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It is often assumed that clearing invasive alien species will lead to the dissipation of their negative impacts and recovery of native plant diversity. However, this is often not the case because clearing of primary invasive alien species can lead to secondary invasion by non-target species. We investigated the effects of vegetation type and application of fire during management of biomass after clearing invasive acacias on secondary invasion in the South African fynbos. Furthermore, we determined how these effects change with years after clearing. We sampled vegetation in lowland and mountain fynbos cleared of invasive Acacia saligna using the "fell, stack and burn" method. During burning of the stacked slash, the area at the centre of the stack experiences a high severity fire while the area at the edge experiences a low severity fire. After fire, burn scars remain in place of the stacked slash. We sampled in and outside of 80 burn scars over three years after clearing. Overall, we set out to (1) identify species that are secondary invaders; (2) determine whether secondary invader richness and cover differ between where there were high and low severity fires and no fires, and how these differences change with years after clearing; and (3) determine whether secondary invader richness and cover differ in and between lowland and mountain fynbos, and how these differences change with years after clearing. We identified 32 secondary invader species. Mean secondary invader richness was lower where there were high severity fires (2.75) compared to where there were low severity fires (3.28) and no fires (3.24). Mean secondary invader proportion cover was lower where there were no fires (0.14) compared to where there were high severity fires (0.19) and low severity fires (0.2). Three years after clearing, secondary invader richness and cover had not changed or was now higher than in the first year, while secondary invader richness was similar between lowland and mountain fynbos. Secondary invader cover was similar between lowland and mountain fynbos up to two years after clearing but was 58% lower in lowland fynbos in the third year. Fire application after clearing invasive acacias can have positive (i.e. reduction of Acacia soil seed banks by triggering mass germination) and negative (i.e. favors the dominance of secondary invaders) effects. As a result, slash should be spread throughout the restoration site instead of being stacked and then burnt to reduce Acacia soil seed banks. To avoid the establishment of a second generation of invasive acacias, the seedlings that germinate can be controlled through manual weeding, mowing and herbicide application. Due to the persistence and abundance of secondary invaders up to three years after clearing at levels similar to or higher than in the first year, we conclude that practicing restoration ecologists must manage these species to ensure successful restoration of native plant diversity. • After alien clearing in the fynbos, we found 32 secondary invader species. • High severity fires after alien clearing reduce secondary invader richness. • Fire application after alien clearing increases secondary invader cover. • Secondary invasion persists up to three years after alien clearing. [ABSTRACT FROM AUTHOR]

Abstract: Riparian ecosystems in South Africa's fynbos biome are heavily invaded by alien woody plants. Although large-scale clearing of these species is underway, the assumption that native vegetation will self-repair after clearing has not been thoroughly tested. Understanding the processes that mediate the recruitment of native species following clearing of invasive species is crucial for optimising restoration techniques. This study aimed to determine native species recovery patterns following implementation of different management interventions. We tested the influence of two clearing treatments (“fell & remove” and “fell & stack burn”) on the outcomes of passive restoration (natural recovery of native riparian species) and active restoration (seed sowing and planting of cuttings) along the Berg River in the Western Cape. Under greenhouse conditions we investigated seed viability and germination pre-treatments of selected native species. There was no recruitment of native species in sites that were not seeded (passive restoration sites), possibly because of the dominance of alien herbaceous species and graminoids or the lack of native species in the soil-stored seed bank. Germination of our targeted native species in the field was low in both “fell & remove” and “fell & stack burn” treatments. However, “fell & stack burn” gave better germination for the species Searsia angustifolia, Leonotis leonurus and Melianthus major. Seedling survival in the field was significantly reduced in summer, with drought stress being the main cause for seedling mortality. Germination rates in the greenhouse were high, an indication that harvested seeds were viable. Most seeds germinated without germination pre-treatments. We conclude that failure of native seeds to germinate under field conditions, secondary invasion of alien herbs and graminoids, the lack of native species in the soil-stored seed bank, and dry summer conditions hamper seedling establishment and recovery on sites cleared of dense stands of alien trees. For active restoration to achieve its goals, effective recruitment and propagation strategies need to be established. [Copyright &y& Elsevier]

Pine plantations and pine invasions have numerous impacts on native ecosystems in the Fynbos biome of South Africa. The severity of these impacts greatly determines the extent of potential ecosystem recovery after the pines are felled. The recovery potential of fynbos after felling of pine plantations of varying longevity and the subsequent application of ecological burns 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 and sites that had been under pines for 30 and 50 years respectively) using 1 m 2 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 had high native species and growth form density (number of species/growth forms per unit area) and similar plant density (number of individuals per unit area) to the reference fynbos areas. Conversely, areas previously under 50 year old pine plantations had significantly lower native species and growth form density and plant density than the reference fynbos and were dominated by alien species. In addition, areas previously under 50 year old pine plantations had lower species diversity than the reference fynbos areas and areas previously under 30 year old pine plantations which were found to be similar to one another. Felled pine plantations were shown to minimally impact on soil abiotic variables, with only soil temperature and pH showing significant differences. Therefore, areas previously under 30 year old pine plantations have higher recovery potential following pine removal than 50 year old plantations, owing to the depleted native soil seed bank in the latter. Consequently, active restoration may be needed to re-introduce the missing long-lived growth forms and to prevent soil erosion. Pine plantation and invasion management in the Fynbos biome should aim to fell pines before the native seed bank is depleted to maintain the recovery potential of fynbos and prevent the need for active restoration. [ABSTRACT FROM AUTHOR]

We present a simple method for assessing the medium-term sustainability of different flower harvesting intensities (i.e. percentage of number of stems harvested per individual) for two re-seeders and re-sprouters of fynbos plants on the Agulhas Plain in the Cape Floristic Region, South Africa. We interpret our results from an ecological point of view, looking at impacts of harvesting on vegetative re-growth and survival of frequently harvested fynbos species, and an economic point of view, determining the cumulative number of stems harvested per year. We analysed the impact of different harvesting intensities on two obligate re-seeding ( Erica corifolia (L.) and Erica imbricata (L.)) and two strongly re-sprouting species ( Brunia laevis (Thunb.) and Staavia radiata (L. Dahl)) on different flower farms. Seventy-five randomly selected plants of each species were experimentally harvested in the same way as is done by flower harvesters. Fifteen plants of each species were left as controls (un-harvested) and 15 each were harvested (cut 15–20 cm below the inflorescence) such that 25%, 50%, 75%, and 100% of the inflorescences were removed. Harvested stems were labelled and the number of new shoots counted. Additionally we recorded plant height and mortality. 100% harvesting resulted in high mortality rates for both re-seeders (for both species 100% of the individuals were dead at the end of the experiment) and resprouters (for one species all 15 individuals were dead at the end of the experiment and for the other species 4 of 15). Re-seeders in particular were highly susceptible to harvesting below the first branching node, which generally also resulted in plant death. Both guilds can survive up to 75% harvesting (resprouters experienced no mortality for one species, while in the other 4 out of 15 died; of the re-seeders, 9 out of 15 died in the one species, while only 1 out of 15 in the other) and are still able to grow in height. For both seeders and resprouters we recommend that flower harvesters do not harvest in young veld. To ensure sufficient seed set and to avoid seed bank depletion we recommend to preferably only harvest between 25 and 50% of stems per individual. [ABSTRACT FROM AUTHOR]