Impact of climate change and extreme events on tree architecture: implications for forest decline and die-back
Bibliographic record
Abstract
Global climate models agree in predicting a warmer climate on most continental areas, with more frequent extreme events such as heat waves and repeated or exceptional droughts. By increasing drought stress, global warming is a direct threat to forest health and survival in all types of forest ecosystems around the world. Two physiological mechanisms can be involved, separately or simultaneously, in tree decline or mortality during these stressing events: hydraulic failure and carbon starvation. \nStudy goals: We present a study performed as an international effort to understand the influence of climate change and extreme events on the architectural development of forest trees, mainly conifers, in several countries. We discuss its potential contribution to forest decline and die-back. Fourteen conifers and one broadleaved species from Europe, USA and Canada were studied with the same protocol. In 47 sites as a whole, nearly 11000 twigs, from 2300 branches of 470 trees were sampled between 2005 and 2014, some of them repeatedly every year or few years. Branch and trunk length growth, architectural development (branching and polycyclism rates) and reproduction were retrospectively measured from morphological markers over a period of 10 to 45 years according to species. Needle or leaf number per growth unit, size and life span were measured on a subsample of twigs. Study sites include four experimental designs with climate manipulation in controlled conditions: rain exclusion, irrigation or heating and combinations of heat and drought on one of them. A phenological survey was performed on three of them to monitor monthly tree architectural development. Study sites cover conditions going from the limit of the desert to the tree line in mountains. We developed a generic architectural model for conifer trunks or branches, based on the relationships between climate and all measured parameters of tree architecture and needles. It aims at simulating the immediate consequences and after-effects of climate stresses on tree architecture and leaf area, for 10-year periods. \nIn both Europe and Northern America, repeated or extreme droughts, heat waves and other stresses considerably reduced tree and branch vigour for all species at all sites, leading to reduced branch length and tree height growth, low polycyclism and branching rates, shorter and narrower than normal needles or leaves, and small number of needles or leaves per growth unit. A strong reduction of the life span of leaves and needles for evergreen species was also measured. \nThus a significant leaf area deficit was observed and modelled during or just after but also several years after severe stresses. Two mechanisms explained the long lasting legacies of these stresses: (i) the slow recovery of the number of active twigs, due to the twig deficit induced by a low branching rate during and after the stress, limiting the number of leaves and needles, and (ii) the persistence, for many years on some species, of the cohorts of small leaves and needles formed in the bad years. The long lasting reduction of tree leaf area may contribute to carbon shortage and, in extreme cases, to delayed die-off by carbon starvation.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 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".