Predicting Treatment Longevity after Successive Conifer Removals in Sierra Nevada Aspen Restoration

Populus tremuloides (quaking aspen) stands throughout the Sierra Nevada Mountains are undergoing succession to conifers. Removal of conifers is being tested, however, little is known about treatment longevity—the time taken for stand density to return to pretreatment levels. To determine longevity of treatments removing conifers below different size limits, we developed tree growth equations from data collected in 1 ha plots around Lake Tahoe in P. tremuloides stands with varying amounts of conifer, and simulated stand development after treatment in two stands. At Ward Creek, cutting all conifer \u3c 35 cm diameter at breast height (DBH) generated the most wood that could practically be piled and burned inside the stand, but only reduced stand density by 16%. After 13 years of predicted treatment longevity, a second treatment was simulated with options of light, medium, or heavy cutting (50, 60, or 75 cm DBH limits). This gave treatment longevity of 23, 29, and 40 years respectively but did not restore P. tremuloides dominance. At Cookhouse Meadow, cutting conifer \u3c 35 cm DBH had 16-year treatment longevity, after which time two treatments were compared. Cutting conifers \u3c 50 cm DBH enhanced P. tremuloides’ representation from 27% to 37% of stand basal area and had 23-year treatment longevity. Raising the DBH limit to 60 cm left P. tremuloides representing 45% of stand basal area, and extended treatment longevity to 36 years. Our findings indicate that a series of treatments will be needed to restore and maintain P. tremuloides communities, and will eventually require removal of large conifers (\u3e 75 cm DBH)

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