CHAPTER2
- 1. Chapter 2. STUDY AREAS, SAMPLING AND STATISTICAL METHODS 2.1 STUDY AREA - GENERAL DESCRIPTION This section is based on working plans for the Rhenosterhoek forest area and Mauchsberg forest area of "MONDI"-Forests (L.t.d) and S.A.F.I (L.t.d.). The Rhenosterhoek area comprising the Blyfstaanhoogte and Rhenosterhoek plantations, and the Mauchsberg area comprising the In Die Diepte and Grootfontein plantations. Climatic data were obtained form the provincial statistics database (CSS, 1995). Figure 2.1: Map of South Africa showing the position of Mpumalanga province and the cities of Cape Town and Sabie. The terminology used in the various reports requires some elaboration of the geographical terms used. The study area (Sabie) currently falls under Mpumalanga province. In the previous system of classification of provinces the study area fell under the Eastern Transvaal province. The Sabie district lies in the northern part of Sabie Pretoria Cape Town Mpumalanga Republic of South Africa N
- 2. the Mpumalanga province and the city of Sabie is the district capital (Figure 2.1). Detailed descriptions of the sampling sites are presented in Appendix A. 2.1.1 Climate The study area falls within the semi-humid subtropical summer rainfall zone (October to April). The average number of rainy days is 90 (C.S.S., 1995). The rain ranges from heavy downpours to light penetrating showers. An appreciable amount of rain falls in the form of gentle drizzle and mist, which is typical of the area, hence the name “the mist belt” given to the area. The Grootfontein area is described (S.A.F.I., 1973) as not being typically “mist belt”. In the rainy season (summer), the soil is permanently well supplied with moisture, which, under summer conditions, seldom rises by capillary forces to the surface. Moreover, during the rainy season precipitation exceeds evaporation. In winter (dry season), there is little rain and the drying-out of the soil is accelerated by strong dry winds. The data presented in Table 2.1 refer to the years 1961-1990. Indicated are the annual mean rainfall and the maximum and minimum temperatures recorded in the Eastern Transvaal-Mpumalanga region (C.S.S., 1995). Table 2.1 : Temperatures and rainfall for the period of 1961-1990 ( C.S.S., 1995). Annual January July Annual January July Rainfall (mm) Temperature (°C) Mean Nelspruit 767 127 10 19.9 24 14.8 Witrivier 687 102 14 21.1 24.8 16.7 Mpumalanga Minimum 516 80 1 13.7 17.3 8 Maximum 1480 264 21 22.2 25.7 17.2 Table 2.1 shows the considerable rainfall variation over Mpumalanga province. The average rainfall ranges from 500mm/a to almost 1500mm/a. Rabie et al. (1994) cite a h lower precipitation limit of 750 mm/acre for commercial forestry. Mondi-Forests (1997) cite a lower precipitation limit for softwood commercial plantation of >900 mm/a. Also important in this context are the maximum rainfall figures. These are for the Graskop area which includes the Mauchsberg plantations. The Mauchsberg area is distinguished by its higher rainfalll in comparison with the surrounding terrain in
- 3. Mpumalanga. Optimum growth temperatures are reported to be between 15 and 30°C (Rundel et al., 1998). The vegetation is typical of dolomite and shale ground (S.A.F.I., 1957), mainly grasslands (short and long grass) on hilly terrain. Trees are found along the valleys and mountain tops. 2.1.2 General geological and mineralogical background The geological description of the area under study is based on the South African Geological Survey - S.A.C.S. (1980), and of reports produced by S.A.F.I (1957, 1973, 1979) regarding specific plantations. Where discrepancies occur between the SACS survey (1980) and SAFI reports (1957, 1973, 1979), the SACS description was preferred. The area studied falls under the lithostratigraphic subdivision of the Transvaal sequence and the Pretoria group (SACS, 1980). The Pretoria group consists predominantly of quartzite and shale with a dominant volcanic unit, the Hekpoort andesitic formation. Minor conglomerates, chemical and volcanic members are also found. Nowicki (1997) gives the clay content of the shales in forest soils of the Eastern Escarpment as being between 20 and 30%. The mineralogy of the clay was described by Nowicki (1997) as consisting mainly of kaolinite. Chlorite, gibbsite and goethite were also reported. 2.2 RHENOSTERHOEK FOREST AREA The Rhenosterhoek forest area consists of the following plantations: Rhenosterhoek, Doornhoek and Blyfstaanhoogte. Afforestation at the Rhenosterhoek plantation was commenced in 1944, at k in 1949 and at Blyfstaanhoogte in 1957. The Rhenosterhoek plantation is 2127 hectares in extent and the Blyfstaanhoogte plantation 3075 hectares. The plantations from which the samples were taken are described below. 2.2.1 Topography Situated 30°35’E and 25°13’S, the forest area lies at the foothills of the Drakensberg
