Very obviously, fire decreases the density of woody stems and late (intense) burning has a greater effect than early burning. In very humid savanna (as in derived savanna regions) the wood volume may sometimes be greater in early burnt plots than in fire protected ones in early successional stages, as smaller mean girth in the fire-protected area may not be compensated for by the increase in stem density. The effect of fire on herbaceous production varies greatly with climate. In drier, more marginal regions early burning or even fire protection may result in higher grass yields than late burning. In the southern derived savanna, time of burning makes little difference in yield, but somewhat greater yield is achieved with late burning. In intermediate (Guinea savanna) regions, late burning usually appears to increase grass above-ground biomass, although no results of long-term experiments are available.