Vegetation Change Over 40 Years in the Weenen/Muden Area, Kwazulu-Natal

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To cite this article: M.T. Hottman & T.G. O'Connor (1999): Vegetation change over 40 years in the Weenen/Muden area, KwaZulu-Natal: evidence from photo-panoramas, African Journal of Range & Forage Science, 16:2-3, 71-88 To link to this article: http://dx.doi.org/10.2989/10220119909485721

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Vegetation change over 40 years in the WeenenIMuden area, KwaZulu-Natal: evidence from photo-panoramas

M. T. HotTman} and T.G. O'Connor2

INational Botanical Institute, Private Bag X7, Claremont, 7735 Republic of South Africa; E-mail: [email protected] 2Department of Range & Forage Resources, University of Nata!, Private Bag X01, Scottsville, 3209 Republic of South Africa

Received 13 October 1998; Accepted 06 December 1999

Abstrad ment (e.g. Pienaar 1980; Grossman & Gandar 1989) have not relied upon a formal methodology except for a The utility of panoramic photographs for studying the few studies based on aerial photographs (e.g. Van extent and pattern of vegetation change. in particular of Vegten 1983). These studies are adequate for revealing bush encroachment, was investigated by revisiting thir- change in woody canopy cover but do not provide details teen sites in the Weenen and Muden areas of KwaZulu- about community composition or structure. Field-based Natal that had been photographed in 1955. The studies of community structure and composition, on the ubiquitous feature of all sites was the marked increase in other hand, are only able to make inferences about woody cover, from a mean of 21 % woody cover for all patterns of historical change (e.g. Tiver & Andrew topographic units (plains, hill slopes, river bank and 1997). Therefore, it is a combination of aerial photogra- river terrace) in 1955, to 59% woody cover in 1998. phy and ground studies that are most effective in Although sample sizes were small, the increase in woody describing the extent, rate (from repeated photographs) cover was greater on hill slopes (45% mean increase in and pattern of vegetation change (e.g. Le Roux 1996; woody cover) than on the plains (26%), and on north- Roques 1997). Although panoramic (lateral) photo- facing slopes (56%) rather than on south-facing slopes graphs have been used to describe the pattern of (32%). The increase in woody plant COl(erwas accompa- vegetation change in the Nama-karoo and semi-arid nied by a change in composition from open or mixed grassland biomes (Hoffman & Cowling 1990). their woodland, to one dominated by Acacia species, in utility for investigating bush encroachment in savanna particular by A. tortilis at lower altitudes and by A. regions has not been widely explored in South Africa. karroo at higher altitudes. In some cases, scrub Acacia The Tugela valley region of KwaZulu-Natal supports individuals were already evident in the photographs in a savanna vegetation which has been subjected to human 1955, and had grown into mature trees by 1998. impact for over 1 000 years (Maggs 1984; Maze11984: Recruitment of both Acaciaand broad-leafed species was February 1994). This has led to changes in its structure also observed in 1998 and there was a tendency for bush and composition (Edwards 1967: Le Roux 1996), with clumps to develop. Broad-leafed species have dominated fire responsible for maintaining open vegetation forma- on moist south-facing slopes and at higher altitudes. tions (February 1994). In 1955, many of the woodland

Downloaded by [Timm Hoffman] at 23:12 19 January 2013 Increases of the arborescent leaf succulents. Aloe spect- elements were interpreted as relicts of a formerly abilis and Opuntia ficus-indica and of the dwarf. stem extensive cover of mainly broad-leafed woodland that succulent shrub, Euphorbia pseudocactus.have occurred. had been depleted by sustained utilization (Edwards Fire is no longer a component of .this landscape which. 1967). The existing knowledge of the vegetation together with the open condition in 1955, resulting from ecology of this area therefore provided an opportunity overgrazing. may account for the vegetation changes that for determining the persistence of savanna structure or have taken place. Panoramic photographs proved an its rate, direction and pattern of change over a half effective tool for monitoring vegetation change because century. changes in composition and structure were revealed. and The purpose of this e:-..-ploratorystudy was twofold. because each photograph samples a large area of ground at an adequate resolution. First, it was to determine whether panoramic photographs could provide a useful ancillary tool for studying Additional index words: Acacia, bush encroachment, vegetation change because their level of resolution environmental history, savanna. would seem to lie between that of aerial photography and ground study. We seek to illustrate what can be Introduction achieved with panoramic photographs in terms of quantitatively describing the extent and nature of veg- Bush encroachment has been widespread within the etation change, in particular of bush encroachment. savanna regions of southern Africa (Grossman & Gan- Secondly, we identify environmental influences that may dar 1989), but details on its extent, rate and dynamics have shaped the rate and pattern of vegetation change of are lacking. Estimates of the extent of bush encroach- the Tugela valley regions of KwaZulu-Natal. 72 African Jownal of Range & Forage Science 16(2&3):71-88

