Artificial Top Soil Drought Hardly Affects Water Use of Picea abies and Larix decidua Saplings at the Treeline in the Austrian Alps

Wieser Wieser,Oberhuber Oberhuber,Hasibeder Hasibeder,Oberleitner Oberleitner,Gruber Gruber,Bahn Bahn

doi:10.3390/f10090777

Wieser Wieser, Oberhuber Oberhuber + Show 4 more

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https://doi.org/10.3390/f10090777

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Abstract

This study quantified the effect of shallow soil water availability on sap flow density (Qs) of 4.9 ± 1.5 m tall Picea abies and Larix decidua saplings at treeline in the Central Tyrolean Alps, Austria. We installed a transparent roof construction around three P. abies and three L. decidua saplings to prevent precipitation from reaching the soil surface without notably influencing the above ground microclimate. Three additional saplings from each species served as controls in the absence of any manipulation. Roofing significantly reduced soil water availability at a 5–10 cm soil depth, while soil temperature was not affected. Sap flow density (using Granier-type thermal dissipation probes) and environmental parameters were monitored throughout three growing seasons. In both species investigated, three years of rain exclusion did not considerably reduce Qs. The lack of a significant Qs-soil water content correlation in P. abies and L. decidua saplings indicates sufficient water supply, suggesting that whole plant water loss of saplings at treeline primarily depends on evaporative demand. Future work should test whether the observed drought resistance of saplings at the treeline also holds for adult trees.

Highlights

Concerns have been raised in regard to high altitude treelines [1,2], as they may undergo significant alterations due to climate change
As shown by the Central Austrian Alps [8], higher temperatures coupled with a decline in relative humidity and a considerable increase in evaporative demand may reduce the water supply of adult trees [9]
These findings suggest that, at treeline where vapor pressure deficit (VPD) is generally considerably lower than at low elevation sites [29,30,31,32], whole tree water loss primarily depends on evaporative demand [9,20,27,33,34]

Summary

Introduction

Concerns have been raised in regard to high altitude treelines (i.e., the ecotone between the upper limit of the closed continuous forest canopy and the treeless alpine zone above) [1,2], as they may undergo significant alterations due to climate change. Global change models predict a further increase by 1.4–5.8 ◦ C in upcoming decades and an increased occurrence of climate extremes, including more frequent and severe drought [6]. At the treeline in the Central Austrian Alps, the observed temperature increase was apparently most pronounced during spring and summer compared with autumn and winter [7]. As shown by the Central Austrian Alps [8], higher temperatures coupled with a decline in relative humidity and a considerable increase in evaporative demand may reduce the water supply of adult trees [9]. Drought effects on tree transpiration have been studied intensively in various climates

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