Useful Species Richness,Proportion of Exotic Species,and Market Orientation on Amazonian Dark Earths and Oxisols<Superscript>1</Superscript>

Useful Species Richness, Proportion of Exotic Species, and Market Orientation on Amazonian Dark Earths and Oxisols Anthropogenic soils of Amazonia, known as Amazonian Dark Earths (ADE), are environments with elevated soil fertility that can produce crops that otherwise yield poorly on the leached and highly acidic Oxisols that dominate much of the basin. While ADE sites near urban centers often attract commercial horticultural production of nutrient–demanding exotics, these soils are also considered possibly unique reservoirs of endemic agrobiodiversity because of their relationship to pre–Columbian indigenous occupation. Through botanical surveys and interviews with smallholder farmers, this study compared useful species richness, proportion of exotic species, and market orientation of farms situated on ADE and non–anthropogenic Oxisols in the municipality of Borba in Central Brazilian Amazonia. Species richness was similar on Amazonian Dark Earth and Oxisol farms (19.6 spp vs. 18.3 spp); however, ADE farms showed significantly higher proportions of exotic species (39% vs. 26%; p = 0.025). Furthermore, ADE farms in Borba demonstrated significantly higher market orientation (61.0% vs. 47.3%; p = 0.028), likely a result of the advantage of Amazonian Dark Earths for production of crops that are nutrient–demanding or pH–sensitive crops that have higher values in the nearby regional market of Manaus.     

Homegardens on Amazonian Dark Earths,Non-anthropogenic Upland,and Floodplain Soils along the Brazilian Middle Madeira River Exhibit Diverging Agrobiodiversity<Superscript>1</Superscript>

Homegardens on Amazonian Dark Earths, Non-anthropogenic Upland, and Floodplain Soils along the Brazilian Middle Madeira River Exhibit Diverging Agrobiodiversity. We test the hypothesis that the agrobiodiversity associated with homegardens on three different soils—upland Amazonian Dark Earths (ADE) and Oxisols (OX), and Fluvent Entisols (FL)—commonly found along the middle Madeira River in the municipality of Manicoré, Amazonas State, Brazil, is different due to the contrasting biotic, abiotic, and cultural settings specific to each of these soils. Using data from interviews with 63 farmers about food and utility species, we compare structural and floristic characteristics of homegarden agrobiodiversity. The density of individuals is higher on ADE than on the other soils (mean ± standard deviation: 715 ± 363 on ADE, 474 ± 283 on OX, 642 ± 399 on FL). ADE and OX have higher species richness (28.2 ± 5.6 on ADE, 25 ± 3.7on OX, 23.6 ± 5 on FL), while ADE and FL have a greater degree of domestication (2 ± 0.6 on ADE, 1.3 ± 0.5 on OX, 2.3 ± 0.6 on FL). ADE and OX have greater proportions of richness, density, and coverage composed of South American species, while FL has greater proportions of richness and density composed of Old World species. ADE has higher proportions of density and coverage of Mesoamerican species. Floristic composition is also different between soils: ADE occupies an intermediate position, composed of species associated with each of the other soil types and species that are most common on ADE. These differences in agrobiodiversity emerge through the interaction of human agency, plant responses, and the unique properties of soils in relation to socioeconomic and historical trajectories over time.     

Crop Diversity on Anthropogenic Dark Earths in Central Amazonia

A recent archaeological survey demonstrates that one of the most durable of all forms of pre-Columbian landscape transformation, Amazonian Dark Earths (ADE; soils formed by pre-Columbian settlement), are widespread along the course of the Madeira River, Central Amazonia, Brazil. We hypothesize that processes of crop cultivation and management by human populations today in landscapes that were intensively transformed during the pre-Columbian period will diverge from those in environments where human agency has not left such a heavy footprint. In order to test this hypothesis, we compare bitter manioc fields, homegardens and secondary forests on ADE with those on non-anthropogenic soils along the lower and middle Madeira River. We demonstrate that crop species and landrace populations diverge on anthropogenic and non-anthropogenic soils as a result of the interaction between human selection and management, soil physical and chemical properties, and plant responses over time. Hence, crop species selection and abundance and therefore agrobiodiversity is contingent on anthropogenic soils in Central Amazonia.     

