Báo cáo khoa học: "Differences in vegetation cover resulting from various methods of site preparation for pine plantations in South Africa"

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article Original Differences in vegetation cover resulting from various methods of site preparation for pine plantations in South Africa JB Zwolinski DGM Donald 1 School of Forestry, Auburn University, Auburn, AL 36849-5418, USA; 2 Faculty of Forestry, University of Stellenbosch, Stellenbosch, South Africa November 1993; accepted 5 October (Received 25 1994) Summary — Species composition, height, cover, and biomass of vegetation were examined in response to forest regeneration methods applied in exotic tree plantations of Pinus radiata in South Africa. The experimental treatments involved 4 soil cultivation techniques (pitting, augering, ripping and disk- ing) and 2 levels of weed control (standard and intensive). Both species cover and composition were significantly affected by the experimental treatments. However, the most important weed species remained common irrespective of the site preparation technique applied. More research is needed to find methods for selective control of weed species. plantations / biodiversity / competing vegetation / weed control / soil cultivation tree Résumé — Effet des méthodes de préparation de site sur la couverture végétale dans les plan- tations de pin en Afrique du Sud. La diversité des espèces, la hauteur, la couverture et la biomasse végétale des plantations exotiques de Pinus radiata ont été examinées en fonction des méthodes de régénération de forêt en Afrique du Sud. Les traitements expérimentaux comprennent 4 méthodes de préparation du sol, et 2 niveaux de contrôle des mauvaises herbes (standard et intensif). Les traitements expérimentaux ont un effet sur la couverture et la diversité des espèces. Pourtant, les espèces adven- tices les plus importantes restent présentes quelle que soit la technique utilisé pour préparer le site. Des recherches supplémentaires sont requises pour trouver des méthodes de contrôle sélectif des espèces adventices. plantations forestières / diversité biologique / compétition végétale / contrôle des mauvaises herbes / préparation du sol
INTRODUCTION ber production from indigenous forests was not sufficient to satisfy the demand. Estab- lishment of exotic tree plantations during There about 7 000 species of plants, of are the last century resulted in suppression of than half are endemic, in the which more natural vegetation ("weeds") on extensive Province of South Africa. Endemic Cape areas. Large areas of fynbos have been families include: Bruniaceae (12 genera, 75 invaded by aliens introduced for land recla- species), Geisolomataceae (1 species), mation or timber production, but most dis- Grubbiaceae (2 genera, 5 species), Penae- turbance occurred at afforestation when ceae (5 genera, 25 species), Retziaceae (5 indigenous vegetation was burnt and the genera, 12 species). The other character- land ploughed. Not only did it take longer istic families are, Ericaceae (c 650 endemic for the vegetation to re-establish itself, but species), Proteaceae (c 320 endemic also a single society returned on the species), Restionaceae (c 180 endemic ploughed ground compared to at least 6 species), Rutaceae-Diosmeae (c 150 societies after spot hoeing ("pitting") (Donald endemic species) (White, 1983). The preva- and Schönau, 1963). Species diversity of lent vegetation in the Cape region is fyn- indigenous vegetation was further reduced bos, occurring in the form of 1-3 m tall scle- once exotic tree species formed a closed rophyllous shrubland. Apart from some canopy (Cowling et al, 1976; Richardson extreme habitats, stands of fynbos contain and van Wilgen, 1986). Other silvicultural a mixture of species. Taylor (1972) recorded treatments, such as controlled burning under 121 species of flowering plants from a single the canopy of mature trees, altered the com- 100 m homogenous stand. Grasses are 2 position and spread of the vegetation (Vlok uncommon and usually occur in disturbed and de Ronde, 1989). areas, but were much more abundant before European settlement (Ackocks, 1971).Itis However, after harvesting, re-establish- now believed that fynbos evolved in the ment of exoticplantations is usually impeded presence of recurrent fires. In the absence by rapid regeneration of competing vege- of fire, many fynbos species become mori- tation. Immediate timber production goals bund and die. Therefore, some species can be achieved by vegetation control became almost extinct due to protection ("weeding"), but continued suppression of against fire, and today, controlled fires are native plant species can have a harmful applied to preserve fynbos. There are also ecological impact on long-term site quality large patches of indigenous forests pre- and productivity (Rapp, 1983; Versveld and served in this region. Plateau forest is a van Wilgen, 1986). Usually, large amounts high, evergreen and