Abstract
The main objective of this study is to analyze the spatial and temporal variability of gross and net primary production (GPP and NPP) in Peninsular Spain across 15 years (2004–2018) and determine the relationship of those carbon fluxes with precipitation and air temperature. A time series study of daily GPP, NPP, mean air temperature, and monthly standardized precipitation index (SPI) at 1 km spatial resolution is conducted to analyze the ecosystem status and adaptation to changing environmental conditions. Spatial variability is analyzed for vegetation and specific forest types. Temporal dynamics are examined from a multiresolution analysis based on the wavelet transform (MRA-WT). The Mann–Kendall nonparametric test and the Theil–Sen slope are applied to quantify the magnitude and direction of trends (increasing or decreasing) within the time series. The use of MRA-WT to extract the annual component from daily series increased the number of statistically significant pixels. At pixel level, larger significant GPP and NPP negative changes (p-value < 0.1) are observed, especially in southeastern Spain, eastern Mediterranean coastland, and central Spain. At annual temporal scale, forests and irrigated crops are estimated to have twice the GPP of rainfed crops, shrublands, grasslands, and sparse vegetation. Within forest types, deciduous broadleaved trees exhibited the greatest annual NPP, followed by evergreen broadleaved and evergreen needle-leaved tree species. Carbon fluxes trends were correlated with precipitation. The temporal analysis based on daily TS demonstrated an increase of accuracy in the trend estimates since more significant pixels were obtained as compared to annual resolution studies (72% as to only 17%).
Highlights
Published: 8 March 2022A full description of the carbon cycle requires detailed information on spatiotemporal patterns of surface–atmosphere carbon fluxes
The results reveal that the greatest gross primary production (GPP) is found for broadleaved forests (1.6, 1.8, and 2.0 kg m–2 y–1 for EBF, HDBF, and LDBF, respectively), while the smallest GPP is found for sparse vegetation and rainfed crops, both presenting GPP = 0.6 kg m–2 y–1
This paper has explored the dynamics of GPP and Net primary production (NPP) variables in Peninsular Spain, which is located in the mid-latitude ecotone (MLE) [54], the zone between 30°–60° latitude that comprises a transition belt between forests and drylands
Summary
Published: 8 March 2022A full description of the carbon cycle requires detailed information on spatiotemporal patterns of surface–atmosphere carbon fluxes. One of the main carbon fluxes characterizing terrestrial ecosystems and biodiversity is the gross primary production (GPP), i.e., the amount of carbon absorbed by vegetation to perform photosynthesis, since it establishes the main carbon and energy inputs to ecosystems for producing food, wood, and fiber [1]. Approximately half of the GPP is respired by plants to provide the energy that supports their growth and maintenance. Net primary production (NPP) is the net carbon gain by vegetation and equals the difference between GPP and plant autotrophic respiration [2]. The role that Earth observation (EO) data play in quantifying carbon fluxes evolved substantially in the last two decades with the beginning of the operational Moderate Resolution Imaging Spectroradiometer (MODIS) GPP product from the National Aeronautics and Space Administration (NASA) Earth Observing System (EOS) program [3].
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