forests and forestry: Africa 467 People also tried to control forest growth In North America people of the central plains set dry grass on fire to clear the land for new growth of forage for their staple food: bison Without their actions over thousands of years the great eastern forests of North America would likely have extended much farther westward than they did In many parts of the world people burned forests to make room for farming In western Africa this was part of a system of rotation A plot would be farmed for a few years and then would be left alone for about 10 years, allowing the soil to recover while other plots were farmed People would again burn away growth on the plot when the time came to replant it Elsewhere, as in Central America, people burned without thought to renewing the land, resulting in ecological catastrophes such as that which befell the Maya The Maya were not unique in this— even in faraway southern Africa, the Great Zimbabwe civilization met with a similar fate in the late 1400s Among some medieval peoples, managing forests was institutionalized In Europe laws were created to govern who could use a forest and how the forest was to be used In India foresters were craftsmen charged with managing forests They determined which trees would be felled at what time, and they took care that animals were not overhunted Further, they were required to replant with trees any areas that had been logged, creating forests that appeared primeval but actually were filled with trees chosen by people because the trees were useful Thus, there were competing needs for the civilizations that arose in and near forests People needed forests to remain intact yet also needed to remove forests to use the wood and to make room for people to settle This conflict sometimes led to outright destruction of forests, but there were examples of the ways in which a culture could manage its forests to preserve them By late medieval times China had nearly eradicated its northern forests and was losing its southern forests all the way to its southern mountains, where logging was difficult, but in much of India forests remained thick upon the land In Europe, even while great swaths of forest were cleared for farms, large tracts were protected by law from destruction In Japan, where wood was used to build almost everything, continuous replanting of forest kept its islands covered by trees Many of the forests that exist today are the result of the efforts of medieval cultures to conserve them and even to nurture them Africa by Leah A J Cohen In modern times the definition of forest varies depending upon the criteria used Definitions can be related to canopy cover, biomass, tree type and size, or land use Forests can be classified as old growth or secondary/fallow and also are classified based on ecological characteristics, such as species, rainfall, and elevation Defining forests has become increasingly complex owing in part to the impact that humans have on forests People can clear forests, selectively harvest species and thereby alter the composition of a forest, replant forests with different species, and plant specific species of trees for a multitude of uses, such as conservation or agriculture These varied uses of forests and forest resources increased dramatically just before and during the medieval period as humans’ activities affected and altered forests more extensively than ever before Reconstructing a picture of forest cover during medieval times is based on archaeological evidence of the human use of forest resources and research on climate and ecological characteristics In general, forest ecology is supported in areas of Africa that receive more than 55 inches of rainfall annually Rainfall of between 15 and 55 inches annually supports savanna or grassland ecology with interspersed trees and woodland areas Furthermore, forests tend to occupy riversides in many areas During the medieval period there were equatorial rain forests in central Africa, forests in the higher elevations of eastern and southern Africa and the Atlas Mountains of northwestern Africa, and coastal forests in western Africa and eastern and southeastern Africa Woodland ecology extended in a band from present-day Cameroon toward the southeast into present-day Mozambique The exact boundaries and expanse of these forests and woodlands varied during the medieval period based on climate changes The changes in the boundaries of these ecosystems have been detected in the archaeological record by the movements of pastoralists Herders avoided forested areas because these were the natural habitat for tsetse flies, which carried the disease trypanosomiasis that infected and killed large livestock At the start of the medieval period forests and woodlands still extensively occupied the mountainous regions extending from Ethiopia into southern Africa Land use during this period reduced the forest cover in this area Furthermore, the climatological and archaeological records from the medieval period show that forests lay farther to the north during the Medieval Warm Period (800–950 c.e through 1300 c.e.) as the result of the northerly route of the seasonal rains As the temperatures dropped during the 1300s and the seasonal rains began to move across a more southerly route, the forest boundaries moved with them Before and during the medieval period the use of forest resources changed forests and human life dramatically Rainfall was no longer the most important factor that determined whether forests thrived The spread of iron-smelting technologies, the Bantu expansion (the third phase of which oc-