Effect Of Plant Cover Research Articles

Effect of Vegetative Cover on Foraging Site Selection by Swainson's Hawk

Foraging bouts of male Swainson's Hawks (Buteo swainsoni) were observed using radio-telemetry to determine the effect of plant cover on the selection of foraging sites. Home ranges consisted of varying amounts of cultivated and uncultivated habitats. Cultivated fields were the most abundant and they supported large amounts of prey, but were not hunted until crop harvest reduced the density of their plant canopy. A negative correlation between estimates of plant cover and foraging suggested that habitat differences such as vegetative cover were of greater importance than prey density in the selection of hunting sites. A correlation between foraging and prey biomass after it had been adjusted for vegetative concealment indicated that models relating prey abundance with raptor foraging should consider the effect of such a habitat difference on the availability of a hunting site's food supply. The efficient selection of hunting sites is critical for foraging birds. Because physical features vary among habitats, it is logical to assume that these differences would influence the availability of food and a bird's hunting success. Discussions of avian foraging have begun to emphasize the importance of such factors as plant cover, distance of travel, and weather in the selection process (Goss-Custard 1970, Royama 1970, Hassell 1971, Smith and Dawkins 1971, Zach and Falls 1976a, b, Kushlan 1979, Eiserer 1980, Fitzpatrick 1980). Although descriptions of habitat use by foraging raptors are limited, they indicate that, for species such as hawks and owls, plant cover and weather may have a greater effect than prey abundance on the suitability of their foraging habitats (Southern and Lowe 1968, Wakeley 1978, Stinson 1980). If this is true, predator-prey models that assume a direct relationship between hunting and prey density (MacArthur and Pianka 1966, Emlen 1968, Simons and Alcock 1971, Alcock 1973, Poole 1974) would need to be reconsidered when applied to raptors. I report here the results of a study I conducted to determine the effect of plant cover on the availability of Swainson's Hawk (Buteo swainsoni) prey. I predicted that, if plant cover limited the productivity of potential hunting sites, a reduction in a habitat's cover would increase its use by foraging hawks. Birds nesting in farmland of southeastern Washington were ideal to study because crop harvest reduced plant cover in large portions of their nesting habitat. Using estimates of plant cover together with estimates of prey density, I compared the distribution of foraging efforts before and after harvest for a possible correlation between a habitat's use and its vegetative cover.

Runoff and the ameliorating effect of plant cover in the Mulga communities of South Western Queensland.

Surface runoff was recorded from mall plots situated in the mulga rangelands of Queensland. Even small falls of rain (< 15 mm) produced runoff equivalent to over 50% of the rain but plant tussocks were instrumental in decreasing the number of rainfall events which generated runoff. Runoff was greater from the hard mulga and residud land zones than from the soft mulga zone. Regression and correlation analysis was used to identify topography, soil and vegetation factors influencing runoff. The maintenance of a perennial grass basal area > 2% is considered essential to reduce the loss of surface soil and nutrients.

Splash Detachment Under Plant Covers: Results and Implications of a Field Study

ABSTRACT FIELD measurements of the detachment of soil par-ticles by raindrop impact were made under cereals on sandy loam, clay and chalk soils and for bare ground on a sandy soil. Although the results are broadly as ex-pected, the data obtained under the cereals indicate that our understanding of the splash erosion process may need to be reappraised. The soils increase in detachabili-ty in the order of clay, chalk and sandy loam/sand. The crop cover was found to reduce splash detachment. A negative relationship was obtained between the rates of splash detachment at the reduced levels prevailing beneath the crop and the kinetic energy of the rainfall received at the canopy. Such a relationship has not been previously reported explicitly in the literature and an ex-planation of it must be sought through research on the way in which a plant cover modifies the volume, drop-size distribution and energy of the rainfall reaching the ground surface. Splash detachment is shown not to be a simple response to raindrop impact as is frequently assumed in laboratory simulations of the process. The in-teractive effects of plant cover, frost action, surface crusting and rainfall intensity must be considered.

Water intake rates of a claypan soil from hydrograph analyses

The hydrographic analyses of rainfall-runoff data from storms occurring during the period 1945–1957 were used to estimate soil intake rates and rainfall retention. The intake rates varied from more than 2 inches to less than .01 inch per hour, depending mostly upon antecedent soil moisture and duration of the storms. Irrigation generally reduced intake rate unless accompanied by fertility treatments that greatly increased plant growth. Since the dominant factor affecting water intake was soil-moisture content, the effects of plant cover and irrigation on intake may be partly attributed to their effects on stored soil moisture. The mean values for the initial intake rates (for the first 30 minutes) and average intake rates for the 29 storms analyzed varied with antecedent moisture, management practices, and season of the year. The mean values for the final intake rates (at the end of storm) were not significantly different for the different management practices.