mixed forest, composed of water and nutrients are released after of dominant tree species such as Olea harvesting timber. These resources are uti- capensis subsp macrocarpa, Podocarpus lized efficiently by the species that invade latifolius and P falcatus, Platylophys trifo- first in a succession. Such species are usu- liatus, and Apodytes dimidiata. Trichocladus ally characterized by rapid growth rates and crinitus, Rhumora adiantiformis, and Blech- high rates of nutrient absorption, thus min- punctulatum are the major understory num imizing nutrient losses from the ecosystem In the moist forest type, the most species. (Chapin, 1993). These species are short- species are Cunonia capensis and common lived and are eventually replaced by woody Platylophys trifoliatus. plants. Very few, if any, dominant species The indigenous forest was heavily are able to utilize all the resources of any exploited in the past, especially for Ocotea area or preserve those that they do not use bullata and Podocarpus spp timber, but tim- for themselves (Grubb, 1977). Preservation
tion had been harvested, producing at felling of the resources by the vegetation is 245 m of good quality timber. In this region, P /ha 3 enhanced by succession (Odum, 1969; radiata is preferred for timber production if fertilizer Vitousek and Reiners, 1975) and diversity is applied on phosphorus deficient sites. It is antic- (Auclair, 1983). Therefore, it seems impor- ipated that timber production will increase by 40% tant to minimize the impact of silvicultural due to appropriate species choice, intensive sil- treatments on the composition and cover of viculture, and fertilization. the natural vegetation while reducing com- A split-split-plot design was used in a facto- petition to levels that allow adequate tim- rial combination to compare 4 methods of soil cul- tivation (whole plots), 2 levels of weed control ber production at the same time. (subplots), and 2 size classes of planting stock This article examines changes in species (sub-subplots). For the purpose of this study, the composition, height, area cover and biomass seedling grade treatment was not taken into con- of competing vegetation in response to for- sideration because the impact of the seedling grade on vegetation regeneration and growth is est regeneration methods applied after har- minimal within the 1 st year after planting. Soil cul- vesting the first rotation of trees. The objec- tivation treatments included pitting, augering, rip- tives are limited to the major species and ping (subsoiling), and ripping and disk-ploughing. potential competitors. It is suspected that Pitting is the standard site preparation procedure intensive silvicultural treatments more in the region and involves digging a pit (45 cm reduce diversity and abundancy of the veg- wide and 20 cm deep) with a hoe. Augering pro- duced a planting pit (45 cm wide and 40 cm deep) etation cover while aggravating the potential with a 2-man mechanical soil auger (Sthil BT 308). for spread of noxious weeds. The effect of Both treatments were applied in May 1989. Rip- reduced competition on tree survival and ping (to 60 cm depth) on parallel planting lines growth is provided by Zwolinksi et al (1994). (spaced at 2.7 m) was done with a D7 bulldozer equipped with a 1-tooth subsoiler. The most inten- sive treatment involved ripping on planting lines, disk-ploughing (to 25 cm depth on average) and STUDY AREA AND METHODS disk-harrowing of the whole area. Ripping and ploughing were preceded by manual removal of The study was located on the Tsitsikamma slash and destumping with a Bellaco Destumper plateau in the southern Cape Province (34° 01’S, mounted on a tractor. Ripping and ploughing treat- 24° 01’E, 200 masl). In the 1950s, almost ments were applied in July 1989. Weeds were 2 000 ha of indigenous vegetation were cleared controlled either with the standard method (slash- and most sites were planted with pines. From the ing of weeds at planting and 1 year later to prevent overtopping of the planted trees) or with inten- north, this plantation is surrounded with fynbos sive ("total") weed control which involved hoeing preserved on extensive areas in the Outeniqua and pulling of the vegetation and application of and Tsitsikamma Mountains while its southern herbicides. Chemical weed control included broad- border is formed by indigenous forest growing cast applications of glyphosate at 2 kg ae/ha 3 on the cliffs of the Tsitsikamma National Park. and 1 months before planting, and a broadcast Soils of the experimental area are relatively uni- application of hexazinone at 2 kg ai/ha 7 months form, moderately deep and are classified with the after planting. In each of the 64 experimental units, South African Binomial Classification as a Kroon- 100 trees were planted at 2.7 m spacing and fer- stad-Oakleaf intergrate (MacVicar, 1990) which is tilized with 208 g/tree of superphosphate (10.5% equivalent to ochric Planosol of the FAO classi- P) in September 