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Download Restoration scale and stream benefits in California rangelands
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Restoration scale and stream benefits in California rangelands Bronwen Stanford Erika Zavaleta University of California, Santa Cruz Riparian tree restoration • Widely used in agricultural systems • Potential to restore ecological function • BUT width matters. • Potential importance of buffer length • • • • Lower temperatures More organic debris and opportunities to trap wood Improved channel complexity Less fine sediment 1. In rangelands, which ecological metrics improved with restoration at narrow buffer scales? 2. Are larger ecological gains possible with longer buffers? - 2nd-4th order streams - Consistent land use: rangelands - Restoration completed >7 years ago NLCD 2011 Treatment (distance along buffer) • Abiotic Rangeland 0m >200 m >500 m 1 • Channel form • Substrate size (D50) • Dissolved solids (specific conductivity) • Water temperature • Biotic 2 3 • Aquatic vegetation (% cover) • Organic debris and wood • Benthic macroinvertebrates • Density • Richness • Percent sensitive -California Aquatic Bioassessment Laboratory Network • 25 sites nested in 8 streams • Primary predictor variable is buffer length – upstream linear length with riparian trees Upstream of buffer Within buffer Upstream of buffer Within buffer Upstream of buffer Within buffer Response of in-stream conditions to Watershed condition (hydrology, land cover) Riparian buffer length Riparian buffer presence Watershed scale controls water quality Buffer length increased % sensitive taxa Sensitive = tolerance level 0 - 2 out of 10, CAMLnet 2003 Buffer length increased % sensitive taxa Sensitive = tolerance level 0 - 2 out of 10, CAMLnet 2003 Buffer length increased % sensitive taxa y=inverse logit (-3.38 + 0.001 * x + ɛ) p < 0.001 Sensitive = tolerance level 0 - 2 out of 10, CAMLnet 2003 Similar responses - Abundance (inverse) - Temperature (inverse) Buffer presence increased in-stream wood Buffer presence increased in-stream wood Paired t-test p < 0.04 No Trees Trees Similar responses - % cover macrophyte (inverse) 1. Response controlled by watershedscale (controls including land use, geology) 2. Buffer length Proportion sensitive insect families Insect abundance Temperature Conductivity Channel form 3. Buffer presence 4. Patterns vary by site Wood Aquatic vegetation Substrate size Insect family richness Year Two - 2016 • Addition of 7 more streams (total 15) • Comparison of contrasting rainfall conditions Conclusions • BUFFERS MATTER – even short buffers (~200 m) • Longer buffers (>500m) can be better than shorter • Recovery is constrained by watershed condition Thanks to Liam Zarri David Herbst Karen Holl [email protected] Stream width Aquatic vegetation Macrophyte cover Increasing buffer length 18% of variance explained Conductivity Woody debris Bare ground Complexity Organic debris Substrate size 39% of variance explained Sun Macrophyte cover Aquatic vegetation % Predators Year Two - 2016 Tolerance value PCA for environmental variables 14.99-0.0068*Buffer Length + ɛ p=0.07