Procedure estimated visually by four vegetation ecologists, and rounded off to the nearest 5% after reaching consensus. Study area Formal methods such as line intercept were rejected The study area extends from approximately 28°45'S to because estimates of woody cover on a panoramic 29°00'S and 30000'E to 30030'E, and forms part of the photograph are influenced by obliqueness (e.g. slope of Bushmans and Mooi river drainage into the Tugela hill) and distance of object from camera. The derived river. The area is of marked relief, ranging in altitude data do not, therefore, reflect an exact estimate of woody from 700 to 1 300 m above sea level (a.s.1.), and is cover, but are considered to offer a reliable, relative located geologically in the Ecca Group (Edwards 1967; estimate of its extent of change. Smith et a/. 1993). The region experiences a mean A non-parametric Mann-Whitney U test was under- annual rainfall of 550-730 mm (Table 1), which falls taken to test for significant differences in the increase in predominantly during the summer months October to woody cover between plains and hill slopes, and between April. Large river valleys are drier and hotter than north and south facing hill slopes. mountain crests because of orographic effects on rainfall and temperature. Aspect and slope further influence Results and discussion moisture and radiation balance. Land-use practices of The Weenen and Muden regions of KwaZulu-Natal relevance to the present study include communal and were cloaked in a substantially greater cover of woody commercial rangeland. A detailed description of the plants in 1998 than in 1955. In only one topographic study area can be found in Edwards (1967). unit in one photograph had woody cover decreased since The vegetation of the highest points tends toward 1955 (Figure 1; Table 1) and this was because the area open grassland, while that of the valleys is a complex had recently been cleared manually along a boundary range of savanna types related to topography and local fence between communal and commercial rangelands. climate (Edwards 1967; Rutherford & Westfall 1986; Woody cover had increased by 38% in all topographic Camp 1995; Le Roux 1996; to which reference should units from a mean of21% in 1955 to 59% in 1998 with be made for further detail). a range of 10% to 75%. Despite there being low sample sizes, the increase in woody cover was significantly Sampling strategy and statistical treatment greater on hill slopes (x=45.0%; n=13) than on the In the course of his survey of the Tugela river basin plains (x=25.9%; n=l1) (U(1l,13)=107;P<0.05). Woody Edwards (1967) took 13 panoramic photographs from cover increase was also greater on north facing slopes the roadside or vantage points during 1955 which were (x=56.0%; n=5) than on south facing slopes (x=31.7%; relocated in 1998 (Table 1). We do not know what n=6) although the difference was not significant biases may have influenced the selection of panoramas (U(5,6)=22;~.05). There were two sites with either a in 1955 other than some obvious ones such as field of riverbank or river terrace (Figures 8 and 1I) and both view: We attempted as best as was possible to match the had increased substantially in woody cover since 1955. photographs in terms of camera position and height, and In almost all cases, Acacia species were the most time of day. We could not match the season of conspicuous encroaching species (Figures 1 to 13; Table photography but differences were taken into account 1). Acacia torti/is was the most conspicuous at lower Downloaded by [Timm Hoffman] at 23:12 19 January 2013 when interpreting images. At each of the sites, field altitudes below 1 000 m a.s.1. (Figures 1 to 9, 12) while notes were taken of the dominant plant species present Acacia karroo was conspicuous at elevations above in the landscape as well as the major changes that have 1 000 m a.s.1. (Figures 11 to 13) and in riverine occurred since 1955. We could not always sample communities (Figures 8 and 11). Acacia nilotica was distant topographic units in the landscape, and binocu- widespread but always sub-dominant to the other Acacia lars were then used to identify the main plant species species (Figures 2, 3, 5, 12 to 14). Acacia cafJra had not present. A 35 mm SLR Minolta X70 camera with a 50 responded as an encroaching species although it was mm lens was used to take the photographs, together with well represented in 1955 (Figure 11). During the course IIford FP4 Plus black and white film. A summary of of his survey in 1955 Edwards (1967) had recorded low Edwards' captions from his 1955 field notes and from Acacia scrub in his notes, although it was not always his thesis (Edwards 1967) have been reproduced in readily evident in the 1955 photographs (but see Figures Figures 1-13. Additional detail to the images are 2 and 5). Thus, many of the large individuals evident in provided by our own captions. The photographs, the 1998 photographs were already in place by 1955, but together with extensive captions derived from our field had not yet experienced appropriate environmental notes are archived at the Kirstenbosch Research Centre conditions for an increase in size. in Cape Town. Taxonomic nomenclature follows The breadth of environmental conditions under Arnold & De Wet (1993). which A. tortilis had established is noteworthy. The In order to quantify the extent of change in woody altitudinal limit to distribution suggests a climatic canopy cover, topographic units (plains, hill slopes, etc.) control, probably temperature or frost, but this has not, were first delineated on the 1955 and 1998 photographs. to our knowledge, been established. Hotter, drier Woody cover in each of the topographic units was conditions would seem optimal and this is reflected in African Jownal of Range & Forage Science 16(2&3):71-88 73

Table 1 Mean annual rainfall (mm a-1), altitudinal range (m) and aspect of landscape units represented in Figures 1 to 13 showing the increase in percentage woody cover between 1955 and 1998 and the main species contributing to the increase in woody cover

Fig. Rainfall Position in Topographic Attitudinal Aspect % woody cover Percent Main species contributing to the (mm a-I) photograph unit range (m) change increase in woody cover 1955 1998 556 Foreground (right) Plain 780 5 45 40 Acacia torti/is Foreground (left) Plain 780 15 10 -5 Decrease in woody cover Background (right) Hill slope 780 -800 SE 25 35 10 Acacia torti/is Background (left) Hill slope 780 -800 SE 30 55 25 Acacia torti/is 2 556 Foreground Sloping plain 780 -800 15 35 20 Acacia torti/is, Acacia ni/otica 3 677 Foreground Sloping plain 760 -800 40 55 15 Acacia torti/is, Acacia ni/otica Background Hill slopes 800 -940 SW 50 75 25 Acacia torti/is 4 544 Foreground Sloping plain 800 -820 5 70 65 Acacia torti/is Midground Sloping plain 800 -820 10 65 55 Acacia torti/is Background (right) Hill slope 820 -880 NE 25 90 65 Acacia torti/is 5 579 Foreground Sloping plain 820 -880 5 20 15 Acacia torti/is, Acacia ni/otica 6 731 Midground Plain 800 -920 60 70 10 Acacia torti/is 7 670 Background Hill slope 920 -960 N 5 45 40 Acacia torti/is 8 700 Midground (left) River bank 920 -940 15 90 75 Acacia karroo Background Hill slopes 940 - 1 400 SW 20 75 55 Acacia torti/is 9 624 Foreground Plain 920 -960 20 30 10 Acacia karroo Midground Plain 920 - I 000 35 60 25 Acacia karroo, Acacia torti/is Background (right) Hillslope 1000-1400 N 20 85 65 Not examined 10 618 Whole image Hill slope 1 000 - 1 100 SW 25 85 60 Coddia rodis, Tarchonanthus camphoratus, Vepris /anceo/ata II 676 Foreground River terrace 1 020 - 1 040 15 45 30 Acacia karroo, Acacia caffra Background Hill slope 1040-1100 N 25 70 45 Acacia karroo 12 611 Foreground Hill slope 1 220 - 1 240 WNW 20 85 65 Acacia karroo, Acacia ni/otica Fore-midground Foot slope 1 160 - 1 220 W 25 85 60 Acacia karroo, Acacia torti/is Mid-background Plain 1 100 - 1 160 20 55 35 Acacia torti/is 13 611 Fore-midground Hill slope 1 220 - 1 300 W 25 80 55 Acacia karroo, Acacia ni/otica, (below escarpment) Acacia caffra, Tarchonanthus camphoratus Background Hill slope 1 300 - 1 400 SW 0 15 15 Acacia karroo, A. ni/otica (above escarpment)

the greater increase in woody cover on north facing phylla, Rhus pentheri, Vepris lanceolata and Tarcho- slopes. However, since 1955, this species has also nanthus camphoratus. The majority of the colonising, established on steep, south facing slopes at relatively broad-leafed species possess fleshy fruits (pooley 1993), high altitudes (Figure 13). Acacia tortilis occurred on and are therefore likely to be bird or animal dispersed. all the main geological substrates including dolerite Although there was some evidence for the development

