First-year response of a Phragmites marsh community to seasonal burning

Abstract

The effect of seasonal burning was determined on a stand of Phragmites australis with an understory of Teucrium occidentale, Urtica dioica, and three less abundant species. Each portion of the stand was subjected to one of three burn treatments: August 1979, October 1979, or May 1980. By August 1980, the summer-burned community had decreased in dominance and increased in species diversity, richness, and evenness. In contrast, these community characteristics were unaltered on the spring and fall burns. Understory species showed three different responses to season of burn: (1) Atriplex patula and Sonchus arvensis were absent on unburned plots; their aboveground biomass increased on summer burns owing to seedling establishment but did not increase on spring burns. (2) Cirsium arvense and Lycopus asper were fairly frequent on unburned plots but had low aboveground biomass; their aboveground biomass increased on summer burns owing to both vegetative spread and seedling establishment but did not change on spring burns. (3) Mentha arvensis, T. occidentale, and U. dioica had both high frequencies and biomass on unburned plots; their biomass was reduced on summer burns but increased on spring burns. Species with responses 1 and 2 increased in biomass to a lesser extent on fall burns, whereas those with response 3 declined in biomass on fall burns.