MSGID: 1:317/3 64acdb48   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Forest can adapt to climate change, but not quickly enough    
    While most forests in the U.S. have the potential to adapt to hotter,   
   dryer conditions, they aren't changing quickly enough to avoid the impending   
   stress    
      
     Date:   
         July 10, 2023   
     Source:   
         University of California - Santa Barbara   
     Summary:   
         America's forests have a tough time in store for them. Climate   
         change is increasing temperatures and decreasing moisture levels   
         across the country, not a winning combination for trees.   
      
      
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   America's forests have a tough time in store for them. Climate change   
   is increasing temperatures and decreasing moisture levels across the   
   country, not a winning combination for trees.   
      
   Researchers at UC Santa Barbara and University of Utah sought to determine   
   how our sylvan ecosystems might fare in the near future. The authors   
   combined mathematical models and data collected by the U.S. Forest Service   
   and plant physiologists to understand the vulnerability of woodlands   
   to drought. Their findings suggest that, while most forests have the   
   potential to adapt to hotter, dryer conditions, they aren't changing   
   quickly enough to avoid the impending stress. The study, published in   
   Global Change Biology, serves as a benchmark for future forest research,   
   as well as a guide for conservation and management.   
      
   "We were concerned to find that forests were not changing fast enough to   
   avoid increased water stress due to climate change," said first author   
   Greg Quetin, an assistant project scientist in the UCSB Department   
   of Geography. "But there is hope, as most forests in the continental   
   U.S. contained enough functional diversity to increase their drought   
   tolerance through shifts in species composition."  There are a few ways   
   forests can adapt to drier conditions. Individual trees can alter their   
   activity, physiology and gene expression to the new conditions they   
   face. Drought-tolerant species already present in the ecosystem can also   
   become more dominant. The forest composition can change as well, with   
   hardier species migrating in as more vulnerable species die off. Evolution   
   can also change species via natural selection, although the effect will   
   be negligible over the next century for such long-lived organisms.   
      
   Quetin and his co-authors investigated whether the traits and species   
   already present in the country's forests are sufficient for them to   
   acclimate to future climate change without widespread mortality. Much   
   of the data came from the Forest Inventory and Analysis program, a   
   comprehensive database run by the U.S.   
      
   Forest Service on the state of the country's woodlands that has been   
   standardized since the year 2000. This database includes forest inventory   
   plots that document location, species, size, density and health of   
   trees, as well as tree growth, mortality and harvesting. Quetin and his   
   colleagues also used data from the Xylem Functional Traits Database,   
   where measurements of tree physiology and hydraulic traits are compiled,   
   cross-referencing this database with the Forest Inventory.   
      
   Finally, the team developed a model that simulates a forest's response to   
   increased water stress. The model predicts photosynthesis (or CO2 in),   
   respiration and growth (CO2 out), as well as plant stress. They also   
   included an optimization technique to look at how changes to leaf area   
   could mediate the stress caused by changing environmental conditions.   
      
   "All the data to date suggest that leaf area is just the biggest lever   
   that individual trees can throw to manage water stress," said co-author   
   Lee Anderegg, an assistant professor in the Department of Ecology,   
   Evolution, and Marine Biology. Forests in drier areas tend toward sparser   
   canopies, while forests in wetter climes can afford thick foliage.   
      
   The researchers found that many of America's forests have the capacity to   
   adapt. The model revealed that 88% of the forests across the continental   
   U.S.   
      
   have the trait and species diversity to acclimate to climate change,   
   and they are starting to. However, most weren't adapting as quickly as   
   the model predicted was necessary to avoid increased water stress and   
   subsequent mortality.   
      
   "It's concerning that we don't see the required shifts that our model   
   predicts need to happen," said co-author Anna Trugman, an assistant   
   professor in the Department of Geography. "But I think there's still   
   room for hope." For instance, biodiversity stood out in its ability to   
   buffer the impact of climate change on a given forest.   
      
   "Trees are slow movers, as we know," Trugman continued. "I've seen the   
   pace of those Ents in 'The Lord of the Rings.'"  "They're still holding   
   the Entmoot at the moment," Anderegg added.   
      
   Higher carbon dioxide concentrations introduce a confounding factor in the   
   team's calculations. Plants lose water through the same pores that they   
   use to take up carbon dioxide. So if there's more CO2 in the atmosphere,   
   plants can decrease the size of these pore openings and still acquire   
   the carbon they need for photosynthesis. This reduces the amount of   
   water escaping from their leaves.   
      
   But the atmosphere is also dryer in a warming climate, Anderegg   
   explained, so leaves lose more water. It's a complex system with a lot   
   of uncertainty and compensating factors, which requires nuanced models   
   to disentangle. And the energy involved in transporting this water is   
   far from negligible, as the authors discovered in a previous paper.   
      
   The team is now collecting their own data on changes in tree physiology   
   following climate-driven fires in Sequoia National Park, trying to   
   empirically verify how much trees can adjust their physiology. The authors   
   are also investigating if trees can avoid future water stress entirely   
   through changes to their leaf area, and whether maximizing carbon gain   
   or stress avoidance is more limiting.   
      
   Forests are already beginning to change. Sparser canopies will become   
   more common as the atmosphere becomes drier. Woodlands will also likely   
   have a different mix of species than they historically had. These factors   
   all impact forest carbon storage as well. Forests currently sequester   
   about 30% of anthropogenic emissions, but the group recently found that   
   this would likely decrease under climate change.   
      
   Management strategies that encourage forests to adapt will be   
   critical. "We need to be thinking about these forests not as static   
   things -- that need to exist just as they are right now -- but   
   as healthy things that need to change to keep up with the climate,"   
   Anderegg said. Facilitating gradual change will help prevent abrupt,   
   catastrophic changes, like wildfires and die-offs, that are detrimental   
   to the forests, wildlife and people living nearby.   
      
   Resource managers could begin planting areas with more drought-tolerant   
   species and conducting prescribed burns to promote healthy woodlands. But   
   most of all, we need to mitigate climate change, the authors said.   
      
   Our future depends on society's emission trajectory. Climate adaptation   
   is no easier than climate mitigation, Quetin noted. And less climate   
   change means less adaptation is necessary.   
      
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   Story Source: Materials provided by   
   University_of_California_-_Santa_Barbara. Original written by Harrison   
   Tasoff. Note: Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. G. R. Quetin, L. D. L. Anderegg, I. Boving, W. R. L. Anderegg, A. T.   
      
         Trugman. Observed forest trait velocities have not kept pace with   
         hydraulic stress from climate change. Global Change Biology, 2023;   
         DOI: 10.1111/gcb.16847   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/07/230710133054.htm   
      
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