Insects, orchids and fire: the effects of fire on orchid pollinators in eucalypt woodlands of South Australia
Date
2017
Authors
Marquart, Anita Evelyn
Editors
Advisors
Facelli, Jose Maria
Austin, Andrew Donald
Faast, Renate
Austin, Andrew Donald
Faast, Renate
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Abstract
Populations of orchids are declining throughout Australia, mainly because of habitat
destruction and the effects of habitat fragmentation (Coates et al., 2002). In addition the
loss of pollinators due to fire events may have an important impact on orchid populations.
Given that orchids are frequently pollen limited they may be particularly sensitive and
responsive to changes in pollinator communities (Ashman et al. 2004; Burd 1994; Faast
et al. 2011). The loss of certain pollinators could have devastating consequences and lead
to decline or even extinction for those orchids that are specialists in their pollination
strategy and rely on a single species of insect pollinator. This study assessed the response
of three families of orchid pollinating insects and their habitat to prescribed burns and
wildfires in eucalypt woodlands in southern Australia. Insects and selected habitat
characteristics were surveyed over three years during spring at four different locations,
and before and after fire events using a “Before-After, Control-Impact” approach.
Fire induced changes of selected insect habitat characteristics including plant
composition, floral abundance and nesting resources were investigated. Both prescribed
burns and wildfires reduced floral abundance, altered the structure of vegetation and
increased the amount of bare ground. Unlike earlier studies (Carrington, 1999; Hubbert
et al., 2006), prescribed burning was shown to not reduce litter depth or the abundance of
logs and standing litter. An increase in logs after prescribed spring burning, due to limb
or tree mortality and fall was also documented. As expected, the impacts of a wildfire
were more severe, as it significantly decreased litter depth and the abundance of logs, due
to the high intensity of the wildfire resulting in destruction of more biomass.
Potential orchid pollinators were identified using DNA barcoding methods combined
with morphological identification. Results show that even just five month after a fire there
was no severe effect on the abundance of members of the three most common orchid
pollinator families (Apidae s.l., Syrphidae, Tiphiidae). Hoverflies (Syrphidae) were not
affected by the fire regimes, but abundance differed among the years of sampling. Native
bee (Apidea s.l.) abundance showed only a marginal decline in the second year after
prescribed burning. Some bee species, especially ground nesters, showed a positive
response to fire, which is most likely associated with fire induced habitat changes such
as the increased availability of bare ground. No effects of fire on the abundance of tiphiid wasps could be found. Thiphiid wasps are from great importance for some sexual
deceptive orchids, which rely on specific wasp species for pollination.
Although prescribed burning and wildfires affected insect habitat differently, pollinator
responses to both fire regimes did not differ. The fire-induced decline in floral resources
did not affect pollinator communities in the first year following fire, but the availability
of nesting sites seems to influence the responses of certain insect species. The results
suggest that pollination success of orchids in South Australia is unlikely to be negatively
impacted by both prescribed burns or wildfires, as orchid pollinators were still abundant
and diverse in fire prone habitats.
School/Discipline
School of Biological Sciences
Dissertation Note
Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Biological Sciences, 2018
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