Thursday, October 1, 2009

Fall comes abruptly to northern states

Much of the northern plains and adjacent Rocky Mountains got a good frost this morning, so Fall has arrived rather abruptly with this big storm system. For weeks now we have had these amazing sunny days and unseasonably warm temperatures over 80 degrees. Half dozen forest fires were sending smoke all over the valleys around Missoula just a few days ago. Now it is clear and cold again. The silver maple (Acer saccharinum) in my yard has about 40% of its branches covered with crimson leaves, so maybe in another day or two it will reach “peak color” phenophase with 50% or more of its branches with colored leaves. Ashes (Fraxinus spp). in general and green ashes (Fraxinus pennsylvanica) in particular are already in full color around town as well as red maples (Acer rubrum) and American lindens (Tilia americana), not to mention the “burning bush”, or Euonymus alata. The later is an ornamental from Europe which has spectacular bright red leaves right now (giving it its name). Here in the Rockies it is well behaved and stays in peoples’ yards, but in the Midwest and east it can be quite invasive and problematical.

For those of you that have recently started budburst now is a great time to start making observations – you don’t have to wait until spring. There is a lot to learn and appreciate by looking at fall color patterns of both native and ornamental plants!

While some parts of the country celebrate fall colors in a big way, such as New England, the

Midwest, and much of the eastern deciduous forest region, any place that can get cool night temperatures (but not freezing), and warm days with deciduous trees and shrubs has a good chance of producing beautiful fall colors. On the Pacific coast, for example, colors are often muted due to mild temperatures, but at high elevations they can still get brilliant colors from huckleberries, cottonwoods, larches and aspens. Here in the Rockies aspen and huckleberries have been in full color at high elevations for weeks already. Reports from northern Wisconsin and Minnesota suggest many full colors there already. Most parts of the country should be reaching peak colors in the next couple of weeks.

Patterns in the fall are quite fascinating. You can really see the influence of both genetics and environment and how they interact at this time of year. For plants timing of phenological events is critical to their survival and their ability to compete with other species. Plants need to be able to shut down their leaf pigments (chlorophyll) and harden up for winter (tolerate freezing) at the “right time” which is a balance between the opportunity to capture energy from the sun and store this energy as sugars and starches as long as possible, leading to greater growth and health vs. the increasing risk of damage from frost. Plants determine the time to change colors by responding to changes in the length of the day. So you can tell where a plant comes from (or where it evolved or was bred in a nursery) just by looking at when its leaves turn color in the fall. Plants from cold northern climates, such as American linden and red maple often turn color first. Plants from more southerly locales such as the common apple (from around Turkey) and the apricot (from Armenia) often are the last to turn color in the fall. So they have a higher risk of frost damage, a fact well known to people in the fruit industry up here!

Even within a species you can see differences in genetics by looking at fall colors. On a given street or park you can often see many individual trees of the same species, say Norway maple (Acer platanoides), paper birch (Betula papyrifera and B. pendula), or around here the ubiquitous honey locust (Gleditsia triacanthos). But some trees may be in full color while a nearby individual is still green. If the trees are side by side presumably they are experiencing the same weather conditions, so there must be a difference in genetics (or where the parents came from). Weather can still affect the speed of color change and the intensities of color. You can see colors develop first in open areas where it is colder at night, and develop last in protected shaded areas where it is warmest at night (the shade from branches holds the daily heat more effectively).

There are several species that are

still flowering, and some are just now starting to have ripe fruit such as green ash (pictured), lilac, sagebrush, and boxelder. There is a lot to see and enjoy out there right now before the grip of winter ends another phenology season.

Paul Alaback


1. Huckleberries (Vaccinium globulare) in full color (and tasty fruit) at 7200' near Bowman Lake in Glacier National Park, last Thursday.

2. Common snowberry (Symphoricarpos alba) in full color at 4300' elevation on Mt. Sentinel open space trail near Missoula, Montana last Sunday.

3. Rocky Mountain maple (Acer glabrum) in full color on rocky gully at 3500' elevation near Missoula, Mt. last Sunday.

4. Fruits beginning to ripen on a green ash (Fraxinus pennsylvanica) in Missoula (elev 3200') on Tuesday. Note these are called "samaras", very similar to maple fruits. When they ripen they turn brown, dry out then quickly disperse in the wind.

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