Selecting plant species and traits for phytometer experiments. The case of peatland restoration

摘要

Phytometers are indicator transplants that provide information on site conditions based on plant survival, growth and reproduction. Since this is a relatively new approach, standards for its implementation remain to be defined, for example, during peatland restoration. Peatland restoration frequently aims at recovering characteristic communities, and a key attribute of successfully restored ecosystems is their capacity to sustain viable populations of target species. When not actively introduced, these species are expected to establish on their own after improving site conditions, for example by rewetting. Assessments to determine whether this goal is met require the long-term monitoring of species' presence, whereas the underlying causes of these observations, i.e. site or dispersal limitation, often remain unknown. Using phytometers within ecological restoration helps addressing this question. The goal of this study is to compare the responses of several species and traits to environmental conditions in restored peatlands. Three target species (Drosera rotundifolia, Eriophorum vaginatum, Vaccinium oxycoccos) were planted in restored montane peatlands in central Germany, while in a greenhouse experiment, the same species were grown on peat from the field sites and exposed to two water levels. Several plant traits were measured and compared with variation in light, water and soil conditions. The response to habitat conditions was species-specific, indicating that the use of different phytometers increases the reliability of monitoring. Survival and growth traits were suitable to assess a wide range of abiotic conditions, while differences in reproductive output were more time-consuming to measure. Survival provided the most conclusive results for species sensitive to stressful habitat conditions. Biomass and other size metrics of the phytometers, as well as growth and reproductive traits were partly redundant. Thus, we suggest recording survival and biomass and use non-destructive growth measurements for repeated assessments, while the choice of the most suitable size trait should depend on the growth form. Our study stresses the potential of phytometers for monitoring the restoration outcome, while highlighting the importance of species and trait selection.