Abstract
Opportunities to directly study infrequent forest disturbance events often lead to valuable information about vegetation dynamics. In mesic temperate forests of North America, stand-replacing crown fire occurs infrequently, with a return interval of 2000–3000 years. Rare chance events, however, may have profound impacts on the developmental trajectories of forest ecosystems. For example, it has been postulated that stand-replacing fire may have been an important factor in the establishment of eastern hemlock (Tsuga canadensis) stands in the northern Great Lakes region. Nevertheless, experimental evidence linking hemlock regeneration to non-anthropogenic fire is limited. To clarify this potential relationship, we monitored vegetation dynamics following a rare lightning-origin crown fire in a Wisconsin hemlock-hardwood forest. We also studied vegetation in bulldozer-created fire breaks and adjacent undisturbed forest. Our results indicate that hemlock establishment was rare in the burned area but moderately common in the scarified bulldozer lines compared to the reference area. Early-successional, non-arboreal species including Rubus spp., Vaccinium angustifolium, sedges (Carex spp.), grasses, Epilobium ciliatum, and Pteridium aquilinium were the most abundant post-fire species. Collectively, our results suggest that competing vegetation and moisture stress resulting from drought may reduce the efficacy of scarification treatments as well as the usefulness of fire for preparing a suitable seedbed for hemlock. The increasing prevalence of growing-season drought suggests that silvicultural strategies based on historic disturbance regimes may need to be reevaluated for mesic species.
Highlights
Infrequent disturbance events can have a profound effect on forest structure and composition [1,2,3], but they are difficult to study due to their rarity
In mesic temperate forests, fire return intervals can range from several centuries to millennia [2]
Our results suggest that soil scarification is a useful method of regenerating eastern hemlock in hemlock-hardwood forests, but the climatic conditions that follow soil disturbance may modulate regeneration success
Summary
Infrequent disturbance events can have a profound effect on forest structure and composition [1,2,3], but they are difficult to study due to their rarity. Even age distributions are common in many eastern hemlock (Tsuga canadensis) stands, suggesting a stand-leveling disturbance origin [12,13,14]. This observation has led several researchers to conclude that the episodic nature of hemlock regeneration is due in part to hemlock’s response to infrequent fires, the evidence is largely anecdotal [14,15,16,17,18]. Our understanding of post-catastrophic disturbance vegetation dynamics in this system is limited, especially with regard to the initial interplay between the resurgent plant community, microsite characteristics, and climate. Given changes in regional species pools, legacy effects, and the increasing role of climate change, it is becoming increasingly important to reevaluate these dynamics in contemporary ecosystems, especially for declining ‘‘foundation species’’ (sensu [20])
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