Papers and Proceedings of the Royal Society of , Volume 121,1987 93

REGENERATION CHARACTERISTICS OF A SWAMP IN NORTHWESTERN TA SMANIA

by N. Gibson, K. Williams, J. Marsden-Smedley and M.J. Brown

(with one table and five text-figures)

GIBSON, N., WILLIAMS, K., MARSDEN-SMEDLEY, J. & BROWN, M.J., 1987 (30:vi): Regeneration characteristics of a swamp forest in northwestern Tasmania. Pap. Proc. R. Soc. Tasm., 121: 93-100. https://doi.org/10.26749/rstpp.121.93 ISSN 0080-4703. National Parks and Wildlife Service, P.O. Box 210, Sandy Bay, Tasmania 7005; and Forestry Commission, 199 Macquarie Street, Hobart, Tasmania 7000 (MJB). The botanical composition and regeneration characteristics are described for a ericifolia­ lanigerum forest from northwestern Tasmania. The size classes of the two dominant species are highly correlated with tree age. Size class analysis shows that the dominants are regenerating continuously. The relationship of this forest type to rainforest and wet forest are discussed. Key Words: Tasmania, swamp forest, regeneration, Melaleuca, Leptospermum INTRODUCTION The of Tasmania traditionally are spermum and/ or Melaleuca forest (Anon. 1982, treated at the formation level as either sclerophyll Jarman & Brown 1983, Jarman et al. 1984, R. forest or as rainforest (e.g. Jackson 1965, Curtis Mesibov pers. comm. 1986). 1965-66, Gilbert 1970-71 ). The sclerophyll forests Jarman & Brown (1983) considered that are broken into two classes, wet and dry sclerophyll, whilst Leptospermum lanigerum, L. nitidum, L. each of which has a characteristic understorey scoparium and Melaleuca squarrosa may be found flora. The dry sclerophyll forests are dominated by in the rainforest canopy, they were doubtful rain­ either or Casuarina (Duncan & Brown forest species, and suggested that detailed studies 1985), whilst wet sclerophyll forests are Eucalyptus­ were required to determine their status. Thus dominated. The dominant species of the two sub­ Jarman et al. (1984) point out that the niche formations have quite different regeneration modes, occupied in rainforest by these myrtaceous species with dry sclerophyll dominants being either con­ may be that of a "good" rainforest species or may tinuous or pulse regenerators while most wet instead be similar to that filled by Eucalyptus in the sclerophyll forests are either even-aged or contain mixed forests of Gilbert ( 1959). only a few age-classes, depending on the past The relationships of the swamp forests to history of fires. either rainforests or to sclerophyll forests have not Jarman & Brown (1983) have defined cool been determined. The floristic variation they con­ in Tasmania as those forest tain apparently ranges from predominantly rain­ communities dominated by species of Nothofagus, forest elements to predominantly sclerophyllous Atherosperma, Eucryphia, Athrotaxis, Lagaros­ and the regeneration characteristics of the non­ trobos, Phyllocladus or Diselma of at least 8 min eucalypt dominants have not been described. The height. Rainforest species are defined as those aim of the present paper is to provide a floristic species able to perpetuate themselves (either vege­ description of one such swamp forest and to tatively or from seed) within forests dominated by investigate the regeneration strategies of the two one or more of the species listed above. forest dominants - Leptospermum lanigerum and In northwestern Tasmania there are large Melaleuca ericifo/ia. tracts of closed swamp forest which are usually dominated by melanoxylon or Melaleuca ericifolia (Kirkpatrick & Dickinson I984, fig. I). THE STUDY AREA These forests subsume a range of community types The study area is located on the Welcome from almost pure A. melanoxylon forests through River in the far northwest of the State. This area A. melanoxylon--Nothofagus(-Phyllo­ lies in the warm-humid climatic zone (Gentilli cladus) dominated forests to almost pure Lepta- 1972) with a winter rainfall maximum. The swamp 94 N. Gibson, K. Williams, J. Marsden-Smedley and M.J. Brown

(a) SWAMP FOREST IN NW TASMANIA.

