A thirst for snowmelt? Tree water use in spring
Bibliographic record
Abstract
Describing the water sources for tree transpiration and how sources vary in time and space is fundamental to understand how vegetation impacts the hydrological cycle. While many tree water source partitioning studies have focused on the growing season, little is known about transpiration sources before, during, and after snowmelt when trees rehydrate and recommence to transpire in spring. Here we investigate spring snowmelt and the onset of tree rehydration and transpiration in two sites within the boreal forest of Saskatchewan, Canada. Specifically, we investigate the source of transpiration during the first days and weeks after transpiration onset relative to snowmelt timing. We document the source of transpiration of three boreal forest tree species— jack pine (Pinus banksiana), black spruce (Picea mariana), and larch (Larix laricina)—by combining observations of weekly stable isotope values of xylem, soil water, rainfall, and snowmelt with physical measurements of soil moisture dynamics, snow depth and high-temporal resolution measurements of tree stem radius and sap flow. We show that the onset of rehydration and transpiration overlaps snowmelt and that trees use snowmelt water during stem rehydration and the onset of transpiration. Soil water showed a rapid shift to isotopically depleted-snowmelt water values during the end of the snowmelt period. But our data showed a delay in the shift in xylem isotope signatures from pre-melt to the clear snowmelt-depleted water signatures that dominate thereafter. This appears to be controlled by tree water transit time that was in the order of 9 to 18 days. Our study shows that snowmelt is an important source for stem rehydration and the onset of transpiration in the boreal forest during spring onset. Our data also highlights the importance of monitoring phenological and physiological responses during tree water source investigations. In a warmer world, the timing of snowmelt and vegetation phenology are likely to continue to change, as well as the decline in water availability via snowmelt in northern ecosystems. Therefore, understanding tree water use dynamics during spring onset is important to identify the impact of climate change on the evolution of forest composition and groundwater recharge.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".