20 Along the Towpath, March 2016

Nature Notes by Marjorie Richman

Trees Without LeavesIn the natural world, competition for survival is fierce. Each member of a species must find its own niche, a space for itself among a host of competitors. In the spring, once trees leaf out, almost overnight there are many contenders for sunlight and nutrients.

In order to beat the competition, some trees and shrubs have adopted a very simple strategy: bloom early, attract pol-linators before others arrive on the scene, and get a head start on reproduction. As the weather warms and days get longer, the first flowers we see are those of early, or prevernal, bloom-ers. Early bloomers produce flowers on bare branches; their leaves appear later.

Prevernal blooming is a survival strategy that serves plants with certain characteristics. For example, the seeds of some plants have a longer period of maturation before they are ready to be dispersed. Fruit trees, such as apple, pear and cherry, produce fleshy sweet fruit that takes time to mature to the point where it is attractive to birds, the major seed disper-sal agent. The fruit has to be ready to be eaten while the birds are still active in the area. Furthermore, since the buffet is limited in the early spring, pollinators have only a few species to choose from and are more likely to cross-pollinate among trees of the same species.

Access to light and nutrients is also an advantage of early blooming for small trees and shrubs that populate the un-derstory. Flowering early gives such plants a short but critical window of opportunity.

Along the towpath we know winter is over when two trees in particular produce flowers before their leaves appear: red-bud (pea family) and shadbush (rose family). Redbud can be found in various places along the towpath; shadbush typically grows along the banks of the Potomac. Both are understory trees.

The flowers of the redbud tree are a dark rose-to-purple in color. Without leaves on the branches, these early bloomers are often the first noticeable flowers in the spring. Shadbush flowers cover the bare branches in drooping clusters of white blossoms. The name of the tree has an interesting etymology. It refers to the fact that it blooms around the time of the shad runs in local streams.

Depending on weather conditions, the flowers of both redbud and shadbush may be seen as early as late March, but April is more predictable.

Above - Redbud; Below - Shadbush

Below - Redbud detailPhotos by Marjorie Richman