BIODIVERSITY: Swaziland Tree Atlas
(Contributed by Linda Dobson-Lofler, 2005)
The first publication to include the flowering plants of Swaziland was completed by Dr J Burtt Davy in 1912 (Burtt Davy & Pott-Leendertz, 1912). An intensive botanical survey of Swaziland followed, over an eleven-year period from 1955 to 1966, carried out by Prof. R H Compton with the help of Miss M C Karsten and Mr Ben Dlamini. In 1976 Compton published the Flora of Swaziland (Compton, 1976), which has remained the standard work for the flora of the country. In 1983 Mrs E S Kemp published a flora checklist (Kemp, 1983) that has recently been revised by Braun et al., (2004). The latter list documents 3678 taxa for Swaziland, 3478 of which are indigenous.
The Swaziland Tree Atlas project was initiated in early 1999 and has been on-going for almost 6 years with the last official outing carried out in August 2004. Field visits, data collection and processing was conducted voluntarily and financed independently by Linda and Paul Loffler. A good representation of the trees was atlassed covering the majority of the grid squares and vegetation types around the country.
The main objective of the Swaziland Tree Atlas was to produce a compilation of distribution maps for individual tree species including a few selected shrubs and climbers, detailing their distribution, abundance, habitat, relationship with land tenure, conservation status and use relative to the country.
The Atlas was published in December 2005 by the Southern African Botanical Network (SABONET) based at the South African National Biodiversity Institute in Pretoria. Prior to the book, there was no tree atlas publication available for Swaziland and distribution data for the country's flora could only be found in various local and regional databases and scattered publications. Much was unpublished and stored personally or in oral tradition.
Centres of Plant Endemism
Floristically Swaziland is important because it falls within the boundaries of two regional phytochoria which are recognized by the World Wide Fund for Nature (WWF) and World Conservation Union (IUCN) as Centres of Plant Diversity and Endemism of global significance (Van Wyk & Smith, 2001). These include: the Maputaland-Pondoland Region and the Drakensberg Afromontane Regional System both of which support high concentrations of endemic taxa.
On a more local scale, Swaziland contains a very important subcentre of the Maputaland Centre of Endemism, consisting mainly of the Lebombo Range. The Maputaland Centre forms part of the Maputaland-Pondoland Region and, by implication, it is also recognized as a site of global conservation significance as far as floristic diversity is concerned. The other important area in Swaziland is the north-western region bordering the Barberton Mountains. This region is part of the Barberton Centre of Endemism, a subcentre of the Drakensberg Afromontane Regional System. Hence a portion of Swaziland is included in floristic regions already recognized as being of global botanical significance.
The main objective of the Atlas was to produce distribution maps for individual tree species including a selection of shrubs, climbers and suffrutices recorded within Swaziland. Shrubs that were above 1.5m in height, robust woody climbers, lianes, scrambling shrubs and some of the more vigorous climbers were included in the Atlas.
Considering the small size of the country, sampling was done at a fine scale of eighth degree squares (approximately 11km x11km grid squares). A total of 109 (out of 115) grid squares were sampled during the project . This scale of mapping has been beneficial, both in that it produces fine scale data and it concurs well with the already published Swaziland Bird Atlas (Parker, 1994) and Mammals of Swaziland (Monadjem, 1998). The database is currently housed privately by the author and electronic copies of it have since been distributed to the National Biodiversity Database Unit (NBDU) currently housed at the University of Swaziland and the Southern African Botanical Network (SABONET) office at the South African National Biodiversity Institute in Pretoria.
Sample plots for the Atlas were conducted using broad 2 km transects. A hand-held Global Positioning System (GPS) was used to obtain coordinates for each plot and all relevant plant species roughly within a 2 km radius of each point were noted. A new sample plot was initiated if a different vegetation type was encountered within the transect. A total of 585 sites were sampled throughout Swaziland.
A total of 632 trees were recorded during the Swaziland Tree Atlas project, with 35 exotic and 597 indigenous species, representing just over 17 percent of Swaziland's indigenous flora. The highest numbers of species are found in the Lebombo mountains in the east, near Lufafa peak in the north-west and Sinceni mountain in central Swaziland. Lower species numbers are found in the lowveld. A correlation between species richness and the Maputaland and Barberton Centres of Endemism can be recognised with relatively high species numbers recorded in both these regions.
Another correlation is that of coastal species generally restricted to the Lebombo mountains in the east appearing on Sinceni mountain in central Swaziland. For example Strychnos gerrardii and Deinbollia oblongifolia. Both of these trees are only found in coastal areas in southern Africa (Coates Palgrave, 2002) yet they appear inland in central Swaziland. This indicates a similarity between coastal, dune, Lebombo forest and inland forest around Sinceni mountain. Other interesting trees that are also generally restricted to coastal habitat in southern Africa (Coates Palgrave, 2002) and which are found in Swaziland include Pavetta gerstneri, Ficus burtt-davyii and Dovyalis longispina.
On a regional scale Swaziland supports a relatively diverse flora. In comparison with Mpumalanga and Kruger National Park which together have over 950 species of trees and shrubs documented (Schmidt et al., 2002), Swaziland which is barely the size of the Kruger Park boasts more than 630 species.
A total of two endemics (Aloe keithii and Euphorbia keithii) were recorded for Swaziland of which both are restricted to the Lebombo mountain range.
Red Data Species
A total of 64 threatened trees were identified of which 50 are listed in the Swaziland Plant Red Data List and 13 are proposed "candidate" species. Of these species 8 are listed as Critically Endangered, 8 as Endangered, 3 Vulnerable, 1 Near-Threatened, 20 Data Deficient and 10 Least Concern. Of the 64 threatened trees, 23 are not recorded in protected areas and will need monitoring in the future to ensure that they do not decline drastically in numbers and that they are recuperating sufficiently.
During this project, 33 new records (species which have not previously been documented for Swaziland) were discovered for the country, the majority of which are confined to the Maputaland and Barberton Centres of Endemism and the quartzite outcrops in the south-west. Of these new findings, two possible relic species were identified, Trilepisium madagascariense (Burrows & Burrows, 2002) and Excoecaria madagascariensis (Burrows et al., 2003) both of which are located within centres of plant endemism. T. madagascariense was found along the Ugutugulo River, near Lufafa in north-western Swaziland in an area which lies within the Barberton Centre of Endemism. This finding represents a more southerly distribution for this species, some 340 km south the Soutpansberg which was thought to be its southernmost record. E. madagascariensis was found in the Mtibhlati gorge on the Lebombo mountains which lie within the Maputaland Centre of Endemism. The nearest locality to this finding is Chirinda Forest in Zimbabwe, some 700km away, representing a considerable disjunction for the species. Both of these interesting records are presumed to represent relic populations that probably existed when their preferred forest type occurred over a broader region.
Distribution maps from this project can be seen for each species in Swaziland's Flora Database