Downloaded by [Timm Hoffman] at 23:12 19 January 2013 (Figure 11), shale (Figure 10), sandstone (Figure 10) of bush clusters through nucleation (see Le Roux 1996), and alluvium (Figw::e 8). This study confirms the there were many broad-leafed individuals whose estab- reputation that has ~n previously accorded to both A. lishment had not apparently been facilitated by other torti/is (e.g. Van Vegten 1983) andA. karroo (e.g. Story plants (Figure 9). Species usually associated only with 1958; On Toit 1967) as encroaching species, especially mesic or closed canopy conditions, for example, Mayte- on overgrazed rangeland and on abandoned fields. A nus undulata, Dombeya cymosa, Vepris lanceolata and noteworthy dynamic at one site was the extension of the Cussonia spicata, which were not mentioned in 1955, tree line from an altitude of about 1 300 m a.s.l. in 1955 had established on the coolest sites (e.g. Figure 10). to 1 350 m a.s.!. in 1998 (Figure 13). This increase These findings lend support to Edward's (1967) inter- consisted mainly of A. karroo and A. nilotica but also pretation of broad-leafed individuals at that time, which included broad-leafed evergreen species. were mainly mature adults, as relicts of a previously The increase in broad-leafed species was determined, well-wooded landscape. The evidence in 1998 suggests to an extent, by environmental conditions, in particular a return to a broad-leafed woodland at some sites. the availability of moisture as reflected by altitude and By comparison with the microphyllous species, and aspect. The greatest increase was evident on a cool, many other broad-leafed and evergreen species, which south-facing slope at higher altitude, on which Acacia had increased substantially over 43 years, adult indi- species were not prominent (Figure 8; Table 1), but one viduals of Boscia albitrunca had shown little change in north-facing slope above 1 220 m a.s.!., was also size (Figures 4 and 5) although some mortality had dominated by broad-leafed species (Figure 13; Table 1). occurred (Figure 7). Some recruitment of this species Broad-leafed species had, however, established on all was also evident, albeit at low density (Figure 5), sites, with the most common being Maytenus hetero- rendering it impossible to judge whether a true popula- 74 African Journal of Range & Forage Science 16(2&3):71-88

tion decline had occurred. density or overgrazing (Figures 5, 8, 11, 12 and 13). A conspicuous increase of some tree and shrub For sites at which there was sufficient fuel for succulents has occurred, especially at the drier, hotter burning, many of the trees were greater than 2 or 3 m sites at lower altitude. Aloe spectabilis was scarcely tall. Since trees greater than 2m tall usually suffer little evident in 1955 but was well established by 1998, direct mortality from fire (Trollope & Tainton 1986), it occurring at seven of the 13 sites surveyed, all below 960 is unlikely that fire alone will significantly influence the m a.s.l. Opuntia ficus-indica was not mentioned by cover of woody plants in the region. Even the high Edwards (1967) and is not evident in the 1955 photo- altitude grassland site, which has been invaded by graphs. In 1998, it occurred at eight of the 13 sites woody elements (Figure 13), has a number of individu- surveyed, albeit at low densities, and at altitudes ranging als capable of surviving an intense fire. In addition, tall from 780 m to 1 300 m a.s.l., although it appeared more individuals of Aloe spectabilis should also endure fire common below 1 000 m a.s.l. The dwarf, stem despite their succulence, because their dead leaves succulent shrub Euphorbia pseudocactus was a common protect them (Bond 1983). The dwarf-shrub succulent and sometimes dominant component of the ground layer Euphorbia pseudocactus, however, is likely to be par- at three of the hotter and drier sites below 880 m a.s.l. ticularly susceptible to fire because it has no obvious Its increase is also likely, in part, a response to the high form of protection against fire. radiation environment which CAM plants require, and Sheet, gully and stream bank erosion features were which has been created by sustained, heavy grazing. evident in five of the matched photographs (Figures 4,5, The tall arborescent succulent Euphorbia ingens had, 8, 10 and 12). Except for Figure 4, the increase in however, neither increased nor obviously declined. In woody cover has resulted in a reduction of the area some situations A. spectabilis is likely to decline in the exposed to the erosive power of water and wind (also in future as it is overshadowed by taller broad-leafed Figure 2). In Figure 4, however, there appears to have species (e.g. Figure 9). Opuntia ficus-indica was the been an increase in the degree (i.e. a deepening of the most conspicuous alien invasive, although Acacia erosion channels) but not necessarily the extent of the mearnsii had invaded the riverine area at one site erosion features. We conclude that panoramic photographs coupled (Figure 11). The region covered by these photographs would therefore seem not as prone to invasion by alien with ground inspection offer a rapid, reliable means of plants as adjacent grasslands in KwaZulu-Natal. assessing macro-vegetation change, which has advan- tages over aerial photographs and ground-based sam- Our ability to identifYchange in the ground layer was pling. Although there is obviously inaccuracy in the successful only if a change of state had occurred (e.g. manner in which we estimated woody cover, the accu- grassland to dwarf shrubland) or if detailed notes had racy of estimates derived from aerial photographs been made in 1955. A conspicuous change of state for depends on the scale (resolution) of the photograph, open areas between bush has been a marked decrease of with trees of less than 4 m crown diameter not usually perennial grasses and an increase of defended dwarf visible at a scale of 1:50000 (Le Roux 1996). This size shrubs, notably Blepharis natalensis and Euphorbia criterion would exclude many of the isolated trees pseudocactus (Figures 4 and 5), although some peren- encountered in this study. Ground estimates of woody nial grasslands were relatively unchanged (Figures 1 to cover, for example by line-intercept sampling, require a 3, 9). In some areas of sustained heavy grazing (Figures Downloaded by [Timm Hoffman] at 23:12 19 January 2013 prodigious effort to sample a very small surface area. 2 and 5), perennial grasses had persisted but were The surface area of land sampled by a panoramic dominated by short-lived, palatable, prostrate species photograph varies from hectares to square kilometres such as SpQrobolus nitens and Urochloa mosambicensis with inverse variation in visible detail, although the rather than by upright bunchgrasses such as the wiry, resolution of this detail is markedly superior to that unpalatable Aristida species or the aromatic Cymbo- available on standard aerial photography (>1:25000). pogon plurinodis, although the latter two species did Aerial photographs cannot reveal change in composition occur in the study area. or structure, both of which were important components Both woody and succulent growth forms are suscep- of change in this study and were effectivelyillustrated by tible to fire. Therefore, the general increase in the simple notes in conjunction with the photographs. Our woody component and the stability or increased abun- ability to detect compositional change using panoramic dance of certain succulent species are interpreted as a photographs was due mainly to the dramatic changes response to the open conditions resulting from sustained that had taken place. It is improbable that more subtle overgrazing which had been created by 1955, and the compositional changes could be revealed without more consequent release of these systems from fire. We found detailed, quantitative information available from the no evidence of recent fire at any of the sites we visited. original survey. This absence is probably the main factor promoting the continued increase of woody cover as evidenced by the Acknowledgements number of small, recruiting individuals of Acacia and broad-leafed species. Indeed, most of the sites no longer We thank CR Hurt, C.D. Morris, 1. Perkins and S. carry a fuel load sufficient for burning because of woody Todd for assistance with estimating change on photo- African Journal of Range & Forage Science 16(2&3):71-88 75

