Insights from Roots to Stems: Comparative Wood Anatomy and Dendroclimatic Investigation of Two Salix Species in Iceland

This study investigates the anatomical characteristics and growth patterns of Salix arctica and Salix herbacea, two prevalent dwarf shrub species in Iceland, to understand their responses to environmental changes. We employed optical and scanning electron microscopy methods and quantitative wood anatomy to analyze the stem and root structures of studied species. Additionally, we developed chronologies and assessed the climatic response of both the stem and root parts for both species. Our results reveal significant differences between the two species, with S. arctica exhibiting larger vessels and fibers compared to S. herbacea, both in stem and root. The growth trends differ between the species: S. arctica shows an overall increase, while S. herbacea exhibits a consistent decline. Both species’ individual parts generally follow these trends, though a recent decline has been observed in the last few years. Climatic responses also differ, highlighting specific climatic parameters influencing each species. S. arctica responds positively to warmer temperatures, while S. herbacea reacts positively to increased precipitation but struggles with rising temperatures, highlighting its role as a drought indicator species. Soil erosion driven by volcanic materials and extreme climates significantly impacts shrub growth, causing rapid changes in growth ring widths and vessel sizes. Understanding these impacts is vital for improving sampling methods in polar environments. This study highlights the importance of integrated wood anatomical studies in comprehending the ecological consequences of climate change on Arctic shrubs, providing new insights into the complexity of shrub expansion both below and above ground.