Despite the heat, fall is here

MINNEAPOLIS (KMSP) - It hasn’t exactly felt much like fall as of late, but it’s starting to look more like the season is here… especially in northern MN.  Yes, the leaves are starting their transition to yellows and reds before becoming a massive pile of brown in just a few short weeks.  Northwest Minnesota has seen the most change so far with up to half of the trees now showing color, but it’s pretty spotty elsewhere, even along the Iron Range.

So if it’s been so warm, how are trees changing?  Trees change color in the fall for a number of reasons.  While a few days of chilly weather can often kick them into high gear, it’s not just the temperature that dictates when a tree loses its leaves.  The other main factor is actually the amount of daylight.  Trees “eat” by using the process of photosynthesis through their leaves.  When the sun isn’t up, activity in the tree slows considerably because they need light to shine on their leaves for maximum production.  

Well, as we get through September, the amount of light seen on a daily basis is falling quickly.  By the equinox, the first day of fall, day and night are both 12 hours, but after that, the amount of daylight continues to plummet.  This is a big indicator for trees that winter is coming and they should go dormant for the year.  

The other main component for changing trees is amount of moisture.  It typically gets drier the further into fall we go.  So a very dry stretch of weather this time of year can also indicate to a tree that winter is near, especially combining that factor with shorter days.

Amazingly, peak colors are not that far away for trees north of the metro and north of I-94.  On average, they peak in just a couple weeks.  For the rest of the state, and much of the region usual peak is during the first half of October.  In recent years though, because of heavier rain and warm September temperatures, peak colors in the metro have generally been around that third or even fourth week of October.  

This year could be similar if some cooler air doesn’t arrive soon.