A method to map riparian exotic vegetation (Salix spp.) area to inform water resource management

Abstract

Hydrological processes within riparian environments worldwide are impacted when introduced species invade. Monitoring and management at substantial expense, are subsequently required to combat deleterious effects on the environment and stream hydrology. Willow species (Salicaceae: Salix spp.) introduced into Australia have spread throughout many riparian systems causing adverse environmental impacts, with high rates of water extraction when located within stream beds (in-stream willows) thus altering hydrology. Strategies exist to manage willows; however, simpler, more cost-effective methods are required to map and monitor spatial and temporal distributions. A method is presented to discriminate willow stands from surrounding native riparian vegetation using a single, very high 2 m resolution multispectral WorldView-2 satellite image. A combination of spectral bands 'coastal blue' (400-450 nm), 'red' (630-690 nm), 'red edge' (705-745 nm) and 'near infrared2' (860-1040 nm), minimum noise fraction transformation, median filtering and maximum likelihood supervised classification provided the highest discriminatory power within a 25 km 2 study area. Of the spectral bands, coastal blue, red edge and near infrared2 are new bands that are not available in other multispectral sensors. These bands proved critical to the success of discriminating willows from other land cover categories (overall accuracy of 97%). Stream channels were defined by incorporating a LiDAR-derived digital elevation model to discriminate between willows on stream banks and within stream beds. Canopy area estimates of in-stream willows, coupled with water savings estimates from willow removal, suggest removal of 10.4 ha of Salix fragilis canopy from within river channels in the study area will potentially return 41 ML year À1 to the environment. The method presented improves our understanding of willow impacts on hydrology and aids decisions regarding willow removal for water resource management.

Ash Decline Assessment in Emerald Ash Borer Infested Natural Forests Using High Spatial Resolution Images

“…A classification work using WV imagery resulted in overall accuracies as high as 96% when classifying four tree species and 82% when classifying 10 species [50]. A study evaluating riparian vegetation using six bands of the WV2 achieved high overall accuracies of 93% [51]. Research mapping endangered tree species using WV imagery resulted in an accuracy of 77% [52].…”

Development of pan coefficients for estimating evapotranspiration from riparian woody vegetation

“…Recent development of remote sensing methods to delineate Salix canopy extents and calculate canopy area (Noonan and Chafer, ; Doody et al ., ) within watersheds provides additional utility for the derived pan coefficients. Total canopy area estimates (of in‐stream Salix ) can be linked with climate, pan coefficients and open‐water models to estimate total potential water savings or water draw down within a target area.…”

“…Doody et al . () have since developed a finer‐resolution method to determine willow extent and calculate canopy area that delineate in‐stream willows from bank willows by incorporating laser optical remote sensing technology (lidar) to identify channel banks. Once mapped, watershed and resource managers can accurately estimate evaporative loss per hectare of in‐stream Salix spp.…”

Comparing Pixel and Object-Based Approaches to Map an Understorey Invasive Shrub in Tropical Mixed Forests

“…The use of these data for remote detection of invasive plants has proved useful in several different ecosystems, and for a variety of species (Mohamed et al, 2011; Doody et al, 2014; Niphadkar and Nagendra, 2016). Comparative studies of VHR data and medium resolution data for invasive species detection have often proved that VHR data were extremely effective (Everitt et al, 2008).…”