Structural and Floristic Variation in the Forest Communities of the West Tamar, Tasmania
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Papers and Proceedings of the Royal Society of Tasmania, Volume 117, 1983. [ms. received 3.9.1982) STRUCTURAL AND FLORISTIC VARIATION IN THE FOREST COMMUNITIES OF THE WEST TAMAR, TASMANIA. by M.J. Brown and R.T. Buckney N.P.W.S., P.O. Box 210, Sandy Bay, Tas. 7005 and School of Life Sciences, N.S.W. Inst. Tech., P.O. Box 123, Broadway, N.S.W. 2007. (with three tables and five text-figures) ABSTRACT BROWN, M.J. & BUCKNEY, R.T., 1983 (31 viii): Structural and floristic variation in the forest communities of the West Tamar, Tasmania. Pap. Proc. R. Soc. Tasm., 117: 135- 152. https://doi.org/10.26749/rstpp.117.135 ISSN 0080-4703. National Parks & Wildlife Service, P.O. Box 210, Sandy Bay, Tasmania and School of Life Sciences, N.S.W. Institute of Technology, P.O. Box 123, Broadway, New South Wales. The forest communities in the West Tamar were sampled by a stratified random process using 55 plots selected after preliminary analy sis of 243 Forestry Commission continuous forest inventory plots, which occur in the area. A total of 13 floristic units were recognised and described. The relationship of the floristic units to changing water availability, drainage, soil fertility and fire frequency are assessed and the problems of structural versus floristic classifications of forest types are discussed. INTRODUCTION The dry forests of Tasmania occupy some of the most heavily utilised areas of the state. Clearing for agriculture and urban development, sawlog extraction, firewood getting and burning combined with stock grazing have all made their mark on this vegeta tion. The extent of relatively undisturbed dry forests has been reduced also by the establishment of softwood plantations of Pinu.s radiata and by the a<lvent of the export woodchip industry. There are only com paratively small areas of dry forest vegetation con tained within State Reserves (e.g. Jackson 1974). It is apparent that the remaining dry forests can only retain their integrity if there is sound management based on adequate ecological knowledge and description. Descriptions of the drier lowland forests in the south and east of the State are accumulating. The vegetation in various parts of the Eastern Tiers has been discussed by Kirkpatrick (1981), Kirkpatrick et al. (1980), Wells et al. (1977), Duncan (1981) and Duncan et al. (1981) . Accounts are also available of the dry forests on �laria Island (Brown & Bayly-Stark 1979a) and Schouten Island (Harris & Kirkpatrick 1982). Descriptions of forests in other areas of southeastern Tasmania have been given by Jackson (1965), Hogg and Kirkpatrick (1974), Ratkowsky & Ratkowsky (1976, 1977), Harris & Brown (1980) and Brown & Bayly-Stark (1979b). There are no equivalent descriptions published of the drier forests of northern Tasmania, but the need is evident. In 1978, the Tasmanian Forestry Commission, Department of Environment and National Parks and Wildlife Service undertook jointly to conduct a survey of State Forests in an area bounded by the Bass Highway, Rubicon River and Tamar River (the West Tamar region, fig. 1). The aim of this survey was to provide base data for the evaluation of the potential impact on flora and fauna of proposed pine plantations in the region. An inter nal report was subsequently produced, but is not generally available. The present paper reports an analysis of the structural and floristic variation found in the forests of the region during that survey. 135 136 The Forest Communities of the West Tamar, Tasmania. Low Head 26 km FIG. 1 - The West Tamar region, showing intensive sampling sites and extent of State Forest. THE STUDY AREA The West Tamar region (fig. 1) is bounded to the west by Port Sorell and the Rubicon River, to the south by the Bass Highway, and to the east by the Tamar River. The region has a temperate maritime climate (Langford 1965) but shows pronounced differences between coastal and inland/upland sites. The differences are recognised by Gentilli (1972) who categorised the region as moist subhumid warm (coastal), humid warm (inland) and humid cool (upland). The variations in temperature and rainfall throughout the study area are approx imated by the data given in table 1 for Low Head, Mt Pleasant and Deloraine. The surface geology of the region is diverse (McClenaghan & Baillie 1975). An unmeta morphosed sequence of interbedded Precambrian