Alpine vegetation refers to the zone of vegetation between the altitudinal limit for tree growth and the nival zone. [1] Alpine zones in Tasmania can be difficult to classify owing to Tasmania's maritime climate limiting snow lie to short periods and the presence of a tree line that is not clearly defined. [2]
Approximately 111 700 ha of Tasmania is alpine and subalpine habitat (2%). Australia wide, there is only 198 400 ha meaning 56% of Australia's alpine & subalpine habitat is restricted to Tasmania. [3] The altitude at which alpine vegetation occurs ranges from 750m in the southwest to 1400m in the northeast. [2]
From the Latin word Alpinus, from Alpes ‘Alps’. [4] Globally, alpine vegetation is defined zone of vegetation between the altitudinal limit for tree growth and the nival zone. [5] In areas where mountains can be considered typically alpine, the vegetation zones are often divided into distinct altitudinal bands. [5] The alpine band usually consists of low growing herbaceous species given the cessation of most woody vegetation at the upper limit of the subalpine band. The upper limit of the alpine band often gives way to bare rock and permanent snow which continues on to the summit. [5]
In Tasmania, such distinctive altitudinal bands do not occur. Typically the tree line is not well defined and usually located close to the mountain summits, often no more than a few hundred meters below. There is no permanent snow lie and vegetation continues to the summits. [5] Often in Tasmania, the dominant species of a mountain's vegetation will gradually decrease in height with altitude to become a component of the alpine shrubbery. [5] This environmental gradient allows for the subtle sorting of species into communities without the existence of an abrupt break from forest to shrubland. Consequently, Tasmanian alpine and treeless subalpine vegetation is often considered as a single vegetation unit given the term alpine. [6] This approach is justifiable as of the 300(+) species found in the alpine and treeless subalpine zones, only 10 are restricted to the area above the climatic tree-line. [7]
Tasmania's alpine landscape is dominated by two bedrock systems originating from different geological periods. In the eastern and central parts of the state, Jurassic dolerite caps the summits having intruded into the Permian and Tertiary sediments. [8] These dolerite caps have a characteristic topography having an elevated rocky rim and a short, steep face above rock scree. [5] Chemically, dolerite is potentially a very rich source of nutrients however the slow rate of its weathering only allows for soils of moderate fertility. [5]
Conversely, the mountains of the west and southwest are made up mainly of Precambrian and Ordovician quartzites, sedimentaries and conglomerates. [9] They occur as a series of elongated ridges in a north–south arrangement. [5] These rocks provide very nutrient poor skeletal soil and the main nutrient resource is accumulated through from degrading vegetation in humus and shallow peats.
It is generally accepted that rainfall increases with altitude and there is considerable rainfall in Tasmania's alpine regions. This does not correspond with water availability for plants however which is also dictated by numerous other factors such as soil type, slope angle, wind action and the presence of snow/ice (plants cannot utilise frozen water). Consequently, the availability of water for alpine plants is not consistent and often inadequate. [5]
Winter drought is not a concerning factor in Tasmania as it is very uncommon for water to freeze below root depth. When snow melt occurs the soil is brought to field capacity and any additional water is lost through run off. The period of maximum water availability correlates with active growth of alpine species and flowering season, however Tasmania's characteristically skeletal alpine soils retain little water even at field capacity. As a consequence, summer drought is a critical determinant of the Tasmanian alpine environment. [5]
At high altitudes wind is often strong and continuous over long periods. Consequently, wind in alpine regions imposes severe mechanical stress on plants. As a consequence, alpine species require strong root systems to maintain anchorage in the soil. [5] High winds also contribute to soil erosion by moving fine soil particles. These particles blown over the vegetation by high winds can effectively prune erect vegetation. Intense glazing winds occur in winter and late spring. [5]
In Tasmania strong winds are most common close to the equinoxes and during winter. During winter, wind direction is predominantly southerly to southwesterly. Such winds can cause localised snow drifts prolonging the snow lie in given areas. Frequent hot northerly airflows also occur during January–March which have a strong desiccating effect on the alpine soils, placing the plants under transpirational stress. [5]
The decline in air temperature with increasing altitude is a well documented phenomenon due to the simultaneous drop in atmospheric pressure and air density. [10] Temperature influences most phases of a plant's life cycle such as vegetative growth, seed germination, seedling emergence and survival, pollinator visits and seed production. [11]
Leaf temperature and air temperature can be very differential and is regarded as the underlying cause of plant dwarfism in alpine regions. [11] Plant leaf temperatures will generally be warmer than air temperatures by day but cooler at night. [12] The greatest differential occurs during spring when solar radiation is high but air temperature is low. Such differentials place the plant under considerable water stress. [12]
In Tasmania the variation in temperature between day and night can be highly significant. For example, a summer day on the Central Plateau could be above 30 °C followed by a night temperature of 0 °C. [5] This differential is less substantial closer to the ground. Additionally, soil temperature is much less variable and at a shallow depth of 5–10 cm, day/night temperatures will be more or less constant. [5]
At alpine altitude, levels of direct radiation are higher than that found at sea level. This is due to the atmosphere being less dense at higher altitudes. Increased exposure to shortwave ultraviolet (UV) is potentially damaging to plants and can cause damage to the plant's protoplasm and possible death. [13] Tasmania's mountains are relatively low in altitude (generally below 1500m) in comparison to that of other regions of the world thus UV radiation is not as big a factor compared to that of other alpine habitats.
