Comparison of Seasonal Variations in Carbon Dioxide Concentrations between a Natural Hardwood Stand and a Fir Plantation at the Guandaushi Subtropical Forest, Taiwan

Abstract

The purpose of this study was to understand variations in carbon dioxide concentrations at different canopy heights in a natural hardwood stand and a China-fir (Cunninghamia lanceolata) plantation at the Guandaushi subtropical forest. The measurements began in September 2004 and continued to the end of June 2005. There were 4 sampling heights, including 0.5, 4, and 12 m above ground level (agl) and 3~4 m above the canopy at the 2 stands. Results showed that the highest concentration of carbon dioxide was near the forest floor, and the lowest ones were at 12 m agl and 3~4 m above the canopy for both the natural hardwood stand and fir plantation. Seasonal and yearly variations of sampling heights between 12 m agl and 3~4 m above the canopy were not significant. The carbon dioxide concentrations of the 4 sampling heights were higher in spring and summer than in winter. Variations in carbon dioxide concentrations of the sampling height at 12 m in the natural hardwood forest were influenced by light intensity, regardless of daily or yearly variations. We concluded that the forest floor soil of the natural hardwood stand had a higher respiration rate, and there was a lower photosynthetic rate at the 12m level of the canopy. Therefore, at all sampling points, the concentrations of carbon dioxide were higher than these in the China-fir plantation. This concentration gradient was more significant in the higher-temperature season (June) than in the lower-temperature season (December to January).