FYNBOS: HERITAGE AT OUR FEET

Cape Floral Kingdom

The Cape Floral Kingdom (CFK) is one of six globally recognized plant kingdoms and occurs in South Africa in the Western Cape Province extending eastwards into the Eastern Cape Province [16]. The Cape Floral Kingdom is the smallest of all six kingdoms and is highly unique as it is the only one fully contained within a single country and is characterized by a high diversity, 8700 plant species, and high endemism, 68% of it’s plant species are confined to this kingdom 90 000km2 large [5]. The CFK consists of the five biomes namely: fynbos, renosterveld, succulent karoo, sub-tropical thicket and afromontane forest [4]. Fynbos is the dominant vegetation of the CFK as 80 percent of the CFK consists of fynbos [8].

Fynbos is evergreen, sclerophyllous shrubland [11] that occurs on nutrient poor soil of the Cape Fold Belt Mountains. It consists of four characteristic growth forms namely proteoids (tall protea shrubs with large leaves), ericoids (heath-like shrub), restiods (reed-like plants) and geophytes (bulbous plants) [4]. The presence of restoid is a distinguishing feature of fynbos as it is always present whereas proteoid and ericoids may be rare and geophytes only appear in winter [8].

Fynbos Biome

There are key biotic and a biotic factors that determine the fynbos distribution, these factors include: summer drought and winter rainfall (mediterranean type climate), low soil nutrients and recurring fire and wind, however, summer drought is a variable component over the South African landscape as it is much more intense in the west than in the east [8]. Biomes are climatically defined but the fynbos biome is not, as the their presence is determined by the absence of nutrients in soils on which they occur [12]. Quartzites and sandstones yield infertile soils whereas the softer shales are more fertile [8]. Fire is a “keystone factor in the long term survival of fynbos” as it plays a major role in its cycle of “destruction, regeneration, maturation and destruction again” [8]. Fire has placed a selective pressure over fynbos and in response small animals and plants have evolved in order to survive. It is not just the physical characteristics of the fire that has such a major influence on fynbos but the complex fire regime i.e. the time lapse between fires, the season in which it burns and the intensity and area it covers [8].

The Origin of Fynbos

Approximately 65 million years ago the present fynbos region was covered with tropical vegetation, ancestral fynbos forms included representatives from the: Proteaceae, Ericaceae and Restionaceae families and were restricted to mountainous areas [8]. Mountains were built of erosion- resistant sandstone that resulted in nutrient poor soils that could have supported heath land-like vegetation [10]. Some CFR palaeoendemics from this era seem to have survived through shelters provided by mountain peaks capturing moisture [14].


About 35 million years ago the climate transformed into a drier and colder type, allowing a form of woodland to occur, this dry period was brought to an end again by the return of a warm moist-tropical period [8]. Then approximately 20 million years ago one of the most historical events in the origin of fynbos occurred, the development of the cold cicum-Antarctic current [8].



This resulted in the complete glaciations of Antarctica approximately 10 million years ago and the formation of the cold Benguela current that ran along the South-Western coast of Africa (Figure 1) [10]. These conditions caused the Mediterranean climatic system typical of the fynbos region as summer-rainfall got blocked off leaving only winter rain [10]. This climatic system was not in favour to the present tropical flora that inevitably became extinct leaving open habitats that the mountainous heath vegetation then occupied [10]. Modern species then radiated from these ancestral lineages, the aridification of the region together with the increase in the fire occurrence played pivotal roles in fynbos diversification [8].

Figure 1:A timeline showing changes in the species diversity and the proportion of area occupied by modern fynbos species [10].

Evolution of Fynbos

This level of endemism observed amongst fynbos vegetation is typically found on islands and is due to the particular geology and geomorphologic evolution of this area: sandy, nutrient poor, acid soils from sandstone and quartzite of the Table Mountain and Wittenberg Groups form the mountains of the Cape Folded Belt tend to be rich in endemism by promotion of speciation [14]. The rugged mountains provided multiple combinations of aspect, substrate and altitude and therefore a vast array of niches for plants to occupy therefore promoting species diversification through niche specialization. Another observation is that the particular location and orientation of the Cape Mountains at the southern tip of Africa favoured speciation as it cut off gene flow from surrounding areas therefore maintaining a “distinct floristic identity” [14].

Adaptations of Fynbos

One important adaptation of fynbos is the high incidence of schlerophylly [12], schlerophyllous plants are hard as they contain ligin that allows plants to resist dry conditions by preventing wilting. Lignin also allows these plants to grow in phosphorus deficient soils (a major nutrient nutrients scarce in the soils) even when phosphorous is lacking for substantial cell growth. In fire-prone ecosystems many plants possess traits that increase their flammability, scherophylly aids in flammability of the vegetation, essential to fynbos as fire is an integral ecosystem process [13].

