Effects of thirty-five years of afforestation with Pinus radiata on the composition of mesic mountain fynbos near Stellenbosch D.M. Richardson and B.W. van Wilgen South African Forestry Research Institute, Jonkershoek Forestry Research Centre, Stellenbosch The fynbos vegetation of Biesievlei, Jonkershoek, was surveyed Introduction and described in 1945. In 1948 the catchment was afforested The Jonkershoek Forest Influences Research Station, as it was with Pinus radiata. This paper presents results of a reassessment of the vegetation in 1984 using the same then known, was established in 1935, chiefly to investigate methods that were used in 1945. Afforestation has reduced the the effects of afforestation on streamflow. Biesievlei is one cover of the vegetation (excluding P. radiata) from 75% to 20%. of seven experimental catchments that was afforested for this The total number of species was reduced by 58% from 298 to 126. At least 190 species found in 1945 were not found in 1984, purpose. A study of the fynbos vegetation of Biesievlei was and at least 18 species were added to the list. The mean plant undertaken in October - November 1945 (Rycroft 1950). This density was reduced from 260 to 78 plants m - 2. Only stream study was the first to analyze sclerophyllous fynbos vegetation bank vegetation, comprising mainly large-leaved sprouting using quantitative methods. Its main purpose was to develop shrubs, persisted in a relatively unmodified state. Away from the stream , annuals, geophytes and hemicryptophytes were methods for sampling vegetation in the fynbos but the results dominant. Dominant spe.cies in the pre-afforestation flora were provide a unique opportunity to assess the effects of afforesta­ not resilient to afforestation. Serotinous Proteaceae, woody tion on the composition of the indigenous vegetation. Invasion small-leaved sprouting and myrmecochorous shrubs and large­ by alien trees and shrubs is a major threat to the conservation leaved sprouting shrubs have been virtuall y eliminated. Certain groups may re-establish after clearfelling, but others, notably of fynbos. Seagrief (1950), Cowling et al. (1976) and Milton various groups of shrubs may have been permanently (1976) have described fynbos plant communities under pine eliminated. The implications for weed control in conservation plantations or infestations near Grahamstown, on Table areas are discussed. Mountain and at Jonkershoek respectively, but no quantitative S. Afr. J. Bot. 1986, 52: 309-315 information is available on the effects of afforestation on the Die fynbos-plantegroei van Biesievlei , Jonkershoek is in 1945 floristics and structure of indigenous vegetation. This study ondersoek en beskryf. Die opvanggebied is in 1948 met Pinus was aimed at quantifying the effects of 35 years of suppression radiata bebos. In hierdie artikel word die resultate aangebied van 'n 1984-heropname van die plantegroei waarin dieselfde by a dosed-canopy stand of Pinus radiata. This may be used metodes gebruik is as die in 1945. Bebossing het die to represent the effects of severe invasion by alien trees and, plantegroei-bedekking (P. radiata uitgesluit) vanaf 75% tot 20% by assessing the effects of such 'invasions', certain hypotheses verminder. Die totale aantal spesies is met 58% verminder, van on the effects of weed-clearing operations can be proposed. 298 tot 126. Ten minste 190 van die spesies wat in 1945 gevind is, is nie weer in 1984 opgemerk nie en ten minste 18 spesies is bygevoeg tot die lys. Die gemiddelde plantdigtheid is The study area verminder vanaf 260 na 78 plante m - 2. Slegs oewerplantegroei, The Jonkershoek Valley (33°57'S, 18°55'E) is situated to the hoofsaaklik herspruitende struike met groot blare, het bly south-east of Stellenbosch in the south-western Cape Province, voortbestaan in 'n relatief onveranderde toestand. Weg van die stroom, was jaarplante, geofiete en hemikriptofiete dominant. South Africa (Figure 1). It is surrounded on three sides by Dominante spesies in die voor-bebossingsflora was nie bestand mountains formed predominantly from sandstones of the teen bebossing nie. Serotiene Proteaceae, houtagtige, smalblaar, Table Mountain Group. The Biesievlei Catchment, 27 ha in spruitende en mirmekochore struike en grootblaar, spruitende struike is so te se geelimineer. Sekere groepe mag hervestig na extent, lies on the south-facing slopes of the valley. The area kaalkap, maar andere, veral verskeie groepe struike is dalk is underlain by Cape Granite with a small band of Malmes­ permanent verdring. Die gevolge vir onkruidbeheer in bury Shale in the upper catchment. The soil of the upper bewaringsgebiede word bespreek. slopes is a grey-brown loam on partly decomposed shale while S.·Afr. Tydskr. Plantk. 