Journal Articles

The maintenance of habitat heterogeneity in agricultural landscapes has been promoted as a key strategy to conserve biodiversity. Animal response to grassland heterogeneity resulting from spatiotemporal variation in disturbance is well-documented; however, the degree to which edaphic variation generates heterogeneity detectable by grassland wildlife has proven more difficult to study in natural settings.

We conducted a field experiment to study how soils directly affect vegetation structure and composition and indirectly affect bird and butterfly assemblages using plantings of tallgrass prairie species managed as agroenergy crops in Iowa, USA. The experimental design included four vegetation treatments of varying species richness replicated on three soil types.

Habitat characteristics varied widely among soils. Crops on sandy loam, the driest, most acidic soil with the lowest nutrient content, developed shorter, less dense vegetation with sparse litter accumulation and more bare ground compared to crops on loam and clay loam.

Birds and butterflies responded similarly to soil-induced variation in habitat characteristics. Their abundance and species richness were similar on all soils, but their assemblage compositions varied among soils in certain vegetation treatments.

In low-diversity grass crops, bird assemblages using sandy loam were dominated by species preferring open ground and sparse vegetation for foraging and nesting, whereas assemblages using loam and clay loam were dominated by birds preferring tall, dense vegetation with abundant litter. In high-diversity prairie crops, the species composition of forbs in bloom varied among soils and strongly influenced butterfly assemblages.

Synthesis and applications. Prairie agroenergy crops established with identical management practices developed variable habitat characteristics due to natural edaphic variation, and this heterogeneity influenced the spatial distribution of bird and butterfly assemblages due to differential habitat use among species. This finding suggests that if unfertilized prairie crops were grown for agroenergy by land managers large-scale, soil-induced habitat heterogeneity would promote wildlife diversity within and among fields, further increasing the habitat value of these crops compared to the fertilized, annual monocultures that currently dominate the agricultural landscape. Our study also highlights the need for managers to consider soil properties when selecting sites to restore grassland habitat for species of conservation concern.

Soil type and species diversity influence selection on physiology in Panicum virgatum.  by Mark E. Sherrard, Lucas C. Joers, Christina M. Carr, and Cynthia A. Cambardella.  Evolutionary Ecology.  2015.

Abstract

Species diversity influences the productivity and stability of plant communities, but its effect on the evolution of species within those communities is poorly understood. In this study, we tested whether species diversity and soil type influence selection on physiology in switchgrass (Panicum virgatum). Plants were grown in 0.33–0.55 ha plots in eight full-factorial treatment combinations: four diversity treatments (1 species—switchgrass monoculture; 5 species—a mix of C4 grasses; 16 species—a mix of grasses, forbs, and legumes; 32 species—a mix of grasses, forbs, legumes, and sedges) and two soil types (Waukee loam “loam” and Spillville–Coland alluvial complex “clay”). We measured selection on photosynthetic rate, chlorophyll concentration, and specific leaf area in each treatment combination and compared the strength of selection between soil types and diversity treatments. When significant, selection favored increased photosynthesis, increased chlorophyll concentration, and decreased specific leaf area in all treatment combinations. Selection for these attributes was stronger in the faster-draining loam soil than the slower-draining clay soil. Selection rarely differed significantly between diversity treatments; however, most instances in which selection differed significantly between soil types occurred in the high-diversity mixes suggesting that diversity alters the impact of soil type as an agent of selection. Selection may have been stronger in the loam soil because of its lower available water capacity. There was a lengthy summer drought during our experiment. Under these conditions, plants with high photosynthesis and chlorophyll concentration would have more resources to invest in their root system for water uptake. Increased capacity for water uptake would benefit plants in both soil types during drought but would have greater adaptive significance in the faster-draining loam soil. Our results suggest that species diversity is a weak agent of selection and only influences physiological evolution by modifying the pressures exerted by other environmental factors.

Butterfly response to floral resources during early establishment at a heterogeneous prairie biomass production site in Iowa, USA.  by Mark C. Myers, Benjamin J. Hoksch, and James T. Mason.  Journal of Insect Conservation.  2012.

Abstract

In the Midwestern USA, current biofuel production systems rely on high input monoculture crops that do little to support native biodiversity. The University of Northern Iowa’s Tallgrass Prairie Center is investigating the feasibility of cultivating and harvesting diverse mixes of native prairie vegetation for use as a sustainable biofuel in a manner that also conserves biodiversity and protects soil and water resources. In 2009, we established 48 research plots on three soil types at an Iowa site with a uniform history of row crop production. We seeded each plot with one of four treatments of native prairie vegetation: (1) switchgrass monoculture, (2) warm-season grass mix (5 grass species), (3) biomass mix (16 species of grasses, legumes, and forbs), or (4) prairie mix (32 species of grasses, legumes, forbs, and sedges). In 2010, we measured vegetation characteristics and studied butterfly use of the plots to investigate the hypothesis that more diverse plant communities would support a greater abundance and diversity of butterflies. Habitat characteristics varied significantly among the plots by treatment and soil type, and butterflies responded rapidly to variation in floral abundance and richness. Averaged over the entire growing season, butterflies were six times more abundant and twice as species rich in the biomass and prairie mix plots compared to the warm-season grass and switchgrass plots. Our results suggest that implementation of biomass production using diverse mixes of native prairie vegetation on marginal lands could have positive effects on the maintenance of butterfly populations in agricultural landscapes.