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International Symposium on the dynamics and ecological services of deadwood in forest ecosystems

Dead wood and dying trees: a matter of life and diversity

Martin Moroni
Forestry Tasmania

Simon Grove and I attended and presented at the International Symposium on the Dynamics and Ecological Services of Dead Wood in Forest Ecosystems that took place in Quebec in May 2011. This was one of the first international meetings devoted solely to dead wood, bringing together experts from around the world who study its quantities, cycles and its contribution to habitat.

dead-wood

A river near James Bay flows through a boreal forest dominated by black spruce (Picea mariana) that was recently burned by a wildfire. Like wet eucalypt forests, black spruce forests are well-adapted to wildfire and regenerate very well after a fire. Fire intensity varied across the landscape.  Patches of live trees were scattered through regions that had been completely killed by fire - a similar pattern to that frequently seen after forest fires in Australia.

Because dead wood (or woody debris) does not form a saleable product it is often overlooked in forestry circles. However, dead wood is an intrinsic part of a forest ecosystem.  Vast numbers of species are dependent on woody debris, many more than rely directly on living trees. Dead wood contains a significant stock of nutrients that only become available to living vegetation after the dead wood has been broken down by the combined actions of the dependent species.  Thus, at the symposium, most of the attention to dead wood was from a biodiversity perspective, including Simon’s two presentations.  One of Simon’s presentations was on saproxylic beetles, based on ten years of date from the long-term log decomposition experiment at Warra; his second was a wide-ranging synthesis of the ten years of ‘deadwoodological’ research that he has overseen in Tasmania.  My keynote presentation compared the quantities of woody debris that accumulate in different forest types, using case studies from Newfoundland (Canada) and Tasmania.  In an international context, Tasmanian forests naturally support very large quantities of coarse woody debris, mostly due to high input rates and slow decomposition rates.  Perhaps more interesting in this era of climate change and carbon storage, I also co-authored a presentation on dead wood buried in organic soils.  This relatively poorly studied form of woody debris can be preserved for centuries and thereby constitutes a (newly recognised) medium- to long-term forest carbon pool.

The symposium was held in a mining and University town that is nestled beside a lake in the boreal forest in northern Quebec.  On arrival we were greeted by cold, windy spring weather.  Over the ten days that we were there it warmed significantly - so much so, that by the time we left it was “shorts-and-t-shirt weather”, coinciding with the forest bud break and the deciduous trees coming into leaf. The aspen and spruce forests in the area were generally under 30 metres tall with a “big” tree measuring only 30 cm in diameter – quite a contrast Tasmania where a tall forest exceeds 55 m in height and a “big” tree might measure 4-6 m in diameter.

Simon and I were fortunate to be able to take part in the post-conference tour. As we drove northtowards the tree line (at one stage through a forest fire!), the trees became progressively shorter.  We met with the Cree First Nations at James Bay (the southeastern extension of Hudson Bay, still frozen at this time of year), and took a tour of one of the world’s largest hydropower schemes – the Rupert-Bourassa hydroelectric station. Here, we were able to see the planned diversion of water from a lake into a power station that was still under development; we stood on the dam wall of a scheme larger than all of Tasmania’s dams combined; and we walked into the underground generation chambers and saw the turbines in action.  A civil engineer’s dream come true!

Simon and I were left with the impression that central Canada is vast and sparsely populated; that you would not have trouble finding spruce trees, which dominated thousands of square kilometres of forest; and that by looking after the live trees in all age classes in our landscape, we will also be looking after the much more interesting dead wood across all its size and decomposition classes.  In so doing we keep our ecosystems resilient and functioning.  For both of us, the visit reminded us of the uniqueness of Tasmanian and Australian forests and the value and quality of the research on dead wood that we’ve achieved locally.

BIOBUZZ ISSUE FIFTEEN, DECEMBER 2011