Comparison of conifer elongation temperature response to climate adaptation
This study compared elongation temperature conditions and resulting adaptation of conifer species native to ranges that cross elevation and moisture gradients in California. Timing and length of elongation were measured at 1-2 week intervals spring and summer for three years in a common garden at Davis California. Hourly temperature data were collected.
Elongation initiated following this sequence: gray pine, ponderosa pine, Jeffrey pine, incense cedar, Douglas-fir, sugar pine, and finally white fir. This sequence is consistent with studies conducted in native ranges and described in the literature. There was overlap in timing of elongation between some species and this varied somewhat from year to year. Data indicates elongation begins under the lowest temperature conditions for gray pine and becomes progressively warmer for species in the listed sequence. As species become progressively adapted to higher elevations and more mesic environments elongation is initiated under warmer conditions. Davis and regions these species are adapted too generally have Mediterranean climates. Mild wet winters and warm dry summers result in spring growth seasons due to mild temperatures and residual moisture from the rainy season. Warmer drier sites lose available moisture earlier and adapted species (gray pine, ponderosa pine) must elongate earlier at lower temperatures to use available moisture. Higher elevation and more mesic sites have moisture available later in spring and adapted species (Douglas-fir, sugar pine, white fir) initiate elongation later under warmer temperatures permitting faster growth and providing greater protection from frost damage.