The impact of pine plantations on fynbos above-ground vegetation and soil seed bank composition

Pine plantations and pine invaded areas have numerous impacts on native ecosystems in the fynbos biome of South Africa. The severity of these impacts greatly determines the potential ecosystem recovery that occurs once the pines are felled. The recovery potential of fynbos following the felling of pine plantations of different durations was investigated in the Helderberg Nature Reserve, Western Cape Province, South Africa. Above-ground vegetation, soil seed bank and abiotic variables were sampled across three treatments (reference fynbos, 30 year old pine and 50 year old pine treatments) using 1 m2 quadrats placed along 50 m line transects. The soil seed bank samples were smoke treated and then monitored in a greenhouse to determine the soil seed bank species and growth form composition. Areas previously under 30 year old pine plantations have high native species and growth form richness and density that is similar to the reference fynbos areas. In contrast, areas previously under 50 year old pine plantations have significantly lower native species and growth form richness and density than the reference fynbos treatment. These areas are in turn dominated by alien species. Areas previously under 30 year old pine plantations have high recovery potential following pine removal; in contrast, recovery potential is low for areas previously under 50 year old pine plantations, due to the depleted native soil seed bank. Consequently, active assistance is needed to restore the missing long-lived growth forms and to prevent soil erosion. Pine plantation and invasion management in the fynbos biome should therefore aim to fell pines before the native seed bank is depleted in order to maintain the recovery potential of fynbos and prevent the need for active restoration.