1989. The size of the whole-plot fication (MacVicar et al, 1977). The topsoils are and the subplot was 0.2916 and 0.1458 ha, very fine textured loam or silt loam. There is an respectively. In total, 4 replications of this exper- abrupt transition to a gleyed yellow clay at a depth iment were established on 4.6656 ha area. of 0.8 m. The soils are hydromorphic and perched water tables occur due to gently undulating topo- A pilot survey of forest floor vegetation was graphy and the presence of an impervious clay conducted before and after harvesting of the pre- subsoil. In the experimental block, the previous vious crop, by laying a transect in the compart- crop was Pinus pinaster established in 1951. In ment and identifying plants that occurred along 1989, P radiata was planted after the 1 st rota- it. In the experimental plots, vegetation was sur-
Frequencies of occurrence of the major veyed before (28 April 1989) and after (1 Febru- ary 1990) treatment application, and 1 year after species in the sample plots during the 3 planting (26 September 1990). During the post- post-harvesting surveys is shown in table harvesting surveys, 5, 1 m circular sampling 2 II. In general, the number of species and plots were established at random in every subplot. occurrence frequency increased after site Total vegetation cover was estimated as per- preparation. One year after planting, how- centage area covered with live vegetation. Height ever, fewer species were recorded, but fre- of the vegetation was recorded as the average height of the estimated major plant biomass com- quency of occurrences generally increased. ponent within the 1 m plots. The major species, 2 Within the 1 st year after treatment, the plant that is, the species which contributed at least species reacted in various ways and could 25% to the total plant biomass of each sample, be divided into the following principal groups: were identified. Vegetation was harvested on a 0.25 m circular area of each sample plot and 2 i) species which occurred more frequently bulked within a subplot. Dry biomass of each after treatment application (Rubus pinna- sample was recorded. tus, Pteridium aquilinum, Themeda trian- Species composition was classified using the dra, Senecio sp, Psoralea ensifolia, Helichry- 2-way indicator species analysis Twinspan (Hill, sum petiolare); 1979). In a phytosociological context, the data matrix consisted of cross classification of sub- ii) species which were initially stimulated, plots between the major species and soil culti- but later became suppressed (Taraxacum vation combined with weed control treatments officinale, Centella coriacea, Helichrysum (samples). In this method, a classification of the cymosum, Pentaschistis angustifolia); samples is used to obtain a classification of the species according to their habitat preference. The iii) species which were initially suppressed 2 classifications are then used together to obtain by the treatments, but later recovered a 2-way table that expresses the species’ syne- (Hypoxis villosa, Tetraria cuspidata, Pinus cological relations. Within each survey, 2 groups pinaster, Oxalis sp, Galopina circeoides); of treatments were defined by 2 distinctive groups iv) species which declined after treatment of species (a and c). The 3rd group of vegeta- tion (group b) consisted of species common for application (Andropogon appendiculare, both groups of treatments. The vegetation cover, Erharta calycina, Myrica serrata, Halleria height, and biomass were compared with analy- lucida, Cymbopogon marginatus). sis of variance. The means for specific treatment A decrease in the number of species, but levels were tested with Tukey HSD test. Details regarding sampling procedure and statistical anal- an increase in occurrence frequency may ysis are discussed by Zwolinksi (1992). indicate domination of the communities by some of the species better adapted to the site conditions modified by the site prepa- RESULTS AND DISCUSSION ration methods. Perennials such as Rubus Pteridium aquilinum, Helichrysum pinnatus, spp and grasses became dominant species The mature stands of the exotic tree species because they can accumulate resources suppressed natural vegetation. However, the and suppress other species. These species number of species recorded 6 months after can be controlled by a pre-harvesting burn harvesting increased by 72%, that is, from (Vlok and de Ronde, 1989). Frequency of 46 under the stand conopy to 79 in the natural regeneration of Pinus pinasterwas cleared field (table I). It is suggested that initially reduced by hand pulling, but new some of the species regenerated from seed regeneration resulted from abundant seed stored in the soil (eg, Asteraceae) or rhi- reserves in the soil. Clearly, the major effort zomes (eg, Pteridium aquilinum), while oth- ers invaded exposed soil from the surround- to control competing vegetation should con- centrate on species of the groups (i) and ing openings (eg, Taraxacum officinale).
