BIOGEOGRAPHY OF SEEDER AND RESPROUTER ERICA SPECIES IN THE CAPE FLORISTIC REGION - WHERE ARE THE RESPROUTERS

The genus Erica L., with more than 600 species, and a high number of e ndemics, represents the most remarkable example of floristic diversity in the Cape Floristic Region (CFR). It is largely confined to nutrien t-poor, acidic, sandy soils; being one of the most characteristic elem ent of fynbos. The ability to survive fires, resprouting from a lignot uber, is a common trait among Euro-mediterranean Erica species. In con trast, resprouting is fairly uncommon among ericas in the CFR (less th an 10%). Most of them are killed by fire, regenerating only but readil y by seed germination. An extensive survey on the resprouting ability of South African Erica species was carried out and the pattern of geog raphical distribution of resprouters and seeders in the CFR was determ ined. The geographical distribution of these two regeneration classes was related to a climatic gradient of seasonality along the CFR. A pat tern of higher proportions of resprouter species towards the mediterra nean, strongly seasonal northwestern CFR and the non-seasonal eastern CFR and summer rainfall area outside the CFR was identified. The numbe r of resprouter species reaches a maximum in the eastern CFR and is lo wer in the southwestern CFR despite the overall higher concentration o f species in this subregion. Summer drought strongly influences the ef fectiveness of postfire regeneration and growth (i.e, new recruits plu s survivors) of Erica species, and is the major selective force accoun ting for the pattern of distribution of seeders and resprouters in the CFR. A mild mediterranean climate with reliable autumn-winter rains a nd a short summer drought, typical of the mountain areas of the southw estern CFR, favours recruitment of seeders but hampers recruitment of resprouters. Resprouter species persist and become dominant under hars h conditions for recruitment (severe summer drought) and would coexist with seeders under situations of no summer stress. Diversification is associated with seeder lineages. Hence, number of seeder species will be higher than number of resprouters, especially in the southwestern CFR, where favourable conditions for recruitment allow a massive conce ntration of seeder species, many of them narrow endemics. (C) 1998 The Linnean Society or London.