Competing drivers lead to non-linear native–exotic relationships in endangered temperate grassy woodlands

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• 作者：Suzanne M. Prober ; Kevin R. Thiele ; Jane Speijers
• 关键词：Fire frequency ; Burning ; Exotic diversity ; Grasslands ; Mowing ; Native diversity ; Weeds
• 刊名：Biological Invasions
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：18
• 期：10
• 页码：3001-3014
• 全文大小：1,496 KB
• 刊物类别：Biomedical and Life Sciences
• 刊物主题：Life Sciences
  Plant Sciences
  Ecology
  Hydrobiology
  Zoology
  Forestry
  
• 出版者：Springer Netherlands
• ISSN：1573-1464
• 卷排序：18

文摘

Relationships between the diversity and abundance of native versus exotic species underpin management of disturbance regimes for conservation. Theory predicts negative, positive or neutral relationships depending on respective drivers, with greatest potential benefit when natives and exotics show opposing responses to management. We examined drivers of exotic plant cover and relationships with native plant richness using 12-year burning, mowing and grazing experiments in two representative temperate grassy eucalypt woodlands with contrasting histories of frequent versus infrequent disturbance. We hypothesized that disturbance and high resources favour exotics, and assessed whether natives and exotics covary positively due to common external drivers or negatively due to contrasting external drivers and/or competition. Positive relationships with rainfall and disturbance explained >80 % of the variation in exotic cover at both sites, supporting our first hypothesis. Native–exotic relationships were non-linear, with native richness first increasing rapidly with increasing exotic cover, then levelling and beginning to decrease. Common external drivers, particularly inter-annual rainfall, explained initial positive relationships, highlighting a prevalence of positive relationships at long temporal (as well as large spatial) scales. At the historically frequently-burnt site, a concomitant increase in native richness and exotic cover after fire contributed to the positive relationship, indicating a management trade-off. At the long-unburnt site, exotics increased but natives decreased with fire, suggesting dual benefits of low fire frequency. We conclude that relationships between exotic cover and native richness emerge from interactions among external drivers and competitive responses, with responses to external drivers dominating at low resources and negative interactions gaining importance as resources increase.