Canadian Forest Service Publications
Mapping of Scotch Broom (Cytisus scoparius) with Landsat Imagery. 2016. Hill, D.A.; Prasad, R.; Leckie, D.G. Weed Technology, 30:539–558.
Issued by: Pacific Forestry Centre
Catalog ID: 37640
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Methods were developed and tested for mapping the distribution of Scotch broom, an invasive shrub species expanding its range and disrupting native species and habitats in several parts of the world. During spring, the Scotch broom produces yellow flowers. Landsat imagery during the flower bloom period and during summer was acquired for several years for a study area on Vancouver Island, British Columbia, Canada. Ground-based reflectance measurements plus statistical separability tests were conducted to determine the effectiveness for identifying Scotch broom with Landsat spectral bands, band ratios, vegetation indices, and combinations of bloom and nonbloom imagery. Maximum likelihood classifications of three Scotch broom density classes (dense, 75% cover; moderate, 25 to 75%; low, 10 to 25%) and other land covers were run with various image and band sets and tested against independent reference sites. Accuracies of classifications using the better band combinations for moderate and dense Scotch broom patches combined were on the order of 80%, with unreliable results for sites of low Scotch broom density. Scotch broom patches less than 0.5 ha were often missed. Some commission error occurred (areas erroneously classified as Scotch broom). Suggested improvements are the use of time series of classifications over multiple years, incorporating knowledge of Scotch broom spread mechanisms or temperature and elevation limitations, and use of higher resolution satellites if the expense warrants it. Despite some limitations, a satellite-based remote sensing approach may be useful for aspects of Scotch broom management.
Plain Language Summary
The paper develops a method to map Scotch Broom from broad area coverage low cost satellite imagery. Procedures for classifying areas of broom were developed and tested. The approach uses the fact that during spring there is a period of flowering with yellow colouration. The result was a viable method useful to various applications (monitoring invasives, planning control programs, fire management, understanding its spread and impact). Applicability to other image data sources and possible methods for improvement are given. A practical tool is provided to practitioners, and scientific insight into the detection of broom reported. Broom is an invasive species impacting native ecosystems, forest management, landscapes, recreation and fire hazard. Results have application to Scotch broom mapping elsewhere in the world and other invasive species with characteristic colouration.