The history and effects of alien plant control in the Cape of Good Hope Nature Reserve, 1941–1987

Concern about the invasion of this reserve by alien trees and shrubs, principally Acacia cyclops, A. saligna, A. longifolia, Eucalyptus lehmannii and Pinus pinaster, was first expressed in 1941, 2 years after its proclamation. Control operations were started by 1943 and were almost totally ineffective for at least the first 35 years; no systematic control strategy was implemented, follow-up control work was inadequate to prevent reestablishment of felled thickets and the supervision of control teams was deficient. Linkage of control operations to firewood production was a significant factor in this failure. In 1974 a 10-year control strategy was drawn up and in the late 1970’s began to be effectively implemented. Surveys of 40 plots in the centre of the reserve in 1966, 1976–80 and 1986 showed increasing densities of species other than the easily controlled P. pinaster up to 1976–80. Since then almost all individuals > 1,8 m in height have been eliminated and indications from smaller height classes are that seed banks are being depleted. Explanations are advanced for the successes and failures experienced during the 47 years of control. Some of the side-effects of these invasions and their control are discussed. One conclusion is that this reserve requires a qualified ecologist on its staff. Bekommernis oor die indringing van uitheemse bome en struike, veral Acacia cyclops, A. saligna, A. longifolia, Eucalyptus lehmannii en Pinus pinaster, was reeds in 1941 uitgespreek, 2 jaar na die proklamasie van die reservaat. Beheeroperasies was in 1943 begin en was heeltemal onsuksesvol vir 35 jaar; daar was geen sistematiese beheerplan nie, opvolgwerk was onvoldoende en gevolglik het afgekapte bome weer gegrooi. Die toesighouding oor die beheerspanne was ook onvoldoende. Die besluit om die beheeroperasies te gebruik om brandhout te kry was skynbaar een rede vir die mislukking van die vroeë pogings. Gedurende 1974 was ’n 10-jaar-beheerstrategie geformuleer en dit was uiteindelik in die laaste jare van die dekade doeltreffend geïmplementeer. Opnames van 40 persele in die middel van die reservaat was in 1966, 1976–80 en 1986 uitgevoer. Die digtheid van al die spesies behalwe P. pinaster het tot 1976–80 vermeeder. Sedertdien was amper al die plante met hoogte > 1,8 m uitgeroei en dit lyk asof die saadbank verminder het. Redes vir die suksesse en mislukkings van die program word voorgestel. Sommige van die ekologiese gevolge van die indringings en hulle beheer word bespreek. Die aanstelling van ’n vakkundige ekoloog as lid van die reservaat se personeel word aanbeveel.