Karen Homegardens: Characteristics,Functions, and Species Diversity

Diversity is one of the most important traits of homegardens and contributes to maintaining their functions. Here, we investigated the diversity, characteristics, and functions of 75 Karen homegardens from four villages in Chiang Mai and Tak provinces in northern Thailand. In each homegarden, all used plant species were registered and classified according to their main use. The diversity and richness in each homegarden was estimated and the stratification of plants in horizontal zones was investigated. A total 268 plant species were recorded, ranging from 100 to 146 species in each of the four villages. These plants were mostly kept in the homegarden yard or along their boundaries. The most common species were mango (Mangifera indica L.), jackfruit (Artocarpus heterophyllus Lam.), guava (Psidium guajava L.), and taro Colocasia esculenta (L.) Schott. Besides these species, most plants differed from one village to another. Distance between the homegardens was important; homegardens in the same village were more similar than those in different villages. However, beyond the individual level, the distances alone could not be used to determine similarity. Despite the variation of species found in homegardens, the function and horizontal stratification of the Karen homegardens shared many traits. They satisfied both physical and aesthetic needs to the Karen people as witnessed by the high proportion of food and ornamental species. The reverse effects of urbanization (we used the distance from the nearest urban area as a proxy) on the diversity of ornamental species was also observed. In general, Karen homegardens had high richness and diversity which directly benefited the conservation of plant species. This diversity promotes food security at the household and community levels.     

Amazonian Dark Earth Shapes the Understory Plant Community in a Bolivian Forest

Amazonian Dark Earths (ADE) are the result of human modification of the Amazonian landscape since pre‐Columbian times. ADE are characterized by increased soil fertility compared to natural soils. In the Amazonian forest, soil fertility influences understory herb and fern species composition. However, little research has been done to evaluate the effect of ADE on the composition of the understory community. We evaluated the effects of ADE and soil in 36 plots (150 m × 4 m) established in a Bolivian moist forest (La Chonta). For each plot, we determined soil nutrients, and the composition, richness, and abundance of terrestrial fern, angiosperm herb, and understory palm species. We found that the presence of ADE created a gradient in soil nutrients and pH that affected the understory species composition especially of ferns and palms. Additionally, the higher nutrient concentration and more neutral soil pH on ADE soils caused a decrease of ferns species richness. We therefore conclude that the current composition of the understory community in this particular Bolivian forest is a reflection of past human modifications of the soil.     

Implications of shifts in coffee production on tree species richness, composition and structure on small farms around Mount Kenya

Small coffee farms around Mount Kenya in Kenya contain many planted and remnant tree species but little is known in the region about the relationship between trees on farms and the methods and dynamics of coffee production. Shifts in production may alter tree diversity and potentially impact on future biodiversity conservation efforts by affecting niches available for indigenous trees on farms. Here, knowledge was gathered on how changes in coffee production on 180 small farms around Mount Kenya may affect tree diversity, categorizing farms according to coffee yield levels over a period of five years as increasing, decreasing or stable production. Tree species richness, abundance and composition were analyzed using species accumulation curves, Rènyi diversity profiles, rank abundance and ecological distance ordinations, and the effects of coffee production examined using quasi-Poisson generalized linear regressions. Species richness were positively correlated with tree basal area but negatively related to coffee, banana and maize yields value. A difference in average tree species richness, abundance and basal area on increasing farms was observed compared to the decreasing and stable farms, even though formal tests on richness and densities differences were inconclusive. These dynamics do not significantly influence vegetation structure but seem to have a bearing on species composition on farms of different coffee production. The overall low abundance (23 % of trees) but high richness (78 % of species) of indigenous trees on coffee farms could change markedly if the dynamics observed in the current study persist, indicating the need for the development of intensified multi-species cropping systems.     

Can Homegardens Conserve Biodiversity in Bangladesh?

In managed landscapes, tree-dominated habitats often show promise for biodiversity conservation. In Bangladesh where natural forest cover is less than 10 percent, homegardens, which are maintained by at least 20 millions households, represent one possible strategy for biodiversity conservation. This study investigated the floristic and structural diversity of 402 homegardens from six regions across southwestern Bangladesh. All plants were censused, totaling 419 species (59% native), including six IUCN Red Listed. The median homegarden (800 m²) contained a mean of 34 species. Each region contained a mean of 293 species in a mean of 67 homegardens. A total of 49,478 individuals (107 per homegarden and 1003 per hectare) of trees and shrubs were counted from 45.2 ha total sampled area. Thus, significant botanical richness was exhibited in the homegardens across southwestern Bangladesh. However, most species were rare: 82 percent of all species including 189 native were found in 50 or fewer homegardens, and 63 species (36 native) were found in only one or two homegardens. Sixty percent of all tree and shrub species had 50 or fewer individuals each. Thus, whereas richness across the landscape was high, serious effort must be made to increase the populations of most species. We propose three main conservation activities: (1) awareness building; (2) protection of existing individuals of rare species; and (3) propagation. Overlaying all of these activities is the inclusion of local communities in the process, who were the ones to retain these species in homegardens in the first place, and the stakeholders who will determine whether homegardens indeed act as long-term repositories to biodiversity conservation.     

