THE CONSERVATION OF AFRICAN PLAINS GAME 351 



SO that a great part of the so-called 'bush' is beUeved to represent fire-climax 

 vegetation (Shantz & Marbut, 1923), degraded and often thorny forms of 

 fire-resistant bushes which have replaced more luxuriant woodlands and 

 which represent lower levels both of water status and nitrogen status. 



Much could be said about the possible effects of unsuitable practices on 

 the vegetation. The main thing to be emphasized is this — that the amount 

 of production depends on the amount of energy absorbed and used. Bare 

 earth, whether from over-grazing or from burning, is useless and the vegeta- 

 tion cover ought to be maintained at a depth sufficient to absorb all or most 

 of the incident light and to fix all the available nitrogen. 



Turning now to the conversion ratios, a major ecological problem is how 

 much of the energy and nitrogen so fixed can be converted into animal 

 population in an eco-system which is in a steady state. We are accustomed 

 to think of stall-fed beasts as requiring about eight times their own dry 

 weight of food in growing to maturity. Thus one might expect that expressed 

 as standing crops in the best conditions the balances of plants : herbivores : 

 carnivores might be represented as 100 : 10 : i. 



In Masai land we have seen that the ratio of herbivore to man is something 

 like 120 cattle and 200 sheep or goats to nine human beings of all ages. In 

 terms of weight this means about forty parts of herbivore to each human 

 being. There is reason to beheve also that the ratio vegetation : herbivore is 

 at least 50 to i in equivalent weights, and possibly as high as 100 to i. One 

 of the difficulties of giving a better approximation here is that no actual 

 measurements of herbage weight are available. One can only say that the 

 ungrazed grasses, for example, suggest an annual dry-weight production of 

 the order 5-10,000 lb/acre (7-14,000 kg/hectare) by comparison with 

 EngHsh examples. Much of the vegetation considerably exceeds this figure. 

 Let us therefore take the estimates to be of the order of magnitude of 



Vegetation Herbivore Carnivore 

 100 : 2 : 0-05 



recognizing that these are probably optimistic and underestimate the con- 

 version losses. Ratios of this order of magnitude show, however, that very 

 large losses of protein and energy take place in these conversions in a semi- 

 natural system like this. Clearly here is a point at which thought on conserva- 

 tion should start. 



Deevey (1956) has suggested that such ratios may well indicate the insurance 

 necessary in an adverse habitat. The argument could be that the fluctuating 

 secondary population will only occasionally build up to the level at which 

 damage to the primary or Tood' population takes place. When this happens 

 there will of necessity be a subsequent decline in the grazing population. 



