A tale of two invasive grasses in tallgrass prairie: Contrasting effects of plant litter on invasive success

Background/Question/Methods Litter is a potential means by which invasive plants can maintain dominance in native ecosystems.   Invasive plant litter can decompose quicker than that of native plant litter, thus speeding up nutrient cycling rates and affecting competitive relationships.  In contrast, invasive plant litter may decompose more slowly than that of native plants and thereby alter the environment and preempt habitat.  We present field studies from a tallgrass prairie site in Eastern Nebraska that illustrate both mechanisms.  Smooth bromegrass (Bromus inermis) is a C3, invasive, non-native grass in tallgrass prairie uplands.  Reed canary (Phalaris arundinacea) is another C3, invasive grass that persists in tallgrass prairie lowlands throughout much of the central North American grasslands. 

Results/Conclusions Relative to native grasses, smooth bromegrass has low C:N tissue, decomposes quickly, has high N mineralization rates in its soil and capitalizes on added soil N more than do native grasses.  Thus smooth brome litter plays a role in helping the species maintain persistence by fostering a positive feedback between plant litter and soil N.  In contrast, we found that reed canary monocultures in lowlands have litter with long residence times, possibly due to low tissue quality and high litter production.  We also found that reed canary litter tended to lower spring tiller development of native C4 grasses to a greater extent than that of the reed canary tillers, possibly due to the cooler soils under the thick litter mat.  In both cases, litter is a key mechanism by which invasive plants change habitat in ways that enhance their own persistence.