Remnant habitats for grassland species in an abandoned Swedish agricultural landscape

Questions: Which factors influence the persistence of vascular grassland plants in long‐abandoned (at least 50 yr) arable fields and meadows? What might be the implications of current levels of species richness on abandoned arable fields and meadows for future restoration? Location: Forested highlands of Kilsbergen, south central Sweden. Methods: The abundance of all vascular plant species was investigated in three habitat types: former arable fields, hay meadows and outlands (pastures) at 27 farms, abandoned for either approximately 50 yr or 90 yr. Time since abandonment, tree cover, soil depth, degree of soil podsol development, size of the infield area and two measures of connectivity were used as predictors for species richness and species composition. Results: Former outland had denser tree cover, fewer species and fewer grassland species than former arable fields and hay meadows, irrespective of time since abandonment. Former hay meadows and arable fields with a longer time since abandonment were less rich in species, more wooded and had greater podsolization than meadows and fields abandoned at a later stage. Species richness was higher in hay meadows and arable fields at farms with larger infield area and deeper soils compared with farms with smaller infield area and shallower soils. The greatest richness of species and most open habitat were former arable fields at larger farms abandoned 50 yr before the study. Former arable fields had the highest number of grassland species. Conclusion: After 50 yr of abandonment, former arable fields were the most important remnant habitats for grassland species and may be a more promising target for restoration than formerly managed grasslands.     

Agroforestry Systems as Habitat for Avian Species: Assessing Its Role in Conservation

In the current scenario of rapid conversion of tropical forests into human-dominated activities landscape, the present study was undertaken to understand the role of existing agroforestry systems in conservation of avian species. Three types of agroforestry systems namely tea gardens, homegardens and agrisilviculture were selected in the Brahmaputra North Bank Landscape of Assam, northeast India for the study. A total of 468 point counts revealed 164 bird species belonging to 51 families and 18 orders across all the three different types of agroforestry systems. Tea gardens showed significantly higher bird species richness followed by homegardens and agrisilviculture systems. As per IUCN, four species were categorized as Near Threatened and one species was categorized as Vulnerable. Out of 164 species recorded, 68.3% species were residents, 30.5% species were winter visitors and remaining were summer visitors (1.2%). Majority of the species (45.7%) were common to all the three types of selected agroforestry systems. The feeding guilds revealed that most of the species were insectivorous (50.0%) in habit. A total of 167 tree species belonging to 54 families and 24 orders was recorded across all the three different types of agroforestry systems. The highest tree species richness was recorded in the homegardens (160), followed by agrisilviculture systems (19) and least in tea gardens (11). No statistically significant correlation was found among bird species richness and patch size, tree species richness and number of bird species individuals. The selected agroforestry systems have provided shelter, nesting space, feeding and foraging grounds for birds during the winter season. This data can be useful for the policy makers, tea garden managers, homegarden owners for framing conservation policies of avian species in an era of natural wildlife habitat loss and degradation.     

Cultural homegarden management practices mediate arthropod communities in Indonesia

Tropical forest loss and transformation to agroecosystems have serious impacts on biodiversity, associated ecosystem services and the livelihood of local people. The high crop plant biodiversity and low intensity management in many homegardens could play an important role in the preservation of biodiversity in modified landscapes, as well as sustain food security of low income households. In this study, we focused on the role of the owner’s cultural background as migrants (from the island of Java) or non-migrants (local residents) for homegarden characteristics, such as size, management diversification, and crop species richness, and their effect on arthropod communities in Jambi province, Indonesia. Vane traps, pitfall traps and sweep netting were used to survey the arthropod communities, in particular bees and wasps, in 24 homegardens. Our results show that the native Jambi locals used a smaller number of management practices and had smaller homegardens than the Javanese transmigrants, whereas crop species richness did not differ. Management diversification and crop species richness were positively related to arthropod abundance as well as species richness of bees and wasps, presumably due to the enhanced homegarden heterogeneity. Our findings suggest that the cultural practices of migrant versus non-migrant land-use managers, which is usually neglected in agroecology, can be a major determinant of management practices shaping community structure and services of beneficial arthropods.     

