Hinojosa-Huertal - 2014 - CEER - Ecosystem response to restoration
Summary
THE ECOSYSTEM RESPONSE TO RESTORATION: BIRDS AND VEGETATION IN THE COLORADO RIVER DELTA The floodplain of the Colorado River in Mexico, covering 12,000 hectares, experienced a recovery in response to inadvertent flows during the 1980s and 1990s. However, the basin has endured a severe drought since 2002, and the average flows been reduced from 93 m3/s in 1998, to 0.2 m3/s in the last 5 years. On the other hand, several restoration projects have been implemented in the floodplain since 2008, covering over 200 hectares. To evaluate the effect of the drought on vegetation and birds in the floodplain we conducted variable distance point counts and evaluated habitat characteristics at 136 sites, from 2002 to 2013. We also conducted surveys [...]
Summary
THE ECOSYSTEM RESPONSE TO RESTORATION: BIRDS AND VEGETATION IN THE
COLORADO RIVER DELTA
The floodplain of the Colorado River in Mexico, covering 12,000 hectares, experienced a recovery in response to inadvertent flows during the 1980s and 1990s. However, the basin has endured a severe drought since 2002, and the average flows been reduced from 93 m3/s in 1998, to 0.2 m3/s in the last 5 years. On the other hand, several restoration projects have been implemented in the floodplain since 2008, covering over 200 hectares. To evaluate the effect of the drought on vegetation and birds in the floodplain we conducted variable distance point counts and evaluated habitat characteristics at 136 sites, from 2002 to 2013. We also conducted surveys with the same procedures at 24 sites at the restored areas.
Between 2002 and 2013, the vegetation cover decreased from 76.1% to 60.3% in the floodplain, and the percent cover of trees decreased 53% (from 27.5% to 12.6% cover). Both cottonwoods and willows decreased, 77.1% and 91.6% respectively, with a combined cover of 7.18% in 2002 and of only 0.84% in 2013. The vegetation at the restoration sites in 2013 maintained an overall cover of 77%, with 55% more tree cover (19.8%), and 7 times more cover of cottonwoods and willows than the rest of the floodplain (3.11% and 2.73% respectively). Between 2002 and 2013, the average bird abundance increased 3.8 times and the average species richness remained without significant trend. However, bird diversity per point (N2) decreased 55.8%, while the relative abundance of the 3 dominant species (Red-winged Blackbird, Mourning Dove and White-faced Ibis) increased from 37% in 2002 to 67% in 2013. The community structure changed and species had different responses: 34 species had significant downward trends and 36 species had significant upward trends. Declining species were mostly riparian dependent land birds and breeding waterbirds, including species of conservation priority such as Song Sparrow (90.2% decline), Yellow-billed Cuckoo (100%, no detections in the last two years), Vermillion Flycatcher (66%), and Yellow-breasted Chat (82%). The species with upward trend included birds related to agricultural/urban development, exotic species and raptors, in particular Red-winged Blackbird, Mourning Dove, Yellow-headed Blackbird, Eurasian Collared Dove, and Great-tailed Grackle. In contrast, at the restoration sites, bird abundance was 27.7% higher, species richness was 33% higher, bird diversity was 53.5% higher and the combined density of 12 species of conservation interest was 156 times higher than throughout the floodplain. The drought resulted in a drastic reduction of flows, causing an important reduction of habitat quality, which in turn was related to a population decline of riparian birds. The efforts at the restoration sites are successfully establishing riparian habitat, with increased populations of species of conservation concern.