Monday, March 7, 2011

Silver Maples and Spring in Colorado

Spring in Colorado - first sign is usually new green blades of grass

Here we are again ready for a new Budburst season, year 5 of our program. Check out new website and all the new things for this season (and check last week's blog for more details). We have lots of new photos and other features to the website. Soon we will be able to announce the new Droid smartphone budburst application. It will be a really easy to use and convenient way to make budburst observations. Stay tuned for more on this. Over 11,000 observations have been submitted to budburst so far! It is rapidily becoming an important resource for scientists, especially since we have volunteers that now cover most parts of the country.

2011 should be a very interesting winter to watch for plant phenology. Its been a wild winter so far with record snowfall in many parts of the Midwest and East, and record floods in many coastal areas. We already had observations of dandelions in the south, even in January and recently have been getting observations on the first spring bulbs emerging or even flowering.

This is an especially interesting spring for me since this is my first spring in a new place, the Colorado Front Range, in between Fort Collins and Boulder in a small rural town called Berthoud. Just walking around local natural areas and taking my dog for many walks in this small town, I can see or imagine many plants that could be good for making budburst observations this year. Like many places there are a few common ornamental plants that you see everywhere, such as green ash (Fraxinus pennsylvanica) and western hackberry (Celtis occidentalis) and of course Colorado Blue spruce (Picea pungens). There are several interesting species here as well, and probably many that I will not recognize until the first leaves or flowers come out. The strange thing here as compared to my former haunts in Montana is the weather. Even in December or January you can get warm winds coming over the mountains resulting in daytime temperatures in the 60's or even the 70's. But night time temperatures still typically plunge to at least the 20's if not the teens. So the transition to spring is quite complicated. Warm days, then snowstorms. Warm days then another snowstorm. Will be interesting to learn how plants figure out when it is really time to start growing here! Gardeners tell me that by St Patricks's day one can plant cold tolerant plants. We shall see.

New leaves of silver maples

Here in Colorado it was at first a very mild and dry winter then with the beginning of the new year we got a series of small snowstorms (at least in foothills or plains along the Front Range) then some severe cold, even below 0. Just in the past week or so the last snow has melted and the soil is getting moist and soft. Just in the past week some early garden bulbs such as grape hyacinth (Muscari spp), day lily (Hemerocallis spp.) have been sending up new green leaves. Irises are starting to send up new leaves as well. Robins were first noticed in early February even though it was quite cold then (below 0ยบ!). In the past few weeks more birds have arrived here including red-tailed hawks, ferruginous hawks and many other interesting species. Whenever the temperature gets above 45 or so we also see European honey bees flying around, especially in the sun. Nothing to pollinate yet, but beekeepers tell me they often are getting some water.

In terms of plants in more natural areas, cool season grasses such as kentucky blue grass (Poa pratensis) are starting to send up new leaves. And dandelions sent up new leaves just in the past two days. Over the past three weeks in particular we have been seeing many trees starting to respond to the changing seasons. Maples, hackberries, aspens, and cottonwoods all have clearly expanding buds, and are changing colors. Tips of willow trees turned bright yellow over a month ago. You can now see the fuzzy coating of aspen flower buds and also what appears to be Chinese hackberries.

Today the first real budburst event of the season was the blooming of silver maple trees (Acer saccharinum), an ornamental species here (native to Midwest and eastern US). These trees are soft maples and are very similar to red maple (Acer rubrum). Maples are often one of the first species to bloom in the spring. Their flowers vary, but mostly come out before the leaves which improves the chances of wind carrying their pollen long distances. Silver maple is usually the earliest, often by many weeks. This year maples are blooming a full month earlier than they did last year, reflecting our warmer than normal, and up to now, mostly snowless winter.

So why do silver maples produce flowers so early in the spring, even in northern areas where they would seem to risk frost, snow or ice damage? One possible explanation is that they commonly grow in river floodplains. In this environment the spring melt and associated floods often create the best conditions for dispersing seeds and also creating new habitats ideal for maple seedlings (moist new flood bars and sediment). By flowering in March they can produce seeds early enough to colonize these critical habits. Even if they sometimes lose flowers to random snow or ice events, they still will end up with more new seedlings by having them ready for colonizing these ideal floodplain habitats.

While red maples are quite colorful with their bright red petals, silver maples are a bit more subtle. Tiny reddish to yellowish flowers emerge from buds on branches. Male flowers have no petals but just have clear, yellowish or whitish anthers which extend out from their yellowish sepals, near the tips of branches, mostly on the upper parts of the tree. The female flowers, which are separate flowers, typically occur on lower parts of the tree, or further back along the branches. You can recognize these by the the distinctive paired reddish stigmas which extend out from around the flower buds. Today I found three maples in bloom out of the dozen or so silver maples that occur on my regular walks around town. All of them went from swollen red buds to open flowers on many branches in just one day. It will be interesting to see how long it takes for the other maples to start blooming, and what happens if they get caught in one of these famous Colorado spring snowstorms!

Let us know what you are seeing by submitting your observations, photos, and also posting notes on our Facebook page. It will be interesting to see what kind of spring we will have after such a weird winter!

Paul Alaback

Photo notes:
Top the first leaf stage last spring here in Colorado. In contrast with red maples, silver maples usually put out leaves quickly, unfolding flat right away, long before the leaf is fully grown.

Middle New leaves of dandelion. They usually emerge soon as the soil thaws in the spring, and often long before flowers develop.

Bottom Flowers of silver maple are a bit hard to see, sometimes you have to grab a low lying branch to see the flowers clearly. Here a male and a female flower are growing side by side. The flower with the yellowish sepals is the male flower. You can just barely see the anthers which have not yet extended outside of the flower bud. On the right is the female flower where you can see the reddish stigmas.