I... :1 swamp forest.

o 10 20km ~I------~I------~I

(b) SWAMP FOREST STUDVAREA. 0/ / Il. I C 11 .. I " ...'Ii /' ~'It~~./ /'" ~ I ~o / /' 1/ I I I J I I I I I 40 'f' piot location and number.

contour - 40 m. o 1 2 3k I I I I

FIG.] - (a) The occurrence of swamp forest in northwestern Tasmania (after Kirkpatrick & Dickinson 1984), and (b) the location of the study area. Regeneration of a Tasmanian swamp forest 95

forests of this area are commonly inundated in the Nomenclature follows Curtis (1963, 1967), winter months. Curtis & Morris (1975), Willis (1970), and Jones & The topography is of a broad flat valley, the Clemesha (1981). vegetation being underlain by Holocene alluvium, sand and gravel. The swamp forest in the area is dominated by Melaleuca ericifolia with Lepto­ RESULTS spermum ianigerum also being present. Vegetation The vegetation of the area is dominated by a METHODS closed canopy of Melaleuca ericifolia with Acacia Vegetation data were collected from nine melanoxylon and Leptospermum ianigerum as plots along the We1come River between Red pa and sub-dominants. The canopy also contains occa­ Boggy Creek. Both structural and floristic data sional individual trees of Eucalyptus ovata and E. were recorded from 20 m diameter plots using the obliqua on better-drained sites. The understorey is T ASFORHAB system of Peters (1984). From dominated by Melaleuca ericifolia with Coprosma quadrifida, Drimys lanceolata, Leptospermum these data a vegetation description was compiled and a generalized vegetation profile was con­ lanigerum and occasionally Pomaderris ape tala, again on better drained sites. The ground layer structed. In the area presently being cleared to make contains and Lepidosperma elatius together with the ferns Polystichum proliferum, drainage channels, 49 basal slabs of Melaleuca ericifolia from 10 to 460 mm diameter were collected Blechnum nudum and Dicksonia antarctica. for ageing of the trees. Nine slabs of Leptospermum Epiphytic ferns, including Microsorium diversi­ lanigerum from 10 to 600 mm diameter were also folium, Hymenophyllum peltatum, Ctenopteris collected. Slab diameters were determined with a heterophylla and Grammitis billardieri were diameter tape and ring counts were made on their occasionally present. A generalized vegetation pro­ file is shown in figure 2. At the time of sampling planed tops. From these data a simple linear regression was made between age and size. Size­ (June) the free water surface was at or above class analyses were undertaken from six sites. At ground level in most of the area traversed. each site, a 10 x 10 m plot was established and all individuals greater than 100 mm diameter were Regeneration Modes of the counted and diameters at breast height (DBH) Dominant Species recorded. A 5 x 5 m subplot was located in one A highly significant correlation was found corner of the plot and all individuals less than between diameter and age for both Melaleuca 100 mm diameter were counted. Size class histo­ ericifolia and Leptospermum lanigerum (figs 3 and grams were constructed from these data. 4). Thus size of stem provides a reasonable means The size distributlons were then modelled of estimating age. Examination of the incremental against the power function y ::: y ox· b and the growth of individual stems indicated that con­ negative exponential y ::: yoe-bx, where y is the siderable suppression of individuals was occurring number of individuals in size class x, Yo is the initial through the stand, but there was no indication that population size and b is mortality. The power the initial regeneration resulted from a single function is appropriate to forest stands in which disturbance event, nor that the release of individuals there is continuous regeneration with a mortality was tied to some broad scale disturbance such as that decreases with increasing age, whilst the fire or wind throw. Thus size class analysis can be .negative exponential reflects constant mortality used to describe adequately the population dyna­ (Rett & Loucks 1976). These models were tested mics of those samples for which data are available. for the four plots of Melaleuca ericifolia for which In all of the plots, there were large numbers of data were available in at least five size classes. seedlings and saplings (individuals less than 100 mm As a further check on the regeneration mode diameter) found under closed canopies (fig. 5). In of the two species, increment counts were made plots 1,2,3 and 5, size class distributions fitted the from rings near the centre and at the outside of power function model (table I). stem slabs. These measurements were made to determine whether there was any indication that episodic release from suppression of more or less DISCUSSION even-aged stems was giving rise to apparent con­ The occurrence oflarge numbers of seedlings tinual regeneration. and saplings scattered through the forest suggests ~

