TY - UNPB

T1 - Quantifying Tree Mortality Drivers - a Case Study in a Boreal Forest

AU - Jääskeläinen, Johanna

AU - Junttila, Samuli

AU - O’Sullivan, Hannah

AU - Cheng, Yan

AU - Horion, Stéphanie

AU - Vastaranta, Mikko

PY - 2023

Y1 - 2023

N2 - Increased tree mortality rates have been observed worldwide in connection to climate warming-related processes such as drought, heat, fire, and pest insect outbreaks. Understanding the drivers of tree mortality during the Anthropocene is urgently needed to estimate forest vulnerability in a warmer and hotter climate. In this study, we assessed tree mortality drivers for a recreational boreal forest area of approximately 830 ha, where increased tree mortality rates have been recently observed. A time series of aerial images was used to quantify tree mortality over the area to detect dead trees from 2005 to 2021 at seven timestamps. Altogether 6,008 dead trees were observed from the aerial images collected during the monitoring period. Forest environmental and climatic variables were used to explore tree mortality drivers for individual trees and tree communities using logistic regression and correlation analysis. Our results showed that drought-related variables, i.e., vapour pressure deficit and Palmer drought severity index, and increased temperatures correlated with rising tree mortality rates. We found that the stand-level basal area predicted tree mortality risk and was linked to site type; a decreasing basal area stands were located on rocky dry soils and resulted in a higher probability of tree mortality. We also detected that trees growing at high elevations or on steep slopes showed a higher mortality risk.

AB - Increased tree mortality rates have been observed worldwide in connection to climate warming-related processes such as drought, heat, fire, and pest insect outbreaks. Understanding the drivers of tree mortality during the Anthropocene is urgently needed to estimate forest vulnerability in a warmer and hotter climate. In this study, we assessed tree mortality drivers for a recreational boreal forest area of approximately 830 ha, where increased tree mortality rates have been recently observed. A time series of aerial images was used to quantify tree mortality over the area to detect dead trees from 2005 to 2021 at seven timestamps. Altogether 6,008 dead trees were observed from the aerial images collected during the monitoring period. Forest environmental and climatic variables were used to explore tree mortality drivers for individual trees and tree communities using logistic regression and correlation analysis. Our results showed that drought-related variables, i.e., vapour pressure deficit and Palmer drought severity index, and increased temperatures correlated with rising tree mortality rates. We found that the stand-level basal area predicted tree mortality risk and was linked to site type; a decreasing basal area stands were located on rocky dry soils and resulted in a higher probability of tree mortality. We also detected that trees growing at high elevations or on steep slopes showed a higher mortality risk.

KW - forest damage

KW - drought

KW - tree mortality risk

KW - dead trees

KW - time-series

KW - VPD

U2 - 10.2139/ssrn.4624979

DO - 10.2139/ssrn.4624979

M3 - Preprint

BT - Quantifying Tree Mortality Drivers - a Case Study in a Boreal Forest

PB - SSRN: Social Science Research Network

ER -