A preliminary account of aerial plant biomass in fynbos communities of the Mediterranean-type climate zone of the Cape Province

Aerial plant biomass has been sampled by harvesting on several sites in fynbos communities of the south­ western Cape Province. Biomass in stands of about two years old ranged from about 2 200 kg per ha to about 7 500 kg per ha. Mature stands comprised about 11 000 to 15 000 kg per ha in heaths and 15 000 to 26 000 kg per ha in sclerophyllous scrub. The data indicate a maximum annual growth rate of 1 000 to 4 000 kg per ha early in the develop­ ment of a stand, but growth rates appear to decline rapidly as communities age. Young stands are dominated by hemicryptophytes, which comprise about 2 000 to 6 000 kg per ha, or about 60 to 75 per cent of the biomass in stands of about four years old. Shrubs become prominent later, but the hemicryptophytes persist. The data indicate that the biomass, growth rates and the shape of the growth curves of fynbos communities are on the whole similar to those of analogous vegetation in other zones of mediterranean type climate. However, there are important structural differences in that analogues of the northern hemisphere (garrigue, chaparral) do not have a significant component of persistent hemicrytophytes. Although Australian heath communities do have this feature, the hemicryptophytes are not as prominent as in fynbos.


R E S U M E R A P P O R T P R E L IM IN A IR E S U R L A B IO M A S S E D E L A V E G E T A T IO N A E R IE N N E D A N S L E S M A Q U IS (F Y N B O S ) D E L A Z O N E C L IM A T IQ U E D E T Y P E M E D IT E R R A N E E N E N P R O V IN C E D U C A P
On a obtenu un echantillonnage de la bio masse de la vegetation aerienne en en recolt ant a divers endroits du maquis (fy n b o s) du sud-ouest de la Province du Cap.
Les donnees indiquent que la biomasse, les taux de croissance et la fo rm e de la courbe de croissance de ces maquis sont au total semblables a celles des associations vegetales analogues dans d'autres zones du type climatique mediterraneen.Neanmoins, il y a d'im portantes differences structurelles en ceci que les analogues de Vhemisphere N ord (garrigue, chaparral) n'ont p a s une constituante significative de sem i-cryptophytes persistants.Bien que les associations de bruyeres australiennes possedent cette caracteristique, les sem i-cryptophytes n 'y sont p a s aussi importants que dans le fynbos.

IN TRO D U C TIO N
The ecology of natural communities of Mediterranean-type ecosystems has recently received con siderable attention, particularly from the point of view of ecosystem convergence, and much more information on plant communities has become avail able (Specht, Rayson & Jackman, 1958, and previous papers;Specht, 1969aSpecht, , 1969b;;Jones et al., 1969;Mooney et al., 1970;di Castri & Mooney, 1973).However, few data on the Cape fynbosf have reached the press.
In this paper data have been collated on the biomass of fynbos communities, which have become available during the course of ecological studies from 1967 to 1974.The studies were not aimed at measuring com munity production nor are the data such that they may be used as direct measures of productivity.Nevertheless, they represent an index of productivity and contain other useful information.

