Recovery of woody but not herbaceous native flora 10 years post old‐field restoration

Abstract

1. Vegetation recovery in old fields towards mature reference states is often limited by abiotic and biotic thresholds resulting from agricultural land use legacies, as commonly highlighted using state and transition models. Old-field restoration may include interventions (e.g. planting of vegetation) to overcome these thresholds and assist transition between states. However, our understanding of the effectiveness of these interventions is limited.2. Using a point-intercept transect method, we surveyed nine sites, each comprising a triplet of fallow cropland, planted old field and woodland reference plots to reflect states of old-field restoration, from the degraded state to the reference state. We compared ground cover attributes, and richness and cover of woody and herbaceous flora species, using ANOVA and multivariate analyses.3. We found that a decade after planting, cover of leaf litter and woody debris in planted old fields were significantly higher than in the fallow croplands; however, woodland reference conditions were not achieved. Cover of logs was similar to the fallow cropland. Woody species cover and richness were similar in planted old fields and woodland reference plots, with planted old fields having more than 60% of the shrub species richness and cover, and similar tree species richness, to the woodland reference plot. 4. In contrast, whilst herbaceous species contributed more than half the plant species richness in reference woodland plots, there were significantly fewer herbaceous species in the planted old fields, which were more similar to the fallow croplands.Cover of exotic annual forbs in planted old fields was about half that of fallow cropland, and exotic annual grass cover was similar to the reference woodland. 5. Our results show that active restoration of old fields increased leaf litter, woody debris and cover and richness of trees and perennial shrubs. However, native herbaceous species richness, and to some extent cover, remained similar to the fallow cropland. To effect transitioning of the herbaceous layer to the woodland reference state, further intervention such as removal of exotics, followed by sowing or planting native herbaceous species, may be necessary.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

P is for persistence: Soil phosphorus remains elevated for more than a decade after old field restoration

“…Interrow spacing averaged 3 m and created sufficiently open areas in the planted old fields, comparable with the woodland reference sites (Appendix S1: Figure S1). Detailed vegetation cover and species data is presented in Parkhurst, Prober and Standish (2021).…”

“…The establishment of native trees and shrubs on nutrient enriched soils following agricultural use may initially reduce P and N availability. This may especially be the case below the tree canopy as growing plants take up available nutrients while nutrient input from leaf litter of young trees is low (Parkhurst, Prober and Standish 2021; Travers & Eldridge, 2012; Ward et al, 1991). Therefore, reestablishing native trees and shrubs could help to reduce N (e.g., Cole et al, 2018; Prober et al, 2005) and P (e.g., Xu et al, 2019) otherwise available to exotic species.…”

Abiotic and biotic responses to woody debris additions in restored old fields in a multi‐site Before‐After‐Control‐Impact experiment

“…In November 2017, one treatment plot at each site was uniformly covered with 13 kg of freshly mulched York gum branches including leaves, and a second treatment plot with three York gum logs (average length and circumference = 80.3 cm [1–121 cm] and 33.2 cm [13–62 cm]) (Figure 1). The mulch and log application rate mimics leaf litter and fine and coarse woody debris cover of the intact York gum woodland remnants as presented in Parkhurst, Prober, and Standish (2021). York gum mulch was sourced from roadside tree lopping of a local shire and the logs were cut to size from recently fallen York gum branches.…”

“…In addition, recovery may also be limited by time lags in the development and repair of fauna habitat and ecosystem functions (Isbell et al, 2019; Prober et al, 2014; Vesk et al, 2008). In particular, resources such as leaf litter, and fine and coarse woody debris in young restoration sites, are less abundant than in mature vegetation states (Manning et al, 2013; Parkhurst, Prober, & Standish, 2021). Yet, leaf litter and woody debris are vital components of the plant–soil feedback (Sayer, 2006) and provide essential resources and important habitat components to fauna (Gibb & Cunningham, 2013; Sandström et al, 2019; Sayer et al, 2006).…”

“…For soils, we focused on biogeophysical measures as those are key functional restoration barriers and are often understudied (Kollmann et al, 2016). For vegetation, the herbaceous layer is particularly vulnerable to degradation and weed invasion, yet supports about half of the diversity in these ecosystems (Parkhurst, Prober, & Standish, 2021), hence is a critical restoration focus. For fauna, we focused on ants because they are responsive to old field restoration interventions and may indicate impending recovery of other fauna (Parkhurst, Standish, Andersen, & Prober, 2021; Sandström et al, 2019).…”