Long-term nutrient imbalances linked to drought-triggered forest dieback.

Area of Science:

• Forest Ecology
• Tree Physiology
• Biogeochemistry

Background:

• Drought-induced forest dieback negatively impacts global productivity, tree survival, and carbon sequestration.
• The influence of chronic nutrient imbalances on drought-induced forest dieback remains poorly understood.

Purpose of the Study:

• To investigate the relationship between long-term nutrient imbalances and drought-induced dieback in European conifers.
• To identify potential early-warning indicators of forest dieback.

Main Methods:

• Analysis of wood anatomical traits (tree-ring width, wood density) and soil properties.
• Retrospective analysis of tree-ring chemical composition (1900-2010) using Micro X-ray fluorescence (μXRF) and ICP-OES.
• Comparison of declining (D) and non-declining (ND) silver fir (Abies alba) and Scots pine (Pinus sylvestris) trees.

Main Results:

• Declining trees exhibited reduced growth and higher wood density, indicating lower hydraulic conductivity.
• Elevated concentrations of manganese (Mn), potassium (K), and magnesium (Mg) were observed in declining trees over recent decades.
• Specific Mn ratios (Ca:Mn, Mn:Al, P:Mn) showed significant differences between declining and non-declining trees, suggesting impaired phosphorus (P) utilization.

Conclusions:

• Reduced hydraulic conductivity and nutrient imbalances, particularly involving Mn, contribute to drought-induced dieback.
• Manganese ratios in tree rings can serve as effective early-warning signals for impending forest dieback.