The Integration of Neighbourhood Effects by Clonal Genets in Solidago Canadensis

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Abstract
When clones of S. canadensis were grown experimentally with pure stands of different species, the neighboring species had different effects on ramet shoot-growth, flower-head production, and clonal growth. In general, S. canadensis shoot growth and flower production were greatest in the neighborhood of Poa pratensis, and lowest among Aster pilosus, whereas clonal growth was greatest among ramets growing in the A. pilosus neighborhood and lowest in the S. canadensis neighborhood. When clones of S. canadensis were grown experimentally with each interconnected ramet among a different neighbor species, the effects of the different neighbors were evened out. All ramets responded more or less equitably in their shoot growth, reproduction, and clonal growth, regardless of the identity of their neighbor. These results suggest that clones integrate local neighborhood variation and that the response of a given ramet to interference from a neighbor species is partly dependent upon the experiences of its interconnected sibling ramets. There are several costs and and benefits associated with maintaining physiological interdependency among ramets. Interdependent ramets may support the growth of ramets experiencing intense interference or resource limitation and may benefit from the ability to regulate internally the position and density of shoots within the clone and to overcome local variation in their environment. The maintenance of a network of long interconnecting rhizomes may be energetically expensive and may allow certain agents of mortality such as pathogens to spread rapidly among ramets. The growth form of a clone may also influence the relationships between clonal plants and neighbors. Within-clonal S. canadensis ramets form pure stands, 1-several m in diameter, that prevent the invasion of neighbors, distribute the effects of surrounding neighbor species, are buffered against neighbor interference, and expand uniformly in several directions regardless of the identity of neighbors. This is in contrast to patterns in other clonal species, e.g. Trifolium repens and Ranunculus repens in which very long rhizomes or stolons are produced and ramet interconnections are rapidly lost. These species are characterized by extensive lateral mobility and sampling of the environment, the avoidance of interference, and the differential growth of different independent portions of the genet in different parts of the habitat mosaic.