Overstory and shrub influences on seedling recruitment patterns in an old-growth ponderosa pine stand
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Seedling recruitment in an old growth ponderosa pine (Pinus ponderosa) stand in central Oregon, USA, was studied to determine its relationship with overstorey trees and nearby shrubs, and to identify the spatial patterns resulting from these relationships. Results showed that the influence of adjacent vegetation was greatest among smaller size classes of regeneration. The strongest relationship between overstorey basal area, and germinant and seedling density was observed when calculated at a very local scale (5-m radius). Seedling and germinant densities were also adversely affected by adjacent saplings but were positively associated with shrubs. Spatial analysis revealed significant aggregation of germinants, seedlings and saplings, with the intensity of aggregation decreasing from smaller to larger size classes. These results suggest that regeneration is most sensitive to adjacent vegetation during the early stages, that the facilitative influence of shrubs diminishes relative to their competitive effect once regeneration reaches the sapling stage, and that the early aggregated condition of regeneration gradually transforms towards a more regular pattern as stand development progresses.