Swaziland's First National Communication to the United Nations Framework Convention on Climate Change

United Nations Framework Convention on Climate Change National Report on Climate Change National Report on Climate Change

Chapter 4 Vulnerability and Adaptation

4.2 FORESTRY

4.2.1 Background

This study examines the extent to which managed forests and other ecosystems in Swaziland are vulnerability to climate change and thereafter, feasible adaptation options available to the country. Table 4.1 presents a panoramic listing of possible impacts due to climate change on forests. Of particular concern are the variation in temperature conditions and changes in the distribution and amount of rainfall. Other factors that are likely to influence the composition, structure and distribution of ecosystems include increasing carbon dioxide levels, ultra-violet radiation, and outbreaks of pests and diseases.

Apart from the climatic processes occurring within the natural environment, human activities also have an influence on the spatial distribution of patterns of ecosystems. Man's cultural practices such as deforestation, grazing and fire serve as short-term effects on the distribution and composition of ecosystems.

Managed forests and woodlands are the main sources of timber for construction, energy and pulp hence contribute to the economy of many countries in the world (Feenstra et al., 1998). Changes in the composition, structure and productivity of ecosystems will not only affect the sustainability of organisms that are associated with the ecosystems but may also lead to effects on the national economy which they support. This is particularly true in the case of managed forests.

Medicinal plants also occur within natural ecosystems. Therefore the impacts of climate change on ecosystems will not only affect the socio-economic status of the nation but it will also have serious effects on health. Swaziland is highly diversified in terms of relief, climate, land-use systems and associated ecosystems.

4.2.2 Land Tenure and Land-use

Swaziland has a dual system of land tenure instituted when the country was still under British protection. The system comprises of Swazi Nation Land (SNL) and Title Deed Land (TDL). Overall, SNL covers 74.2% (1 287 300ha), while the TDL makes up 25.6% (444 100 ha) of the total area (Remmelzwaal and Vilakati, 1994).

Swazi Nation Land comprises of communal (948 000ha) or non-communal (14 200ha) land under the control of chiefs. Part of the land under SNL is controlled by Tibiyo (49 500ha), the Ministry of Agriculture and Co-operatives (117 300ha), the Swaziland National Trust Commission (46 000ha) or leased (112 300ha).

TDL constitutes land owned by companies (estates and commercial forests) and individuals in rural areas (43 1600ha). Urban areas make up a small portion (125 00ha) of TDL.

Generally, access to land is limited on SNL compared to TDL. Most settlements on SNL are less than 2 hectares in size, and only 2% of the total holdings (63 583) are larger than 5 hectares (Central Statistical Office report, 1993). Land-use practices and the exploitation of natural resources in the country vary according to the land tenure system in each area. According to Remmelzwaal and Dlamini (1994), the main land uses in the country are small-scale subsistence crop agriculture, large-scale crop agriculture, extensive communal grazing, ranching, plantation forestry and others.

Table 4.2: Coverage of the main land uses in each physiographic region of Swaziland

The other land uses include hunting, parks and reserves, water reservoirs and areas that are used for settlements, industry and recreation. Table 4.2 shows the areal coverage of the main land uses in the country per physiographic region. Small-scale crop agriculture (SA), extensive communal grazing (CH) and some extraction and collection (E) occur on SNL. Land-uses that are associated with TDL include large-scale crop agriculture (LA), ranching (RH), plantation forestry (F). Parks and reserves (P) are either under SNTC or TDL. Although water reservoirs (W) mostly serve TDL, they are found on SNL.

4.2.3 Ecosystems

Swaziland has quite a high diversity of ecosystems for a small country. Generally, each physiographic region is associated with specific ecosystems (veld types) with a number of units. I'ons and Kidner (1967) subdivided the veld types of Swaziland into eleven (11) units on the basis of climate and composition of the communities.

Sweet and Khumalo (1994) recognise five vegetation units in the highveld, which are associated with short sour grassland. Patches of montane and riparian forests occur along river valleys and interfluves in the highveld. The middleveld is characterised by tall grasses, hillside bush and broadleaf savanna. Five vegetation units are recognised in the lowveld consisting of broadleaf, microphyllous or acacia savanna. Lubombo is characterised by bush or broadleaf savanna and has three vegetation units. Each of the six physiographic regions of the country is associated with at least one ecological zone. These zones and the associated physiographic regions are shown on Table 4.3. Table 4.4 gives the areal extent of indigenous forests.

Table 4.3: Physiographic regions and Ecological Zones of Swaziland

Table 4.4: Areal extent of forests in Swaziland

4.2.4 Climatic requirements for forests

The mountain sourveld is located within an area of rainfall exceeding 1 250 mm a year. This zone is associated with fairly light or severe (especially in the valleys) winter frost. The highland sourveld occurs in a slightly drier zone where the annual rainfall does not exceed 1 000 mm.

