Growth, biomass, and productivity of a bracken (Pteridium esculentum) infested pasture in Marlborough Sounds, New Zealand

Abstract

Abstract With cessation of grazing, bracken (Pteridium esculentum) quickly dominated a pasture in Marlborough Sounds sampled at 0, 1, 4, 7, and 17 years. Bracken frond density increased from 1/m2 at year 0 to 32/m2 at year 7 and declined to 27/m2 at year 17 with living fronds peaking at year 4 and dead fronds at year 7. Frond height peaked at 1.83 m at year 7 and weight per frond reached 81 g at year 4. Pasture herb and tree seedling density and height strongly decreased to year 7 as frond density and height increased and then slowly increased to year 17 as the bracken canopy opened. Biomass peaks of 6800 g/m2 above-ground in year 7, of 7100 g/m2 below-ground in year 17, and of 12 500 g/m2 total in year 17 were higher than other pioneer New Zealand vegetation except Pinus radiata. Biomass accumulation increased to 1480 g/m2/yr in year 4, declined to 250 g/m2/yr in year 17 and was predicted to be nil in year 20. Above-ground net primary productivity (NPP) reached 1500 g/m2/yr in year 4 while maximum below-...