Alpine environments in Tasmania often feature an intricate mosaic of different plant communities such as dwarf forest, conifer shrubbery, sclerophyll shrubbery, heath, bog, bolster moor, grassland and herbfield. This mosaic is not just a response to exposure or edaphic factors but is also strongly influenced by fire disturbance. [14] Fire disturbance strongly influences alpine plant community distribution due to alpine vegetation's slow successional response. [14]
Fires in alpine environments are often intense because they usually occur during extreme fire promoting weather or after prolonged drought. Additionally alpine shrubby vegetation contains aromatic oils and contain large accumulations of dead foliage which burns rapidly. [14] As a consequence much of the peat surface layer is consumed and woody plants such as conifers are completely killed off. Re-establishment is an extended process as a consequence of the very low rates of survival and the uncertainty of seed availability and distribution.
Cushion plant and bolster moor species are active in the early phases of succession. Over the first 10 years these species slowly increase amongst grass colonisers. After 20 years of succession a network of small cushions emerges through grass and herbs and displaces these species in wetter areas. [14] These species actively grow in areas where there is surface flow of water and consequently these bolster communities make shifting areas of very wet conditions. [14] Consequently, the water is unable to form permanent water courses and is dispersed in small dams. [15] Because of this, these species are often referred to as ecological-engineers.
Grasses and dry herbaceous communities are replaced by sedges, Astelia bog and bolster. [14] After 50 years of succession, heaths and shrubberies form progressive invasion of woody species most of which become established in old bolster moor cushions which have dried. Coniferous heath takes much longer to establish. Estimations based on areas that have been burnt in the past suggest that 150–200 years of succession is required to develop 10-20% cover of conifers as a low mat under 10 cm in height.
The direct effects of grazing such as eating and trampling the vegetation causes a reduction in structural complexity and an increase in bare ground cover. These effects are much more pronounced in areas of higher productivity. The indirect effects of grazing can be equally destructive such as the introduction of exotic weeds and fertilizer application by aerial spreading. [5]
The varying levels of impact activities such as skiing, walking and camping are not adequately assessed. Alpine plants such as cushion plants can be particularly sensitive to trampling and occasionally escaped camp fires have resulted in devastating consequences. [5]
Natural wildfires have been part of Tasmania's alpine environment for a long period in the recent evolutionary life of the present alpine flora. [5] It is unlikely that indigenous fire practices would have caused much alteration to wildfire frequency in alpine environments. However fire frequency has likely been altered by the activities of European settlers and their industries since 1803. [5] Observations suggest that areas occupied by fire sensitive species have dwindled (e.g. Athrotaxis) while fire adapted species have expanded. [5]
Global ambient temperatures have increased considerably (average 0.7oC) over the last 100 years (Slatyer 2010). In alpine areas, changes in precipitation regimes have already had a noticeable impact on snow persistence, depth and area. Such changes to snow regimes are expected to alter the composition and distribution of alpine vegetation communities. [16] Additionally, many species may face additional competition due to expansion of species ranges to higher altitudes. [16] Wildfires poses an additional threat to alpine plants and animals, with many species apparently vulnerable to an increase in fire frequency. [16]
Increased levels of UV radiation may penetrate to the earth's surface as a consequence of damage to the ozone layer in recent times. As a consequence the detrimental effects of shortwave UV may become more apparent in Tasmania's alpine regions especially in the lower latitudes. [5]
Tasmania's alpine plants have developed a variety of physiological, morphological and behavioral adaptations to deal with the challenges they face in their environment. Typically, Tasmanian alpine plants have a low primary productivity and correspondingly slow growth rates. [5] For example, Epacris petrophila shoots grow on average only 1 cm y-1. Alpine plants are often opportunistic in their growth with seasonal variation in their growth rate being manifest through internode extensions. [5] Additionally Tasmania's alpine plants have life cycles which are very precisely linked to their short growing season. This is accomplished following a rapid growth surge in spring.
