Friday, May 22, 2009

Phenology and Invasive Species

I’ve been thinking about the relationship between phenology and invasive species this week as I’ve been pulling garlic mustard (Alliaria petiolata), one of the worst woodland invaders in the eastern U.S. Garlic mustard is a biennial herb; it forms a small rosette of leaves its first year, then bolts, flowers, sets seed, and dies its second year. Pulling it out at the right phenophase is the key to its control. It spreads by seed and a single plant can make thousands of seeds. It is crucial to pull it before those seeds are produced! The onset of flowering is the best time for control because garlic mustard is easy to spot (due to its white flowers), but no seeds have been formed. Right now is a great time to pull garlic mustard in the upper Midwest!

Another phenological observation about invasive species, at least in my part of the country, is that they often have a longer growing season than our native species. For instance common buckthorn and glossy buckthorn (Rhamnus cathartica and R. frangula), shrubs that invade woodlands in this region, are two of the first plants to leaf out in the spring and two of the last to drop leaves in the fall. This extended growing season may be one of the keys to their successful competitive ability. They can shade out anything growing under them and can capture sunlight and make sugar long before and after the oaks leaf out above. I’m wondering if this is a common phenomenon in species that invade forested areas. If you live near a woodland, please keep an eye out for what species green up first in the spring and drop their leaves last in the fall and let us know!

Lastly for a native species highlight, a colleague caught me in the hall this morning and said, “You have to go for a walk in the prairie, the shooters are out.” I must have looked a little confused before realizing she meant the shooting stars (Dodecatheon meadii). They are in full bloom right now in Chicago and are absolutely beautiful!

Wednesday, May 13, 2009

Why do we use first leaf rather than budburst in Project BudBurst?

It might strike you as a bit odd that in Project Budburst we generally do not record the date of budburst (!). It all has to do with keeping things simple and also making things as accurate as possible. Budburst, when you see leaf buds swelling up then “bursting” open, unfurling tiny rolled up leaves is the very symbol of spring in most northern climates. How plants actually do this, and the pattern that unfolds is quite variable, reflecting clever adaptations of plants to many different climates, habitats and stresses in the environment. Some plants such as Antelope bitterbrush, and most dogwood species, such as red osier dogwood don’t budburst at all, since their leaves are not inside buds in the winter.

They produce tiny leaves in the late summer or fall which turn red or brown in winter (and change their chemistry to protect against frost). In the spring they turn green and then expand into the mature form. Other plants such as western serviceberry, have leaves tightly rolled up, which expand out of the winter buds then later begin to unroll. Some plants have leaves which expand out of bud green, for others the leaves are various shades of red or brown when they come out of the buds (making them a little hard to see), then they turn green and unroll, or unroll first then turn green. For others there is a distinctive stage where the tip of the bud turns green, just before budburst occurs (such as American linden and black locust) . So budburst is not as simple as you might think! But this makes sense in terms of plant adaptations. Plants that begin growing when heavy frost is common such as bitterbrush, western serviceberry and chokecherry, and apples should have adaptions to frost that are less critical for species which emerge later in spring such as oaks, locusts, and elderberries.

First leaf on the other hand seems a bit more straight-forward to identify. When a leaf emerges from the bud you can clearly see the widest part of the leaf emerge, and usually see the stem (petiole) at the base. Usually the leaf then unfolds or unrolls and becomes flat, finally reaching our “first leaf” stage. How a leaf reaches this stage still can vary depending on the species. Lilacs and aspen for example first produce thick stiff leaves which emerge flat, so reach the first leaf stage quickly (and take a while to reach the all leaf stage). Red maple emerges in a droopy, limp state and takes a while to turn green and become flat.

Others such as chokecherry have leaves which emerge folded and take a while to become flat as well. It is important that we all agree on these definitions since it can effect the dates at which a plant reaches a given stage. This is also why we are working towards having better photos to document first leaf and the other stages in our phenophase field guides. So please send us your photos of first leaf and other stages as you observe them this spring. It should be a great help it making sure we are all making comparable observations.

Figure captions:

  1. Droopy new leaves of red maple
  2. Early stages of budburst for western serviceberry. Note the new leaves are thickly covered with hairs, helping protect them from severe frost.
  3. Red osier dogwood with tiny winter leaves (no bud scales)
  4. Stiff young leaves of common lilac – well adapted to heavy frosts that may occur at this time of year.

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Here in the northern Rockies this week spring is still developing slowly. We had a winter storm advisory the other night again, and have snow above about 4,000’ today. Balsamroot is in full bloom now, turning some grassy south-facing hillslopes bright yellow. Most of our shrubs are at the first leaf stage, (some for weeks), and you can see many swelling flower buds. Soon as we get some warm days things may change fast!

Wednesday, May 6, 2009


Spring is at its peak right now in Chicago.

The Chicago Botanic Garden is in full bloom. In the last ten days I saw the first flowers open for several trees and shrubs, including lilacs (Syringa vulgaris), juneberry (Amelanchier canadensis), and redbud (Cercis canadensis). The magnolias (Magnolia spp.) are waning and the crabapples (Malus spp.) are just starting to open their colorful blossoms. The spring ephemerals such as bluebells (Mertensia virginica), white trillium (Trillium grandiflorum), and dogtooth violets (Erythronium americanum), rue anemone (Thalictrum thalictroides) and celandine poppy (Stylophorum diphyllum) are in full bloom in the region’s woodlands. Most of these observations were within a few days of last year’s observations of these phenophases.

We expect to see the greatest variation in the early spring phenophases. Plants that bloom early in the spring and leaf budburst for many species are tightly correlated with temperature. For plants that bloom in mid-summer, bloom time is more often cued by daylength rather than temperature. As our dataset grows, we will be able to test these predictions. Do we see a greater spread in the first flower opening date for something like Forsythia (Forsythia x intermedia), one of the first spring bloomers, compared to a grass like big bluestemAndropogon gerardii) which typically blooms in the summer.

Mayapples (Podophyllum peltatum) have almost completely expanded their umbrella shaped leaves, so I’m thinking it is about time to start hunting for morel mushrooms! Given all the rain we’ve had this spring it might be a good year for morels. And no, I’m not telling you where I go to look for them!