The relationships between forest and mountain fynbos communities in the southwestern Cape Province of South Africa
Evergreen forests are believed to be restricted to moist sites in the southwestern Cape because of seasonal drought and high fire frequency in adjacent fynbos shrublands. However, soil moisture has not been demonstrated as the controlling factor. Succession to forest has been observed in some areas and not all forest trees in the fynbos are killed in some fires. This thesis determines whether forest and fynbos communities are separated by habitat factors or whether they are different successional stages of the same vegetation type. The effects of fire on forests, regeneration processes and habitat factors were studied in Swartboskloof, near Stellenbosch. Establishment requirements of forest seedlings were investigated in nearby Assegaiboschkloof. The effects of habitat factors on germination, establishment, growth and competitive abilities of forest and fynbos species were determined in controlled growth experiments. Established forest stands in Swartboskloof were stable in response to fire. Studies on the relationship between plant size and ability to survive fire showed fire intensity to be the overriding factor. Unlike regeneration in fynbos, regeneration of forest species is not coupled to disturbance. Forests had smaller soil seed banks than nearby fynbos but had the same set of species. Dispersal of ·forest species seeds into fynbos occurs immediately after fire for wind- and bird-dispersed species. Therefore colonization of fynbos by forest species soon after fire is not limited by seed dispersal. Evidence of facilitation of forest development was found in mature fynbos. Forest seedlings were associated with tall vegetation, high cover and deep litter layers as well as proximity to perches. Facilitation is enhanced in nuclei of forest species within fynbos communities. These studies refute the concept of forest and fynbos as distinct vegetation types. The relationships between forest and fynbos are explained on the basis of successional processes. Germination of forest species may occur in post-fire conditions, but establishment is unlikely until habitat amelioration occurs. Soil moisture and nutrients affect the rate of forest development. It is the frequency of fire, in relation to the rate of forest development, which determines the extent of forest development.
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