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Organized Oral Session

Session: : Examining Species Interactions with Long-term Tree Plots

OOS 30-2 - Phylogenetic and spectral similarity predict redundancy in biodiversity-ecosystem function relationships in two long-term forest diversity experiments

Tuesday, August 8, 2023
3:45 PM – 4:00 PM PDT
Location: 257
Relationships have long been demonstrated between biodiversity and ecosystem function, particularly productivity. At local scales, these relationships can emerge from species interactions and niche partitioning. The extent to which phylogenetic diversity predicts productivity better than species is an issue of continued controversy. Most biodiversity-ecosystem function experiments have not been designed to use phylogenetic information and tend to exclude phylogenetically similar species. Due to the expected non-linear relationship between traits and phylogenetic distance, ecological dissimilarity necessary for niche partitioning is not expected to increase linearly with phylogenetic distance. Consequently, near phylogenetic distances should be more important than far distances in predicting functional similarity, and close relatives are likely to be ecologically similar along axes of variation relevant to niche partitioning, and overyielding at local spatial scales. Spectral similarity based on reflectance spectra across solar electromagnetic radiation (400 – 2500 nm), both at the leaf and canopy scale, is frequently closely associated with phylogenetic similarity and is increasingly recognized as an important measure of phenotypic and functional similarity.

Here we test these theoretical predictions over ten years of growth in two tree diversity experiments that explicitly incorporate close relatives—the Forest and Biodiversity experiment at Cedar Creek Ecosystem Science Reserve and the Cloquet tree diversity experiment at the Cloquet Forestry Center, both in Minnesota and both part of the International Diversity Experiment Network with Trees (IDENT). We hypothesize that closely related species are more ecologically redundant and less likely in mixtures to enhance ecosystem function than more distant relatives. We further hypothesize that close relatives are more spectrally similar and show lower complementarity. We find that plots with high phylogenetic similarity (congeners) and high leaf and crown spectral similarity show less overyielding (net biodiversity effects) than plots with the same number of species but higher phylogenetic diversity (non-congeners) or spectral diversity. Close relatives show lower net biodiversity effects than more distant relatives, and the differences in these effects between plots with close and distant relatives increases consistently over time. Spectral similarity, both at the leaf and canopy level, is strongly associated with phylogenetic similarity, and also predicts net biodiversity effects. In short, congeners behave much like monocultures in having similar spectral signatures, reduced complementarity effects and lower net biodiversity effects than diverse tree mixtures.