Natural Fynbos Research Articles

Soil compaction and surface-active arthropods in historic, agricultural, alien, and recovering vegetation

Soil compaction is a major threat to natural resources. However, little information is available on the impacts of soil compaction on arthropod diversity especially relative to different types of vegetation, land use and restoration activities. In response to this dearth of information, we studied soil compaction, as well as percentage soil moisture and mean leaf litter depth, associated with four vegetation types: natural vegetation (fynbos, the historic condition), agricultural land (vineyards), invasive alien trees, and vegetation cleared of invasive alien trees (recovering vegetation). Our study took place in the Cape Floristic Region, South Africa, a biodiversity hotspot, yet also an area of intense viticulture and heavy invasion by alien plants. We sampled soil surface-active arthropods using pitfall traps, and compared species richness and abundance in different vegetation types with various levels of soil compaction and other soil variables. Overall, vineyards had the highest soil compaction while natural fynbos and aliens had low and comparable compaction. For both arthropod species richness and abundance, the order of the four vegetation types was, from highest to lowest: natural fynbos, alien cleared sites, vineyards, and alien infested sites. Level of soil compaction negatively correlated with arthropod species richness but not with abundance. Neither soil moisture nor leaf litter depth on their own significantly affected arthropod species richness or abundance. While alien trees overall had a strong negative effect on both arthropod species richness and abundance, and much more so than vineyards, the situation is reversible, with removal of aliens being associated with rapid recovery of soil structure and of arthropod assemblages. This is an encouraging sign for restoration.

Effects of storage under low temperature, room temperature and in the soil on viability and vigour of Leucospermum cordifolium (Proteaceae) seeds

Seed longevity, the control of dormancy and the eventual fate of seeds were studied in two experiments simulating conditions in natural fynbos. In one experiment a batch of mature, freshly harvested, intact achenes (“seeds”) of the myrmecochorous species Leucospermum cordifolium was divided into lots, of which one was buried in mesic mountain fynbos (experiencing a mediterranean-type climate with hot summers). Other seed lots were stored open at room temperature and in closed nitrogen filled containers at 3°C, respectively. Stored seeds were sampled and germinated under optimal laboratory (viability estimate) and seed bed (vigour estimate in fynbos) conditions, during autumn, after 0 (control), 1, 2 and 4years. Low temperature stored seeds maintained a high viability and vigour for c. two years but ambient temperature storage led to a marked decline after 1year ending in almost complete mortality after 4years of shelf storage. Four year soil-stored seeds, by contrast, maintained a high viability and vigour, of 80% and 60% respectively of the original seed source values. The soft pericarp/elaiosome in soil-stored seeds disappeared completely whilst the testa became progressively scarified over time. The strongly increased germination rate (velocity) in soil-stored seeds was attributed to natural oxygenation mediated by testa scarification. In another experiment freshly matured intact achenes were oxygenated with 1% H2O2 and the pericarps removed. Disinfection and benzyladenine growth regulator soaking (200mgL−1 for 24h) were applied as separate treatments. The seeds were then sown at 1cm depth in a standard seed bed in autumn and germination was recorded in the first winter season and, in the undisturbed seed bed, in each subsequent winter for 5 germination seasons. H2O2 oxygenated seeds gave a much higher germination percentage and rate than non-oxygenated seeds, although sporadic germination continued over five germination seasons in all treatments. Seeds germinated only during autumn and early winter each year.The results of the combined experiments suggest that, in nature, Leucospermum seeds can persist underground for long periods. We propose a model of soil-stored seeds in which the intact testa of freshly dispersed seeds is gradually scarified, leading to uneven, extended germination of the young (mainly current season) seed cohort over the first (and possibly several) post-fire germination seasons; and the synchronous germination of the older (scarified), larger, portion of the seed bank, leading to massive species recruitment during the early stages of the first post-fire winter germination season. The numerous wet–dry cycles due to natural rainfall, over prolonged periods in fynbos, may contribute to seed longevity via cellular repair processes.

Symbiotic diversity, specificity and distribution of rhizobia in native legumes of the Core Cape Subregion (South Africa).

