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Citation. Dovciak, M. 2001. Spatial patterns of white pine regeneration in relation to seed rain, safe sites, competing vegetation and resources. Ph.D. Thesis, University of Minnesota.
Abstract. A sharp decline in the abudance of white pine due to past logging, and the failure of this species to regenerate, have raised concern about its future in the Great Lakes region. Fine-scale ecological studies have provided insight into the short-term response of white pine to environmental variation, while broader-scale studies have increased our understanding of seedling dispersion around parent trees. I have integrated these two spatial scales in order to understand their roles in longer term (ı20 years) dynamics of white pine populations in two contrasting Minnesota ecosystems, an old-field within the Anoka Sand Plain, an originally oak-savanna system, and upland near-boreal mixed forests of the Arrowhead region.
Within the old-field, shaded edge habitat, seed rain density, and climate variations were responsible for three different successional pathways. While the center of the field may remain in a long-term prairie stage, as documented in other Anoka old-fields, I document different successional pathways in the areas near the forest edge. Shaded areas near the forest edge that receive low seed rain experience slow "creeping" white pine invasion, while areas with large seed influx experience fast "step-like" invasion as seed is abundant enough to overcome initial mortality in less shady areas further from the forest edge. The pace of succession increases in moist cool years, facilitating white pine establishment even within the field center.
In contrast, population dynamics in the near-boreal forest are characterized by a sequence of regeneration bottlenecks imposed by the spatial distribution of substrates suitable for germination and early survival, and later by spatial distribution of shrubs, overstory trees, and deeper soil pockets. While the best germination and early survival conditions may occur on moss and decaying wood under dense forest canopy, the best longer-term growth and recruitment occurs within areas of low overstory density. In the absence of disturbance, rocky outcrops with sparse canopy serve as refugia from competition from shrubs and overstory. In this patchy system, white pine population dynamics consist of invasions of the deciduous matrix during years of high seed crop, followed by population retraction to rocky refugia over time.