Density and Development of Bracken Fern (Pteridium aquilinum) in Forest Plantations as Affected by Manual and Chemical Application

Abstract

disturbance on 5 study areas (forest plantations) in northern California favored development of bracken fern (Pteridium aquilinum [L.] Kuhn var. pubescens L. Underw.), which can be an impediment to successful reforestation. Velpar herbicide (hexazinone) offered short-term control of vegetation, including bracken fern, sufficient to establish pon-derosa pine (Pinus ponderosa Dougl. ex Laws. var. ponderosa) seedlings and ensure vigorous growth. Our examination of site preparation techniques, including burning residual logging debris followed by chemical and mechanical control of vegetation , indicated that bracken fern density, foliar cover, and height were highly variable both within and among study areas. After 5 growing seasons, bracken density in the control (site preparation only) ranged from 5800 to 40850 fronds/ha (2345 to 16 530 fronds/ac), foliar cover from 1% to 24%, and height from 0.5 to 0.6 m (1.8 to 1.9 ft). Among conifer release treatments (control of unwanted vegetation), Velpar effectively controlled bracken, but Garlon herbicide aided bracken by killing competing shrubs. After 10 growing seasons, more than 22000 bracken fronds/ha (8910/ac) were present in all treatments. Bracken fern demonstrated remarkable ecological amplitude, was virtually independent of other species, and was only moderately influenced by a wide range of environments. Growers and planters should be aware of these findings and use herbi-cides that show demonstrated effectiveness. K E Y W O R D S ecology, conifer plantations, interference, northern California, ponderosa pine, Pinus ponderosa N O M E N C L AT U R E (trees) Little (1979); (plants) Hickman (1993) A B S T R A C T (Pteridium aquilinum) ew people grow bracken fern (Pteridium aquilinum [L.] Kuhn var. pubescens L. Underw.) and even fewer plant it in their fields or forests. Many growers and planters, however, have lost outplantings of more valuable species to this widespread and competitive fern. Knowledge about bracken's morphology, development, and control could be key to successful establishment of other desirable species. Currently , only limited information is available on the autecology of bracken fern in California and even less on its response to various physical and chemical treatments.