Combining in-situ monitoring and remote sensing to detect spatial patterns of volcanic sulphur impact on pine needles

Volcanic eruptions have a strong environmental impact on surrounding forests. Trees are affected by mechanical damage, tephra deposition and volcanic gases. Oceanic islands are shaped by relatively frequent volcanic eruptions and thus offer the opportunity to study the effect of volcanic activity on biodiversity. We investigate the impact of volcanic gas emissions and tephra deposition during the 2021 Tajogaite eruption on the Canary Pine forests of the island of La Palma, Spain, characterized by monospecific stands of the endemic pine species Pinus canariensis C. Sm. ex D.C. Large quantities of volcanic sulphur dioxide caused chlorotic damage up to approximately 7 km around the crater, followed by widespread resprouting of P. canariensis. To detect the spatial pattern of impacts, we sampled P. canariensis needles from all over the island of La Palma and analyzed their sulphur (S), nitrogen (N) and carbon (C) content. We found a strong increase of S needle content close to the crater, while C decreased significantly. S levels were strongly related to distance to the crater, C and N were mostly influenced by S content. Trees affected by volcanic gases allocate resources to resprouting, leading to lower levels of C due to translocation of C as a building block. Surprisingly, we found higher N levels in needles with high levels of S and a less clear pattern compared to C, likely due to a multitude of environmental factors influencing N needle levels. We investigated how canopy damage patterns detected in Sentinel-2 remote sensing imagery after the eruption correlated to the in-situ needle contents. However, we did not find a clear correlation between in-situ needle values and spectral responses in remote sensing. While satellite images were well suited to analyse large scale patterns of canopy damage following the eruption, needle levels varied strongly on a local, tree-based level, which is not reflected in remote sensing imagery.

Automated summary

Volcanic eruptions have significant environmental impacts on surrounding forests, including mechanical damage, volcanic gas emissions, and tephra deposition. The 2021 Tajogaite eruption on the island of La Palma, Spain, caused chlorotic damage to Canary Pine forests due to high levels of volcanic sulphur dioxide. However, the affected trees exhibited widespread resprouting. Needle samples of Pinus canariensis taken from different locations on the island showed a strong increase in sulphur content near the eruption site, while carbon content decreased significantly. The impact of volcanic gases on trees led to resource allocation for resprouting, resulting in lower carbon levels. Surprisingly, we found higher nitrogen levels in needles with high sulphur content, indicating complex environmental factors influencing nitrogen levels. Remote sensing imagery was effective in analyzing large-scale canopy damage, but variations in needle levels at a local and tree-based level were not reflected.