Fallow Grassland Research Articles

Factors affecting the component community structure of haemoparasites in common voles ( Microtus arvalis) from the Mazury Lake District region of Poland.

The prevalence and abundance of infections with haemoparasites were studied over a 4-year period in Microtus arvalis (common vole, n =321) sampled from fallow grassland sites in north-eastern Poland. Total species richness was five (prevalence= Haemobartonella sp. 63.9%, Bartonella spp. 27.7%, Babesia microti 9.0%, Trypanosoma sp. 8.4% and and Hepatozoon lavieri 3.1%) with 76.9% of the voles carrying at least one species and a mean infracommunity species richness of 1.1. Variation in species richness was determined primarily by season and year, the interaction of these factors, and that of year with host age. The observed frequency distribution of infracommunity species richness did not differ from that predicted by a null model, suggesting that there were no marked associations between the species. Analyses of prevalence and abundance of infection with each species in turn, revealed that overall the principal causes of variation were temporal and seasonal, their interaction, and interactions with intrinsic factors (age and sex), the latter playing only a minor role in their own right. However, the relative importance of these combinations varied and was distinct for each of the species in the study. Prevalence data revealed eight sets of two- and three-way associations between species, mostly dependent to some extent on one of the intrinsic and extrinsic factors in the model. Analysis of quantitative associations suggested two sets of positive two-way interactions, none of which remained after controlling for the effect of extrinsic and intrinsic factors on the abundance of each species. These data are discussed in the context of the changing ecological profiles in this region of Eastern Europe and, in a wider context, in relation to current understanding of the factors that shape component community structures of haemoparasites in wild rodents.

A multi-scale approach of runoff generation in a Sahelian gully catchment: a case study in Niger

Runoff production conditions in a small gully catchment are studied at four different scales: the point scale (0.001 m 2), the local scale (1 m 2), the field scale (of the order of 100 m 2) and the catchment scale (0.2 km 2). At the point scale, infiltration measurements were conducted using a tension infiltrometer. At the local and the field scale, runoff plots were setup on typical soil surface conditions of the catchment (plateau bare soil, hillslope bare soil and fallow grassland). At the catchment scale, stream discharges were measured at two gauging stations. The overland flow yield is significantly nonuniform in space, due to the high spatial variability of infiltration capacities and the depressional storage of the soil surface. The runoff and the infiltration data collected confirmed the major role played by soil crusting on runoff generation in that part of Sahel. At the point scale, hydraulic conductivity measurements have shown that infiltration and runoff were driven by the hydraulic properties of the crust. At the field scale, microtopography and heterogeneity in the soil surface crusting decreased discharge volumes. The influence of vegetation growth on runoff yield was evident in the case of the fallow sites. Analysis of discharge data at the catchment scale highlights that infiltration through the bottom of the gully between two gauging stations leads to considerable runoff water transmission losses.

Recovering Surface Temperature and Emissivity from Thermal Infrared Multispectral Data

In 1992 Thermal Infrared Multispectral Scanner (TIMS) data were acquired from the NASA C-130 aircraft over the Sahelian region of West Africa as part of the Hydrological and Atmospheric Pilot Experiment in the Sahel (HAPEX). TIMS measures the radiation from the surface modified by the atmosphere in six channels located between 8 mm and 12.5 μm in the thermal infrared. By using a variety of techniques it is possible to extract both the surface temperature and surface emissivity from the areas over which TIMS data were acquired. One such technique was tested with the data acquired during this experiment. Several TIMS images of both the east and west central sites on 2 and 4 September were processed, and the spectral behaviors of different land cover types were determined. These included tiger bush, millet, and fallow grassland sites. There was a 5–10 K difference in the brightness temperature over the six channels when significant bare soil was visible. Channels 1–3 (8.2–9.4 μm) were cooler than the longer wavelength channels (9.6–12.5 μm), which is characteristic of soils rich in quartz. These differences in brightness were converted to emissivity differences using the max–min difference (MMD) method. This method relies on an empirical relationship observed between the range of emissivities and the minimum value for the six TIMS channels. The MMD method was applied iteratively to several entire scenes for the east central site on the two days with the interesting results that Channel 5 showed very little spatial variation in emissivity and the short wavelength channels observed substantial regions with emissivities of about 0.8 or less. There is excellent reproducibility when the same area is seen in different lines on the same day. However, there are differences when the same area is seen on the two days especially for the low emissivity values. Some of these differences may be due to soil moisture differences of 2–3%, which were observed for the two days. The observed surface temperatures were in good agreement with other measures, for example, vegetation temperatures agreed well with the measured air temperatures. Published by Elsevier Science Inc.

