FORUM 51

FORUM

SOME DIFFERENCES BETWEEN OF THE AND THE

R.M. GREENWOOD 107 Atawhai Road New Zealand

A number of plants show less wind than the adults, and other things being equal, morphological differences from related plants on one would expect the leaves of juvenile plants to be mainland New Zealand. These differences could larger, but on the New Zealand mainland this is not the have arisen as a result of freedom from brows- norm. In fact a number of New Zealand forest plants ing on the Chatham Islands. A possible test for this have markedly smaller juvenile leaves, for example, hypothesis is suggested. Hoheria sexstylosa, and the lianes Rubus schmidelioides, Passiflora tetrandra, Parsonsia Keywords: Chatham Island plants; moa browsing; heterophylla and australis. The last of juvenile forms. these also occurs on the Chatham Islands, and the form there does not have the small-leaved juvenile so Some differences between Chatham Island and New characteristic of the New Zealand mainland plants. Zealand mainland plants are fairly widely known: the propinqua var martinii, which grows in presence of several endemic large-leaved herbs on the open wet areas on the Chatham Islands, has small leaves Chatham Islands (the forget-me-not Myosotidium and dense branching but the branching angle is hortensia*, the sow thistle Embergeria grandifolia, and somewhat less than that characteristic of most mainland Aciphylla dieffenbachii), the lack of divaricating forms of the species, so that the branches remain juvenile forms in the Chatham Island ribbonwood separate. Coprosma acerosa growing on Chatham (Plagianthus) and kowhai (Sophora), and the juvenile Island sand has more open and less interlaced hoho (Pseudopanax chathamicus) not having the stiff branching than mainland forms of the species. Another deflexed leaves so characteristic of the juvenile showing differences from New Zealand mainland lancewood on mainland New Zealand. A recent first plants is Aciphylla traversii. It is now rare as a wild visit of one week to 'the main Chatham Island not only plant because of browsing by cattle, and I did not see it. brought home these differences to me but' also let me It has leaves somewhat similar in form and appearance see several other morphological differences not widely to some mainland Aciphylla species, but not sharply reported. pointed (Atkinson and Greenwood, 1989). The juvenile nikau (RhopaJostylis) has much It seems reasonable to assume that where related broader "leaflets" giving the plants a very distinct, plants occur on the Chatham Islands and on the New more leafy appearance. The Chatham Island form of Zealand mainland, the Chatham Island plants would Phormium tenax has leaves somewhat broader and not have originated from the mainland, and differences in as stiff as the mainland forms with the tops of the leaves morphology that have arisen would reflect bending over in a similar way to Phormium cookianum. environmental differences between the Chatham Islands Three Chatham Island forest trees ( and mainland New Zealand. One environmental factor arboreum, Coprosma chathamica (Dawson, 1991), and on mainland New Zealand in the past which did not Pseudopanax chathamicus) have juvenile forms with occur on the Chatham Islands was browsing by moa and leaves markedly broader than the adult. Juveniles of some other leaf-eating birds (Atkinson and Millener, forest trees and lianes in all forests grow under 1991). All the morphological differences noted above conditions of much lower light, greater humidity and could have evolved as a result of freedom from moa browsing on the Chatham Islands. This is also *Nomenclature follows Connor and Edgar (1987) and sources consistent with the devasting effect domestic stock have therein. on Chatham Island forest vegetation, where no juvenile

New Zealand Journal of Ecology (1992) 16(1): 51-52 ©New Zealand Ecological Society 52 NEW ZEALAND JOURNAL OF ECOLOGY, VOL. 16, NO. 1, 1992

woody forest plants appear to show any resistence to browsing by mammals. Among the large-leaved herbs, References Urtica australis stands out as being one species resistent Atkinson, I.A.E.; Greenwood, R.M. 1989. Relationships to browsing, although it has few stinging hairs. between and plants. In: Rudge, M.R. If lack of moa browsing in the past is the reason for (Editor), Moas, mammals and climate in the the morphological differences of the Chatham Island ecological . New Zealand plants, it seems likely that these plants would be better Journal of Ecology 12 (Supplement): 67-96. adapted than mainland forms to growth under forest Atkinson, I.A.E.; MilIener, P.R. 1991. An ornithological conditions in the absence of browsing. This could be glimpse into New Zealand's pre-human past. Acta tested for by growth rate comparisons under reduced XX Congressus Internationalis Ornithologici: 127- light. 192. Differences in chemical constituents and Connor, H.E.; Edgar, E. 1987. Name changes in the palatability may also have arisen and could be tested indigenous New Zealand flora, 1960-1986 and for. Is chathamica (now uncommon as a wild Nomina Nova IV, 1983-1986. New Zealand plant because of browsing by introduced mammals) Journal of Botany 25: 115- 170. actually more palatable than related mainland species Dawson, J.W. 1991. New Zealand botany with a such as Astelia grandis or A fragrans? Is the juvenile difference - the Chatham Islands. Tuatara 31: 23- broad-leaved form of more 42. palatable to mammals than mainland Dracophyllum species? It certainly appears to be relatively palatable from observations along a reserve fenceline.

Acknowledgements This study could not have been undertaken without the "Checklist of vascular plants on Chatham Islands", compiled by A.P. Druce.