graphs, and K. Camp for his insights provided during a G, Avery DM, Wilson ML & Humphreys (eds). field trip to the study area in March 1998. The Frontiers: southern African archaeology today. BAR Computing Centre for Water Research, Pietermaritzburg International Series 207: 194-206. are thanked for supplying us with rainfall data for the Mazel AD 1984. Through the keyhole: a preliminary study site locations. Denzil Edwards had the foresight peep at the lithic composition of Later Stone Age sites to catalogue carefully the photographic collection he in the central and upper Tugela River basin, Natal. In: assembled, for which we are indebted. Hall M, Avery G, Avery DM, Wilson ML & Hum- phreys (eds). Frontiers: southern African archaeology References today. BAR International Series 207: 182-193. Pienaar AJ 1980. Handelinge van werksessie in Arnold TH & De Wet BC 1993. Plants of southern verb and met bosindringing en -verdigting. Department Africa: names and distribution. Memoirs of the of Agriculture and Fisheries, Pretoria. Botanical Survey of South Africa 62. Pooley E 1993. The complete field guide to the trees of Bond W 1983. Dead leaves and fire survival in southern Natal, Zululand and Transkei. Natal Flora Publica- African tree aloes. Oecologia 58:110-114. tions Trust, Durban. Camp K 1995. Valley bushveld of KwaZulu-Natal: Roques KG 1997. Shrub encroachment in Swaziland: natural resources and management. National Depart- dynamics, and the relative importance of causal fac- ment of Agriculture, Pretoria. tors. MSc thesis, University of East Anglia, Norwich. Du Toit PF 1967. Bosindringing met spesifieke verwys- Rutherford MC & Westfall RH 1986. Biomes of ing na Acacia karroo indringing. Proceedings of the southern Africa - an objective categorization. Memoirs Grassland Society of Southern Africa 2: 119-126. of the Botanical Survey of South Africa 54. Edwards D 1967. A plant ecological survey of the Smith RMH, Eriksson PG & Botha WJ 1993. A review Tugela river basin. Memoirs of the Botanical Survey of the stratigraphy and sedimentary environments of of South Africa 36. the Karoo-aged basins of Southern Africa. Journal of February E 1994. Palaeoenvironmental reconstruction African Earth Sciences 16:143-169. in the Natal Drakensberg using wood charcoal as a Story R 1952. A botanical survey of the Keiskamma- conservation management tool. South African Journal hoek district. Memoirs of the Botanical Survey of of Science 90:549-551. South Africa 27. Grossman D & Gandar MY 1989. Land transformation Tiver F & Andrew MH 1997. Relative effects of in South African savanna regions. South African herbivory by sheep, rabbits, goats and kangaroos on Geographical Journal 71:38-45. recruitment and regeneration of shrubs and trees in Hoffman MT & Cowling RM 1990. Vegetation change south-east Australia. Journal of Applied Ecology in the semi-arid, eastern Karoo over the last two 34:903-914. hundred years: an expanding Karoo - fact or fiction? Trollope WSW & Tainton NM 1986. Effect of fire South African Journal of Science 86:286-294. intensity on the grass and bush components of the Le Roux IG 1996. Patterns and rate of woody vegetation eastern Cape thornveld. Journal of the Grassland cluster development in a semi-arid savanna, Natal, Society of Southern Africa 3:37-42.

Downloaded by [Timm Hoffman] at 23:12 19 January 2013 South Africa. MSc thesis, University of Natal, Pieter- Van Vegten JA 1983. Thornbush invasion in a savanna maritzburg. ecosystem in eastern Botswana. Vegetatio 56:3-7. Maggs T 1984. Iron Age settlement and subsistence West 0 1951. The vegetation of Weenen county, Natal. patterns in the Tugela River basin. In: Hall M, Avery Memoirs of the Botanical Survey of South Africa 23. oOoooסo 76 African Jownal of Range & Forage Science 16(2&3):71-88

Figure 1a D. Edwards 8157. 07 Oct 1955. Keafs Drift to Muden road. Difference between veld of Native Trust and European- owned land which has been conserved and allowed to grass over. Right foreground native land with Boscia a/bitrunca relicts. Note grass cover on left of fence as compared with hill on right with bare soil. Relict trees on hill are Bos- cia a/bitrunca, Euphorbia ingens, Combretum apicu- tatum, Cussonia spicata and other deciduous trees. Secondary Acacia torti/is - deciduous - abundant low tree or shrub.

