Page 213 - Life & Land Use on the Bahrain Islands (Curtis E Larsen)

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water sources ranging from rivers to seepage zones fed by groundwaters. Strict
limits may have been imposed upon the carrying capacities of such settings by the
first domesticated plants and the extent of land available for their cultivation.
The land available for cultivation is an important consideration. Allan
(1973) has presented a workable plan for land use analysis. Based on work in
Turkey, he has defined major ecological zones with specific productivities. This
concept is transferable to Bahrain. Bahrain has two major zones of potential
agricultural productivity. These are the soils of the coastal plain and colluvial and
alluvial soils of the the coalescent fans at the toe of the Khobar dipslope. The soils
of the fans are found between 6 and 12 m in elevation, while the coastal soils,
utilized most frequently for garden crops, lie below 6 m. The zone of coastal soils
is also frequently watered by gravity flow irrigation. The colluvial soil zone, on
the other hand, utilizes artesian water only when it is found near enough to the
surface to make gravity-flow irrigation practical. In any event, irrigation and
hence cultivation of the colluvial fans is aided by higher artesian water levels. The
fans also possess the "permanent" soils which Allan sees as periodically renourished
by new colluvial deposits.
These ecological zones have differing productivities, and their carrying
capacities vary accordingly. Each zone can be expected to support a critical
population density. Were conditions ideal for the spread of agriculture, Allan’s
concept of a population increase in response to reliance on agriculture might well
apply. In this framework, the area of cultivation would expand until a "critical
population density" was exceeded. At this sensitive stage falling yields resulting
from soil exhaustion or lack of water might lead the settlements into a decline
unless excess population moved elsewhere. Allan’s (1973:216) remark that African
folklore is "full of stories of such movements in the recent past, when the land for
cultivation became too small for the people," is apropos.
The problem here is to assess the productivity of Bahrain’s soils when no
hard data exist. We must, therefore, turn to the work of others for useful
analogies. Pertinent work has been done by both Allan (1973) and Jarman and
Webley (1975). Allan presented a synthesis of changing world crop productivities