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- Title
Loss of a dominant nitrogen-fixing shrub in primary succession: consequences for plant and below-ground communities.
- Authors
St. John, Mark G.; Bellingham, Peter J.; Walker, Lawrence R.; Orwin, Kate H.; Bonner, Karen I.; Dickie, Ian A.; Morse, Chris W.; Yeates, Gregor W.; Wardle, David A.; Austin, Amy
- Abstract
1. Many ecosystems are gaining some species and losing others, leading to large shifts in community composition. Plants that support nitrogen ( N)-fixing symbionts (hereafter N-fixers) are major ecosystem drivers but human-induced environmental changes can lead to their loss; the impacts of this loss have seldom been studied. In New Zealand, the gain of some invasive herbivorous mammals leads to the loss of N-fixing shrubs that are pioneers during primary succession. 2. We studied primary successional surfaces caused by river floods and landslides in a remote valley in New Zealand's South Island. We set up and maintained a removal experiment over 10 years, with N-fixing Carmichaelia odorata (hereafter Carmichaelia) either left intact or removed to represent the effects that invasive herbivorous mammals could cause under high densities. 3. Above-ground effects of 10 years of Carmichaelia removal included a 7-fold reduction of woody plant biomass, but had no effect on the shorter non-woody vegetation. Foliar N concentrations of two woody species were also reduced. Carmichaelia removal reduced local or α-diversity but enhanced β-diversity of the remaining vegetation at the functional group but not the species level. 4. Below-ground effects of 10 years of Carmichaelia removal included large reductions in soil carbon ( C) and N levels, and biomass or abundance of several groups of soil biota occupying three consumer trophic levels as well as the root-, bacterial- and fungal-based energy channels. Invertebrate bacterial consumers were more adversely affected than were fungal consumers. Carmichaelia loss reduced α-diversity of some below-ground groups, while β-diversity was unresponsive or enhanced. 5. Synthesis. Our results reveal that loss of a single functionally distinct plant species, such as occurs through herbivore invasion, can cause substantial effects both above-ground and below-ground. This may affect the trajectory of the ecosystem over successional time, especially in primary seres that otherwise have very low soil carbon ( C) and nitrogen ( N) reservoirs. More generally, our results support the view that the simultaneous gains of some organisms (e.g. invasive herbivorous mammals) and resultant losses of others (e.g. palatable N-fixing plants) are a major element of human-induced global change that may be transforming many communities and ecosystems world-wide.
- Subjects
NEW Zealand; PLANT species; SHRUBS; PLANT communities; BIOTIC communities; NITROGEN; PLANT biomass
- Publication
Journal of Ecology, 2012, Vol 100, Issue 5, p1074
- ISSN
0022-0477
- Publication type
Article
- DOI
10.1111/j.1365-2745.2012.02000.x