Notes from the Field

Siberia 2012: After the Fire

July 20th, 2012 by Joanne Howl

Embenchime River    65°16’35’’N    101°9’21’’E

11:00 p.m.  Siberia      11:00 a.m. EDT

78° F  High    49°F  Low       Sunny

Dr. Ranson reports:

We hopped out of our tents early this morning, broke camp, grabbed a quick breakfast and headed into the forest to make our measurements.  We were in the woods by 8:30 this morning, and didn’t return until around 5:30 this evening.  A nine hour workday – that should be enough for anybody. But expedition days are long, long days.

Once we returned to camp, we ate a quick dinner, loaded up our boats, and headed downriver.  Three hours later, we found a spot to sleep, unloaded the boats, set up an overnight camp, and had a little late-night dinner.  After a long day in the woods, we have begun our race to Tura.  The plane to Krasnoyarsk leaves on Monday – and we intend to make that connection.

The day’s work included making tree measurements along GLAS footprints, collecting samples for fire-return studies, and then spending hours on the river, heading to Tura. Here Slava and Sergei work collecting samples for fire return studies.

Today we left our last camp on the Embenchime.  Tonight we’re camping on the Kochechum River.  We were on this river in 2007, and our last two days will be spent retracing the last days of that Expedition.  It will be interesting to see if there are noticeable changes.

Today we had quite a lot of measurements to make.  We walked the lines where the GLAS instrument on the ICESat satellite had collected data, and we planned to measure all of the GLAS footprints.  We discovered that some of those footprints fell in burned areas.  That wasn’t a total surprise, but we found that in several of those plots, there were no trees at all to measure.  The fire had taken everything, and there was no regeneration at all.  In other GLAS footprints there had been fire as well, but also some reproduction. In those plots, we took made our standard measurements.

Slava collected some fire-return data, including several discs in the general area.  He said that, based on his quick field examination, the last fire here had burned about 25 years ago.  If that is accurate, then there has been remarkably little regeneration here over the last 25 years. Larch grows very slowly, and they don’t take up a lot of carbon until they get big.  We cut one tree that was 7-8 feet tall and it was only 17 years old.

The fires here appear to have been really extensive, as well as really frequent.  In some locations, there are drainage ditches and wet areas, and in those wetter areas stands of older trees have resisted fire and survive.  These survivors provide a source of seed, so some regeneration is occurring.  And many stands show normal heavy regeneration after the fires.  However, the lasting impression I have of today’s work is walking in the burned areas, and seeing very little regeneration in some of them.  Such a thing is so unexpected that it was an amazing, and sobering, experience.

As we’ve traveled downriver, my mind keeps turning over what I’ve seen.  The lack of regeneration in some of these areas challenges the traditional notion of vigorous regrowth of larch after fire.  It also has bigger implications in regards to the forest response to a warming climate.  I do not think we really understand what is going to happen to our boreal forests, and how the fate of the boreal forests will affect our Earth and our own lives, in a warming climate.

After a fire, larch stands tend to reproduce very vigorously. In some of today’s plots, reproduction was very sparse or nearly non-existent. The last tree-killing fire in this area was estimated to have passed about 25 years ago – but in that time, no larch has regrown. This finding may challenge traditional thinking about the dynamics of larch forests after fire, and brings forward questions about the effect of more rapidly returning fires on the reproductive ability of larch forests.

The traditional notion is that the boreal forests, especially these larch (larix gmelinii) forests, live in a rather symbiotic or at least balanced relationship with fire.  It is accepted that fire helps larch regenerate by improving the soil to make it more favorable for larch seed germination, and by reducing competition, allowing for the rapid growth of larch saplings.  Also, mature larch form a thick, fire-resistant bark, so most fires allow mature trees to remain, so seed sources are preserved.

What we saw in the northern forests was compatible with this traditional hypothesis.  We saw burned stands with thick regeneration.  And in the northern forests, the burning seemed to be somewhat controlled, because small areas of the forest were dry, with wet areas right next to them.  It appeared that the dry areas would burn, but the wet areas might tend to control fires, so vast hillsides were not destroyed at one time.  Also, we know from several studies that in the northern boreal forest fire return interval in any one stand is very long. All this, put together, means that small areas of forest burn regularly but infrequently, leaving time for replacement trees to grow back to adult size, so they become seed sources long before the next fire comes through. It also means that mature trees survive nearby to the burned area, and they could provide an immediate source of seed. However, as we move south, in this area, we seem to be seeing, in at least some areas, a failure of regeneration after fire.  That is a very troubling thought.

