Nutrient enrichment diminishes plant diversity and density, and alters long-term ecological trajectories, in a biodiverse forest restoration

Canary in the coal mine: Lessons from the Jarrah Forest suggest long-term negative effects of phosphorus fertilizer on biodiverse restoration after surface mining

“…While over the longer term, self-sustaining and biodiverse Jarrah Forest ecosystems have been successfully restored (Koch and Hobbs, 2007) there can also be negative impacts on soil biogeochemistry and species composition. Further, any initial growth benefits of applying P -but not the legacy -disappear over time (Spain et al, 2018;Daws et al, 2019aDaws et al, , 2021a. In short, increased initial growth does not mean improved long-term outcomes, not least by upsetting the balance of competitive interactions between species.…”

“…In regions with weathered nutrient-deficient soils a significant proportion of species can have specialised adaptations for nutrient acquisition, such as cluster roots and exudation of carboxylates (e.g., Lambers et al, 2008), and/or have conservative growth rates (Daws et al, 2021a). These traits likely contribute to the sensitivity of restored ecosystems in these nutrient-deficient environments to applied-P.…”

“…A single initial fertilizer application to bauxite mining restoration in the Jarrah Forest can elevate available (bicarbonate extractable) soil P concentrations for more than 20 years (Banning et al, 2008;Daws et al, 2021a) suggesting that applying P at the onset of restoration, may have long-term ongoing impacts on vegetation responses. In addition, at Gove bauxite mine, Spain et al (2018) demonstrated that labile-P and long-term P concentrations in near-surface soils increase over a 26-year period following an initial P-application suggesting fertilizer-induced alterations to geochemical processes and nutrient-cycling.…”

“…Fertilizer addition can benefit weeds in restored systems (Daws et al, 2021a;Holmes, 2001). P can also preferentially benefit species such as N 2 -fixing legumes (e.g., Acacia spp.).…”

“…Therefore, any potential growth benefit of applying N is short-term while P may be available over the longer term. A vigorous growth response of weeds and/or legumes can result in other species being outcompeted leading to reduced understorey diversity (Daws et al, 2015(Daws et al, , 2019a(Daws et al, , 2021a. These reductions in species richness can be significant.…”