favors more rapid growth, which in turn reduces the menace of the black locust borer and twig borer. Black locust is a sun-loving tree which produces only a light shade, offering insufficient shade for retaining good soil moisture. In regions where the borers are not a serious pest and in good-quality soils where growth will likely be rapid, plantings of locust alone will often give satisfactory results.
The filler trees of other species may be planted alternately in each row or solidly in alternate rows or otherwise (fig. 12). Various kinds of trees are suggested as filler trees for different regions. However, as there are few experimental data on the subject, the suggestions are largely based upon general observations. In the northeastern or cooler portion of the black locust range, red oak, sugar maple, and white ash might be planted. Farther south the trees might include
southern red oak, on the better soils yellow poplar (tuliptree) and white ash, and on the best or agricultural soils black walnut. On the drier and poorer soils, the black oak may be considered because it is relatively hardy, although the timber product is of low grade. In connection with planting black locust, some conifers should be considered for planting pure in small blocks or patches because they will grow well on relatively dry and sterile soils not adapted to black locust. On such local areas or portions, the red, white, and jack pines may be planted in pure stands in the northeastern region, and in the middle South shortleaf and loblolly pines. There appear to be good grounds for advising against closely interplanting pines with black locust. The results appear to be poor whenever this is done. The pines should, therefore, be planted pure in small or larger blocks on the drier ridges or areas and the locust in the better soils (fig. 13). Red cedar is a very hardy tree on dry and low-grade soils; except in districts of commercial apple production, it should be used quite extensively as a filler tree, either alternately or in pure stands locally on unfavorable soils in the black locust plantation.