~ :<: c;') c;') ~ I Figure 2 Vegetation Profile of a Swamp Forest in Northwest Tasmania f ~ ?; ~ § :§ s· ;::: '\:l .Y>~ (S ~ :-.. ~ VEGETATION SCALE ~ ;:;~ !::> 1} ~ ;::: ~ ~ ~'" 'Ci' ~ ~ ;:;. 3m s· ~ ;::: 2m ~ o.... :-.. ;; 1m ~ ~ o ~ SWAMP FOREST SWAMP FOREST OPEN FOREST SWAMP FOREST SWAMP FOREST § 3 M. ericifolia M. ericifolia M. ericifolia M. ericifolia M. ericifolia (Main Channel) ~ A. melanoxylon E. ovata A. melanoxy Ion E', ovata L. lanigerum c.., D. antarctica P. apetala L. lanigerum E. obliqua C. quadrifida M. ericifolia ::l L. elatius C. quadrifida c. quadrifida A. melanoxylon D. lanceolata I:l G. grandis G. granc!is D. antarctica ;::: P. apetala G. grandis Blechnum spp. Blechnurn spp. L. elatius C. quadrifida Blechnum spp. is' G. grandis L. elatius Blechnurn spp. P. proliferum Regeneration of a Tasmanian swamp forest 97

0,5 1 DIA = 1.8182 + 0.2393 AGE 0.4 r49 = 0.9353 0 ...... 0 E P< 0.001 0 a: 0.3 w 0 I- W 0 ~ -< 0.2 0 0

0.1

40 80 120 160 200 AGE (yrs)

FIG.3 - Regression of diameter on age for Melaleuca ericifolia.

that Melaleuca ericifolia is capable of continuous and that suppression can occur for periods in regeneration in an essentially closed-canopy forest. excess of 20 years. Further analyses of the pattern This observation is confirmed by the age and size class analyses and the fit to the power function. 260 3:rJ. PLOT 3 However, although there is a highly significant 4;on~PLOT2 correlation of size and age, it is apparent from the 20 20 increment counts that growth rates are variable DlA = -7.5155 + 0.6105 AGE 10 10

r9 = 0.9353 o 0.6 ----,---F=1 +-F=l=1--F=t-~~~ P< 0.001 12345678 12345678

M

...... 0.4 10 • .....E o lh a: w 12345678 12345678 I­ o W 360J'}- 924:rJ. ::E 30 « 3 PLOT 8 PLOT 9 is 0.2 20 20

10 10

o 12345678 12345678 o o SIZE CLASS 20 40 60 80 100 AGE (yrs) FIG.5 - Frequency-size class distributions for FIG.4 - Regression of diameter on age for Melaleuca ericifoliafrom six sample plots. Stems Leptospermum lanigerum. grouped into 100 mm size classes. 98 N. Gibson, K. Williams, 1. Marsden-Smedley and M.J. Brown

TABLE 1 Size class (x) and frequency (y) relationships for four samples taken within the Melaleuca ericifolia swamp forest. (a) Exponential function, (b) Power function. Sample no. Relationship r P

(a) In(y+ I) := 38.411-0.513x -0.608 (b) In(y+ 1) :: 20. 796-1.277ln x -0.633 <0.05 2 (a) In(y+l) :: 88.269-0.864x -0.648 (b) In(y+l) := 67.997-2.347In x -0.762 <0.05 3 (a) In(y+l) :: 897.823-1.417x -0.850 <0.05 (b) In(y+l) 488.947-3.72Oln x -0.920 <0.01 4 (a) In(y+l) :: Ill.756-O.848x- 0.634 (b) In(y+l) 108.400-2.566In x -0.783 <0.05