Figure 1b M.T. Hoffman negative no. 23A124. 23 Jun 1998: 11h10. 4.4 km from Keafs Drift on road from Keat's Drift to Muden. 28°53.1'5 3Q029.2'E. The fence line separates the Entembeni Mission communal area on the right from the commercial farm, Im- pala 1853, on the left. The open gravelly plain in the foreground (right) is comprised of a relatively even stand of Acacia tortilis

Downloaded by [Timm Hoffman] at 23:12 19 January 2013 trees. Occasional Acacia ni/otica and Lippia javanica individuals are also present in this woodland of low di- versity, while a single Opun- tia ficus-indica individual was also recorded. Some of the large, relictual Boscia a/bitrunca individuals grow- ing in the drainage line, and evident in Edwards' 1955 photograph, are still present in 1998. Although the grass layer is currently heavily grazed it has, nonetheless, increased in cover since 1955. The cut-line immediately on the left side of the fence has been re-cleared and widened and is dominated by 1-m high Acacia torti/is and Lippia javanica shrubs comprising about 10% of the cover. The foreground area to the left of the cut-line, which was not cleared, is comprised mainly of tall Acacia torti/is and Dichrostachys cinerea trees. Acacia nilotica individuals up to 3 m high are also present with broad-Ieafed and succulent trees and shrubs such as Combretum apicu/atum, Ziziphus mucronata, Ehretia rigda, Boscia a/bitrunca, Euphorbia ingens and Lippia javanica comprising a more diverse woodland than on the communal side of the fence. Both sides of the fence in the foreground appear heavily browsed and signs of woodcutting, especially of adult Combretum apicu/atum and Ziziphus mucronata, are evident. The background slopes were not examined in the field. However, on the ridge in the communal area (right), the abundance of broad-leafed and succulent trees such as Combretum apicu/atum, Cussonia spicata, Boscia a/bitrunca and Euphorbia ingens has decreased since 1955, while the abundance of Acacia tortilis has increased. On the ridge, on the left side of the fence, the abundance of broad-leafed tree species appears unchanged, while Acacia torti/is has increased significantly. African Journal of Range & Forage Science 16(2&3):71-88 77

Figure 2a D. Edwards B156. 07 Oct 1955. Near Keat's Drift on Muden to Keat's Drift road. A Euphorbie ingens (relict) - Acecie tortilis secondary community. Boscie elbitrunce (relict) also seen. Acecie torti/is secondary. Note stump to right. Area has been protected from overgrazing hence relatively abundant grass regeneration.

Figure 2b M.T. Hoffman negative no. 18N19. 23 Jun 1998: 1Oh30. 5.2 km from Keat's Drift on road from Keat's Drift to Muden. 28°53.2'5 30029.1'E. The low, open shrubland, evident in the foreground of the 1955 photograph, has increased in height to between 3 and 4 m. The woodland is dominated by microphyllous trees, mainly Acecie torti/is, with some Acecie ni/otice and a few Downloaded by [Timm Hoffman] at 23:12 19 January 2013 Dichrostechys cineree and Acecie ceffre individuals. Broad-leafed trees include Peppee cepensis, Ehretie rigide, Boscie elbitrunce, Ziziphus mucronete and Combretum epiculetum. Chopping scars were evident on the latter two species. There exists a reason- able density of low shrubs «1.5 m) including Coddie rudis, Uppie jevenice, Terchonenthus cemphoretus, Protesperegus sp. and Rhus pentheri. With regard to succulents, Euphorbie ingens is still present at about the same density as in 1955 (±6 plants ha-1) while the recent recruitment of Aloe spectebilis is conspicuous. Opuntie ficus-indice also appears to be recently recruited although it currently exists in low numbers. Stands of Euphorbie pseudocectus were recorded just outside the field of view to the right of the photostation. The grass layer is taller than in the 1955 image and most species had produced seed during the last season. Grass cover has increased to nearly 100% and few open areas are evident in the recent photograph. The main species present in the foreground are: Urochloe mosembicensis, Themede triendre, Sporobolus fimbrietus, Sporobolus nitens, Penicum meximum (protected within shrubs), Eregrostis curvule, Eregrostis superbe, Melinis repens and the occasional tuft of Cymbopogon p1urinodis. 78 African Journal of Range & Forage Science 16(2&3):71-88

Figure 3a D. Edwards 8121. 31 Mar 1955. 3 miles from Weenen on Nko- sine road. Showing extensive Acacia torti/is consocies in typical situation at foot of hill. Half- way uphill is lighter coloured Vitex rehmannii community. Dense path above on hill is Euphorbia triangularis c0m- munity.

Figure 3b M.T. Hoffman negative no. 26126A. 17 Mar 1998: 13h53. 4.8 km from Weenen on road to Nkosine. 28°49.3'5 3Qo05.6'E. The increase in cover of the sloping rocky plain of the foreground has mostly been of Acacia torti/is and Acacia ni/otica, and to a lesser extent Acacia karroo. These microphyllous, woody species now dominate the land-

Downloaded by [Timm Hoffman] at 23:12 19 January 2013 scape. Many small Acacia torti/is individuals and a few large Dichrostachys cinerea individuals are evident. Broad-leafed trees and shrubs of the foreground include Ziziphus mucronata, Olea europaea subsp. africana, Maytenus heterophyl/a, Rhus pantheri, Caddia rudis, Mund- ulea sericea and Boscia a/- bitrunca. The presence of Aloe spectabilis in the foreground appears to be a n8W phenomenon. No Opuntia ficus-indica individuals or Euphorbia pseudocsctus populations were seen. The grass layer of the foreground is taller than in 1955 although basal cover appears unchanged. Important foreground grasses include Aristida diffuse, Themeda triandra, Melinis repens, Cymbopogon plurinodis, Eragrostis superba, Bothriochloa insculpta, Sporobolus fimbriatus and Chloris virgsta. There are numerous homesteads in the vicinity and evidence of woodcutting is present, although there were no signs of fire. The background hill slope is more thickly bushed than in 1955. Cussonia spicata individuals are evident on the upper slope. Acacia tortilis, Vitex rehmannii and Euphorbia triangularis occur in similar positions on the hUI slope as before. African Journal of Range & Forage Science 16(2&3):71-88 79

Figure 4a D. Edwards 8152. 06 Oct 1955. Muden to Keat's Drift road. Relic Boscia albitrunca - secondary Acacia torti/is - secondary Euphorbia pseudocactus community typical of heavily disturbed areas of Dry Valley Scrub and Savanna. The grass field layer has been largely replaced by secondary low shrubs as a result of cultivation and continuous overgrazing. Muden, lower Mooi river valley.