Within the moist tall grassveld rainfall is about 1 000 mm a year or more. Winters in this zone are usually frost-free. The tall grassveld receives an annual average of about 900 mm. The dry tall grassveld on the other hand receives about 750 mm of rainfall a year. It is also characterised by slightly higher temperatures than the tall grassveld. The upper broad-leaved tree savanna is characterised by hot summer temperatures. The amount of rainfall in this zone is about 1 000 mm a year. Though cooler than the rest of the middleveld, the upland tall grassveld receives between 800 and 900 mm of rainfall per year.

Associated with the lowveld regions are the lower broad-leaved tree savanna, the acacia savanna and the dry acacia savanna. The occurrence of these ecological zones is partly influenced by climatic conditions and soil types.

The broad-leaved tree savanna found in the western lowveld, occurs on granites soils. In the eastern lowveld is the acacia savanna, which is associated with fertile soils derived from basalt. The dry acacia savanna occurs along the southern Lubombo foothills where that annual rainfall varies between 500 and 625 mm per year. On the Lebombo mountain is the mixed bush and savanna.

Managed (plantation) forests in Swaziland consist of soft and hardwoods such as pine, eucalyptus and wattle. Table 4.5 shows the area of land under managed and natural forests in some of the companies in Swaziland. Each of the species found within plantation forests strives within specific tolerance ranges in terms of climatic conditions.

Table 4.5: Area under Forestry in various companies in Swaziland

Most plantations are found in the highveld region of Swaziland with a few wattle forests found in the upper middleveld.

Managed forests in the country consist of eucalyptus trees (Eucalyptus saligna and E. grandis), Pine trees (Pinus elliottii,, P. patula and P. sylvestris) and wattle (Acacia mernsii).

Each of the species has a specific tolerance to climatic conditions. The mean annual temperature and rainfall requirements for some of the species are shown on Table 4.6.

Changes in these climatic conditions may also cause an increase in the susceptibility of these species to pests and disease outbreaks.

Acacia mernsii, for example, is susceptible to bag worm and mirid attacks whose incidences increase when the mean annual temperature is above 1 200mm.

Table 4.6: Mean annual temperature and rainfall requirements for some forest species

4.2.5 Methodology

Assessment of the vulnerability of the country’s forests and ecosystems was conducted on the basis of three Global Circulation Models (GCMs) recommended for the country; GFDL, CCCEQ and UKTR. Results presented in this report are based on these models and on the country’s observed climatological data supplied by the meteorological service, and serving as inputs to the GCMs.

4.2.5.1 Types of Ecosystems

The current and projected ecosystem types in Swaziland were assessed using the Holdridge Life Zone Classification Model. Using data on annual biotemperature and precipitation to classify ecosystems, the model gives the potential land cover for each study site (Hartshort, 1992). The potential land cover is assessed on the basis of the various life zones shown on the life zone chart and on the basis of both latitudinal and altitudinal differences. The assessment was conducted for the current (baseline) situation and the GCM scenario projections.

4.2.5.2 Tree growth

In assessing the vulnerability of tree species to climate change, the Forest GAP model was used. This model simulates the distribution of plant populations as well as the growth and mortality of individual species. The performance centres on environmental conditions and interactions between the species found on the plot. The growth of individual plant species is indicated by variations in the diameters and changes in biomass production and basal area.

4.2.5.3 Forest Species Assessed

This model was run using two exotic species and four indigenous species. The exotic species used in the assessment were Pinus and Eucalyptus. The indigenous trees were Combretum sps, Syzygium cordatum, Sclerocarya birrea and Pterocarpus angolensis. Choice of the species used in the assessment was based on the occurrence, commercial value and social value of each of the tree species.

In terms of occurrence, most of the selected indigenous trees are found in all the physiographic regions. The only exception is Syzygium cordatum, which occurs mainly in the Highveld and Lubombo regions. The exotics are also generally confined to the highveld and Middlevled regions of the country.

(i) Exotic Trees

Forest plantations are an important source of revenue in the country. Pinus and Eucalyptus cover a large area of the plantations. For example, Mondi forest had about 17 345 ha and 3 745 ha under pine and eucalyptus respectively. The tree species are grown for timber and pulpwood for paper and non- paper products.

(ii) Indigenous Trees

Combretum spp are used as timber and fuelwood. According to Mtetwa and Vilakati (1992), Combretum species are amongst the trees whose wood has high calorific value.

Some species of the genus also have cultural value in that they are used during Incwala (Dlamini, 1981). As such these species are amongst the protected in the country. Syzygium produces edible fruits, which are sold by members of communities where the species occurs.

