Do the rich get richer? Varying effects of tree species identity and diversity on the richness of understory taxa

Abstract

length: 236 words 2Number of references: 54 3 Tables and Figures: 3 figures and 1 table 4 5 Supplementary material: 6Appendix S1-5: 3 supplementary tables and 2 supplementary figures 7 5 ABSTRACT 1 Understory herbs and soil invertebrates play key roles in soil formation and nutrient cycling 2 in forests. Studies suggest that diversity in the canopy and in the understory are positively 3 associated, but they often confound the effects of tree diversity with those of tree species 4 identity and abiotic conditions. We combined extensive field sampling with structural 5 equation modeling to evaluate the simultaneous effects of tree diversity on the species 6 diversity of understory herbs, beetles, and earthworms. The diversity of earthworms and 7 saproxylic beetles was directly and positively associated with tree diversity, presumably 8 because species of both these taxa specialize on certain species of trees. Tree identity also 9 strongly affected diversity in the understory, especially for herbs, likely as a result of 10 interspecific differences in canopy light transmittance or litter decomposition rates. Our 11 results suggest that changes in forest management will disproportionately affect certain 12 understory taxa. For instance, changing canopy diversity will affect the diversity of 13 earthworms and saproxylic beetles more than changes in tree species composition, whereas 14 the converse would be expected for understory herbs and detritivorous beetles. We conclude 15 that the effects of tree diversity on understory taxa can vary from positive to neutral and may 16 affect biogeochemical cycling in temperate forests. We recommend to maintain high tree 17 diversity, thereby promoting the diversity of multiple understory taxa, and to reduce the 18 abundance of tree species that may reduce understory diversity. 19 20 21

Specialisation and diversity of multiple trophic groups are promoted by different forest features

“…These modifications directly affect the amount, type and heterogeneity of resources or microhabitats, as well as abiotic conditions, all of which can strongly affect forest communities (Duguid & Ashton ; Chamagne et al . ; Zellweger et al . ; see detail in Table ).…”

“…To promote timber production, forest managers modify several features, such as tree species composition, stand age and density, or deadwood amounts (Bengtsson et al 2000;Seidl et al 2011;Schall & Ammer 2013). These modifications directly affect the amount, type and heterogeneity of resources or microhabitats, as well as abiotic conditions, all of which can strongly affect forest communities (Duguid & Ashton 2013;Chamagne et al 2016;Zellweger et al 2016; see detail in Table 1). The effects of some forest features on particular taxa are starting to be understood (Table 1), however, a clear link with management is still lacking (but see Schall et al 2018) and the mechanisms behind many of these effects are unclear.…”

Forest diversity promotes individual tree growth in central European forest stands

“…We therefore take a broader view in investigating the general costs and benefits of increased forest diversity (Chamagne ; Chamagne et al . ) focusing here on above‐ground net biomass production (tree growth rates).…”

“…Nevertheless, where there is a conservation motivation to increase levels of diversity, some decrease in productivity may be an acceptable trade-off. We therefore take a broader view in investigating the general costs and benefits of increased forest diversity (Chamagne 2014;Chamagne et al 2016) focusing here on above-ground net biomass production (tree growth rates).…”

Community reorganization in forest understories buried by volcanic tephra

“…, Chamagne et al. ). In contrast to the tree canopy, analysis of relationships among understory strata produced little sign of interference: Only three of 30 significant relationships among growth forms and widespread species were negative and those three disappeared after year 2.…”