Assessing Forest Vulnerability to Climate Change Combining Remote Sensing and Tree-Ring Data: Issues, Needs and Avenues

Abstract

Forests around the world are facing climate change. Increased drought stress and severe heat waves in recent decades have negatively impacted on forest health, making them more vulnerable and prone to dieback and mortality phenomena. Although the term vulnerability is used to indicate an increased susceptibility of forests to climate change with a worsening of their vigour status that can compromise their ability to respond to further climate extreme events, there are still uncertainties on how to evaluate it. Indeed, evaluation of forest vulnerability is complex both because of some critical issues in the estimation methods used and because of the multiple factors influencing the response of forests to ongoing climate change. A way to assess the vulnerability to environmental stresses is by combining remote sensing and dendroecological data. However, these two approaches entail multiple uncertainties, including growth/photosynthetic relationships, carbon allocation dynamics, biases of tree-ring data and noisy remote sensing data, which require further clarification for proper monitoring of pre- and post-drought forest trajectories. Our review aims to create an overview of the current literature and knowledge to understand the critical issues, needs and possible solutions that forest vulnerability research is addressing. We focus on Mediterranean forests located in a climate warming hotspot and showing a high vulnerability to increased aridification.

Cutting the Greenness Index into 12 Monthly Slices: How Intra-Annual NDVI Dynamics Help Decipher Drought Responses in Mixed Forest Tree Species

“…Tree vigor is usually reported using qualitative visual criteria in the upper canopy (e.g., current percentage of crown transparency or defoliation; see [9]), conferring an inherent bias to the subjectivity of the assessors, as well as their partial perspective of the canopy. However, it is important to note that remote sensing through NDVI per se does not account for tree vigor as such but instead presents reflectance rates that should not be considered as true photosynthetic rates.…”

“…However, these complex ecological mechanisms represent a research challenge given the multifactorial nature of the drivers underlying the forest response to the interconnectedness of biotic and abiotic factors [9]. For example, in response to drought stress, the tree limits its nutrient supply, with a reduction in radial growth [10], defoliation, and Remote Sens.…”

“…2024, 16, 389 2 of 20 crown decline [11]. In other words, although the phenomenon is multifactorial, climatic adversity can be manifested in symptoms of reduced radial growth and modification of photosynthetic activity with implications for the dynamics of carbon allocation [9].…”

“…However, certain inconsistencies or divergences, such as foliage production over growth ring increase, still require clarification [18,19]. Thus, the combination of dendrochronological data and drones offers a promising alternative for refining our understanding of tree growth in the face of climatic variation and is now clearly positioned as a research strategy on the research agenda [9,20].…”

How Are Pine Species Responding to Soil Drought and Climate Change in the Iberian Peninsula?

“…The Mediterranean region and especially the Iberian Peninsula have been identified as prominent hotspots of unprecedented climate change due to limited water availability [11]. As a result of rapidly progressing environmental changes associated with episodic droughts and heat waves, this region is expected to become hotter and drier, leading to more intense and prolonged droughts and thus a decrease in water available for plants [12][13][14].…”