The bark is used in the treatment of diarrhoea. This species plays an important role in hydrological processes and is also used as timber. Sclerocarya birrea bears fruits that are used by rural communities to brew a highly potent drink rich in calcium.

The nuts are used both as relish and as an important food supplement to rural communities whilst the bark is used for medicinal purposes (Dlamini, 1982). Pterocarpus angolensis on the other hand is an important source of timber and carving material.

Any negative impact of climate change on these tree species would have not only an effect on the natural environmental processes of their habitat, but also an impact on the income generation and other cultural and social activities that they support.

4.2.5.4 Representative study sites

The vulnerability assessment of the selected species was based on climatic data from four representative sites of the main physiographic regions. In the assessment of exotics, climatic data from Bulembu was used. This study site represents the Highveld where most exotics are grown. For the vulnerability assessment of indigenous trees, the representative sites are Mpisi (Middleveld), Big Bend (Lowveld) and Siteki (Lubombo).

Table 4.7: Current Vegetation zones in globally selected grids within Swaziland

4.2.6 Results and outputs

4.2.6.1 Holdrigde

All the model runs suggest that Swaziland is currently predominantly characterised by two types of ecosystems. These are the Subtropical moist forest and the Subtropical dry forest. The south eastern corner of the country is also observed to support a tropical very dry forest (Table 4.7 and Figure 4.1). The results provide an indication of the current potential ecosystem types in the country.

There is a relationship between the current potential ecosystem types and the existing ecological zones in the country. Theories on the evolution of grasslands suggest that areas within the highveld

Table 4.8: Current forest ecosystems associated within specific sites in Swaziland

and upper middleveld regions are ideally suited for growth of sub-tropical forests. Considering that the model was run using the global data that uses grids, an attempt was made to correlate the results with specific areas in the country. This was achieved by running the model using local weather data from nine sites. Almost similar results to the global data were obtained from the country specific data (Table 4.8). The only exceptions are Mbabane and Lavumisa, which the model suggests, are capable of supporting warm temperate moist forest and a Tropical very dry forest forest respectively.

With Mbabane characterised by summer rainfall and severe winters, the type of temperate forest suggested by the model is the deciduous.

Figure 4.1: Current ecological zones in the country

KEY TO 4.1

Dark green - subtropical moist forest
Light green - subtropical dry forest
Grey - tropical very dry forest

(Chapman and Reiss, 1999). As such, areas in the highveld and upper Middleveld regions of Swaziland (Bulembu and Mbabane) have a potential to support a sub-tropical moist forest. The Lower middleveld, Lowveld and Lubombo regions have a potential to support a sub-tropical dry forest.

Figure 4.2: Potential future scenario of ecological zones

KEY TO 4.1

Dark green - subtropical moist forest
Light green - subtropical dry forest
Grey - tropical very dry forest

Table 4.9: Projected changes in ecosystems in Swaziland for each of the GCMs

Model projections suggest changes in forest ecosystems in Big Bend, Mananga and Mbabane (Figure 4.1). All the model scenarios suggest an ecosystem in Mbabane changing from the current warm temperate moist forest to a Subtropical moist forest forest.

There are some variations in the case of Big Bend and Mananga. Big Bend is likely to be covered by a subtropical thorn woodland (CCCEQ) or a Tropical very dry forest forest (GFDL) whilst Mananga is likely to have a Tropical very dry forest forest (CCCEQhigh) or subtropical desert scrub (GFDL- low). Table 4.9 and Figure 4.2 present future scenarios of forest cover in the country.

These possible changes are due to the estimated slight decrease in precipitation and increase in temperature in the country. This suggests a possible change not only in species composition but also in the geographical areas that they support.

Regarding species composition, the results imply that xerophytes such as the Acacia species are likely to flourish in the country with changing climate. This will have implications on the availability of medicinal plants. Secondly, the conversion of ecosystems is likely to have implications on the overall structure of nutrient cycles within the ecosystem. Such would therefore require changes in lifestyles and resource use in the affected areas.

4.2.6.2 Pine biomas distribution and growth

A general slight increase in biomass production in pine trees is projected with respect to the GCM models compared to the current climatic scenario. With the current climate scenario, biomass production in pine trees is estimated at an average of 22.55/ha/yr. The GCMs used in the study however give lower average estimates of biomass at Bulembu. Figure 4.3 shows the projected biomass production in pine trees at Bulembu.

