veg_sim: Modeling Greater sage-grouse habitat suitability 15-years post simulated fire event and sagebrush transplanting (2015-2030)

To assess the degree to which transplanting sagebrush (Artemisia spp.) could quickly restore former Greater sage-grouse (Centrocercus urophasianus; hereafter, sage-grouse) habitat and the strategies by which sage-grouse habitat restoration is best accomplished, we linked vegetation transitions with habitat selection models to evaluate habitat recovery. There are few data-driven approaches to identify efficient restoration strategies that maximize benefits to wildlife. To test the efficiency of alternative planting strategies in recovering multi-scale habitat needs for the sage-grouse in the Great Basin, we developed a spatial vegetation-habitat recovery model. Within our modeling extent (near Tuscarora, Nevada), we simulated the fire-induced loss of habitat, planting of sagebrush seedlings, and the regrowth of sagebrush and other vegetation over 15 years. We used sagebrush growth equations and vegetation state transitions to return and grow vegetation within the burned and planted areas. Every year, we updated seasonal sage-grouse habitat selection maps by re-applying pre-fire resource selection equations to re-calculate the proportion of suitable habitat gained by sagebrush restoration efforts. We evaluated alternative planting designs to identify the key factors influencing habitat selection outcomes. Specifically, we varied the number of plants, patch sizes, densities, location of planting sites (i.e., random versus within sage-grouse nesting habitat), as well as post-transplant survival (30, 70, or 100%). We assumed all planting occurred in a single year. We measured the amount and suitability of sage-grouse habitat at 15-years post-fire to indicate the degree to which wildlife-focused restoration could quickly regain suitable habitat. Sagebrush transplant efforts are likely to shorten the time to habitat recovery; however, highly intensive planting projects are required to overcome high seedling mortality rates and cover the large areas required by sage-grouse.
We used the following steps to develop time-stamped data products reflecting vegetation changes resulting from a simulated wildfire and transplanted sagebrush seedlings. This workflow (Figure 1) is reflected in the code presented here. Time since fire (TSF[0-15]), time since planting (TSP), resource selection functions (RSF; seasonal habitat models), and habitat suitability indices (HSI) are frequently referenced in the code and documentation.
1. We replicated resource selection function (RSF)/habitat suitability index (HSI) models of seasonal habitat for a pre-fire event.
2. We then simulated a fire on the landscape in a sagebrush ecosystem.
3. We identified planting sites based on different planting design criteria.
4. We updated individual vegetation components within the simulated fire extent and transplant sites.
5. We updated resource selection function models reflecting seasonal habitat each year to reflect changes in vegetation.