A functional trait approach to fen restoration analysis

Abstract

Questions Ecological restoration has traditionally been evaluated with analyses focused on species identities and abundances. These analyses provide no ecological explanation to why certain species change in abundance. One solution may be a functional trait analysis. We asked whether shifts in functional traits could explain vegetation changes in fens restored through tree cutting and rewetting, and how the functional traits in the restored sites compare to those of the reference site? Location Three former rich fens in east‐central Sweden. Methods Tree cutting and rewetting were applied in a factorial design, and species and abundance data were recorded for 8 yrs. Abundance data and trait data of canopy height, specific leaf area (SLA) and diaspore mass were used to calculate functional richness (FRic), functional divergence (FDiv), functional dispersion (FDis) and community‐weighted mean (CWM) of functional traits. Data were analysed in a linear mixed effect model for vascular plants and bryophytes jointly, and for vascular plants separately. Results of restoration treatments were compared to data from a reference site. Results Among vascular plants, tree cutting caused a decrease in SLA, as shade‐sensitive species increased. In accordance with the change in SLA, FDis increased. In the joint analysis, tree cutting led to increased FDis, FDiv and FRic, indicating reduced filtering caused by the removal of the shading canopy, which allowed shade‐sensitive species to establish. The comparison to the reference site shows that even after 8 yrs, the restoration treatments have higher trait diversity than the reference site, indicating that the restoration sites have a too relaxed trait filter compared to conditions in an undisturbed fen. Our interpretation is that this is primarily caused by insufficient rewetting (and increased nutrient availability) that allow species of both natural and degraded fen conditions to co‐exist, and which failed to suppress the regrowth of trees. Conclusions Analysis of functional diversity improves our understanding of the ecological mechanisms affecting restoration results, and allows comparison among regions and communities with different species composition.

The hierarchy of predictability in ecological restoration: are vegetation structure and functional diversity more predictable than community composition?

“…Analyses of trait‐based metrics can be more informative than community composition because they can provide functional explanations for why certain species change in abundance (Hedberg et al . ), and changes in composition are less deterministic than changes in functional traits (Helsen, Hermy & Honnay ). Trait‐based metrics may be more useful and flexible for restoration practitioners when setting goals and assessing responses because specific functional objectives can be met with a range of species assemblages (Brancalion & Holl ).…”

“…Two trait‐based metrics that describe distinct modes of trait distributions are easily evaluated in restoration projects: community‐weighted mean (CWM) trait values describe the central tendencies of functional traits in a community (Sandel, Corbin & Krupa ; Brancalion & Holl ), and functional diversity (FD) describes the variation of functional traits in a community (Laliberté & Legendre ; Hedberg et al . ). However, the location of each of these metrics in the hierarchy of predictability is unknown because two communities could have the same trait mean but different variances or the same trait variance but different means.…”

Photosynthetic traits of Sphagnum and feather moss species in undrained, drained and rewetted boreal spruce swamp forests

“…Functional trait analysis is a useful method for assessing the outcome of ecological restoration (Hedberg et al 2013), but the established traits, developed for vascular plants, do not reflect bryophyte ecology or performance (Rice et al 2008). Photosynthetic properties of mosses are directly linked to their evolutionary strategies.…”

Restoration of riparian vegetation: A global review of implementation and evaluation approaches in the international, peer-reviewed literature

“…We believe that an alternative to assessing processes that require intensive field surveys, such as seed dispersal and nutrient recycling, could be the use of functional traits, which are biological attributes of species that determine their capacity to establish and persist in a specific environment (Violle et al, 2007). They are increasingly used to elucidate mechanisms driving community assemblies (Mayfield et al, 2010) and have started to be incorporated into restoration success assessment such as in wetlands or forests (D'Astous et al, 2013;Hedberg et al, 2013;Bachand et al 2014). Very few articles in our review have included functional traits (e.g., 141 Appendix S1), and when done, functional and life-history traits were indirectly evaluated such as via the classification of species into a priori functional groups, such as in regard to species regeneration mode (e.g., article 22 Appendix S1) or species shade tolerance and Nfixing ability (e.g., article 34 Appendix S1).…”