Monday, September 19, 2011

Why Leaves Change Color

Red Oak in Tennessee, photo courtesy Ashley Bradford
There is hardly anything more beautiful than a forest at the height of color change, and the annual autumn show is already beginning in some parts of the country. Have you ever wondered why leaves change color?

Leaves contain many pigments. During most of the season the green chlorophyll is the predominant pigment and it masks the presence of the other pigments. Chlorophyll is the pigment that allows leaves to photosynthesize, creating the sugars that provide energy for the plant. Chlorophyll is not particularly stable so it is continuously synthesized and broken down when the weather is warm.

In the autumn, when the temperatures cool and day length shortens, chlorophyll synthesis shuts down. As it breaks down, the yellow and orange carotenes are unmasked. This gives many plants their characteristic yellow fall color.

Anthocyanins, which are red to purplish-blue, are the third type of plant pigment. Anthocyanin production can be triggered by many things including high sugar concentration in the leaf which happens when sugars from photosynthesis are trapped in the leaf as it prepares to separate from the plant. Anthocyanins can also be triggered by environmental stresses to a plant, such as too much or not enough water, too much or not enough nutrients, fungal disease, damage to the bark by animals or string trimmers, and many other things. If you see a tree, or part of tree, change color significantly earlier than others of the same species, it is likely due to stress!

Weather can also affect fall colors. The best colors are seen when there are sunny, warm days and cool, crisp (but not freezing) nights, as well as adequate soil moisture. So hope for good weather, enjoy nature’s spectacle this fall, and report your observations to Project BudBurst!

Kayri Havens-Young

(Editor's note: Kay Havens is on travel and asked me to submit this for her.)

Wednesday, September 14, 2011

Fall into Phenology - will be starting soon!


Fall Colors near Berthoud, Colorado last October


All across the country September marks an important transition to a new season. In some places, like here in Colorado it can become dramatic, going from complaints about hot summer nights, just a few weeks ago to the threat of the first snow or at least a killing frost. In other places it may still be warm, but now you can start getting storms coming in and more variation. And in many parts of the country people are recovering from record floods and winds associated with another very destructive year for natural disasters.

Just in the past two days we have had our first cool fall days, with temperatures in the 50's instead of the 70's or 80's. Even though our peak colors generally occur in October or even early November nearly a third of the green ash trees today had some bright yellow leaves, and I found one aspen and several cottonwoods with close to 50% leaf color. Clearly the crazy weather we have had this year, a warm summer, with a pronounced early monsoonal season, dry hot weather lately, and now cool weather is effecting how some of our plants are transitioning for the dormant winter season!

This variability in weather conditions makes it particularly interesting for scientists and budburst volunteers to try to figure out how plants are responding to these changes, and how they compare from region to region and from year to year. In theory, fall leaf color, and the development of fruits and flowers for species that reproduce this time of year should have some degree of consistency, at least compared to the spring season. This is because plants often have internal clocks, or ways they can judge the time of year, usually from measuring day length, which they use to determine when to start hardening off for the winter season. But many other factors of weather, habitat and plant condition can also influence the rate at which fall colors emerge, leaves drop, or fruits and flowers emerge. Each part of the country, especially this year, have been subject to different kinds of weather events so we should see some interesting patterns in how plants vary in their progression to the fall season.

This year, Project Budburst is launching its first ever "Fall into Phenology" fall campaign. The concept is to use this dynamic season as a special time to create a "snapshot" of how plants all across the country are responding to the fall season. We want to get as many volunteers and especially new volunteers as possible to make observations during a 10 day time period (Sept 17-26th) which surrounds the official or astronomical definition of fall, the fall equinox on Sept 23rd. We will make it easier than ever for people to make observations and contribute to Project Budburst, especially for the first time, since it only requires making a single observation during this 10 day period of time. Of course we still hope that all of you that are making regular budburst observations on your registered plants continue to submit your observations, but we would like to supplement this with a single pulse of observations from a larger group of people, in more locations to get an even broader picture of how fall is progressing from year to year. The goal is to collect at least 500 observations from around the country. Check out the Project BudBurst map as we update it with the latest observations coming in. There will also be highlights of the first observations from each state on the website and frequent updates on the Project BudBurst Facebook page.

To participate in Fall into Phenology volunteers simply need to make an observation with the new data sheet, or with the information written down on your smartphone or notepad, then share your observations, by entering the information directly onto the Budburst website. All the definitions for the stages you can note are provided in the datasheets which you can download (deciduous trees and shrubs, wildflowers, and grasses). You need to choose a plant and a location to make your observations. For example you might see a red maple tree along a walk you take on a day during this 10 day period. You could then make an observation on how many leaves had fall colors: (just a few (<10%), many, or most of the leaves (>90%). Then, you need to logon to the budburst website (budburst.org), to share the observation. If you have an Android phone, you can make observations and share them almost instantly with the Project BudBurst mobile app. We estimate it will only take about 10 minutes of your time to participate after you register. The whole idea is to make this very simple and straightforward, yet still scientifically accurate since everyone is using the same set of definitions and procedures.

Please spread the word on participating in this campaign. It should be a fun excuse to go outside with your family and friends and enjoy the beautiful weather that often occurs this time of year, and at the same time participate in an important scientific program!

We will report the results later in the season soon as we get all the data, so watch for an upcoming blog on this.

It should be interesting to see what we discover about how Fall is progressing this year. As always please also post comments or questions on our Facebook Page as you discover new or interesting things outside.

Paul Alaback


Photos taken on September 14th around Berthoud, Colorado
Green ash (Fraxinus pensylvanica) just beginning to turn colors, in the past few days.
Virginia creeper (Parthenocissus quinquefolia) with a full set of ripe fruit which just ripened in the last week.