Activité saisonnière et distribution des parasitoïdes de pucerons du froment d’hiver

Activity of antagonists in winter and early spring as well as in late summer and autumn plays an important role in the control of cereal aphid populations. Indeed, parasitoids active early in the year are important to avoid high aphid densities. Late summer and autumn correspond to the transition period between two wheat cultures, and parasitoid activity would thus reduce aphid infestation. During these critical periods, other crops like rye-grass and red clover containing alternative hosts could play the role of parasitoid reservoirs. During 1996, parasitoid activity was measured by trap planting in wheat, rye-grass, red clover and fallow grassland. In each plot, early spring was characterized by an important parasitoid activity, while aphids remained at a low level. Later in spring, activity decreased, and aphid development began even during this period. During the summer, when aphids reached their population peak, parasitoid activity rose again. Percentage of parasitism of aphids sampled was only important during summer in red clover and rye-grass. In wheat and fallow grassland, percentage of parasitism remained at a low level. The role of synchronization between parasitoid activity and aphid development is discussed.

Estimating hydraulic conductivity of crusted soils using disc infiltrometers and minitensiometers

Although soil crusting has long been recognized as a crucial runoff factor in the Sahel, very few field methods have been developed for the measurement of the crust hydraulic conductivity, which is difficult to achieve because of the small thickness of most surface crusts. A field method, based on the simultaneous use of disc infiltrometers and minitensiometers is proposed for determining the crust hydraulic conductivity and sorptivity near saturation. On crusted soils, the classical analysis of the steady state water flow was found to be inadequate. The proposed method is based on sorptivity measurements performed at different water supply potentials and uses recent developments of transient flow analysis. A minitensiometer, placed horizontally at the crust-subsoil interface, facilitated the analysis of the infiltration regime for the crust solely. Results are shown for representative soil units of the East Central Super Site of the HAPEX-Sahel experiment: fallow grasslands, millet fields and tiger bush. Non-crusted soils were also considered and validated the transient method as demonstrated by comparison with Wooding's steady state solution. This validation was obtained in the case of fallow grasslands soil but not for the millet fields. In this latter case, the persistent effects of localized working of the soil to remove weeds caused large variations in infiltration fluxes between the sampling points, which tended to dominate over effects of differences in applied potential. For the tiger bush crusted soils, the ratio of the saturated hydraulic conductivity of the crust to that of the underlying soil ranges from 1 3 to 1 6 , depending on whether the crust is of a structural (ST) or sedimentation (SED) type. The method also allows the estimation of a functional mean pore size, consistent with laboratory measurements, and 40% less for the crusts in comparison with the underlying soil. The results obtained here will be used in hydrological models to predict the partition of rainfall between infiltration and runoff.

