The relationship between relative CPC deficits in a specific month and P/ET in previous months
Table 1. The relationship between relative CPC deficits in a specific month and P/ET in previous months. In general, summer droughts lasted from June to August, and we will focus only on the monthly CPC deficits in those three months.
Increasing occurrences of climate extreme events urge us to study their impacts on terrestrial carbon sequestration. Ecosystem potential productivity deficits could characterize such impacts and display the ecosystem vulnerability and resilience to the extremes in climate change, whereas few studies have analyzed the yearly dynamics of forest potential productivity deficits. Based on a perfect-deficit approach, we used in situ eddy covariance flux data and meteorological observation data at Qianyanzhou station from 2003 to 2010 to explore the relationship between potential productivity and climate extremes, such as droughts in 2003 and 2007, ice rain in 2005, and an ice storm in 2008. We found (1) the monthly canopy photosynthetic capacity (CPC) deficits could be mainly explained by air temperature (Ta) deficits (R2 = 0.45, p < 0.000 01); (2) a significant correlation was noted between seasonal CPC deficits and co-current Ta deficits (R2 = 0.45, p < 0.000 01), especially in winter (R2 = 0.79, p = 0.003); (3) drought in summer exerted a negatively lagged effect on potential productivity (R2 = 0.59, p = 0.02), but at a short time scale; and (4) annual CPC deficits captured the impacts of climate extremes on the forest ecosystem potential productivity, and the two largest potential productivity deficits occurred in 2003 (relative CPC deficits = 0.34) and in 2005 (relative CPC deficits = 0.35), respectively. With the perfect-deficit approach, the forest ecosystem vulnerability to extremes was analyzed in a novel way.