Low neighbor abundances are often necessary but insufficient for establishing seeded shrubs

Authors: Rinella, Matthew - Matt

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2022
Publication Date: 3/28/2022
Citation: Rinella, M.J. 2022. Low neighbor abundances are often necessary but insufficient for establishing seeded shrubs. Rangeland Ecology and Management. 82:37-41. https://doi.org/10.1016/j.rama.2022.02.004.
DOI: https://doi.org/10.1016/j.rama.2022.02.004

Interpretive Summary: Shrubs seeded during grassland restoration very often nearly or completely fail to establish. One factor differentiating the few successful shrub seeding efforts from the many failures is competition from neighbors, particularly weeds and grasses seeded with shrubs. Despite efforts to control neighbors in experiments, neighbor abundances have often remained high, and this opens the possibility that neighbors have limited shrubs in much existing seeding research. In the northern Great Plains, I disentangled neighbor competition from other factors that influence shrub recruitment by evaluating seeded shrub survival and growth across a grass and weed biomass gradient spanning from very low to high. The treatment that held neighbor cover lowest provided the greatest shrub density and size. However, the density was just 0.13 shrubs m-2, which is too few to achieve typical restoration goals. Although densities were low, the data support existing evidence indicating controlling neighbors can greatly benefit shrubs. Controlling neighbor competition is often necessary to establish shrubs, but currently, shrubs can fail to establish even where neighbors are well-controlled. Additional research is needed to overcome barriers to establishment unrelated to competition.

Technical Abstract: Shrubs seeded during grassland restoration very often nearly or completely fail to establish. One factor differentiating the few successful shrub seeding efforts from the many failures is competition from neighbors, particularly weeds and grasses seeded with shrubs. Despite efforts to control neighbors in experiments, neighbor abundances have often remained high, and this opens the possibility that neighbors have limited shrubs in much existing seeding research. In the northern Great Plains, I disentangled neighbor competition from other factors that influence shrub recruitment by evaluating seeded shrub survival and growth across a grass and weed biomass gradient spanning from very low to high. The treatment that held neighbor cover lowest provided the greatest shrub density and size. However, the density was just ~0.13 shrubs m-2, which is too few to achieve typical restoration goals. Although densities were low, the data support existing evidence indicating controlling neighbors can greatly benefit shrubs. Constraining neighbors increased shrub density ~25× (from about 0.005 to 0.13 m-2). This large proportional effect could easily make the difference between shrub restoration success and failure when greater emergence occurs due to factors unrelated to competition, such as shrub seed rate or environmental conditions. Controlling neighbor competition is often necessary to establish shrubs, but currently, shrubs can fail to establish even where neighbors are well-controlled. Additional research is needed to overcome barriers to establishment unrelated to competition.