1986, 52: 309-315 at the lower elevations, grey heavy loam soils on yellow clay Keywords: Afforestation, alien plants, ecosystem stability, predominate (Rycroft 1950). Elevation ranges from 290m at fynbos, Pinus radiata the stream-recording weir to 580 m at the highest point. The mean aspect and slope of the catchment (each measured at 200 random points) are 226° and 19° respectively (Rycroft 1950). The upper portion of the catchment has steep rounded D.M. Richardson* and B.W. van Wilgen ridges separated by steep-sided gullies; the average slope of South African Forestry Research Institute, this portion is 26°. The lower portion flattens out below 355 m J onkershoek Forestry Research Centre, Private Bag X 50 I I, to a gentle slope of about 9° (Rycroft 1950). Stellenbosch, 7600 Republic .of South Africa The climate of the area is mediterranean [Koppen's (1931) *To whom correspondence should be addressed humid-mesothermal type Csb] with a dry summer and the average temperature of the warmest month below 22°C. The Accepted 4 March 1986 mean annual rainfall is 1427 mm, of which about 630Jo falls 310 S.-Afr. Tydskr. Plantk., 1986, 52(4) Figure I The Jonkershoek Valley near Stellenbosch showing the position of Biesievlei. between May and August (unpublished records, Forestry aethiopicum and Leucadendron sa!ignum was estimated on Branch). each plot. Each species was assigned to a life form (after Rycroft (1950) described the natural vegetation of the area Raunkiaer 1934) and the cover of each life form on each plot and distinguished 13 communities. Dominant species included was determined. The life forms were stem succulents, epi­ Protea burchellii, P. neriijolia [listed as P. !epidocarpodendron phytes, megaphanerophytes and mesophanerophytes, micro­ by Rycroft (1950)], Leucadendron sa!ignum (Proteaceae), phanerophytes, nanophanerophytes, chamaephytes, hemi­ Anthospermum aethiopicum (Rubiaceae), Rhus angustijolia cryptophytes, geophytes, helophytes and hydrophytes, and (Anacardiaceae), Clijjortia cuneata (Rosaceae), and Widdring­ therophytes. The proportion of the flora in each life form tonia cupressoides (Cupressaceae). Nomenclature in this paper was then determined. follows Bond & Goldblatt (1984). Families with 15 or more In November 1984, 39 years after the initial study, the species (number of species in brackets) were: Asteraceae (59), vegetation was re-surveyed. Two hundred quadrats were Fabaceae (36), Iridaceae (31), Poaceae (24), Cyperaceae (17), positioned at random in the area. Seven of these fell outside Oxalidaceae (17) and Proteaceae (15). Ten species of Restiona­ the catchment boundaries and were excluded. A portable steel ceae and nine of Ericaceae were present. The vegetation of frame was used to demarcate each of the remaining 193 quad­ upper Biesievlei was last burnt approximately 19 years before rats. Data were collected in such a way as to be directly compar­ afforestation (Van Wyk 1977). Vegetation in the lower part able to Rycroft's (1950) survey. In addition, we also estimated of the catchment was burnt in a wildfire in 1942 (unpublished the cover of individual species in each quadrat. Specimens records, Forestry Branch). In 1947 the vegetation around which could not be identified in the field were collected, and individual planting sites was slashed but not burnt. Almost these were identified by matching them with herbarium speci­ the whole catchment (980Jo) was afforested with P. radiata mens at Jonkershoek. Specimens that could not be identified in 1948. Areas not afforested were steep cliffs where planting (very small individuals or seedlings with no flowers or fruit) 1 was not possible. Trees were planted at 1200 stems ha- • were given serial numbers so that an accurate assessment of the Thinnings to 740, 494, 320 and 158 stems ha- 1 were carried number of species present was made. out in 1959, 1964, 1971 and 1976 respectively. Trees were As Rycroft (1950) did not give cover values for individual pruned to 7 m in 1962. The catchment was clearfelled in 1985. species, direct comparison of dominant components of the vegetation was not possible. In order to compare the dominant Methods components of the vegetation in 1945 and 1984, lists of the In the 1945 survey, 200 quadrats of 0,1 m2 each (0,40 x most important species encountered in the two surveys were 0,25 m) were located at random in the catchment. Species compiled. Rycroft (1950) described 13 vegetation communities were listed on each quadrat. Individual plants rooted in the based on his survey. From these accounts, we listed all those quadrats were counted on each quadrat to estimate density. species described by Rycroft variously as abundant, charac­ Total plant cover and the cover of all Poaceae; Restionaceae teristic, chief, common, conspicuous, dominant,