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Keywords:

  • anthropogenic disturbance;
  • conservation value;
  • deterministic vs. stochastic succession;
  • Floristic Quality Assessment;
  • Floristic Quality Index;
  • invasion impacts;
  • Mean C;
  • remnant flora;
  • restoration monitoring;
  • successional trajectory

Summary

1. Simple, conservation-relevant, plant community measures are sought by resource managers. In this context, the use of Floristic Quality Assessment (FQA) has increased exponentially over the past 30 years. FQA measures a habitat’s Floristic Quality and conservation value by summarizing the relative anthropogenic disturbance tolerances of its plant species (i.e. their Conservatism). However, despite their widespread use in research, restoration and conservation work, the behaviour of FQA values in communities during succession is not understood.

2. We analysed FQA values in 10 old fields over 50 years of unaltered succession. We determined whether Floristic Quality followed a predictable increasing successional trend, assessing four specific predictions: (i) FQA values will follow an asymptotically increasing, rather than peaked or linearly increasing trajectory; (ii) field initiation treatments (abandoned as hayfield or cropfield) will not lead to long-term differences in FQA values; (iii) trajectories will be consistent regardless of the particular species composition of fields and (iv) trajectories will be robust to common variations in FQA metric formulations (non-native species, varied spatial scale).

3. In all cases, a negative exponential rise to an asymptote best described FQA value trajectories over time. Field abandonment treatments did not affect FQA value trajectories. Furthermore, trends were consistent among fields despite differences in species composition among fields. Overall, the results suggest a predictable, deterministic path for FQA values over the early- to mid-successional timeframes studied.

4.Synthesis and applications. Understanding the temporal behaviour(s) of Floristic Quality is necessary for setting realistic restoration goals, evaluating habitat recovery and adapting management to achieve high conservation value natural areas. By illustrating the temporal consistency of Floristic Quality metrics during succession, this article demonstrates the robustness of FQA for such uses. The FQA value trajectory described here also establishes a background trend model for expected values in recovering habitats, which will allow for the assessment of an individual habitat’s progression relative to the background trend. Such comparisons en masse will highlight the constraints of greatest importance to community-level Floristic Quality restoration. For example, FQA values in this study were ultimately limited by Conservative understorey plant re-establishment from adjacent old-growth forest. As this is not unlike species recovery patterns observed in other habitats, it suggests that restoration practitioners would do well to focus on Conservative species.