Rhizobial diversity and host preferences were assessed in 65 native Fynbos legumes of the papilionoid legume tribes Astragaleae, Crotalarieae, Genisteae, Indigofereae, Millettieae, Phaseoleae, Podalyrieae, Psoraleeae and Sesbanieae. Sequence analyses of chromosomal 16S rRNA, recA, atpD and symbiosis-related nodA, nifH genes in parallel with immunogold labelling assays identified the symbionts as alpha- (Azorhizobium, Bradyrhizobium, Ensifer, Mesorhizobium and Rhizobium) and beta-rhizobial (Burkholderia) lineages with the majority placed in the genera Mesorhizobium and Burkholderia showing a wide range of host interactions. Despite a degree of symbiotic promiscuity in the tribes Crotalarieae and Indigofereae nodulating with both alpha- and beta-rhizobia, Mesorhizobium symbionts appeared to exhibit a general host preference for the tribe Psoraleeae, whereas Burkholderia prevailed in the Podalyrieae. Although host genotype was the main factor determining rhizobial diversity, ecological factors such as soil acidity and site elevation were positively correlated with genetic variation within Mesorhizobium and Burkholderia, respectively, indicating an interplay of host and environmental factors on the distribution of Fynbos rhizobia.

Biological quality of a podzolic soil after 19 years of irrigated minimum-till kikuyu–ryegrass pasture

Conversion of natural rangeland to minimum-tillage kikuyu (Pennisetum clandestinum) based pastures for dairy production in the southern Cape of South Africa, may be beneficial to soil biological quality. The objective was to evaluate whether 19 years of minimum-till kikuyu-ryegrass pasture had altered the distribution and quality of biological properties formerly developed under natural rangeland. An irrigated minimum-till kikuyu-ryegrass pasture soil was compared to virgin soil with natural rangeland. Soil organic matter, soil organic C, active C, microbial biomass C, total N and enzymatic activities (β-glucosidase, urease and alkaline phosphatase) behaved similarly by having higher values in the surface layers of the cultivated pasture soil than in virgin soil, decreased with depth until they become similar at the 200–300 mm depth. Acid phosphatase activity was similar (P > 0.05) between soils. Vertical distribution of potentially mineralizable N was similar (P > 0.05) at 0–100 mm soil depth, but higher (P ≤ 0.01) in the cultivated pasture soil than in the virgin soil. The microbial indicated along with stratification ratios for different biological indicators that the cultivated pasture soil’s ecosystem functionality improved. Soil microbial functional diversity and carbon source utilisation patterns of the cultivated pasture soil and virgin soil was influenced by plant species present and root exudate composition. The soil microbial diversity, as shown by the Shannon-Weaver and Enrichment Indices, was significantly altered between cultivated pasture and the virgin soil, especially at different soil depths. A general appraisal of biological soil properties indicated that conversion of natural fynbos vegetation to irrigated minimum-till kikuyu-ryegrass pasture after 19 years of cultivation on a podzolic soil beneficial.

The role and value of water in natural capital restoration on the Agulhas Plain

The Agulhas Plain is a low-lying coastal area within the Cape Floristic Region. It is heavily invaded by alien vegetation that infringes upon the sustainable supply of ecosystem goods and services provided by the native fynbos vegetation. Alien clearing and natural capital restoration is expected to recover these ecosystem goods and services and in particular to increase water availability. The study conducts cost-benefit analyses to assess whether alien clearing and natural capital restoration would add value to the Agulhas Plain through sufficiently increasing the supply of marketable ecosystem goods and services. The results indicate that the costs of alien clearing and restoration cannot be justified in the absence of water as a valued commodity. Other ecosystem goods and services included have a negligible impact on justifying costs.

THE EFFECT OF ACACIA MEARNSII INVASION AND CLEARING ON SOIL LOSS IN THE KOUGA MOUNTAINS, EASTERN CAPE, SOUTH AFRICA

ABSTRACTConcerns exist over increasing sediment yields in areas of South Africa with a Mediterranean climate that result from the clearing of invasive woody vegetation from steep slopes, as part of the Working for Water Programme. Erosion rates were monitored with erosion pins over a 26‐month period. Measurements were made on slopes covered with indigenous fynbos vegetation, intact Acacia mearnsii stands (the invasive species) and on slopes from which A. mearnsii had been cleared either within the last 2 years or 11 years ago. Net erosion was observed at all sites following the largest storm during the monitoring period, whereas smaller storms were often accompanied by net deposition. Cleared locations showed the most variable response through time and sites with native fynbos vegetation the least. A stepwise multiple regression showed that vegetation cover, slope gradient and stone cover were the main variables affecting soil loss, but the relationship varied between sites and measuring periods. Soil loss was negatively related to vegetation cover and stone cover, as could be expected; the negative relationship with slope was more surprising. Stone cover, which increases with slope gradient, is considered to be an important control on soil loss. The findings of this study suggest that the rehabilitation of hillslopes invaded by alien woody vegetation needs to take into account the slow recovery of vegetation after initial clearing as, 11 years since clearing, significant erosion still occurs during severe storms. Copyright © 2012 John Wiley & Sons, Ltd.

