The effect of grass on trees

In the meadows and pastures of the temperate regions and the tropics, trees flourish when surrounded by communities of grasses and herbs. Such grassland is, with few exceptions, an artificial product, created by man from areas originally forest, and maintained in its present condition by such agencies as grazing, cropping, mowing and manuring. If left to themselves most of the meadows and pastures on the earth’s surface would soon revert to the original forest, the rate depending on a number of circumstances, including the nature of the weapons possessed by the trees in suppressing the grasses and herbs. In the tropics, where pastures are much fewer than in the temperate zone, grassland after enclosure becomes covered by shrubs and trees with remarkable rapidity. Although trees soon oust grasses from the habitat under conditions of free competition, nevertheless cases occur in which grass is able to suppress certain species of trees. One such example has recently been investigated in great detail in Great Britain by the Duke of Bedford and the late Mr. S. U. Pickering. At the Woburn Experiment Station fruit trees such as apples, pears, plums and cherries failed to flourish under grass on a heavy clay soil. Similar results have been obtained in the United States and also on the Gangetic alluvium at Pusa.