Accelerated Conversion of Native Prairie to Cropland in Minnesota

Abstract

SummaryUnplowed native grasslands are among the most endangered ecosystems in the world, due in large part to their agricultural suitability and widespread conversion to cropland. Despite this, remaining locations of these species- and carbon-rich landscapes are neither well monitored nor effectively protected. A recent spike in US prices for corn (Zea mays) and soybeans (Glycine max) intensified incentives to bring new land into production, potentially hastening the conversion of grasslands to crops. We combined satellite-based land cover data with aerial photographs and a field-based inventory of remaining native grassland (hereafter prairie) in Minnesota to assess the areas, rates, and locations of prairie conversion since 2008. Our results reveal that during 2008–2012, prairie was converted at average annual rates more than four times greater than the previous decade and a half. Corn and soybeans were the initial crops planted on 73% of converted prairie, and more than 80% of conversion occurred in recently established conservation priority zones, thereby magnifying the urgency to protect these sites. Broader land-use trends in Minnesota suggest that expansion of both croplands and developed lands continues to threaten all grasslands, including the subset that is prairie, and that the growth of developed or built-up land may be amplifying the conversion pressure exerted by agriculture, though further research is needed. Despite the small total area of prairie lost, the multi-fold increase in conversion rates and the confirmation of native habitat clearing may have substantial conservation implications, especially given the very limited prairie that remains in the region. The overall results reveal challenges for federal policies, including a loophole in the crop insurance Sodsaver provision surrounding alfalfa hay and limitations in the current enforcement of the Renewable Fuel Standard.

Cropland expansion in the United States produces marginal yields at high costs to wildlife

“…The subset of conversion which occurs on long-term habitat is likely to lead to particularly high losses in native plant diversity, wildlife provisioning, and other ecosystem services 18,19 . The large area of long-term grassland conversion we identified provides strong evidence of widespread clearing of previously undisturbed lands, especially when considered alongside other reports of confirmed native prairie conversion throughout the US 20,21,57,58 . This ecologically significant loss of intact habitat indicates that if remaining virgin land is to be preserved, stronger protections will be required such as those afforded through federal policy, conservation incentives, and/or supply chain interventions 59 .…”

“…In addition, remaining grassland tracts that have never been plowed harbor some of the greatest concentrations of native plant species across the country 18,19 . Yet, despite increasing threats to these landscapes through cropland expansion 20,21 , the habitat quality of lands that are typically converted remain largely unknown-hindering efforts to conserve affected biota or mitigate the impacts of conversion.…”

Local climate and habitat continuity interact to alter contemporary dispersal potential

“…Relatively continuous prairie habitats increases the likelihood that dispersing propagules will land in suitable habitat, contributing to selection for increased dispersal (Travis and Dytham 1999). However, previous and ongoing agricultural conversion may increase the scale of isolation for populations within a matrix of inhospitable environments (Wright and Wimberly 2013;Lark et al 2018;Wimberly et al 2018). Thus, increasing fragmentation across prairie environments has the potential to shift the direction of selection for dispersal traits in these historically continuous habitats.…”

“…Prairie populations have historically experienced higher levels of genetic connectivity (Hamilton and Eckert 2007), but contemporary fragmentation over the last century (e.g. Wright and Wimberly 2013;Lark et al 2018) has led to increased isolation. In contrast, historically isolated alvar populations are not only disjunct from the main contiguous range across the midwestern prairies, but also are isolated from each other.…”

Private lands conservation: A vision for the future

“…Agricultural conversion has contributed to the degradation and loss of formerly extensive native ecosystems, including the eastern tallgrass prairie (Bachand , Lark et al ), Lower Mississippi Alluvial Valley bottomland hardwoods (King et al ), and longleaf pine ( Pinus palustris ) forest (Noss et al ), among others. These native ecosystems were once expansive areas patterned through physiography and natural disturbance to create a heterogeneous mosaic of vegetation structure.…”