Short-term responses of the understory to the removal of plant functional groups in the cold-temperate deciduous forest |
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Authors: | Alexandre Lenière Gilles Houle |
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Institution: | (1) Département de biologie, Université Laval, Québec, QC, Canada, G1V 0A6 |
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Abstract: | It is widely believed that functional diversity contributes to the stability of ecosystems. Indeed, greater redundancy among
species within functional groups and greater complementarity among functional groups within communities should increase the
resistance and resilience of ecosystems. In the present study, we tested for functional group complementarity by examining
how the loss of specific functional groups may alter the role that other groups play in ecosystem functions. We removed different
functional groups, one at a time, from the understory of three maple-dominated forests in southern Québec (Canada) and followed
the understory response over a 2-year period. The experimental design included a control and five removal treatments. Five
functional groups were defined: spring-flowering ephemeral species; spring-flowering persistent species; summer-flowering
species; fern species; and seedlings and juveniles of woody species. Richness, cover, soil pH and organic matter content were
determined after two years of removal. The results of our experiment revealed that richness was significantly lower than what
we expected when spring-flowering persistent species or seedlings and juveniles of woody species were removed, suggesting
not only direct but also indirect positive effects of both of these groups on understory richness (mostly through effects on summer-flowering species and fern
species). Removal of the seedlings and juveniles of woody species and, to a lesser extent, of spring-flowering persistent
species and of fern species lead to a decrease in the cover of summer-flowering species, implying a positive effect of the
former groups on the latter. The cover–richness relationship in the control and in each one of the five removal treatments
was positive and well fitted by a linear regression. Yet, the slope of the relationship differed among treatments, but not between the control and any one of the removal treatments (pair-wise comparisons). Our results suggest that the different functional
groups are complementary and that positive interactions predominate over negative ones. Contrary to common belief, understory
plants can respond quite rapidly to changes in community functional composition. Although we have not investigated the specific
mechanisms responsible for the short-term responses reported here, we suggest that complex intergroup interactions may favour
functional diversity and enhance ecosystem functions. |
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Keywords: | Cold-temperate deciduous forest Complementarity Cover-richness relationship Experimental removal Functional diversity Functional group Interdependence Understory |
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