Carbon dioxide exchange in a cool-temperate evergreen coniferous forest over complex topography in Japan during two years with contrasting climates

Abstract

We investigated carbon dioxide (CO(2)) exchange and its environmental response during two years with contrasting climate (2006 and 2007) in a cool-temperate mixed evergreen coniferous forest dominated by Japanese cedar (Cryptomeria japonica) and Japanese cypress (Chamaecyparis obtusa). The study, which was conducted in a mountainous region of central Japan, used the eddy-covariance technique. Our results (crosschecked using the common u (*) approach and van Gorsel's alternative approach) showed that annual gross primary production (GPP) and ecosystem respiration (RE) were at least 6% higher in the dry year than in the wet year, whereas net ecosystem exchange (NEE) was similar in both years. Without soil water stress, strong light stress or seasonality of plant area index during most of the study period, the forest had high metabolic activity. GPP and RE differed greatly between the two years, especially in spring (April-May) and summer (July-September), respectively. The spring GPP difference (>20%) was influenced by different winter air temperatures and snow melt timing, which controlled photosynthetic capacity in spring, and by different spring light intensities. The annual NEE differed depending on the evaluation method used, but the mean 2-year NEE estimated by the u (*) threshold approach [-3.39 +/- 0.11 (SD) MgC ha(-1) year(-1)] appears more reasonable in comparison with results from other forests.

Estimation of Leaf Area Index in a Mountain Forest of Central Japan with a 30-m Spatial Resolution Based on Landsat Operational Land Imager Imagery: An Application of a Simple Model for Seasonal Monitoring

“…Consequently, because satellite imagery does not distinguish between wooden and photosynthetic canopy parts, but instead records only the reflectance of the canopy roughness [7], the in situ effective LAI is better correlated with the remote-sensing-based LAI. In fact, Saitoh et al [32] estimated the PAI at TKC as 4.9 and 5.2 in 2006 and 2007, respectively, via the PAR transmittance method [28], a result consistent with the simple-model-estimated LAI reported here.…”

“…The area, which is about 60 km 2 , has an elevation gradient of 1000 m-from approximately 600 m to 1600 m a.s.l.-and a steep topography [31]. The climate, which is cool and temperate, is influenced by the Asian Monsoon and is characterized by a mild, humid spring and autumn; a hot, humid summer; and a cold, snowy winter [32]. The study area includes various forests-deciduous broadleaf forests (DBFs), deciduous coniferous forests (DCFs), and evergreen coniferous forests (ECFs)-paddy fields, and urban areas [31,33].…”

“…Therefore, we examined leaf seasonality at the deciduous plots (DBF and DCF) making use of the available PAR transmittance-based LAI estimates at TKY and the dependency of LAI phenology on the air temperature during the growing season. We only examined LAI seasonality at three deciduous forest sites, because in the previous study, Saitoh et al [32] showed that LAI has little seasonality at TKC (an ECF study plot). In temperate deciduous forest areas, LAI increases in spring because of warmer air temperatures and reaches its maximum in the middle of summer following the phenological cycle of the ecosystem.…”

“…Summer in situ LAI was higher at the two coniferous forest study plots, where it was estimated using the allometric equations for the determination of dry leaf litter mass. Because ECF underwent only a slight seasonal variation [32], LAI at TKC was assumed constant throughout the season. In the cool-temperate Takayama area, leaf expansion generally occurred in the middle of May, foliage density (leaf area) matured in late June, and leaf fall occurred in October [3].…”

“…2 m above the ground) were used to estimate LAI in 2013 [2]. To eliminate the effects of weather, we only used PAR measurements made on cloudy days; cloudy days were determined using the method described by Saitoh et al [32,55]. The seasonal LAI was estimated based on the PAR transmittance method [3,21].…”