FACTORS AFFECTING THE RECOVERY OF ORCHIDS IN A POST-MINING LANDSCAPE Margaret Thora Collins BSc. Honours (Science), MSc. (Science) This Thesis is presented for the degree of Doctor of Philosophy of The University of Western Australia School of Earth and Geographical Sciences Discipline of Soil Science 2007 Photograph on title page: Prasophyllum hians Rchb.f. in flower. Abstract Currently, Alcoa World Alumina Australia (Alcoa) mines and undertakes procedures to rehabilitate approximately 550 ha of jarrah forest each year at two open-cut bauxite mines in South-West Western Australia. Alcoa aims to establish a self-sustaining jarrah forest ecosystem that maintains the functions of the landscape prior to mining, including biodiversity, on areas that have been mined for bauxite. Indigenous terrestrial orchids form a significant proportion of the indigenous geophytic plant species that either fail to colonise rehabilitated areas or do so very slowly. Terrestrial orchids are considered to be particularly sensitive to competition from weeds and disturbance, which combined with the obligate nature of the orchid-mycorrhizal fungus association suggests that orchids would colonise rehabilitation areas only when both microhabitat sites and soil microflora have established. Occurrence of certain orchids may therefore be expected to be useful as indicators of ecosystem health, the success of vegetation establishment and the recovery of edaphic conditions suitable for orchid mycorrhizal fungi. Vegetation surveys were undertaken to compare orchid species richness and population size of a chrono-sequence of rehabilitation areas with adjacent unmined forest. Total orchid and clonal orchid population sizes of rehabilitation areas had returned to densities not significantly different to those of the adjacent unmined forest within five years of rehabilitation establishment. The total number of orchid species and clonal species richness had also returned to levels that were not significantly different to those of adjacent unmined forest within the same time frame. However, orchid populations in rehabilitation areas often contained large numbers of species identified as disturbance opportunists, which were absent from 25+ year old rehabilitation areas and undisturbed jarrah forest sites. Six orchid taxa were identified as recalcitrant species; Cryptostylis ovata R.Br., Cyrtostylis heugelii Endl. In Lehm., Eriochilus dilatatus Lindl., Prasophyllum parvifolia Lindl., Pyrochis nigricans (R.Br.) D.L.Jones and M.A.Clem. and Thelymitra crinita Lindl.. These taxa were either very rare (compared to unmined forest populations), or absent from rehabilitated areas. The role of orchid mycorrhizal fungi (OMF) in the recruitment of orchids in the rehabilitated landscape was investigated using a seed baiting technique in a subset of the rehabilitation survey areas. These consisted of single transects that were 1, 10 and 26 i years old (established in 2001, 1992 and 1976) and their adjacent unmined Jarrahforest. Fungal baits consisted of buried six chambered nylon mesh packets containing seed of the six jarrah forest orchid taxa; Caladenia flava R.Br. subsp. flava (C. flava), Disa bracteata Sw., Microtis media R.Br. subsp. media, Pterostylis recurva Benth., Pyrorchis nigricans and Thelymitra crinita. Germination of seed and development of protocorms to stage 4 (initiation of shoot primordia) was regarded as evidence of the presence of a particular orchid’s mycorrhizal fungus. Detection of orchid mycorrhizal fungi was infrequent, especially in the youngest rehabilitation site examined, where only mycorrhizal fungi associated with P. recurva were detected. Mycorrhizal fungi of the other orchid taxa were widespread but sparsely distributed in older rehabilitation and forest areas. Detection of mycorrhizal fungi varied between taxa and baiting sites for the two survey years (2002 and 2004). Caladenia flava and T. crinita mycorrhizal fungi were the most frequently detected. The presence of C. flava mycorrhizal fungi was correlated with high levels of leafy litter cover, and high maximum depth, and soil moisture at the vegetation type scale (50 x 5 m belt transects), as well as tree and litter cover at the microhabitat scale (1 m2 quadrats). The presence of T. crinita mycorrhizal fungi was positively correlated with soil moisture in rehabilitation areas and low shrub cover in forest. The frequency of detection of orchid mycorrhizal fungi in both rehabilitated sites (15 - 25% of baits) and unmined forest (15 - 50% of baits) tended to increase with rehabilitation age as vegetation recovered. The failure of some orchid taxa to reinvade rehabilitation areas is unlikely to be entirely due to absence of the appropriate mycorrhizal fungi. However, the infrequent