Patterns of wood carbon dioxide efflux across a 2,000-m elevation transect in an Andean moist forest.

During a 1-year measurement period, we recorded the CO(2) efflux from stems (R(S)) and coarse woody roots (R(R)) of 13-20 common tree species at three study sites at 1,050, 1,890 and 3,050 m a.s.l. in an Andean moist forest. The objective of this work was to study elevation changes of woody tissue CO(2) efflux and the relationship to climate variation, site characteristics and growth. Furthermore, we aim to provide insights into important respiration-productivity relationships of a little studied tropical vegetation type. We expected R(S) and R(R) to vary with dry and humid season conditions. We further expected R(S) to vary more than R(R) due to a more stable soil than air temperature regime. Seasonal variation in woody tissue CO(2) efflux was indeed mainly attributable to stems. At the same time, temperature played only a small role in triggering variations in R(S). At stand level, the ratio of C release (g C m(-2) ground area year(-1)) between stems and roots varied from 4:1 at 1,050 m to 1:1 at 3,050 m, indicating the increasing prevalence of root activity at high elevations. The fraction of growth respiration from total respiration varied between 10 (3,050 m) and 14% (1,050 m) for stems and between 5 (1,050 m) and 30% (3,050 m) for roots. Our results show that respiratory activity and hence productivity is not driven by low temperatures towards higher elevations in this tropical montane forest. We suggest that future studies should examine the limitation of carbohydrate supply from leaves as a driver for the changes in respiratory activity with elevation.