Professor Kansas State University Division of Biology, Kansas, United States
Changes in climate and land management have facilitated the rapid expansion of woody species into tallgrass prairie. Woody expansion has resulted in an ecosystem state transition from grassland to shrubland and loss of grassland biodiversity and ecosystem function. Despite extensive research focused on the drivers and consequences of woody expansion, our understanding of the physiological traits that facilitate the growth and spread of encroaching shrubs is limited. In this project, I assessed whether clonal shrubs encroaching in tallgrass prairie have common physiological and functional traits or unique traits that differentiate species niches. In 2021, we measured traits related to carbon gain and drought tolerance for six rapidly encroaching shrubs at Konza Prairie (Manhattan, KS). These traits included leaf-level physiological traits (turgor loss point, water use efficiency, quantum yield) and functional traits (leaf dry matter content, wood density) that are commonly used as metrics of plant growth at larger scales. Physiological and structural traits are drivers of species success on the landscape and likely relate to the abundance of dominant and subdominant encroaching species. We used basal area (per m2) of each species to assess if traits associated with plant carbon and water-use strategies are associated with species abundances.
The most abundant encroaching clonal shrub, Cornus drummondii, had over 4x greater basal area per m2 than the second most abundant shrub (Prunus americana). Despite the dominance of C. drummondii, many of its physiological and functional traits did not differ from less dominant clonal shrub species. Water use efficiency (assessed via leaf δ13C) and turgor loss point (TLP) did not differ among species except for P. americana, which had significantly lower TLP than all other species (p < 0.01). TLP values for P. americana were more similar to values reported for herbaceous species than other shrubs or forbs. Lack of differences in TLP and water use efficiency suggest that these deeply rooted shrubs have similar water-use strategies. These results show limited interspecific trait variability among encroaching shrubs and indicate that common underlying physiological strategies promote the growth and spread of clonal shrubs into tallgrass prairie.