Dale S. Solomon

Maximum size-density relationships for mixed softwoods in the northeastern USA

Abstract The maximum size–density relationships or self-thinning lines were developed for three mixed-softwood climax forest habitats (hemlock-red spruce, spruce-fir, and cedar-black spruce) in the northeastern USA. The plot data were collected from an extensive data base used in growth studies from 1950 to 1970, and represented a wide range of species compositions, sites, management options, and densities. Plots having late successional species compositions with relative density index higher than 0.7 were selected as the most fully-stocked plots for model development. Reduced major axis regression was used to fit the self-thinning lines to the data. The differences between the three forest habitats were tested using the 95% confidence intervals of the coefficients of the self-thinning lines. The results indicated that there were no differences between the hemlock-red spruce and spruce-fir habitats for both relationships of the mean tree volume versus number of trees, and the quadratic mean tree diameter versus number of trees. Thus, these two habitats were combined to develop a single self-thinning line. However, the cedar-black spruce forest habitat required a separate self-thinning line. These maximum size–density relationships can be readily used to construct stand density management diagrams.

Migration of tree species in New England based on elevational and regional analyses

With field measurements of migration patterns, we used two complementary approaches to examine tree-species movement after a documented increase in temperature. The advancing-front theory was used to examine age trends over distance and elevation for both a mountain site in New Hampshire and a regional comparison across the State of Maine. Well-defined stationary fronts were identified for red spruce (Picea rubens) and beech (Fagus grandifolia), while a catastrophic front was depicted for sugar maple (Acer saccharum) and a constant slow-moving advancing front was exhibited by hemlock (Tsuga canadensis). The regional analysis, in Maine, indicated that white pine (Pinus strobus) and balsam fir (Abies balsamea) decreased significantly in average latitude and elevation over a 24-year period. The potential ranges of the major species in terms of elevation and regional position appear stable.

Optimizing the horizontal structural diversity in uneven-aged northern hardwood stands

Two mathematical programming formulations are presented which allow the determination of diameter distributions that maximize the diameter class diversity in uneven-aged northern hardwood stands. Distributions generated from these models were found to be comparable from a management standpoint and could be incorporated into existing linear programming models as alternative management scenarios. The models presented here provide an initial framework for quantitatively addressing the requirements of the US National Forest Management Act in matters of diversity in the planning process.

Modeling the regeneration of northern hardwoods with FOREGEN

Describes the stochastic model FOREGEN that simulates regeneration in openings in northern hardwood stands that range in size from clearcuts of 2,000 by 2,000 feet to single-tree openings of 25 by 25 feet. The model incorporates the effects of seed development, dispersal, germination, seedbed conditions, advanced regeneration, and weather. Users can specify options on stand age, species composition, size of opening, harvesting in winter vs. summer, mechanical scarification, seed trees, advanced regeneration, and stump treatment for red maple. The output is percent species composition of the regeneration 3 years after harvest.

A Matrix model for Predicting Foliage Weight of Trees by Age Classes

Abstract A Leslie-type matrix has been developed to model the annual growth of foliage on individual trees for any species that retains its foliage for more than one year. In order to apply the model to any given species, one must know: (1) age-specific foliage photosynthetic efficiencies; (2) the proportion of foliage of each age class that remains to become one year older; and (3) the diameter of the tree at any two points in time, several years apart. These diameters are used to estimate the maximum eigenvalue of the matrix, which is needed in the determination of the specific numerical matrix which corresponds to a particular individual tree. Although the model is a general one, applicable to any species that has age classes of foliage, it is developed with occasional references to balsam fir, Abies balsamea (L.) Mill. For a data set of 66 dominant and codominant balsam fir trees, the model predicted the weights of the first three age classes of foliage accurately (less than 10% error) over a 6-year period. There was a 23% error for all age classes combined.

Tree demography and migration:What stand level measurements can tell about the response of forests to climate change

Renewed interest in plant migration has developed due to the potential impacts of global climate change. Predictions from general circulation models and bog/lake pollen analyses suggest major shifts in species ranges, and even extinctions, over the next 50 to 200 yr in response to temperature shifts of up to 4.5°C (e.g., Davis & Zabinski 1992; Overpeck et al. 1991; Pastor & Post 1988; Peters 1990). Using computer simulation, Overpeck et al. (1991) predicted shifts in plant ranges of as much as 500 to 1000 km within periods as short as 200 yr. Others (e.g. Davis & Zabinski 1992) suggest the possibility of near extinction of species such as sugar maple Acer saccharum Marsh, and American beech Fagus grandifolia Ehrh. because establishment in newly suitable sites would fail to keep pace with a changing climate. In developing simulation models, relationships between species’ occurrence and climatic variables are developed or inferred using modern or historical data (Denton & Barnes 1987; Gajewski 1987; Prentice et al. 1991; Spear et al. 1994). Future ranges are then predicted assuming a strong relationship between species and climate, which can be compared to estimated migration rates by species as evidenced in the pollen record.