Ohio Christmas Tree Producers Manual

Bulletin 670

Determination of Site Productivity

Of the species that might be grown for Christmas trees in a given area, some may be much more exacting in their moisture and fertility requirements than others. For example, Scotch pine has relatively low requirements for both moisture and nutrients and, consequently, can be grown successfully on a variety of sites having a wide range of conditions. In contrast, many true firs, spruces and Douglas-fir are more demanding and do well only on sites that are at least relatively moist and/or fertile.

Knowledge of characteristics and productive potential of individual planting sites, added to an understanding of species requirements, helps reduce some of the uncertainties of Christmas tree production. It is an area, however, that is badly neglected by many growers. All too often lands are planted without regard to site characteristics or species requirements. Consequently, survival and growth in some plantations can be unnecessarily poor, resulting in reduced tree quality, longer rotations and greatly increased costs.

Site quality determination can be done in a number of ways. Thorough evaluation of planting sites, either by the grower or by professional outside help, can provide the necessary information. Special emphasis should be placed on factors that affect moisture availability. These include soil texture, depth and drainage class, topographic slope position and aspect and slope steepness. Where topography is diverse, integration of all these factors into an accurate and meaningful estimate of available soil moisture can be difficult. Tables 1 and 2 have been prepared to aid in integration of these factors. Table 1 is designed to indicate the relative "moisture regime" or moisture supplying capacity of different topographic-soil combinations.

Table 2 gives the general suitability of each Christmas tree species for planting under each moisture regime: S = suitable, L = limited suitability and N = not suitable. An example of the use of Tables 1 and 2 follows: Examination of a field to be planted indicates that the site is located on the upper portion of a 20 percent slope that faces to the northeast. The soil is a well drained loam (medium texture), and depth of the soil to bedrock is 20 inches. Using this information in Table 1, one obtains a soil moisture rating of "3," indicating a dry soil moisture regime. Looking at Table 2, one can see that the dry soil moisture regime is most suitable (S) for Scotch white and Austrian pines. Additionally, limited suitability (L) is indicated for the spruces, true firs and Douglas-fir. These species could probably be grown on the site, but growth and/or foliage quality would probably be reduced to some extent. Although Tables 1 and 2 are most applicable to areas where topography is varied such as southeastern Ohio, they should also be helpful for use in choosing species for planting on specific soil-topography combinations in other areas.

Soils maps prepared by the Soil Conservation Service offer another excellent means of determining site potential (Fig. 13). These are available as parts of county soil surveys or through mapping of individual farms by SCS soil scientists as a service available when growers participate as cooperators with local soil and water conservation districts. These maps not only delineate specific soils and their characteristics but also subdivide them into mapping units based on slope and degree of erosion. Accompanying soil descriptions provide an excellent basis for evaluating potential mois ture and nutrient supplying capacity. Additional interpretive data related specifically to Christmas trees are also available in some locations. These interpretations include specific species suitable for planting, constraints on equipment operation, probable seedling mortality and intensity of vegetative competition.

Fig. 13: Soils maps can be used to evaluate characteristics of planting sites and to choose species for planting. They can also provide the basis for subdivision of the Christmas tree farm into similar units for more efficient management.

Because these maps and interpretations relate to specific soil mapping units occurring in Ohio, it would be impossible to provide a comprehensive list in this publication. However, Table 3 provides guidelines for selection of Christmas tree species for planting in the broad "Soil Conservation Service Woodland Suitability Groups" to which different soil mapping units are assigned. The woodland suitability classes, with ratings from 1 (best) to 5 (poorest) are designed primarily to designate potential growth and yield of timber crops growing on soil- topographic combinations (soil mapping units) assigned to each class. Subclasses indicate possible "limiting factors" within each major suitability class as follows: 0 = none, R = relief or slope steepness, F = fragmental or skeletal soil, S = sandy soil, C = high clay content soil, D = restricted rooting depth, W = excessive wetness and X = stoniness or rockiness. Guidelines in Table 3 are set up similar to Table 2 to indicate the relative suitability (S, L, N) of different Christmas tree species for planting on each woodland suitability class- subclass combination.

Interpretations in Tables 2 and 3 relate primarily to the moisture status of soils and planting sites. Additional laboratory analyses of soil samples to evaluate fertility status may also be needed, particularly if some of the spruces, true firs or Douglas-fir are to be planted. Soil sampling "kits," including instructions and sample bags, are available from county agricultural extension agents.