish (Lepomis megalotis peltastes)

Qualitative surveys of 22 lakes in southern Michigan indicated that relative abundances of the northern longear sunfish (Lepomis megalotis peltastes) and pumpkinseed (L. gibbosus) depended upon amount of plant cover and sediment type. The longear sunfish occurred only in lakes with marl sediments and regions of sparse vegetation cover. The pumpkinseed occurred in all lakes surveyed and increased in abundance in lakes with greater vegetation density and/or more organic sediments. Quantitative measurements of habitat and food use were made in five lakes with sympatric populations. Data from underwater transects indicated that large (> 75 mm standard length) longear sunfish occurred primarily in shallow regions containing moderate to low vegetation cover whereas large pumpkinseeds were concentrated in deeper areas with heavy vegetation cover. The smaller size-classes of both species occupied the vegetation in deeper areas of the littoral zone. Large longears consumed predominantly large, sediment-dwelling mayfly or odonate nymphs regardless of the lake or habitat types. Pumpkinseeds consumed mainly gastropods and other prey from the vegetation. Preliminary studies of seasonal food use indicated that the pumpkinseed and longear sunfish both consumed more food in the spring and exhibited greater overlap in diet during this period. The relationship between foraging behaviors of these two species and the types of prey consumed is discussed as well as the complications of assessing competition between species when food and habitat use are dependent on size.Key words: Habitat use, size-class, lake types, food overlap, competition, Lepomis, Michigan

A quantitative survey of the biota of intertidal soft substrata on Aldabra Atoll, Indian Ocean

Intertidal, soft substrata on the peripheral reef flat and within the lagoon of Aldabra Atoll were sampled at 24 stations chosen to represent a wide range of habitats. At each station, densities and biomass were estimated from sieving, or from samples of vegetation; by using a random series of quadrats in the case of smaller species; or searches of a wider area in the case of larger, more dispersed species. Where appropriate, the area of substratum covered by plants was recorded and samples of plant material were retained for estimating biomass. The degree of tidal emersion was noted. Estimates of biomass were derived from laboratory determinations of the ash free dry masses of samples of each species, previously fixed in saline formalin and from their estimated densities. Biomass was finally presented as being in units of kcal m-2 from published energy (calorific) values for the different taxa (1 cal = 4.184J). Very approximate estimates of secondary productivity were made by multiplying the total station animal biomass by the P/B ratio of 1.76 derived from Moore (1972). An ordination of the stations produced a graphical display reflecting the different categories of habitat surveyed. The station groupings on the ordination diagram were derived solely from species distributions, thus lending support to our conclusions of how community structure was determined by the environmental conditions. The main categories of habitat were marine angiosperm beds in the lower intertidal, sand flats above the level of angiosperm growth, mobile sand bars and anaerobic mud associated with mangroves. The faunal equitability at each station was studied by using relative abundances of species expressed as their proportional contribution to the total biomass. In all cases, most of the biomass was represented by 3-14 species which tended to have widespread distributions within the area surveyed. Species richness was minimal on the mobile sand bars, increased with the amount of plant cover, and was maximal where angiosperms were covered by a multispecific algal mat. The group of stations with plant cover had a significantly greater animal biomass than the sandy stations. Since this greater biomass was largely distributed among a few dominant species, it was probably due to the increased primary production. In contrast, species richness increased with topographical complexity. The mean estimate of angiosperm biomass (2172 kcal m -2 ) was similar to the value derived from Moore et al. (1968) for a subtidal bed of Thalassia testudinum in Florida. Secondary productivity was least on the mobile sand bars and anaerobic mud ( < 10 kcal cm -2 a -1 ). Sand flats were more productive (10- 100kcal m -2 a -1 ) with values close to those derived from Moore (1972) for subtidal muddy sand in Florida and Massé (1972) for the sublittoral of a clear, sandy bay in the northwest Mediterranean. Secondary productivity was greatest in the angiosperm beds (100-1000 kcal m -2 a -1 ) with values similar to those of intertidal angiosperm beds in Florida (from Moore 1972).

Factors Influencing Plant Colonization of Mine Dumps at Park City, Utah

The relationships between vegetation and the environment of dumps from silver, lead and zinc mines were explored by statistical analyses of field and laboratory data. Soil temperature, phosphorus and calcium content of the soil, and soil texture differ significantly among sites stratified according to amount of plant cover and floristic diversity. Comparisons of high density stands of one species with high density stands of another demonstrated that many species pairs differed significantly in respect to preferences for site temperature and levels of phosphorus and calcium in the soil. Soil phosphorus was strongly correlated with the amount of vegetative cover and sum of density of all species combined. Three species showed significant regressions onto phosphorus. Phosphorus differences among stands are related to parent material. 11 references, 2 figures, 6 tables.

Sprinkler‐Induced Soil Temperature Changes Under Plant Cover1

AbstractAn experiment was conducted to determine the amount of soil temperature reduction to be expected from irrigating potatoes (Solanum tuberosum) at various intervals. Soil temperatures were measured at the 10‐cm depth under potato ridges with various amounts of plant cover. The mean daily soil temperature at the 10‐cm depth in a silt loam soil after 7 days following irrigation increased as much as 2 C above the daily irrigated plot with full cover and 4 C above the daily irrigated plot without cover. Similar soil temperature increases occurred in a loamy fine sand soil irrigated after 5 days which is the normal irrigation intervals for these soils.

Seed-setting in subterranean clover (Trifolium subterranean L.). III. The effect of plant density

Various aspects of seed production in a number of strains of subterranean clover sown at fire seeding rates at two sites in the Western Australian wheat-belt were investigated. Dry matter yields and percentage leaf in the foliage were also recorded. Percentage leaf increased with plant density in the earlier-maturing, stemmy strains, so that differences amongst strains diminished as density increased. The differences amongst strains in number of inflorescences when grown as single plants were largely eliminated under dense sward conditions, so that the two main factors in seed production were number of seeds per inflorescence and mean seed weight. The proportion of burrs above and below ground varied widely amongst strains, and was influenced by plant density in some strains. It is postulated that the extent of burr burial depends on the interaction between strain, environment, and condition of the surface soil. Burr burial improved the efficiency of seed-setting, particularly in the more severe environment. Strain differences in seeds per inflorescence below ground were relatively small, but within each strain, values were higher in the more favorable environment. The efficiency of seed-setting above ground differed considerably amongst strains and between the two environments, and tended to increase with plant density particularly in the earlier-maturing strains. Correlations were established between seeds per inflorescence above ground and the amount of plant cover in these strains. An artificial covering of wood-wool also improved seed-setting above ground. Mean seed weight followed the same general pattern as seeds per inflorescence.