The alpine vegetation community in Tasmania has generally adopted stress tolerance rather than stress avoidance mechanisms. [5] As stresses imposed on an environment become more intense, the range of adaptive biological solutions lessens. Consequently, there is a trend of morphological convergence and similar life/growth forms. [17] The cushion community in the alpine environment is a perfect example, as the seven major cushion forming species in Tasmania are representative of five different families. [5] The densely crowded shoots with a high degree of branching, restrict air movement and maintain a moist internal atmosphere within the cushion. This provides insulation against extreme temperature fluctuations and minimal wind disturbance. [5]
Another example of morphological convergence is the predominance of small-leaved species in alpine vegetation. Small needle-shaped leaves with a relatively large surface-area to volume ratio are efficient in rapid energy transfer and heat dispersion while retaining structural strength. Scleromorphy is a common feature amongst alpine species and has provided an evolutionary advantage as Australia's recent climate has become more arid. [5]
Typically, most of Tasmania's alpine plants are evergreen perennials. The main advantage of the evergreen habit is that the plant does not have to expend energy on new photosynthetic organs each year. It also allows the plants to conduct photosynthesis all year round when conditions are favourable. [18]
Plants in alpine environments are subjected to water stress from a combination of inadequate precipitation, thin soils, periodic high winds and insolation. Numerous morphological adaptations are therefore situated around reducing transpirational water loss. [5] Adaptations include thick cuticles, rolled leaf margins, sunken stomata or lacking leaves altogether. Some plants have dense hairs on the underside of their leaves or thick wax coated trichomes.
Photosynthetic production may be limited not just by low temperature and desiccation but also by mineral nutrient stress. [19] Nitrogen and phosphorus are frequently limiting in Tasmania's alpine environment. Adaptations include mycorrhizal associations, proteoid roots, daucoid roots, and being carnivorous or semi-parasitic.
As part of the research in Tasmania's Central Highlands, part of the Australian Mountain Research Infrastructure Facility project, researchers installed monitoring infrastructure to collect real-time climate, weather, and soil data. Experiments include climate manipulation, such as using a rain exclusion shelter to study the effects of drought on alpine flora and invertebrates. Additionally, phenocams are being used to track vegetation response to weather changes, aiming to understand ecosystem-level changes. [20] [21]
Bolster heath or cushioned moorland is a patchwork of low growing very compact plants. Five families (6 species) occur in Tasmania. A further three families (7 species) contain plants which regularly present a cushion habit but not exclusively. [5] Young cushions may grow vigorously in the presence of permanent free water. The high mountain cushion community is typically composed of Dracophyllum minimum, Pterygopappus lawrencei, and Phyllachne colensoi.
The dominant species of this vegetation is Nothofagus gunnii, which grows as a small tree up to 3 m in height. It is Tasmania's only deciduous tree. It prefers well-drained areas, and, as a consequence, often grows on slopes or amongst boulder scree. The species is very fire sensitive and thus limited to areas where fire access is prevented or severely restricted. [5]
The coniferous vegetation is represented by two gymnosperm families, Cupressaceae (Diselma archeri, Athrotaxis cupressoides, A. selaginoides) and Podocarpaceae (Michrocachrys tetragona, Microstrobos niphophilus, Podocarpus lawrencei). This vegetation type has a patchy distribution in areas topographically protected from fire. This vegetation would likely be the climax vegetation of the region in the absence of fire. [5]
Alpine heath is the most widespread, most diverse vegetation type in Tasmanian alpine environments. Many families are present however this vegetation is dominated by species from Ericaceae and Proteaceae. The diverse range of communities is distributed according to variation in soil conditions, drainage, exposure and fire history. [5] Tall heaths with plants up to 2m (Orites acicularis, Leptospermum rupestre, Coprosma nitida) are usually found in areas of better drainage usually with a rock strewn surface. Low heaths (15-50+ cm), (Baeckea gunniana, Epacris serpyllifolia, Richea sprengelioides) are more frequently found on more peaty soils and frequently border wet areas.
