Do diverse overstoreys induce diverse understoreys? Lessons learnt from an experimental-observational platform in Finland

TitleDo diverse overstoreys induce diverse understoreys? Lessons learnt from an experimental-observational platform in Finland
Publication TypeJournal Article
Year of Publication2014
AuthorsAmpoorter E., Baeten L., Koricheva J., Vanhellemont M., Verheyen K.
JournalForest Ecology and Management
Volume318
Start Page206
Pagination215
KeywordsAlpha diversity, Beta diversity, FunDivEUROPE, Tree species identity effect, Tree species richness effect, Understorey dynamics
TagsFunDivEUROPE, Alpha diversity, Beta diversity, Tree species identity effect, Tree species richness effect, Understorey dynamics
Abstract

The understorey fulfils many important
ecosystem services, such as mediation of carbon dynamics, provision of
habitats, and it contains most of the plant diversity in forest ecosystems. Changes
in the overstorey diversity may affect understorey diversity as trees have a
species-specific impact on resource availability and soil conditions that
influence the understorey. In an attempt to disentangle the
overstorey-understorey diversity relations, we combined the strengths of an
experimental and observational approach in the boreal vegetation zone in
Finland.

The Satakunta tree diversity
experiment was planted in 1999 using a pool of five tree species and four
species richness levels (1, 2, 3, 5 species per plot) (only the first three levels
were analysed in this study). Each level was replicated with different species
composition to avoid complete dilution, which allows the separation of identity
and diversity effects. Understorey surveys were performed in three subplots per
plot in 2003 (young phase) and 2011 (established phase). In the full-grown forest surrounding Joensuu, a
similar design was used in an observational plot-based study with three tree
species richness levels (1, 2, 3 species per plot), containing trees from a
pool of three species. The understorey was surveyed in 2012, also in three
subplots per plot. We unravelled the relations between (1) tree species
richness and (2) understorey composition, diversity, compositional
dissimilarity within and between plots and temporal turnover, and searched for tree
species identity effects.

Tree species richness had a
significant influence on the understorey composition in the established phase
of the experiment. In contrast with the expectations, plot-level understorey
diversity showed no significant differences between the tree species richness
levels, neither at the experiment nor at the full-grown forest. At the
established phase of the experiment, interplot compositional dissimilarity was significantly
higher for monocultures than for mixtures. Monocultures have distinct
influences on resources and soil conditions, leading to larger differences with
other plots, while mixtures often share the same tree species or species with
similar environmental impact. Tree species identity effects were present in
monocultures but were predominantly tempered in mixed stands due to stronger
dilution.

Neither research
approach found a clear relation between tree species richness and understorey
diversity. The presence of tree species identity effects may partially have
skewed the diversity relations. However, results on interplot compositional
dissimilarity indicated that creating mixtures using a chessboard pattern of
monocultures may positively influence understorey diversity at the forest level.

DOI10.1016/j.foreco.2014.01.030

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