Factors affecting early plant survival in restoration of Mediterranean‐type climate shrublands

Abstract As in other Mediterranean‐type climate regions, frequent fire and drought can degrade native shrublands necessitating active restoration. We conducted a restoration experiment in type‐converted shrubland in southern California and focused on four questions: (1) Which factors contribute most to the survival of restored species over 1 year? (2) Does irrigation at practical levels increase restored shrub survival over 2.5 years? (3) Does native species habit (shrubs, herbaceous monocots) or shrub community affiliation (California sage scrub CSS shrub or chaparral shrub) relate to survival over 2.5 years? and (4) Is shrub survival linked to resource use associated functional traits of each species? We established 16 restoration plots, each planted with 49 individuals selected from 18 locally occurring CSS and chaparral species. Restored plots received 9 months of irrigation. In addition, we included an upslope non‐irrigated sub‐plot containing 8 planted species. After 1 year, a generalized model of paired CSS and chaparral species identified time, vegetation type and species as explaining the majority of variation in survival, with plot and treatment (irrigated or not) explaining minimal variation. After 2.5 years, survival was slightly higher in irrigated compared to non‐irrigated plants and by community affiliation, CSS species with irrigation had significantly higher survival (68% CSS vs. 11% chaparral). In terms of functional traits, CSS species had higher survival and were associated with higher growth rates, lower embolism resistance (less negative P50), and lower photoinhibition (higher seasonal minimum F v / F m ) consistent with an acquisitive and stress avoidance resource use strategy. In an era of increasing hot droughts, restoration strategies to limit species mortality associated with high temperatures and vapor pressure deficits are a priority. We identified two key findings for resource managers undertaking restoration in Mediterranean‐type climates: planting CSS species with drought avoidance strategies is more likely to achieve restoration goals; however, supplemental irrigation may not be necessary to achieve such goals.