Figure 4b M.T. Hoffman negative no. 27AJ28. 23 Jun 1998: 12h10. 18.7 km from Keat's Drift on road to Muden. Photograph taken standing on boot of car. 28°57.05'S 3Q023.75'E. The most marked change of the rocky foreground slope is the development of a dense woody cover dominated by 3-m-high Acacia tortilis individuals and a fair density of newly recruited Aloe spectabilis individuals,

Downloaded by [Timm Hoffman] at 23:12 19 January 2013 also up to 3 m high. Occa- sional to rare broad-leafed trees and shrubs include May tenus heterophyl/a, Ehretia rigida, Coddia rudis, Spirostachys africsna, ProtsspersgtJs sp., Lycium sp., and Boscia albitruncs. Opuntis ficus-indics is also present, but in low numbers. The ground layer has a cover of more than 80%, and is dominated by Blepharis natalensis. Urochlos mossmbicensis, Eragrostis sp. and a few Cymbopogon plurinodis tufts have also established. Stands of Euphorbia pseudocsctus are present. About 80% of the woody cover in the mi~round sloping rocky plain is now comprised of Acscis tortilis while Combretum apiculatum contributes about 10% to this cover. Adult Boscis slbitruncs individuals are also present but it could not be determined effectively if they have declined in number since 1955. Populations of Aloe spectsbi/is are now conspicuous on this slope. In 1955 the plateau in the top left of the photo was perhaps an old land or open grassland. The recent photograph shows that it is now a closed woodland dominated by Acacia spp. The degree, but not necessarily the aerial extent of sheet, gully and donga erosion on this slope has increased since 1955. The red eroded soils support a dense stand of Euphorbis pseudocsctus while a large population of Yuccs sp. is present to the right of the red eroded patch in the middle of the photograph. Microphyllous and a few broad-leafed trees have now colonized the bed of the erosion gullies. The population of Euphorbia trisngulsris on the north-facing hill slope on the extreme right of the photograph appears unchanged. The most significant increase here has been that of microphyllous woody Acscia species. 80 Afiican Jowna] of Range & Forage Science ]6(2&3):7]-88

Figure Sa D. Edwards B151. 06 Oct 1955. Muden to Keafs Drift road. Boscia albitrunca (relict tree) - Acacia torti/is secondary community on old lands. Euphorbia pseudocactus dominant in patches. Grass - Sporobcr Ius sp.? - cover is here developing due to a mea- sure of protection from overgrazing.

Figure 5b M.T. Hoffman negative no. 13N14. 23 Jun 1998: 13hOO. 3.5 km from Muden on road to Keafs Drift. Slightly in front of Edward's location. 28°57.2'5 30024.OS"E. The increase in woody cover on the sloping sandy plain of the foreground is due mainly to the increase of Acacia torti/is and, to a lesser extent, Acacia nilotica. Broad-Ieafed trees and shrubs include Boscia

Downloaded by [Timm Hoffman] at 23:12 19 January 2013 albitronca, Ehretia rigda, May tenus heterophyl/a, Caddia rodis, Pro/aspsre- gus sp. and Lycium sp. Al- though heavily browsed, the size distribution of Boscia albitronca individuals suggests that it is regenerating in this area. Aloe spectabi- /is and Opuntia ficus-indica are not evident in the 1955 photograph but occurr every 30 - 40 m throughout the foreground area. Euphorbia pseudocactus stands have also increased in extent since 1955. Extensive sheet erosion is still evident in the foreground and many footpaths currently criss-cross the area. Despite this, there has been an increase in cover of the ground layer and dwarf shrubs and grasses currently comprise about 50% cover. About half of the ground layer cover is comprised of B1epharis natalensis and well~b1ished stands of Felicia sp. The abundance of these two species is not apparent in the 1955 photograph. The main grasses in the foreground are Urochloe mosambicensis, Sporobolus nitens, Sporobolus fimbriatus, and the occasional tuft of Cymbopogon plurinodis. Although difficult to establish from the 1998 photograph, woody cover on the south-west facing hill slopes in the background has increased. This has largely been as a result of an increase in Acacia spp. African Journal of Range & Forage Science 16(2&3):71-88 8\

Figure 6a D. Edwards 8123. 01 Apr 1955. Over- looking Weenen from Est- court road. Extensive secondary Aca- cia tortilis Scrub on flat, severely eroded area around Weenen (top right). Much of the area represents old land sites. Foreground: edge of dense form of semi- deciduous bush. Weenen, Interior Tugela Valley.

Figure 6b M.T. Hoffman negative no. 28128A 24 Jun 1998: 14h30. In Weenen Game Reserve . standing at edge of old road. 28°50.5.5 3Q001.TE. The main species dominating the mid-ground region on the gently undulating hills of the Weenen valley are Acacia tortilis and Dichrostachys cinerea. Popu~ons of Aloe ~- abi/is are more common in the vicinity of the main road Downloaded by [Timm Hoffman] at 23:12 19 January 2013 than in 1955, while Euphor- bia ingens remains abundant on the pediment immediately below the photostation. Many broad-leafed elements are also evident on the foreground slope including Tarchonanthus cam- phora/us, Olea europsea subsp. africana, Plaeroxy- Ion obliquum and Cassine sp. Isolated Opuntia ficus-indica individuals are also present in 1998. The old lands in the top left of the photograph have increased in woody cover presumably as a result of Acacia torti/is encroachment. Because the valley was reasonably well-wooded in 1955 it shows less of an increase in woody species than many of the other sites. 82 Afiican Journal of Range & Forage Science 16(2&3):71-88

Figure 7a D. Edwards 6181. 22 Oct 1955. Weenen: farm area - Moo; River road. Hills completely denuded of woody vegetation. Note a few relict Boscia a/bitrunca in foreground and along ridge to the right. Low Aca- cia torlilis shrubs seen on the hillside.