Species richness in agroecosystems: the effect of landscape, habitat and farm management

It has been suggested that biodiversity in agroecosystems depends on both landscape heterogeneity and farm management, but at the same time, studies of biodiversity in relation to both landscape variables and farm management are rare. We investigated the species richness of plants, butterflies, carabids, rove beetles and the diversity of spiders in cereal fields, leys (grass and clover crop) and semi-natural pastures at 16 farms in Central East Sweden. The farms were divided into eight pairs of one conventional and one organic farm to enable us to separate the effects of landscape and farm management on biodiversity. The pairing was based on land use, location, and landscape features. Species richness of different taxonomic groups was generally not correlated. There were no differences in species richness between the farming systems, except for carabids that had higher numbers of species on conventional farms. The species richness generally increased with landscape heterogeneity on a farm scale. Habitat type had a major effect on the species richness for most groups, with most species found in pastures and leys. The correlations between species richness and landscape variables on a farm scale, and not on a scale of multiple farms, identify farmers as the important decision-maker in conservation issues for these taxonomic groups. We discuss the role of species richness of pests' natural enemies for biological control and conservation strategies of the more common species in the agricultural landscape.     

Assessing the Impacts of Agrobiodiversity Maintenance on Food Security Among Farming Households in Sri Lanka’s Dry Zone

Farmers’ maintenance of agrobiodiversity is fundamental to global food security, particularly in a world increasingly affected by climate change. Biodiversity helps to buffer agroecosystems from stresses like climatic variability, and the crop genetic diversity conserved with biodiverse agroecosystems is critical for plant breeding both locally and globally. Yet, despite these benefits, few studies have directly assessed the implications of household–level agrobiodiversity maintenance on household food security. Drawing on survey data collected in Sri Lanka’s Hambantota District, we evaluated the plant diversity maintained by small–scale farming households in both homegardens and crop fields and determined the relationships between this diversity and their households’ food security. We also considered how a suite of additional demographic, household, community, and farm characteristics relate to both the plant diversity maintained by a household and their food security. Similar to previous studies, the age of the agricultural decision-maker and the age and size of households’ homegardens positively correlated with the overall species richness of farming systems. Older homegardens were also identified to be more evenly distributed in their species abundance, and market–oriented households had significantly higher species richness but lower Shannon Indices. Most notably, household socioeconomic status and material wealth were important to both agrobiodiversity maintenance and household food security, while no significant relationships between species richness and food security measures were detected. These findings suggest that effort aiming to increase the food security of small–scale farming households in Sri Lanka, and elsewhere, should target those farming households with a paucity of socioeconomic assets, as these households lack both agroecological and economic resources to overcome shocks, such as those associated with climate change.     

Species richness in vascular vegetation of the West Head,New South Wales

We present data on vascular plant species richness, at the 0.1 ha scale and below, of sclerophyll vegetation on infertile sandstone, and some neighbouring types, in a non-mediterranean climate area of temperate, east coast Australia The vegetation of sandstone is richer in species than is that of a permanently wet swamp (18/0.1 ha) or of more fertile soils (36, s.d.- 2). On sandstone, woodlands on moderate benched slopes (77, s.d. = 9) are richer in species than are the scrubs found on skeletal (56, s.d.= 7) or impeded drainage (48, s.d.= 8) soils, and this difference appears in the species-area curve from 100 m² up. Species richness of the sandstone vegetation, like its growth-form mix, is very similar to species richness of South African fynbos and southwestern Australian heath. which supports the idea that the community properties of this sort of vegetation are not determined by climate but are determined by soils. The strong contrast in species richness, noted by Naveh & Whittaker (1979), between the mediterranean-climate vegetation of South Africa and southwestern Australia on the one hand, and California and Israel on the other, need not be attributed to different evolutionary histories of the floras. The present environment, in the form of the soil factor, could well be the main determinant.     

Plant management and biodiversity conservation in Náhuatl homegardens of the Tehuacán Valley,Mexico

Background

The Tehuacán Valley is one of the areas of Mesoamerica with the oldest history of plant management. Homegardens are among the most ancient management systems that currently provide economic benefits to people and are reservoirs of native biodiversity. Previous studies estimated that 30% of the plant richness of homegardens of the region are native plant species from wild populations. We studied in Náhuatl communities the proportion of native plant species maintained in homegardens, hypothesizing to find a proportion similar to that estimated at regional level, mainly plant resources maintained for edible, medicinal and ornamental purposes.