Deconvolution of remotely sensed spectral mixtures for retrieval of LAI, fAPAR and soil brightness

Linear mixture models have been used to invert spectral reflectances of targets at the Earth's surface into proportions of plant and soil components. However, operational use of mixture models has been limited by a lack of biophysical interpretation of the results. The main objectives of this study were (1) to relate the deconvolved components of a mixture model with biophysical properties of vegetation and soil at the surface and (2) to apply the mixture model results to remotely sensed imagery. A radiative transfer model (SAIL: Scattering by Arbitrarily Inclined Leaves) was used to generate reflectance ‘mixtures’ from leaf and bare soil spectral measurements made at HAPEX-Sahel (Hydrological Atmospheric Pilot EXperiment) study sites. The SAIL model was used to create canopy reflectances and fractions of absorbed photosynthetically active readiation (fAPAR) for a range of mixed targets with varying leaf area index (LAI) and soils. A spectral mixture model was used to deconvolve the simulated reflectance data into component fractions, which were then calibrated to the SAIL-generated LAI, fAPAR and soil brightness. The calibrated relationships were validated with observational ground data (LAI, fAPAR and reflectance) measured at the HAPEX Sahel fallow bush/grassland, fallow grassland and millet sites. Both the vegetation and soil component fractions were found to be dependent upon soil background brightness, such that inclusion of the soil fraction information significantly improved the derivation of vegetation biophysical parameters. Soil brightness was also shown to be a useful parameter to infer soil properties. The deconvolution methodology was then applied to a nadir image of a HAPEX-Sahel site measured by the Advanced Solid State Array Spectroradiometer (ASA). Site LAI and fAPAR were successfully estimated by combining the fractional estimates of vegetation and soils, obtained through deconvolution of the ASAS image, with the calibrated relationships between vegetation fraction, LAI and fAPAR, obtained from the SAIL data.

Runoff generation processes: results and analysis of field data collected at the East Central Supersite of the HAPEX-Sahel experiment

Within the scope of the HAPEX-Sahel experiment, the hydrological functioning of two small nested catchments was studied at two different scales: the plot scale (of the order of 100 m 2) and the catchment scale (0.2 km 2). At local scale, four runoff plots were set-up on the typical soil surface conditions observed on the catchments (plateau bare soil, two plots on fallow grassland) and an additional one was installed on a millet field. soil moisture investigations at the plot scale have shown that infiltration was limited between 0.6 to 2 m deep on three sites, but was deeper than 3.4 m on the most pervious site (millet). The maximum water storage on all the sites was found to be reached at the maximum activity of the rainy season (late August), and not at the end of the season. During the dry months, the soil was fully dried off by evapotranspiration, resulting in the absence of inter-annual soil water storage. No influence of vegetation cover on runoff was observed on the fallow sites, but runoff generation was found to be very sensitive to tillage on the millet field. The parameter P u, calculated from a rainfall hyetograph and defined as the rainfall depth that can actually produce runoff, is shown to be relevant to compute runoff on untilled soils, as it explains more than 87% of the variance in runoff depth. On tilled soils, it is necessary to take into account additionally the temporal evolution of the soil surface, especially the days after weeding operations. Simple linear relationships were derived to compute runoff depth from P u on the plots for the most typical soil moisture conditions observed, and modified SCS equations have been derived for the catchments. Using the linear equations derived at the plot scale in a simple, empirical, semi-distributed model lead to formulate the assumption that the partial source area concept applied on the catchments. Analysis of discharge data at the catchment scale highlights that seepage through the bottom of a gully between two gauging stations leads to the abstraction of non negligible volumes of water. Moreover, the water totally infiltrates in a spreading zone downstream from the outlet of the largest catchment showing that discontinuities occur in the surface water transmission within a catena. Such discontinuities constitute a major problem for the concern of aggregation of hydrologic processes.