Figure 7b M.T. Hoffman negative no. 31131A. 17 Mar 1998: 14h40. 6.9 km from Ween en on Mid- dlerestiMooi River road. 28°54.8'5 3Qo05.3'E. The foreground remains a cultivated field although many abandoned lands in the vicinity are now dominated by dense, 3 - 4 m high Acacia ka"oo stands. The Boscia a/bitrunca individual seen in 1955 has dis- appeared although a new Downloaded by [Timm Hoffman] at 23:12 19 January 2013 bushclump has appeared at the base of the slope. This bushclump is comprised of Ziziphus mucronata, Aca- cia caffra, Maytenus heterophyl/a, Acacia ka"oo and Grewia occidenta/is, amongst a few other species. Woody cover on the rocky hill slope is now dominated by Acacia torli/is. A few broad-leafed species including Boscia a/bitrunca are also present. Isolated Opuntia ficus-indica individuals are evident while a single Aloe spectabilis individual was observed on the hill slope to the left of the field of view of the photograph. The density of human settlement is similar to 1955 and indicates that stands of Acacia torlilis can increase in close proximity to human habitation. African Journal of Range & Forage Science 16(2&3):71-88 83

Figure 8a D. Edwards B182. 24 Oct 1955. Weenen: farm area - Mooi River road. Depth of soil at bottom of valleys. Acacia ka"oo left along stream bank. Uko- humbe mountain in background. Relict tree veld on hillside.

Figure 8b M.T. Hoffman negative no. 4/4A. 17 Mar 1998: 14h57. 8.2 km from Weenen on MiddlerestlMooi River road. 28°55.1'S 3Qo06.05'E. The erosive power of this Bushman's river tributary has decreased considerably since 1955. There has been an accretion of sedi- ments and a stabilization of the right hand river bank. Acacia ka"oo trees, up to 4 m high, now colonize the flat

Downloaded by [Timm Hoffman] at 23:12 19 January 2013 river terrace on the right while many young Acacia ka"oo seedlings, Maytenus heterophyl/a and Ziziphus mucronata individuals are also present. The grass sward on the right hand bank is mostly comprised of Cynodon dacty/on, Hypar- rhenia hirta and Setaria sphace/ata. The exposed erosion wall of the river bank on the left-hand side of the photograph has flattened somewhat and is covered with vegetation. Woody cover is now dominated by Acacia karroo, which reach 10 m in places. Other species in abundance are Maytenus heterophyl/a, Vepris lanceo/ata, Rhus dentata, Celtis africana, Ziziphus mucronata and Combretum erythrophyllum. Acacia tortilis is also present. The vegetation of the upper terrace, beyond the erosion wall, is dominated by Acacia karroo individuals of all sizes. The increase in woody cover on the south-west facing hill slopes of the Nkolombencane mountain in the background is largely as a result of an increase in Acacia ka"oo, with Acacia tortilis dominating the vegetation at the base of the mountain. Populations of Combretum apiculatum and A/oe bainesii are also evident on the hill slope. Some erosion dongas are still evident on the exposed blue shale at the base of the mountain. 84 African Journal of Range & Forage Science 16(2&3):71-88

Figure 9a D. Edwards 8172. 20 Oct 1955.

I Weenen - Muden road about 6 miles from Weenen. Relict tree (evergreen mainly or with leaves) - Aca- cia torti/is community. Aca- cias leafless.

Figure 9b. M.T. Hoffman negative no. 34/34A. 16 Mar 1998: 15h45. Weenen to Muden road about 8.2 km from MiddlerestlMooi River road tumoff in Weenen or 9.6 km from Nkosine tumoff in Weenen. 28°52.1' S 3Qo09.4'E. The legume-dominated woodland of the gently sloping, south-facing slope in the foreground has increased in height and is now comprised mainly of

Downloaded by [Timm Hoffman] at 23:12 19 January 2013 Acacia karroo, Dichrostachys cinerea, Acacia nilotica and Acacia caffra. Numerous juveniles of broad-leafed tree and shrub species are evident with the most common being Maytenus heterophyl/a, Coddia rudis, Vitex rehmannii, Rhus pentheri, and Olea europaea subsp. africana. No signs of fire were evident in the foreground and there is a tendency to bushclump formation. Aloe spectabi/is, with a spacing 'of 15 - 20 m, appears to be newly recruited to the foreground slope. The grass sward in the foreground is now comprised predominantly of perennial species including Themeda triandra, Cymbopogon p1urinodis, Eragrostis obtusa, Eragrostis spp., Aristida diffuse, E/ionurus muticus, Sporobolus fimbriatus, and Bothriochloa insculpta. Acacia tortilis dominates along the drainage line at the base of the north-facing slope in the mid-ground and Acacia karroo is probably the dominant Acacia species further upslope. African Journal of Range & Forage Science 16(2&3):71-88 85

Figure 10a D. Edwards B800. 24 Oct 1955. Weenen: farm area - Mooi River road. Severely eroding hillside with mutilated relic trees of Semi-deciduous Bush and continuous overgrazing and browsing. Bantu kraals immediately to right of photo. Principal trees shown are: Schotie brechypete/e, Eu- phorbie ingens, O/ee efricene, Acecie ceffre, Euc/ee schimperi, Ozoroe penicu- lose, Peppee cepensis, Vi- tex rehmennii, Ziziphus mucronete, and the secondary species, Acecie torti/is and A. ni/otice. Low shrub cushions of Coddie rudis.

Figure 10b M.T. Hoffman negative no. 1AJ2. 17 Mar 1998: 15h20. 12.3 km from Ween en on Middlerestl Mooiriver road. 28°56.8'5 3Q007.0'E. This south-facing slope hill is comprised of sandstone rocks and boulders with exposed shale beds in places. The lower half of the hill is more dense, in terms of woody cover, than the top half, and is comprised predominantly of broad-leafed Downloaded by [Timm Hoffman] at 23:12 19 January 2013 trees and shrubs such as Coddia rudis, Terchonen- thus cemphoretus, Vepris /enceo/ete, Olea europeee subsp. efricene and Euc/ee crispe. Other, less-common, broad-leafed species include Cussonia spicata, Uppia jevanica, Maytenus heterophyl/a, Maytenus un- deta, Rhus pentheri, Grewie occidenta/is, Pfaeroxy/on obliquum, Schotia brechypeta/e, and Dombeya cymosa. No Boscia a/bitrunca or Ozoroa penicu/osa individUals were evident. While this south-facing slope has generally promoted the increase of broad-leafed trees and shrubs, Acacie tortilis is still common at the bottom of the hill, and Acacia ni/otica, Acacia caffra, and Acacia ka"oo are also present on the slope. Succulent trees include adult Euphorbia ingens individuals and the occasional Opuntia ficus-indica. There is a sward of perennial grasses and a fair proportion of herbs. The uppermost 50 - 100 m of the slope, (i.e. just below the summit of the hill) is more of an open shrubland than the dense lower slope. It is comprised mainly of Coddia rudis, and isolated individuals of Pappaa cepensis, Brechyleene elliptica, Pfaeroxy/on obliquum, Vepris /anceo/eta, Terchonenthus camphoratus, Vitex rehmannii, and Rhus pentheri. Acacia ka"oo is also common, and Acacia caffra and Acacia torti/is are present. 86 African Journal of Range & Forage Science 16(2&3):71-88

Figure 11a D. Edwards B170. 20 Oct 1955. Muden - Weenen. Acacia caffra community on the north aspect dolerite.

