Nurses are surplus trees or shrubs introduced into the plantation for a temporary purpose, for the occupancy of the ground, to shelter and protect the permanent plants that are designed to constitute the future forest, and to aid in forming them into well-shaped trees as well as for their use as subsidiary products.
The trees, shrubs, or bushes selected for use as nurses should not so greatly exceed in size and vigor the permanent trees as to endanger the growth of the plants designed for the future forest; they need to be looked after lest they crowd and injure those trees which are to form the permanent stock. This is especially necessary if they be free-growing—such as many of the kinds grown in this country. Hence, for the purpose of nurses, we should select trees which are of the second class in respect to size. Of the many in use as nurses to different species of trees, the cotton-wood, box-elder, hack-berry, white maple, elms, green ash, and white willow are the most easily obtained or produced, and in cases where the first cost of the young trees is small, the nurse-plants may consist of supernumeraries of the species planted.
Shrubs may be utilized as nurses if set in alternate rows and cultivated with the trees, and may be brought into requisition as a source of profit in use as wattles for temporary fences, as osiers, hoops, hurdles, and hazels or filberts, for their nuts. Wherever labor could be controlled for the cutting and preparation of the crop of herbage, so useful now for tanning, the sumac would promise a valuable return. Many of the smaller-growing osier willows might be planted in the same way, with prospect of yielding good returns. They may all be grown from cuttings, that should be planted at the same time as the trees—the latter, being put into rows eight feet apart, could have a double row of the willows set between them. Eighteen inches wide would be sufficient for the willows, with spaces of three feet three inches on either side between them and the permanent trees. This plan would be particularly applicable to plantations of some of our oaks and hickories, which are usually slow in their growth.
It is recommended in planting the black walnut, that instead of an entire block of this species, which is uncertain in its results, every fifth row be planted with nuts, while the four intervening rows on either side be set with any of the common kinds as nurses, and as their growth increases, and consequently space is needed for the thrift of the walnut, the adjoining rows of nurse-trees may be cut down, and so the next, till a clear space of sixteen feet is made to allow of the development of the permanent tree. This manner of proceeding, though remunerative in the case of the black walnut, has proved to be with other species a false economy on the part of the planter, under the delusive idea that he could grow among the trees a half crop of other plants to pay him for the labor of cultivating his trees. For the first jTear he may reap his reward; in some cases, perhaps, also for the second year, but, meanwhile, when so widely planted, the trees suffer from branching and by leaning out on either hand for the light and air. It is true that in some cases, with very strong and rapid-growing species, tall-growing kinds of Indian corn in the alternate rows might supply the need of the supernumerary trees.
The white willow has been used as a nurse to the sugar maple and oaks with the object of saving the more valuable stock-plants, by filling up with willow-cuttings to shade the ground, thus diminishing the expense of planting and cultivation, and at the same time to force the upward growth of the trees and to prevent their branching.
In planting the oaks at eight feet apart each way, with alternating willow-cuttings in the rows, and with alternating rows of willows set four feet apart, after the second year's growth the ground will be found so shaded as to require no other culture, and it becomes necessary to cut off the interfering branches from the willows. Meanwhile the oaks will have made satisfactory progress and have reached a greater height than those of blocks planted with the same stock set at four feet apart and continuously cultivated so as to keep the ground loose and clean.
Unless care be taken to subordinate these nurses they will be likely to overwhelm the more valuable plants, and they are not, therefore, recommended for all purposes, as their growth is so vigorous that their excessive thrift supplants the more valuable tree. As soon as the permanent tree has reached sufficient size to shade the ground, little trouble need be experienced by the sprouting of the willow-stumps, as they will in their turn furnish material cuttings for other plantations.
Evergreens which have been used as nurses to other evergreens are to be treated in the same way.
When the thickly set trees have reached a height of from eight to twelve feet and make a dense thicket, so as to endanger the sturdiness of the plants, instead of chopping them at the ground the stems are lopped off at the height of four, five, or six feet, leaving all below to shade the ground and for the important work of aiding in the destruction of the side-limbs of the other trees, which thus soon lose their lower branches by the processes of nature, and not only is this more cheaply, but it is also much better done than by the laborious process of trimming. The lopped trees do not recover their upright habit of growth, but are soon overpowered by those which are left, that now grow with renewed vigor, and, while the beheaded trees continue to drag out a miserable existence, they are still doing a good work in aiding in the perfection of the shafts of their more favored fellows.
The white ash, hard maples, oaks, elms, hickories, chestnuts, beeches, and many other desirable species, may ah be economically grown by the aid of the cheap nurse-trees in the manner recommended for the walnut.
Some persons have thought the recommendation to plant trees at every four feet, or even more closely, was a waste of good material. It is not so, but a gain rather than a loss always follows from the close setting of the trees. The first cost of most of the stocks planted is a small matter compared to the labor of cultivation, to say nothing of the improved shape of the young trees and the economy that follows in the matter of cultivation. Therefore, to produce a tall and healthy growth of trunk on trees, whether planted on hill-side, in valley, or on open plain, be assured that, after a judicious selection of the species best adapted to soil and situation, they should be planted very thickly, say every four feet, or about three thousand trees to the acre, and the happiest results with the least expenditure of labor may be anticipated."
The following varieties, all things considered, are the best for general cultivation in the northwest: Cottonwood, soft maple, silver poplar, black cherry, ash-leaved maple, catalpa, black walnut, and white walnut. R. C. Raymond, of Council Bluffs, Iowa, states that the following-named varieties, planted when one foot in height, attain the following diameters and heights when ten years of age:
The Hon. Suel Foster, of Muscatine, Iowa, reports the following as the growth of the varieties named, twenty years after transplanting:
The chestnut, twenty-four years from seed, grew to be 10 to 16f inches in diameter, and 30 to 36 feet in height. The European larch, ten years transplanted, attained a diameter of 4 to 7± inches, and were 20 to 30 feet in height.