Does anybody have any information about hygrophilous plants behavior linked with the amount of light available? I'd like to know if most of plants in wetlands are not shade tolerant. I'm searching for articles about this subject. Thanks.
This key review discusses light limitation in context of other factors. Given that nutrients are often abundant in wetlands, light limitation can become an issue for those plants that are not tall-growing, unlike many of their wetland counterparts.
http://www.sciencedirect.com/science/article/pii/S1433831904700475
Interesting question --in gramineacous wetlands, light would not be a limiting factor, except for really small plants (say < 10 cm in height) growing amidst thickets of rushes/sedges/reeds, or for submerged aquatic vegetation. In forested wetlands, like cypress stands, light limitation could affect a larger fraction of the plant community. Yet, low-light adapted plants are not very common in wetlands, as compared to say rainforests ( i may be wrong here).
I think flood-tolerance is another important factor that can limit certain species. While most wetland plants have various adaptations to anoxic environments in order to survive, changes in hydroperiod, water column depth and flow can push a plant to the limits of its tolerance range and affect growth. Species in a community differ in their flood-tolerances.
Traditionally, wetlands display some of the highest levels of primary productivity among all ecosystems. Seems to suggest they are well adapted to existing light levels.
I wouldn't generalize wetland plants as shade-intolerant vs. shade tolerant--it depends on the landscape setting, and, as Eric Struyf suggests above, nutrient levels. I agree as well that flood tolerance, or perhaps tolerance to flashy hydrology, may be more important in ordering plant communities in wetlands. Again, it depends on the context. Coastal tidal systems, whether they are graminaceous or shrubby, seem to be adapted to high levels of light. Yet there are plenty of forested systems in the continental US and in subtropical Puerto Rico, that are rich with shade-tolerant understories. Here in the Pacific Northwest, where old growth systems still occur, you will find plenty of plants in wetland pockets in these systems, where shade is the norm. The wetland trees in those systems aren't as long lived, but they do just fine in shade. You will often see species with small sizes in other systems (like ombrotrophic bogs or montane systems) which tend to ensure that you don't get the canopy structure that would promote shade-tolerant wetland species. The point is that wetland communities, like other communities, have a lot of other things ordering plant composition. There are a lot of examples of shade-tolerance in wetland communities, so generalizing that they are all high light adapted probably isn't warranted.
Thank you for your answers. My question is coming from a field survey. I've noticed that under poplar stands, some hygrophilous plants are more common than under other alluvial forest stands (alder, ash, oaks) with the same site conditions (soil, groundwater level...). The main difference between stands is light at ground level (poplar stands are more luminous than other stands). I gathered L (light) and F (moisture) Ellenberg’s indicator values for more than 5.000 french species to build a contingency table (excluding F10, F11 and F12 that are values given to aquatic plants). The correspondence analysis (linked to this message) gives interesting results: the first axis is obviously a light axis. High values for light (L8 and L9) seem to be linked to dry soils plants (F1, F2, F3 and F4) but also to wet-site indicators (F8 and F9). That is why I am looking for advices and bibliographic references to back me up.
Hi Sylvain,
I think Mary’s answer above is still the most helpful to your question. Wetland plants will cover a full range of light/shade tolerances. There are also studies looking at the importance of sunflecks (size and duration) which I would expect you might have a higher occurrence under Populus spp. than the others. There is variation even within genera of different species ability to utilise small brief sunflecks. Shade tolerant species are better able to use diffuse light and/or capitalise on brief sunflecks.
In the CA are you able to define groups that correspond to some or all of the canopy tree species?
This depends on what type of wetland, for instance, marsh, fen, bog swamp forest. Hakan Rydin and I have listed some of the plants that are light demanding and shade tolerant. The shade tolerant ones are found beneath well-canopied thicket swamps or forested swamps. Ours was completely a subjective rating. see Rydin and Jeglum. 2013. The biology of peatlands, 2nd ed. Oxford U. Press.
One more thought on this. Two negative effects (among many) associated with the invasive variety of Phragmites australis in brackish marshes along the mid-Atlantic region is the loss of shallow inter-tidal banks along creeks (they often become vertical) and the shading of the marsh surface by the dense canopy. Both effects reduce the primary productivity of benthic microalgae thought be important components of the marsh food web.
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