ï~~ 2011 THE MICHIGAN BOTANIST 107 DEMOGRAPHY OF OLD-GROWTH WHITE PINE STANDS AT THE HURON MOUNTAIN CLUB RESERVE AND ESTIVANT PINES IN UPPER MICHIGAN Dennis A. Riege University of Maryland University College 17 Longmeadow Avenue Middletown, RI 02842 driege@umuc.edu ABSTRACT Few old-growth white pine (Pinus strobus) stands remain in the Upper Midwest after the lumbering era. White pine shows poor recruitment in mature mesic stands. Long-term studies are needed to examine succession in these forests and the ability of white pine to reproduce. I established permanent plots and examined forest demography in two preserved forests in Upper Michigan. Adjacent 1.54- and 0.92-ha plots in the Huron Mountain Club Reserve included a white pine-hemlock (Tsuga canadensis)-hardwood forest and an atypical white pine-white spruce (Picea glauca) stand with dense undergrowth of sugar maple (Acer saccharum) saplings. At Estivant Pines a 0.78-ha plot contained a stand of white pine-sugar maple-balsam fir (Abies balsamea), while a second 0.75-ha plot held a similar stand with large gaps. All stems > 5 cm dbh were measured and mapped and small saplings (1-4.9 cm dbh) were tallied in transects. Only the Huron white pine-white spruce stand showed a broad size distribution of white pine trees (but no saplings) that indicated dominance well into the future. White pine trees in the other plots were virtually limited to large emergents above a maple or hemlock canopy. Only the Estivant gap site contained a number of white pine saplings but these face competition with eight other sapling species to reach the canopy. Future results in these long-term permanent plots will track the ability of white pine to persist in these forests, to see if small gaps or other factors allow episodes of reproduction without a major disturbance. KEYWORDS: Pinus strobus, Huron Mountains, Estivant Pines, forest succession, tree demography INTRODUCTION White pine (Pinus strobus) forests are a symbol of Michigan's north woods. Almost all of the original mature pine forests were harvested in the lumbering era. Most of the remaining old-growth white pine stands show poor recruitment, which is a barrier to maintenance or restoration of this once major part of regional ecosystems (Carleton et al. 1996; Peck and Zenner 2009). While some argue that white pine requires a major disturbance to establish in mature forests (Frelich 1992; Carleton et al. 1996; Weyenberg et al. 2004), others report that it can remain in old-growth stands via gap-phase replacement (Hibbs 1982; Holla and Knowles 1988; Quinby 1991). In the late-successional mesic forests of the northern Great Lakes region, most white pines are found as emergent trees above a closed canopy that is dominated by hemlock (Tsuga canadensis) or sugar maple (Acer saccharum). As succession proceeds, white pine may be replaced by hemlock or shade-tolerant
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