The role of fire in the mid-Holocene arrival and expansion of lodgepole pine ( <i>Pinus contorta</i> var. <i>latifolia</i> Engelm. ex S. Watson) in Yukon, Canada
Bibliographic record
Abstract
In north-west Canada, Pinus contorta (lodgepole pine) has been migrating northwards and westwards for millennia. Its regeneration is currently enhanced by fire, which may act as a trigger for local population expansion. Using Holocene charcoal records from four small (<10 ha) lakes in southern Yukon, we investigated the relationship between long-term Pinus population dynamics and fire. Fossil stomata extracted from dated lake sediments indicate pine was present at low densities in southern Yukon forests by ~6000 cal. yr BP. At each site, the main population expansion (indicated by an increase in Pinus pollen from <5% to values as high as 60%) occurred 2000–>4000 years after the first local appearance of Pinus, suggesting a long period of stasis at low densities. Population increases – based on pollen accumulation rates (PARs) – occurred at different times at the four sites. Estimated expansion periods were ~2500–800 years, and population doubling times were ~150–600 years, similar to previous estimates. Estimated fire return intervals (FRIs) fluctuated over time. At all sites, the Pinus expansion began during a phase with a relatively short FRI, but only one difference between the mean FRIs before and during the Pinus rise was statistically distinguishable. Nor was the subsequent higher abundance of pine associated with shorter FRIs. It is unlikely that regional pine expansion is primarily linked to changes in climate or a climate-mediated fire regime, although expansion may have been triggered at individual sites during a period of high fire frequency. The long period of stasis at low population densities suggests intrinsic control of population growth; possibly Pinus expansion was initially constrained by lowered reproductive fitness (Allee effect) and/or interaction with local site-based factors.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".