As mentioned earlier, fire is a major ecological and selective agent in this vegetation as a correct fire regime plays an integral part in fynbos plants and their future generations [7]. Fynbos have adapted to fire by becoming reseeders, which complete their life cycle within a time period and produce seeds (normally fire-protected), or as resprouters [7].

Many fynbos species have established specialized root systems in order to adapt to poor nutrient soil status; root systems include: proteoid roots and versicular arbuscular mycorrhizal root systems [3]. Adaptations of roots have been observed in fynbos plant species, namely mycorrhizal infected and proteoid (cluster) roots. These nutrient aquiring adaptations increase species diversity in the Fynbos biome by promoting co-existence of mycorrhizal and non-mycorrhizal families [1].

Mycorrhiza is a form of mutualism between roots and soil fungi and two forms exits namely: ectomycorrhizde and endomycorhizzae, the hypae of endomycprrhizae develop extensively within the cortical cells of host roots; vesicular-arbuscular mycorrhiza (VAM) is a form of endomycorhizzae and 62% of flora found with the CFK form VAM [1]. Endomycorrhizas have been found in abundance in certain fynbos plants namely in Ericaceae species [8]. Members of the Rosidae family also possess VAM [3].

Proteaceae and Restionaceae are perennial families that dominate in older fynbos vegetation and contribute a large biomass that does not form mycorrhizal roots but develop proteoid roots (Figure 2) [2]. Most members of the Proteacea family are able to survive and flourish on substrates, typical to that of fynbos, indicating proteoid roots are also a highly effective mechanism for metabolic absorption [15].



Figure 2:A proteoid root formation on a protea plant, also named cluster roots for its obvious appearance [6].

Numerous pollination adaptations have also been observed in the fynbos area but special mention has to made about the Ericaceae family that have the most astonishing display of floral attractions [8]. Ericas are highly adapted to their specific pollinators and attractions come in the form of many visual and olfactory cues.

Adaptations to two ecological drivers namely: soils with a low nutrient status and fire are clearly evident in the Fynbos biome. Fynbos’ extremely high diversity and endemism emphasises its success. Root, fire and pollination adapatations are just a few general mechanisms that have allowed Fynbos to become so successful in such a harsh environment.

References:
1. Allsopp N and Stock WD (1993) Mycorrhizal status of plants growing in the Cape Floristic Region, South Africa. Bothalia 23(1): 91-104


2. Allsopp N and Stock WD (1994) VA mycorrhizal infection in relation to edaphic characteristics and disturbances regime in three lowland plant communities in the South-Western Cape, South Africa. Journal of Ecology 82:271-279

3. Allsopp N and Stock WD (1995) Relationship between seed reserves, seedling growth and mycorrhizal responses in 14 related shrubs (Rosidae) from a low nutrient environment. Functional Ecology 9:248-254

4. Anon. Cape Floral Kingdom [Internet]. [Cited 2007 Mar 23] Avaliable from:
http://www.oceansafrica.com/floralkingdom.htm

5. Anon. Fynbos Biome [Internet]. [Cited 2007 Mar 23] Avaliable from:
http://www.plantzafrica.com/vegetation/fynbos.htm

6. Anon. Phytogen [Internet]. [Cited 2007 Mar 23] Available from: http://www.plantsci.org.au/Phytogen/PhytApr01.html

7. Barraclough TG (2006) What can phylogenetics tell us about speciation in the cape flora?.Diversity and Distributions 12:21-26

8. Cowling RM and Richardson D (1995) Fynbos:South Africa’s Unique Floral Kingdom.Fernwood Press, Vlaeberg ,pp 21-40;46-49. ISBN 1-874950-10-5

9. HigginsKB,Lamb AJ and Wilgen (1987) Root systems of selected plant species in mesic mountain fynbos in the jonkershoek valley, south-western cape province. South African Journal of Botany 52(3): 249-257

10. Linder HP and Hardy CR (2004) Evolution of the species-rich cape flora. The Royal Society 359:1623-1632

11. Moll EJ, Jarman (1984) Classification of the Term Fynbos. South African Journal of Sicence 80:351-352

12. Moll EJ, Jarman (1984) Is Fynbos a Heathland. South African Journal of Sicence 80:352-354

13. Schwilk DW and Kerr B (2002) Genetic niche-hiking:an alternative explanation for the evolution of flammability.OIKOS 99:431-442

14. van Wyk A and Smith GF (2001) Regions of Floristic Endemism in Southern Africa: A review with emphasis on Succulents. Umdaus Press, Hatfield, South Africa, pp23-25. ISBN 1-919766-20-0

15. Vorster PW and Jooste JH (1986) Potassium and phosphate absorption by exised ordinary abd proteoid roots of the Proteaceae. South African Journal of Botanty 52(4): 277-282

16. Wikipedia Contributors. Cape Floristic Region [Internet]. [Cited 2007 Mar 13] Available from:
http://en.wikipedia.org/wiki/Cape_floristic_region