Article

Factors influencing the maintenance of an inverted Eucalyptus coccifera tree‐line on the Mt Wellington Plateau, Tasmania

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Abstract

The Tasmanian snow gum, Eucalyptus coccifera Hook.f., forms low-open woodlands on the dolerite plateau of Mt Wellington, Tasmania. The species occurs at the inverted and upper slope tree-lines, and its spatial distribution appears to be strongly influenced by soil drainage characteristics. Both experimental work and field observations indicate that water-logging is the principal agent determining the inverted tree-line limits of E. coccifera on Mt Wellington. However, deficiencies of moisture also play a role in limiting the distribution of snow gums. There was no evidence to indicate that frost influences the lower tree-line limits of the species, despite the genetic variation shown in the frost resistance of trees from various provenances. Strong ice-bearing winds influenced the morphology of E. coccifera individuals, but was not a factor in limiting the distribution of the species.

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... The major discrepancy in direction of distortion is between our Mount Wellington site and the others. As with our plants at the other sites, the trees in the subalpine forests on Mount Wellington lean away from the southwest (Gilfedder, 1988), whereas, in our quadrats near the summit, the plants lean away from the northwest. Leaf damage from wind-blown ice is greater on the windward (southwest) side of treeline eucalypts, which, combined with the asymmetric crown form, suggests ice-bearing southwesterly winds are the controlling factor (Gilfedder, 1988). ...
... As with our plants at the other sites, the trees in the subalpine forests on Mount Wellington lean away from the southwest (Gilfedder, 1988), whereas, in our quadrats near the summit, the plants lean away from the northwest. Leaf damage from wind-blown ice is greater on the windward (southwest) side of treeline eucalypts, which, combined with the asymmetric crown form, suggests ice-bearing southwesterly winds are the controlling factor (Gilfedder, 1988). Gilfedder (1988) presents evidence that the upper altitudinal limit of trees on Mount Wellington is related to drought. ...
... Leaf damage from wind-blown ice is greater on the windward (southwest) side of treeline eucalypts, which, combined with the asymmetric crown form, suggests ice-bearing southwesterly winds are the controlling factor (Gilfedder, 1988). Gilfedder (1988) presents evidence that the upper altitudinal limit of trees on Mount Wellington is related to drought. Hot, dry northwesterly winds occur during the summer growing season. ...
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Woody plants in windy environments have been used as indicators of prevailing wind direction, because wind can influence plant growth form. We investigated whether non-woody plants also display consistent prevailing wind deformation by observing the direction of asymmetry in growth form of cushion plants, graminoids, and prostrate shrubs growing in highly wind-exposed treeless environments in alpine Tasmania and subantarctic Macquarie Island. Wind distortion of individual plants was inferred from vertical photographs of feldmark and alpine heath vegetation. High correspondence in growth direction between plants of different types suggests a uniform wind influence on plants at the local scale (within <2 m). Dominant wind direction inferred from plant distortion was not consistent with the strongest and most frequent winds. On a relatively dry mountain with shallow soils the plants responded to strong northwest winds in an apparent desiccation response. Elsewhere, they responded to strong southwest winds in an apparent ice abrasion response. We conclude that, in maritime alpine and subantarctic environments, the direction of wind distortion can be measured using any of shrubs, graminoids, or cushion plants, but that this direction is not necessarily a response to the prevailing strongest winds, but rather winds that most damage foliage, the cause of damage varying with environmental context.
... Precipitation is the principal driving force on the third hillside (p < 0.01, Figures 9c and 10e,f). The following reasons explain why precipitation has a significant impact on the alpine timberline; first, precipitation defines the nutrient availability and growth restrictions of vegetation in alpine timberline ecotones [71][72][73]. Second, vegetation possess the limited capacity of precipitation use efficiency on the Tibetan Plateau, leading to wilted seedlings and limited tree growth at high altitudes [74][75][76]. ...
