More and more of the world’s trees and plants are in “recovery mode” from past droughts, and they’re starting to take longer to recover, according to a recent study in the journal Nature.
The results indicate that “we are likely headed to a new normal where time between droughts is shorter than the recovery time,” lead author Dr. Christopher Schwalm of the Woods Hole Research Centre told CarbonBrief. That gap “could lead to widespread changes to ecosystems, reducing the amount of CO2 they can take up from the atmosphere,” notes Science Editor Robert McSweeney.
The Woods Hole study tracks what happens in the months or years after rains returns to a drought-stricken area, time the vegetation needs to return to pre-drought growth rates. The results show that global average areas recovering from drought increased decade by decade through the last century—but have dropped off for most of the last 10 years.
“Here it’s the case that droughts have started, but that no recovery has been observed,” Schwalm said. “We can’t ‘see’ these events, but we know they are there—so they pull down the trend.”
The study also notes that recovery times are slower when temperatures are unusually high, suggesting an accelerating problem as the atmosphere warms.
“In general, plants react to a lack of water by closing the pores in their leaves to prevent moisture escaping,” CarbonBrief explains. “But with closed pores the plants can’t then take up CO2, which they need to photosynthesis and grow.”
Which means that “vegetation growth tends to stall in a drought. During the European heat wave in 2003, for example, tree and plant growth fell by 30%. That meant the land surface in Europe actually produced more CO2 than it absorbed that year.”