- 4. range in the Eastern Transvaal escarpment area. The elevation is between 1400 to 2200m above sea level. The area comprises of two main drainage basins - the Nelspruit river and the Blyfstaanspruit river, both of which are part of the Crocodile river catchment area. On the northern and the western part of the Rhenosterhoek forest area, the topography is one of steep slopes levelling off towards the south- east. The topographical features of the area are typical of the Eastern Transvaal. The terrain consists of irregular undulating gentle slopes, but becomes steep towards the northern, eastern and western boundaries, which run along the summits of the ridges. 2.2.2 Geology and soils The underlying bedrocks are predominantly dolomite, shale, and occasional quartzite of the Transvaal sequence with intrusions of diabasic dykes and sills in all three bedrocks (Figure 2.2). The stratigraphic sequence dips to the west with the dolomite overlying quartzite of the Black Reef formation. The dolomitic terrain is deeply dissected with underground aquifers (S.A.F.I., 1957). Shales of the basal Pretoria Group overly the dolomites. The soils derived from the shale are predominantly clay loam. On the plateau, the soils are shallow to moderate in depth. The depth to the unweathered bedrock of the shale zone is reported to be 10-15 m (S.A.F.I., 1957), in the Rhenosterhoek-Doorenhoek area, and 600-700m in the Blyfstaanhoogte area (S.A.F.I., 1979). The shale in the Blyfstaanhoogte area is described as thinly bedded brown shale, very fissile in parts. The colour is slightly darker in the lower portions. Bands of micaceous, shaley sandstones are common throughout the area. The shale is generally highly jointed, and in some places highly ferruginous (S.A.C.S, 1980). The soils of the area studied are typical of the “Mistbelt” and are derived from shale and quartzite of the Pretoria Group. The soils in the Rhenosterhoek plantation were described (S.A.F.I., 1957) as comprising mainly a sandy loam and sandy clay. The soil texture of the Blyfstaanhoogte plantation was described as being a sandy loam- clay loam. Both plantations were reported (S.A.F.I., 1957) to be of low pH (4.4 -
- 5. Figure 2.2: Sampling sites and the Basic geology of the Sabie area. 4.9, in water suspension), adequate levels of nitrogen in the A and B mineral horizons as well as low P and K (Appendix A). The soil is acidic (esp. in the upper horizons) with a tendency towards nutrient depletion (N,P,K) as the profile deepens (S.A.F.I., 1957). Blyfstaanhoogte ANDESITE SHALE DOLOMITE GRANITE Sabie Graskop Rhenosterhoek In Die Diepte Blyfstaanhoogte - Sampling site Grootfontein km100 Klipkraal
- 6. 2.2.3 Sampling sites Eleven compartments were sampled. Six samples were taken from the Rhenosterhoek plantation (Appendix A) and five from the Blyfstaanhoogte plantation (Appendix A). The samples were labelled in a sequence specific for this study. The conversion of the official compartment identification to that used in this study is presented in Table 2.2. 2.3 GROOTFONTEIN FOREST AREA The Grootfontein forest area is part of the Mauchsberg forest plantation area, and consists of the Grootfontein and Die Diepte plantations (Appendix A). The terminology used in characterising the area in the various reports and maps is not very consistent. This is attributable to changes in forest management and reporting policies over the years. The terminology needs to be tidied up.. Prior to 1978, the Grootfontein forest area comprised a single plantation: Grootfontein. From 1978 onwards, the references are to Grootfontein as including the Grootfontein plantation and In Die Diepte plantation. In this study the forest area will be referred to as Mauchsberg area and the two plantations will be referred to by their name i.e. Grootfontein and In Die Diepte. As regards for the history of afforestation in this area, commercial planting commenced in Grootfontein in 1948 and in In Die Diepte in 1959. 2.3.1 Topography The Mauchsberg forest area is situated behind the first range of hills west of the Drakensberg mountain range, and incorporates a portion of the Blyde river canyon. The approximate geographical location is 30°45’E and 24°25’S. The topography of the plantation is rugged with steep, broken slopes, deep gorges and very little flat land. The plantation is bisected, roughly from South to North by the Blyde river with minor tributaries emerging from cliffs and running in all directions. The altitude varies from 1830 m above sea level in the South east corner, to 1280 m at the Blyde river in the north of the forest area. The mountain slopes face predominantly east and west.