detection of orchid mycorrhizal fungi suggests that they occur in isolated patches of soil, so the majority of dispersed orchid seeds are likely to perish especially in recently disturbed habitats. The ecological specificity of mycorrhizal associations of the three orchid taxa: Caladenia flava, Thelymitra crinita and Disa bracteata were determined. The disturbance opportunist D. bracteata appears to be promiscuous in its mycorrhizal associations, although the promiscuity is limited to fungi within the Tulasnallales. The two common sympatric orchids C. flava and T. crinita used fungi from different taxonomic groups as mycorrhizal fungi which suggests that they are not competing directly for the same nutrient resources. Several orchid plants contained more than one ii mycorrhizal fungus, and in two individual orchids the second endophyte was a fungus more commonly associated with an ericoid mycorrhiza or ectomycorrhiza. Phylogenetic analysis using ITS rDNA region sequences of orchid mycorrhizal fungi (OMF) isolated in this study were generally in agreement with previous studies: C. flava was associated with fungi from the Sebacinales; and T. crinita and D. bracteata were associated with fungi from the Tulasnellales. Evidence from this study indicates that with increasing age, the vegetation of rehabilitation areas develops structural and soil surface cover characteristics similar to that of unmined forest. Younger rehabilitation areas (between 1 and 15 years old) are very different to unmined forest in both vegetation structure and plant species assemblages, while the oldest rehabilitation areas examined (26 and 27 years old) were not significantly different to adjacent areas of unmined forest. It is evident that vegetation of the post-mining landscape is more homogeneous than that of unmined forest as there were fewer plant species and species assemblages present. Plant species assemblages of 1 to 15 year old rehabilitation areas were characterised by the presence of disturbance opportunist plant species. However, both the cover and species richness of these disturbance opportunist species had returned to unmined forest levels in rehabilitation areas over the chrono-sequence examined. The post-mining landscape appears to be developing a ‘new’ jarrah forest ecosystem that is structurally similar to unmined jarrah forest, but appears, floristically, less species rich and with fewer plant species assemblages. This lower species richness is in part due to the lower cover and species richness of tufted, rhizomatous and herbaceous species. Orchid taxa present in each vegetation assemblage were generally not exclusive to these assemblages, with the following broad exclusions: D. bracteata was found only in species assemblages associated with rehabilitation areas; and Eriochilus sp. and T. crinita were found only in species assemblages associated with unmined forest. No single orchid species appears to be an indicator of ecosystem recovery. However, the presence of populations of C. flava, P. sp. crinkled leaf (G.J.Keighery 13426) or P. recurva in combination with the absence of the disturbance opportunist orchid taxa D. bracteata and M. media appears to be a measure of the maturity of the rehabilitation vegetation. iii Orchid species richness and clonal orchid population size were correlated with changes in vegetation structure, but apart from the absence of orchids in 1 year old rehabilitation areas, these orchid population characteristics did not show any direct relationship with rehabilitation age or vegetation maturity. Only two orchid taxa appeared to have potential as indicators of vegetation characteristics: T. crinita as an indicator of undisturbed jarrah forest; and D. bracteata as an indicator of disturbed ecosystems. The results of this study suggest that most jarrah forest orchid taxa will readily colonise the post bauxite mining landscape, but that the unassisted colonisation by recalcitrant orchid taxa may be a prolonged process. It is recommended that field-based transplantation and/or seeding trials be undertaken with these recalcitrant taxa to determine if these procedures will enhance recruitment. The results of this work have applications not only in the management of post-mining landscapes but also in vegetation monitoring and conservation work in Western Australia and elsewhere. iv Table of Contents Abstract i Table of Contents v Acknowledgments viii Candidates Declaration ix Definitions and terminology used in this document x Orchid Nomenclature xiii Fungal Nomenclature xiii Plant Nomenclature xiii Papers arising from this thesis xiv INTRODUCTION 1 CHAPTER 1 LITERATURE REVIEW 5 Introduction 5 Jarrah forest 5 Bauxite Mining 7 Orchidaceae 9 Recovery of Orchids in Disturbed Habitats 12 Mycorrhizal Associations