Effect of variation in winter and early spring temperature on carbon storage by coniferous and deciduous forests in the northeastern United States

Evergreen coniferous trees have the ability to store carbon whenever temperatures are warm enough and there is enough available water to carry out photosynthesis. This contrasts with deciduous trees, which in most of the northern temperate zone are leafless for at least six months. Thus warmer temperatures in fall, winter and spring provide an opportunity for conifers to benefit by increasing their annual carbon storage and growth. Deciduous trees in contrast are likely to lose more carbon during the leafless period, because warmer temperatures stimulate respiration. Four years of eddy covariance data from forests dominated by the coniferous species eastern hemlock (Tsuga canadensis), and the deciduous species red oak (Quercus rubra) show that warmer air and soil temperatures in October through April were associated with greater carbon storage by the hemlock forest, especially in March and April. In each of these months, carbon storage was about 0.4 Mg C/ha higher in the year with the warmest temperatures compared to the coolest, and the difference in C storage for March and April combined (0.8 Mg C) was 20-25% of annual C storage, depending on which year the annual C storage was calculated for. There was not a clear relationship between air or soil temperature during these months and carbon loss by oak-dominated forests. However, oak-dominated forests did benefit from earlier leaf development and later leaf abscission linked to mild spring and autumn temperatures.