Drought-driven tree health risk lasts a decade

We already know droughts damage trees. But according to a study by Duke University in Durham, North Carolina, drought can reduce trees’ long term survival for as long as a decade after the drought ends. The study hopes to give forest managers and scientists a way to spot and deal with drought-led damage before it’s too late, a vital tool in any rainforest conservationist’s kit.

Long term drought damage revealed

Aaron Berdanier, a Ph.D. student in forest ecology at Duke’s Nicholas School of the Environment, headed up the research, identifying the tree species at highest risk and the varied environmental factors that affect the likelihood of survival. He and his team looked at around 29,000 trees across two special research forests in North Carolina and were surprised to find that the damage is so unpredictable and long-term. It’s the first ever study into drought damage that actually shows declines in tree growth during a drought dramatically cutting tree survival in the long term.

A quiet decline just as deadly as dramatic tree die-offs

It looks like the damage suffered by trees during a drought sets a quiet decline in place, which can last years and kill them way down the line.

Trees slow down the growth process when there’s a drought, decreasing their ability to take up Carbon, therefore their ability to stay alive. If a tree is too weak to reverse the loss, it gets unhealthy and eventually dies. But the decline is much slower than anyone previously thought, and the long-term impacts can be just as severe as the more dramatic tree die-offs we occasionally see. In fact the study quantifies things to an alarming degree, showing how 72% of the trees affected by drought and unable to recover their natural equilibrium died within 10 years.

The results show that a tree’s long-term mortality risk increases when its cumulative diameter growth falls below 54% percent of the growth of nearby trees of the same species. And the effect happens across all species.

The good news…

Luckily the research also highlights the symptoms of future death, great news when climate change is making droughts more common and more extreme in some places. Again on the bright side, it looks like thinning out competing trees around a drought-affected tree can cut the death risk.

Knowing what to look for means the longer term affects of drought can me mitigated, and knowing how to mitigate the damage makes a huge difference to tree survival, in a world where every tree lost is a tragedy.

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