Physics Maths Engineering
Signs of frost drought in stem diameter variations
Peer Reviewed
Abstract
Frost drought refers to the chronic or acute desiccation of trees exposed to high evaporative pressures while being rooted in cold or frozen soils. This phenomenon has been known for more than a century but is still poorly characterized. Summer desiccation manifests itself as long-term stem contractions. Similar contractions have been reported in winter. In this study, we investigated the causes of total winter stem contraction (WSC) using 14 years of dendrometer data from evergreen (P.abies) and deciduous (L.decidua) mature trees growing along an elevational transect (from 800 to 2200 m asl) in the Swiss Alps. Results indicated that WSC varied between and and were strongly dependent on species, elevation, and tree height. Moreover, the magnitude of contractions was strongly associated with stem contractions subsequent to freeze–thaw events ( F). We suggest that both F and WSC are the consequences of water losses due to ice blockage associated frost drought, occurring when the distal parts of the tree are thawed and transpiring, while the larger basal parts remain frozen, thus inhibiting water uptake and creating a hydraulic imbalance.
Key Questions and Answers
1. What is frost drought?
Frost drought refers to tree desiccation caused by high evaporative pressures while trees are rooted in frozen soils. It leads to water imbalance, especially when ice blocks water uptake in tree roots during freeze–thaw cycles.
2. How does winter stem contraction (WSC) relate to frost drought?
WSC is closely linked with freeze–thaw cycles, where contractions occur due to water losses. Both WSC and freeze–thaw contractions are driven by ice blockage, inhibiting water uptake and creating hydraulic imbalance.
3. What factors influence the magnitude of WSC?
The magnitude of WSC depends on species, elevation, and tree height. Additionally, it is strongly associated with freeze–thaw events that cause significant stem contractions.
4. How does frost drought affect trees at higher elevations?
At higher elevations, frost drought is more common due to high evaporative forces, such as wind and solar radiation, while trees are still rooted in frozen soils, making them vulnerable to water loss.
5. What is the ecological significance of frost drought?
Frost drought is debated in terms of its ecological importance, with some believing it contributes to tree line establishment, while others suggest mature trees may have enough reserves to mitigate its effects.
