Abstract
Success of invasive non-native plant species management is usually measured as changes in the abundance of the invasive plant species or native plant species following invader management, but more complex trophic responses to invader removal are often ignored or assumed. Moreover, the effects of invader removal at different stages of the invasion process is rarely evaluated, despite a growing recognition that invader impacts are density or stage-dependent. Therefore, the effectiveness of invasive species management for restoring community structure and function across trophic levels remains poorly understood. We determined how soil nematode diversity and community composition respond to removal of the globally invasive tree species Pinus contorta at different stages of invasion by reanalysing and expanding an earlier study including uninvaded vegetation (seedlings removed continuously), early invader removal (saplings removed), late removal (trees removed), and no removal (invaded). These treatments allowed us to evaluate the stage-dependent belowground trophic responses to biological invasion and removal. We found that invaded plots had half the nematode taxa richness compared to uninvaded plots, and that tree invasion altered the overall composition of the nematode community. Differences in nematode community composition between uninvaded nematode communities and those under the tree removal strategy tended to dilute higher up the food chain, whereas the composition of uninvaded vs. sapling removal strategies did not differ significantly. Conversely, the composition of invaded compared to uninvaded nematode communities differed across all trophic levels, altering the community structure and function. Specifically, invaded communities were structurally simplified compared to uninvaded communities, and had a higher proportion of short life cycle nematodes, characteristic of disturbed environments. We demonstrate that a shift in management strategies for a globally invasive tree species from removing trees to earlier removal of saplings is needed for maintaining the composition and structure of soil nematode communities to resemble uninvaded conditions.
Highlights
Invasive species management programs are widely pursued to prevent or mitigate the impacts that invaders have on native communities (e.g., [1,2])
We demonstrate that a shift in management strategies for a globally invasive tree species from removing trees to earlier removal of saplings is needed for maintaining the composition and structure of soil nematode communities to resemble uninvaded conditions
sigma maturity index (SMI) and structure index (SI) were lower in no-removal plots compared to seedling, sapling- and tree-removal plots (Fig 2A and 2C; SMI: F = 22.359, P < 0.001; SI: F = 21.222, P < 0.001), but no differences were observed for enrichment index (EI) (F = 1.166, P = 0.347; Fig 2B)
Summary
Invasive species management programs are widely pursued to prevent or mitigate the impacts that invaders have on native communities (e.g., [1,2]) Despite these efforts, many invasive plant eradication programs either fail to meet their stated management goals or do not rigorously evaluate success (e.g., [3,4,5]). Many invasive plant eradication programs either fail to meet their stated management goals or do not rigorously evaluate success (e.g., [3,4,5]) Those plant invasive removal programs that do measure effectiveness typically focus on responses of the targeted invasive plant species to management per se [6], even though assessing the recovery of ecosystems should represent an important part of the evaluation of success, as it is usually an implicit goal of management (e.g., [7]). Invader impacts are usually measured in terms of effects on species numbers [15,19], more holistic approaches, like the use of ordination techniques, can help to capture community-level effects by quantifying shifts in the composition of species assemblages [20,21]
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