If you live in a region with a mixed deciduous hardwood forest, then you have the pleasure of witnessing the amazing fall leaf color display every year. I just read a recent 25 year study tracking the onset of autumn and the results are not surprising – leaves on the trees are falling 10 days later than 25 years ago.
This trend, along with drought, increased temperatures and projected changes in forest species composition, may have a detrimental impact on fall leaf color displays in the years to come.
“Using satellite-based measurements of the Normalized Difference Vegetation Index (NDVI), which gauges leaf cover over wide areas, researchers at the Seoul National University in South Korea found that the end of the growing season occurred progressively later over the course of their 26-year study. By noting the time of year changes in color occurred most rapidly, the researchers could track when fall started between 1982 and 2008.” (Source: Climate Central)
So what makes leaves turn color and eventually fall from the tree?
When leaf bud occurs in spring (triggered by sunlight, warm temperatures and longer day length), the leaves are green in color because of presence of chlorophyll. As the leaves actively photosynthesize throughout the summer months, chlorophyll is converted into much-needed sugars and carbohydrates giving trees the resources to grow, flower and produce seeds.
Like the onset of leaves budding, in the fall when temperatures cool, day length shortens, photosynthesis slows from the closing off of the flow of nutrients from the leaf to the tree. Chlorophyll begins to break down and is not actively replenished. Other pigments already present in the leaves don’t break down as quickly as chlorophyll so their pigment begins to dominate. Carotene is the pigment responsible for making leaves appear yellow.
Anthocyanins are responsible for leaves appearing red or purple. “The color produced by these pigments is sensitive to the pH of the cell sap. If the sap is quite acidic, the pigments impart a bright red color; if the sap is less acidic, its color is more purple. Anthocyanin pigments are responsible for the red skin of ripe apples and the purple of ripe grapes. Anthocyanins are formed by a reaction between sugars and certain proteins in cell sap. This reaction does not occur until the concentration of sugar in the sap is quite high.” (Source: University of Wisconsin)
FALL COLOR DISPLAY AND CLIMATE CHANGE
Drought & Heat
The fall color display this season in central Minnesota is dismal. With our region in a severe drought, our trees are stressed, leaves are forgoing color change and instead turning brown and dropping to the ground. As areas of the nation are projected to become more arid and warmer it may significantly impact the fall color display. Further reading: Climate Central: Climate Change and Fall Foliage: Not a Good Match
Change in Forest Species Composition
“Climatic effects such as increases in wind and ice damage, hurricane intensity, heavy precipitation events, drought in the later parts of the growing season, flooding during the growing season, and warmer winter and summer temperatures (Hayhoe et al., 2006) can increase stress on species, leading to further changes. An analysis of 806 northern temperate trees and shrubs (worldwide) showed that few species can tolerate more than one of the following stresses: shade, drought, or waterlogging (Niinemets and Valladares, 2006).” (Estimating Potential Habitat for 134 Eastern US Tree Species Under Six Climate Scenarios)
I’ll just mention a few of the many potential economic impacts:
Areas like New England rely upon fall tourism – visitors viewing the fall leaf color displays.
Maple Syrup Production
Maple syrup production may be severely impacted as the sugar maple tree range is projected to move northwards. If you purchased maple syrup from a producer this spring, you’ll know how small their harvest was and how much more a bottle of maple syrup costs. Further reading: Changing Climate May Substantially Alter Maple Syrup Production
Should we be reconsidering what native species to plant in our wildlife gardens?
How can we prepare for climate change?
I’m constantly evaluating the plantings in my own landscape. How are certain species being impacted in the short-term by the drought, what does this mean for long-term climate warming? Would my landscape in central Minnesota be more resilient to climate change if I started to restore it to a white and bur oak savanna rather than a deciduous woodland?
Other Posts by the NPWG Team
Native Trees for a Changing Environment
Climate Change: What to Do? What to Do.
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