Results of this study point out the complex nature of the interactions between survival, growth, and foliage quality of trees of "Canaan" fir and various combinations of plantation management, topographic, and soil factors (Figure 10). Weed control that effectively reduces the density of vegetation can be critical to survival, growth, and foliage quality of trees. On plots evaluated in this study, use of residual herbicides for at least the first four years after trees were planted, in combination with mowing, provided effective control of herbaceous vegetation. An earlier study (Brown et al., 1989) showed the benefits of annual applications of herbicides over a six-year period, particularly to Fraser fir, Douglas-fir, and Colorado spruce (but less so to Scotch pine and white pine). Another study (Brown, 1980) detailed the benefits of vegetation removal/reduction and showed that use of herbicides and mechanical removal (shallow tillage), which kept herbaceous vegetation out of plots, were equally effective. A third study (Heiligmann et al., 1985) found that control of vegetation in strips along rows of trees and applications of herbicides to the whole planting area were equally beneficial to survival and growth.
Fertilization, particularly with nitrogen, can also enhance foliage quality of trees. For trees in this study, evaluation of the effects of fertilization was difficult because of the limited number of trees fertilized and the variety of combinations of materials and frequencies of applications used. In a study at OSU/OARDC, nitrogen fertilization was effective in improving foliage quality of trees (but not growth) of "Canaan" fir growing on a variety of sites, all of which received annual applications of herbicides (Brown, 1998). In another study, nitrogen fertilization was beneficial to trees of "Canaan" fir, Colorado spruce (Picea pungens), and Scotch pine (Pinus sylvestris) on plots where chemical weed control was used in combination with mowing, while growth and foliage quality of trees was poorer on plots which were fertilized without chemical weed control than on plots having chemical weed control only (Brown, 2000).
Results of the study show that trees of the Canaan Valley seed source of balsam fir can survive, grow, and produce marketable Christmas trees on a wide range of sites, including many somewhat "wetter" areas where Fraser fir and Douglas-fir (Pseudotsuga menziesii) do not do well. It was not possible to develop useful multiple regression equations which could be used to develop planting guides for choosing sites and predicting survival and growth of the Canaan Valley seed source of balsam fir. However, the correlation and regression analyses and observations from individual plots do provide good insights into response of trees to a wide variety of site conditions. As with essentially all Christmas-tree species, tree performance was best on "moist" but not "wet" sites on north- and east-facing slopes and on medium-textured, well- to moderately well-drained soils. On finer-textured soils where surface drainage was good, growth and foliage quality were generally somewhat poorer but still acceptable for producing marketable trees. On concave-shaped, gently sloping to bottomland sites which were somewhat-poorly to poorly drained, survival, growth, and/or foliage quality of trees was generally below acceptable levels on finer-textured soils but acceptable on coarser-textured loams to sandy loams which were usually associated with seasonally high water tables. Based on the statistical analyses and in-the-field observations and measurement, the author believes that the "Qualitative Planting Guide" (Table 6) developed from results of the study should provide good information for choosing sites and estimating performance of trees of "Canaan" fir planted on a wide variety of areas.
The average soil nutrient levels found on study plots appear to be adequate for good growth and foliage quality of trees, with the values of 59, 198, 1,710, and 277 pounds per acre, respectively, for phosphorus, potassium, calcium, and magnesium being equal to or above those reported as being adequate for other higher quality trees such as Douglas-fir, Fraser fir, and more northerly sources of balsam fir. Average foliar levels of 1.85, 0.22, 0.83, 0.59, and 0.14 percent, respectively, for nitrogen, phosphorus, potassium, calcium, and magnesium were also at or above those reported as being acceptable for good growth and foliage quality of the same Christmas tree species.
