Ecology of orchids in urban bushland reserves – can orchids be used as indicators of vegetation condition?

The loss of urban native vegetation is a global crisis particularly as cities continue to expand and populations grow. Native vegetation often remains as small isolated fragments embedded in the human matrix of urban development. These remnants become islands of biodiversity that experience varying degrees of degradation due to their high perimeter to area ratio. Habitat loss in the biodiversity hotspot of south west Western Australia is considered to be one of the major threats to native terrestrial orchids, and is in part responsible for the current listing of 35 species as critically endangered (Western Australian Government 2006). Diminishing habitats and fragmentation of populations by urban development raises questions as to the sustainability of remnant populations. However, despite the loss of habitat, orchids continue to persist in the urban environment although little is known in detail of their ecological response to such pressures. Orchids are a highly specialized group of plants, their pollination methods and mycorrhizal associations ensure complex interactions with their environment. Do these interactions provide a measurable way to assess the health of ecosystems? Six orchid species of varying pollination mechanisms, associated mycorrhiza and growth form are used in this study. Although the study species are common to the Swan Coastal Plain, many are congeners to much rarer species currently under threat of extinction. This study provides insights into orchid ecology by examining pollination rates, mycorrhizal relationships and field plant establishment. Measurement and quantification of ecological responses of orchids in reference to varying site condition variables aims to determine whether orchids can be successfully utilized as indicators of vegetation condition