Plant invasions, restoration, and economics: Perspectives from South African fynbos

Abstract Restoration is gaining importance in the management of plant invasions. As the success of restoration projects is frequently determined by factors other than ecological ones, we explored the ecological and financial feasibility of active restoration on three different invaded sites in South Africa's Cape Floristic Region. The aim of our study was to identify cost-effective ways of restoring functional native ecosystems following invasion by alien plants. Over three years we evaluated different restoration approaches using field trials and experimental manipulations (i.e. mechanical clearing, burning, different soil restoration techniques and sowing of native species) to reduce elevated soil nutrient levels and to re-establish native fynbos communities. Furthermore we investigated the possibility of introducing native fynbos species that can be used for sustainable harvesting to create an incentive for restoration on private land. Diversity and evenness of native plant species increased significantly after restoration at all three sites, whereas cover of alien plants decreased significantly, confirming that active restoration was successful. However, sowing of native fynbos species had no significant effect on native cover, species richness, diversity or evenness in the Acacia thicket and Kikuyu field, implying that the ecosystem was sufficiently resilient to allow autogenic recovery following clearing and burning of the invasive species. Soil restoration treatments resulted in an increase of available nitrogen in the Acacia thicket, but had no significant effects in the Eucalyptus plantation. However, despite elevated available soil nitrogen levels, native species germinated irrespective whether sown or unsown (i.e. regeneration from the soil seed bank). Without active introduction of native species, native grasses, forbs and other shrubs would have dominated, and proteoids and ericoids (the major fynbos growth forms) would have been under-represented. The financial analysis shows that income from flower harvesting following active restoration consistently outweighs income following passive restoration, but that the associated increase in income does not always justify the higher costs. We conclude that active restoration can be effective and financially feasible when compared to passive restoration, depending on the density of invasion. Active restoration of densely invaded sites may therefore only be justifiable if the target area is in a region of high conservation priority.

Drought-tolerance of an invasive alien tree, Acacia mearnsii and two native competitors in fynbos riparian ecotones

Invasive alien plants (IAPs) have successfully invaded many riparian zones in South Africa, especially Australian Acacia spp. which are prevalent along riverbanks in the south-western Cape of South Africa. This Mediterranean-type climate region is predicted to endure severe future water shortages under likely scenarios of increased population growth and climate change, and IAPs aggravate this problem due to their profligate water use. Acacia mearnsii competes aggressively with native species, however, it remains unclear what physiological advantage the species has over co-occurring native species under the predicted reduced streamflow scenarios. A mechanistic approach was used to investigate how key native fynbos riparian woody tree species compare in vulnerability to drought-induced cavitation against A. mearnsii by comparing findings from three Mediterranean-type fynbos river systems that differ in streamflow. A. mearnsii showed lower water potential at 50% hydraulic conductivity loss (P50 values) compared to native species at certain sites, an indication of drought-tolerance. This suggests it is likely to persist under future drier conditions and it therefore remains a top priority for control. The native Brabejum stellatifolium had consistently higher water potentials across all sites than the other studied species, and is a potentially valuable species for restoration of south-western Cape riparian zones. Consistency in the shapes of species vulnerability curves across sites illustrated a species-specific hydraulic response to different water availability, strengthening the argument that this approach to distinguish site-level drought-tolerance between trees is a practical technique, with great application in understanding future geographic distribution under climate change, and potential for use in restoration research. Additionally, streamflow was an inaccurate predictor of species drought-tolerance along these riparian systems.

