Abstract
The tropical African forest cover prevents an excessive warming above it, and pushes to its margins the heat lows, lows occupied by low-level wind discontinuities (Meteorological Equator and Inter-Oceanic Confluence); thus the forest keeps out the dry airstreams, such as the continental trades, which are restricted to its margins. Because it extends as far as the ocean, it maintains the maritime advection permanently over itself; so that the forest ensures its own protection. The aerological influence of a compact forest cover concerns only low-levels; as soon as the surface influence disappears, the Meteorological Equator recovers its usual structure and the distribution of heavy rains, connected with its mid-level I.C.Z. structure is then no longer modified. Present and past conditions (especially during the Last Glacial Maximum and the Holocene Climatic Optimum) show that its abilities to protect itself are limited, its survival depending on an always precarious equilibrium between opposing streams, on the one hand the maritime airstream and on the other hand, in the opposite direction, the dry continental trades blowing from north and south towards the forest margins.
The recent evolution of meteorological conditions with heavy rainfall distribution in a narrow belt closer to the Equator, connected with the strengthening of the continental trades, makes the equilibrium of most forest margins more fragile and susceptible to becoming abruptly destabilised. Consequently it appears that the protection of the present forest cover is really the first priority.
The tropical forest is at present a major concern and we have to protect the “lung of the planet”, which is often evoked in relation to rainfall (the contribution of transpiration allowing several reutilisations of precipitable water potential (Leroux, 1983; Monteny, 1986; Pouyaud, 1986)), and more recently in relation to the absorption of carbon dioxide; however, the tropical forest is rarely considered as a meteorological factor able to determine the surface pressure field and the wind field at low-levels.
When the destruction of forest is evoked, responsibility normally rests with either a decrease of rainfall or exploitation by man; but the cause is not sought in the increasing power of continental trade winds, precisely characterized by a strong saturation deficit.
Our purpose is, to observe the interactions between a compact forest over and its aerological environment, in order to understand how the forest ensures itself — at the present — its own protection, and also why the forest was — in the past — unable to stop the dry air at its boundary, and consequently to maintain itself. Then we observe the present state of the Guineo-Congolese evergreen forest (Fig. 1) and chiefly the conditions required by nature for the establishment and survival of this tropical forest cover.
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Leroux, M. (1990). Natural Protection and Voluntary Extension of the Tropical African Forest Cover. In: Paepe, R., Fairbridge, R.W., Jelgersma, S. (eds) Greenhouse Effect, Sea Level and Drought. NATO ASI Series, vol 325. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-0701-0_15
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