(iii). Rubus pinnatus, Senecio sp, Pteridium of the plant species for the Grouping aquilinum, Tetraria cuspidata, Helichrysum plots (table III) showed that the treatment petiolare, Pinus pinaster, Themeda trian- experimental area demarcated for ripping dra, and Psaralea ensifolia are believed to and augering combined with total weed con- be among the most competitive species trol was covered with specific plant species retarding the establishment of commercial (group c) which were only sporadically tree species in this region. recorded in plots allocated to the other treat-
ments. The differences in species compo- Pinus pinaster and Themeda triandra - were sition were reduced by treatment applica- recorded frequently throughout the survey tion. Five months after the treatments had period, forming a vegetation group (group b) not related to any specific treatment. been applied, only augering combined with standard weed control was represented by Vegetation height, cover and dry biomass specific vegetation group. One year after a are shown in table IV for each of the sur- planting, augering, pitting and ripping, each veys. The vegetation cover was best con- combined with standard weed control, were trolled in disked plots. Disking combined covered with uniform vegetation (group a). with total weed control reduced the vege- A 2nd group, consisting of all the soil culti- tation to 2.9% in cover, 0.1 % in height, and vation treatments combined with total weed 1.1% in biomass compared to the pre-treat- control, had significantly reduced cover. ment values. Disking results in existing veg- Disking combined with standard weed con- etation and humic soil horizons being cov- trol resulted in almost total control of vege- ered with mineral soil from deeper horizons. tation, and weed control treatment was irrel- This prevents immediate re-colonization of evant. Species considered as the strongest the sites by the vegetation. Despite a rela- competitors - Rubus pinnatus, Senecio sp, tively low mean vegetation cover and height, Pteridium aquilinum, Tetraria cuspidata, however, individual trees could be subjected Helichrysum petiolare, Psoralea ensifolia, to severe competition where Senecio spp
etation and to reduce costs of weed con- is regenerated on the exposed mineral soil. trol. More research is needed to find bet- Senecio spp spread quickly on bare ground ter control measures against the important and grew rapidly, overtopped the trees and weeds. caused occasional mechanical damage through wind buffeting. The amount of vegetation increased after ACKNOWLEDGMENTS augering or pitting combined with standard weed control. One year after planting, auger- ing and standard weed control produced This study was funded by the Department of Water Affairs and Forestry and conducted by the 2 641 kg ha of vegetation, that is, 47 times -1 Division of Forest Science and Technology of more than the combination of disking and CSIR in South Africa. Messrs J Vlok and M Viviers total weed control. The standard method of are thanked for their help in the identification of site preparation in the region (ie, pitting and plant species. standard weed control) yielded the 2nd largest amount of vegetation not differing significantly from augering and standard REFERENCES weed control. Frequently, pits were invaded by grasses taking advantage of the fertil- (1971) The distribution of certain ecolog- Ackocks JPH izer applied on the soil surface around the ically important grasses in South Africa. Mitt Bot planted trees. The average reduction of veg- Staatssamml Munch 10, 149-160 etation biomass by 90% through "total weed (1983) "Natural" mixed forests and "artificial" Auclair D monospecific forests. In: Disturbance and ecosys- control" was achieved by repetitive mechan- tems: components