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

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.

Amplifying effects of recurrent drought on the dynamics of tree growth and water use in a subalpine forest

“…In addition to our experiment on mature trees, we performed a drought experiment on saplings of L. decidua and P. abies growing in an open gap adjacent to our study site composed only of young trees, where precipitation was excluded during the same treatment periods. In contrast to what we found for mature trees, tree growth and the water use of saplings of both species was largely unaffected by the drought treatment (Wieser et al, 2019). This supports the notion that mature trees have a lower drought acclimation capacity than young and small trees (Fajardo et al, 2019; Olson et al, 2018).…”

Alpine and Polar Treelines in a Changing Environment

“…Oberhuber et al [11] analyzed the growth trends of conifers along environmental transects in the Central European Alps and explain the missing adequate growth response to climate warming, competition for resources in increasingly denser stands at subalpine sites, and by frost desiccation injuries of evergreen tree species at the Krummholz-limit. Wieser et al [12] investigated the effects of artificial topsoil drought on the water use of Picea abies and Larix decidua Mill. saplings at the treeline in the Austrian Alps.…”

Effects of Climate Change at Treeline: Lessons from Space-for-Time Studies, Manipulative Experiments, and Long-Term Observational Records in the Central Austrian Alps

“…However, experimental studies on the effects of top-soil drought indicated that three years of rain exclusion did not considerably reduce sap flow density of P. abies and L. decidua saplings at the treeline in the Stubai Valley. The lack of a significant sap flow-soil water content correlation in both tree species indicated sufficient water supply, suggesting that whole tree water loss of young trees at the treeline primarily depends on evaporative demand [40]. Furthermore, roots of the treeline-associated conifers are able to penetrate into rocky undergrounds, allowing for the utilization of water sources in deep and wet soil layers, as shown for L. decidua trees using hydrogen stable isotope analysis [107].…”

“…In-situ manipulative warming and rain shelter experiments are common methodologies for assessing the effects of rapid climate change [35]. They can be quite effective in simulating climate warming [36][37][38][39] and top soil drought [40,41] in high elevation forests. Compared to the space-for-time approach, such techniques provide an explicit control in simulating climate warming or artificial soil drought.…”