Wed, Aug 04, 2021:On Demand
Background/Question/Methods
In the southwestern US, climate change is exacerbating a legacy of fire-exclusion that has increased high-severity wildfire risk. Evidence from large high-severity burn patches shows low rates of post-fire conifer establishment. Two factors, dispersal distance and climate, are contributing to low rates of establishment. Post-fire planting can overcome dispersal limitations. However, warmer and drier conditions are causing low rates of survival in post-fire planting efforts. We implemented a planting experiment in the footprint of the 2011 Las Conchas fire in northern New Mexico to quantify the effects of aspect and vegetation cover type on planted seedling survival for four common southwestern tree species (Pinus ponderosa, P. edulis, P. strobiformis, Pseudotsuga menziesii). We planted individuals of each species, stratified by aspect (north, south) and cover type (under shrubs, no cover). We hypothesized that individuals planted on north facing aspects would have higher survival and individuals planted under the cover of shrubs would have higher survival, due to the reduction in solar insolation and the resultant lower temperature and higher moisture availability. We planted five individuals of each species in each replicate treatment, across a total of twenty replicates, half of which were planted in 2016 and half in 2017.
Results/Conclusions We found a significant effect of aspect on survival, with north aspects having higher rates of survival for all species (p=0.02). We did not find significant survival differences between individuals planted under the cover of shrubs and in the open. This may be due to the fact that we planted under the species Robinia neomexicana, which has a relatively low leaf area that varies with water stress. The winter of 2016/2017 was an average year in terms of snowpack, while the 2017/2018 winter was a severe drought. We found significant differences in survival by species for individuals planted during fall 2016 (p<0.001), with P. ponderosa (70%) and P. edulis (55%) having the highest rates of survival after the first growing season. Survival rates for P. menziesii (41%) and P. strobiformis (25%) were considerably lower after the first growing season. The subsequent winter drought caused additional mortality for all species, but the greatest impact was on P. ponderosa, in which survival dropped to 27% by the end of the second growing season. Our results demonstrate that post-fire planting techniques can mitigate some of the effects of warming and drying on survival. However, climate will continue to exert a strong effect.
Results/Conclusions We found a significant effect of aspect on survival, with north aspects having higher rates of survival for all species (p=0.02). We did not find significant survival differences between individuals planted under the cover of shrubs and in the open. This may be due to the fact that we planted under the species Robinia neomexicana, which has a relatively low leaf area that varies with water stress. The winter of 2016/2017 was an average year in terms of snowpack, while the 2017/2018 winter was a severe drought. We found significant differences in survival by species for individuals planted during fall 2016 (p<0.001), with P. ponderosa (70%) and P. edulis (55%) having the highest rates of survival after the first growing season. Survival rates for P. menziesii (41%) and P. strobiformis (25%) were considerably lower after the first growing season. The subsequent winter drought caused additional mortality for all species, but the greatest impact was on P. ponderosa, in which survival dropped to 27% by the end of the second growing season. Our results demonstrate that post-fire planting techniques can mitigate some of the effects of warming and drying on survival. However, climate will continue to exert a strong effect.