Abstract
The choice of revegetating via direct seeding or planting nursery-grown seedlings influences the potential stresses suffered by seedlings such as herbivory and drought. The outcome of the balance between both revegetation methods may ultimately depend on how species identity and traits such as seed and seedling size interact with environmental conditions. To test this, we will conduct a continental-scale experiment consisting of one mini-experiment replicated by multiple participants across Europe. Each participant will establish a site with seeded and planted individuals of one or more native, locally growing oak (Quercus) species; the selection of this genus aims to favour continental-scale participation and to allow testing the response of a widely distributed genus of broad ecological and economic relevance. At each site, participants will follow the present protocol for seed collection, seeding in the field, nursery cultivation, outplanting, protection against herbivores, site maintenance, and measurement of seedling performance and environmental variables. Each measurement on each species at each site will produce one effect size; the data will be analysed through mixed-effects meta-analysis. With this approach we will assess the main effect of revegetation method, species, plant functional traits, and the potential effect of site-specific effect moderators. Overall, we will provide a continental-scale estimate on the seeding vs. planting dilemma and analyse to what extent the differences in environmental conditions across sites, seed size, functional traits, and the phylogenetic relatedness of species can account for the differences in the effect of revegetation method on seedling performance across study sites and species.
Highlights
2 billion ha of land are in need of ecological restoration [1]
Restoring oak forests through direct seeding or planting: Protocol for a continental-scale experiment maintenance should begin in early 2022, when the seedlings are emerging from seeded acorns, and it must be conducted carefully to avoid damaging the oaks that are the target of the experiment
Bias results from comparing plots containing outplanted nursery seedlings with plots where direct seeding was conducted at the same time, and the plants are younger in the latter plots, and seeds do not come from the same batch
Summary
2 billion ha of land are in need of ecological restoration [1]. In recognition of the importance of restoration for climate mitigation and the provision of ecosystem services [2, 3], the UN Decade on Ecological Restoration provides an opportunity to advance the science and practice of restoration ecology [4]. Root morphology is affected by the choice of revegetation method, with potential implications for the access to soil resources of plant species that develop deep roots This is the case in oaks, as the tap root of nursery-grown seedlings is often pruned or deformed [6]. We outline the protocol for an experiment designed to address the seeding vs planting dilemma and identify the drivers of differences in effects at a continental scale It will be conducted at multiple sites across Eurasia encompassing large climate differences. The experiment will aim at: i) providing continental-scale evidence on the balance between seeding and planting for oaks, ii) testing whether this balance depends on species choice, and iii) assessing whether climatic conditions and soil characteristics interact with species traits to explain heterogeneity across sites. The study shall produce new knowledge for improving forest and agroforestry ecosystem restoration
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