Direct assessment of competitive ability and defoliation tolerance in perennial grasses
Bibliographic record
Abstract
Stipa clarazii is a dominant, late-seral perennial grass species under exclosure or lightly grazed rangelands in semiarid Argentina, whereas S. tenuis and S. ambigua are earlier-seral perennial tussock grasses. Recent studies have demonstrated that late-seral species are more competitive and can have either similar or greater herbivory tolerance than earlier-seral species. We hyphothesized that (1) tolerance to defoliation is greater on defoliated plants of S. clarazii than on those of S. tenuis and S. ambigua, (2) competitive ability is greater in S. clarazii than in S. tenuis and S. ambigua when plants remain undefoliated or are exposed to a comparable defoliation intensity, and (3) competitive ability decreases in S. clarazii when this species is selectively defoliated within a non-defoliated, nearby neighbourhood of S. tenuis or S. ambigua. The study objectives included obtaining a direct measure of competitive ability and defoliation tolerance in the three perennial grasses when they grew either in isolation or in different neighbourhoods and were exposed to various defoliation patterns in the field. In 1998, two parallel studies were conducted within a 2-yr-old field exclosure during one growing season. In one study, responses were evaluated on either defoliated or undefoliated plants of all three species without neighbours. In a second experiment, four types of neighborhoods were selected such that a central (target) plant of one species was surrounded by five neighboring plants of a different species. Three different defoliation patterns were imposed on each neighbourhood type. Results led to acceptance of the first and second and rejection of the third hypothesis. When plants grew without nearby neighbours, greater growth rates for height, dry matter production and end-of-season daughter tiller production per parent tiller in S. clarazii relative to S. tenuis and S. ambigua contributed to greater regrowth in S. clarazii. Amounts of 15N atom excess were always greater in S. clarazii than in S. tenuis and S. ambigua independently of neighbourhood type and pattern of defoliation. However, uptake of 15N was similar in S. clarazii to that in S. tenuis or S. ambigua when S. clarazii was selectively defoliated within a non-defoliated, nearby neighbourhood of any of the other two species. Selective herbivory of S. clarazii, rather than factors associated with its competitive ability and defoliation tolerance, were found to be the major determinant driving its replacement by earlier-seral, less desirable perennial grasses in rangelands of central Argentina. Key words: 15N, Argentina rangelands, biomass, nitrogen uptake, species replacement, Stipa
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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".