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The alpine timberline, an ecosystem ecotone, indicates climatic change and is tending to shift toward higher altitudes because of an increase in global warming. However, spatiotemporal variations of the alpine timberline are not consistent on a global scale. The abundant and highest alpine timberline, located on the Tibetan Plateau, is less subject to human activity and disturbance. Although many studies have investigated the alpine timberline on the Tibetan Plateau, large-scale monitoring of spatial-temporal dynamics and driving mechanisms of the alpine timberline remain uncertain and inaccurate. Hence, the Gongga Mountain on the southeastern Tibetan Plateau was chosen as the study area because of the most complete natural altitudinal zonation. We used the Otsu method on Google Earth Engine to extract the alpine timberline from 1987-2019 based on the normalized difference vegetation index (NDVI). Then, the alpine timberline spatiotemporal patterns and the effect of topography on alpine timberline distribution were explored. Four hillsides on the western Gongga Mountain were selected to examine the hillside differences and drivers of the alpine timberline based on principal component analysis (PCA) and multiple linear regression (MLR). The results indicated that the elevation range of alpine timberline was 3203-4889 m, and the vegetation coverage increased significantly (p < 0.01) near the alpine timberline ecotone on Gongga Mountain. Moreover, there was spatial heterogeneity in dynamics of alpine timberline, and some regions showed no regular trend in variations. The spatial pattern of the alpine timberline was generally high in the west, low in the east, and primarily distributed on 15-55 • slopes. Besides, the drivers of the alpine timberline have the hillside differences, and the sunny and shady slopes possessed different driving factors. Thus, our results highlight the effects of topography and climate on the alpine timberline on different hillsides. These findings could provide a better approach to study the dynamics and formation of alpine timberlines.
... The differences in vegetation composition change between the north-and south-facing slopes may relate to the greater dryness and instability on the steep, wellinsolated north-facing slope, where snow accumulates to greater depth in winter than on the gentler south-facing slope. E. coccifera is better suited to well-drained rather than waterlogged conditions (Gilfedder 1988, Kirkpatrick & Gibson 1998. Although there was a greater increase in tree density on the north-facing slope, in most quadrats the increase was not sufficient to influence vegetation composition as shown by the lack of relationship between the variables related to E. coccifera and those related to species composition. ...
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Alpine areas by definition have summer temperatures too cool to support trees. Concerns have been raised that trees may invade these distinctive habitats where global climate change results in an increase in summer temperatures beyond the threshold limiting tree growth. In 2016, we investigated changes in the treeline and vegetation immediately above it by resampling quadrats and rephotographing from the set points established in the Alpine Treeline Ecotone Monitoring Program on Mount Rufus, Tasmania, in 2006. Within the study area, the only species with the potential to reach a tree height > 3 m is Eucalyptus coccifera Hook.f. The height, density, basal diameter and diameter at breast height were recorded for all E. coccifera within the study area, together with an estimate of percentage cover of each vascular plant species. No change was found in the location of the treeline over the 10-year period, although E. coccifera height and density above the treeline did increase. The vegetation on the north-facing slope shifted to a composition more closely related to the forest below the treeline, while on the south-facing slope forest species reduced in abundance and the vegetation became more dominated by alpine species. Historical aerial photographs suggest that there has been a minor and inconsistent establishment of E. coccifera plants at higher altitudes since 1953. The area was burned by bushfire in 1965, making it difficult to separate the effects of putative climate change and recovery after the fire event on vegetation changes, although data from Lake St Clair suggest a local constancy of mean growing season temperatures and rainfall.
... The main forested areas occur primarily on low ridges, and both frost and waterlogging may play a role in the distribution of trees within the property. For example, waterlogging is known to be a limiting factor in E. coccifera colonisation in inverted tree-lines on Mount Wellington (Gilfedder 1988). Similarly Eucalyptus gunnii is known to be highly tolerant of both seasonal waterlogging and hard frosts (Pemberton 1986;Corbett 1996) and, within the study area, this species is restricted to forest margins around open ground and frost hollows with poor drainage ...
... Sugar maple samaras are capable of traveling up to 100 m from the parent because of their papery wings (Burns and Honkala, 1990). Similar environmental limiting factors are evident where inverted treelines exist in other temperate ecosystems (Gilfedder, 1988; Paton, 1988 ) and, according to Burns and Honkala, sugar maple grows best on welldrained loam soils and is rarely found in waterlogged sites. (2)Perhaps less limiting to the species, sugar maple seedlings will need to compete in a well-established forest community. ...
