COS 203-6 - Higher rainfall, non-native removal, and their interactions promote post-fire recovery in demographic modeling of the native shrub Artemisia californica

Abstract: Mediterranean-climate shrublands support high levels of biodiversity and provide important carbon storage services, but are increasingly threatened by biological invasions, climate change, and altered fire regimes. Fires are important to the historic disturbance cycles of these communities but can also facilitate establishment of non-native competitors, potentially limiting native shrub recovery. Increasing drought due to climate change is creating another potential barrier to post-fire shrub regeneration. I developed a stochastic, individual-based demographic model (IBM) for the native California shrub Artemisia californica over the first seven years after fire. The model was parameterized from a non-native removal experiment, implemented after a small-scale fire in southern California sage scrub and spanning both drought and non-drought rain years. Artemisia california recruitment, survival, and growth were linked with non-native removal treatments and annual rainfall conditions using mixed effects statistical models. I then used the IBM to simulate A. californica recovery under a range of rainfall (drought vs. non-drought) and non-native removal scenarios, addressing two questions 1) How do drought, non-native removal, and their interactions affect post-fire recovery of A. californica? 2) Can non-native removal in a subset of years achieve benefits comparable to those of removal in all 7 years?

Rainfall conditions influenced A. californica canopy volume at 7 years after fire more than management. Rainfall in the second year after fire, when most A. californica germination occurred, had particularly strong effects. Canopy volume after 7 years also differed significantly across management (non-native removal) strategies, and management interacted with the amount of second year rainfall. Non-native removal in the second year post-fire enhanced the benefits of higher rainfall in that year. Under drought conditions, increasing the number of years with non-native removal almost always increased A. californica canopy volume. In contrast, under non-drought rainfall conditions removing non-natives only in the first and second years achieved the same total canopy volume as removal in all 7 years These findings suggest that drought may be the most important limitation on post-fire native shrub recovery, if recruitment is highly pulsed and seeds cue germination more to fire than rainfall. Non-native removal also strongly enhanced regeneration, even more so under drought conditions. Targeting non-native removal in the first two years proved highly effective, nearly as much so as removing non-natives in all years. More generally, this study illustrates how demographic models can help optimize the targeting of scarce management and restoration resources to maximize benefits.