Pasteurizing or boiling for a short period does not destroy the nutritional value, as numerous experiments have without doubt demonstrated, although physicians have from time to time claimed that heated milk as a diet for small children is conducive to scurvy. Where any doubt concerning this point has existed the feeding of small amounts of orange juice has been sufficient to allay fear. Sour milk is not beneficial on account of the acid or acidproducing bacteria which it contains, but, like sweet milk, tends to encourage the development of an intestinal flora from which the putrefying bacteria are greatly reduced or absent. This property milk seems to owe to the sugar which it contains. Skim milk exerts the same influence. FOREST GROWTH ON ABANDONED By P. L. BUTTRICK NEW HAVEN, CONN. LTHOUGH the process of clearing forested land for agri cultural uses continues in nearly all sections of our country, another, generally less conspicuous, but almost as important, process occurs along with it-the abandonment of cultivated land and its reversion to forest. This reversion to forest, or "afforestation" as it is called, is of great interest both to the forester and to the agriculturalist. To the former because it helps to replenish the waning timber supply, and to the latter because it provides a means of utilizing lands no longer used for raising crops and grazing. Reasons for Abandonment of Agricultural Lands.-This abandonment of agricultural lands takes place in all sections, but chiefly in relatively remote although long-settled regions, such as some parts of rural New England. There are several reasons for its abandonment, such as: (1) loss of fertility, an example of which is the abandonment of many acres in parts of New England; (2) change of economic conditions rendering further cultivation unprofitable. The classic example of this is the large cotton acreage in Virginia and the Carolinas abandoned during the Civil War. (3) Discovery that certain lands are not suited for agriculture, at least as it has been practised in the locality. Examples of this are to be found in every region which has been settled for any length of time, where isolated fields in swampy sites, or hilltops, and the like, have been neglected when it has become evident that their cultivation was not profitable. General shifts in rural population from long-settled regions in the east to the west, and to the urban districts, have frequently caused land to be abandoned that was actually good farm land, but on the whole most of the abandoned lands have been of inferior quality. Favorable Conditions for Tree Growth Found on Abandoned Lands.-Generally speaking, conditions are very favorable for tree growth on abandoned lands. The soil, although possibly worn out from an agricultural point of view, has been refreshed during its period of cultivation in those constituents which make it desirable for tree growth. It is well broken so that the seed can easily reach the soil itself (often a difficult thing in the natural forest) and the roots of the seedlings can easily penetrate it. Seedlings do not have to compete with the older trees for light, moisture and growing space. If the field happens to be turfed over, once the seedlings have become established, the competition of the turf is of no great moment, although it may delay the seeding up of the field considerably in the first place. Because of the lack of inflammable litter on the ground, fire seldom interferes with old field stands, as stands growing upon abandoned lands are commonly called, during their period of establishment. This fact gives such stands a great advantage over stands coming in on cut-over lands, which must frequently cope with severe fires in the slash formed by the old cuttings. The fire hazard may, however, be quite high for old field stands during the middle period of their development, because of their frequent crowding and high density. These conditions do not favor all trees, as there are certain species which do much better to start with under the shade of other trees, and do not take kindly to the exposed conditions of open fields, but this fact has little bearing on the situation, since it merely rules those particular species out of the race for the capture of clearings. Every humid region seems to have a sufficiency of trees capable of becoming established and growing well under open field conditions. Influence of Other Vegetation.-Abandoned agricultural lands fall into two classes: (1) Fields not covered with turf, (2) pastures. It frequently happens that when it develops that a field is no longer valuable for crops it is seeded down as a pasture and grazed for a period before its final abandonment. This delays materially the return of the forest, but it comes back in time, nevertheless. In sections where soil erosion is common and turf does not grow especially well, such as is the case in portions of the south, its entire absence may allow such action to get the upper hand and wash away rapidly the seeds. and seedlings, so that final recapture is greatly retarded or altogether prevented for long periods. Sometimes, because of close proximity of seed plants or other causes, an abandoned field is quickly seeded up by worthless brush before tree seed has a chance to reach it. This may delay but does not prevent the return of forest conditions. It seems that throughout most of the eastern portion of the United States the forest rather than the grass or brush type of vegetation is the ultimate type, VOL. V.