Biodiversity Assessment: moving towards an evidence-based index for biodiversity offsetting A thesis submitted for the degree of Doctor of Philosophy, School of Biological Sciences, University of Essex. April 2016 Leslie J Cousins “incommensurables are commensurable given a criterion of judgement and a system of weighting” (Hardin, 1968). I Summary Biodiversity offsetting is a mechanism for providing physical compensation to redress losses to species and habitats caused by development projects. As offsetting becomes more widespread, so has the evolution and development of frameworks, tools and methodological approaches for assessing biodiversity and implementing offsets. In this context and with a specific focus on assessment methodology this research takes a scientific and pragmatic approach to bridge the gap between empirical approaches to biodiversity assessment and the practical, often subjective, methods used by practitioners. Although commonalities among methodologies exist, systematically reviewing the state of the art, revealed a complicated situation which would benefit from methodological standardisation. The challenge of determining which components of biodiversity should be assessed by a standardised approach was informed with data gained through a survey that questioned biodiversity practitioners on which criteria and attributes they considered the most important indicators of biodiversity value. Results of an extensive field study of three habitat types are reported and the new data are employed; (a) to examine the sensitivity of a metric proposed for pilot offsets in England, and (b) to develop a novel multi-metric index with potential for wide use in biodiversity offsetting. From an array of forty five metrics a reduced index was produced which conveys information from measurements pertaining to four important biodiversity components. The new index is objective, relatively quick to produce, replicable and scientifically defensible. Compatible with existing frameworks the new index comprises information practitioners would expect to see i.e. biodiversity data (beta-diversity), temporal risk, (time to maturity) habitat rarity and structural connectivity. It can reliably provide a measure of value to biodiversity, inform spatial planning decisions, generate data for monitoring and aid the comparison of two or more sites of similar habitat. In concluding, the thesis discusses practical limitations of the index and, more generally, limitations for biodiversity offsetting. II Acknowledgements Dr Leanne J Appleby-Hepburn for support, constructive criticism and encouragement Professor Graham J.C. Underwood for support, constructive criticism and encouragement Dr Steven McMellor for encouragement support and ideas Mr Adrian Jowitt (Natural England) for advice support and encouragement Mr Andy May (Essex Wildlife Trust) for advice, support, training and encouragement All staff at Essex University, School of Biological Sciences for their support, I’m particularly grateful to Russ Smart for his time and help in the laboratory. I am very grateful to the following land owners and managers for their cooperation in kindly permitting me to conduct fieldwork on their lands; Mr Adam Rochester (Essex Wildlife Trust) Mr Will Cranstoun (Suffolk Wildlife Trust), Mr Stuart Warrington (The National Trust), Natural England, Mr Spencer Garnham, Mr Geoffery Latham (Billaricay and District Angling Club), Mr Richard Gallant (Colchester Golf Club), Mr Peter Tutton, Mr Timothy Ruggles-Brise (Spains Hall Estate) and Mr Patrick McKenna (The Essex Woodland Partnership). My wife Megan Cousins for patiently bearing with me, her loving support, faith, encouragement and invaluable practical assistance. I am indebted to my mum, Margret Edney nee Miskimmin, for her support and help with our family. This thesis is dedicated to the memory of my father Ken “Tom” Cousins (1936-2016). A great man and born naturalist. By sharing his curiosity and wonder of the natural world he instilled in me an enduring fascination for wildlife and a love for natural places. Without dad’s belief and continued encouragement this work would not have been possible. This research project was a NERC CASE studentship partnered with Natural England and benefitted from additional support from the Essex Wildlife Trust. III Table of Contents Summary………..……………………………………………………………………………… II Acknowledgements……….…………………………………………………………………… III Table of Contents……………………………………………………………………………… IV List of Figures………………..………………………………………………………………… VII List of Tables…………………………………………………………………………………… IX List of Abbreviations…………………………………………………………………………… XI Chapter 1 Measuring components of biodiversity: a review of the scientific, the subjective and the offset………………………………………………………………………………….. 