STUDY AREAS
Biomass surveys were conducted on various sites in three research areas, each described below.1. Jonkershoek Forest Research Station (sites 1.1-1.4).The research area at Jonkershoek is situated at about 33°57'S and 18°55'E.The ecosystem has been * Jonkershoek Forest Research Station, Stellenbosch.+ Also known as sclerophyll bush (Adamson, 1938), and including the types described by Acocks (1953) as Macchia, False Macchia and Coastal Macchia.
described by Wicht et al. (1969).The communities sampled are situated on the slopes and near the bottom of a steep-walled valley (Fig. 1) and occur on soils derived from Cape granites.Soils are about one metre deep with a brown structureless loam A-horizon on a yellow-brown apedal B. They are acid, with pH ranging from about 4,50 to 5,00.Extractable phos phorus (citric acid extract) amounts to about 12 to 40 p.p.m. and total nitrogen and organic carbon con tent amount to 0,1 to 0,2 per cent and three to eight per cent respectively, in the A-horizon (Joubert, 1965).2. Zachariashoek Research Catchment (sites 2.1-2.3).This catchment research area is situated at 34°49'S and 19°02'E and has been described by van der Zel (1974).The communities studied are situated in the Kasteelkloof subcatchment (Fig. 2).Soils are derived from sedimentary orthoquartzites and shales of the paleozoic Table Mountain Group.The soils here have not been studied, but would resemble those at Jakkalsrivier rather than those at Jonkershoek.Site 2.2 is phreatic and the soil has an organic A-horizon.
Few climatic data are available.Rainfall at the top of the catchment amounts to about 1 300 mm per annum, and at the bottom, 1 100 mm per annum (six-year records at 701 m and 274 m a.s.l., respect ively).3. Jakkalsrivier Research Catchment (sites 3.1-3.10).
Plathe & van der Zel (1969) and Kruger (1974) have described the Jakkalsrivier area in some detail (Fig. 3).It is centred at 34°09'S and 19°09'E.Soils are derived from the orthoquartzites and shales of Table Mountain Group.In most cases, these are coarse rocky sands with a humic A-horizon, dystrophic, with pH ranging from 3,5 to 5,0, total exchangeable cations from 0,2 to 7,9 me/100 gm, and cation exchange capacity from 0,5 to 44,0 me/ICO gm.Base saturation is very low.Phosphorus is present at about one to four parts per million (Bray No. 2 extract).Total nitrogen ranges from 0,01 to 0,1 per cent, and organic carbon from about two to four per cent, in the A horizon.
The principal climatic features of Jonkershoek and Jakkalsrivier are illustrated by means of Walter dia grams (Walter, 1963) in Fig. 4. The mean total radia tion for the region is 450 to 500 cal per square centi metre per day.Table 1 summarizes the principal physical features of the sample sites, and includes names of plant communities.Fosberg's (1967) struc tural-functional classification was used and refers to the mature community.Community names based on character species are given where possible and are those assigned in prior studies (Kruger, 1972;1914).Figs. 1, 2 and 3 illustrate typical communities.

M ETHODS
Communites which appeared structurally homo geneous were selected for sampling.Stratified random sampling was used wherever conditions permitted, and in these cases a ranked-set sampling procedure (Halls & Dell 1966) was followed.Most samples were collected in late summer or early autumn, when the communities are nearly dormant.Successive harvests were completed on sites 2. 1, 2.2, 2.3, 3.1, 3.2, 3.3, 3.4, 3.5 and 3.6.Biomass was determined by clipping aerial plant parts from one-metre-square quadrats in all cases except site 1.1, where 0,5 m2 plots were used, and the six-year stand at 2.2, where 2 ,5 x 2 ,5 m plots were used.In most cases an apparatus described by Hetherington (1967) was used to define the cylinder within which material was collected.Plants were   Mesophyllous open evergreen broad-sclerophyll scrub; clipped as close to the soil surface as possible, using secateurs.If litter was present in significant quantities, it was collected by raking the soil surface with the fingers.Dead plants were included as litter.Clipped material was segregated into growth-form categories 1 during the clipping routine.The plant material was £ stored in 2 mm-mesh plastic-coated fibre-glass gauze °' bags and hung in a well-ventilated place until it * could be treated in the laboratory.# The categories used for the segregation of clipped * material are detailed below.s (i) Shrubs: microphanerophytes and nanophanerophytes of families such as Proteaceae, Ericaceae and Leguminosae.
(v) Herbs (forbs): non-ligneous elements not in cluded in above categories, and including ferns.
In the laboratory the fresh mass of the contents of each bag was determined before the material was chopped mechanically in lengths of 0,5 to 3,0 cm.A sample of four 50-100 gm units was drawn from the chopped material after thorough mixing.The moisture content of these was determined by normal oven-drying procedures (105°C for 24 hours).The mean moisture content of the subsample was used to estimate the oven-dry mass of the original material.
Table 2 includes the 'age' of the communities.This represents the time since the last burn and closely approximates the real age of the shrubs that have regenerated from seed.Age was determined from Department of Forestry records or, where this was not possible, by node-counts on Proteaceae as described by van der Merwe (1969).2.

