Facilitation and herbivory during restoration of California coastal sage scrub

Abstract

Using nurse plants to facilitate native plant recruitment in degraded habitats is a common restoration practice across various arid and semiarid environments. Living trees or shrubs are typically considered nurse plants, whereas dead shrubs left in the landscape from prolonged drought are understudied prospective facilitators for native plant recruitment. The interaction between nurse plants and biotic pressures, such as herbivory, on native recruitment is also not well understood in semiarid plant communities. We investigated the effects of facilitation and herbivory on native seedling germination, growth, and survival in the restoration of degraded coastal sage scrub (CSS) habitat. Native shrub seedlings (Artemisia californica and Salvia mellifera) were planted, and native annual species (Amsinckia intermedia, Deinandra fasciculata, Phacelia distans, and Pseudognaphalium californicum) were sown in three Shrub Type treatments (live shrub, dead shrub, and exposed areas), with a nested Cage treatment (no cage and cage) in each Shrub Type treatment. Annual species grew equally well in all Shrub Type treatments; shrub seedlings grew largest in exposed areas. While there was little evidence of facilitation for all species tested, there were strong positive effects of caging on growth and establishment of all species. Caging palatable native species or planting species with anti‐herbivory traits around target plants may be more strategic approaches compared to using nurse plants in restoring degraded CSS after extended drought.

Herbivore Influence on Post-Fire California Sage Scrub Plant and Soil Microbial Assemblages

“…At the beginning of the experiment, we were unsure how herbivores would impact A. californica seedling recruitment and survivorship, and thus CSS recovery. While recent research has shown that herbivores reduce shrub seeding survivorship in intact CSS [39,40], we were unsure if similar patterns would be found in burned habitats. In particular, we wanted to explore the relative importance of competition with non-native annual grasses, which are often consumed by the herbivore community, as opposed to the direct effects of herbivores in limiting A. californica recruitment [15,59,60].…”

“…Similar actions are not be required for native forbs, except near the fire edge where caging may be critical for CSS recovery. For example, we recommend that restoration studies explore the efficacy of caging individual seedlings [39,40] or larger areas like we did here, and potentially targeting non-native grass removal efforts in these treatments [15], as this could increase shrub survivorship and enhance the likelihood of CSS recovery.…”

“…The limited attention to the effects of herbivores following fire may have resulted from early work in CSS, conducted primary in the cool-moist spring and early summer months, which found that herbivores preferentially consumed herbaceous vegetation facilitating shrub seedling survivorship [10,11,38]. However, recent studies conducted through the hot-dry late-summer and autumn months highlight that herbivores reduce CSS shrub seedling survivorship and growth [39,40]. Therefore, while reductions of non-native annuals may help CSS shrub germination and survivorship in the cool-moist Mediterranean season [10,11,38], shrub recovery will only occur if herbivory pressure is low enough in the hot-dry season.…”

“…Low rainfall years reduce shrub recruitment and survivorship, particularly in areas with elevated N-deposition [4,10,15,41]. Though recent research suggests that herbivory may be a significant factor structuring CSS plant assemblages [39,40], research was conducted in unburned CSS, so the extent to which herbivores influence CSS shrub recovery following a fire remains difficult to predict.…”

Latitudinal resource gradient shapes multivariate defense strategies in a long‐lived shrub

“…Vertebrate herbivore communities in coastal sage scrub ecosystems are diverse, consisting of squirrels ( Sciurus niger and Otospermophilus beecheyi ), rabbits ( Sylvilagus audubonii ), and woodrats and mice ( Nassella lepida , Nyctinomops macrotis , Peromyscus eremicus , and Cantharellus californicus ) (Quon et al, 2019 ). Some prefer young grasses or forbs over fresh shoots of A. californica during the growing season, but shift their feeding onto shrubs during the summer and fall when shrubs are particularly vulnerable (Genin & Badan‐Dangon, 1991 ; Genin & Pijoan, 1993 ).…”