A potential positive of climate change

Researchers have warned that global warming will take a toll on our planet, especially our plant populations and communities.  High inputs of carbon dioxide into the atmosphere from vehicles, manufacturing, and industry will surely affect the distribution, ecology, and adaptation mechanisms of plants across the globe both directly and indirectly. 

The question is: how will plants be affected?  Little research has been done to try to quantify the impacts that excess carbon dioxide will have on various communities of plants, although scientists are certain that it will be negative.  However, the following study shows that increases in CO2 could actually be a good thing for forest recovery and succession.



Understory of a sweetgum forest
Image from http://www.nativetreesociety.org

Souza et al. (2010) conducted a ten year (1998-2008) field experiment which quantified understory aboveground biomass in a temperate deciduous sweetgum forest in Tennessee.  This natural, sweetgum-dominated site was located within the free-air carbon dioxide enrichment (FACE) facility, which was capable of providing extra carbon dioxide to experimental units; CO2 can be delivered to units via pipes and blowers.  The researchers set up 3 natural air (aCO2) 25m diameter experimental rings and 2 carbon dioxide enriched (eCO2) 25m diameter experimental rings.  On average, the daytime understory CO2 concentration in the eCO2 forest was 100ppm greater. 

For each of several years, randomly located subplots within each of the rings were clipped at the ground level, and measured for species composition and biomass.  Biomass was separated into i) total aboveground understory biomass, ii) species specific biomass, and iii) herbaceous and woody species biomass.



Figure 1 from Souza et al. demonstrating
significantly higher biomass production in
eCO2 rings throughout study years.

Souza et al. found that total aboveground biomass was approximately 25% higher in the understory of eCO2 rings than aCO2 rings across sampling years (2001, 2002, 2003, and 2008).  In the earlier sampling years, increases in biomass were mostly the result of increases in herbaceous biomass; herbaceous biomass was 30% greater in the eCO2 plots in 2001-2003 and then declined.  However, the increased understory biomass in the later years was attributed to increases in woody plant biomass; biomass did not initially differ between eCO2 and aCO2, but by 2008 woody species biomass was 60% greater in eCO2 rings. 

As well, only 6-14% of the variation in the composition of the understory community across the ten years was the result of eCO2. 

Clearly, the overall biomass of a forest increases significantly faster with enriched carbon dioxide than without and moves from a herbaceous dominated forest to one dominated by woody trees and shrubs: CO2 accelerates biomass production and succession!  Too, the overall species composition does not change in response to increased levels of carbon dioxide; species abundance may change, but not composition.

Considering most of the expected outcomes of global warming are negative and depressing, this is a little tidbit of good news!  Most of the logging operations near my hometown are done via selective or shelterwood logging and if the above study holds true, all of the pre-cut forest inhabitants will have their natural home back sooner after a cut.  Too, loggers will be able to harvest more often, to supply the wood and paper demand of today’s society. 

I’m not saying we should go ahead and idle our cars carelessly, avoid buying locally produced goods, or keep the lights on when we’re not home.  But, if we can’t stop the ever-looming climate change from happening, we should try to figure out all the impacts the globe will face, prepare ourselves, and think positively – some changes may be surprisingly beneficial!

Sources:

Souza L, Belote RT, Kardol P, Weltzin JF, Norby RJ (2010) CO2 enrichment accelerates succesional development of an understory plant community. J Plant Ecol, 3:1, 33-39.

http://www.nativetreesociety.org/fieldtrips/alabama/oak_mtn/oak_mountain_state_park.htm