of response (HA Mooney, M Gor- ical and chemical measures. don, eds), Springer-Verlag, Berlin, Heidelberg, New York, Tokyo, 71-82 Chapin FSIII (1983) Patterns of nutrient absorption and CONCLUSIONS use by plants from natural and man-modified envi- ronments. In: Disturbance and ecosystems: com- ponents of response (HA Mooney, M Gordon, eds), Springer-Verlag, Berlin, Heidelberg, New York, i) Natural vegetation regenerates rapidly Tokyo, 175-187 and colonizes bare ground when released Cowling RM, Moll EJ, Campbell BM (1976) The eco- from tree competition after timber harvesting. logical status of the understorey communities of Its natural successional development, how- pine forests on Table Mountain. S Afr For J 99, 13- ever, is disturbed by site preparation for tree 23 planting and rapid natural regeneration of Donald DGM, Schönau APG (1963) Some preliminary results from a fertilizer/cultivation experiment with exotic trees. The impact of this repetitive Pinus radiata. For S Afr2, 53-69 disturbance on regeneration potential of the (1977) The maintenance of species-richness Grubb PJ native species and their continued presence plant communities: the importance of the regen- in on the sites is unknown. eration niche. Biol Rev 52, 107-145 ii) The cover of competing vegetation is sig- (1979) Twinspan: a Fortran programme for Hill MO arranging multivariate data in an ordered 2-way table nificantly reduced by intensive soil cultivation by classification of the individuals and the attributes. and weed control. However, the most impor- Cornell Univ, New York, 90 p tant weed species in tree plantations remain MacVicar CN (1990) Soil classification for South Africa. common irrespective of the site preparation Memoirs on the Agricultural Natural Resources of South Africa 15. Dept of Agricultural Development, method applied. Pretoria, 257 p iii) It is recommended that the time between MacVicar CN et al (1977) Soil classification: a binomial harvesting and re-establishment be reduced system for South Africa. Dept of Agricultural Tech- to decrease competition from natural veg- nical Services, Pretoria, 150 p
Odum EP (1969) The strategy of ecosystem develop- Vitousek PM, Reiners WA (1975) Ecosystem succes- ment. Science 164, 262-270 sion and nutrient retention: a hypothesis. BioScience 22, 376-381 M (1983) Some problems of disturbance on the Rapp nutrient cycling in ecosystems. In: Disturbance and Vlok JHJ, de Ronde C (1989) The effect of low-inten- ecosystems: components of response (HA Mooney, sity fires on forest floor vegetation in mature Pinus M Gordon, eds), Springer-Verlag, Berlin, Heidelberg, elliottii plantations in the Tsitsikamma. S Afr J Bot New York, Tokyo, 117-128 55, 11-16 Richardson DM, van Wilgen BW (1986) Effects of 35 White F (1983) The vegetation of Africa. A descriptive years of afforestation with Pinus radiata on the com- memoir to accompany the Unesco/AETFAT/UNSO position of mesic mountain fynbos near Stellenbosch. vegetation map of Africa. Unesco, 356 p S Afr J Bot 52, 309-315 Zwolinski JB (1992) Regeneration procedures and mortality Taylor HC (1972) Notes on the vegetation of the Cape of Pinus radiata D. Don in the southern Cape Province. Flats. Bothalia 10, 637-646 PhD Thesis, University of Stellenbosch, xxiv + 257 p Versveld DB, van Wilgen BW (1986) Impact of woody Zwolinski JB, Donald DGM, van Laar A, Groenewald aliens on ecosystem properties. In: The ecology WH (1994) Regeneration procedures of Pinus radi- and management of biological invasions in South- ata in the southern Cape Province. V. Post planting em Africa (IAW Macdonald, FJ Kruger, AA Ferrar, mortality and growth of trees in response to the eds), Oxford University Press, Cape Town, 239- experimental treatments and planting site environ- 246 S Afr For J 168, ment. 7-12