. The Canadian field-naturalist. Natural history. 574 The Canadian Field-Naturalist Vol. 116 CO CO CO, CM unburned burned 100 days ago. bulldozed burned 465 days ago 1 () <P 00 CM -< B unburned burned 100 days ago bulldozed burned 465 days ago 1 () Figure 2. Plots of four alvar woodland plant communities based on principal coordinate analysis of distance coefficients with nearest neighbours of each community joined by a straight line forming a minimum spanning tree. A, b
. The Canadian field-naturalist. Natural history. 574 The Canadian Field-Naturalist Vol. 116 CO CO CO, CM unburned burned 100 days ago. bulldozed burned 465 days ago 1 () <P 00 CM -< B unburned burned 100 days ago bulldozed burned 465 days ago 1 () Figure 2. Plots of four alvar woodland plant communities based on principal coordinate analysis of distance coefficients with nearest neighbours of each community joined by a straight line forming a minimum spanning tree. A, based on % frequency data. B, based on total cover data. woodland community to unburned and bulldozed tracks probably relates to longer time available for species to move in from the surrounding woodland. The community that develops in the same year as a spring fire is evidently entirely dependent on the soil seed bank or surviving roots (Catling et al. 2001). The undisturbed alvar woodland is very different from the disturbed woodland but community change over a very short time following disturbance may also account for substantial variation in the commu- nities; in the present case up to 34% (second axis). The type of disturbance may also contribute to varia- tion in community development, which in the pre- sent case is almost 20% (third axis). Not only does disturbance have a major impact on creation of new communities in alvar woodland, but in addition, the new communities may change very rapidly in early succession suggesting that maximum community diversity is achieved by disturbances that are nearly continuous in time on different parts of the alvar. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ottawa Field-Naturalists' Club. Ottawa, Ottawa Field-Naturalists' Club
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