THE EFFECTS OF CONTROL ON THE BIOMASS, CARBOHYDRATE CONTENT AND BUD RESERVES OF BRACKEN (PTERIDIUM-AQUILINUM (L.) KUHN), AND AN EVALUATION OF A BRACKEN GROWTH-MODEL

This paper examines the initial effects of bracken control on frond nu mbers and biomass, and the biomass, carbohydrate reserves and bud dens ities of bracken stands cut once per year, twice per year, subject to a single application of asulam or left untreated. The seasonal dynamic s of these parameters are displayed; carbohydrate and biomass are both removed from the rhizome system to produce frond tissue, and are repl enished at the end of the growing season. Asulam application reduced d ensities of both active and dormant buds, and both frond biomass and d ensity. It did not significantly reduce rhizome biomass or carbohydrat e reserves in the two years after treatment. Cutting, either once or t wice per year reduced both rhizome biomass and rhizome carbohydrate re serves, as well as bud densities, though the latter were reduced in pr oportion to biomass. Cutting twice a year reduced the production of fr onds, both in numbers and biomass. The collected data were used to eva luate a model of bracken growth, and subsequently to improve estimates of some of the model parameters. The model simulations of control tre atments were compared to field data. The effects of cutting once per y ear and spraying with asulam were predicted accurately, but the bracke n stand was more resilient to cutting twice per year than would be exp ected from model predictions. The combination of cutting and spraying is discussed as a potential tool in land management and the deficienci es of the model are discussed in relation to the need for future resea rch into the biology of bracken.