Cottonwood Lessons: Can Best Management Practices Increase Restoration Effectiveness?
Lisa Markovchick1*, Catherine A. Gehring2, Tessa Deringer3, Kevin Grady4, and Thomas G. Whitham5
1Department of Biological Sciences and Merriam-Powell Center for Environmental Research, Northern Arizona University, Flagstaff, AZ 86011, U.S.A.; Lisa_Markovchick@nau.edu.
2Department of Biological Sciences and Merriam-Powell Center for Environmental Research, Northern Arizona University, Flagstaff, AZ 86011, U.S.A.; Catherine.Gehring@nau.edu
3Department of Biological Sciences and Merriam-Powell Center for Environmental Research, Northern Arizona University, Flagstaff, AZ 86011, U.S.A.; tld94@nau.edu
4School of Forestry, Northern Arizona University, Flagstaff, AZ 86011, U.S.A.; Kevin.Grady@nau.edu
5Department of Biological Sciences and Merriam-Powell Center for Environmental Research, Northern Arizona University, Flagstaff, AZ 86011, U.S.A.; Thomas.Whitham@nau.edu
We investigated whether cottonwood restoration best practices could synergistically offset the negative impacts of tamarisk legacy and a warming, drying climate, including changes in above- and below-ground species known to facilitate cottonwood survival and growth. Although a few studies have shown each of the best management practices to be effective individually, research addressing their combined effects on restoration is relatively non-existent. We planted an experimental garden near Cameron, AZ to test the impacts of planting: a) regionally local cottonwoods (Populus fremontii) versus those sourced from 3°C warmer locations, b) with or without regionally local willow (Salix exigua) nurse plants, c) with or without inoculation by live soil unaffected by tamarisk invasion (containing a fuller suite of symbiotic fungi [mycorrhizas]), d) in land patches with and without a history of invasion by tamarisk (Tamarix spp.). The first year of survival and growth data revealed four major trends: 1. Regionally local trees outperformed trees transferred from 3°C warmer locations. 2. Tamarisk legacy soils reduced survival, but the effect was larger for trees transferred from warmer locations. 3. Inoculation increased initial survival in tamarisk legacy soils, but reduced survival in non-tamarisk legacy soils. 4. Willow nurse plants demonstrated no early effects on cottonwood survival. These findings are contrary to research findings where these best management practices were investigated individually, indicating a more complex interaction between best management practices than previously anticipated. Our research demonstrates that critical interactions between tree source population, mycorrhizal fungi, and tamarisk legacy should be incorporated into successful restoration.