1 1.1 Introduction……………………………………………………………………………… 1 1.1 What drives and regulates biological diversity (origin and maintenance)? ........... 2 1.2 The importance of biodiversity………………………………………………………… 5 1.3 Threats to biodiversity ………………………………………………………………….. 6 1.4 The conservation of biodiversity…………………………………………..…………… 8 1.5 Introduction to offsetting…………………………………………………….…………. 9 1.6 Offsetting; differing framework requirements …………………………….………….. 11 1.7 The delivery of biodiversity offsets………………………………………….…………. 12 1.8 Surrogates for measuring biodiversity………………………………………………… 13 1.9 Further issues concerning offsetting…………………………………………………… 14 1.9.1 Can there be a perfect offset?................................................................................. 16 1.10 Scientific methods for measuring biodiversity………………………………………… 19 1.10.1 Compositional Diversity and species identity ………………………………………… 20 1.10.2 Composition and diversity indices…………………………………………………….. 21 1.10.3 Point, alpha, beta, gamma diversities………………………………………………… 22 1.10.4 Taxonomic diversity…………………………………………………………………….. 23 IV 1.11 Naturalness, rarity and fragility………………………………………………………… 23 1.12 Structural diversity………………………………………………………………………. 27 1.13 Connectivity………………………………………………………………………………. 28 1.14 Functional Diversity……………………………………………………………………… 29 1.15 Rationale…………………………………………………………………………………. 30 Chapter 2 The assessment of biodiversity for conservation and offsetting; a conspectus of component selection and methodological approaches……....................................... 32 2.1 Introduction……………………………………………………………………………… 32 2.2 Methods………………………………………………………………………………… 35 2.2.1 Identification of methodologies……………………………………………………… 35 2.2.2 Data collation………………………………………………………………………….. 36 2.2.3 Statistical analysis…………………………………………………………………….. 36 2.3 Results…………………………………………………………………………………. 37 2.3.1 Which criteria occurred most frequently? …………………………………………. 38 2.3.2 Additional attributes and functions assessed by MBAs ……………………………. 39 2.3.3 Time taken for habitat to mature…………………………………………………….. 41 2.3.4 Combining methodologies into thematic groups…………………………………… 42 2.3.5 Which metrics or method of aggregation appeared most frequently? …………. 43 2.3.6 Subjectivity ……………………………………………………………………………… 47 2.4 Discussion………………………………………………………………………………. 48 Chapter 3 A Survey of Practitioners Opinions on Offsetting and the Use of a Metric Based Approach to Biodiversity Assessment………………………………………………………………… 53 3.1 Introduction……………………………………………………………………………… 53 3.2 Methods and Materials………………………………………………………………… 55 3.3 Results…………………………………………………………………………………… 57 3.4 Discussion……………………………………………………………………………….. 69 V Chapter 4 Comprehensive comparison of biodiversity assessed using standard protocol across three contrasting habitats of woodland, salt marsh and urban fringe grassland…. 73 4.1 Introduction……………………………………………………………………………… 73 4.1.1 Measuring species diversity with statistical power…………………………………. 75 4.1.2 The importance of landscape and habitat connectivity…………………………….. 77 4.1.3 The importance of widespread habitats and their susceptibility to development… 78 4.1.4 Rationale for habitat selection…………………………………………………………. 80 4.2 Methods………………………………………………………………………………….. 81 4.2.1 The Selection and description of Survey sites………………………………………. 81 4.2.2 Botanical Surveys………………………………………………………………………. 84 4.2.3 Bird Surveys…………………………………………………………………………….. 86 4.2.4 Invertebrate Surveys…………………………………………………………………… 87 4.2.5 NVC phytosociological communities…………………………………………………. 88 4.2.6 Occurrence evaluation (NBN) ………………………………………………………… 88 4.2.7 The Defra metric for biodiversity offsetting………………………………………….. 89 4.2.8 Desk study (Search for designated and listed species)……………………………. 91 4.2.9 Spatial analysis…………………………………………………………………………. 91 4.2.10 Data analysis ………………………………………………………………………….. 92 4.3 Results…………………………………………………………………………………… 94 4.3.1 The distribution and abundance of vascular plants, birds and arthropods in woodlands……………………………………………………………………………….. 94 4.3.2 Woodland birds…………………………………………………………………………. 105 4.3.3 Woodland invertebrates………………………………………………………………… 109 4.3.4 The connectivity; isolation and buffer of woodland habitats………………………… 111 4.3.5 Defra Metric for Woodland Sites……………………………………………………….. 112 4.4 Biodiversity within salt marshes………………………………………………………… 113 4.4.1 Salt marsh Plants………………………………………………………………………… 113 4.4.2 Salt marsh birds………………………………………………………………………….. 117 VI 4.4.3 Salt marsh invertebrates………………………………………………………………… 122 4.4.4 The connectivity of salt marshes………………………………………………………. 124 4.4.5 Offsetting metric and salt marshes……………………………………………………. 125 4.5 Biodiversity within 6 Essex urban fringe grasslands………………………………… 125 4.5.1 Grassland plants…………………………………………………………………………