Plant community recovery following Sericea lespedeza (Lespedeza cuneata) removal: testing for a soil legacy effect

Abstract

Restoration of plant communities can be hindered by the legacy of previously established invaders, despite their physical removal from the community. Current evidence, mainly built on short-term greenhouse experiments, suggests that Sericea lespedeza (Lespedeza cuneata) invasion not only suppresses native plant species, but also alters soil conditions in host communities. As a result, L. cuneata may create a soil legacy that impedes plant community restoration. We examined the response of a Kansas grassland following L. cuneata removal to determine if historical L. cuneata abundance affected (1) plant community composition and (2) the establishment of additional native species. To address these questions, L. cuneata seeds were sown into 300 plots at a wide range of densities under different combinations of simulated disturbance and soil fertilization. After a three-year establishment period, L. cuneata was removed from the community, and 13 native forb species were sown into all plots. Over 4 years, we found little evidence for a soil legacy effect that influenced community response post-removal. Although there was a detectable relationship between community composition and L. cuneata, the variation explained by this relationship was very low. Similarly, the establishment of sown native species was unrelated to the historical abundance of L. cuneata. These results indicate that, regardless of initial density, L. cuneata does not impede plant community recovery in this system if effectively controlled within the first 3 years of invasion, and legacy effects inferred from greenhouse experiments may not translate to impacts on the plant community in the field.

Drivers of Plant Invasion in Stream Restoration

“…With an extensive taproot, L. cuneata can survive extended drought conditions in the well-drained soils that it frequents, and it can also survive in a wide range of soil pH conditions from strongly acid to slightly basic [12]. Modes of invasion in this species have been studied, with general consensus that L. cuneata is able to modify its environment and facilitate localized dominance [15,16]. The species has a high level of tannins in its tissues, making it unpalatable to wildlife and thus resistant to herbivory [17,18].…”

“…The species has a high level of tannins in its tissues, making it unpalatable to wildlife and thus resistant to herbivory [17,18]. In addition, phenolic compounds emitted into the soil through root exudates or decomposing plant residues have been shown to have allelopathic properties, increasing its competitive ability by altering nutrient uptake efficiency and decreasing germination in other species [12,16]. Lespedeza cuneata can reduce nutrient availability for other species via the rapid acquisition of essential nutrients (e.g., phosphorus, potassium) and slow release back to the soil via lower rates of decomposition than other plants, a phenomenon mediated by secondary compounds [17].…”

“…Lespedeza cuneata can reduce nutrient availability for other species via the rapid acquisition of essential nutrients (e.g., phosphorus, potassium) and slow release back to the soil via lower rates of decomposition than other plants, a phenomenon mediated by secondary compounds [17]. All of these properties contribute to localized L. cuneata dominance, making the species a nuisance in ecosystem restoration and a particularly problematic invader of riparian restoration projects [16,19]. Lonicera japonica (Japanese honeysuckle), a perennial vine that turns woody with age, is from eastern Asia and was introduced to the USA in the early 1800s as a garden plant [13].…”

“…The negative relationships between L. cuneata abundance and soil N and K were unexpected but could have been predicted from the literature. As an "N-fixing" plant, L. cuneata benefits from N subsidies via a symbiotic relationship with Rhizobium bacteria in root nodules, which allows L. cuneata to inhabit nutrient-poor soils with low available N pools [16]. Lespedeza cuneata has been shown to reduce the availability of other macronutrients, including K, by rapid uptake and slow release back to the soil, a phenomenon that is apparently mediated by high levels of phenolic compounds (e.g., tannins) that reduce decomposition rates of its senescent tissues [17].…”