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Sugar maple reaches its northern limit along the eastern shore of Lake Superior marking the transition from the deciduous forest of eastern North America to a predominantly boreal forest community. In light of regional warming trends over the past 100 years and projections for even warmer conditions in the future, we sought to characterize the current age structure and regeneration status of both sugar maple and boreal tree species within this ecotone zone. Within Lake Superior Provincial Park (Ontario, Canada), a series of east-west trending hills create numerous deciduous-boreal transition zones as sugar maple occupies uplands and boreal species occupy valley bottoms; then, once north of the sugar maple limit, boreal species dominate all topographic positions. Unlogged forest stands were sampled in the transition zone on ridges and slopes both north and south of the sugar maple limit. Overall tree density and basal area in sugar maple and boreal stands were similar across the ecotone, but seedling density was significantly higher in plots dominated by sugar maple. Moreover, sugar maple seedlings, but not saplings, were found slightly beyond the adult sugar maple tree hillside limit, indicating that the potential for range expansion may be limited by microclimatic variables, namely cold air drainage.
... Finally, cold-air drainage has been the favored explanation for analogous grasslands in concave basins in the mountains of Australia and New Zealand (Wardle 1971; Moore & Williams 1976; Paton 1988), where the term ʻinverted treelineʼ or ʻinverted timberlineʼ is widely used to describe the shift from grassy basins to forested slopes. However, grass competition (Fensham & Kirkpatrick 1992) and waterlogged soils (Gilfedder 1988) have also been proposed as causes of treelines in these systems. Grassy openings in the Rockies also occur on steep, south-facing slopes and mountain tops, where fire (Langenheim 1962; Allen 1984) or reduced soil depth and moisture availability (Rydberg 1913; Moir 1967; Daubenmire 1968) are thought to be responsible. ...
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Objective: Treeless meadows and parks are widespread but poorly understood features of the montane vegetation of the western USA. These communities frequently form reversed treelines where grassy valleys occur below forested slopes above. Our purpose was to assess the environmental correlates of such treelines, as well as patterns in the composition and diversity of grasslands and forest margins in the Valles Caldera National Preserve. Location: Valles Caldera National Preserve (35°50'-36°00' N, 106°24'-106°37' W, 2175-3150 m), Jemez Mountains, New Mexico, USA. Methods: We conducted a gradient analysis based on 200 nested quadrats on transects crossing reversed treelines and spanning the compositional heterogeneity of grasslands. We used cluster analysis and non-metric multidimensional scaling to assess relationships between compositional variation and environmental variables. Results: We found strong, highly significant relationships of the vegetation to gradients in slope inclination, soil texture, moisture, nutrient availability, and nighttime minimum tempera-tures. Reversed treelines are most strongly associated with shifts in the thermal regime, exhibit weaker relationships with soil texture and nutrient content, and show no relationship with gravimetric soil moisture. Gradients in aspect, soil moisture, and annual mean temperature are associated with compositional variation within grasslands and forest margins. Conclusions: Lower nightly minimum temperatures and fewer consecutive frost-free days resulting from cold-air drainage may prevent tree seedling establishment in valley bottoms via photo-inhibition, tissue damage, or frost heaving. Fine-textured soils may also impede tree seedling establishment in valley bottoms. These findings lay the groundwork for experimental and physiological tests of these potential causes of these reversed treelines. Abbreviations: NMS = Non-metric Multidimensional Scaling; VCNP = Valles Caldera National Preserve.
... Fine-textured soils in valley bottoms have been proposed to impede conifer establishment by slowing root growth and limiting access to soil moisture (Daubenmire 1943, Patten 1963). Excessively wet soils (where drainage is impeded by high clay content and/or topography) could also maintain treeless meadows (Ives 1942, Gilfedder 1988). However, soil moisture shortages have been proposed to limit tree growth in a park in Wyoming, USA (Doering and Reider 1992). ...
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Montane and subalpine grasslands are prominent, but poorly understood, features of the Rocky Mountains. These communities frequently occur below reversed tree lines on valley floors, where nightly cold air accumulation is spatially coupled with fine soil texture. We used field experiments to assess the roles of minimum temperature, soil texture, grass competition, and ungulate browsing on the growth, photosynthetic performance, and survival of transplanted ponderosa pine (Pinus ponderosa) seedlings at 32 sites straddling such reversed tree lines in the Valles Caldera National Preserve (VCNP) of the Jemez Mountains, New Mexico (USA). Seedling growth increased most strongly with increasing nighttime minimum temperatures away from the valley bottoms; seedlings experiencing the coldest temperatures on the caldera floor exhibited stunted needles and often no measurable height growth. Based on the chlorophyll fluorescence ratios PhiPSII and Fv/Fm, we found that low minimum temperatures, low soil moisture, and fine soil texture all contributed to photoinhibition. Neighboring herbs had only minor negative effects on seedlings. We found no effect of ungulates, but golden-mantled ground squirrels (Spermophilus lateralis) caused substantial seedling mortality. Second-year seedling survival was highest on sandy soils, and third-year survival was highest at sites with higher minimum temperatures. We conclude that differential tree seedling establishment driven by low minimum temperatures in the valley bottoms is the primary factor maintaining montane grasslands of the VCNP, although this process probably operated historically in combination with frequent surface fire to set the position of the tree line ecotone. As at alpine tree lines, reversed tree lines bordering montane and subalpine grasslands can represent temperature-sensitive boundaries of the tree life form.