Tussock grassland is mainly restricted to comparatively deep, well-drained soils. In drier areas, Poa labillardieri is dominant in tall, dense tussocks with shrubs of Pimelea pygmaea , Leucopogon stuartii , and Epacris petrophila , which may merge into Eucalyptus coccifera woodlands. In wetter, more peaty soils, tall tussock grassland gives way to a lower, sod tussock community in which Poa gunnii is dominant with rosette shrubs such as Velleia montana , Celmisia asteliifolia , and Plantago antarctica . [5]
Diselma archeri is a species of plant of the family Cupressaceae and the sole species in the genus Diselma. It is endemic to the alpine regions of Tasmania's southwest and Central Highlands, on the western coast ranges and Lake St. Clair. It is a monotypic genus restricted to high altitude rainforest and moist alpine heathland. Its distribution mirrors very closely that of other endemic Tasmanian conifers Microcachrys tetragona and Pherosphaera hookeriana.
A cushion plant is a compact, low-growing, mat-forming plant that is found in alpine, subalpine, arctic, or subarctic environments around the world. The term "cushion" is usually applied to woody plants that grow as spreading mats, are limited in height above the ground, have relatively large and deep tap roots, and have life histories adapted to slow growth in a nutrient-poor environment with delayed reproductivity and reproductive cycle adaptations. The plant form is an example of parallel or convergent evolution with species from many different plant families on different continents converging on the same evolutionary adaptations to endure the harsh environmental conditions.
Eucalyptus coccifera, commonly known as the Tasmanian snow gum, is a small to medium-sized tree in the Eucalyptus genus, endemic to Tasmania. It has smooth, grey and cream-coloured bark, elliptic to lance-shaped adult leaves, flower buds in groups of between three and nine, usually white flowers and conical, hemispherical or cup-shaped fruit.
Donatia novae-zelandiae is a species of mat-forming cushion plant, found only in New Zealand and Tasmania. Common names can include New Zealand Cushion or Snow Cushion, however Snow Cushion also refers to Iberis sempervirens. Donatia novae-zelandiae forms dense spirals of thick, leathery leaves, creating a hardy plant that typically exists in alpine and subalpine bioclimatic zones.
Ewartia planchonii, commonly known as creeping cushionherb, is an endemic herb to alpine areas of Tasmania. E. planchonii is commonly found in the western highlands of Tasmania. The Ewartia genus is described as cushion plants/herbs due to the characteristic growth habits of low growing, highly compact mats which are made up of highly packed stems. These mats are slow-growing and are often located in soils that contain low nutrients.
Pterygopappus is a genus of flowering plants in the tribe Gnaphalieae within the family Asteraceae. There is only one known species, Pterygopappus lawrencii, which is endemic to alpine Tasmania. It forms thick, light blue/green mats with densely packed leaves. It is most common in the mountains of the northeastern part of the island. It is a slow grower and prefers cool, moist environments.
Orites revolutus, also known as narrow-leaf orites, is a Tasmanian endemic plant species in the family Proteaceae. Scottish botanist Robert Brown formally described the species in Transactions of the Linnean Society of London in 1810 from a specimen collected at Lake St Clair. Abundant in alpine and subalpine heath, it is a small to medium shrub 0.5 to 1.5 m tall, with relatively small, blunt leaves with strongly revolute margins. The white flowers grow on terminal spikes during summer. Being proteaceaous, O. revolutus is likely to provide a substantial food source for nectivorous animal species within its range.
Tasmanian cushion plants are low growing, highly compact, woody, spreading mats that can grow up to 3 m in diameter, located mainly on the island of Tasmania. These mats are made up of tightly packed stems that grow at the same rate so that no apical rosettes protrude above the rest. The term cushion plant refers to a characteristic growth habit adopted by various species from a range of families to adapt to alpine and subalpine environments and areas of high latitude. They are adapted to grow in low nutrient areas and typically have deep taproots. Cushion plants are very slow growing and do not grow high above ground; mounds typically remain under 30 cm high. Underneath the living surface of the cushion, the plants either allow dead leaves to persist or produce non-photosynthetic material, resulting in an insulating effect.
