The Influence of Sunlight on Trees.

Otago Witness, Issue 1957, 23 May 1889, Page 9

The Influence of Sunlight on Trees.

In the latest report of the head of the Forestry department of the United States, reference is made to the effect of light on the growth of various trees. It is well known, says Professor Ferrow, that light is necessary for the development of chlorophyll, and therefore for the life of all grfien plants, and especially for that of trees. Tho hfat alone which accompanies tbe light is not sufficient, although the relative in(lueuces of the light and the heat on the growth is Htill an open question, as well as the relative requirements in light of different species of trees. Iv the case of forest weeds, which in forestry serve as an indication of the amount of shade which the trees exert, and with their capaoity of impeding evaporation, j(ome require full sunlight for their development, others are averse to a high degree of light. To this must be due the ohange in the plants of a district whew the forests are removed. Then the amount of shade needed is modified by site. Where the sunlight is strong, in higher altitudes, drirr climates, or where the growing season is longer, or there are more sunny days, some species will endure more shade. The flora of high altitudes in general requires light.

Trees nearly always develop best — in other words, make most wood— in the full enjoyment of light, but .their capacity of developing under shade varies greatly. The yew will thrive in the densest shade, while a few years overtopping kills the larch ; the beech will grow with considerable energy under partial shade, where the oak would only just keep alive, and the birch would die. When planted in moist places all species are less sensitive to the withdrawal of

light. In the open, maples, elms, sycamores, and others grow well and make good shade trees ; in a dense forest they thin out and have but scanty foliage. Conifers, such as spruces and firs, which preserve the foliage of several years, have perhaps the greatest capacity if growing under shade and preserving their foliage in spite of the withdrawal of light.

In America sufficient data to group the forest trees according to the amount of light required by them have not yet been collected, but rules based on experience have been formed in Garmany, where the behaviour of trees under different conditions of light has been carefully studied. It has been found, for instance, that on the same branch those leaves which are developed under the full influence of sunlight are not only larger and often tougher in texture and thicker, but that they have a larger number of stomata or breathing pores than those less exposed to light. The whole subject is one of the utmost importance in forestry, and observations and experiments are to be carried out in regard to it in the United States. — " Builder and Woodworker." >