Nucleation in temperate woodland regeneration: Dual mycorrhizal willows
facilitate ectomycorrhizal tree establishment
Abstract
There is an urgent need for woodland expansion to help mitigate climate
change and biodiversity loss. However, the process of natural
regeneration of forest ecosystems is often slow, requiring active
reforestation approaches. Factors limiting regeneration are complex, but
there is increasing evidence that natural expansion of woodlands onto
sites that have been treeless for a long period of time may be limited
by the loss of microbial woodland-soil properties. This study explored
the potential role of mycorrhizal associations in facilitating obligate
ectomycorrhizal (ECM) tree establishment. We determined the spatial
distribution patterns of ECM tree seedlings – Pinus sylvestris and
Betula spp. - outwith the existing woodlands, in relation to established
dual-mycorrhizal Salix. There was very strong evidence that ECM tree
seedlings were more likely to be found growing within groups around
dual-mycorrhizal Salix than as isolated individuals, supporting the view
that Salix drives the current spatial distribution patterns by
supporting tree establishment. We suggest that the ability of Salix to
form dual-mycorrhizal associations with both arbuscular (AM) and ECM
fungi allows these plants to become established across the open AM
dominated vegetation. Over time these plants can become colonised by ECM
fungi via aerial spores and then act as a source of inoculum for
obligate ECM tree seedlings, which land as seeds in the vicinity of
Salix. This study highlights the potential role of dual-mycorrhizal
Salix as a nurse plant in supporting secondary forest succession of
obligate ECM boreal/temperate woodland species onto adjacent open areas
through nucleation. Overall, we concluded that there is potential for
existing ECM networks to aid tree establishment and propose a
nature-based approach to maximize reforestation efforts by targeting
existing symbiotic fungal networks as nucleation points for tree
planting. Our findings contribute to understanding the ecological
dynamics involved in woodland expansion and restoration.