Current status and future trajectories for the riparian forest along the South Platte River in Colorado

Transcription

1 Current status and future trajectories for the riparian forest along the South Platte River in Colorado Gabrielle Katz 1, Andrew Norton 2, Ahmed Eldiery 3, Reagan Waskom 4 1 Department of Earth and Atmospheric Sciences, Metropolitan State University of Denver 2 Department of Bioagricultural Sciences and Pest Management and Graduate Degree Program in Ecology, Colorado State University 3 Department of Bioagricultural Sciences and Pest Management, Colorado State University 4 Colorado Water Institute, Colorado State University

2 2013 William A. Cotton/CSU Photography.

3 South Platte River history Pre-development river: Seasonal hydrograph: snowmelt peak flow, low flow in late summer; high inter-annual variability Wide, braided channel Goodrich, CO in 1867: Active river channel width = 535 m (Nadler and Schumm 1981) Vegetation mosaic (marshes, prairie, woody vegetation patches)

4 South Platte River history Post-development river: Beginning in 1880 s: Ditches, impoundments, trans-basin diversions, irrigation return flows augmented and stabilized hydrology, elevated riparian water table 1990: 370,000 AF imported vs. 1,200,00 AF native flow (CWRRI 1990) Eschner et al. 1983

5 South Platte River history Post-development river: Inter-annual variability

6 South Platte River history Post-development river: Establishment of woody vegetation on former active channel bed stabilized geomorphology, broad cottonwood gallery forest Process complete by 1930 s (Johnson 1994) Goodrich, CO in 1977: Active river channel width = 109 m (Nadler and Schumm 1981)

7 2013 William A. Cotton/CSU Photography. South Platte River near Kersey, Colorado, June 3,

8 South Platte River riparian forest dynamics Historic condition Current condition Future condition? Wide channel bed; Isolated cottonwood patches Altered hydrology Narrowing Flooding (erosion, widening) Narrow channel; Broad continuous cottonwood forest Modified from Friedman et al. 1997, Strange et al Succession Succession Narrow channel; Grassland Narrow channel; Modified latesuccessional forest (green ash, boxelder, Siberian elm, Russian olive)

9 Study Area

10 Methods 15 study sites 2-3 transects per site Woody vegetation sampled in 10x20m plots (belt) Trees: species, dbh, height, canopy condition Saplings: Species, dbh class, canopy condition Seedlings: density 10

11 Riparian Forest Composition Plains cottonwood Peach-leaf willow Russian olive* Green ash Siberian elm* Box elder Crack willow* Other Tamarisk* Number of trees Basal area All sites combined, n = 2,182 stems measured.*not native to US. Not native to CO.

12 2013 William A. Cotton/CSU Photography. South Platte River at Weldona, Colorado, June 20, 2013.

13 1.4 Cache la Poudre River Individuals/ha Dbh size class (cm) POPDEL SALAMY ULMPUM ACENEG FRAPEN Two study sites, 21.2 hectares sampled

14 Two study sites, 23 hectares sampled

15 Two study sites, 19 hectares sampled

16 Three study sites, 27 hectares sampled

17 Six study sites, hectares sampled

18 Conclusions South Platte River riparian forest is dominated by native species plains cottonwood, peachleaf willow Non-native species uncommon: Russian olive, Siberian elm, crack willow, tamarisk

19 Future of the forest? Based on size classes, there appears to be some ongoing cottonwood recruitment (Saint Vrain, South Platte mainstem) Is this sufficient for steady state forest? Succession may present challenges for management: nonnatives, green ash, ecological functions

20 Acknowledgements This project was funded by the State of Colorado and the Colorado Water Protection Board (SB14-195). Many thanks to: Lindsey Young, Aaron Schoelkopf, Janet Hardin, and Graham Tuttle for help with field work. Steve Miller (CWCB) and Tina Booton (Weld County) for logistical assistance. Colorado Parks and Wildlife, City of Thornton, Boulder County Open Space, and many private landowners for site access!

21 2013 William A. Cotton/CSU Photography. South Platte Valley near Fort Lupton, Colorado, June 3, 2013.