I believe the loblolly pine forest is a good indicator of long-term climate trends. They and their long tap roots are sensitive to long term soil moisture levels. The lost pines of Bastrop are there because it's an island of sandy soil that is permissive so that more of the region's rainfall is available for tree growth versus becoming surface runoff. Likewise the east Texas pines indicate both sandy soils and greater and more dependable rainfall. There are islands of loblolly forest between Bastrop and Houston whereever sandy soil inclusions exist in what is largely a sea of heavy clays.
How old is the pine forest around Bastrop? I'd guess it's been there since before the end of the Pleistocene when rainfall was higher than today and temperatures were cooler. Probably the pines were continuous or nearly so between Austin and Houston. I'd also guess that it survived the Holocene optimal as I've heard from other biologists that there is significant genetic differences between the Bastrop pines and those of east Texas.
So if the Bastrop pine forest dies before we get rain, then I'd say the drought and high temperatures are unprecendented since at least the last interglacial and that this is no longer weather but climate change that is killing Texas.
The forest might have been there the end of the Pleistocene but was it the same forest?
ReplyDeleteIf I had to guess (and that is all I am doing here) I would say no.
At the very least the forest management since the area became a park has altered the forest (as it has everywhere else).
Something as simple as fire suppression (which is almost always done in parks) can have many unwanted effects on a forest, even ironically, making giant unmanageable forest fires inevitable.
This can happen because over time, as small fires are quickly put out, non-fire resistant trees can gain a foot hold and even become dominant.
But also because small fires when left to burn in forests of fire resistant trees burn up much of the dead dried wood that naturally accumulates on the forest floor.
So over time the forest becomes less resistant to fire and with of fuel on the forest floor. This combined with a dry year leads to a powder keg that can be set off by the smallest spark. (This happens fairly regularly in the British Columbia interior where the forests are far more similar to Texas forests than most people realize)
This is a simple example of how forest management alters a forest. Other management practices can have far more complex effects
Well, I wish it were that simple. The lost pines area isn't really a timber production forest. The rate of growth isn't there. Yes, there has been fire suppression and a lot of unwise hodge podge development in the woods, but the 25,000 acres of state park have been aggressively burned based on the prehistoric burn cycle (as determined from embedded burn scars) and it hasn't mattered much. The parkland has for the most part been burnt. The trees were dying before the fires began. Which is why the fire is so bad. Here in Houston the trees haven't burned but about 30% are dead and the rest are stressed.
ReplyDeleteIf NYC got 8" of rain and 70 days of 100+ temps in a year then Central Park would also go up in a conflagration. Houston normally gets 52" of rain a year and one or two days over 100f. The desert is 600 miles to the west. Think cypress, spanish moss, bayous, alligators, palmettos. The hardwood forest here isn't prone to ever burn. Yet it is dying and burning now or simply dying in place where there has been an absence of sparks.
I don't believe that climate change will cause ecosystems to slowly migrate north and east with the SW deserts expanding to take up the slack here in the U.S. Trees have a very long life and seed source is important. Ecosystems try to hang on.
Texas is on the edge of the eastern forest as evidenced by its frequent grassland understory component on certain xeric (deep sands) or hydric/xeric sites (clay pans). So things are starting here. I think much of the eastern deciduous forest and western montane forests will change abruptly with climate warming through catastrophic fire.
Thanks for your input Andy S the Texan (not the Canadian Andy S)...
ReplyDeleteI had wondered about the catastrophic fires in a far less biologically sophisticated way. What happens to a forest when it is suddenly maladapted?
The sudden transition by fire scenario is double scary, of course, because if it scales up it starts to add carbon back into the atmosphere...
I for one am making no promises that Texas will not have unheard of flood years as well as the climate system keeps adjusting to new boundary conditions. This means that even xeric landscaping will fail, and we end up with lunar landscaping...
As the UT slogan says, "What Starts Here Changes the World".
Thanks Andy, lots of specific information there about the lost pines (my comment was based on very general knowledge).
ReplyDeleteSudden transition by fire is quite scary and it applies to many forests all over the world. The Boreal forest is at particular risk (and contains a large amount of carbon) as much of its southern boundary is controlled by fire frequency. The northern boundary is mostly controlled by permafrost, which means that the southern fire controlled boundary can move north much faster than the northern boundary.
If the park's been aggressively prescribe burned in the past, then it's a very strong bet that this IS "mattering much", affecting the current fire's behavior. That's the whole point of doing the burns.
ReplyDeleteFire behavior always depends critically on landscape scale vegetation condition, including density and continuity, which have been greatly altered pretty much everywhere via fire control, roads and agriculture, etc. You can't just attribute the current fires to uniqueness of the current climate conditions. Too simplistic.
This fire might be one of the best things that could have happened to the park.
I have read that the Lost Pine Forest exists there because of the geologic formation lying underneath it, which provides more soil moisture than the geologic formation that surrounds it. So its area is limited, and that is why it seems so odd the first time one come upon it.
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