Environmental, spatial and temporal drivers of plant community composition in British forest habitat. Adam Robert Kimberley (B.Sc.) This thesis is submitted in partial fulfilment of the requirement for the award of the degree of Doctor of Philosophy August, 2015 Abstract Broadleaved forest habitat is important for a number of ecosystem functions and as a refuge for many rare plant species in human-modified landscapes. It is however, threatened by global change drivers such as deforestation and the associated fragmentation of remaining habitat areas, along with increased disturbance and exposure to nutrient inputs from surrounding intensive agriculture. This thesis uses a unique combination of data on plant species occurrence, local environmental conditions and forest spatial extent in order to investigate the ways in which species richness and functional diversity in forest communities are dependent upon local and landscape scale drivers, and to quantify the strength of these relationships. This provides novel understanding of the response of forest plants with different life history traits to the configuration and quality of available habitat, and therefore the way in which understorey assemblages are likely to alter over time following landscape change. Results highlight the importance of local environmental conditions within forest patches but also suggest that patch area and landscape connectivity have an important effect on the trait composition of communities. Preserving large, well connected areas of habitat is therefore likely to be key for the conservation of many species, particularly rarer forest specialists which often possess traits linked to low dispersal ability. Furthermore, there is evidence that species are slow to respond to changes in the spatial extent of habitat. As such, considering the history of forest patches is necessary in order to explain present day patterns in plant species occurrence and to devise effective conservation measures. This highlights the need to integrate understanding of local and landscape scale processes with temporal data i in order to properly understand the way in which forest communities are formed and to predict ongoing change under expected global change scenarios. ii Table of Contents 1.1. Thesis aims and structure ............................................................................... 1 1.2. Data sources .................................................................................................... 4 2.1. Introduction ..................................................................................................... 7 2.1.1. Habitat loss and fragmentation ............................................................... 7 2.1.2. Forest habitat ........................................................................................... 8 2.1.3. Biotic homogenization ........................................................................... 10 2.2. Effects of habitat spatial configuration on forest plant species ................... 11 2.2.1. Forest patch area ................................................................................... 11 2.2.2. Patch isolation ........................................................................................ 14 2.2.3. Landscape connectivity .......................................................................... 17 2.2.4. Edge effects ............................................................................................ 20 2.2.5. Interdependence of spatial variables .................................................... 21 2.3. Time lags in species response to landscape change ..................................... 23 2.3.1. Extinction debts ..................................................................................... 23 iii 2.3.2. Immigration credits ................................................................................ 25 2.4. Forest protection and expansion strategies ................................................. 28 2.5. Summary ....................................................................................................... 32 Abstract .................................................................................................................... 35 3.1. Introduction ................................................................................................... 37 3.2. Material and methods ................................................................................... 41 3.2.1. Classification and regression tree analysis ............................................ 41 3.2.2. Testing for effects of phylogeny ............................................................ 44 3.2.3. Effects of rarity and regional AWI status ............................................... 44 3.2.4. Plant species data .................................................................................. 45 3.3. Results ........................................................................................................... 47 3.3.1. Trait analysis .......................................................................................... 47 3.3.2. Phylogeny and AWI status ..................................................................... 49 3.3.3. Regional AWIs ........................................................................................ 50 3.4. Discussion ...................................................................................................... 50 3.5. Conclusions .................................................................................................... 55 Abstract .................................................................................................................... 58 4.1. Introduction ................................................................................................... 60 4.2. Materials and methods ................................................................................. 63 4.2.1. Plant trait data ....................................................................................... 63 4.2.2. Local conditions ..................................................................................... 64 4.2.3. Spatial woodland variables & patch age ................................................ 65 iv 4.2.4. Statistical modelling ............................................................................... 67 4.3. Results ........................................................................................................... 69 4.3.1. Selection probability .............................................................................. 69 4.3.2. Model averaged effect sizes .................................................................. 71 4.4. Discussion ...................................................................................................... 76 4.4.1. Abiotic conditions .................................................................................. 76 4.4.2. Importance of habitat configuration ..................................................... 78 Abstract .................................................................................................................... 82 5.1. Introduction ................................................................................................... 83 5.2. Methods ........................................................................................................ 86 5.2.1. Survey data ............................................................................................ 86 5.2.2. Species and plant trait data ................................................................... 86 5.2.3. Spatial ..................................................................................................... 88 5.2.4. Local abiotic conditions.......................................................................... 88 5.2.5. Modelling approach ............................................................................... 89 5.3. Results ........................................................................................................... 95 5.3.1. Trait data ................................................................................................ 95 5.3.2. Species data ........................................................................................... 98 5.4. Discussion ...................................................................................................... 99 Abstract .................................................................................................................. 106 6.1. Introduction ................................................................................................. 108 6.2. Methods ...................................................................................................... 112 v 6.2.1. Species richness data ........................................................................... 112 6.2.2. Forest connectivity ............................................................................... 113 6.2.3. Species niche modelling ....................................................................... 116 6.2.4. Matrix composition .............................................................................. 117 6.2.5. Modelling approach ............................................................................. 118 6.3. Results ......................................................................................................... 119 6.3.1. Niche models and connectivity estimates