Tasmania can be broadly divided into two distinct regions, eastern and western, that exhibit major differences in climate, geology and vegetation. This divide, termed Tyler's Corridor, runs from just south of the northwestern corner, and continues south, cutting roughly down the center of the island. The vegetation changes occur principally due to variations in soil types, which are a result of the geological composition, and the vast difference in climate across the state. Generally, the west has a higher mean rainfall but poor acidic soil while the east has a lower mean rainfall but slightly more fertile soil. This results in a larger proportion of rainforest, moorland and wet sclerophyll vegetation dominating in the west and predominantly dry sclerophyll in the east.
Astelia alpina called pineapple grass, silver astelia, or perching lily is a commonly found species in alpine and subalpine areas of Tasmania and the Australian Alps. It is a perennial herb that typically dominates its environment by growing in dense clusters, called mats, in alpine bogs. There are two subspecies: Astelia alpina var. novae hollandiae from New South Wales and Victoria and Astelia alpina var. alpina endemic to Tasmania. Both subspecies appear very similar to each other. The species was originally described by Robert Brown.
The vegetation in Tasmania's alpine environments is predominately woody and shrub-like. One vegetation type is coniferous shrubbery, characterised by the gymnosperm species Microcachrys tetragona, Pherosphaera hookeriana, Podocarpus lawrencei, and Diselma archeri. Distribution of these species is relevant with abiotic factors including edaphic conditions and fire frequency, and increasingly, the threat of climate change towards species survival exists. Conservation and management of coniferous shrubbery are necessary considering that the paleoendemic species, Microcachrys,Pherosphaera and Diselma, have persisted in western Tasmanian environments for millions of years.
Pherosphaera hookeriana, or Mount Mawson pine, is a dwarf conifer endemic to Tasmania, at altitudes above 600 meters. There are roughly 30 known sites, with population numbers in the tens of thousands. The species occurs in a range of habitats typically in areas near water bodies, mostly on dolerite derived soils. The species is highly fire sensitive and an increase in fire events associated with climate change may lead to local extinction and fragmentation of habitat.
Cotula alpina, also known as the alpine cotula, is a perennial herb in the family Asteraceae. It is a small flowering plant that forms ground covering mats and is well adapted to alpine environments.
Abrotanella forsteroides, commonly known as the Tasmanian cushion plant, is an angiosperm endemic to Tasmania, Australia. The plant is a dicot species in the daisy family Asteraceae and can be identified by its bright green and compact cushion like appearance.
Abrotanella scapigera is an endemic angiosperm of Tasmania, Australia. It is a member of the family Asteraceae, commonly found in alpine regions of northwest and south-central Tasmania. This species is named after its characteristic sparsely leaved flowering stem that distinguishes it from the other 18 species of the Genus.
Olearia ledifolia, commonly known as rock daisy bush, is a species of flowering plant of the family Asteraceae. It is endemic to Tasmania and found at higher altitudes where it grows as a low, compact bush with tough, leathery leaves and small white and yellow daisy-like "flowers" in summer.
Dracophyllum minimum, commonly known as heath cushionplant or claspleaf heath, is a species of bolster cushion plant endemic to Tasmania, Australia. It is a low growing, highly compacted plant with white flowers, commonly found in alpine areas of the south, centre and west of Tasmania.
Ewartia meredithiae, commonly known as the rusty cushion plant, is a Tasmanian endemic cushion plant species. Out of the four species in Australia from this small genus, Tasmania has three, all of which are low growing, alpine species.
Diplaspis cordifolia is an endemic Tasmanian herb, known commonly as western mountain-pennywort. It is found in alpine vegetation communities across Tasmania, most commonly in the West and South-western areas.
Plantago gunnii is endemic to Tasmania and is commonly referred to as bolster plantain or bolster plantago. The etymology of the genus Plantago comes from the Latin words planta and the suffix –ago, which is represented by the leaves pressed flat against the ground. The species name gunnii is in honour of Ronald Campbell Gunn of Launceston, who first discovered the species.
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