Beleaf it or not!

Last fall I felt somewhat cheated. We had a very cold week in early October that effectively took care of all the beautiful fall foliage.

This year seems to be making up for the lost time we had last year; it just seems to be keep going on, which is just fine with me. It raises a question I have long sought to know, and I was recently reminded of by my friend Andrew. Why do leaves change color?

Throughout my life, I have heard a number of reasons for this but I am going to attempt to put this seasonal question behind me.

To begin, we must return to biology for a brief lesson in leaves. Plants are autotrophic, meaning they make their own food. They are able to accomplish this through a process we call photosynthesis. Simply put, this is a reaction in which light energy, carbon dioxide, water and chlorophyll all work together to make sugars. It is the pigment chlorophyll that is responsible for the green we see during the summer.

The colorful pigments we see in the fall are called carotenoids (oranges, yellows and browns) and anthocyanins (reds, purples). Carotenoids are present year round, we just do not see them because chlorophyll is continually being produced and broken down. As days get shorter, there is less light for the trees to utilize to make food.

In response to this, chlorophyll production starts to slow down and eventually stops. It is at this point that the carotenoids and anthocyanins are able to show their brilliance; how long they show their colors is dependent on the weather.

Last fall, we had about two weeks of nice colors because of the cold. This year, it keeps continuing. The reason for this is the beautiful weather we had.

In the warmth of the days, lots of sugars are produced. When night temperatures are cool and not freezing, the veins of the leaves close and prevent the sugars from moving out. All of these sugars enhance the production of the anthocyanins and keep the leaves around a little longer for us to enjoy.

Finally, the leaves fall off. The leaves fall off as an adaption these trees have to deal with the cold weather.

Trees that do not lose their leaves, such as pine trees, have developed other ways of coping with the freezing temperatures. Their needles contain a waxy coating, and the fluid inside their cells contains substances that resist

freezing.

I am able to process all of this, but as always there is one outlier that defies what I have learned. Larix occidentallis, or more commonly called the larch or tamarack, has needles like a pine tree but is deciduous like a maple. Scientists are trying to figure out why a tree would behave this way. They believe this life strategy allows the tree to live in some of the harshest environments, like Montana.

In conclusion, shorter days and weather both influence the fall foliage; shorter days are what trigger the whole process.

I can live with that!