Effects of Alien Plants on Ecosystem Structure and Functioning and Implications for Restoration: Insights from Three Degraded Sites in South African Fynbos

We investigated the type and extent of degradation at three sites on the Agulhas Plain, South Africa: an old field dominated by the alien grass Pennisetum clandestinum Pers. (kikuyu), an abandoned Eucalyptus plantation, and a natural fynbos community invaded by nitrogen fixing-Australian Acacia species. These forms of degradation are representative of many areas in the region. By identifying the nature and degree of ecosystem degradation we aimed to determine appropriate strategies for restoration in this biodiversity hotspot. Vegetation surveys were conducted at degraded sites and carefully selected reference sites. Soil-stored propagule seed banks and macro- and micro-soil nutrients were determined. Species richness, diversity and native cover under Eucalyptus were extremely low compared to the reference site and alterations of the soil nutrients were the most severe. The cover of indigenous species under Acacia did not differ significantly from that in reference sites, but species richness was lower under Acacia and soils were considerably enriched. Native species richness was much lower in the kikuyu site, but soil nutrient status was similar to the reference site. Removal of the alien species alone may be sufficient to re-initiate ecosystem recovery at the kikuyu site, whereas active restoration is required to restore functioning ecosystems dominated by native species in the Acacia thicket and the Eucalyptus plantation. To restore native plant communities we suggest burning, mulching with sawdust and sowing of native species.

Comparative footprint of alien, agricultural and restored vegetation on surface-active arthropods

Both invasive alien trees and agricultural conversion have major impacts on biodiversity. We studied here the comparative impact of these two types of land transformation on a wide range of surface-active arthropod species using pitfall traps, with evergreen sclerophyllous natural vegetation (fynbos) as the control. The study was in the Cape Floristic Region, a global biodiversity hotspot, where alien trees are of major concern and where vineyards replace natural fynbos vegetation. Surface-active arthropods were selected as they are species rich, relatively immobile, and occur in high abundance. We hypothesized that the impact of the two types of land cover transformation would produce similar qualitative and quantitative effects on the arthropods. We also compared the results in the transformed and natural areas with those in areas cleared of alien trees. Arthropod species richness in cleared areas was higher than in vineyards and more similar to that in natural fynbos, while alien trees had the lowest. Overall abundance scores were highest in cleared areas, closely followed by fynbos, then vineyards and lowest in alien trees. Several species were restricted to each vegetation type, including alien trees. In terms of assemblage composition, all vegetation types were significantly different, although fynbos and vineyards grouped, suggesting that vineyards have less impact on the arthropod community than do alien trees. When rare species were excluded, vineyards and cleared sites grouped, indicating some recovery but only involving those species that were common and habitat tolerant. Our results suggest that vineyards retain a greater complement of indigenous species than alien trees, but that clearing of these aliens soon encourages establishment of indigenous species. Although there were significant differences in soil moisture and litter depth within and between vegetation types, we did not record them as significantly affecting species richness or abundance, even in alien vegetation, an encouraging sign for restoration.

Recovery of invertebrate diversity in a rehabilitated city landscape mosaic in the heart of a biodiversity hotspot

We investigate here invertebrate response to alien pine plantations, their removal in comparison with natural vegetation, recovering indigenous forests and a botanical garden around Cape Town, South Africa, within a biodiversity hotspot. Pines had low invertebrate species richness and abundance. The botanical garden had the highest species richness and abundance. Natural fynbos vegetation was more similar to pines than to recovering fynbos, while recovering forest was more similar to pines than to any other site. The botanical garden is a major refugium for invertebrate species. Surprisingly, invertebrate assemblages in natural fynbos were more similar to those in pines than in recovering fynbos after the removal of pines. This suggests that some invertebrate species colonize the fynbos soon after rehabilitation disturbance, a response similar to the influence of fire. However, it takes longer for other natural climax invertebrate species to establish, some of which find refuge in pines and the botanical garden. Invertebrate assemblages of indigenous natural forests are more difficult to restore than those of fynbos, thus the protection of the remaining natural forests is a conservation priority. Invasive alien Argentine ant ( Linepithema humile) was far more abundant in recovering fynbos than in natural fynbos or in the botanical garden and pines. It benefits from initial restoration disturbance, although is likely to decline as the natural fynbos mature. This study strongly supports removal of alien pines in an urban context, and also emphasizes that an urban botanical garden of indigenous plants has major invertebrate conservation value.