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The heights, diameters and regrowth basal areas of 22-yr old fire-initiated regeneration of Eucalyptus delegatensis ssp. tasmaniensis, E. urnigera, E. coccifera and E. johnstonii were measured over altitudinal, solar radiation and drainage gradients on Mt. Wellington, Tasmania. The growth rate responses to the altitude gradient-complex vary from linear to curved depending on the performance measure, the species and the gradient. Much of the variation in growth rate appears to be a direct response to the physical environment. However, disparities between trends in growth rate and trends in re-growth basal area are consistent with the hypothesis that competition (sensu Grime 1979) is more important in productive environments and less important in stressful environments. A glasshouse trial with Eucalyptus seedlings indicated that potential growth rates decline with increasing altitude of seed source.
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Compares germination, growth and survival of mountain beech Nothofagus solandri var. cliffortioides and exotic timberline species through an altitudinal range of 900-1780 m and 3 levels of shade. All species germinate at all altitudes but growth rates are inversely related to altitude. In unshaded plots, beech seedlings survive only at or below 1300 m. Shaded beech seedlings at 1600 m had heavy initial mortality, and eventually died because of repeated frosting and winter die-back of shoots. Even at 1300 m plants tend to die back once they grow above surrounding shelter, thereby forming krummholz. Unshaded seedlings of Picea engelmannii are severely damaged by early summer frosts; and from 1450 m upwards, this prevents them from growing taller than surrounding shelter. Pinus contorta grows best in full sunlight, and there are vigorous seedlings at 1780 m; but wind-exposed plants at 1600 m are developing krummholz forms, because of winter death of their taller shoots. The tropical-subalpine P. hartwegii is surviving up to 1450 m. Saplings of Eucalyptus pauciflora and E. coccifera are growing vigorously at 1300 m and seedlings will probably survive at 1450 m, but not exceed the height of surrounding shelter.-from Author
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Leaf water potential (), leaf diffusion resistance (r 1) and net photosynthesis of leaves of Eucalyptus pauciflora Sieb at timberline (2,040 m) were measured in winter and spring in the Snowy Mountains area of southeastern Australia. Four treatments were established in a 22 factorial design involving exposure to direct sunlight, screening to reduce solar radiation by approximately 50%, exposure to direct radiant cooling at night, and screening to reduce radiant cooling. A less comprehensive set of measurements was also made in summer.No significant water deficits developed in any of the treatments, water potentials remaining above =-14 bars in winter, and above =-10 bars in spring, well above the levels needed to cause tissue damage in this species. These results contrast with the extreme desiccation reported in trees at timberline in other regions and suggest that winter dehydration is not an important factor in limiting tree distribution in the Snowy Mountains.Tissue damage was observed in all treatments and was most pronounced in those exposed to natural radiation frosts, in which shoot die-back occurred. Although factors other than frost incidence may have been influenced by the treatments, the results suggest that low temperatures, possibly associated with periods of clear weather and cold nights in the spring, when the tissue was no longer winter-hardy, may have been the main factors responsible.