- 7. Table 2.2 : Site description - Rhenosterhoek forest area. Plantation Compar- tment No. Sample labelling Year established Comp- artment age (y) Present rotation No. Pinus species Rhenosterhoek R-13 R-1 1946 52 2 pat+ell R-15a R-2 1946 52 2 pat+ell R-22 R-3 1947 51 3 Elliottii R-23c R-4 1945 53 3 Elliottii R-23d R-5 1945 53 2 Patula R-24 R-6 1945 53 2 Patula Blyfstaanhoogte M-27a B-1 1958 40 2 Patula M-47a B-2 1976 22 1 pat+ell M-48b B-3 1976 22 1 Patula N-3b B-4 1960 38 2 Patula M-35a B-5 1959 29 2 Patula pat -patula ; ell - elliottii 2.3.2 Geology and soils The geological nature of this area is similar to that of the Rhenosterhoek area. Sediments of the Transvaal Group underlie most of the area of the study. The soils derived from these rock types vary in depth. In the lower slopes, they are deep, rich and of dolomitic origin while on the higher areas the soils are shallow and poorer in respect to nutrients and are predominantly after shale. 2.3.3 Sampling sites Ten compartments were sampled. Seven samples were taken from the In Die Diepte plantation and three from the Grootfontein plantation (Appendix A). The site description is presented in Table 2.3. Table 2.3: Site description - Mauchsberg forest area. Plantation Compar- tment Sample labelling Year established Compart -ment Present rotation Pinus species
- 8. No. age (y) No. Grootfontein A-3a G-1 1949 49 2 pat+ell A-3b G-2 1950 48 2 pat+ell E-3a G-3 1955 43 2 taeda In Die Diepte L-1 I-1 1966 32 2 taeda M-20 I-2 1970 28 2 pat+ell M-22 I-3 1969 29 2 patula N-15 I-4 1972 26 1 elliottii N-16 I-5 1972 26 2 elliottii J-20 I-6 1964 34 2 patula P-4b I-7 1973 25 1 patula pat -patula ; ell - elliottii 2.4 KLIPKRAAL FOREST The oldest site available for sampling was near MONDI's dam in the Klipkraal plantation (10km north east to Sabie). The plantation was established in 1931. The sampled compartment (R-15b) was never harvested, and the trees on this site are still of the first rotation (67 years of age). The geology of the site is predominantly granitic. It is of a western aspect and is some 400m lower than the average sampled site in the Rhenosterhoek and Mauchsberg forest area. 2.5 SAMPLING METHODS Soil sampling was carried out at suitable sites where the pine plantations were: • Facing a North-West to North-East aspect. • Similar parent material (shale). • Varied slopes. • High altitude (1500-2000m). • Maximum available spread of plantation age. Twenty-two sites were selected to represent similar geological and geographical properties, with plantation age ranging between 22 to 67 years. One exception is a pine plantation chosen for its progressive age (67 years) in view of its slightly different characteristics (granitic parent material, western slope, lower altitude). All
- 9. sites were sampled within a time span of 48 hrs. No substantial change in climate liable to affect soil properties was noted during the sampling period. The data and records of the various plantations and compartments were collected from “Mondi” regional offices in Sabie. The records were used to decide which of the compartments were to be sampled, and to obtain data regarding the history of each of the compartments. Only topsoils were sampled for this study (0-20 cm). Any overlying organic material was removed. The reasoning for this was the assumption that most of the root mass (and root surface) responsible for water and nutrient uptake are in the topsoil (de Vries, 1991). In addition, it is the topsoil that is most sensitive to acid deposition, and thus most likely to reflect any change in the chemistry of the solid and aqueous phases in forest soils. Given the silvicultural and different littering manners in the various pine species, the organic horizon was not sampled and was excluded from the samples. A composite soil sample was created according to the following method: A sampling site, with an average size of 200*200m was selected. Four individual soil samples were obtained by removal of the upper organic horizon. A hole, 20-25cm deep and 25cm wide was dug. The soil was mixed in the hole and excavated. The four individual samples were consolidated, thoroughly mixed and a composite sample was taken (3-4 kg). The samples were air-dried, sieved (2mm) and stored for further analysis. The soil samples were analysed by common methods of soil analysis. The main objective was characterising the chemistry of the exchangeable phase and the soil solution. All of the analytical work reported in this study was carried out on these 22 samples. 2.6 STATISTICAL TREATMENT The relationship between the soil chemical properties of pine plantations and age of these soils under commercial forestry is statistically evaluated by using a non- parametric, one way anova test (Kruskal- Wallace). The reasoning behind the use of this statistical treatment is the number of samples (22) and the ability to evaluate the
- 10. data while disregarding the distribution of the parent population. In this study, for most variables, the data is not normally distributed. The assessment of a statistical treatment is done by obtaining the p-values which provides an indication as to whether the result is statistically significant or not (commonly a 95% confidence limit is used, i.e. p≤0.05). Precision of the various methods used for the chemical analysis of the soil samples is evaluated by using mean, variance and standard deviation based on descriptive statistics. Relationship between various parameters (such as Ca/Al ratio and Age of afforestation) is obtained by using non-parametric treatments such as Shapiro-Wilks test for determining the distribution and obtaining trend lines (using Spearman r2 criterion). All the statistical calculations are carried out using the STATISTICA software program (StatSoft Inc., 1995).