Trees are in big trouble, but science may have a solution

This winter season, disturbing news emerges about our trees that could reshape our understanding of forest resilience in the face of climate change. Recent scientific findings reveal a counterintuitive trend: trees from wetter climate regions are more vulnerable to drought compared to their arid counterparts.

This discovery challenges long-held beliefs about tree resilience and has significant implications for forest management and conservation.

Shifting Perceptions on tree resilience

Traditionally, the scientific community has been divided on whether trees in dry conditions are more or less resilient to drought.

The common assumption was that trees at their biological limits in arid regions would be most affected by climate change, as even minor environmental stressors could push them over the edge. However, the latest research suggests a different narrative.

In a concerning new study, a team from UC Santa Barbara and UC Davis has found that greater water availability may actually hinder a tree’s ability to adapt to drought conditions.

Ecologist Joan Dudney from UCSB’s Bren School of Environmental Science & Management highlights the critical importance of this discovery, especially in the context of global forest carbon stocks and overall forest health.

“That’s really critical to understand when we’re thinking about the global vulnerability of forest carbon stocks and forest health,” said Dudney. “You don’t want to be a ‘spoiled’ tree when facing a major drought.”

Comprehensive analysis of tree rings

The research team, including lead author Robert Heilmayr and co-author Frances Moore, conducted an extensive analysis of over 6.6 million tree ring samples from 122 species worldwide.

By correlating tree growth patterns with historical climate data, they unearthed a startling trend: trees in drier regions display a remarkable resilience to drought.

“As you move to the drier edge of a species’ range, trees become less and less sensitive to drought,” said Heilmayr. “Those trees are actually quite resilient.”

Inspired by UCSB professor Tamma Carleton’s work on climate change and human populations, the researchers leveraged cross-disciplinary methodologies.

Frances Moore emphasized the value of adapting economic methods to study ecological responses, offering new perspectives on forest sensitivity to drought.

“This paper highlights the value of cross-disciplinary scientific work,” added Moore. “We were able to adapt methods from economics originally developed to study how people and businesses adjust to a changing climate and apply them to the ecological context to study forest sensitivity to drought.”

Dual nature of trees and forest resilience

The study also sheds light on how regional adaptations to climate affect forest resilience. Heilmayr draws a parallel with human populations, noting how people in cooler cities like Seattle are more vulnerable to heatwaves compared to those in hotter regions like Phoenix.

“A heatwave is likely to kill more people in a cool place like Seattle than in hotter cities like Phoenix,” Heilmayr said.

Heatwaves scorch the already quite hot Southwest. The region’s cities have adapted to an extreme climate, he points out. Forests also show similar trends.

Trees in wetter climates show less resilience and not equipped to handle drought conditions. However, the research indicates that a significant portion of species’ ranges will face unprecedented dry conditions in the future, presenting a major challenge for forest ecosystems.

“There is a pretty large portion of species’ ranges that are going to face a completely novel climate, something that those species don’t see anywhere in their range today,” Heilmayr explained.

The authors discovered that, by 2100, 11% of an average species’ range will surpass the driest parts of their historical range in dryness. For some species, this figure will exceed 50%.

“Broadly, our research highlights that very few forests will be unaffected by climate change,” Dudney said. “Even wetter forests are more threatened than we thought.”

A glimmer of hope

The study also offers a glimmer of hope. It suggests that the genetic diversity found in drier parts of a species’ range could be key to bolstering forest resilience in wetter areas.

This finding underscores the potential for assisted migration as a tool for forest conservation, given the slow natural migration rate of trees.

What does this mean for your Christmas trees and forests worldwide? The research indicates that regardless of whether trees grow in dry or wet regions, they are likely to experience growth declines due to climate change.

However, understanding these dynamics is crucial for preserving not just the iconic Christmas tree but also the broader forest ecosystems they represent.

In summary, this study overturns previous assumptions about tree resilience, while providing vital insights for future forest management strategies in the face of escalating climate challenges.

The full study was published in the journal Science.

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