Habitat and Time Are More Important Predictors of Weed Seed Predation than Space on a Diversified Vegetable Farm in Maine, USA

Abstract

Postdispersal weed seed predation is a significant source of weed mortality in agroecosystems. The magnitude of seed predation, however, is variable. Understanding the relative importance of factors driving variability in seed predation rates will increase the potential utility of seed predation to farmers. We conducted landscape-scale field experiments to quantify and compare the effects of space, time of sampling, and habitat on weed seed predation. Seed predation assays, with and without vertebrate exclosures, measured seed predation rates at spatially explicit sample sites across 8.5 ha of crop and noncrop habitats on a diversified organic vegetable farm in Maine. Total and invertebrate seed predation averaged 8% and 3% d−1, respectively. Vertebrate seed predators detected by motion-sensing cameras included small mammals and birds. A ground beetle,Harpalus rufipes, was highly dominant in pitfall traps, comprising 66% of invertebrate seed predators captured within crop fields. Seed predation was randomly distributed in space. However, time of sampling and habitat were highly significant predictors of seed predation. Variance partitioning indicated that habitat factors explained more variation than did time of sampling. Total seed predation was greater in crop and riparian forest habitats than in mowed grass, meadow, or softwood forest. Generally, invertebrate seed predation was greatest at sites with an intermediate degree of vegetative cover, whereas habitat type was the chief biotic determinant of vertebrate seed predation rates. These results suggest cover cropping and wetland conservation as practices that may bolster seed predation rates.

A Systems Comparison of Contrasting Organic Weed Management Strategies

“…Activity-density of carabid beetles, including Harpalus rufipes Deg., a well-known seed predator (Gallandt et al 2005), was greatest in the critical period system (Table 5), possibly due to the habitat provided by weeds, but activity-density was least in the natural mulch systems. Indeed, weed seed predation has been positively correlated with living vegetative cover but negatively correlated with residue (Birthisel et al 2015), possibly due to hindrance of carabid mobility (Thomas et al 2006). Earthworms were more abundant in natural-mulched systems (Table 5), as found by Schonbeck and Evanylo (1998b).…”

Changes in weed seed bank and flora as affected by soil tillage systems

“…Weed seed bank analysis provides knowledge on the effect of agricultural management practices on weed community dynamics. Such knowledge is difficult to acquire from short-term studies based on actual weed flora, whose composition is subjected to considerable variation in time and space (Birthisel et al, 2015). Weed communities are also affected by crop type and sequence.…”

Molecular analysis indicates high levels of carabid weed seed consumption in cereal fields across Central Europe

“…Detection frequencies of plant DNA were high—across all regions independently of carabid species, sex and sampling time. We hypothesize that the plant DNA detected in regurgitates mainly originates from consumed seeds as has been demonstrated in numerous studies (Tooley and Brust 2002 ; Honek et al 2003 ; Lundgren et al 2013 ; Daedlow et al 2014 ; Kulkarni et al 2015 ; Cutler et al 2016 ; Talarico et al 2016 ; Birthisel et al 2017 ). Our logic for this hypothesis is that while carabid beetles can eat fruit, pollen and sometimes plant leaves (Toft 2002 ), previous studies have shown that herbivory (i.e.…”