quartzwackes and phyllites occurs within the Dazzler and Asbestos Ranges. A variety of metamorphosed igneous and sedimentary rocks of Precambrian age occur near Port Sorell and Beaconsfield. Ordovician siltstones, mudstones, sandstones and limestones are found in the Cabbage Tree Hill area ,and at Flowery Gully. Quartzites and slaty siltstones of Silurian-Lower Devonian age occur near Frankford. The Parmeener Supergroup lunmetamorphosed marine se'ctiments) is represented near Frankford, Glengarry and Beaconsfield. Triassic sandstones and mudstones of fluviatile origin are 137 M.J. Brown and R.T. Buckney TABLE 1 CLIMATIC DATA FOR SELECTED STATIONS NEAR THE STUDY AREA Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year LOW HEAD (Coastal, elevation 28 m) 41 0 3'S, 146°47'E A '57 38 41 55 66 80 79 71 60 60 46 46 681 B 8 7 9 11 13 15 17 16 15 13 11 19 145 C 20.6 21.3 20.0 17.7 14.6 12.8 12.1 12.8 13.8 15.4 16.9 18.7 16.4 D 13.2 13.5 12.3 10.7 8.3 6.9 6.0 6.4 7.4 8.7 10.3 11.7 9.6 MY PLEASANT (at Launceston, 50 km inland, elevation 140 m) 41 0 28'S, 147°9'E A 43 54 45 61 79 76 95 99 70 64 54 57 797 B 7 6 8 11 12 13 16 16 14 11 11 9 134 C 23.2 24.0 21.2 17.5 14.0 11.6 11.2 12.3 13.9 16.7 18.5 20.6 17.1 D 10.9 11. 7 9.8 7.8 5.1 2.8 2.5 3.6 5.0 5.9 7.8 9.9 6.9 DELORAINE (45 km inland, elevation 253 mJ 41°31 'S, 146°38'E A 45 68 50 87 104 98 144 150 101 82 61 71 1061 B 8 8 9 14 14 14 18 19 16 13 12 12 157 C 22.7 22.3 20.2 16.2 12.9 10.9 10.5 11.3 12.4 15.2 16.8 19.0 15.9 D 9.6 10.3 8.7 6.2 3.1 2.2 1.5 2.8 2.8 4.5 6.2 7.2 5.4 A precipitation (mm); B = number of raindays; C = mean daily maximum temperature (OC) ; D = mean daily minimum temperature (OC) . found near Parkham. The southern half of the study area is dominated by Jurassic dolerite. Isolated patches of Tertiary sediments occur widely in the lowland areas and extensive Quaternary deposits have been laid down by the present river systems. The region has been divided into land systems by Pinkard (1980), who provides detail ed descriptions of the land units which occur there. The topography is generally hilly in the north, being dominated by the Asbestos and Dazzler Ranges, which rise to 520 m. In the south, the land surface is more undulating at an average altitude of 150-200 m, but reaching 500+ m on some hills. A map of the vegetation (after Kirkpatrick & Dickinson, 1983) is shown in fig. 2. The approximate area of State Forest in the region is 38 400 ha. Existing pine plantations occupy 1 700+ ha of State Forest and the establishment of a further 2 200 ha of such plantations is planned by 1990. The remaining 34 500 ha of State Forest are to be managed primarily for hardwood extraction for the sawlog and woodchip industries. MATERIALS AND METHODS A two-stage process was used for sampling the forests in the region. The forests were classified initially using the Forestry Commission data from 243 continuous forest inventory (CFI) plots, established in the region. CFI plots are permanently marked, ran domly allotted locations, 0.2 ha in area, within a stratified system of forest types determined by photographic interpretation (PI). In addition to the standard forestry data collected for estimates of volume and growth, the height, coverage and species of eucalypts are listed for each plot, and the understorey and ground vegetation are recorded in broad floristic groups characterised by one or several commonly occurring species con sidered by the Forestry Commission to be indicative of the sites (Anon. 1977). For example, the "wet sclerophyll" group (As, table 2), is characterised by the presence of such species as Pomaderris apetaZa, OZearia argophyZZa, and/or PhebaZium squameum. 138 The Forest Communities of the West Tamar, Tasmania. , 30 Km , FIG. 2 - Vegetation of the West Tamar region (after Kirkpatrick & Dickinson, 1983). o - cleared land; 1 - coastal dune complex; 2 - heath; 3 - woodland; 4 - grassy forest on dolerite; 5 - heathy forest; 6 - E. obZiqua (tall) open-forest; 7 - E. deZegatensis tall open forest; 8 - E. regnans/E. obZiqua very tall open-forest; 9 - complex of eucalypt forest with varying understorey and rainforest. 139 M.J. Brown and R.T. Buckney TABLE 2 CHARACTERISTICS OF THE VEGETATION. Data obtained from the continuous forestry inventory plot sheets and used in the initial analysis of 243 sites. (A) HEIGHT OF DOMINANT VEGETATION Native eucalypts: 45-60 m (E2); 30-45 m (E3); 12-30 m (E4) (B) EUCALYPT SPECIES Eucal-yptus obliqua (obI); E. amygdalina (amy); E.