Population dynamics of Leysera gnaphalodes: a statistical modelling approach

Namaqualand is world-renowned for its mass springtime wildflower displays, common in highly disturbed areas. Leysera gnaphalodes is a short-lived perennial shrub that encroaches on these wildflower displays, lessening their aesthetic appeal. For this reason, populations of L. gnaphalodes need to be kept as small as possible. This is usually achieved by tilling the area regularly, but a less disruptive method would be preferable. Alternatives to this approach were explored. An eight-year study was conducted to determine the effects of tilling, grazing and other environmental factors, including rainfall and temperature, on seedbank and population sizes of L. gnaphalodes. Multivariate statistical models were developed to determine the effects of all of these factors on L. gnaphalodes populations. Tilling was confirmed to be effective in reducing population size, but grazing had no effect. Low rainfall was also effective in controlling population size but had the disadvantage of being out of management control and deleterious to desirable wildflowers.