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Dry Sclerophyll Forests of Tasmania

Dry Sclerophyll Forest dominated by Eucalyptus tenuiramis

The word sclerophyll is derived from the Greek words skleros - meaning "hard" and phullon - meaning leaf and this accurately describes the majority of shrub species found in these forests. In Tasmania approximately 26.3% of the state is covered in Dry Sclerophyll.

Description

A dry sclerophyll forest is characterized by low rainfall, low nutrient soils, periodic droughts and short fire frequency of 5-25 years. The vegetation consists of an open canopy between 8-30m with little understory or shrublayer and the groundlayer is quite bare.The limiting factor is usually water.

Flora

These forests can contain a high diversity of species with most of the diversity appearing in the shrub layer. The Eucalypts are usually the dominant tall trees due to their ability to live in a variety of environmental conditions but there can also be Allocasuarina or Callitris dominated woodlands. The actual species of Eucalypt dominating can vary greatly with 25 of the possible 29 species present in Tasmania able to grow in the Dry Sclerophyll conditions.

Plants of the understory and shrub layer usually have small, hard, narrow leaves and are adapted to xerophytic conditions. Many of these species are tolerant to low nutrients as well as low water supply. Many of the individuals in these forests will be slow growing due to the competition for resources.

Layers

The vegetative structure can be divided into four sections, this varies greatly depending on local conditions - see Variation.

Canopy

The canopy typically covers 20-25% of sunlight at a height of 30m and tends to be multi-storied of different aged trees. The dominant species is usually E.obliqua or E.tenuiramis but can also be one of a great number of Eucalypts such as E.globulus or even Allocasuarina or Callitris. When Eucalypts are present they tend to have a representative from both Monocalyptus and Symphyomyrtus with one usually sub-dominant to the other. Recruitment into the canopy usually requires a form of disturbance to initiate.

Understory

Exocarpus cupressiformis growing under Eucalyptus. sp

Trees of the understory are few and scattered, common species include Exocarpus, Allocasuarina, Banksia and Bursaria as well as sub-dominant Eucalypts in the process of growing to canopy height.

Shrub

This is where the majority of the sclerophyllus plants and the diversity of the forest is located. The shrub layer is still patchy and scattered but intercepts the most light of any layer. Plants in this layer usually sit between 30cm-1m and are quite robust with small, pointy leaves. A great number of species can be present here and they most commonly hail from the families Asteraceae, Fabaceae, Ericaceae and Myrtaceae. Seedlings of dominant and sub-dominants are also quite common although a great percentage of these will not grow past this phase.

Table 1. Common shrubs species of Dry Sclerophyll forests

• 
  Pultenaea juniperina
• Epacris impressa.
  Epacris impressa.
• Leptospermum scoparium
  Leptospermum scoparium

Groundcover

Primarily covered in dry leaf litter that is broken up by rocks and there are also patches of lichens. The leaves found here take longer to degrade than other forest types leading to this build up of dry leaf litter that will completely cover the surface up to an inch thick.

Distribution

Due to the ability of Eucalypts to grow in a variety of conditions which in turn leads to many slightly different dry sclerophyll forests the distribution is over almost the entire state. The highest concentrations of Dry Sclerophyll forests are on the east coast from top to bottom of Tasmania.

Variation

With such great variability in dominant species and the environments they can grow in, Dry sclerophyll forests are classified due to their understory/shrub layers. They can be put into four main classes - Sedgy, Heathy, Grassy and Shrubby of which all can be found in Tasmania. The variability that allows these different classes comes from the conditions the forest has grown in, factors such as geology, soil type, soil nutrients available, rainfall and species present will all effect which classification of forest is created.

For example in a very dry area of Permian mudstone E.tenuiramis is likely to be the dominant species

Fire Ecology

Burnt bases of Eucalyptus tenuiramis in a Dry Sclerophyll Forest demonstrating fire frequency and survival of the individuals

Dry sclerophyll forest communities of Australia are considered to be among the most fire-prone communities in the world and fire ecology tends to be the most researched aspect of Dry Sclerophyll forests. Fire is an important part of Dry Sclerophyll forests and the frequency at which a forest is effected by fire can have significant outcomes. Species like the Eucalypts require fire as a part of their life cycle - without it they may not even be able to reproduce. When a fire breaks through the leaf litter and most shrubs will be completely burnt with some Eucalypts severly effected, but this often triggers seed release and/or germination from Eucalypts in the newly disturbed soil. The removal of competition allows new seedlings to grow and establish before the shrubs and understory trees return and compete. In order to retain the structure of these forests a fire regime of between 7 and 30 years is estimated. If there is an extended absence of fire it can change the composition of species in the forest and usually leads to a decrease in diversity as single species take over, although many of the species that were present above ground can still be found in the seed-bank

The pre-adaptations Eucalyptus species have to fire are what enable them to be so successful in Dry Sclerophyll environments. The release and germination of seeds in response to fire is critical as well as have decorticating stringy bark that promotes fire and its spread. Other species of Eucalyptus have a thicker bark designed to burn and leave the cambium of the tree relatively undamaged by the fire. Methods of regeneration also include epicormic buds - if the trunk is left intact new branches can sprout again from these and underground lignotubers - the entire trunk of the tree can be lost/burnt only for new saplings to spring from these lignotubers.

There is however a balance to the fire frequency, too many fires too quickly can be damaging to the populations. Shrubs that obligately regenerate from seed can decline in numbers and success in the presence of constant fires and many shrubs will actually regenerate vegetatively so a strong, hot fire can be quite detrimental to their survival

Fauna

The high species diversities of these forests supports a large number of animals species. The open ground is ideal for some species to forage.

Comparison to Wet Sclerophyll

The border between wet and dry sclerophyll is often quite mixed and difficult to distinguish, many species can be present in both although fires can create more definitive borders where they stop. The valleys and gullies of Dry Sclerophyll forests will often transition into Wet Sclerophyll providing there is ample rainfall. Wet sclerophyll tends to be a higher production forest with a dense understory, tall shrub layer and dominant Eucalypts that can grow up to 90m. In contrast the Dry Sclerophyll forests have a noticebly absent tall shrub layer and sparse understory. . The rainfall, nutrient availability and soil quality is generally greater in wet than dry.

Further Reading

Reid, JB and Hill, RS and Brown, Michael and Hovenden, MJ, Vegetation of Tasmania, (2005)

DPIPWE, Dry Eucalypt Forest and Woodland Vegetation Benchmarks (2012), http://www.dpiw.tas.gov.au/inter.nsf/WebPages/LJEM-6RF6JF?open