Adaptation of red and white fir to elevation across an ecotone

Background/Question/Methods

In the Sierra Nevada Mountains of California red fir (RF) dominates the upper montane forest, and white fir (WF) is important in the midmontane mixed conifer forest. In the southern-most Sierra Nevada the ecotone between these communities occurs between 2400–2700 m. Microcalorimetric measurements of temperature dependence and timing of respiration (R_CO2) and heat rate (q) were made on RF and WF sampled across the ecotone in the southern-most Sierra Nevada.

Results/Conclusions

R_CO2 and q increased when bud break and elongation occurred, peaked during elongation and declined as elongation ended, which is consistent with previous studies on ponderosa pine.  WF q and R_CO2 accelerated earlier and remained high longer than RF.  RF q and R_CO2 were higher than WF for a shorter later period. This is consistent with WF-RF elongation seasons on the study sites.  WF bud break occurred first and elongation continued longer than RF.  Total elongation is similar for both species.  RF elongated faster for a shorter later period. Lower elevation WF sites are expected to lose available moisture earlier therefore WF must elongate earlier. Higher elevation RF sites have moisture available later therefore RF elongate later at warmer temperatures permitting faster growth and greater protection from frost damage.