Eucalypt Forest Life CycleEucalypt Forest Life Cycle
Eucalypt forests cover much of Tasmania and feature in most rural landscapes. Eucalypt trees and forests follow a natural biological life cycle that progresses from germination of seed, growth to maturity to over maturity and finally death and replacement. Some eucalypt species have a life span of about 250 years, whereas others live up to 400 years.
Whilst eucalypts form the dominant plant species for most Tasmanian forests, the forest ecosystem includes a variety of other plants, woody shrubs and trees, and species of insects, animals and birds. Throughout a forest’s life cycle, population densities of different flora and fauna will increase or decrease depending upon the forest’s stage of life and condition, and their own habitat requirements.
The life cycle of trees and forests may be viewed as four stages. The age at which trees change from one stage to another varies with the species of eucalypt and the site conditions.
Stage 1: Disturbance, germination and early growth (Trees - 0 to 5 years)
Eucalypts have small seed and for effective regeneration the seed needs to be in contact with the mineral soil. Once germination occurs, eucalypts grow quickly, allowing them to establish and grow ahead of shrubs and other tree species.
Over the ages, wildfire has been the primary means of preparing the seed bed for eucalypt regeneration. These wild fires killed or damaged large areas of forest and give rise to large areas of even-aged forest. Currently, managed forests use regeneration burns on much smaller harvested coupes to create a good seedbed for regeneration.
Stage 2: Saplings and regrowth forests (Tree - 5 to approx. 100 years)
Young eucalypts increase in height very quickly. Each competes with the other for the available light, nutrients and water. Often several thousand eucalypt seeds will germinate on each hectare but only about 250 will survive to grow to maturity.
Although the tree size will vary depending on the species and site fertility, for forest of commercial timber quality, one would see trees develop to a height of 40 metres with a diameter at ground level of about 1 metre. As the tree reaches maturity, the crown widens and vertical growth slows. Some minor dieback of branches may start occur especially during dry seasons. In wet sites, trees of species that can survive and grow in the shade, such as Myrtle or Sassafras, develop as an understorey.
Stage 3: Mature trees (Trees – approx. 100 to 250 years)
At a mature stage, trees add little or no height but continue to add girth. During dry seasons there will be considerable die back in the crown and strong winds may break off branches. This allows insect and pathogens to enter. As the tree ages further, growth in girth slows and rot becomes established in the older wood at the centre of the tree. This spreads outward and upward from the ground.
Stage 4: Overmature and senescent trees (Trees - older than 250 years)
Overmature trees are subject to further loss of larger limbs and increased attack by insects and pathogens. As the centre rot of the trunk increases, the trees lose strength. Some blow over during strong winds while others collapse under their own weight. In wet eucalypt forests, the understorey species, such as Myrtle, grow and fill any space this leaves in the canopy. As this restricts eucalypt regeneration, these understorey species become and remain the dominant forest tree until wildfire or some catastrophe allows eucalypt to regenerate.
The whole cycle then begins again.
For further information log on website :
http://www.tastimber.tas.gov.au/SusArticle_View.aspx?articleid=167
Eucalypt forests cover much of Tasmania and feature in most rural landscapes. Eucalypt trees and forests follow a natural biological life cycle that progresses from germination of seed, growth to maturity to over maturity and finally death and replacement. Some eucalypt species have a life span of about 250 years, whereas others live up to 400 years.
Whilst eucalypts form the dominant plant species for most Tasmanian forests, the forest ecosystem includes a variety of other plants, woody shrubs and trees, and species of insects, animals and birds. Throughout a forest’s life cycle, population densities of different flora and fauna will increase or decrease depending upon the forest’s stage of life and condition, and their own habitat requirements.
The life cycle of trees and forests may be viewed as four stages. The age at which trees change from one stage to another varies with the species of eucalypt and the site conditions.
Stage 1: Disturbance, germination and early growth (Trees - 0 to 5 years)
Eucalypts have small seed and for effective regeneration the seed needs to be in contact with the mineral soil. Once germination occurs, eucalypts grow quickly, allowing them to establish and grow ahead of shrubs and other tree species.
Over the ages, wildfire has been the primary means of preparing the seed bed for eucalypt regeneration. These wild fires killed or damaged large areas of forest and give rise to large areas of even-aged forest. Currently, managed forests use regeneration burns on much smaller harvested coupes to create a good seedbed for regeneration.
Stage 2: Saplings and regrowth forests (Tree - 5 to approx. 100 years)
Young eucalypts increase in height very quickly. Each competes with the other for the available light, nutrients and water. Often several thousand eucalypt seeds will germinate on each hectare but only about 250 will survive to grow to maturity.
Although the tree size will vary depending on the species and site fertility, for forest of commercial timber quality, one would see trees develop to a height of 40 metres with a diameter at ground level of about 1 metre. As the tree reaches maturity, the crown widens and vertical growth slows. Some minor dieback of branches may start occur especially during dry seasons. In wet sites, trees of species that can survive and grow in the shade, such as Myrtle or Sassafras, develop as an understorey.
Stage 3: Mature trees (Trees – approx. 100 to 250 years)
At a mature stage, trees add little or no height but continue to add girth. During dry seasons there will be considerable die back in the crown and strong winds may break off branches. This allows insect and pathogens to enter. As the tree ages further, growth in girth slows and rot becomes established in the older wood at the centre of the tree. This spreads outward and upward from the ground.
Stage 4: Overmature and senescent trees (Trees - older than 250 years)
Overmature trees are subject to further loss of larger limbs and increased attack by insects and pathogens. As the centre rot of the trunk increases, the trees lose strength. Some blow over during strong winds while others collapse under their own weight. In wet eucalypt forests, the understorey species, such as Myrtle, grow and fill any space this leaves in the canopy. As this restricts eucalypt regeneration, these understorey species become and remain the dominant forest tree until wildfire or some catastrophe allows eucalypt to regenerate.
The whole cycle then begins again.
For further information log on website :
http://www.tastimber.tas.gov.au/SusArticle_View.aspx?articleid=167
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