Vegetation structure influences the retention of airfall tephra in a sub-Arctic landscape

Abstract

1Vegetation cover mediates a number of important geomorphological processes. 2 However, the effect of different vegetation types on the retention of fine aeolian 3 sediment is poorly understood. We investigated this phenomenon, using the retention 4 of fine, pyroclastic material (tephra) from the 2011 eruption of the Grímsvötn volcano, 5Iceland, as a case study. We set out to quantify structural variation in different 6 vegetation types and to relate structural metrics to the thickness of recently deposited 7 volcanic ash layers in the sedimentary section. We utilised a combination of vegetation 8and soil surveys, along with photogrammetric analysis of vegetation structure. We 9 found that indices of plant community composition were a poor proxy for vegetation 10 structure and were largely unrelated to tephra thickness. However, structural metrics, 11 derived from photogrammetric analysis, were clearly related to variations in tephra 12 layer thickness at a landscape scale and tephra layers under shrub patches were 13 significantly thicker than those outside the shrub canopy. We therefore concluded that 14 a) vegetation cover was a critical factor in the retention of fine aeolian sediment for 15 deposit depths up to few centimetres and b) structural variation in vegetation cover 16 played a major role in determining the configuration of tephra deposits in the 17 sedimentary section. These findings have implications for the analysis of ancient 18 volcanic eruptions and archaeological/palaeoenvironmental reconstructions based on 19

Impact of small-scale vegetation structure on tephra layer preservation

“…As both sites received a similar initial tephra deposit and only differed in terms of vegetation cover, this result suggested enhanced tephra retention within woodland. This finding supports the conclusions of Cutler et al 1. who also found correlations between vegetation structure and tephra thickness at a landscape scale.…”

“…Based on the data in this paper and the findings of Cutler et al 1,. we propose the following conceptual model of small-scale tephra-vegetation interactions in temperate, humid climates.…”

“…This metric is not as sensitive to outliers (e.g. slim, individual stems) as maximum vegetation height, and provides a robust indicator of vegetation structure1. By dividing each image into seven 5 cm sections, we were able to calculate vegetation height at intervals which corresponded to the tephra measurements (Fig.…”

“…Variations in tephra layer thickness reflect both volcanic processes and post-depositional changes that take place as tephra are stabilised and incorporated into the sedimentary section. Recent work has suggested that vegetation cover at the site of deposition may influence the morphology of thin, terrestrial tephra layers on a landscape scale1 (smaller-scale relationships remain largely unexplored). If vegetation structure does influence preservation, then some tephra layers could, in principle, be used to infer characteristics of the surface environment contemporaneous with the eruption.…”

“…Recent research has demonstrated that vegetation structure can influence mean tephra layer thickness on a landscape scale111. Given that most land surfaces have some sort of vegetation cover, a greater understanding of the interaction between plants and tephra deposits would have global utility in the interpretation of tephra layers and their origins.…”