The influence of flooding regimes on forest distribution and composition in the Tana river floodplain, Kenya.
Abstract
Different forest types, related to frequency and duration of flooding on the Tana river floodplain, are described: active levee evergreen forest (Ficus sycomorus, Sorindeia madagascariensis, Sterculia appendiculata typical overstorey species); inactive levee forest (as above, with shrub species typical of areas further from river); Acacia forest, dominated by A. elatior; clay evergreen forest, dominated by Diospyros mespiliformis and Garcinia livingstonei; vegetation on low-lying point-bars, commonly Populus ilicifolia and Pluchea dioscoridis; and pioneer vegetation in ox-bow infills, such as Terminalia brevipes and/or Spirostachys venenifera. Flood tolerance appears to be a major determinant of forest distribution, and floodplain forest growth can only be sustained at or above heights which receive floods of critical maximum frequency and duration. Probable changes to the floodplain forest, resulting from construction of a series of dams in the Tana headwaters, are discussed. It is suggested that while tolerance to maximum flood levels is important in all floodplain forests, floodplain forests in semi-arid zones also depend on minimum flooding frequencies and durations.