Constraints on the Establishment of Plants Along a Fluctuating Water-Depth Gradient

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Moloney, Kirk
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van der Valk, Arnold
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The Botany Graduate Program offers work for the degrees Master of Science and Doctor of Philosophy with a graduate major in Botany, and minor work for students majoring in other departments or graduate programs. Within the Botany Graduate Major, one of the following areas of specialization may be designated: aquatic and wetland ecology, cytology, ecology, morphology, mycology, physiology and molecular biology, or systematics and evolution. Relevant graduate courses that may be counted toward completion of these degrees are offered by the Departments of EEOB and GDCB, and by other departments and programs. The specific requirements for each student’s course distribution and research activities are set by the Program of Study Committee established for each student individually, and must satisfy all requirements of the Graduate College (See Index). GRE (and if necessary, TOEFL) scores are required of all applicants; students are encouraged to contact faculty prior to application.
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We used simulation modeling to investigate the relative importance of current environmental conditions and factors affecting establishment of different plant species on the formation of vegetative zonation patterns. We compared the results from a series of six models that incorporated increasing amounts of information about key factors affecting species' ability to adjust to water-level fluctuations. We assessed model accuracy using aerial photographs taken of a 10-yr field experiment, in which 10 wetlands were flooded to 1 m above normal water level for 2 yr, drawn down for 1 or 2 yr, and reflooded for 5 yr to three different water levels (normal, +0.3 m, +0.6 m). We compared each model's ability to predict relative areal cover of five dominant emergent species and to recreate the spatial structure of the landscape as measured by mean area of monospecific stands of vegetation and the degree to which the species were intermixed.

The simplest model predicted post-treatment species distributions using logistic regressions based on initial species distributions along the water-depth gradient in the experimental wetlands. Subsequent models were based on germination, rhizomatous dispersal, and mortality functions implemented in each cell of a spatial grid. We tested the effect on model accuracy of incrementally adding data on five factors that can alter the composition and distribution of vegetative zones following a shift in environmental conditions: (1) spatial relationships between areas of suitable habitat (landscape geometry), (2) initial spatial distribution of adults, (3) the presence of ruderal species in the seed bank, (4) the distribution of seed densities in the seed bank, and (5) differential seedling survivorship.

Because replicated, long-term data are generally not available, the evaluation of these models represents the first experimental test, of which we are aware, of the ability of a cellular-automaton-type model to predict changes in plant species' distributions.

Establishment constraints, such as recruitment from the seed bank, were most important during low-water periods and immediately following a change in water depth. Subsequent to a drop in water level, the most detailed models made the most accurate predictions. The accuracy of all the models converged in 1–2 years after an increase in water level, indicating that current environmental conditions became more important under stable conditions than the effects of historical recruitment events.


This article is from Ecology 82 (2001): 2216, doi: 10.1890/0012-9658(2001)082[2216:COTEOP]2.0.CO;2. Posted with permission.

Mon Jan 01 00:00:00 UTC 2001