Tom's Blog

Friday, August 20, 2010

Clonal growth patterns

It is estimated that 70% of the plant flora of temperate regions exhibit clonal growth, including many invasive species (both native and nonnative). An understanding of clonal growth patterns is important in developing strategies for control of invasive species.

Two major types of clonal growth patterns have been recognized, which have been called guerrilla and phalanx (Lovett Doust, 1981, Journal of Ecology Vol. 69: 743-755).

Both of these terms come from warfare, and reflect the idea that the spread of a clonal plant across a site has an element of "force" about it.

In warfare, a phalanx represents a massed army formed in closed, deep ranks. A botanical example is Missouri goldenrod (photo below), whose advancing front is very compact, with many short, highly branched rhizomes. Woodland sunflower is another example.

A guerrilla, on the other hand, is a person engaged in independent warfare, becoming established in an outlying part of an area. An example of guerrilla growth is aspen. Aspen plants send out lengthy unbranched rhizomes which send up new shoots far away from the main front. Other examples of guerrilla plants are black locust and wild sarsaparilla.

Guerrilla's wander through space and one clone may intermingle with others, whereas phalanx clones tend to form distinct clumps or patches. The phalanx clone is thus easier to recognize than the guerrilla one.

If undesirable, the phalanx clone, being very obvious, is generally an early candidate for eradication, although because of the density of the shoots, eradication may be difficult to achieve. However, such clones are good candidates for herbicide treatment.

Eradication of guerrilla clones requires different tactics, as well as much more extensive surveys of the site to find the centers of colonization.

The rate of clonal growth is a function of the conditions of the soil into which the rhizomes are extending. Very compact soils resist rhizome growth, slowing down the spread of the clone. Also, soil moisture, nutrients, and presence of other plants, can markedly affect clonal growth. There is a vast amount of research on the physiology of clonal growth, but since most of the information is species specific, it is difficult to apply to other species.


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