Water vapour, carbon dioxide and energy fluxes in a chronosequence of planted white pine forests in southern Ontario, Canada.

摘要

Energy, carbon dioxide and water vapour fluxes were measured from June 2002 to May 2005 in a chronosequence (planted in 1939 (WPP39), 1974 (WPP74), 1989 (WPP89), 2002 (WPP02)) of four white pine (Pinus strobus L.) forests located in southern Ontario, Canada using the eddy covariance technique. A close-path eddy covariance system was continuously operated at the mature site, while an open-path system was rotated on a monthly or bi-weekly basis among the three younger sites.; Meteorological and other ancillary data were measured at all four sites. Mean annual evapotranspiration and (net ecosystem productivity) values over the three year period were 398 (246), 428 (387), 677 (661), 302 (-1) mm (g C m-2 yr-1) at the WPP39, WPP74, WPP89 and WPP02, respectively. High net ecosystems productivity at the WPP89 site was associated with the peak growth rate observed in forest ecosystems during the first one to two decades of their development stage, and the availability of high soil water content. WPP89 also showed the lowest inter-annual variability in response to variations in climate variables. The seedling site (WPP02) was a source of carbon in the first two years after planting and became a small sink in the third year. These results show that inter-annual variability in climate variables played a less significant role in surface exchanges of carbon dioxide and water vapour in this forest chronosequence, while forest age was a dominant factor influencing these exchanges.; Water and carbon fluxes as well as key climate variables measured in this chronosequence were compared with similar measurements from other temperate coniferous forests across the globe. This comparison showed that differences in carbon uptake (photosynthesis) among plantations and between plantations and natural temperate coniferous forests are not only because of differences in temperature and precipitation (water availability) patterns, but also because of physical and physiological factors, such as tree density, site history, and the adopted management practices in the case of plantation forests. A strong negative correlation between productivity as well as evapotranspiration and latitude was observed for both natural and plantation forests i.e. both productivity and water loss decreased from north to south. This analysis further indicated that evapotranspiration is controlled by radiation and growing season temperatures, rather than by precipitation and leaf area index. Evaporative fluxes from sources other than the tree canopy strongly influenced annual water loss in these forest ecosystems. However, net ecosystem productivity had a strong correlation with leaf area index.; Results of this study have significance for land surface interaction modelers, forest industry and government management staff and policy makers to improve land-use management practices, while meeting carbon sequestration objectives. Planting forest on abandoned and former agricultural lands with forests has the potential to not only sequester atmospheric carbon dioxide until new technologies are developed to better manage waste carbon dioxide, but also to improve local and regional environmental quality.