The Potential of Restored Landfill Sites to Support Pollinating Insects

The Potential of Restored Landfill Sites to Support Pollinating Insects

The potential of restored landfill sites to support pollinating insects Submitted for the Degree of Doctor of Philosophy at the University of Northampton 2009 Sam Tarrant UNIVERSITY OF NORTHAMPTON /\V £ I f c bARY i D V V 1 ACC. No. 10*54-^ CLASS N O j)gSS C1657<(o TftQ Abstract Habitat restoration is an important tool in reducing the current decline in biodiversity. To determine the success of restoration, ecologists have previously focused on species richness or on the presence of rare species; little is known of species interactions. This study examines both the potential of restored landfill sites to support pollinating insects and how flower-insect interactions can be used in determining successful restoration. These are important attributes of ecosystem function. Standard belt transects were used to record flowering insect pollinated plants and flower-visiting insects on nine paired restored landfill and reference nature sites, in the broader Northamptonshire region (UK). Over the duration of this study, an area of 25,000m2 was surveyed for floral characteristics and approximately 138,000 floral units were counted from c)8 plant species. A total of 201 flower visitor surveys were performed, with 942 flower-visiting insect samples taken. Flowering plant species richness and abundance of floral resources on restored landfill sites were not found to be significantly different from those on reference sites and the flower-visiting insect assemblages were similar in terms of species-richness and abundance. Interaction structures were examined and whilst the plant-insect assemblages had few species in common, both showed similar levels of nestedness and connectance. The differences in the species but similarity in the functioning of these assemblages emphasise the importance of examining interaction structures within a functional approach to the evaluation of restoration. There are 2,200 landfill sites in England and Wales covering some 28,000 ha, and this study highlights that their restoration can potentially provide an important resource for the conservation of pollinating insects and the services that they provide for both natural and agricultural plants. © Sam Tarrant 2009 This thesis is copyright material and no quotation from it may be published without proper acknowledgement. For my family and friends, 1 thank you for your motivation, inspiration and love. Contents Abstract Acknowledgments Dedication Contents List of figures List of tables Chapter descriptions, aims and objectives Chapter 1 - Introduction Pollinator decline and the global biodiversity crisis The importance of restoration Landfill restoration and the waste industry Pollinators in restored habitats. General aims Chapter 2 - General methods Introduction Selection of study sites Site selection criteria Fieldwork Floral surveys Floral resources Floral-visitor insect surveys Habitat quality characteristics Chapter 3 - The floristic characteristics of restored landfill sites Summary Introduction Habitat restoration methods Aims Methods Data analysis methods Results Discussion Results summary 84 Chapter 4 - A comparison of flower-visiting insects on restored landfill 86 and reference sites. Summary 87 Introduction 88 Aims 89 Methods 91 Data analysis methods 97 Results 100 Discussion 124 Results summary 132 Chapter 5 - The flower-insect interaction web on restored landfill sites. 134 Summary 135 Introduction 136 Aims 139 Methods 141 Data analysis methods 142 Results 146 Discussion 169 Results summary 181 Chapter 6 - Conclusions and Recommendations 183 Recommendations for landfill site operators and the waste industry 202 Data limitations 208 Further research 209 Appendices 211 References 223 v List of Figures Figure Page Pollinating insects in relation to decreasing habitat and mitigation through 1.01 10 restoration. A modem landfill site, showing engineering structures and capped profile. 1.02 13 Example of a restored landfill site - Wootton. 1.03 13 Example of a restored landfill site - Brixworth 1.04 19 Maps of: a) Study region within the UK, Counties outlined, b) Selected study 2.01 22 sites. Example of the floral unit of White Clover (Trifolium repens). 2.02 29 The author undertaking fieldwork on Cranford landfill site, 2007. 