PDF - Wallace Online

I CLIMATE AND ASPECTS OF THE EQUATORIAL ZONE 231conditions. Whether we are at Singapore or Batavia, in theMoluccas or New Guinea, at Para, at the sources of theRio Negro, or on the Upper Amazon, the equatorial climateis essentially the same, and we have no reason to believe thatitmaterially differs in Guinea or the Congo. In certainlocalities, however, a more contrasted wet and dry seasonprevails, with a somewhat greater range of the thermometer.This is generally associated with a sandy soil, and a less denseforest, or with an open and more cultivated country. Theopen sandy country with scattered trees and shrubs or occasionalthickets, which is found at Santarem and Monte- Alegreon the lower Amazon, are examples, as well as the opencultivated plains of Southern Celebes ;but in both cases theforest country in adjacent districts has a moister and moreuniform climate, so that it seems probable that the nature ofthe soil or the artificial clearing away of the forests, areimportant agents in producing the departure from the typicalequatorial climate observed in such districts.Effects of Vegetation on ClimateThe almost rainless district of Ceara on the north-east coastof Brazil, and only a few degrees south of the equator, is a strikingexample of the need of vegetation to react on the rainfall.We have here no apparent cause but the sandy soil and barehills, which, when heated by the equatorial sun, produce ascendingcurrents of warm air and thus prevent the condensation ofthe atmospheric vapour, to account for such an anomaly ;andthere is probably no district where judicious planting wouldproduce such striking and beneficial effects. In Central Indiathe scanty and intermittent rainfall, with its fearful accompanimentof famine, is perhaps in great part due to theabsence of a sufficient proportion of forest -covering to theearth's surface ;and it isby a systematic planting of all thehill -tops, elevated ridges, and higher slopes that we shallprobably cure the evil. This would almost certainly inducean increased rainfall ;but even more important and morecertain is the action of forests in checking evaporation fromthe soil and causing perennial springs to flow, which may becollected in vast storage tanks and serve to fertilise a greatextent of country ;whereas tanks without regular rainfall or