Invasion of Forest Floor Space, Clonal Architecture, and Population Growth in the Perennial Herb Clintonia Borealis

Abstract

SUMMARY (1) We investigated the pattern of clonal spread of the forest perennial herb, Clintonia borealis (Liliacae), in the Hubbard Brook Experimental Forest in New Hampshire. This species has underground rhizomes which persist for up to 15 years, allowing precise determination of the number and position of ramets, the branching and elongation pattern of rhizomes, and the amount of forest floor occupied by each clone during each of the previous years. (2) We excavated 1659 internodes of 194 clonal fragments in the population. Rosettes only produce one or two new rhizome segments each year, and each segment has one bud. (3) Average internode length was 4.6 cm, and slightly longer internodes were produced as the clone aged. Only 14-4% of ramets produced two new rhizome segments in a year. New rhizomes tend to diverge from the direction of the previous year's growth (22-90 for single rhizomes, 48. 1% for each rhizome when produced as a pair). (4) As a consequence of these rules of average growth, clones invade a wedge-shaped section of the forest floor, moving from a point of branching at an initial rate of 6 cm yr-I decreasing in later years to 2 cm yr-'. The branching frequency and angle of orientation of new rhizomes result in the perimeter of the wedge (the distance across all ramets present in a year) to increase at a constant rate of 8- 3 cm yr-'. (5) There is much between-clone variation in the rate of invasion of the forest floor, caused by the interaction of genotype and microhabitat differences with the basic morphological plan. Architectural analyses of clonal growth may be significantly influenced by conditions in the natural community. Population growth and statistics of space occupation can describe population events but have very low predictive value for any single clone in this population.