Carbon sequestration and environmental effects of afforestation with Pinus radiata D. Don in the Western Cape, South Africa

A three-step methodology to assess the carbon sequestration and the environmental impact of afforestation projects in the framework of the Flexible Mechanisms of the Kyoto Protocol (Joint Implementation and Clean Development Mechanism) was developed and tested using a dataset collected from the Jonkershoek forest plantation, Western Cape, South Africa, which was established with Pinus radiata in former native fynbos vegetation and indigenous forest. The impact of a change in land use was evaluated for a multifunctional, a production and a non-conversion scenario. First, the carbon balance was modelled with GORCAM and was expressed as (1) C sequestration in tC ha−1 year−1 in soil, litter, and living biomass according to the rules of the first commitment period of the Kyoto Protocol, and (2) CO2 emission reductions in tC ha−1 year−1, which includes carbon sequestered in the above-mentioned pools and additionally in wood products, as well as emission reductions due to fossil fuel substitution. To estimate forest growth, three data sources were used: (1) inventory data, (2) growth simulation with a process-based model, and (3) yield tables. Second, the effects of land use change were assessed for different project scenarios using a method related to Life Cycle Assessment (LCA). The method uses 17 quantitative indicators to describe the impact of project activities on water, soil, vegetation cover and biodiversity. Indicator scores were calculated by comparing indicator values with reference values, estimated for the climax vegetation. The climax vegetation is the site-specific ecosystem phase with the highest exergy content and the highest exergy flow dissipation capacity. Third, the land use impact per functional unit of 1 tC sequestered was calculated by combining the results of step 1 and step 2. The average baselines to obtain carbon additionality are 476 tC ha−1 for indigenous forest and 32 tC ha−1 for fynbos. Results show that the influence of the growth assessment method on the magnitude of C sequestration and hence on the environmental impact per functional unit is large. When growth rate is assessed with the mechanistic model and with the yield table, it is overestimated in the early years and underestimated in the long term. The main conclusion of the scenario analysis is that the production forest scenario causes higher impacts per functional unit than the multifunctional scenario, but with the latter being less efficient in avoiding CO2 emissions. The proposed method to assess impacts on diverse components of the ecosystem is able to estimate the general tendency of the adverse and positive effects of each scenario. However, some indicators, more specifically about biodiversity and water balance, could be improved or reinterpreted in light of specific local data about threat to biodiversity and water status.

First Report of the Root-Knot Nematode Meloidogyne javanica on Buchu (Agathosma betulina) in South Africa.

Agathosma betulina, commonly known as buchu, has been used for centuries by the indigenous people of South Africa for medicinal purposes. Currently, the essential oils from buchu are used in medicine, food flavorings, and aromatic oils. Increased exploitation of natural growing buchu in the Fynbos biome and a worldwide shortage of buchu oil encouraged commercial cultivation in South Africa. The root-knot nematode (Meloidogyne spp.) is one of the most common plant-parasitic nematodes found on commercial crops grown in the Western Cape. It has also been isolated from the soil and roots of plants in the natural Fynbos vegetation (2). In June 2003, a nursery propagating buchu plants experienced problems with poor growth. Examination of the buchu roots under a stereo microscope showed extensive galling with large numbers of female root-knot nematodes with eggsacs. Nematode extractions of the soil were also done. Only second-stage juveniles of Meloidogyne spp. (311 per 250 ml of soil) were recovered. A polymerase chain reaction (PCR)-based diagnostic method (1) was used for the identification of the root-knot nematode species. Ten intact females were dissected from the roots and individually placed directly in 5 μl drops of 1× PCR reaction buffer (16 mM [NH4]2SO4, 67 mM tris-HCL, pH 8.8, 0.1% vol/vol Tween 20) ontaining 60 μg/ml of proteinase K. The tube was kept at -80°C for a minimum of 10 min. The tube was incubated at 60°C for 15 min and 5 min at 95°C. The PCR amplifications were then prepared directly in the same tube. Amplified DNA fragments were digested with HinfI and DraI. The digested DNA was loaded on a 2% agarose gel, separated by electrophoresis, and detected by ethidium bromide staining. The digested amplified DNA fragments correspond to those of Meloidogyne javanica. Morphological characteristics were used to verify the PCR-based identification of the nematode. To our knowledge, this is the first report of M. javanica causing extensive galling on the roots of Agathosma betulina. Visual damage to the roots indicates the root-knot nematode to be an important threat to the commercial cultivation of buchu.

