Restoration of invaded temperate grasslands: species phenology adds to microsite and seed availability

Prepared by Cecilia D. Molina, Pedro M. Tognetti and Pamela Graff

Selective clipping treatment within experiment carried out on the Flooding Pampa grassland (Buenos Aires, Argentina) in an exclosures dominated by Festuca arundinacea. Photo credit: Pedro Tognetti

Conserving plant diversity in temperate grasslands faces significant challenges due to biological invasions. Understanding the main limiting factors that hinder the restoration of plant communities in native grassland stands as a pivotal inquiry in ecology. Addressing this concern holds practical significance, as it can help the development of effective management strategies and policies.

It is well recognized that employing clipping as a restoration technique is useful, as it creates favorable microenvironments for native species establishment, particularly when native propagules are available. Nevertheless, in cases where the invasion has depleted the native soil seed bank, solely relying on clipping might prove inadequate for achieving full native community restoration, and supplementary seeding efforts become necessary. Indeed, temperate grasslands host a diverse array of both cool and warm-season native plant species, and thus restoration endeavors hold the potential to facilitate the recovery of both functional groups. Among the remarkable invasive species in these grasslands is the cool-season grass, Festuca arundinacea (commonly known as tall fescue), which experiences peak growth during winter and spring, but suppresses the growth of native species throughout the entire year. In this context, we undertook a controlled field experiment in the Pampa grasslands of southern South America to investigate how the interplay between two distinct clipping regimes (selective versus non-selective) and the phenology of sown native species in relation to tall fescue phenology could promote restoration of invaded grasslands.

Field experiment of selective and non-selective clipping in combination with seed addition. Photo credit: Pedro Tognetti

We found that clipping led to a reduction in tall fescue cover, releasing microsites to native plant establishment. Consequently, both total native richness and cover were recovered independently of clipping type. Interestingly, there were differences in the seed limitation between warm-and cool-season native grasses. Native warm-season grasses, the group with the least phenological overlap with invaders, increased in cover and richness with clipping, and this increase was independent of sowing their seeds. Contrarily, native cool-season grasses, marked by a greater temporal match with the invasive species, increased subtly in cover with clipping and only with propagule addition. In conclusion, our study elucidated that biomass removal through clipping constitutes a prerequisite for enhancing microsite availability, consequently fostering the reestablishment of total native plant communities. Moreover, our findings underscored the differentiation in the recovery dynamics of native species, contingent upon the degree of phenological overlap with the invasive species. Species with minimal phenological overlap, like native warm-season grasses, showed remarkable recovery through clipping, obviating the necessity of propagule inputs. Conversely, species exhibiting greater phenological overlap, such as native cool-season grasses, demanded a dual approach involving biomass removal (i.e., clipping) and the incorporation of propagules for successful restoration.

This is a plain language summary of the paper of Molina, C. D., Tognetti, P. M., & Graff, P. published in Applied Vegetation Science (