Plant community composition and relationships of disturbed and undisturbed alvar woodland

Abstract

In order to quantify the difference between a recently disturbed and undisturbed alvar woodland, thus indicating the impact of disturbance, and to determine differences in the effects of bulldozing and burning, we analyzed quadrat data and compared species lists from four situations: (1) a burned area 100 days after the fire, (2) the same burned area a little more than a year after the fire, (3) bulldozed tracks through unburned woodland a little more than a year after bulldozing, and (4) adjacent unburned woodland. Correspondence analysis and coordinate analysis based on distance coefficients suggested that the greatest differences were between unburned woodland and burned woodland 100 days after the fire. Bulldozed tracks and burned woodland more than a year after disturbance occupied an intermediate position. It appears that initially after a major disturbance event involving both removal of woody biomass and soil disturbance, mixed or conifer-dominated alvar woodland develops a very different plant community which is quickly replaced by one that more closely resembles the unburned woodland. Species strongly or exclusively associated with unburned woodland included (in descending order of suggested association): Abies balsamea, Arctostaphylos uva-ursi, Waldsteinia fragarioides, Rhamnus frangula, and Carex eburnea. Species particularly associated with unburned woodland and bulldozed tracks were: Cypripedium parviflorum var. pubescens, Prunella vulgaris and Bromus kalmii. At the other end of the scale, species associated with alvar woodland burned 100 days earlier were (in descending order of importance): Calystegia spithamea, Viola cf. adunca, Populus tremuloides, Maianthemum canadense, Corydalis aurea, Scutellaria parvula, Geranium bicknellii, Dracocephalum parviflorum, Rhus radicans ssp. negundo, and Aralia nudicaulis. Verbascum thapsus and Potentilla argentea and a number of other introduced species were uniquely associated with bulldozed tracks. Since burning was associated with fewer alien colonizers than bulldozing, it is potentially a more desirable form of disturbance management, but bulldozed tracks did include many native species. Alien species may decline over the longer term. Disturbance management, involving woody biomass removal and substrate disturbance, is an important consideration in maintaining biodivesity at both the community and species levels in alvar landscapes.