March 17, 2020
One of the aims of the Winning Against Wildings research programme is to better understand how ecosystems are affected by wilding trees. We want to know how different impacts change with the density of infestations, and we also want to know if once we remove wildings, how will ecosystems respond.
In this blog post, we’ll be diving into the soil and how it is affected by wildings. Soil functions underpin (literally!) the functions of aboveground ecosystems. In fact, soil is like an ecosystem in itself, with nutrient cycling, organisms, and food webs. Today, we’ll focus on one of the stars of the soil food web: nematodes.
Nematodes are a diverse group of roundworms; some are parasitic (for example, hookworms are nematodes) but today we’ll be focusing on nematodes which live in the soil. Many of them are too small to see, but they play an important role in the functioning of soil. They regulate fungi and bacteria food webs, and they can be thought of as indicators of the soil ecosystem and its processes. The communities of nematodes (i.e., which nematode species are present in the soil) can indicate whether the soil has been disturbed or not.
Dr Guadalupe Peralta at Manaaki Whenua - Landcare Research and collaborators have been studying nematodes and how they are affected by wilding conifers. She has found that when comparing an uninvaded area to an invaded area, the nematode communities in the invaded area were simpler, meaning that they had fewer species of nematodes than the communities in uninvaded areas. The invaded nematode communities also had a higher proportion of short life-cycle nematodes. Because nematodes regulate soil food webs, this change in nematode communities causes the nutrient cycling processes in soil to change. This in turn affects the aboveground ecosystem, by favouring certain plants over others which can thrive in faster nutrient cycle environments (often exotic grasses).
If we remove wilding conifers from an area, will nematode communities return to how they were before? Does it matter when we remove the wildings (i.e., if we are removing saplings vs established adults)?
Dr Peralta has also examined the effects of removing wildings at different infestation stages (mid, late) on nematode communities. She found that only for early invasion stages (when saplings were removed), did the nematode communities resemble an uninvaded state.
These findings show that early management is key to avoid effects on soil ecosystems. If early management cannot be achieved, soil functioning (e.g., nutrient cycles) will be altered and therefore it will be hard to restore the ecosystem to its uninvaded state. If wilding trees are removed late in the invasion process and restoration is the goal, introducing nematode species which were lost in the invasion could help restore the ecosystem functioning to its previous state.
What all this means to me is that wildings can have a large effect on ecosystems, above and belowground. Early management of wildings can reduce the negative impacts or at least make the restoration process quicker and smoother.
Peralta G, Schon NL, Dickie IA, St John MG, Orwin KH, Yeates GW, and Peltzer DA. (2019). Contrasting responses of soil nematode communities to native and non-native woody plant expansion. Oecologia, 190: 891-899. https://doi.org/10.1007/s00442-019-04456-3
Peralta G, Dickie IA, Yeates GW, and Peltzer DA. (2020). Community- and trophic-level responses of soil nematodes to removal of a non-native tree at different stages of invasion. PLoS ONE 15(1): e0227130. https://doi.org/10.1371/journal.pone/0227130.