Shade in north-east Indian Tea plantations. I. The shade pattern. II. Foliar illumination and canopy characteristics.
(I) The selection of suitable shade trees for use in Tea plantations (Camellia sinensis) is a major problem in NE India since the destruction of large areas of Albizzia chinensis by a canker disease in the late 1940's. Since then, a number of species have been planted, and this study reports a survey, made between 1962 and 1964, of the pattern of shading, and the intensity and spectral composition of the light, in a Tea plantation established in 1920 near the Tocklai Experimental Station, Assam, with shade trees planted at 7.5 x 7.5-m spacing in 1950. The site was selected for the uniformity of the shade trees (mean height 12 m), of which 50% were A. odoratissima and the remainder 10 other leguminous species. The pattern of shading was also investigated beneath 12 shade-tree species, all 5 years old, in order to study light patterns under both pure stands and mixtures of shade trees, by superimposing data for the various species on the basic pattern obtained for A. odoratissima. It is concluded that most of the light reaching a Tea bush is unmodified sunlight, either from large gaps in the canopy between trees or from sunflecks. The methods used make it possible to characterize the intensity and composition of nearly all the light on the surface of a bush in both clear and uniformly overcast conditions, and form a suitable basis for crop physiology studies. A brief historical review of the use of shade trees in India and other Tea-growing countries is given, and the reasons for the 'shade problem' and apparent contradictions betweeen results of natural and artificial shade experiments are discussed. [Cf. FA 28, 2288] (II) Reports investigations of light penetration into five distinct foliage patterns of Tea bushes, and discusses the effect of the foliage pattern on the distribution of light.