Methods

We analysed the composition of plant species of homegardens and their similarity with surrounding Cloud Forest (CF), Tropical Rainforest (TRF), Tropical Dry forest (TDF), and Thorn-Scrub Forest (TSF). We determined density, frequency and biomass of plant species composing homegardens and forests through vegetation sampling of a total of 30 homegardens and nine plots of forests, and documented ethnobotanical information on use, management, and economic benefits from plants maintained in homegardens.

Results

A total of 281 plant species was recorded with 12 use categories, 115 ornamental, 92 edible, and 50 medicinal plant species. We recorded 49.8 ± 23.2 (average ± S.D.) woody plant species (shrubs and trees) per homegarden. In total, 34% species are native to the Tehuacán Valley and nearly 16% are components of the surrounding forests. A total of 176 species were cultivated through seeds, vegetative propagules or transplanted entire individual plants, 71 tolerated, and 23 enhanced. The highest species richness and diversity were recorded in homegardens from the CF zone (199 species), followed by those from the TRF (157) and those from the TDF (141) zones.

Conclusion

Homegardens provide a high diversity of resources for subsistence of local households and significantly contribute to conservation of native biodiversity. The highest diversity was recorded in homegardens where the neighbouring forests had the least diversity, suggesting that management of homegardens aims at compensating scarcity of naturally available plant resources. Cultivated species were markedly more abundant than plants under other management forms. Diversity harboured and management techniques make homegardens keystones in strategies for regional biodiversity conservation.

     

Countryside Stewardship Scheme and Butterflies: A Study of Plant and Butterfly Species Richness

Butterfly and plant species richness were recorded from 1997 to 2000 on 2 and 6 m grass margins created at three farms in Essex which had entered the Countryside Stewardship Scheme (CSS) in October 1996. On both the 2 and 6 m margins there was a significant relationship between the length of hedgerow and the number of plant species observed on the margins, but the seed mixtures used may not have been ideal and natural regeneration should not have been used on the clay soils of Essex. Butterfly species richness was significantly greater on the 2 m margins than on the control sections, and was greater when a higher number of grass species were included in the original seed mixture. Plant species richness was greater on the 6 m margins when established by natural regeneration. CSS grass margins could be improved as butterfly habitats if they are linked to existing habitats such as hedgerows, are sown with a better range of native grasses and herbs and are managed in a way more conducive to wildlife. These changes to the policy of establishment of CSS margins could help combat habitat loss and fragmentation within the countryside.     

Effect of size and altitude on soil organic carbon stock in homegarden agroforestry system in Central Himalaya,India

Homegarden agroforestry system has potential to sequester carbon while simultaneously producing agriculture yield and tree products. This study analyzed relationship between homegarden size and soil organic carbon stock (SCS) along an altitudinal gradient in Central Himalaya, India. Homegardens were selected at four altitudes (very low, low, mid and high) and categorized into three size classes viz. small, medium and large. Soil samples from surface (0–15 cm) and sub surface soils (15–30 cm) were collected seasonally and analyzed. Results indicated that SCS ranged between 22.56 and 81.51 t C ha⁻¹ and increased with increasing altitude for small homegardens. For medium and large homegardens, it increased up to mid altitude and then decreased in high altitude homegardens. At each altitude, maximum SCS (38.56–66.16 t C ha⁻¹) was recorded for medium sized homegardens except at high altitude where it was maximum (66.01 t C ha⁻¹) for small homegardens. Seasonal variation in SCS showed inconsistent pattern along the altitudinal gradient. The differences in SCS due to size and altitude recorded in the present study are possibly caused by distinct quality of plant material and management practices.     

Species composition,similarity, and structure of mayan homegardens in tixpeual and tixcacaltuyub,yucatan, Mexico

We studied species composition, similarity, and structure of homegardens in two Yucatecan Maya communities, Tixpeual and Tixcacaltuyub, Yucatan, Mexico. The number of gardens sampled per village was 20 and 22; total area sampled was very similar, 45,265 m² and 40,150 m²; the number of trees and shrubs present was 5651 and 5603; and number of species was 135 and 133, respectively. Diversity was low for both sites (H′= 1.6), as were the correlation coefficients (r) for the species-area and individuals-area correlations. The relatively low values obtained for the structural parameters reflect the random pattern of plant incorporation to the gardens, the variability in the proportion of constantly used and not constantly used garden area, and a certain uniformity in the number of species used and number of individuals present, and the relationship between these parameters and garden size. All these reflect the uniqueness of each homegarden, which depends upon the cultural background of the owner. We noticed a trend towards a change in homegarden structure and function in response to the modernization process. Homegardens in villages in the outskirts of cities tend to have more ornamental species and commercial fruit plants than homegardens in isolated villages.     

