TREE CLUSTERS AND GROWTH FORM DISTRIBUTION IN PINUS CEMBRA, A BIRD-DISPERSED PINE

Two North American bird-dispersed pines, Pinus albicaulis and Pinus flexilis, were previously found to occur in three growth forms: single-trunk, single genet multi-trunk, and multi-genet tree cluster. The latter two forms are morphologically similar and distinguishable only by genetic analysis; they are together referred to as ''tree clumps.'' In the Upper Engadine, Switzerland, we studied Pinus cembra to determine whether this pine species, which is dispersed by Nucifraga caryocatactes, also occurs in three growth forms. Examining the relative frequency of single-trunk trees and tree clumps, we surveyed P. cembra in three different forest areas and at elevations ranging from 1810 to 2300 m. Tree clumps occurred at 19 to 30% of the tree sites and up to 45% of the seedling sites. We sampled foliage from all trunks of 23 tree clumps (2 to 7 trunks per clump, ($) over bar x = 3.4, SD = 1.3) for analysis by starch gel protein electrophoresis at four gene loci: FE, PGI, PGM-1, and PGM-2. Sixteen of the 23 tree clumps (70%) contained more than one genet and thus were tree clusters. Extrapolation of this percentage suggests that tree clusters occupied from 13 to 21% of the P. cembra tree sites surveyed. A comparison of genotypes and degree of fusion between adjacent trunks in tree clumps confirmed that morphology is a poor indicator of growth form.