A two-generation analysis of pollen pool genetic structure in flowering dogwood, Cornus florida (Cornaceae), in the Missouri Ozarks

Anthropogenic landscape change can disrupt gene flow. As part of the Missouri Ozark Forest Ecosystem Project, this study examined whether silvicultural practices influence pollen-mediated gene movement in the insect-pollinated species, Cornus florida L., by comparing pollen pool structure (Φ_st) among clear-cutting, selective cutting, and uncut regimes with the expectation that pollen movement should be least in the uncut regime. Using a sample of 1500 seedlings - 10 each from 150 seed parents (43 in clear-cut, 74 in selective, and 33 in control sites) from six sites (each ranging from 266 to 527 ha), eight allozyme loci were analyzed with a pollen pool structure approach known as TWOGENER (Smouse et al., 2001; Evolution 55: 260-271). This analysis revealed that pollen pool structure was less in clear-cut (Φ_C = 0.090, P < 0.001) than in uncut areas (Φ_U = 0.174, P < 0.001), with selective-cut intermediate (Φ_S = 0.125, P < 0.001). These estimates translate into more effective pollen donors (N_cp) in clear-cut (N_cp = 5.56) and selective-cut (N_cp = 4.00) areas than in uncut areas (N _cp = 2.87). We demonstrate that Φ_C ≤ Φ_S ≤ Φ_U, with Φ_C significantly smaller than Φ_U (P < 0.034). The findings imply that, as long as a sufficiently large number of seed parents remain to provide adequate reproduction and to avoid a genetic bottleneck in the effective number of mothers, silvicultural management may not negatively affect the effective number of pollen parents, and hence subsequent genetic diversity in Cornus florida.