Showing papers in "Journal of Ecology in 1942"

Further Studies of the Vegetation on Islands in the Indian Ocean

Abstract: THE floras of the elevated granitic islands comprising the Seychelles have been described in a previous paper. The present paper deals with a f-irther series of islands which come under the same administration. These islands form collectively those known as the Amirantes and the Aldabra Islands. The former are sand cays at present worked as coconut estates, and so their primary vegetation has been destroyed. The latter are limestone islands which still largely retain their former vegetation, and it is these which will form the subject of the present paper. In order to make the study complete, however, in addition to the Aldabra Islands proper, namely, Aldabra, Assumption, Astove and Cosmoledo, it is necessary to include the more distant islands of St Pierre and Farquhar which also belong to the limestone series. Fryer (1910) has given a description of the geological structure of these islands, so in the present study it is only necessasy to note that they are islands of coral origin which at some time in the past have become raised in relation to the surface of the sea and are at the present time in the process of being worn down. Before recording the vegetation, however, the forces acting upon these islands must be considered. There is a very marked wet and dry season, the latter extending from March to November. The islands are not big enough to have rivers, so there is no washing of the land surface into stream channels. The islands have a very small rainfall, e.g. on Aldabra about 38 cm. (15 in.) per annum, which rapidly percolates into the ground. The precipitation has the effect, however, of etching the metamorphic limestone into a fretted surface which gives it a very rugged appearance known locally as 'champignon'. In the main the surface of the islands is level and at an elevation of about 5 m. above sea-level. Around the seaward coast the pounding of the waves eats into the land rim, breaking it down or forming overhanging cliffs. In the centre of most of the islands there is a lagoon. The shores of these lagoons are being continually dissolved away so that the lagoon surfaces are increasing and the land surfaces decreasing. Around the open coasts of the islands fragments of coral in various degrees of disintegration are deposited as shingle and sand. In places where the waves have broken down the coastal cliffs the wind is able to blow the finer coral sand up on to the island. The prevailing winds of the latitudes in which the islands are

The Algae of Miles Rough Bog, Bradford

Abstract: Algae were collected from Miles Rough bog at approximately monthly intervals from March 1923 to August 1927. The composition of each sample was determined as to species and at each collection the quantity of alga was noted. Miles Rough bog (see Fig. 1) is at the upper end of a glacial overflow channel in the Millstone Grit. It is about 25 m. in length and the same in breadth and lies at an altitude of some 220 m. At the upper western end is a steep slope, and from the base of the slope issues the water, chiefly by one spring, which flows over the bog and finds its exit at the lower eastern end. The bog is a sphagnum bog and scattered among the sphagnum are: