“Despite being portrayed as a villain, timber harvesting in the form of thinning can substantially counteract the impact of fire regrowth on water yield. The benefits of regrowth thinning have been widely studied throughout Australia. In Melbourne’s catchments, strip-thinning trials have shown that up to 2.5 million litres a year of additional run-off can be generated from each hectare of thinned regrowth. A program of thinning the 1939 regrowth could add billions of litres of water to our storages.
Western Australia has been quicker to take advantage of thinning as a water management tool. Earlier this year, a $20 million, 12-year thinning program was initiated in a substantial segment of Perth’s catchment following four years of exhaustive public and stakeholder consultation. Every 1,000 hectares thinned is expected to deliver an additional one billion litres of run-off into the Wungong Dam a year.”
This is an extract from an opinion piece by Mark Poynter first published in The Age and just republished by On Line Opinion, entitled ‘Fired-up Forests, Have More Impact Than the Loggers‘. Read the full article here: http://www.onlineopinion.com.au/view.asp?article=5213
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
I can’t help but think that someone will come up with the idea that water run-off is associated with erosion, and therefore loss of “precious topsoil that is our heritage,” and so forth.
If you take a thousand acres at the depth of two inches, and move all that one-eighth of an inch towards the nearest watershed, eco-whackos will scream about “millions of tons of erosion that is perpetually lost.”
Brace yourself.
They may try but will not do so on scientific grounds. There is absolutely minimal soil movement from thinning operations. The root systems remain in situ, most ground cover remains alive and understorey biodiversity is improved due to increased sunlight. They all perform the same water quality service as the unthinned trees but use less water doing it.
And even if there was a decline in water quality then it is a bit rich for anyone to raise it as an issue when the alternative to improved catchment yield is to recycle sewerage.
It appears necessary to inform public debate that it is so much easier and cheaper to filter out a few extra parts per million of silt than to bring turds and urine up to potable standard.
Mark: It’s a good article. Thanks. However I’m a bit too dry at the moment to comment further.
No reference to the links between reduced vegetation and reduced rainfall then? Would be interesting to see the comparisons over long term studies, though unfortunately the effects of tree thinning on air moisture are not as localised so become those great ‘externalities’ that economists love to bundle the outside occurring knock-ons under…
May we ask how thinning is normally carried out – what’s chosen, how are the trees felled, are the culled trees used, and what does it “look like” after thinning. Just asking – no hidden agenda.
Presumably it would matter what the soil water store might be; and no rainfall in the catchment would also be an overriding factor. I concede in between, there is an effect – how much ??
And mechanism – reduced leaf area index/foliage projective cover/canopy cover? How long till “regrows” or remaining forest “compensates”.
Looking forward to being fully Mottified !
Luke: In my region thinning used to occur when they went into plantations and regrowth after “poles”. These poles were either for the Hydro (Tasmanian electricity grid) out of hardwood or as treated spars for agriculture eg chicken coops etc from pine. A good forester in those days would also take out deadwood and twisted stuff at the same time leaving only thicker stems to go on into sawlogs.
But the practice changed with hardwood woodchip operations. A more likely scenario today would be grab everything except the oldest and ugliest trees and hope they reseed all the fired up trash and ash underneath. But note; our native forest regrowth is naturally culled by its own giants on the make.
From direct observation of various vigorous eucalypt crops after severe disturbance, fire or road making, the spindly stems die more from competition at root level than the crown. I’ve seen mountain ash sprout up thick again like overgrown lawn, this is a most important aspect of native forest recovery and with fast growing gum trees. It all takes quite a while before that deadwood from natural selection is completely recycled into the tall forest we call old growth today. IMHO this intermediate stage is the dangerous one.
I see others also notice how rainfall is likely to be triggered by healthy forest however I don’t see enough science picking up on this point. There is a whole lot to be understood yet around just what triggers due point at the lowest altitudes around big forests. In Tasmania a good airman watches the rise and fall of “clag” on the ranges. I watch when clag joins the clouds and vice versa. On the hobby farm the mist rises up the gully from way below. The adjacent farms with out forest cover don’t get it.
“But the practice changed with hardwood woodchip operations. A more likely scenario today would be grab everything except the oldest and ugliest trees and hope they reseed all the fired up trash and ash underneath”.
What aload of bollocks, Gavin, you are describing a clearfall and burn here, not a silvicultural thin.
The extent of a thin depends on the condition of the stand. If there was a uniform regeneration after a wildfire then there may be in excess of 40,000 saplings per hectare. And as a mature forest may have less than 40 giants per hectare then clearly, nature itself, will have an interest in doing some serious culling to get to that climax condition.
40,000 stems/ha is 4/m2 or a root diameter of 50cm each stem. And that means the stem diameter is unlikely to get any thicker than 1/15th of that root diameter which comes to 33mm. On the standard 1% taper this would mean the saplings will get to a height of 3.5 metres and then start choking each other to get some space.
If every second tree was removed this would allow an average root diameter of 70cm, a stem diameter of 46mm and a height of 4.5 metres. And this amount of growth would mean you would need to come back again in 12 months, and again 12 months after that.
So at this stage of the growth cycle it is better to take out all but 1000 stems so the remaining ones can grow feely for a decade or two.
If the existing stem density is about 3,000/ha it would mean an average root diameter of 1.8m, a stem diameter of 12cm and a height of about 12 metres. The only markets for this size wood is as woodchip or landscaping material. And the aim of the thin would be to remove all the bent, damaged or smaller stems so the better formed ones can thrive.
The number of stems removed at this stage would depend on the purposes to be achived by the thin. If maximising water yield is the prime objective then the numbers could easily be reduced to 400/ha but it would only be effective if the understorey was subsequently grazed to ensure that the understorey does not grow to a point where it challenges the retained stand and defeat the purpose.
If there was a good market for small poles then numbers migh only be reduced to 1000 but this would mean a shorter interval before the stand got back to full capacity and minimum water yield.
From this point on, the normal procedure would be to halve the number of stems each time they reached the point of excessive competition. So 1000 stems with average root/crown area of 10m2, with root diameter of 3.1m, stem diameter of 20cm and height of 20 metres would be thinned to 500 so these trees could then grow to have 4.5m root/crown diameter, 30cm trunk diameter and, assuming a good moist site, 30 metres in height.
Note, Koalas would be unlikely to move into the stand until the trunks get to 20cm diameter, with preference for 30-60cm stems. And most trees produce maximum leaf, sap and flowers when they are reaching out to occupy a newly created gap. And that is why the entire leaf, sap and flower based food chains prefer thinned regrowth over old growth.
And Luke, that stuff about reduced rainfall from reduced vegetation is of only marginal relevance in relation to thinning where the predominant vegetation remains intact. And when you can find an entire region that has undergone a simultaneous thinning event on a scale that is capable of influencing rainfall patterns then by all means give us a call. Until then, spare us the red herrings.
In the real world forested landscapes exhibit a broad mosaic of stands in various stages of the silvicultural cycle.
Ian – thanks for a comprehensive description of thinning – appreciated.
I was not suggesting reduced rainfall from reduced vegetation. I think you have me incorrectly ID’ed.
But how much thinning can a koala bear?
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“And when you can find an entire region that has undergone a simultaneous thinning event on a scale that is capable of influencing rainfall patterns then by all means give us a call” is a key statement from Ian.
It’s my guess we can’t find any sizable area on crown land today where managed thinning is occurring at a scale that will prevent major bushfires either. The most significant threat to our native forest ecology is the extent of severe bushfire damage today. Obtaining the maximum biomass again in our remaining bush reserves will be a tricky business from here on.
I proposed that we look first at forest management of our remote water catchments for major city supply infrastructure as a stepping stone to finding timber again in other reserves including national parks. The idea came after the acute case in the ACT (2003 bushfires) where we lost most of our pine plantations and much of our water supply.
From the subsequent McLeod inquiry we gained the concept of a Bushfire Abatement Zone (BAZ) and that all but eliminated our commercial forestry east of the Murrumbidgee River. Further studies revealed a conflict of interest in our recovery upstream from the old Cotter Dam. After that came the Namadgi National Park Draft Management Plan.
I’ve been saying; hey, what about access to our natural resources ever since. The irony is I only wanted to eliminate volatile pine tree crops right under our noses. Returning the bush to some form of hardwood forests it seems is the most difficult option in this parched country. Regarding our reaction to climate change; transition is difficult. Various principles get in the way as we blunder on.
But guess what happened, pines where they were hastily replanted after a previous bushfire and pines as wildlings are now doing better than anything else in this drought.
Eliminating pine has become another issue for the purists however I keep reminding them, our long term sustainability as a community has more to do with developing some resource independence and cunning.
In selecting the next dominant species we must go with the flow. By eliminating ground cover in the garden I’m making a good start to the current fire season.
Dear Jennifer, I have enjoyed reading Mark’s articles at On Line Opinion and agree with much of what he says but he must check his facts re thinning in Perth water supply catchments. The Wungong catchment is only 3.8% (THREE POINT EIGHT PERCENT) of the area of Perth catchments. So it is incorrect to say, “Western Australia has been quick to take advantage..”
This thinning is only a tiny TRIAL, just a PR effort so the WA Govt water orgs can trumpet that they are doing something and most of what they say has to have spin “fine tooth combed” out before truth emerges.
The reality of what is happening in Perth water supply catchments can be seen in my graphic at http://au.geocities.com/perth_water/ scroll down to, “Graphic of Catchment Efficiency 1980-2005 showing disastrous falloff 1996-2005 after ceasing catchment management.” Click on thumbnail for a larger graphic.
It is perfectly clear from my graphic that the WA Govt is de facto decommissioning Perth catchments. If catchments had been managed post 1996 as they were before that date so as to keep yields steady, Perth would have enjoyed about 90 GL extra water per year on average. Equal to production from two Kwinana sized seawater desalination plants, which require an investment of ~$500 million each now. That puts on scale the cost of catchment neglect.
This colossal bungling extends into other areas of water resources.
North of Perth a pine plantation at Gnangara suppresses the potential of the
groundwater there by about 100 GL per year. With incremental water valued by investment required in seawater desalination, Govt claims that the pines are needed to support a proposed plywood industry is simply ludicrous. Timber can easily be sourced on the open market if anyone is of a mind to make plywood and the pines must have a negative net present value now in view of their manifest Billion dollar damage to groundwater potential.
The Avon, Murray and Collie Rivers pass about TWICE Perth’s total water
consumption each year but in a weakly saline state. Surely desalination of a
small part of these flows would be cheaper and lower impact than seawater desal and could take place away from the fragile and crowded coast. In fact a private company, Agritech has been valiantly trying to interest the Govt. in a proposal to desalinate water currently wasted to sea each year from the Wellington dam near Collie. This proposal would be at no capital cost to Govt and would produce water at half Govt desal costs and would I am told use gravity in the process thus cutting back greatly on electricity.
Perth is not running out of water, the water is running out of Perth.
The Ancient Romans were vastly better water managers than the WA Govt.
The Archers et al of this world have long criticised the supposed “fragmentation” of private native forest and the implications for biodiversity. But this view has always been based on an intellectually sloppy use of native vegetation as a surrogate for habitat.
In the real world, most species derive habitat services from a whole range of landscape attributes that do not get mapped as native vegetation. How many orchards, for example, are mapped as habitat for flying foxes? The answer, none, but we know that orchards have played a critical role in the expansion of flying foxes into areas well beyond their historical range with resulting population increases.
The recent large scale wild fires, with numerous examples of localised “extinctions” in the continguous national parks estate is now making it very clear that the supposed fragmentation of the private native forest estate is actually the key to the long term viability of many forest dependent species.
In short, nothing stops a forest fire like an absence of forest. And the numerous gaps in native vegetation that have been assumed by many to be impacting on lifecycles and colony viability have actually been critical in excluding habitat destroying fire.
And far from being cooped up in small, unviable habitat clusters, the resident species have never been reluctant to include crops, orchards, barns and widely spaced paddock trees in their home ranges.
It seems the best thing one could do to maximise the ecological value and durability of a large forest area would be to put a golf course smack in the middle of it.
Centralised production has never worked. So why would anyone believe that centralised ecology would be any better?