of occurrence of seedlings in relation to tree death forest dominants. However there is no evidence in and canopy gaps would be necessary to determine the present case of colonization by any rainforest absolutely whether the observed release from species sensu Jarman & Brown (1983) (see suppression is light (cf. Duncan 1981, Ogden 1985, appendix). An alternative interpretation is that the Read & Hill 1985) or moisture-related (cf. Bowman Melaleuca (and/ or Acacia melanoxylon) swamp & Kirkpatrick 1986). However, regenerating seed­ forests represent a deflected climax vegetation, lings and saplings of Leptospermum lanigerum whose occurrence is related to the poor drainage were always present in higher numbers than and longevity of seasonal inundation. Further Melaleuca ericifolia under canopy gaps and adja­ work is necessary to determine whether Melaleucaj cent to forest edges. Leptospermum are able to grow in periodically The goodness-of-fit to the power function anoxic conditions which may limit the growth of model suggests that highest mortality occurs in the Nothofagus and Phyllocladus. Until such work is smaller size classes, but once stems are larger than undertaken, it is not possible to determine whether about 100-200 mm DBH, there is a high probability Melaleuca ericifolia or Leptospermum lanigerum that they will grow through to old age (i.e. in excess in these swamp forests are behaving as "good" of 200 years). Less data are available for Lepto­ rainforest species (cf. Jarman et al. 1984). spermum lanigerum, but it also appears to have a linear size-age relationship. The oldest trees in this forest are approxi­ REFERENCES mately 200 years old. The age to senescence of Melaleuca ericifolia (and of Leptospermum lani­ ANON., 1982: DRAFT BLACKWOOD WORKING gerum) is unknown but species of both Melaleuca PLAN. Forestry Commission, Tasmania. and Leptospermum are found as codominants in BOWMAN, D.M.J.S. & KIRKPATRICK, J.B., 1986: rainforests (e.g. Jarman & Crowden 1978, Jarman Establishment, suppression and growth of Eucalyptus delegatensis R.T. Baker in multi­ et al. 1984), some of which are known to be at least aged forests. III. Intraspecific allelopathy, com­ 300 years old (e.g. Brown & Podger 1982). Else­ petition between adult and juvenile for moisture where in the northwestern region, these species and nutrients and frost damage to seedlings. occur in swamp forests together with Nothofagus, Aust. J. Bot., 34: 81-94. Phyllocladus and such rainforest understorey BROWN, M.J. & PODGER F.D., 1982: Floristics and species as Trochocarpa cunninghamii and Anop­ fire regimes of a vegetation sequence from terus glandulosus (Anon. 1982), and the whole of sedgeland-heath to rainforest at Bathurst Har­ the region is climatically suited to the growth of bour, Tasmania. Aust. J.. Bot., 30: 659-676. rainforest (Jackson 1965). CURTIS, W.M., 1963: THE STUDENT'S FLORA OF TASMANIA. PART 2. Government Printer, Thus there may be a seral and/ or successional Hobart. relationship in which these relatively young CURTIS, W.M., 1965-66: The vegetation of Tasmania. Myrtaceae-dominated forests are eventually re­ In WALCH'S TASMANIAN ALMANAC. placed by forests containing the more usual rain- Government Printer, Hobart: 23-25. Regeneration of a Tasmanian swamp forest 99

