PS 29-154 - Untangling the effects of shade and potential feedback mechanisms on understory species biomass and diversity in a young eastern redcedar stand

Abstract: We investigate whether eastern redcedar Juniperus virginiana, a rapidly spreading North American woody encroacher, produces plant-soil feedbacks or allelopathic effects that influence neighboring plants. Most research into redcedar feedbacks has been conducted in laboratory or greenhouse conditions; we extend this research to field conditions and manipulate shading to assess the effects of feedback. We manipulated the amount of shading on understory species by removing branches of redcedar trees in three separate treatments. Samples of understory biomass and functional group cover and richness were collected at regular intervals near redcedar trees. We assessed differences in the biomass production and functional group cover and richness of understory species based on shade-manipulation treatments using linear mixed-effects models. We found overstory shading to have a strong effect on understory biomass production. A distinct signal of suppression of understory biomass that was not attributable to shading was detected by comparing the biomass production in shaded and unshaded subplots at varying distances from the redcedar stem. We found the half removal treatment group, where 50% of shading branches were removed, failed to recover biomass following the removal of shading branches. These results suggest redcedar-mediated negative feedbacks could exert large influence on understory herbaceous species—especially during management activities that damage redcedar, but do not fully remove treated trees. These negative feedbacks should be taken into consideration when planning redcedar restoration projects as they could have a large impact on treatment outcomes