Population biology of Ammophila breviligulata and Calamovilfa longifolia on Lake Huron sand dunes. I. Habitat, growth form, reproduction, and establishment

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Abstract
Some aspects of the population biology of 2 dune-forming perennial grasses, A. breviligulata Fern. and C. longifolia (Hook) Scribn., growing along Lake Huron shoreline, were investigated under natural and controlled conditions. Plants of A. breviligulata exhibit erratic flowering, ranging from no panicles in some areas to 16 per hundred tillers in others. C. longifolia plants occur as single clumps of varying diameters and flower profusely. A. breviligulata expands into adjacent areas by producing plagiotropic rhizomes ranging in length from 1 to several meters and then producing ramets on some of the nodes. Such a growth form is best suited for rapid colonization of bare areas. Clumps of C. longifolia expand outward in concentric circles through the development of diving rhizomes, and the radius of a clump increases by .apprx. 15-31 cm/yr. This growth form is well suited for local occupancy. A. breviligulata is more tolerant of burial (100 cm) in sand than C. longifolia (60 cm). C. longifolia produces a larger number of caryopses per square meter than A. breviligulata. The weight per caryopsis of both species is similar, but the significantly greater surface area per fruit of A. breviligulata improves its flotation ability in water, thus facilitating long-distance dispersal of fruits. Establishment of C. longifolia plants under natural conditions occurred almost exclusively from seedlings. In contrast, the establishment of A. breviligulata seedlings was rare and almost all new plants along the beach originated from clonal fragments cast on the drift line by high waves.