Research: Forest Stand Structure and Composition

The Holt Research Forest study area comprises 38 stands 51% mixed stands growing on mesic soil, 10% mixed xeric, 8% deciduous mesic, 17% coniferous mesic, and 14% coniferous xeric.  We have done three 100% inventories of the study area for all trees with dbh > 10cm (4in): pre-harvest (1984), immediate post-harvest (1988), and 8 years post-harvest (1996).   Principal tree species, in order of both trees per hectare and total stand basal area, are eastern white pine, red maple, northern red oak, and red spruce.

The winter 1987-88 harvest removed 44% of the basal area in the harvested 1-ha blocks. Volume and relative abundance of the large, rough white pines decreased from 44% to 38% of merchantable volume.  Relative abundance red oak increased from 16% to 22% of cords/acre. The total volume removed was 210 cords of firewood, 304 cords of pulpwood, and 117 mbf of sawlogs.   Between 1988 and 1996, all tree species gained in volume except the "other" softwood group in the control blocks. The latter suffered enough mortality over the eight years that it had a negative annual growth rate (-3% in cords/acre and -5% in board feet/acre). In contrast, red maple and red oak are grew at slightly over 6% annually in board feet /acre in the harvested blocks.

The sustainability of managed forests depends as much on the establishment and culture of seedlings and saplings as it does on the growth of the residual overstory trees. Since 1984 we have monitored the recruitment and development of new trees using several sampling designs, both in the forest as a whole, and in the canopy gaps. To date we have discovered that white pine, red maple, and red oak are all more abundant and taller in the canopy gaps than under the undisturbed canopy (control) adjacent to the gaps, considering both stump sprouts and seedlings.  

Red maple and white pine are both more abundant and taller than red oak. This difference appears to be due to deer preferentially browsing the red oak seedlings and sprouts. 1993 was a major seed year for red oak.  Clark (1996) followed the fate of oak seedlings that germinated following the 1993 mast year and found that while new seedlings were abundant under mature oaks and at the base of slopes, few new seedlings occurred in the canopy gaps. Because the only way for acorns to get into gap areas would be through animal (e.g., blue jays and chipmunks) dispersal, it is assumed that these animals chose not to cache acorns in the relatively open environment of the gaps. 

In contrast, oak seedlings that were established prior to the harvests appear to grow well in gaps, but only if they are not browsed by deer. Thus, oak mast years probably are important in establishing oak seedlings under the forest canopy, but for those seedlings to make it into the canopy, they must be released from competition and protected from deer.  Please see Al Kimball's oak seedling protection experiment with Bitrex and tree shelters under "Ancillary" in the Research category.