Small Tree Farm: Deciduous Tree Nursery

Chrissy's Contributions

"This article was printed as an Opinion piece by the West Australian in a slightly edited form entitled "Old Trees the Key to SW Forests" on 5/11/12

The big gap in the new Draft Forest Management Plan is its lack of a restoration plan. The legacy of past intensive logging has created forests that are more vulnerable to drought but confront a drier future. This serious challenge is raised in the Draft but remains unresolved. Although the public discourse remains focussed on the familiar and bitter battle between the loggers and conservationists, the bigger question is can we keep our forest ecosystems alive and healthy through drier times?

Ironically to do so may require a new form of cutting that leaves the better stands alone and the largest trees that are usually taken for sawlogs untouched, instead thinning out the very dense stands of small trees that have grown up after past “gap creation” removed the canopy. We must aim to restore a forest that once again has large dominant trees that are both more water efficient and resilient.

As our climate has become an average nearly one degree hotter and 15% drier since 1975, and a further 12% drier again since 2001, the water table under the forest has progressively dropped. As a consequence the trees must reach many meters deeper to find water in summer. Fortunately the remarkable Jarrah is able to develop immensely deep root systems over time and despite the climate changes of the past thirty five years it had shown little obvious damage.

However last year was a wake up call. After the 2010 winter, the driest ever recorded, over the following summer some 16,000ha of Jarrah forest collapsed in patches in the Northern Jarrah Forest. After the 2011 winter some of these dead crowns re-sprouted from the root in coppice shoots only to die back again last summer. Meanwhile further south, miles of Jarrah Forest near Bridgetown suffered severe insect attack that browned off all the leaves. Insect predation is often a secondary symptom of drought stricken trees that cannot metabolise properly and thus stop production in their sap of bitter alkaloids that would normally deter insect pests.

Visiting American forest ecologist Craig Allen told a packed UWA audience earlier this year about his global survey of regional to continental scale forest deaths attributed to drought and secondary insect predation. He found over eighty examples world wide of large scale forest collapse in all climates from the tropics to the cool temperate zones. In Canada alone three quarters of a million hectares of pine forest died from beetle attack. This raises concerns that dying forests can change from sinks into major sources of atmospheric carbon.

Not only are the South West forests getting less rain but also the structure of much of the forest is now more prone to drought. Regrowth forests need significantly more water, using up to twice the water of old growth forest. This is because the tree trunks contain relatively more sapwood than wood in young trees. At that point the choked Jarrah regrowth tends to “lock-up” and stop growing because, being the tough survivor that it is, Jarrah does not readily self-thin. So young dense forest stands struggle for decades to restore a natural structure. They also have greatly reduced flora and fauna value.

Whilst these altered forests need much more water than the old forests they have replaced, they are actually receiving less. They are very vulnerable. The draft Management Plan touches on the predicament but proposes yet more logging which will create yet more drought prone young stands whilst offering no programmes to restore the existing legacy of the tens of thousands of hectares of Jarrah regrowth.

The only significant thinning proposal in the Draft Plan is in Perth’s water catchments. However in order to bring back any useful stream run-off into the dams, this proposes a radical combined logging and thinning programme that will reduce these parts of the Jarrah Forest to only 8m2 density per hectare. This is much more intense than non-commercial thinning practice in the past and, like all logging, will require follow up control of the subsequent dense regrowth ten years later to maintain the objective of restoring 1990 stream flows and riparian ecosystem.

Why is there no attempt in the Plan to address this acknowledged legacy of vulnerable young forests by phasing out business-as-usual sawlog harvesting in order to keep all the remaining dominant older trees, instead working to the increase the resilience of the young stands that we have created with a new era timber industry that thins only the crowded young regrowth?

The reason is a stand off. Whilst admitting this regrowth legacy is the biggest problem facing management in the context of the drying climate, foresters persist with their ingrained professional thinking that sawlogs are their only raison d’etre. This is of course well suited to the current State Government who do not want to see any more closures of mills on political principle, after losing the fight over old-growth logging. Yet if thinning is combined with saw logging which removes the dominant trees, it is no longer restorative, and only compounds long term problems.

So there is no restoration plan for the regrowth stands that risk collapse in significant numbers over the life of the ten year plan if climate trends persist. Indeed the conservation movement has deep mistrust of any management whatsoever. However, if done correctly, thinning out young trees will improve the long term health prospects of the ecosystem. So we are at an impasse where the current plan is to make yet more forests vulnerable to collapse, whilst most activists also oppose any restoration forestry, preferring to let our stressed young forests take their chance.

Independent trials could be undertaken in disturbed forest to demonstrate the benefits of restoration, and to build community trust in this type of forest management. It is vital that all sides in the logging v conservation debate move on from their entrenched positions and start working together on a restoration plan to address this legacy before the young forests collapse while we continue arguing. It is time to give back to forests that have given so much, rather than taking more.

Chrissy.   4 November 2012


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