We investigated the effects of monthly nutrient applications on succession in two old-field plant communities. Succession was monitored for 3 yr in 1-yr (younger) and 4-yr (older) experimental plots. Three 0.1-ha plots in each old field were treated with sludge, three with fertilizer, and two were left as untreated controls.In the younger community, herbaceous perennials and winter annuals replaced summer annuals by the 3rd yr of succession in control plots. Summer annuals, however, dominated enriched plots throughout the study. Species richness was significantly higher in enriched plots than in control plots during the 1st yr, but was significantly lower than control plots thereafter. Annual aboveground net primary productivity (ANPP) was significantly greater in enriched plots than in controls in the 1st yr, but the converse occurred in the 3rd yr. The type of nutrient enrichment affected ANPP; sludge plots had significantly lower ANPP than fertilizer plots in the 1st and 3rd yr.In the older community, two summer annuals and a biennial displaced dominant perennial grasses in enriched plots. In contrast to the younger community, ANPP was consistently greater in nutrient-enriched plots than in controls, and nutrient enrichment did not alter species richness. The type of nutrient enrichment affected the older community in an opposite manner from the younger community; sludge plots had significantly greater ANPP than fertilizer plots in the 3rd yr. We concluded that the age and physiognomy of the old-field community, the type of nutrients applied, and the duration of enrichment, each influenced the course of succession; responses observed in the 1st yr of enrichment were not indicative of later trends.

The effects of a carbamate insecticide, Sevin, on plant, arthropod, and mammal components within a grain crop grassland ecosystem were investigated. A single application of 2 lb. of the insecticide was applied in July to 1 of 2 comparable and adjacent once—acre fenced enclosures, each planted in a crop of millet (Panicum ramosum) and stocked with three species of small mammals, the cotton rat (Sigmodon hispidus), the house mouse (Mus musculus) and the old—field mouse (Peromyscus polionotus). Intensive and frequent sampling of plants, arthropods, and mammals on both control and treated enclosures provided the data for evaluating the effects of the insecticide on productivity, density, diversity, and equitability of the three components. Sevin residues on plants decreased rapidly from 35 ppm on the first day following spraying to 0.37 ppm on the 16th day. No effect of the insecticide could be detected on producer standing crop or net community primary production which averaged for the two areas 567 g dry wt/m2 for season or 3.96 g/day. A highly significant decrease in litter decomposition in the treated area was measured 3 weeks after spraying, presumed to be the result of a reduction in microarthropods and other decomposers. The total biomass and numbers of arthropods were reduced more than 95% in the treated area and remained well below the control area for 5 weeks; after 7 weeks total biomass but not total numbers returned to the control level. Photophagous insects (Homoptera and phytophagous Hemiptera were dominant at the time of spraying) were more severely affected than predaceous insects and spiders; density of the latter returned to control levels in 3 weeks. Species—numbers diversity in terms of S—1/1nN also was markedly reduced in all orders of insects immediately after treatment, but with the exception of the Hemiptera and Hymenoptera, returned to control levels within 1—2 weeks. Diversity in spiders was not affected by the treatment, even though numbers were reduced. In terms of trophic groupings, species diversity of phytophagous insects, although more severely reduced, "recovered" more quickly than did diversity in predaceous insects. The equitability index of Lloyd and Ghelardi (1964), in contrast to species/numbers diversity, tended to rise 1 to 3 weeks after treatment, especially in the phytophagous insect group. In terms of the seasonal succession, equitability index values for the predator populations increased to about 1.0 while that of herbivores remained at lower levels of 0.5 to 0.6 throughout the study on the control area, suggesting that predators tended to be food limited and to occupy non—overlapping niches. Cotton rat reproduction was delayed with ultimate density reduced in the treated grid; laboratory tests indicated this was a probable direct effect of the insecticide. However the total mammal population, which grew in sigmoid fashion to an asymptotic level of about 180/acre in both grids, was not affected by the treatment because there was a compensatory increase in the house mouse po...

Specialized cash grain production, emergent in the midwestern United States during the post-WWII era, typifies the Upper Four Mile Creek watershed in southwestern Ohio. This style of agriculture intensifies cropland use, with consequent increases in soil erosion and stream sedimentation -a serious problem in the lower reservoir, Acton Lake. Agricultural statistics and aerial photographs compiled between 1934 and 1984 were used to quantify agricultural dynamics and landscape change in the watershed, including land-use apportionment, diversity, and the structural configuration of forest, woodland, and old-field/brushland patches and corridors. A questionnaire sent to all land owners in the basin documented farm-level characteristics and factors that influence management decisions. Crop diversity (H') in Preble County, Ohio decreased from 1.42 in 1934 to 1.17 in 1982, as corn and soybeans dominated the landscape mosaic. Yields rose, but net profits were reduced by declining prices per bushel and increases in fertilizer and petroleum-based subsidies. Landuse diversity in the county also declined (H' = 1.37 in 1934 tot 0.80 in 1982) in response to cropland expansion, whereas forest land in the watershed increased from 1605 to 2603 ha. Fragmentation declined and the landscape became polarized after 1956, with a concentration of agricultural patches in the upper watershed and forest-patch coalescence in stream gullies and state park land in the lower watershed. The questionnaire (-29~ return) further supported, at the farm-level, observed regional trends toward expansion (farm coalescence and lease contracts) and specialization (conversion toward corn and soybeans). The most important factors influencing farm size and management were better equipment and family traditions. Thus, cultural and technological factors that operate at the farm-level, coupled with meso-scale variation in the physical conditions of a catchment basin, tend to influence landscape-level patterns more than regional socioeconomics and governmental policies.

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We tested the effects of increased landscape corridor width and corridor presence on the population dynamics and home range use of the meadow vole (Microtus pennsylvanicus) within a small-scale fragmented landscape. Our objective was to observe how populations behaved in patchy landscapes where the animals home range exceeded or equaled patch size. We used a small-scale replicated experiment consisting of three sets of two patches each, unconnected or interconnected by 1-m or 5-m wide-corridors, established in an old-field community (S.W. Ohio). Control (0-m) treatments supported significantly lower vole densities than either corridor treatment. Females were the dominant resident sex establishing smaller home ranges (< 150m 2) than males (> 450m2). Significantly more male voles dispersed between patches with corridors than between patches without corridors. However, no difference was observed regarding the number of male voles dispersing between patches connected by corridors when compared to the number dispersing across treatments. Dispersal between connected patches was restricted to corridors based on tracking tube data. Corridor presence was more important than corridor width regarding the movement of male voles within their home range.