Abstract
Abstract. Recent studies based on remote sensing and carbon process models have revealed that terrestrial net primary production (NPP) in the middle and high latitudes of the Northern Hemisphere has increased significantly; this is crucial for explaining the increased terrestrial carbon sink in the past several decades. Regional NPP estimation based on significant field data, however, has been rare. In this study, we estimated the long-term changes in aboveground NPP (ANPP) for Japan's forests from 1980 to 2005 using forest inventory data, direct field measurements, and an allometric method. The overall ANPP for all forest types averaged 10.5 Mg ha−1 yr−1, with a range of 9.6 to 11.5 Mg ha−1 yr−1, and ANPP for the whole country totaled 249.1 Tg yr−1 (range: 230.0 to 271.4 Tg yr−1) during the study period. Over the 25 years, the net effect of increased ANPP in needle-leaf forests and decreased ANPP in broadleaf forests has led to an increase of 1.9 Mg ha−1 yr−1 (i.e., 0.79 % yr−1). This increase may be mainly due to the establishment of plantations and the rapid early growth of these planted forests.
Highlights
Net primary production (NPP) is defined as the rate of accumulation of organic matter by vegetation and equals the difference between carbon assimilated by plants through photosynthesis and the carbon consumed by plant autotrophic respiration (Chapin et al, 2002)
Because of limitations in the earlier data from Japan’s Forest Resources Statistics, we have focused on the changes in aboveground NPP (ANPP) of Japan’s forests only from 1980 to 2005
The largest increase was for C. japonica forests, with a total increase of 7.3 Mg ha−1 yr−1 over the 25 yr, followed by Pinus forests, L. leptolepis forests, Abies and Picea forests, and C. obtusa forests, with increases of 3.3, 2.5, 1.5, and 0.8 Mg ha−1 yr−1, respectively (Table 3)
Summary
Net primary production (NPP) is defined as the rate of accumulation of organic matter by vegetation and equals the difference between carbon assimilated by plants through photosynthesis and the carbon consumed by plant autotrophic respiration (Chapin et al, 2002). A systematic forest inventory has been conducted in Japan at about 5 yr intervals since 1947, and the surveys have intensified since the 1980s (Fang et al, 2005) These direct field measurements and systematic forest inventories make it possible to investigate the historical changes in NPP for Japan’s forests. In order to estimate changes in biomass in Japan’s forests over time, we reviewed the research literature on Japan’s forests and compiled a database for Japan’s forest biomass (Fang et al, 2005) Based on this database and forest inventory data, we investigated changes in the biomass of Japan’s forests from 1947 to 1995 in the previous study (Fang et al, 2005). We further complemented the database with NPP datasets, developed allometric relationships between aboveground biomass (AB) and aboveground NPP (ANPP) for Japan’s major forest types, and investigated the changes in ANPP in Japan’s forests from 1980 to 2005
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