Geographic Variation and Local Growth Superiority for Coastal Douglas-fir – Rotation-age Growth Performance in a Douglas-fir Provenance Test

Rotation-age growth performance of 16 provenances and local growth superiority were assessed from a rotation- age reciprocal coastal Douglas-fir [Pseudotsuga menziesii var. menziesii (Mirb.) Franco] provenance test established in the Pacific Northwest of America. Provenance differences for total volume per plot were highly significant. Due to the significant provenance × site interaction effect, the best provenances varied across planting sites in terms of rotation-age volume growth. Local provenance trees exhibited superior volume growth at two of the six planting sites. At the remaining four sites, local provenances performed equally well as average non-local provenances. At the three low-elevation (< 460 m) sites, low-elevation provenances performed significantly better than high-elevation provenances. By contrast, high- and low-elevation provenances had similar growth at the two high-elevation (> 800 m) sites. Southern provenances generally grew faster than northern provenances at the Oregon sites, while northern provenances performed better than southern provenances at the sites in British Columbia.

Regression analyses showed that although local growth superiority increased with the geographic distance between provenance’s origin and the test site in general (r=0.47, P<0.001), it only became obvious when the geographic distance is larger than 435 km in latitude or 370 m in elevation. Significant spatial autocorrelation was found via Mantel test, and geographically or climatically closely located provenances tended to have similar rotation-age volume growth.

The results suggested that breeding zones larger than the current second-cycle zones would lead to little loss of rotation-age total volume for coastal Douglas-fir in this region.