Weather affects post‐fire recovery of sagebrush‐steppe communities and model transferability among sites

Abstract

Altered climate, including weather extremes, can cause major shifts in vegetative recovery after disturbances. Predictive models that can identify the separate and combined temporal effects of disturbance and weather on plant communities and that are transferable among sites are needed to guide vulnerability assessments and management interventions. We asked how functional group abundance responded to time since fire and antecedent weather, if long-term vegetation trajectories were better explained by initial post-fire weather conditions or by general five-year antecedent weather, and if weather effects helped predict post-fire vegetation abundances at a new site. We parameterized models using a 30yr vegetation monitoring dataset from burned and unburned areas of the Orchard Training Area (OCTC) of southern Idaho, USA, and monthly PRISM data, and assessed model transferability on an independent dataset from the well-sampled Soda wildfire area along the Idaho/Oregon border. Sagebrush density increased with lower mean air temperature of the coldest month and slightly increased with higher mean air temperature of the hottest month, and with higher maximum January-June precipitation. Perennial grass cover increased in relation to higher precipitation, measured annually in the first four years after fire and/or in September-November the year of fire. Annual grass increased in relation to higher March-May precipitation in the year after fire, but not with September-November precipitation in the year of fire. Initial post-fire weather conditions explained 1% more variation in sagebrush density than recent antecedent 5-yr weather did but did not explain additional variation in perennial or annual grass cover. Inclusion of weather variables increased transferability of models for predicting perennial and annual grass cover from the OCTC to the Soda wildfire regardless of the time period in which weather was considered. In contrast, inclusion of weather variables did not affect transferability of the forecasts of post-fire sagebrush density from the OCTC to the Soda site. Although model transferability may be improved by including weather covariates when predicting post-fire vegetation recovery, predictions may be surprisingly unaffected by the temporal windows in which coarse-scale gridded weather data are considered.

Interannual variation in climate contributes to contingency in post‐fire restoration outcomes in seeded sagebrush steppe

“…Spatial variation in the importance of weather suggests that the predictability of restoration outcomes may vary with the severity or nature of the environmental factors constraining community recovery (as proposed by Brudvig et al, 2017). Further, our findings emphasize that the weather effects detected by smaller‐scale studies may not translate to improved prediction or management across large landscapes (Applestein et al, 2021). Considerations about the transferability of studies (given their environmental context) are particularly important considering that restoration treatments may be disproportionately applied to more stressful or degraded sites, compared to the full climatic range of sagebrush steppe ecosystems (Reid et al, 2018; Simler‐Williamson & Germino, 2022).…”

“…The relationships between spring weather and sagebrush growth, detected by coarse‐scale remotely sensed data, reflect ecophysiological mechanisms identified in past field‐based studies of sagebrush. Mean temperatures, spring precipitation, and late‐winter snowpack retention have been linked to the occurrence and growth of reseeded sagebrush, primarily by influencing soil–water availability, specifically in the early stages of sagebrush development (Apodaca et al, 2017; Applestein et al, 2021; Nelson et al, 2013; O'Connor et al, 2020; Schlaepfer et al, 2014b). The overall negative effects of maximum and minimum temperatures detected here indicate a role for water deficit in influencing sagebrush recovery at a larger scale (Figures 3 and 4), as these factors drive the phenology of spring snowmelt, recharge, soil moisture, and seedling success during subsequent periods of summer drought.…”

“…Future work should aim to explicitly isolate the extent to which weather conditions improve the prediction of restoration outcomes at new sites in management‐relevant ways (Applestein et al, 2021), rather than explaining within‐sample effects. In addition to temporal replication of treatments, datasets with frequent observations may be key to isolating the management relevance of annual weather, compared to long‐term climate, given high correlations between these variables (Groves et al, 2020).…”

Herbivory Amplifies Adverse Effects of Drought on Seedling Recruitment in a Keystone Species of Western North American Rangelands

“…Although plants in semiarid and arid ecosystems have different strategies to cope with drought, their natural recruitment or seedling establishment following seeding and outplanting can be very low [ 17 , 18 ]. A semiarid habitat where this has been commonly observed is the sagebrush steppe in western North America [ 18 , 19 , 20 ]. This habitat covers approximately 450,000 km 2 and is characterized by a vegetative community composed of perennial grasses, forbs, biological soil crusts, and several subspecies of the shrub Artemisia tridentata Nutt (big sagebrush) [ 21 , 22 ].…”

Evaluating Effects of Post-Fire Climate and Burn Severity on the Early-Term Regeneration of Forest and Shrub Communities in the San Gabriel Mountains of California from Sentinel-2(MSI) Images

“…Applestein et al (2021) evaluated a dataset from the Soda Fire area on the Idaho/Oregon border and found that sagebrush density increased with increasing temperature and rainfall. The annual sagebrush area increase was associated with increased spring rainfall in the year following the fire, but not with fall rainfall in that same year [14]. This suggests that the climate in the first growing season experienced by vegetation may be very important for the post-fire regeneration of vegetation communities [15].…”