Sample efficiency
The coefficients of variation for total biomass shown in Table 2 clearly indicate that, in many cases, random samples of clipped quadrats need to be large for reasonably precise biomass estimation.The number of sample units used here was seldom adequate to ensure a confidence interval equal to or less than 20 per cent of the mean, at five per cent probability of error.For a confidence interval of 20 per cent of the mean, about thirty to sixty quadrats would be required (and in some cases a great deal more).Furthermore, the samples were not large enough to show a signifi cant difference (at P = 0,95) between harvests in suc cessive years on the same site, though the vegetation had obviously grown.
These estimates are much less precise than those reported by Jones & Specht (1967) and Jones (1968), who obtained estimates with 95 per cent confidence interval of about 12 per cent of the mean, using 12 to 20 one-metre-square quadrats.These authors con cluded that successive harvests were not appropriate in production studies in heath.
Since the information reported here was collected with the aim of monitoring long-term trends in 20000 10000 5 0 0 0 biomass, it was not thought profitable to improve precision by increasing sample size.Nevertheless, future studies would benefit if larger quadrats were used.Where greater precision is required and alter native techniques of production measurement (such as gas-exchange measurement) are not feasible, a combination of sampling by vegetation strata and allometric subsampling of dominant species popula tions should solve some of the problems due to heterogeneity in fynbos communities.
Precision in these data sets is felt adequate for the purposes of this discussion.

Rates o f growth
Fig. 5 may be used to indicate means and ranges in the rate of growth of fynbos communities.The data do not cover a full range of fynbos communites: old stands of tall sclerophyllous scrub are hardly represented.Nevertheless, a reasonable picture has emerged.The highest rate was exhibited by the phreatic community at site 2.2-about 4 000 kg per ha per annum during the first two years.In contrast, the heath community in the same locality, at site 2.3, grew at about 1 000 kg per ha per annum during the same period.These values are close to the upper and lower limits of mean annual increment represented by the curves in Fig. 5.A rate of 2 500 kg per ha per annum appears to be a reasonable average.
Growth rates appear to fall off rapidly as com munities age.
Sclerophyllous scrub (represented by sites 1.1 to 1.3) would seem to grow about as fast as the phreatic community, although that at Jakkalsrivier (site 3.5) appears subnormal.Heath communties show rates between normal and the minimum.

Fynbos as fu el
Fynbos communities readily sustain a running fire under average summer conditions once they have reached four years of age and may burn at three years under severe fire hazard conditions.
Several communities of about four years old have been sampled.These had biomasses of about 5 000 to 10 000 kg per ha, which may be accepted as reason able minimum fuel levels for a successful burn.Site 3.4, with about 7 000 kg per ha at four years, sustained a hot fire in a prescribed burn 11 months later.
At four years of age most communities are domin ated by graminoid and restioid plants.These are all fine fuel (i.e. with particle diameters less than six millimetres).
Furthermore, cured material forms a significant proportion of the fuel after the second or third year when leaves and stems from the first and second growing seasons die, but remain attached and erect for a further one or two seasons.At this stage, therefore, the vegetation provides a fine, porous but reasonably compact fuel bed, much like a grass land fuel.This would explain why they burn readily at this age in spite of the rather small quantities of available fuel.
The rapid rate of growth of a phreatic community like that at site 2.2 does not necessarily imply inflam mability at an earlier age.Plant material in such com munities is green and does not cure readily in the early stages: in fact, an inflammable stage is often delayed longer than in other communities.
Heaths from Jakkalsrivier have a low biomass (11 000 to 15 000 kg per ha at 16 years), but dead plants and litter can comprise up to a quarter of the total.As a result, and because the communities are dominated by plants with fine leaves and branches, they burn fiercely under dry conditions, and fires are often extremely difficult to control.
The mature sclerophyllous scrub communities at Jonkershoek provide considerably more fuel, but much of this is coarse and available only under extreme fire hazard conditions.

Community structure and development
Most plants in the fynbos sprout after fire (Wicht, 1945;van der Merwe, 1966).The graminoid and restioid plants are almost all of this nature, whereas many shrubs and subshrubs are not.Communities in the early stages are dominated by the former (which comprise about 60 to 75 per cent of the biomass at three to four years) and the vegetation has the phy siognomy of a grassland.Since individual shoots and leaves of the hemicryptophytes do not live longer than about two years, and fall after another two years, this component reaches its maximum in about the fourth year.Thereafter woody elements become prominent if conditions are suitable, although herbs persist and maintain their biomass for many years.Communities on moist or wet sites (as at 2.2 and 3.3) have a rather different initial physiognomy, since they frequently contain a high proportion of sprouting shrubs, which reach early prominence in develop ment.
C O N CLU SIO N Considerable data on growth and biomass of shrub communities in mediterranean type ecosystems have become available recently.Specht (1969aSpecht ( , 1969b) has compared analogous communities from the southern regions of France, California and Australia.He estimated mean annual increments (M.A.I.) for the first five years after fire, as follows: Maximum biomass reported was about 49 700 kg per ha at 13 years for garrigue, and 49 100 at 37 years for chaparral (of which 21 800 kg consisted of standing dead sticks).
Specht suggests that his data for the garrigue near Montpellier are atypical, and this is confirmed by Long & Thiault (pers. comm.).Data from more typical garrigue indicate a mean annual increment of about 1 400 kg per ha per annum during the first six years, and total biomass of about 15 000 kg per ha at 18 years (Long et al., 1967in Specht, 1969b;Long & Thiault, pers. comm.).These also show that the garrigue growth curves also resemble the typical cases illustrated by Specht (1969b) and Jones et al. (1969).
Aerial biomass of an evergreen chaparral communi ty of unspecified age at Echo Valley, California (mean annual precipitation 450 mm) amounted to 23 000 kg per ha; that of a similar community on a similar site in Chile amounted to about 7 400 kg per ha (Mooney, pers.comm.).
Jones et al. (1969) have collated growth data for Australian heath communities.They produced two curves for growth of aerial portions of the com munities, one representing the drier and the other the wetter limits of the geographical range of heat in Southern Australia.Growth rates during the first five years amount to about 800 kg per ha per annum in the first instance, and 1 500 kg per ha per annum in the second.Maximum biomass for coastal sites was about 16 000 kg per ha at 18 years (sand heath at Tidal River, Victoria).They caution that: " The growth curves do not necessarily indicate the maxi mum production of each site.This may be influenced by the development (or invasion) of taller-growing species . . .." .Such cases are reported by Specht et al. (1958).Communities dominated by Banksia ornata have a biomass of almost 20 000 kg per ha at 15 years of age.
The data for fynbos are similar to those for analo gous communities in other areas with mediterranean type climates.The curves in Fig. 5 indicate a mini mum rate of growth of about 1 000 kg per ha per annum, and a maximum of 3 400, over the first five years after fire.The most vigorous community is that on the phreatic site (2.2), but the maximum biomass measured is that of a 17-year old sclero phyllous scrub community at Jonkershoek: this is about the same as that of the 18-year old chaparral community sampled by Specht.The mature heath communities at Jakkalsrivier, however, have a lower biomass than all those of equivalent age studied elsewhere except the mallee-broombush (Specht, 1969b), which is not a good fynbos analogue.
On the whole the figures support Specht's conclu sion that "The growth rates of these distinctive plant communities, composed of entirely different species, are largely controlled by the major factors-solar radiation and available water.In similar homoclimes essentially the same growth rate results."More infor mation is necessary to explain differences within the data sets, but there is good evidence that soil moisture availability overrides the effect of soil fertility, and that community production is strongly affected by the presence or absence of tall long-lived shrubs, at least in Australia and South Africa.
Data for the biomass of growth-form categories in fynbos stands provide a limited basis for comparisons of community structure.They do indicate that persistent perennial herbs, particularly hemicryptophytes, are a feature which distinguishes fynbos from northern analogues.Chaparral is known for the rich herbaceous annuals which appear after fire, with peak abundance within one to five years, and disappear almost completely thereafter (Sweeney, 1956;Vogl & Schorr, 1972;Mooney & Parsons, 1973;Biswell, 1974).These comprised 75 and 14 per cent respectively of total live biomass in oneand three-year old chaparral sampled by Specht (1969b), but were absent in the nine-year old stand.
The herbaceous flora of the mediterranean maqui and garrigue also respond strongly to fire, but include perennials which persist in old stands in small quanti ties (Naveh, 1974;Long & Thiault, pers. comm.), though their biomass is never large.The communities studied by Specht were dominated from the start by phanerophytes and chamaephytes: herbs amounted to 30 per cent of total biomass in the first year after fire, of which hemicryptophytes contributed about 500 kg per ha or 10 per cent of total biomass.The hemicryptophytes became insignificant after the sixth year of development, but other herbs persisted.
Long & Thiault report that biomass of herbs may often be over 10 per cent of the total in the first year.
In fynbos, herbs contribute up to about 4 500 kg per ha after two growing seasons; as noted, hemi cryptophytes dominate communities up to at least four years after burning.Herbs in sixteen-year old heaths have biomasses up to 8 000 kg per ha, with restioid and graminoid plants predominant.
Australian communities are similar in this respect, but the perennial herbaceous component is not as large as in fynbos.Data from a " sand heath" at Frankston, Victoria (Jones & Specht, 1967;Jones, 1968) show that hemicryptophytes (Restionaceae and Cyperaceae) reached a maximum of about 2 100 kg per ha at four years, comprising about 32 per cent of the biomass.At eight years the proportion was 26 per cent.Comparative studies on Wilson's Pro montory in the same State (Groves & Specht, 1965) showed that hemicryptophytes in a " wet heath" had twice the mass of those in a " sand heath" (2 000 vs 1 000 kg per ha), but persisted in old (twelve-year) stands in both cases.Specht et al. (1958) noted, of Dark Island " sand heath", that certain understorey plants including hemicryptophytes regenerate rapidly after fire and persist for 25 years in the ageing com munity.Some Restionaceae and Cyperaceae continue to increase as the community develops, but the bio mass of the herbaceous elements does not appear to have exceeded about 1 000 kg per ha.
Certain Australian communities of infertile soils, such as the Gymnoschoenus hummock sedgelands or " Button-grass plains" and Restionaceous sedgelands of Tasmania (Jackson, 1965;1972;Paton & Hosking, 1975) and forb heaths of Southern Queensland (Coaldrake, 1961) have a high proportion of perennial hemicryptophytes, and resemble fynbos in this way.
Fynbos and the Australian equivalents therefore have a characteristic persistent herbaceous com ponent, which distinguishes them from analogous shrublands elsewhere, but they differ in that the component is more prominent in the former.Most of the field work was undertaken by research foresters of the Jonkershoek Forest Research Station.In this connection, the work of Ross Haynes and Maarten van der Riet was invaluable, as was their assistance in the preparation of this paper.
Dr G. Long and M. M. Thiault of the Cepe, M ont pellier, very kindly supplied new information on garrigue biomass and composition.Prof. R. L. Specht provided useful comment on the manuscript.

Biomassa van opstande met 'n ouderdom van ongeveer twee ja a r wissel van omtrent 2 200 kg per ha tot
alter diagrams for Jonkershoek (M anor House Station) and Jakkalsrivier (M ain Station).

A
CK N O W LED G EM EN TSThis report is based on work undertaken as part of the catchment conservation research programme of the South African Department of Forestry and published with the permission of the Secretary for Forestry.