Warner Corner - September 2009

It's all in the leaves...
Bekah Dalen, Interpretive Naturalist

As summer turns to fall, I am reminded of how lucky we are to live in Minnesota. We are able to experience something people living in Florida or California don't...genuine seasons. Now, I will admit that in the middle of February I do not feel so lucky. However, spring does eventually arrive and I quickly cheer up. But, what signal does Mother Nature give that lifts my spirits so? How do I know that winter is over? It is not the weather...that can be tricky. For me it is the leaves.

I'm sure we have all experienced this. You are driving down the highway and you catch a glimpse of something you have not seen for many months. It is so faint and blurry you don't trust your own eyes, so you rub them and look again. Yep, there it is, that green smudge covering the tops of the trees in the distance...leaves! Spring has sprung and there is no doubt about it.

It is amazing how telling leaves can be about the changing seasons. The trees seem to know what is coming before we do. And at this very moment they are preparing for something we Minnesotans refuse to think about...at least until the State Fair is over. Ah yes, winter.

We'll get to that season soon enough, however. For now, let's focus on my favorite season of all time, autumn. The signals the leaves give us during these few months are just as clear as in the spring, if not more so. That lone red leaf in a sea of green. The picturesque landscape of yellows and oranges along the river bluff. Telltale signs that deciduous trees (trees that lose their leaves) are kicking their winter prep into high gear.

What gives us those beautiful red, oranges, yellows...and brown for that matter, seems magical, but is actually quite explainable. The main job of a leaf is to produce food for the tree. It uses the sun's light to turn water and carbon dioxide into sugars, which the tree uses for energy to grow. This process is called photosynthesis. One of the necessary elements of photosynthesis is chlorophyll, which happens to be green in color. In the spring and summer the leaves are packed with chlorophyll and this is why the leaves look green. Also present in the leaves are carotenoids (which produce yellows, oranges and browns) and anthocyanins (which are responsible for many of the reds). They are in the leaves all along, but the abundance of green chlorophyll masks their colors. As the days grow shorter, temperatures begins to drop, and the growing season comes to a close, trees shut down the process of photosynthesis and chlorophyll production stops, making those other eye catching colors visible.

When the trees start preparing for winter, Mother Nature is hinting at us to do the same. So, turn off the air and open the windows. Put on a sweatshirt and go for a nice long walk. Harvest those juicy, red tomatoes from your backyard. And track down your hat, gloves and scarf from the back of the closet and hang then in the front hall. Soon, the leaves tell us, it will be February.