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eastern redbud (Cercis canadensis)

Redbud is a midstature tree widespread in the eastern and southeastern United States. Redbuds flower early in spring before they develop leaves. Their flowers occur in clusters along branches and cover their branches providing an attrative lavender hue to the relatively stark colored forests of early spring.

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Although small in stature and often sparse in density, this species of tree is very important because of how they affect soil fertility. Redbud trees are one of a few tree species in eastern deciduous forests that are legumes (also see black locust). Many herbaceous legumes exist including: peas, beans, clover, and lupine. Legumes are important because of the mutualisms they form with nitrogen-fixing bacteria. A mutualism is a mutually beneficial interaction between two unrelated organisms (e.g. plant and soil bacteria). In this case, the bacteria live in root nodules (arrows to right indicate nodules on roots of a black locust) produced by the plant. The legumes provide the bacteria with a place to live and carbon (i.e. food) in the form of carbonhydrates that they acquired via. photosynthesis. In exchange the bacteria provide the plants with nitrogen. This is significant because the bacteria actually convert atmospheric nitrogen (the most abundant gas in our atmosphere) into forms that plants can use. Atmospheric nitrogen (dinitrogen) is otherwise unavailable to plants. Since nitrogen is often a limiting soil nutrient, legumes play an important role in naturally increasing soil fertility and that is why farmers often rotate crops with alfalfa (a legume). This natural form of fertilization is very important in natural plant communities and affects succession (see Panorama section to learn more about succession).

In contrast to this form of "natural" fertilization, the nitrogen used in most synthetic fertilizers is derived from an industrial process (i.e. Haber process) which consumes natural gas. Because vast amounts of synthetic fertilizer are produced annually to fertilize crops, approximately 3-5% of global supplies of natural gas are used to produce nitrogen for fertilizer (more specifically ammonia).

The redbud video sequence above was shot over 36 hours using a digital camera set to take one picture every 10 minutes.