Inter and intra-annual links between climate, tree growth and NDVI: improving the resolution of drought proxies in conifer forests

Marín Pompa-García,Marcos González-Cásares,J Julio Camarero,Michele Colangelo

doi:10.1007/s00484-021-02170-5

Abstract

The inter- and intra-annual variability in radial growth reflects responses to climatic variability and water shortage, especially in areas subjected to seasonal drought. However, it is unknown how this variability is related to forest productivity, which can be assessed by measuring changes in canopy greenness and cover through remote sensing products as the Normalized Difference Vegetation Index (NDVI). We combine xylogenesis with measurements of inter-annual changes in seasonal wood production (earlywood width, adjusted latewood width) and NDVI to improve the understanding of climate and drought impacts on growth and forest productivity in a Pinus teocote stand located in northern Mexico. Cambial dynamics accelerated in March and a high production of radially enlarging and thickening tracheids were observed from April to October and from June to October, respectively. Tracheid maturation was very active in October when latewood production peaked. Wet conditions in winter-spring and summer-autumn enhanced earlywood and latewood production, respectively. Earlywood and latewood were constrained by long (4–10 months) and short (2–3 months) droughts, respectively. The earlywood production depended on April soil moisture, which agrees with the peak of radially enlarging tracheid production found during that month. Aligning drought proxies at inter- and intra-annual scales by using growth and productivity measures improves our understanding of conifer forest responses to water shortage.

Highlights

The world’s forests are the largest carbon reservoir in terrestrial ecosystems, which affect global carbon fluxes and climate change mitigation (Pan et al 2011)
The number of thickening tracheids peaked from June to December (DOY 160–356), whereas the rates of production of earlywood and latewood mature tracheids peaked from mid to late October (DOY 286–299) increasing afterwards and reaching maximum values in winter
Despite that we hypothesized latewood to be a more robust proxy of intra-annual changes in water shortage as compared with Normalized Difference Vegetation Index (NDVI), we found that earlywood showed the strongest responses to changes in precipitation and estimated soil moisture

Summary

Introduction

The world’s forests are the largest carbon reservoir in terrestrial ecosystems, which affect global carbon fluxes and climate change mitigation (Pan et al 2011). The carbon sink of forests subjected to seasonal drought depends on annual and seasonal variability in precipitation showing the outstanding role of soil moisture as driver of radial growth and carbon uptake (Humphrey et al 2018). To complement the understanding of the dynamics of radial growth in response to drought, a better temporal resolution of tree-ring proxies is required (Timofeeva et al 2017). The measurement of earlywood and latewood widths is often used to study seasonal growth responses to climate and drought (e.g., Griffin et al 2011, 2013; CabralAlemán et al 2017; Camarero et al 2020).

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