Data from: The importance of forest structure to biodiversity-productivity relationships

While various relationships between productivity and biodiversity are
found in forests, the processes underlying these relationships remain
unclear and theory struggles to coherently explain them. In this work, we
analyse diversity–productivity relationships through an examination of
forest structure (described by basal area and tree height heterogeneity).
We use a new modelling approach, called ‘forest factory’, which generates
various forest stands and calculates their annual productivity
(above-ground wood increment). Analysing approximately 300 000 forest
stands, we find that mean forest productivity does not increase with
species diversity. Instead forest structure emerges as the key variable.
Similar patterns can be observed by analysing 5054 forest plots of the
German National Forest Inventory. Furthermore, we group the forest stands
into nine forest structure classes, in which we find increasing,
decreasing, invariant and even bell-shaped relationships between
productivity and diversity. In addition, we introduce a new index, called
optimal species distribution, which describes the ratio of realized to the
maximal possible productivity (by shuffling species identities). The
optimal species distribution and forest structure indices explain the
obtained productivity values quite well (R2 between 0.7 and 0.95), whereby
the influence of these attributes varies within the nine forest structure
classes.