Researchers analyzing over a century’s worth of growth in tree rings have revealed that climate change is synchronizing forest growth across vast swaths of dramatically different habitats – from frigid central Siberia to the mild, Mediterranean climes of Spain. The findings are published in Proceedings of the National Academy of Sciences this week.
Forests play a huge role in the carbon balance of the planet’s terrestrial ecosystems, but we have yet to figure out whether climate warming will result in longer, more effective growing seasons or worsen droughts, increase heat stress, and reduce productivity.
To better understand how climate change and increasing variability affect tree growth across continents, Jordi Voltas from the University of Lleida in Spain and colleagues examined 120-year tree-ring chronologies spanning 1890 through 2009. They studied six species of conifers (or evergreens) in two contrasting Eurasian settings: 45 chronologies from boreal forests in Siberia where tree growth is constrained by the cold, and 48 chronologies from Spain where Mediterranean forests are water-limited. Siberia has a prolonged cold season, large temperature variations throughout the year, and moderate amounts of precipitation. Spain, on the other hand, has mild to cool, wet winters and droughts in the summertime.
Spatial synchrony in tree growth refers to the extent of comparable changes in ring-width patterns among geographically disjoined tree populations. These tree ring samples reveal that synchrony in annual growth patterns peaked in the 21st century for these disparate biomes. Their response to climate change increased growth synchrony among forest stands separated by a thousand kilometers to levels we’d expect of those within the same stand.
“Enhanced synchrony is becoming a widespread, although regionally dependent, phenomenon related to warmer springs and increased temperature variability in high latitudes and to warmer winters and drier growing seasons in mid-latitudes,” the team writes. In boreal forests, wood formation is getting an earlier start, for example, while Mediterranean forests are experiencing an advanced onset of growth.
High temperatures, as well as increasingly intense climate extremes, exert about as much influence as local drivers of tree growth – such as topography, nutrient availability, and competition among trees. One day, large-scale synchrony may overwhelm regional differences.