Shifts in botanical composition of flatwoods range following fertilization

Abstract

Three annual applications of a factorial combination of N (0, 40, 80, 120 kg ha-1), P (0, 25 kg ha-1) and K (0, 100 kg ha-1) were applied to Florida flatwoods range where 45 plant species were initially present. Addition of P and K had no effect (P > 0.05) on indices of plant diversity, density, or above-ground biomass. Both Shannon's (Y = 1.6 - 0.005N, where N is kg ha-1) and Simpson's index (Y = 0.28 + 0.002N) indicated diversity decreased with increasing N because the community was being dominated by goldenrods (Solidago fistulosa and Euthamia minor) and dogfennel (Eupatorium spp.). Density of all fortes increased with increasing N (1990 plants m-2 = 17.4 + 0.4N and 1991 plants m-2 = 35.1 + 1.4N). Density of beaked panicum (Panicum rhizomatum) increased quadratically with increasing N, while density of decumbent carpetgrasses (Axonopus spp.) and low panicums (Dichanthelium spp.) declined linearly. Broomsedge (Andropogon virginicus), wiregrass (Aristida stricta), and bottlebrush 3-awn (A. spiciformis) were eliminated from the site. Above-ground biomass of fortes increased with N (1988 kg ha-1 = 934 + 16.1N and 1990 kg ha-1 = 227 + 60.6N). Grass and grasslike biomass increased linearly as N increased, but N effects were independent of year, which were different (1988 = 1,530 kg ha-1 and 1990 = 2,140 kg ha-1). The plant community at this location became less diverse when the naturally low soil N was increased by 40 kg ha-1 or more. Early successional species replaced later successional species, especially creeping bluestem (Schizachyrium scoparium).