Releases of the greenhouse gases carbon dioxide (CO2) and methane (CH4) from thawing permafrost are expected to be among the largest feedbacks to climate from arctic ecosystems. However, the current net carbon (C) balance of terrestrial arctic ecosystems is unknown. Recent studies suggest that these ecosystems are sources, sinks, or approximately in balance at present…. More

in    0

Two indirect gap fraction methods for estimating leaf area index (LAI) are compared with estimates from litterfall collections in a mixed-age oak-hickory forest. One indirect method uses averaged, direct beam penetration data obtained with a moving tram. The second uses a portable light sensor system that measures diffuse light penetration for five sky sectors between… More

in    0

Aerodynamic canopy height (ha) is the effective height of vegetation canopy for its influence on atmospheric fluxes and is a key parameter of surface‐atmosphere coupling. However, methods to estimate ha from data are limited. This synthesis evaluates the applicability and robustness of the calculation of ha from eddy covariance momentum‐flux data. At 69 forest sites,… More

in    0

There are few whole-canopy or ecosystem scale assessments of the interplay between canopy temperature and photosynthesis across both spatial and temporal scales. The stable oxygen isotope ratio (δ18O) of plant cellulose can be used to resolve a photosynthesis-weighted estimate of canopy temperature, but the method requires independent confirmation. We compare isotope-resolved canopy temperatures derived from… More

in    0

It is necessary to partition eddy covariance measurements of carbon dioxide exchange into its offsetting gross fluxes, canopy photosynthesis, and ecosystem respiration, to understand the biophysical controls on the net fluxes. And independent estimates of canopy photosynthesis (G) and ecosystem respiration (R) are needed to validate and parametrize carbon cycle models that are coupled with… More

in    0

The traditional hypothesis that old-growth forests are carbon neutral is under debate as recent studies show evidence of net carbon sequestration. Here, we present a decade (1998–2008) of carbon dioxide, water and energy fluxes from an old-growth stand in the American Pacific Northwest to identify ecosystem-level responses to climate variability, including teleconnection patterns. This study… More

in    0

Carbon dioxide, water vapor and other passive scalars are physically transferred between a plant canopy and the atmosphere by turbulence. Intense and intermittent sweep and ejection events transfer most of the mass. Although the capacity for turbulence to transfer material is high, mass transfer is coupled to the diffusive source or sink strength of the… More

in    0