Abstract
Tree rings have long been used to calibrate the net primary production (NPP) time-series predicted by process-based models, based on an implicit assumption that ring-width indices (RWI) can well reflect temporal NPP change. However, this assumption has seldom been tested systematically. In this study, 36 plots were set in three forest types from four sites along a latitudinal gradient in northeast China. For each plot, we constructed chronologies and stand NPP of the past 20 years to examine: is RWI a good proxy of inter-annual variation of forest NPP for different forest types under different climate? If it is, why? Our results indicate that RWI was closely related to stand NPP in most cases, and could be used as a good proxy of NPP in temperate forests. Standard and arstan chronologies were better related to NPP series than residual chronology. Stand NPP time-series were mainly determined by large trees, and the correlation between RWI and NPP was also higher for larger trees. We suggest that large trees and dominant species of canopy layer should be sampled for chronology construction. Large trees are major contributors of forest biomass and productivity, and should have priority in forest conservation in a rapid-warming world.
Highlights
Net primary production (NPP) is a key component of terrestrial carbon cycle, and the response of net primary production (NPP) to climate change has long been a focus in ecology[1, 2]
We hypothesized that the reason why ring width index (RWI) can be used as proxy for forest NPP dynamic is that stand NPP is predominantly determined by the annual NPP variation of large trees, while the latter is closely related to annual DBH growth of large trees
For each forest type in each site, RWI series were significantly correlated with stand NPP, except for the deciduous broadleaved forest (DBF) at Mt
Summary
Net primary production (NPP) is a key component of terrestrial carbon cycle, and the response of NPP to climate change has long been a focus in ecology[1, 2]. Using RWI to validate modeled NPP time-series is based on an implicit assumption that RWI can well reflect the temporal change of stand NPP. This assumption has seldom been tested systematically, despite that a number of studies have used RWI for model validation. The first aim of our study is to test whether RWI is a good proxy of annual change in stand NPP, for different forest types under different climate. (3) In forest communities, the tree-ring cores used for chronology construction are commonly sampled from large trees at canopy layer This sampling strategy is aimed to obtain longer time-series, and helps to reduce the influence of competition between trees in order to maximize the climate signals in tree ring data. We hypothesized that the reason why RWI can be used as proxy for forest NPP dynamic is that stand NPP is predominantly determined by the annual NPP variation of large trees, while the latter is closely related to annual DBH growth of large trees
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