Mismatch between Annual Tree-Ring Width Growth and NDVI Index in Norway Spruce Stands of Central Europe

Presently, the forests of one of the most economically important tree species in Europe-Norway spruce [Picea abies (L.) Karst.]-have been disrupted and are in rapid decline due to a combination of several natural factors: extreme drought, heatwaves, and secondary damage caused by bark beetle outbreaks. The vulnerability of these forests has increased considerably over the past decade, and remote sensing methods can theoretically improve the identification of endangered forest stands. The main objective was to determine the relationship between remotely sensed characteristics of vegetation (using the normalized difference vegetation index-NDVI) and annual tree-ring growth in 180 trees through precipitation and air temperature. The research was conducted at six research plots in lowland spruce forests (319-425 m a.s.l.) in the central Czech Republic. No significant correlation between NDVI and annual ring width was observed. The primary factor limiting radial growth was lack of precipitation in the growing season; subsequently, spruce trees reacted negatively to air temperatures. A higher correlation with NDVI was observed on sites susceptible to drought, but overall, NDVI and RWI did not show similarities. This result describes that NDVI is a poor indicator for identifying low radial growth in Norway spruce stands on non-native localities in the studied area.

Automated summary

The forests of Norway spruce in Europe, one of the most economically important tree species, are facing disruption and rapid decline due to natural factors such as drought, heatwaves, and bark beetle outbreaks. This study conducted in the central Czech Republic aimed to determine the relationship between remotely sensed characteristics of vegetation (using NDVI) and annual tree-ring growth. However, no significant correlation between NDVI and annual ring width was observed.