In the drier, mid- and low-elevation portions of the Southern Rockies LCC, Fremont cottonwood represents the only native vegetation of tall stature, and cottonwood-dominated woodlands provide critical habitat for a large array of neotropical migratory birds and other animals. These woodlands likely dominated alluvial reaches of all streams where a snowmelt-driven spring flood was the major factor driving geomorphic and vegetation dynamics. These woodlands were also among the first habitats to undergo transformation as the regions land and water resources were developed.
The PI coauthored a paper (Andersen et al. 2007) on assessing the amount of native Fremont cottonwood forest remaining on floodplains in 26 subbasins in the Upper Colorado River Basin (UCRB). Given the high degree of streamflow management in the UCRB and the potential for adverse effects from flow management on cottonwood population processes, it was encouraging to find that more than half of the floodplain area along mainstem rivers was cottonwood forest. Of great concern, however, was the fact that nearly 70% of that forest area featured a sparse canopy (5% cover), strongly suggesting it was made up solely of old trees. Stands with >50% canopy, typical of young trees, occupied <1% of the floodplain. These patterns suggest that, on a regional basis, there is insufficient recruitment to replace stands of old trees and that a major reduction in forest extent will occur when the old trees die. The results also suggest that the increase in Fremont cottonwood abundance noted on some streams and rivers in the American Southwest (Webb and Leake 2006) is probably limited to the extreme southern portion of the Southern Rockies LCC and on streams where the largest floods were historically associated with monsoon or winter rains rather than spring snowmelt.
FY2012In the drier, mid- and low-elevation portions of the Southern Rockies LCC, Fremont cottonwood represents the only native vegetation of tall stature, and cottonwood-dominated woodlands provide critical habitat for a large array of neotropical migratory birds and other animals. These woodlands likely dominated alluvial reaches of all streams where a snowmelt-driven spring flood was the major factor driving geomorphic and vegetation dynamics. These woodlands were also among the first habitats to undergo transformation as the regions land and water resources were developed.
The PI coauthored a paper (Andersen et al. 2007) on assessing the amount of native Fremont cottonwood forest remaining on floodplains in 26 subbasins in the Upper Colorado River Basin (UCRB). Given the high degree of streamflow management in the UCRB and the potential for adverse effects from flow management on cottonwood population processes, it was encouraging to find that more than half of the floodplain area along mainstem rivers was cottonwood forest. Of great concern, however, was the fact that nearly 70% of that forest area featured a sparse canopy (5% cover), strongly suggesting it was made up solely of old trees. Stands with >50% canopy, typical of young trees, occupied <1% of the floodplain. These patterns suggest that, on a regional basis, there is insufficient recruitment to replace stands of old trees and that a major reduction in forest extent will occur when the old trees die. The results also suggest that the increase in Fremont cottonwood abundance noted on some streams and rivers in the American Southwest (Webb and Leake 2006) is probably limited to the extreme southern portion of the Southern Rockies LCC and on streams where the largest floods were historically associated with monsoon or winter rains rather than spring snowmelt.
