Using aerial mapping to analyse factors affecting the spread of Scotch broom

Doreen OdomA, G.R. GriffithA,B, Mellesa SchroderC and J.A. SindenA

A Graduate School of Agricultural and Resource Economics, University of New England, Armidale, New South Wales 2351, Australia.

B NSW Agriculture, Armidale, New South Wales 2351, Australia.

C NSW National Parks and Wildlife Service, Nelson Bay, New South Wales 2315, Australia.


Scotch broom is an invasive weed in many subalpine ecosystems. It often has substantial negative effects on ecosystem structure and functions. Decisions on optimal management strategies require predictions of the rates and patterns of Scotch broom spread. This paper explores the environmental and management factors that influence the rate of spread of Scotch broom in Barrington Tops National Park.

The NSW National Parks and Wildlife Service (NPWS) and the then neighbouring NSW State Forests prepared aerial maps showing Scotch broom infestation in the Park for 1989, 1993 and 1999. These maps were used to generate data for the current analysis. Map reference points 1 km apart along the southern boundary of the 1989 area of infestation were examined and 1993 and 1999 differences from the reference points were measured. Also measured were environmental factors including natural vegetation type, natural vegetation density, soil type, slope, altitude and the presence of private property or crown land. The incidence of natural disaster, feral animal activity and NPWS management activities were also included in the analysis.

The regression analysis shows that the three variables contributing most to an expansion of broom are sparse vegetation (62 m pa), flat slopes (23 m pa) and State Forest land (23 m pa). The three variables contributing most to a reduction in broom spread are NPWS general treatment activities (-14 m pa), NPWS specific wetlands treatment (-40 m pa) and steeper slopes (-59 m pa).

Key words: aerial mapping, Scotch broom, spread, park management, regression models.


Plant Protection Quarterly (2003) 18 (1) 6-10.