The impact of alien plant invasion on mycorrhizas in mountain fynbos vegetation

We examined the effect of dense alien plant invasion on vegetation development following clearing, from a nutrient-acquisition perspective. The majority of fynbos plants form arbuscular mycorrhizas but Hakea and Pinus, two of the most invasive alien plant genera in mountain fynbos, do not. We hypothesised that these aliens would negatively impact on arbuscular mycorrhizal infectivity and thereby influence post-clearing vegetation development. The mycorrhizal status of vegetation at two mountain fynbos sites was compared between invaded and uninvaded sites before clearing and after alien clearing and fire. On cleared sites, nonmycorrhizal guilds were under-represented and arbuscular mycorrhizal guilds were over-represented. Soil arbuscular mycorrhizal infectivity and spore numbers were not affected by alien plants, possibly because an understorey of arbuscular mycorrhizal species had persisted in the alien stands. We conclude that following a single cycle of dense alien vegetation, arbuscular mycorrhizal plant species are not negatively affected and that other effects of alien vegetation on the environment are responsible for changes in plant guilds. Soil under alien plants was enriched and this may have contributed to the success of the arbuscular mycorrhizal guild after clearing.