Tree species control wetland food webs

Posted on July 25, 2012

Although several studies have shown that variations in tree leaf litter can influence the composition of stream communities, almost no work of this kind has been done in a wetland context.  Researchers in Pennsylvania simulated wetland ecosystems by inoculating 60 water-filled plastic pools with nutrients, leaf litter, periphyton, phytoplankton and tree frog tadpoles.  There were 15 experimental treatments, which differed in terms of the type of leaf litter used.  Twelve common North American tree species (including willow, oak, beech, chestnut, sycamore, maple, pine and spruce) were represented and three treatments were based on mixtures of species.  Data on pool water quality and biota were collected over a three-week period and showed that the various types of leaf litter had very different effects, reflecting the wide variability in chemical composition even among species in the same tree family.  For example, zooplankton abundance was exceptionally high with black willow (Salix nigra) litter, which has a high nitrogen content, but very low with aspen (Populus grandidentata) litter.  On average,  periphyton production was higher with conifer than broadleaf monocultures.   While treatment comparisons showed that different litter species generally had an additive effect in combination, some species mixtures had antagonistic effects on periphyton and amphibian body mass, possibly as a result of the preferential colonization of favoured litter species by microbes.   It seems that wetland food webs are strongly dependent on the species and types of trees in the surrounding forests.

Reference:  Aaron B. Stoler and Rick A. Relyea 2011.  Living in the litter: the influence of tree leaf litter on wetland communities.  Oikos 120, 862–872.