Notes on the Phytogeography and Flora of the Mountain Summit Plateaux of Tasmania Author(s): L. S. Gibbs Source: Journal of Ecology, Vol. 8, No. 1 (Mar., 1920), pp. 1-17 Published by: British Ecological Society Stable URL: http://www.jstor.org/stable/2255210 Accessed: 26-06-2016 20:21 UTC Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://about.jstor.org/terms JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. British Ecological Society, Wiley are collaborating with JSTOR to digitize, preserve and extend access to Journal of Ecology This content downloaded from 163.118.172.206 on Sun, 26 Jun 2016 20:21:33 UTC All use subject to http://about.jstor.org/terms VOLUME VIII MARCH, 1920 No. 1 NOTES ON THE PHYTOGEOGRAPHY AND FLORA OF THE MOUNTAIN SUMMIT PLATEAUX OF TASMANIA By L. S. GIBBS. CONTENTS. PAGE INTRODUCTION 1. Geological History . 1 2. Physiography . 2 3. Meteorology . 3 GENERAL PLANT FORMATIONS (i) Austral-montane flora of the Mountain Summit Plateaux 4 (ii) Mixed Forest of the West Coast . 5 (iii) Eucalyptus Formation of Australian Type A. Forest . 7 B. Open Forest . .8 C. Secondary Open Forest . .8 DESCRIPTION OF MO-UNTAINS . .10 (To be continued.) INTRODUCTION. Tasmania, a comparatively small island, about 27,000 square miles in area, lies on the S.E. of the Australian continent, where it is exposed on the west coast to the full sweep of the South Pacific gales, which, unintermittently blowing from west to east, know no break in land between Tasmania and Cape Horn. The northern coast is about 184 miles from that of Victoria' and an elevation of only 180 feet would suffice for broad bridges on which one could pass dryfoot from Tasmania to the Australian mainland2 . These shallow areas point to a former land connection, confirmed by geological evidence. 1. GEOLOGICAL HISTORY. The isolation is considered to have occurred in the later quaternary period during an era of subsidence accompanied by volcanic outbursts3. A glacial period subsequently intervened, during which "Tasmania must have formed an island of about three-quarters its present area, and there existed no land connection with Australia 4." "We can assume that during that time the climate was perhaps that of the Kerguelen Islands, with no vegetation to 1 F. Noetling. "The Antiquity of Man in Tasmania." Proc. R. Soc. Tas. 1910, p. 232. 2 F. Noetling. "Entwurf einer Gliederung der Jungterziiiren und diluvialen Schichten Tasmaniens." Zentralb. f. Min. Geol. und Pal. 1909, p. 10. 3 F. Noetling. "Ant. Man. in Tas." Loc. cit. p. 246, 4 F. Noetling. Loc. cit. p. 251. Journ. of Ecology VIII 1 This content downloaded from 163.118.172.206 on Sun, 26 Jun 2016 20:21:33 UTC All use subject to http://about.jstor.org/terms 2 Mountain Summit Plateaux of Tasmania speak of but moss and low shrubs'," then "Tasmania would have had an area of 18,000 square miles, one-third of which was under ice and snow2." 2. PHYSIOGRAPHY. It must be obvious to the most casual observer familiar with the re- sults of volcanic activity in other parts of the globe, that the country was formerly one huge plateau formed of horizontal lava flows. The present con- figuration has been determined by the subsequent erosion of these sheets of diabase; the graphic evidence is as conclusive for other parts of the country as Graham Officer3 has already described for the country round Lake St Clair. This plateau, as already shown, was glaciated, and huge glaciers stretched down into the valleys of the present time4. Progressive sub-aerial weathering and denudation accounts for the breaking down of the superimposed strata into tier upon tier of this greenstone country, and the now isolated groups of high tablelands. The diabase, or greenstone region, extends over the whole central portion of the island, from the West Coast mountains to Ben Lomond on the east, and Mts Field, Wellington and Hartz in the south; some of the so-called mountains being simply high tablelands of large extent with flat summit plateaux, while others are worn down to mere bilateral ridges and isolated peaks. In fact the whole sculpturing of this portion of the country is remin- iscent of Iceland, with its recent horizontal lava flows and the similar effects of glacial and sub-aerial denudation. In the present-day Tasmania is distinguished by three geological regions, viz. (1) The great Central Diabase or Greenstone Plateau, commonly called the Central Lake Plateau, about 2500-3300', from which the river systems of the island radiate, is more or less surrounded by the