Title: Estimating western juniper cover with NAIP imagery and evaluating the relationships between potential cover and environmental variables Authors
|Steven, Petersen -|
|Dustin, Johnson -|
|Davis, David -|
|Daniel, Zvirzdin -|
Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 13, 2010
Publication Date: November 3, 2010
Repository URL: http://hdl.handle.net/10113/48833
Citation: Davies, K.W., Steven, P.L., Dustin, J.D., Davis, D.B., Madsen, M.D., Daniel, Z.L., Bates, J.D. 2010. Estimating western juniper cover with NAIP imagery and evaluating the relationships between potential cover and environmental variables. Rangeland Ecology and Management. 63:630-637. Interpretive Summary: Western juniper woodlands are expanding from their historic range and causing significant declines of other plant communities. The encroachment of juniper can degrade wildlife habitat, reduce livestock forage, and increase erosion. However, landscape-scale restoration projects are hindered by time consuming and expensive methods to inventory juniper cover. We investigated the utility of aerial photographs to measure western juniper cover and the relationships between remotely sensed environmental characteristics and juniper cover at stand closure. Our results demonstrated that aerial photographs can be used to measure juniper cover. This information is useful to restoration ecologists and land managers to make landscape scale restoration of western juniper encroached lands more feasible.
Technical Abstract: Western juniper (Juniperus occidentalis spp. occidentalis Hook.) woodlands are expanding from their historic range and causing significant declines of other plant communities. However, landscape-scale restoration projects are hindered by time consuming and expensive methods to inventory juniper cover and prioritize landscapes based on developmental phase of juniper encroachment. We investigated the ability of feature extraction software to estimate western juniper cover from color aerial photographs obtained from the National Agriculture Imagery Program (NAIP) and explored the relationships between juniper cover at stand closure (potential juniper cover) and remotely sensed environmental indices and characteristics. Estimates of juniper cover derived from NAIP imagery and ground measurements were similar (R2 = 0.74; P < 0.01). Neither method consistently estimated juniper cover higher or lower than the other method (P = 0.79). Environmental indices were either not correlated or weakly correlated with juniper cover at stand closure. However, the environmental characteristics (slope, aspect, and elevation) could be used to explain 40% of the variation in juniper cover at stand closure (R2 = 0.40; P < 0.01). Thus, remotely measuring environmental characteristics can be used to assist in determining potential juniper cover. This information can then be compared to current juniper cover to determine juniper woodland developmental phase. Knowing the developmental phase is important because management strategies and effectiveness of restoration treatments differ between phases of juniper encroachment. Our results suggest that NAIP imagery can be a valuable tool to effectively estimate juniper cover over large areas to make landscape scale restoration more feasible. The model of the relationship between remotely measured environmental characteristics and potential juniper can be used to assist in restoration planning and prioritization, but could be improved with further refinement.