Post-dispersal weed seed predation in Michigan crop fields as a function of agricultural landscape structure

Weed seed predation by invertebrates and vertebrates was compared between a simple (large crop fields embedded in a matrix of widely scattered woodlots and hedgerows) and a complex (small crop fields embedded in a matrix of numerous hedgerows and woodlots) agricultural landscape in southern Michigan. The structural differences between landscapes were evaluated by analysis of aerial photographs and digital land-use data. Seed predation experiments were conducted in four conventional tillage corn (Zen mays L.) fields within each landscape type. Trials included four common agricultural weed species, i.e., crabgrass (Digitaria sanguinalis). giant foxtail (Setaria faberii), pigweed (Amaranthus retroflexus), and velvetleaf (Abutilon theophrasti). Treatments to exclude vertebrates, invertebrates + vertebrates and no exclusion were established at 27 m from hedgerows. Fields in the complex landscape were 75% smaller, had 63% more wooded perimeter, and 81% more wide hedgerow perimeter than fields in the simple landscape. Fields in the simple landscape were surrounded mainly by herbaceous roadside and crops, whereas the complex landscape had fields surrounded primarily by wide hedgerows. In both the landscape types there was considerable post-dispersal weed seed removal with a tendency towards higher removal rates in the complex landscape. Although there were no differences in the rate of seed removal among the four weed species, seed predation showed a high degree of variability within and among fields. (C) 2000 Elsevier Science B.V. All rights reserved.