A dominant problem in ecology is that so much seems idiosyncratic and species-specific. Southwood (1977) likened ecology to a chemistry without the periodical table of the elements: "each fact had to be discovered by itself, and each fact remembered in isolation". Another metaphor would be personality-dimensions in psychology. Individual personalities can be positioned along axes such as prudent/quiet to expressive/enthusiastic, and reliable/controlled to restless/aggressive. Common opinion is that there may be about 5 major dimensions (Atkinson et al. 1990). These personality-dimensions summarize much that is known about human psychology. They also serve as covariates, helping to resolve variation in experiments that might otherwise be inexplicable.

Previous research has built towards a view that in plant ecology, at least 4 major strategy-dimensions of ecological variation among species can be identified (e.g. Westoby 1998; Weiher et al. 1999, summarizing an international workshop). Each reflects a continuum of economic or allocation "choices" by the species. Each has one or more species traits that serve as an indicator. These strategy-dimensions potentially will become as central in ecology as personality-dimensions are in psychology. Synoptic aims of this research are (1) to establish strong understanding of each individual strategy-dimension (by many specific hypothesis-tests about costs, benefits and correlations underpinning each dimension) and (2) eventually to move plant ecology to a new plane of consistency and consensus founded on these strategy dimensions.

Four dimensions are currently targeted:

1. The leaf mass per area – leaf lifespan (LMA-LL) dimension expresses slow turnover of plant parts (at high LMA and long LL), low palatability, long nutrient residence times and slow response to favorable growth conditions. Key aim is to test the proposition that the LL-LMA relationship is fundamentally mediated by leaf engineering strength. Further, that leaf nitrogen concentration has an important connection through its influence on the proportion of soft tissues.
2. The seed mass-seed output (SM-SO) dimension is an important predictor of dispersal to establishment opportunities (seed output), and of establishment success in face of hazards (seed mass). Key aim is to test the hypothesis that the upward shift in community median seed size towards the tropics is due to higher total seed biomass production of the community.
3. The leaf size-twig size (LS-TS) spectrum has conspicuous consequences for the texture of canopies, but costs and benefits of large vs small leaf and twig size are poorly understood. Key aim is to demonstrate and quantify the advantage of large leaves and twigs in terms of higher leaf mass fraction and reduced self-shading, and to understand the circumstances under which clades can evolve towards smaller leaf size in the face of this advantage.
4. The height dimension (canopy height when full-grown) has universally been included in ecological strategy schemes. But height strategy includes several different elements: pace of vertical height-gain versus lateral spread; the relative height within the canopy at which a species typically operates; and the time-span over which that height can be sustained in face of physical and biological degradation of stems. It remains unclear how strongly these different elements are aligned with each other across species. Key aim is to understand how mixtures of height strategies come to exist. While a "tall" strategy is highly competitive (since light comes from above), it is not so dominant as to occupy 100% of the ecological space available. It can be invaded by strategies that operate economically in the shade beneath, and also by strategies that grow rapidly in gaps before being overtopped by the "tall" strategy. Our question is how different types of invasibility relate, and what traits characterize them.

Rapid progress has become achievable now, through a combination of recent advances: (1) Describing dimensions by easily-measured traits (Westoby 1998), whereas previous conceptual schemes required species to be related by comparing performance or distribution in a landscape where they occur together (Grime 1979; MacArthur and Wilson 1967; Southwood 1977; Whitmore 1975). (2) The dimensions summarize essentials of plant economics, rather than being couched in terms of adaptive opportunities or environmental preferences. Theory can be applied of cost-benefit analysis, investment analysis including time-discounting, and game theory for the broad mixtures of strategies that coexist competitively. (3) Though the list of potential strategy-dimensions is open-ended, reasonable consensus has emerged about a working shortlist, along with substantial advances in published experimental and comparative-survey knowledge about them. (4) Databases that describe species traits are accumulating to critical mass.

General significance:- Major dimensions of plant ecological strategies can provide a strong, simple framework for organizing knowledge about plants and landscapes – they can be central to the next generation of ecology textbooks. They offer prospects for putting in order the thousands of few-species experiments on competition, herbivory and ecophysiology, where results are often divergent for reasons not yet understood. Dealing with fundamental transactions of dry matter and nitrogen, the strategy-dimensions provide information about major ecosystem processes as well as about species mixtures. For modelling vegetation dynamics under global change a worldwide system of plant functional types is needed. The latest models already use the LMA-LL dimension for categorizing species (Moorcroft et al. 2001).

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