Article
The spatial and temporal variation of lead conductance (g) in Eucalyptus pauciflora was analysed with respect to photon flux area density (I), temperature (T), water vapour concentration deficit (Δw), and leaf water potential (Ψ) at four different sites between 940 m and 2,040 m altitude in the Snowy Mountains of south-eastern Australia. Along this altitudinal gradient the precipitation/evaporation ratio increases from 1 to 4. The results show that gas diffusion in this tree species is primarily controlled by I and Δw at all sites, independently of the specific soil moisture regime. Even under dry midsummer conditions with predawn leaf water potentials of-1 MPa at the lowest altitude, Ψ had no striking effect on g. The humidity threshold for the onset of stomatal closure does not vary greatly between the study sites (12.2±1.3 Pa kPa-1). The highest and lowest values observed for Ψ, the osmotic potential at water saturation (from pressure/volume curves), the mean and maximum g and stomatal dentity, all increase with elevation. The highest (least negative) osmotic potentials were obtained at all sites in midsummer. It therefore appears that there is no osmotic adjustment to drought in the seasonal course. The maximum difference between osmotic potentials obtained at the lowest and highest sites is 0.46 MPa. In general osmotic potential varies less than has been reported for other plant species exposed to varying water regimes. This may be the consequence of the pronounced feed-forward response of the stomata to evaporative demand, which led to only moderate tissue desiccation, never exceeding the turgor loss point. E. pauciflora is a tree species with a very conservative utilisation of soil water, which adjusts to drought via stomatal control of water loss, rather than via osmotic properties. These results explain previous reports of the comparatively high susceptibility of E. pauciflora to severe drought and its positive influence on the hydrological balance of mountain ecosystems in the Australian Alps.
A study of the ecosystems of the Monaro region of
  • A B Costin
Costin A. B. (1954) A study of the ecosystems of the Monaro region of New South Wales. Government Printer, Sydney. Costin A. B. (1970) Subalpine and alpine communities. In: Australian Grasslands (ed. R. Milton Moore), pp. 55-87. Australian National University Press, Canberra.
The vegetation of the Kosciusko Plateau
  • J Mcluckie
  • A H Petrie
McLuckie J. & Petrie A. H. (1927) The vegetation of the Kosciusko Plateau. Proc. Linn. Soc. NSW 52. 187-221.
Geographic variation in Eucalyptus gtobulus. Eorestry and Timber Bureau Bull. No. 47 The impact of man on the vegetation of the West Coast region
  • Jackson W D Hobart
  • J B Kirkpatrick
Jackson W. D. (1973) Vegetation of the Central Plateau. In: The Lake Country of Tasmania (ed. M. R. Banks), pp. 61-86. Royal Society of Tasmania, Hobart. Kirkpatrick J. B. (1975) Geographic variation in Eucalyptus gtobulus. Eorestry and Timber Bureau Bull. No. 47. Kirkpatrick J. B. (1977) The impact of man on the vegetation of the West Coast region. In: Landscape and Man (ed. M. R. Banks and J. B. Kirkpatrick), pp. 151-6. Royal Society of Tasmania, Hobart. Korner C. & Cochrane P. M.( 1985) Stomatal responses and water relations of E. paucifJora in summer along an elevational gradient. Oecologia 66, 443-55.
Notes on some species occurring in the Upper Williams River and Barring-ton Tops Districts. II. The rainforest formations
  • Fraser L R Vickery
Fraser L. R. & Vickery J. W. (1939) Notes on some species occurring in the Upper Williams River and Barring-ton Tops Districts. II. The rainforest formations. Proc. Linn. Soc. NSW 62, 284-93.
Ecological studies on the Bennison High Plains
  • T P Farrell
  • D H Ashton
Farrell T. P. & Ashton D. H. (1973) Ecological studies on the Bennison High Plains. Vic. Nat. 90, 286-98.
The tolerance of Eucalyptus species to waterlogging. MSc thesis
  • R W Boden
Boden R. W. (1962) The tolerance of Eucalyptus species to waterlogging. MSc thesis. University of New South Wales. gie R. (1972) Effects of water table height on root development of Pinus contorta on deep peat in Scotland. Oikos 23, 304-12.
Notes on the phytogeography and flora of the mountain summit plateaux of Tasmania
  • L S Gibbs
Gibbs L. S. (1920) Notes on the phytogeography and flora of the mountain summit plateaux of Tasmania. / Ecoi. 8, 1.1-17, 2.89-117.
Differential frost resistance within one Eucalyptus species, .'lust
  • R W Boden
Boden R. W. (1958) Differential frost resistance within one Eucalyptus species,.'lust. J. Sci. 21, 84-6.
Vegetation of the Central Plateau
  • W D Jackson
Geographic variation in Eucalyptus gtobulus
  • J B Kirkpatrick
Vegetation and insect predation of eucalypts
  • F M Marks
Geology of the Hobart District
  • A N Lewis
  • Gibbs L. S.
The impact of man on the vegetation of the West Coast region
  • J B Kirkpatrick
Subalpine and alpine communities
  • A B Costin