Shrubland Restoration Following Woody Alien Invasion and Mining: Effects of Topsoil Depth, Seed Source, and Fertilizer Addition

AbstractInvasion by woody alien plants, construction, and mining operations are among the major disturbances degrading vegetation in the Cape Floristic Kingdom, South Africa. The aim of this study was to assess whether native fynbos shrubland vegetation could be restored following dense alien invasion and disturbance by mining. An area supporting dense alien trees was cleared and topsoil was stripped and stockpiled to simulate mining disturbance. A field trial investigated the effects of topsoil depth, seed mix application, and fertilizer on native species recruitment and vegetation development over a three‐year period. Soil‐stored seed banks contributed 60% of the species recruited, indicating that areas invaded for three decades have good restoration potential. The addition of a fynbos seed mix, which included serotinous overstory species, improved both the richness and structural composition of the vegetation. Most species sown in untopsoiled plots established, but survival and growth was low compared to topsoil plots. Poor growth in combination with a lack of soil seed bank species, indicate that restoring a diverse and functional cover of indigenous vegetation on subsoil is not possible in the short‐term. Soil amelioration is required to improve rooting conditions and initiate ecosystem processes. Shallow and deep topsoil treatments yielded high plant density, richness, and projected canopy cover, but canopy cover was higher in deep topsoil plots throughout the trial. Fertilizer addition increased canopy cover in untopsoiled and shallow topsoil plots via an increase in alien annual species. Fertilizer addition ultimately may lead to increased native vegetation cover in untopsoiled areas, but as it increased proteoid mortality on deep topsoil plots, it is not recommended for sites where topsoil is available. A species‐rich and structurally representative fynbos community may be restored on topsoiled areas provided that the native disturbance regime is simulated and seeds of major structural guilds not present in the soil seed bank are included in the seed mix.

Potential of colour-infrared digital camera imagery for inventory and mapping of alien plant invasions in South African shrublands

Australian Acacia plant species invade the fynbos biome of southern Africa and threaten the exceptionally high plant diversity in the Cape Floristic Region. We examine the utility of very-high spatial resolution (0.5 m) colour infrared (CIR) digital image data for discriminating Acacia species from native fynbos vegetation, other alien vegetation and bare ground. Image data were acquired at a very low cost with a single-chip, digital CIR camera mounted on a light aircraft. Shrub and tree features were uniquely identified using visual or computer-assisted interpretation. However, increases in dynamic range and accuracy of interpolation schemes for the single chip sensor will be required if semi-automatic and accurate mapping of invasive plants is to be achieved.

Growth and gas exchange responses of Leucadendron xanthoconus (Proteaceae) seedlings to different nutrient and water regimes

Potted seedlings of Leucadendron xanthoconus (Proteaceae) were grown in native mountain fynbos soil under different nutrient and water regimes. Nutrient treatments comprised addition of nitrogen, phosphorus and a Long Ashton macronutrient solution (LA). Water was applied at three levels, ranging from near drought to maintained saturation. Rates of gas exchange were measured on a subset of the experimental plants under a range of irradiance levels prior to harvesting of all plants at an age of six months. Measurement of biomass and its distribution showed that increasing water had a significantly positive effect on productivity, and that drought reduced root:shoot ratio and leaf specific weight. Total productivity was highest with LA-addition and lowest in the control, whereas phosphorus and nitrogen additions had an intermediate effect. None of the treatments included in the gas exchange work was shown to affect significantly photosynthetic capacity or water use efficiency. Droughted individuals showed an increased ability to reduce carbon dioxide concentration in the substomatal cavity, and a lower stomatal conductance overall. Stomatal conductance was found to be independent of irradiance in all treatments. The relationships investigated are placed in the context of fynbos utilization and the management of natural fynbos landscapes with regard to the reclamation and maintenance of component natural ecosystems.

The Effects of Fire in FelledHakea sericeaand Natural Fynbos and Implications for Weed Control in Mountain Catchments

SYNOPSIS Dense stands of the alien shrub Hakea sericea were felled and later burned accidentally under severe weather conditions. The recovery of the natural vegetation was monitored for 19 months on 12 permanent plots. Cover increased slowly to 13% and 42 species were recorded. Data were collected at a similar but uninvaded site burnt in the same fire. Mean cover on 12 plots at this site 19 months after the fire was 34% and the total number of species was 95. Sprouters were adversely affected at the invaded site, where species regenerating from seed stored in the soil predominated. Sprouters were dominant at the uninvaded site. Fire behaviour was simulated using Rothermel's fire model. Simulated fire intensity at the invaded site was particularly high (79 700 kW/m). Managers should attempt to burn felled hakea under conditions that will lead to less intense fires to reduce the adverse effects caused by high fuel loads. Fire behaviour prediction models should prove useful in this regard. Alternative control strategies for dense stands should also be investigated.