2.03 36 Species richness of flowering plant families found on restored landfill and 3.01 56 reference sites Frequency of flowering plant species present on restored landfill and reference 3.02 57 sites NMDS Ordination plot of plant species and abundance for restored landfill site 3.03 58 and reference sites for 2007 Mean total species richness of plants in flower for restored landfill sites and 3.04 60 reference sites 2007 & 2008 Mean seasonal species richness of plants in flower for restored landfill sites and 3.05 61 reference sites 2007 & 2008 Mean seasonal floral abundance per m: per site for landfill sites and reference 3.06 63 sites 2007 & 2008 Mean total species richness of plants in flower on sown and naturally revegetated 3.07 65 landfill sites in 2007 Mean seasonal floral abundance per m: per site on sown and naturally 3.08 66 revegetated landfill sites 2007 Mean bulk density of soils per sample (g cm'3) for restored landfill and reference 3.09 68 sites Mean moisture content per sample (%) for restored landfill and reference sites 3.10 69 Mean organic content (%) for restored landfill and reference sites 3.11 69 Stone content per sample for restored landfill sites and reference sites 3.12 70 Mean floral cover per season for restored landfill and reference sites 2007 & 3.13 74 2008 Mean seasonal total floral cover per site for restored landfill and reference sites 3.14 75 2007 & 2008 Cumulative seasonal floral cover for restored landfill and reference sites 2007 3.15 76 VI Schematic of floral resource provision in the landscape from restored landfill 3.16 81 sites and reference nature sites Theoretical curve of relationship between plant species richness and soil nutrients 3.17 82 A typical restored landfill sites floral character - Brixworth June 2008 3.18 85 Examples of habitat quality assessment features 4.01 96 Comparison of flower visitor groups between pairs of restored landfill sites and 4.02 103 their associated reference sites NMDS Ordination plot of flower visitor species and abundance on restored 4.03 106 landfill sites and reference sites for 2007 Frequency of flower visitor species present on restored landfill and reference 4.04 108 sites 2007 Frequency of flower visitor species present on restored landfill and reference 4.05 108 sites 2008 Total flower visitor abundance and frequency on restored landfill and reference 4.06 109 sites 2007 Total flower visitor abundance and frequency on restored landfill and reference 4.07 110 sites 2008 Mean flower visitor abundance per survey for landfill sites and reference sites 4.08 112 Mean flower visitor abundance per survey for landfill sites and reference sites 4.09 113 Mean annual cumulative flower visitor species richness per site for restored 4.10 114 landfill sites and reference sites Mean flower visitor species richness per survey for restored landfill sites and 4.11 115 reference sites Mean seasonal flower visitor species richness per survey for landfill sites and 4.12 116 reference sites Flower visitor abundance per survey correlated with on-site seasonal total floral 4.13 118 cover Flower visitor species richness per survey correlated with on-site seasonal 4.14 119 richness of flowering plants Flower-insect visitor interaction structure in 2008 a) Brixworth restored landfill 5.01 149 site, b) Pitsford reference site Flower-insect visitor interaction structure in 2008 a) Wootton restored landfill 5.02 150 site, b) Barnes Meadow reference site Flower-insect visitor interaction structure in 2008 a) Sidegate Lane restored 5.03 151 landfill site, b) Ditchford reference site Species abundance and number of interaction connections for restored landfill 5.04 154 and reference site 2008 Mean annual connectance (C) for restored landfill and reference sites 5.05 156 Mean annual connectance for sites sampled in both years 5.06 157 Annual connectance for sites sampled in 2007 and 2008 5.07 158 Mean Connectance for plants and insects on restored landfill and reference sites 5.08 160 Richness of plants in flower from annual interaction webs and on site annual 5.09 163 richness of plants in flower for restored landfill and reference sites 2007 Richness of plants in flower from annual interaction webs and on site annual 5.10 163 richness of plants in flower for restored landfill and reference sites 2008 Examples of interaction binary matrixes 5.11 165 NODF annual values and matrix size for restored landfill and reference sites 5.12 168 2007 Frequency of insect species connectivity with plant species, for both restored and 5.13 174 reference sites 2008. Plant and insect species richness for interaction matrixes on restored landfill and 5.14 175 reference sites Examples of plant and animal species richness for interaction matrixes 5.15 175 Theoretical sampling with relation to Connectance, Interaction abundance, 5.16 178 Matrix species richness and Sampling effort Interaction recorded over seasons for Brixworth restored landfill site 2008 5.17 180 Core floral species with open flower types 5.18 182 Landfill sites in Great Britain with a 2 km buffer zone 6.01 199 Earth cracks and holes on restored landfill sites due to subsidence 6.02 205 Vlll List of Tables Table Page Habitat requirements for principle pollinating insects 1.01 7 Details of restored landfill sites and reference

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