| Abstract: | Eleven populations of ponderosa pine (Pinus ponderosa) located on an east-west transect of the Palmer Divide of Central Colorado were studied. Within each population transects of approximately 20 × 250 m were established. In seven populations the transects represented contrasting ecological conditions such as north and south facing slopes. Within each transect 200–250 trees greater than 10 cm in height were tagged, their locations mapped, their ages determined and their diameters and heights measured. Electrophoretic analyses of mature needle tissue indicated that while most of the allozyme variation resided within transects, significant genetic heterogeneity could be found between populations and transects. Among populations consistent patterns of genetic variation were observed at only two loci. Five of the 13 loci had consistent but very small differences between transects within populations. Considerable genetic heterogeneity occurred among 20 m sections of the transects and among age classes within transects. The genetic structure of these populations can be explained by mosaic patterns of seedling recruitment characteristic of these ponderosa pine stands. Only a few maternal trees contribute to each patch of seedlings, and this localized founder effect produces the genetic structure observed in these populations. |