now isolated mountain summit plateaux, from 3500-5000', with which it was formerly connected. The rivers rise in the five large lakes, whence this high tableland derives its popular name, viz. Great Lake, 3300'; Lake Echo, 2500'; Lake St Clair, 2500'; and Lakes Sorell and Crescent, 2600'. (2) The West Coast. Composed of pre-cambrian schists, gneisses, granite and allied rock types5, in rugged mountain masses, whose summits do not exceed 4500'; these are simply high tablelands weathered in tiers, like the diabase mountain summit plateaux of the central and southern regions. The western region is characterised by an exceedingly heavy rainfall of over 150 inches. I F. Noetling. Loc. cit. p. 249. 2 F. Noetling. Loc. cit. p. 251. 3 Graham Officer. "The Geology of the Lake St Clair District." Proc. R. Soc. Tas. 1893, p. 156. 4 F. Noetling. Loc. cit. Zentrbl. Min. Geol. Pal. 1909, p. 9. 5E. C. Andrews. "Notes on the structural relations of Australasia, N. Guinea and N. Zealand." Journ. Geol. CIhtcajo, 24, 1916, p. 753. This content downloaded from 163.118.172.206 on Sun, 26 Jun 2016 20:21:33 UTC All use subject to http://about.jstor.org/terms L. S. G-IBBS 3 (3) The Lowlands and Uplands of the N. and N.E. Coasts, chiefly diluvial, forming undulating sandstone plains. 3. METEOROLOGY. The climate is temperate in character, judged by thermometric readings alone. Taking the following stations it will be seen that the variation in temperature is not great and compares favourably with places of equivalent position in the northern hemisphere1. Mean Yearly Locality Latitude Temperature Winter Summer range 0 , ft 0 0 0 0 Hobart 42 53 32 S. 54*41 46 8 61F95 15410 Edinburgh 55 58 N. 47 15 38 4 57 17 18 72 London 51 30 N. 50 83 39 50 62 93 23 43 Paris 48 50 N. 51F31 37 85 64 50 26 73 The rainfall varies. It is-heaviest on the West Coast, where the records for the mountain stations are: Mt Read, 165*77; Mt Lyell, 131-47; Zeehan, 122-71; Queenstown, 112-71 inches for the year 19172. For the Central Plateau, Interlaken, Oatlands and Ross on the east show 40-48, 37*32 and 29*11 inches respectively. The precipitation on the western portion of the Plateau is nearly three times that of the eastern portion3. There are apparently no records for the mountain summit plateaux, but the stations on Mt Wellington (Gap) and at the "Springs" at 2500' record 98-51 and 96*29 in. respectively, while Hobart, which lies at the foot of the mountain, shows 41*69 in. Scamander and Swansea on the sheltered and dry east coast have a total rainfall of 26*18 and 33*31 in. respectively, the latter corresponding more or less with Launceston on the north coast. Schenck4 has already emphasised that the nature of the plant covering is determined by the barometric and not the thermometric readings, for all the scattered austral lands of the sub-antarctic. He quotes Ross as being the first to observe that the character of the seas and islands geographically belonging to the south temperate zone, lies in the low summer temperature and the constant severe storms, in contrast to those of the north temperate zone with their mild climate and rich organic life. On the high tablelands and West Coast of Tasmania, winter and summer, the wind is incessantly from the N.W. to S.W. 5, with constant cyclonic disturbances, irrespective of seasons. A heavy swell always prevails round the West Coast. The constant precipitation of the storm driven clouds causes such excessive rainfall that the 1 Walsh's Tasmanian Almanac, 1918, p. 13. 2 Tas. Alm. pp. 14-15. 3 R. M. Johnston. "The Glacial Epoch of Australia." Proc. R. Soc. Tas. 1893, p. 95. 4 H. Schenck. "Vergleichende Darstellung der Pflanzengeographie der subantarktischen Inseln." Wiss. Erg. Deutsch. Tiefsee-Exp. ii. i. Jena, 1905, p. 7. 5 W. V. Legge. " Contribution to the Physiography of Tasmania." Pine, Island, Great Lake. 1902, P. 759. 1-2 This content downloaded from 163.118.172.206 on Sun, 26 Jun 2016 20:21:33 UTC All use subject to http://about.jstor.org/terms 4 ]oiotutain Summit Plateaux of Tasmania foothills and upper slopes of the ranges are clothed in a dense miixed forest, only the extreme summits being exposed. The north and north-east portion of the island, though more or less pro- tected from the prevailing west winds of the antarctic region by the West Coast mountains and the Central Plateau, resulting in a lesser rainfall, is however exposed during the summer to the hot north winds from Australia, and the vegetation consequently approximates to the Australian type.