Parasitoid diversity reduces the variability in pest control services across time on farms

Recent declines in biodiversity have increased interest in the link between biodiversity and the provision and sustainability of ecosystem services across space and time. We mapped the complex network of interactions between herbivores and parasitoids to examine the relationship between parasitoid species richness, functional group diversity and the provision of natural pest control services. Quantitative food webs were constructed for 10 organic and 10 conventional farms. Parasitoid species richness varied from 26 to 58 species and we found a significant positive relationship between parasitoid species richness and temporal stability in parasitism rates. Higher species richness was associated with lower variation in parasitism rate. A functional group analysis showed significantly greater parasitoid species complementarity on organic farms, with on average more species in each functional group. We simulated parasitoid removal to predict whether organic farms experienced greater robustness of parasitism in the face of local extinctions. This analysis showed no consistent differences between the organic and conventional farm pairs in terms of loss of pest control service. Finally, it was found that the different habitats that make up each farm do not contribute equally to parasitoid species diversity, and that hedgerows produced more parasitoid species, significantly more so on organic farms.     

Ecology of algal communities of different soil types from Cierva Point, Antarctic Peninsula

During summer 2005/2006, we characterized three sampling sites on mineral soils and four on ornithogenic soils from Cierva Point, Antarctic Peninsula, in terms of topographic and abiotic features (altitude, slope, magnetic direction, temperature, texture, pH, conductivity, organic matter, moisture and nutrient concentrations), and compared their microalgal communities through taxonomic composition, species richness, diversity, chlorophyll a content and their variation in time. Average values of pH, moisture, organic matter and nutrient concentrations were always significantly lower in mineral than in ornithogenic soils. Low N/P mass ratio showed potential N-limitation of biomass capacity in the former. On the other hand, the results suggested that physical stability is not as a key stress factor for mineral soil microalgae. Chlorophyll a concentration was not only higher in ornithogenic soils, but it also showed a wider range of values. As this parameter was positively correlated with temperature, pH, nutrients, organic matter and moisture, we cannot come to conclusions regarding the influence of each factor on algal growth. Communities of mineral soils were significantly more diverse than those of enriched ornithogenic soils due to higher species richness as well as higher equitability. Also, their structure was steadier over time, as shown by a cluster analysis based on relative frequency of algal taxa. Although Cyanobacteria and Bacillariophyceae dominated almost all samples, Chlorophyceae represented 34% of the 140 taxa recorded, and most of them observed only in cultures. The detection under controlled conditions of a high latent species richness in harsh mineral soil sites shows that the composition and equitability of these microalgal communities would be more prone to modification due to the manifold local consequences of climatic change than those of ornithogenic soils.     

Plant species richness and diversity of the serpentine areas on the Witwatersrand

Soil chemistry can play an important role in determining plant diversity. Serpentine soils are usually toxic to many plant taxa, which limits plant diversity compared to that on adjacent non-serpentine soils. The usually high concentrations of toxic metals in serpentine soils are considered to be the edaphic factors that cause low diversity and high endemism. This paper aimed primarily to determine whether there is a relationship between serpentine soil chemistry and species richness on the Witwatersrand and to compare species richness of the serpentine areas with that of adjacent non-serpentine areas as well as with the species richness of the serpentine areas in the Barberton Greenstone Belt. The alpha- and beta-diversity of the Witwatersrand serpentine and non-serpentine areas was also investigated. A secondary aim of this study was to determine which of the non-serpentine taxa were more common on the serpentine than off the serpentine, which taxa were more common off the serpentine than on the serpentine and which taxa were equally common on and off serpentine soils. There was no significant difference in alpha-diversity between the serpentine and the adjacent non-serpentine areas, but beta-diversity is higher between serpentine plots than between non-serpentine plots. Although soil factors do affect species richness and diversity of plants on the Witwatersrand to a limited extent, the concentrations of soil chemicals in serpentine soils are not sufficiently different from those in non-serpentine soils to significantly influence the species richness and diversity of the serpentine soils. The high, but similar, diversity on serpentine and non-serpentine soils on the Witwatersrand indicates that soil factors do not play a significant role in determining diversity on potentially toxic soils in the area.