Leaves are starting to change in Anchorage and around Southcentral. This season’s change might look a bit different than years past, and there are a few reasons for this. Temperatures, drought, and leaf miners are to blame.

A unique summer

This past summer was one of warmth and drought. Officially the warmest summer on record for Anchorage and the second warmest for the state. In addition to the heat, a lack of rain contributed to the worst drought in recorded history for Anchorage.

The combination of heat and a lack of moisture plays into the changing leaf color earlier than normal.

Drought and change

Trees require water to live. That water plays an intricate role in the color of the leaves. The green color typically predominant throughout the summer.

The green color in leaves comes from chlorophyll. Chlorophyll is used for photosynthesis or the process in which a plant uses sunlight to convert carbon dioxide and water into food and the byproduct of food production — oxygen.

A lack of water, like what we saw this past summer, causes the tree or plant to go dormant to avoid serious water loss and injury.

According to Matthew Carlson, Ph.D., from the Alaska Center for Conservation Science at the University of Alaska Anchorage, leaves need to develop an anatomical layer at the base that inhibits movement of materials in and out of the leaves.

Without the transfer of materials through the leaf, the leaf loses color and the degradation of the chlorophyll leads to the color change. As it degrades, and isn’t replaced, the carotenoid pigments become more visible. These are the yellow and orange colors popping up on some trees around Southcentral.

According to Carlson, drought is presumably responsible for certain trees and shrubs changing color and losing leaves about two weeks ahead of schedule.

 
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Birch and the leaf miners

Two different species of invasive birch mining sawflies are responsible for the brown leaves and early loss of leaves on birch trees across Southcentral and parts of the Interior. The amber-marked birch leaf miner and late birch leaf edge miner are stingless wasps or sawflies.

The female sawfly deposits eggs in late June or early July. When larva emerges, it begins feeding on the leaves of the birch trees, creating little tunnels or mines within the leaves as it eats. This feeding or eating of the leaves is what causes the brownish-yellow color. The damage to the leaves typically becomes most apparent by early August. The leaves damaged by the miners can drop 2–3 weeks earlier than they otherwise would.

The evidence of leaf miners is all around Anchorage and the Valley. Early browning occurred on many trees and a significant amount of birch trees already dropped the damaged leaves.

Stephen Burr, Ph.D. of the U.S. Forest Service believes our birch trees will not die from the leaf miners. He explained that Alaska’s long summer days and the late-season occurrence of the damage the birch trees likely produce enough photosynthate, or sugar, to survive. Dr. Burr did, however, go on to say that the leaf miners will likely make trees less resilient to climate change. For instance, in the presence of a prolonged drought, the leaf miners may make the trees more susceptible to the impacts of the lack of water.

Image result for us forest service birch leaf miner

Drab fall color

As daylight fades away and temperatures drop, fall won’t be met with the familiar vibrance of the changing leaves in Southcentral Alaska. The yellows, oranges, and reds that typically cover the landscape won’t be near as prominent.

Leaf miners caused many leaves on birch trees to brown and drop early, and ongoing drought caused many other tree species to fade from green earlier than usual.

The remaining leaves, now starting the transition to fall color, are changing at a time that is considered normal for Southcentral Alaska.

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