The destruction caused when tropical storms sweep across cool, high-elevation areas may open up enough ecological space for warm-adapted plant species to establish themselves, speeding up the ecological shifts caused by climate change
at the University of Cambridge began tracking vegetation plots that are about 1580 metres above sea level in the Blue mountains of eastern Jamaica in the mid-1970s, suspecting that a hurricane might come through his study area at some point during his academic career. Hurricane Gilbert struck Jamaica in 1988.
“I think, at that time, it was the strongest hurricane to ever cross the Caribbean,” says Tanner.
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The hurricane caused damage to the plots Tanner had been observing every few years since 1974. Tanner and his colleagues, with support from local organisations including the Jamaica Conservation and Development Trust, tracked the damage caused by the storm every 10 years, with the most recent survey occurring in 2014.
The researchers found that the mortality rate for trees peaked between 1984 and 1994, the decade in which the hurricane occurred. The mortality rate during this decade was 66 per cent higher than in the pre-hurricane decade. Mortality rates then dipped to pre-hurricane levels between 1994 and 2004 and between 2004 and 2014.
Meanwhile, the “recruitment” of new trees to the plots also peaked between 1984 and 1994 – again, it was about 66 per cent higher than in earlier and later decades.
Altitude preference
The researchers also counted the number of trees belonging to each species in the plots and used already published data on the altitude preference of each species to work out a “mean community altitude score” for the plots. They found that this score decreased by almost 60 metres over the 40 years of the study. This means the plots contained fewer trees with a preference for high altitudes and more trees with a preference for low altitudes in 2014 than in 1974.
What’s more, beginning in the decade 1984 to 1994, the “recruited” trees that established themselves in the plots had a mean altitude score significantly lower than expected by chance, meaning the recruits included a high number of trees with a lower altitude preference.
“Higher altitude species are dying preferentially,” says Tanner. “It turned out that the effects [of the hurricane] lasted for decades.”
The hurricane itself killed relatively few cold-adapted trees in the mountains – just 2 per cent died during or immediately after the storm. But of the cold-adapted trees that were standing during the hurricane, a total of 13 per cent had died by 2004, 16 years after the hurricane. Tanner speculates that trees damaged in the storm later succumbed to disease or competition from the faster-growing, warm-adapted trees that began growing in the mountains after the hurricane.
Some climate change forecasts show that the intensity or frequency of hurricanes could increase in coming years. This study shows that such a shift might help speed up the ecological changes resulting from climate change, as warmer-suited species fill the gaps created from hurricane disturbance.
at the Georgia Institute of Technology, who has studied the ecological effects seen in the aftermath of hurricanes in mountains in Puerto Rico, says this paper is interesting. He has found that tree diversity often gets skewed towards palms after tropical storms because they are relatively resistant to the damage caused. “The impact of the hurricanes on the environment is terribly important on top of the temperature change,” he says.
Ecography
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