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The Distribution of Light Reaching the Ground Vegetation in a Tropical Rain Forest

1960; Wiley; Volume: 48; Issue: 1 Linguagem: Inglês

10.2307/2257318

1365-2745

G. C. Evans, T. C. Whitmore, Y. K. Wong,

Species Distribution and Climate Change

A survey of light reaching the undergrowth of a Tropical Rain forest in Bukit Timah Nature Reserve, Singapore, was made on two days during March 1957. A description of the site and vegetation, and an account of the observations made under sunny conditions, has already been published (Whitmore & Wong 1959). The apparatus, using a reflecting paper plate viewed from above by a photocell, and the method of survey and of evaluation of the data followed that used in Rain forest in Nigeria by Evans (1956). Two sample plots of 5 x 25 ft (1 5 x 7*6 m) were marked out, each being divided into five equal, square sub-plots. Owing to the hilly nature of the ground these two sample plots were not completely identical, but gave a representative idea of the variation likely to be encountered in the mature forest in this area. Twenty-five observations were made, one in each corner and one in the middle of each square sub-plot, thus surveying 30 % of the area of the whole plot, and these were repeated at approximately quarter-hour intervals. Records were made (i) of the galvanometer reading; (ii) of whether the sun was obscured by cloud (c), or by haze (h), or was shining brightly (s) and in the last instance (iii) of the proportion of the reflecting paper plate occupied by sunflecks. The category 'hazy' was used to describe those occasions when the sun's disc was obscured by a veil of mist or light wispy cloud so thin that vague bright patches appeared on the forest floor. This state of affairs, negligible at the time of Evans's observations in Nigeria, was recorded in Singapore on 12 % of occasions. The climate of Singapore also differs from that of southern Nigeria (during the dry season) in having very frequently cloud and rain during the afternoon and occasionally at mid-day-predominantly sunny afternoons being a rarity. Thus, while we have an opportunity to compare conditions in the two tropical forests while the sun is shining, by considering also the cloudy periods we are enabled to tackle a number of questions which have not so far been considered in previous analyses: