Tuatara: Volume 25, Issue 1, July 1981
The Species Rich, Highly Endemic Serpentine Flora of New Caledonia
The Species Rich, Highly Endemic Serpentine Flora of New Caledonia
What is generally known as serpentine vegetation occurs in localised areas throughout the world on soils derived from ultrabasic rocks. Such soils provide a difficult medium for plants, being highly infertile with low levels of potassium, phosphorus and calcium and often high concentrations of iron and magnesium and the toxic metals nickel and chrome.
As a result serpentine vegetation often has a very different appearance from that of surrounding areas, with fewer trees, and more sclerophyllous shrubs, grasses and sedges.
In higher latitudes, such as northern Europe, serpentine floras are usually impoverished with relatively few individuals and species. It is sometimes assumed that this is true of serpentine floras generally but, as Whittaker (1954) has pointed out, those in middle and tropical latitudes can be floristically rich with many endemic species.
Whittaker investigated a 400 sq. km. serpentine area at about 42° North in Oregon, U.S.A. and recorded 113 species, which was comparable to the 101 species in adjacent non-serpentine vegetation. It is not clear how many serpentine endemics were present, but three species and four varieties are mentioned.
In New Zealand there are localised areas of ultrabasic rocks in the south and the north of the mountain axis of the South Island. At one such area of about 150 sq.km. at 42° South (Red Hills), 120 species have been recorded, but only a few species and varieties are considered to be serpentine endemics.
At Kerr Point, the northernmost tip of the North Island at about 34° South, there are a few square kilometres of ultrabasic rock from which 144 species have been recorded and of these 10 varieties and two species are endemic (Druce et al. 1979).
These examples of middle latitude serpentine vegetation, then, are floristically quite rich, but have relatively few endemic species or varieties.page 2
The different plant communities relate to soil types and altitude and include sclerophyllous shrub associations (maquis) (Figs. 2, 3); sedge associations, with or without shrubs; open forests dominated by conifers particularly species of Araucaria and Agathis (Fig. 4); and closed forests, mostly at higher moister altitudes, in which angiosperms predominate, including species of Nothofagus which commonly occur in distinct groves (Fig. 5).
Whittaker (1954) states “Most serpentine vegetations throughout the world appear to be dominated by some one or by some combination of three adaptable growth forms - coniferous trees, sclerophyllous shrubs, and grasslike plants.”
This is certainly true of New Caledonia. Conifers are prominent in most types of serpentine vegetation - Araucarias, of which New Caledonia has 13 of the 19 species in the genus, are particularly prominent and are a distinctive feature of many New Caledonian landscapes; podocarps too are well represented and include two unusual species - the small semi-aquatic Ducussocarpus minor with swollen trunk bases growing at stream and lake margins and the even more remarkable Parasitaxus ustus, the only known gymonsperm parasite, again a small shrub with an unusual reddish-purple colouration.
Sclerophyllous flowering shrubs are even more numerous, a number of them having relatively large, bright, red or yellow flowers.
Sedges are also conspicuous in some serpentine communities, particularly on swampy plains but also on drier hill slopes. Grasses however are uncommon, a puzzling feature of the New Caledonian flora.page 4
Recently Jaffré (1974a and b) has made detailed studies of serpentine vegetation in new Caledonia and in his account of the Koniambo massif he says:
“The vegetation of Koniambo, like that of other massifs of ultrabasic rocks in New Caledonia, is clearly distinguished from the vegetation which covers the surrounding sedimentary or basaltic terrain. This difference involves a change in the flora and a more marked diversification of the plant formations…”
The list of the species recorded (453 species, undoubtedly far from exhaustive) representing approximately 15% of the species of the New Caledonian flora, demonstrates the richness of the flora of Koniambo whose area is about 170sq.m. (less than 1% of the area of the territory). This floristic richness, which is even more remarkable in the case of certain massifs whose plant cover has been less degraded (Boulinda massif, the great southern massif) seems to be a general characteristic of the vegetation of ultrabasic rocks in New Caledonia.
“Almost all the species recorded on the Koniambo massif are New Caledonian endemics and the majority are only found on ultrabasic rocks.”
So, according to Jaffré, more than half the species on Koniambo, i.e. more than 200, are serpentine endemics. He was not able to be more precise as there is still no complete account of the New Caledonian flora. However, a Flora is now in progress and revisions of several families have been published. This enables an estimate to be made of the number of serpentine endemics among about a sixth of the estimated 3000 species in the flora.
In Table I the first six entirely woody groups, of which all except the Sapotaceae are known to have a long history in the southern hemisphere, have more than half their species as serpentine endemics with an average of 65.5%. Mostly fewer than a third of the species in each group occur on both serpentine and non-serpentine - average 20.5% and less than a quarter have not been recorded on serpentine - average 13.5%.
Thus of the total of 287 species in these six woody groups 184 are serpentine endemics.
The three remaining groups of mostly herbaceous plants have less than half their species serpentine endemics, considerably less in the cases of the Tubiflorae and Pteridophytes, with an average of 24.5%. The proportion of species occurring on both serpentine and non-serpentine is much higher with an average of 58%. As with the woody groups the percentage of species not recorded on serpentine is low, average 17.5%, although the Tubiflorae at 40% are relatively high.
Combining all the groups gives a total of 569 species of which 253 (44%) are serpentine endemics, 225 (40%) occur on both serpentine and non-serpentine and only 91 (16%) have not been recorded on serpentine.
It is appropriate to conclude this article with a further quotation from Jaffré from his account of the Koniambo flora - “In the light of this study it is reasonable to suggest that the occurrences of ultrabasic rocks, which occupy a third of the territory and are distributed in several isolated massifs, have played an important role in the differentiation of the New Caledonian flora, one of the richest and most distinctive in the Pacific”.
Druce, A. P., Bartlett, J. K., Gardner, R. O., 1979: Indigenous Vascular Plants of the Serpentine area of Surville Cliffs and adjacent Cliff Tops. Tane 25; 187-206.
Jaffré, T., 1974: La Végétation et la Flore d'un Massif de Roches Ultra-basiques de Nouvelle Calédonie: Le Koniambo. Candollea 29: 427-456.
Jaffré, T., Latham, M., 1974: Contribution a l'étude des Relations Sol-Végétation sur un Massif des Roches Ultrabasiques de la Cote Ouest de la Nouvelle Calédonie: Le Boulinda. Adansonia ser. 2, 14: 311-336.
Whittaker, R. H., Walker, R. B., Kruckeberg, A. R., 1954: The Ecology of Serpentine Soils. Ecology 35: 258-288.
1 + serpentine endemic: ° serpentine and non-serpentine; - non-serpentine.
2 Revision in progress (Dawson)
3 Acanthaceae, Bignoniaceae, Boraginaceae, Solanaceae.