The theory is that these forests are generally a carbon sink for the world – they are growing, and as they grow they absorb carbon. They hold carbon in their roots and trunks, binding it and helping keep it out of the atmosphere.  We know that when forests burn, carbon is released, and at that time, the forests are a carbon source.  However, the thinking is that the regeneration is so strong afterwards, it allows the rapidly growing trees quickly to absorb a lot of carbon, so that even with intermittent forest fires, the boreal forests remain a sink.

There also seems to be an assumption that as the climate warms, and as permafrost thaws, that the soil will be more favorable for tree growth, so the trees will become bigger and more robust.  This should, theoretically, allow the forest to take up even more carbon, and potentially mitigate, to some degree, the effect of warming.  This all makes sense – but we do NOT know, for sure, if it is true.

Based on what we see, I’m not really sure we can assume the traditional notions.  It is clear that in a warming climate, the forests become dryer and fire returns more often.  Even with strong regeneration, fire has a limiting effect on the size of the forest, however.  It is really not clear if the forests will ultimately be bigger and faster-growing in a warming world, or if fire will limit the growth potential of these forests.

If fire returns quickly enough to kill off trees before they reach sexual maturity, then it may well be that we lose the regeneration – and without new trees, we won’t have replacement forests to uptake the carbon.  A lot of current climate theory is counting on regenerating and growing forests to take up carbon, to mitigate the effects of warming.   But what if rapidly returning fires end up killing off the forest before the trees are old enough to reseed?   We need to consider this possibility in our modeling of carbon, and include the potential impact of such a scenario.

In addition, there is a lot of data that suggests that as permafrost melts, it doesn’t just become more fertile soil for tree growth.  As the ice melts, the highly organic soil begins to decompose.  Decomposition of permafrost releases carbon as well as methane – both powerful greenhouse gases.  It may well be that in a warming climate, when a tipping point is reached, these forests may not only be unable to mitigate the effect of the carbon we humans pump into the atmosphere, but may also become a source of carbon and methane from both thawing permafrost and repeated fires. I don’t know what will happen – but we need to take a hard look at these issues, and soon.

Ross and his group worked on the south side of the river today, and found a lot of burned areas there, as well.  He, too, found little larch reproduction.   So what we have both found is that the larch is not reproducing well here.  On both sides of the river, it appears that fire is returning more frequently, and that they may not have time to reach seed-bearing age before fire returns.  If there is no seed available, because the fire returns too soon, then the next generation of larch may be wiped out.

Interestingly, what Ross did find was that birch was growing fairly well in some burnt areas, where larch was not regrowing.  We found a little birch on the north side of the river, as well, but not as much as Ross has found on the south side.  I’m not sure what this means, but it is different than what we are used to seeing.  We are used to seeing strong larch regeneration after a fire – and there is some evidence that it does not always occur.

We all need to consider this finding carefully – it challenges our comforting hypothesis that the forests will be able to mitigate climate change.   To a point, we can expect to forests to help.   But when the climate is so warm and dry that fire returns to an area quickly – I don’t think we really know what will happen then.  It is possible that under rapidly returning fire, the forest may not be able to maintain itself.   We really need to study these questions earnestly – and quickly.   It is truly important for us to understand what is happening to our home planet, our beautiful Earth.

The last camp on the Embenchime River. From here, the scientific team begins their return to Tura. As they join the Kochechum River, they look forward to finding higher water and faster current to speed them on their way back home.

The forests here have a great deal of diversity, especially in response to fire.  It’s really valuable to see this diversity, and to be able to make measurements in all the various types of regeneration situation.  We’ve seen a few plots with very little regeneration.  To understand what this means, we need to gather data to find out if this is occurring in rare areas, or if this lack of regeneration is occurring in widespread areas.  Remote sensing, either by satellite or by our G-LiHT instrument, is going to prove very useful to help us understand these forests.  I am looking forward to getting back out here next year, with our instrument package, and applying it to this year’s data.

For us, tomorrow will be another big day on the river.  We’re in a race against time, a race to Tura. Slava is working on the boats now, putting a new propeller on the motor.  He thinks the river is deep enough to use a better propeller – one that hasn’t been beaten up by rocks already.  The old propellers have been kept running – Sergei and Pasha file the blades down each night, to smooth out the areas damaged by rocks during the day.  The old propellers are working, but the new should help us gain a little speed.

It seems like a really long way to go, but the river is faster, the water is higher, and we are excited to be heading towards home.  It’s not easy travel. Every time we come to a turn, Slava slows everything down and we have to look at the waters carefully.  We don’t want to run headlong into shallows and tear the boats.  Even in the Kochechum, we all too often have to jump out of the boats and pull them through the shallows.  But we’re on our way back.  We will be in Tura, soon.

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