Figure 11b M.T. Hoffman negative no. 13/13A. 16 Mar 1998: 10h50. About 12 km from Muden on Weenen road. 28°56.6"5 3Q016.TE. Acacia karroo has been the species which has increased most in the narrow river valley and river terrace of the foreground. Other common species found in the river valley are Acacia ca"ra, Celtis africana, Combretum erythrophyl-

Downloaded by [Timm Hoffman] at 23:12 19 January 2013 fum, Grewia occidenta/is, Lippia javanica, Ehretia rigida, Maytenus heterophyl/a. Acacia meamsii is present close to the water. There is a thick herbaceous sward comprised of Pani- cum maximum beneath the trees, Themeda triandra in the open, and Hyparrhenia hirta in places. The north- facing hill slope is comprised mainly of Acacia karroo, with Dichrostachys cinerea, Acacia ni/otica, Acacia torti/is and Acacia ataxacantha also present. Acacia caffra is still evident. Broad-leafed trees and shrubs include Rhus pantheri, Schotia brachypata/a, Tarchonanthus camphoratus, and Cussonia spicata while the succulent tree, Euphorbia ingens, is also evident as isolated individuals. There is a tall grass sward dominated by Themeda triandra in open patches. Other grasses include Hyparrhenia hirta, Cymbopogon plurinodis, Panicum maximum, Sporobolus fimbriatus and Eragrostis spp. Afucan JOWllaJof Range & Forage Science 16(2&3):71-88 87

Figure 12a D. Edwards B177. 22 Oct 1955. Weenen - Muden road near Middlerest tum off. General view from Um- hlumba Neck of extensive soil erosion and secondary vegetation of Weenen area. In foreground a narrow zone, a few hundred yards wide, of Acacia kaffoo-A. ni/otica Thorn Veld, forming boundary of Valley Vegeta- tion. In middle and far distance, Acacia torti/is and other secondary species with relict trees of Semi- deciduous Bush.

Figure 12b M.T. Hoffman negative no. 818A. 17 Mar 1998: 1Oh2O. About 20.5 km from Weenen on Muden roac:l.28°55.4'S 3Q012.9'E. The foreground has thick- ened up considerably since 1955 to form a closed woodland. Acacia kaffoo and Acacia ni/otica are still dominant, together with Tar- chonanthus camphoratus and to a lesser extent Aca- cia caffra. Cussonia spicata, Schotia brachypeta/a

Downloaded by [Timm Hoffman] at 23:12 19 January 2013 and Dovya/is caffra are also present. Many of the broad- leafed species, evident as scattered individuals on the footslope in 1955, are still present in 1998. Acacia karroo and Acacia torti/is, however, have filled in the open spaces between the relict trees. Woody cover has increased on the footslope and now covers most of the erosion channel at centre, which cut into the pediment in 1955. The valley bottom, forming the wide plain in the mid-background, is comprised predominanUy of highly dispersive and eroded red soils, which has left the underlying blue shales exposed in places. Although there are still a number of open patches, woody cover increase has occurred as a result of the expansion of Acacia torti/is along drainage lines and onto the undulating ridges of the valley bottom. The bare, open patches, evident in the centre and along the road at the top left of the photograph in 1955, suggest that cultivation still occurred in the valley at this time. These fields have all been abandoned and Acacia torti/is has colonised many of the bare areas. Human habitation is now confined to a few settlements along the roadside. 88 African Journal of Range & Forage Science 16(2&3):71-88

Figure 13a D. Edwards 6178. 22 Oct 1955. Weenen-Muden road near Middlerest tum-off. Abrupt transition of thom- veld to grassland. Uhlumba range in background. North-west aspect. Acacia caffra in flower. Other species are: A. karroo (dominant at other margin), A. nilotica (lower down in tore- ground). The area has been considerably damaged and is a secondary condition.

Figure 13b M.T. Hoffman negative no. 5Af6. 23 Jun 1998: 15hOO. About 20.5 km from Weenen on Muden road. 28°55.4"S 3Q012.9'E. The west-facing foreground hill slope below the escarpment has shown a dramatic increase in woody cover with the most important contribution to this cover coming from Acacia karroo, Acacia nilotica, and to a lesser extent, Acacia caffra. Downloaded by [Timm Hoffman] at 23:12 19 January 2013 The broad-leafed tree, Tar- chonanthus camphoratus is also dominant. Other broa- d-leafed species include Cussonia spicata, Schotia brachypetala and Dovyalis caffra. The only common succulent trees are Euphor- bia triangularis and theoc- casional Opuntia ficus- indica. Although not in- spected closely, the grass sward on the slopes appears very sparse, with mainly torbs occurring beneath bushes. There has been a distinct gain in altitude of the tree line by about 50 m and it now extends above the escarpment onto the west and south-west facing mountain slopes. Even the peak in the background in 1998 has some woody elements on its upper slope, although they do not extend all the way around the right-hand side of the southem aspect of the hill. The extension of the tree line is due mainly to Acacia karroo and Acacia nilotica, although Tarchonanthus camphoratus, Euclea crispe, Coddia rodis, Lippia javanica are now also present. A relatively extensive bush clump is also starting to deVelop beneath one of the ridges of the escarpment. The relatively good fuel load and size structure of most of the trees renders their populations vulnerable to fire. However, there are now a number of larger adults that would not be affected. The ground cover is mostly Hyperrhenia hirta although there are many other species as well.