CURTIS, W.M., 1967: THE STUDENT'S FLORA OF JARMAN, S.J. & BROWN, M.J., 1983: A definition of TASMANIA. PART 3. Government Printer, cool temperate rainforest in Tasmania. Search, Hobart. 14: 81-87. CURTIS, W.M. & MORRIS, D.I., 1975: THE STU­ JARMAN, S.J., BROWN, M.J. & KANTVILAS, DENT'S FLORA OF TASMANIA. PART 1, G., 1984: RAINFOREST IN TASMANIA. Second Edition. Government Printer, Hobart. National Parks and Wildlife Service, Hobart. DUNCAN, F., 1981: Regeneration and species diversity JARMAN, S.J. & CROWDEN, R.K., 1978: A survey of in a Tasmanian dry sclerophyll forest. In vegetation. In LO WER GORDON SCIENTIFIC Kirkpatrick, J.B. (Ed.): FIRE AND FOREST SUR V EY. H ydro-Electric Commission, Hobart. MANAGEMENT IN TASMANIA. Tasmanian JONES, D.L. & CLEMESHA, S.C., 1981: AUSTRA­ Conservation Trust, Hobart: 33-44. LIAN FERNS AND FERN ALLIES. Second DUNCAN, F. & BROWN M.J., 1985: Dry sc1erophyll edition. Reed, Sydney. vegetation in Tasmania. Wild/. Divn Tech. Rept KIRKPATRICK, J.B. & DICKINSON, K.J.M., 1984: 85/1. National Parks and Wildlife Service, VEGETATION MAP OF TASMANIA. Hobart. 1:500000 map. Forestry Commission, Tasmania. GENTILLI, 1., 1972: AUSTRALIAN CLIMAI1C OGDEN, J.,1985: Past, present and future: studies on PATTERNS. Nelson, Melbourne. the population dynamics of some long-lived GILBERT, 1.M., 1959: Forest succession in the Floren­ trees. In White, J. (Ed.): STUDIES IN tine Valley, Tasmania. Pap. Proc. R. Soc. Tasm., DEMOGRAPHY. Academic Press, London. 93: 129-151. PETERS, D.G., 1984: TASFORHAB. In Myers, K., GILBERT, 1.M., 1970-1971: The forests of Tasmania. In Margules C.R. & Musto, I. (Eds): SURVEY WALCH'S TASMANIAN ALMANAC. Govern­ METHODS FOR NATURE CONSERVA­ ment Printer, Hobart: 33-39. TION. Volume 2. CSIRO Divn Water & Land HETT, 1.M. & LOUCKS, D.L., 1976: Age structure Research, Canberra. models of balsam fir and eastern hemlock. J. READ, J. & HILL, R.S., 1985: Dynamics of Nothofagus Eco!.,64: 1029-1044. dominated rainforests on mainland JACKSON, W.D., 1965: Vegetation. In Davies, J.L. and lowland Tasmania. Vegetatio, 63: 67-78. (Ed.): ATLAS OF TASMANIA. Lands and WILLIS, 1.H., 1970: A HANDBOOK OF IN Surveys Department, Hobart. . Volume 1. Melbourne University Press, Melbourne. (accepted 17 March 1987) 100 N. Gibson, K. Williams, J. Marsden-Smedley and M.J. Brown

APPENDIX Check-list of vascular plants found in the Melaleuca ericifolia swampforest.

PTERIDOPHYT A Myrtaceae Eucalyptus obliqua Aspidiaceae E.ovata Polystichum proliferum Leptospermum lanigerum Blechnaceae Melaleuca ericifolia Blechnum nudum M. squarrosa Blechnum wattsii Onagraceae Dennstaedtiaceae Epilobium hirtigerum Histiopteris incisa Oxalidaceae Hypolepis rugosula Oxalis corniculata Dicksoniaceae Pittosporaceae Dicksonia antarctica Billardiera longifiora Grammitidaceae Polygonaceae Ctenopteris heterophylla Muehlenbeckia gunnii Grammitis billardieri Ranunculaceae Hymenophyllaceae Clematis aristata Hymenophyllum peltatum Ranunculus sp. Hymenophyllum sp. Rhamnaceae Polypodiaceae Pomaderris apetala Microsorium diversifolium Rosaceae ANGIOSPERMAE: DICOTYLEDONEAE Acaena novae-zelandiae Apiaceae Rubiaceae Hydrocotyle javanica Coprosma quadrifida Apocynaceae Thymelaeaceae Parsonsia straminea Pimelea drupacea Asteraceae Winteraceae Cirsium sp. Drimys lanceolata Helichrysum dendroideum Senecio sp. ANGIOSPERMAE: MONOCOTYLEDONEAE Brassicaceae Cyperaceae Brassica sp. Carex appressa Cardamine heterophylla Gahnia grandis Lepidosperma elatius Elaeocarpaceae Schoen us maschalinus Aristoteliti peduncularis Scirpus fluitans Mimosaceae Juncaceae Acacia melanoxylon Juncus eJJusus