February 01, 2010
Global Warming Speeding Tree Growth?

Faster tree growth in eastern US forests in recent years.

Speed is not a word typically associated with trees; they can take centuries to grow. However, a new study to be published the week of Feb. 1 in the Proceedings of the National Academy of Sciences has found evidence that forests in the Eastern United States are growing faster than they have in the past 225 years. The study offers a rare look at how an ecosystem is responding to climate change.

For more than 20 years forest ecologist Geoffrey Parker has tracked the growth of 55 stands of mixed hardwood forest plots in Maryland. The plots range in size, and some are as large as 2 acres. Parker's research is based at the Smithsonian Environmental Research Center, 26 miles east of the nation's capital.

Parker's tree censuses have revealed that the forest is packing on weight at a much faster rate than expected. He and Smithsonian Tropical Research Institute postdoctoral fellow Sean McMahon discovered that, on average, the forest is growing an additional 2 tons per acre annually. That is the equivalent of a tree with a diameter of 2 feet sprouting up over a year.

If this trend continues the amount of biomass tied up in these forests will continue to increase.

The researchers suspect higher temperatures, longer growing seasons, and more CO2 (which is nutritious for a plant) as causes.

It was not enough to document the faster growth rate; Parker and McMahon wanted to know why it might be happening. "We made a list of reasons these forests could be growing faster and then ruled half of them out," said Parker. The ones that remained included increased temperature, a longer growing season and increased levels of atmospheric CO2.

During the past 22 years CO2 levels at SERC have risen 12%, the mean temperature has increased by nearly three-tenths of a degree and the growing season has lengthened by 7.8 days. The trees now have more CO2 and an extra week to put on weight. Parker and McMahon suggest that a combination of these three factors has caused the forest's accelerated biomass gain.

Ecosystem responses are one of the major uncertainties in predicting the effects of climate change. Parker thinks there is every reason to believe his study sites are representative of the Eastern deciduous forest, the regional ecosystem that surrounds many of the population centers on the East Coast. He and McMahon hope other forest ecologists will examine data from their own tree censuses to help determine how widespread the phenomenon is.

Some plants benefit from more CO2 because they open their stomata to let in CO2 for shorter periods of time. This reduces moisture loss. Of course, if warming causes a drought in an area then the net effect on plant growth from warming will be negative.

Share |      Randall Parker, 2010 February 01 11:43 PM  Climate Biosphere


Comments
Mike Anderson said at February 2, 2010 3:45 AM:

"We made a list of reasons these forests could be growing faster and then ruled half of them out,"

...and this methodology is called the Just-So Story. How about some data and causal inference?

JAY said at February 2, 2010 6:56 AM:

Good. More lumber.

Bob Badour said at February 2, 2010 7:05 AM:

Good. More firewood. ;)

Bruce said at February 2, 2010 9:32 AM:

"the mean temperature has increased by nearly three-tenths of a degree"

Only .3 degrees? UHI. SERC is between Baltimore and Washington DC.

Mike said at February 2, 2010 10:13 AM:

Makes sense. Just look at the Cretaceous; 600% higher CO2 levels and massive plant growth.

Theo Richel said at February 2, 2010 2:20 PM:

If you check out www.co2science.org there is a compilation of the many hundreds of studies that have been done with CO2 and plants and that show that a doubling of the CO2 concentration in the atmosphere will lead to an increase of about 30% in the growth of plants (like rice and other foodcrops) and an increase of 50% in the growth of trees. This is why greenhouse owners supply their crops with extra CO2, and this is also why (Nasa?) satellites have concluded that the earth has become 6% greener in the past decades as a result of our emission of CO2. It isnt really surprising since CO2 is one of the ingredients for photosynthesis and that scientists say that (I do not know how many) billion years ago, when plantlife started on this planet, ambient concentrations of CO2 were in the area of 1200-2000 PPM (Now it is 384). Plants love that, as you can read on the site above. It is sadly a point that is often ignored in the warming debate. On purpose imho.
In the predictions for global warming it is expected that some areas on earth will become dryer. This is not good for plants, but the CO2 makes them more drought resilient, a phenomenon that is much more common than you describe. So coalplants are - contrary to what alarmists say - are not the destroyers but the fertilizers of the planet.

th said at February 2, 2010 3:12 PM:

Was this peer reviewed by the usual warming mongrels, sounds like an echo chamber from distant CRU attempts.

th said at February 2, 2010 3:28 PM:

Using weed growth and summer rainfall as a proxy, this study indicates just how pathetically stupid academia is.

isaac said at February 2, 2010 9:02 PM:

I am amazed that you continue to post the term "global warming" as if it is some well defined fact after the IPCC continues to drop the ball time and time again. It really starts to reduce your credibility for someone who ostensibly is interested in science. The IPCC is the furthest thing from a scientific organization possible.

Allan said at February 2, 2010 11:11 PM:

Let's see ... Warmer temperatures, longer growing season, and more CO2 lead to faster tree growth ... well ... DUH!

I hope they didn't spend much money or use too many brain cells on that one.

Randall Parker said at February 3, 2010 6:32 PM:

Allan,

It is not easy to calculate just how much increased CO2 will increase plant growth. The answer depends very much on the particular plant, available precipitation, and other available nutrients. Justus von Liebig's law of the minimum holds that plant growth will be limited by the nutrient(s) in shortest supply.

Reality is more complicated than the simplest reading of the law might suggest since, for example, both CO2 and water can help supply plants with needed water. Still, it is a useful way to look at things and suggests we can not predict a priori that increasing the supply of a single nutrient will help.

Since calculation alone is not sufficient real experiments must be done - and lots of them have been done as Theo Richel points out.

Isaac,

The IPCC isn't the ultimate fount of climate science knowledge. One can read about the work of individual climate scientists and one can learn about the underlying physics. In fact, if one wants to attempt to form a meaningful opinion about whether humans are heating up the planet one should read scientists and even, if possible, question scientists on this topic.

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