Understory Responses to Restoration in Aspen‐Conifer Forests Around the Lake Tahoe Basin: Residual Stand Attributes Predict Recovery

The removal of conifers from aspen (Populus tremuloides) stands is being undertaken throughout the western United States to restore aspen for local- and landscape-level biodiversity. Current practices include mechanically removing conifers or hand thinning, piling, and burning cut conifers in and adjacent to aspen-conifer stands. To evaluate the effectiveness of restoration treatments, we examined tree regeneration and herbaceous vegetation cover in thinned, thinned and pile burned, and non-thinned control stands. Growth rates of small conifer saplings threatening to outcompete and replace aspen were also measured. Two to four years after pile burning, herbaceous vegetation cover within the footprint of burned piles (i.e. burn scars) was 35–73% of that in adjacent areas. Aspen was more likely to regenerate inside burn scars where fewer surrounding trees were true firs. Conifer seedlings were more likely to regenerate in burn scars where more of the surrounding trees were conifers (pine or fir) as opposed to aspen. Fir saplings had much slower growth than did aspen saplings. Overall, our findings show that restoration treatments are promoting desirable outcomes such as enhancing aspen regeneration but that follow-up treatments will be needed to remove numerous conifer seedlings becoming established after restoration activities. Eliminating conifers, while they are small, growing slowly, and contributing little to fuel loads may be an economical way to prolong restoration treatment effectiveness