Figure 4.3: Projected Eucalyptus tree Biomass Production at Bulembu

4.2.6.3 Eucalyptus biomas distribution and growth

The assessment of biomass production in eucalyptus indicates a change in climate change will increase the biomass. On the basis of the current climate scenario, the average annual biomass production in Eucalyptus is projected at 159.67 t/ha/yr at Bulembu. The GCMs used in the study give biomass values of over 200 at Bulembu as indicated on Figure 4.3. In summary, both the biomass and basal area of exotic trees in plantations are projected to increase under climate change compared to the current climate scenario

4.2.6.4 Stem size

For all the exotic species used in the study it is projected that the stem size will be slightly lower under climate change compared to the present climate scenario. As expected, there will be a large number of individuals with a diameter that ranges between 0 and 10 cm followed by those with a diameter of 10 - 20 cm. Very few individuals with the larger diameter classes are expected in 2075.

Figure 4.4: Projected Size class distribution of eucalyptus at Bulembu in 2075

4.2.6.5 Distribution and Growth of Indigenous trees

a) Biomass

The Global Change models indicate variations in biomass productivity in the four indigenous species assessed in the study. Also noted are the differences in the performance of the species in the different regions that are represented by the selected study areas.

In the case of Combretum the projections indicate the highest biomass at Mpisi followed by Mananga where the difference between the business as usual scenario and the scenario under climate change is highest. Projected biomass quantity for Sclerocarya and Syzygium are highest at Mananga. General indications from the projections are that Pterocarpus and Combretum will be the most negatively affected of all four species. This is particularly true at Siteki than Mpisi and Mananga.

The general reduction in biomass production in the four species could be attributed to the general increase in temperature, which could also cause an increase in potential evapotranspiration. Although climate change is likely to increase the amount of rainfall received, available water for plant growth will be low. Overall, Combretum seems to have the lowest biomass of all the four species assessed.

Examining the performance of each species, it is observed that Sclerocarya is likely to dominate over the other three species in all the regions. The effects of climate change on Syzygium are also not as pronounced whilst Combretum and Pterocarpus indicate a general decline in biomass production under both the business as usual and climatic change scenarios. This observation highlights the need for sustainable use and protection of the species whose future is uncertain.

Overall biomass production in indigenous forests is projected to decline under climate change with the highest decline at Mpisi and the lowest at Siteki. The only exception is the UKTR model which suggests an increase in biomass under climate change. The same applies with regard to the basal area of indigenous trees in the three study areas.

b) Stem size

The Global Climatic Models are projecting a general decline is stem sizes for Syzygium and Sclerocarya at Siteki compared to the current climatic scenario. This is particularly true for the 10 - 20 cm diameter class. At Mpisi, the GCMs are projecting a slight increase in the stem sizes of Syzygium and Pterocarpus.

At Mananga, there is no major difference between the current climatic scenario and the predictions of the GCMs in the number of Combretum and Sclerocarya trees in almost all the diameter classes, particularly in the classes 0 to 10 cm and 10 - 20 cm. Regarding Combretum, the pattern is not quite clear, especially when comparing the data from the three study areas.

Based on the results on indigenous trees, it appears that the existence of Syzygium and Sclerocarya trees is likely to be compromised by climate change, except at Mpisi or in the middleveld region. On the other hand Sclerocarya and Syzygium will be the least affected, particularly in the Lubombo region.

4.2.7 Adaptation

Apart from the effects of climate, managed forests and other ecosystems in the country are threatened by agricultural activities. Of major concern are small-scale (SNL) and large scale crop (TDL), extensive communal grazing (SNL), ranching (TDL) and some extraction and collection on SNL.

The expansion of settlements is another threat to ecosystems in the country. This is particularly true for the indigenous forests in the lowveld and Lubombo regions and other ecosystems such as wetlands in the Middleveld and Highveld regions. Indigenous forests and wattle plantations are used as sources of firewood and construction timber both in the rural and urban areas. As such deforestation is another serious threat in the country.

Frequent, uncontrolled fires are also major threats to the maintenance of managed forests and other ecosystems in the country. In a study of indigenous knowledge practices in the country (Fakudze, 1998) forty five percent (45%) of the respondents attested to the frequent use of fire due to the opinion that fire has a positive impact on land in that it encourages regeneration of grass, increases in soil fertility and destroys pests such as ticks and mice.

Increased frequency of fires will contribute to a paucity of fire prone species such as grasses and trees whilst encouraging the growth of fire tolerant species. Policy guidance, amongst other controls, is a necessary tool to enable adequate preventative and adaptive actions that are key to sustaining the country’s forest resource, especially in the light of an impending climate change.

Considering the paucity of information on the key parameters of indigenous trees in the country, there is need for research on these parameters in the country. This will enhance understanding of the impacts of climate change on the ecosystems in the country. Changes in plant distribution also need to be monitored on a periodic basis, especially in the protected areas where anthropogenic impacts are controlled.

This page was last updated on 11 October 2004