Do Seed Traits Mediate Plant Community Changes in Wisconsin's Unburned Prairies?

Abstract

Historically, both natural and human-induced fires have played a key role in North American prairies, providing a disturbance regime that grassland systems are adapted to. With human activity fragmenting these prairies at an accelerated rate since the 1950s, the few prairies that do remain are often fire suppressed, and woody plant species with larger seeds may have a competitive advantage under contemporary conditions. This study seeks to quantify the mechanisms underpinning biodiversity loss from invading woody plants in order to better understand prairie alteration and disappearance. To do so, I investigated the effects of seed functional traits, fire history, and prairie extent. Among seed traits, I found that while seed coat thickness has remained relatively constant over the past 60 years, seed size and shape were impacted by fire regime. More specifically, larger and rounder seeds have increased in prevalence with recent fire exclusion. In addition, the prevalence of woody species at sites was affected by fire regime, but not by prairie size. Overall, this work documents a significant increase in woody vegetation in Wisconsin’s prairies over the last 60 years in burned and unburned remnants. Such species also appear to have large, round seeds. This study also contributes valuable information on best management practices for prairies, like the importance of consistent prescribed burning and use of seed size and shape to predict which species are likely to increase without such management practices.