Spatial patterns of dispersal, seed predation and germination during colonization of abandoned grassland by Quercus petraea and Corylus avellana

Key processes during recruitment of Quercus petraea and Corylus avellana were investigated in abandoned calcareous grasslands and adjacent scrub using the following methods: (1) observation of hoarding animals during the main period of ripening of acorns and hazel nuts, (2) exposition of seeds on the soil surface and in 5–6 cm depth to test differences in predation and germination, and (3) mapping of seedlings in the grasslands. European jays (Garrulus glandarius) and mice were the main disperser of seeds. Jays preferred acorns, whereas the rodents were less selective, but probably more important for dispersal of nuts. The maximum dispersal distance was about 10–20 m for mice and was estimated several hundred metres for jays. Mice collected hoards of several seeds in about 2 cm depth in the soil, whereas jays stored single seeds. Seed predation and probably hoarding by mice were highest under scrub and in unmown grassland, while jays preferred mown sites for hoarding. However, hiding of seeds in the soil reduced losses in all sites. Predation of nuts was slightly less intensive than that of acorns. Seeds of Corylus were more sensitive to desiccation than Quercus, but in both species germination was lower for seeds exposed on the soil surface and in drier sites. Quercus and Corylus were the most abundant woody species in the fallow grasslands, probably due to the effective multi-staged dispersal by jays and mice, whereas wind-dispersed and fleshy-fruited species were less common; the latter restricted to margins of adjacent scrubland. The study provides several examples for discordance in suitability of patches for seeds and seedlings due to different habitat requirements of successive developmental stages. This result emphasizes the need for studies in the multiple stages during recruitment of vertebrate-dispersed plants.

Standortsabhängige Entwicklung von Sträuchern und Bäumen im Sukzessionsverlauf von brachgefallenem Grünland in Südwestdeutschland

In 1975 an experimental programme in Southwest Germany has been established for the study of extensive maintenance methods and the course of succession on fallow grasslands and will be continued for an indefinite period. It includes 14 experimental areas with different site conditions distributed all over the country. The development of trees and bushes on the undisturbed succession plots has been observed and mapped. Summing up the results, there are a few interesting aspects related to the site conditions. Soon after the start of the experiments, on some experimental areas could be observed a remarkable development of trees and shrubs. After almost 20 years dense and nearly 10 m high forests with annual growth rates of 60-80 cm have raised on the productive sites

Pflanzengesellschaften und Blütenbesucher- Gemeinschaften: biozönologische Untersuchungen in einem nicht mehr bewirtschafteten Halbtrockenrasen (Mesobrometum) im Kaiserstuhl (Südwestdeutschland)

Pflanzengesellschaften und Blütenbesucher- Gemeinschaften: biozönologische Untersuchungen in einem nicht mehr bewirtschafteten Halbtrockenrasen (Mesobrometum) im Kaiserstuhl (Südwestdeutschland)

IDENTIFICATION OF CROPLAND AND AREA ESTIMATION FROM AERIAL PHOTOGRAPHY AND SATELLITE IMAGERY

The feasibility of using multiband aerial photographs and ERTS-1 imagery for manual field identification and measurements is presented for a Moderately Cold Subhumid Soil Climatic region of Saskatchewan. Using a simple six-step scale criterion, numeric values were assigned to the grey-level densities on black and white photographs (August 1972) for the infrared and red radiation bands. The grey-level densities were calibrated to known crops or other features, determined from data taken on the ground from training sites. A classification key was developed from the calibrated grey-scale values for the two spectral bands. Using the classification key, > 90% of the cereal crops — harvested, cereal crops not harvested, rapeseed, and fallow land — were identified on areas adjacent to the training site. It was not possible in this study to distinguish between wheat and barley from August photography. Nearby sites were used to verify the criteria. For nonnumeric analyses, infrared color was useful to substantiate the results. In general, the green spectral reflection appeared to be similar to the red for most of the fields except for a few of the fallow fields and grassland. However, further studies are required to evaluate the place of the green band in crop identification. The transference of known physiographic features from topographic survey maps and high-altitude aerial photographs onto ERTS imagery facilitated establishment of field boundaries and area measurements. By comparing the values of unknown fields to those calibrated with known features on the same photograph, variation in exposure, photographic development, and reproduction are eliminated.