Atmospheric CO_2 Concentrations Within a Mixed Forest: Implications for Seedling Growth

Abstract

We studied carbon dioxide concentrations in a mixed deciduous forest in New England, USA by making continuous measurements at 0.05, 0.2, 3, and 12 m above the soil surface. The measurements began in early March and continued until the end of November 1985; therefore, they spanned the growing season and parts of the dormant seasons both before and afterwards. The data were compared with those from Mauna Loa, Hawaii, which represent global atmospheric CO2 levels in the Northern Hemisphere. The results show strong seasonal and daily variations in CO2 concentrations at all heights in the forest. On average, during the growing season, CO2 levels were generally higher in the forest than in bulk air at Mauna Loa. The highest level of CO2 was found near the forest floor and the lowest at the 12—m level. Daily levels of CO2 were constant throughout the day in the dormant season and were the same for all heights in the forest. However, during the growing season, the CO2 concentrations were lowest during the middle of the day, especially at the 12 m height. Thus, this study shows that the CO2 concentrations in the forest may be quite different than those in bulk air and that seedlings, saplings, and mature trees may experience different CO2 environments for which they may show different responses in photosynthesis, growth, and water use. Moreover, a tree may experience different CO2 environments as it grows towards the canopy, and different modules of an individual may also be growing in different CO2 atmospheres.