-6. and toward it all types evolve. It is entirely probable that if all the land in the eastern United States were abandoned it would eventually be clothed in forests similar to those found here when the white man came. Types of Natural Reforestation on Abandoned Lands.There are two types of recapture-immediate and gradual. In the first case, almost immediately a field is abandoned a young homogeneous even-aged stand springs up over the entire area. In the second the recapture is slow and may extend over many years, the resulting stand being all-aged, in which case some of the seed which goes toward stocking the area is often produced by the earlier arrivals, so that the trees do not all belong to the same generation. On very large clearings the second type must perforce prevail, since seed can not be sown naturally over sufficient area to yield at once a full stand. It sometimes happens that several bands of growth of different ages occur on a field, that farthest from its edge being the youngest. The forester describes such a stand as "even-aged in groups." On average-sized clearings it is generally the case that fields abandoned directly from the plow are reclaimed practically at once and support therefore even-aged stands; while pastures owing to the competition of the turf are more apt to be recaptured slowly, particularly if grazing takes place upon them, and in consequence their stands are uneven aged. Transportation of Seed.-The recapture of abandoned fields depends primarily upon the ability of tree seed to reach them in sufficient abundance. The several agencies which aid in its transportation are: (1) wind, (2) birds and animals, (3) gravity, (4) water. Wind is the most important, it being the only one capable of disturbing seed abundantly over large Its action, however, is limited to seeds of light weight with some sort of a winged attachment by which it can grip them. Wind-disseminated seeds are of three classes: (1) Very light thistledown-like seeds such as those of willows and poplars, which will float on light airs and travel for many miles; (2) medium-light seeds such as those of the birches, which can be blown for long distances, but will not float on light airs; and (3) medium-heavy, generally winged, seeds, such as those of the pines, ashes, maples, tulip poplar1 and many others, which will flutter to the ground except in the face of a considerable breeze, and even then are not apt to travel more than 1 Liriodendron tulipifera. With a few exceptions scientific names of trees have been omitted, since common names are so well standardized as to make it unnecessary. a few hundred yards in sufficient abundance to form a stand. Birds and animals generally limit their activities to the transportation of such seeds (or fruits) as are in whole or part edible (from their points of view). The fruits of the common red cedar and the black cherry are examples. The fruit is eaten by birds and the indigestible seed is deposited wherever they happen to fly. Animals such as squirrels and other rodents generally operate by taking nuts, acorns, etc., from the seed trees or the ground beneath them into the open and burying them for food stores. It is possible that certain birds, for instance the blue jay, also do this. Gravity plays its distinctive part only on sites where heavy seed roll down-hill. Water plays its part in washing seeds down-hill and covering them with earth once they have reached their resting places. The flooding of bottomlands by overflow from streams does not seem ever to leave a sufficient deposit of seed to make any impression after the water has subsided. Trees which Succeed in the Capture of Abandoned Fields. -As has already been intimated, a species to succeed in the capture of open fields must have several characteristics, the chief of which is that it must have seed which may easily be transplanted by natural agencies, and is produced regularly and in abundance. After that it is necessary that the species be able to start in the open, and, if necessary, to compete with grassy or brushy vegetation, and to get along with comparatively little moisture. Swamp-loving species seldom succeed well on abandoned fields. The most successful old field species are also rapid growing so that they are able to forge ahead of the brush and worthless growth which often crowds in with or ahead of them. Successful slow-growing species, such as the red spruce and the red cedar, are either very tolerant, so that they are not affected by the light competition, or are early comers and succeed by being the first on the ground. A tree must also be able to grow in closed stands, which some lightseeded species like the ashes are unable to do. On pastures or in sections where stock is allowed to range species which for some reason are objectionable as food plants for the stock have an advantage, since they are less liable to be eaten off or broken down. The tulip poplar seems to be liked by cattle and is in consequence badly damaged where grazing is allowed, while thorny trees like the black locust are almost immune from their attacks, and conifers suffer far less in this way than broad-leaved species. Difference between Old Field and Natural Forest Types. |