Why has restoring old fields been a challenge for practitioners for decades? In their latest research, Tina Parkhurst, Suzanne Prober and Rachel Standish explore the efficacy of intervention efforts to understand limitations in current practices.
Globally, there is a trend towards widespread abandonment of marginal agricultural land. Land abandonment is often associated with land degradation following long-term unsustainable agricultural practices, resulting in low productivity. Whilst land abandonment can provide opportunities for ecological restoration, it is not without challenges.
Ecological restoration of old fields is often challenging due to extensive modification of soil properties and vegetation communities following cultivation. Consequently, old fields do not spontaneously recover – they may get ‘stuck’ due to land use legacies such as soil compaction, limited soil seed banks and fertiliser residues. Old fields can remain in a depauperate state, with little or no vegetation development.
Established agricultural weeds are also an issue as they can hinder the establishment of native species. Interventions such as direct seeding or planting of seedlings are often needed to overcome the legacies of agriculture and facilitate vegetation development.
In our recent study, we tested if we could ‘kickstart’ vegetation development on old fields in Western Australia by planting local native trees and shrubs. We compared the number of native plant species, their cover and composition in old fields planted with trees and shrubs, to those in the nearby reference ecosystem.
We found that a decade after planting of trees and shrubs on old fields, there was recovery of woody plant species but not herbaceous plant species.
Our reference study system, a semi-arid eucalypt woodland, plant species richness is made up approximately of 50% woody species and 50% herbaceous species (including wildflowers, everlastings, and native grasses). However, there were significantly fewer herbaceous species in the planted old fields making up only 25% of the woodland reference plant species richness.
Herbaceous species are important for supporting biodiversity and ecosystem functioning in restored old fields; they contribute more than half the plant species richness in herb-rich woodlands and provide habitat and food resources for wildlife. Therefore it is ecologically significant that these species were missing from the planted old fields in our study.
The lack of herbaceous species recovery can be attributed to several barriers, particularly in agricultural landscapes; elevated soil nutrient levels from fertilizer inputs, altered soil microbial and fungal composition, depleted soil seed banks, and competition with agricultural weeds are key potential barriers to establishment.
How can we rewild our old fields?
Active restoration of herbaceous vegetation has received little research and practical attention.
Whilst our study shows that woody vegetation establishment can be achieved to some extent by actively planting trees and shrubs, the establishment of herbaceous vegetation remains challenging. Currently we have no established methods available to undo the legacies of agriculture and re-establish wildflowers and other herbaceous species, so they can persist long-term in restored old fields.
Restoration practitioners and researchers need to explore how best to overcome the barriers posed by agricultural legacies to facilitate establishment and persistence of native herbaceous species. This will likely require a range of approaches such as the reduction of elevated soil nutrients, control of the highly competitive agricultural weeds, investigation of the role of soil microbes, as well as the facilitation of herbaceous plant establishment and persistence through direct seeding or planting.
Read the full research: “Recovery of woody but not herbaceous native flora 10 years post old-field restoration” in Issue 2:3 of Ecological Solutions and Evidence.
Discover more articles from our cross-society, cross-journal Special Feature on the UN Decade on Ecosystem Restoration“