Thu, Aug 05, 2021:On Demand
Background/Question/Methods
Chaparral in southern California, with its evergreen, sclerophyllous shrubs has long been considered resilient to wildfire disturbances and tolerant of climate stressors (e.g., drought). However, these ecosystems can become degraded due to anthropogenic stressors (e.g., the introduction of invasive species, an increase in fire frequency). As these communities become degraded, the need for restoration arises. In this study, we aimed to determine if native seedling establishment can be facilitated by early successional soft-leaved shrub species that recruit within degraded sites. These shrubs could act as nurse plants, reducing stressful abiotic conditions (i.e., high solar radiation), thereby leading to increased seedling survival. To test this hypothesis, we planted 3-5-month-old seedlings of Salvia apiana, Ceanothus oliganthus, Rhus ovata, and Heteromeles arbutifolia within established stands of Malacothamnus fasciculatus (MAFA) in a degraded chaparral site in Piru, California. We implemented three canopy treatments: no, half, and full MAFA canopy removal. MAFA shrubs were removed at their base and treatments were maintained. We transplanted seedlings in January 2019 and monitored survival and growth through 2021.
Results/Conclusions In November 2019, total seedling survival was 19.4%. H. arbutifolia had greatest survival in half removal plots (42% of the seedlings survived) compared with full and no removal plots (22% and 22% of the seedlings survived respectively). S. apiana had greatest survival in full removal plots (37% of the seedlings survived) compared with the half and no removal plots (26% and 28% of the seedlings survived respectively). Nurse plants seemed to have no effect on C. oliganthus and R. ovata seedling survival; both species had low seedling survival in all treatments. In Spring 2021, total seedling survival was 3.3%. One H. arbutifolia seedling survived (no removal plot) and 12 S. apiana seedlings survived (four seedlings in full removal plots; six seedlings in half removal plots; two seedlings in no removal plots). Our results suggest the nurse plant affect is species specific where nurse plants may facilitate establishment of shade tolerant species (e.g., obligate resprouters), interfere with sun tolerant species (e.g., obligate seeders), and, for some species, may not be beneficial enough to overcome challenging abiotic conditions.
Results/Conclusions In November 2019, total seedling survival was 19.4%. H. arbutifolia had greatest survival in half removal plots (42% of the seedlings survived) compared with full and no removal plots (22% and 22% of the seedlings survived respectively). S. apiana had greatest survival in full removal plots (37% of the seedlings survived) compared with the half and no removal plots (26% and 28% of the seedlings survived respectively). Nurse plants seemed to have no effect on C. oliganthus and R. ovata seedling survival; both species had low seedling survival in all treatments. In Spring 2021, total seedling survival was 3.3%. One H. arbutifolia seedling survived (no removal plot) and 12 S. apiana seedlings survived (four seedlings in full removal plots; six seedlings in half removal plots; two seedlings in no removal plots). Our results suggest the nurse plant affect is species specific where nurse plants may facilitate establishment of shade tolerant species (e.g., obligate resprouters), interfere with sun tolerant species (e.g., obligate seeders), and, for some species, may not be beneficial enough to overcome challenging abiotic conditions.