The ecology of the invasive moss Campylopus introflexus in the North York Moors National Park by Miguel Eduardo Equihua Zamora A thesis presented for the degree of Doctor of Philosophy in the Department of Biology at the University of York November 1991 I hereby declare that the work presented in this thesis is the result of my own investigation and has not been accepted in previous applications for the award of a degree. Exceptions to this declaration are part of the field data used in chapter 4, which was collected and made available to me by Dr. M.B. Usher. The distribution map on Campylopus introflexus was provided by P.T. Harding (Biological Records Centre, ITE, Monks Wood). R.C. Palmer (Soil Survey and Land Research Centre, University of York) made available to me the soil and climatological data of the area, and helped me to obtain the corresponding interpolation values for the sampled sites. Miguel Eduardo Equihua Zamora 1 CONTENTS page Acknowledgements . 4 Abstract................................................. 5 1. Introduction 1.1 The invader: Campylopus introflexus ..................... 7 The invasion of the Northern Hemisphere ............... 7 Taxonomyand identity ............................ 13 Ecology....................................... 16 1.2 The problem ...................................... 19 1.3 Hypothetical mechanisms of interaction ................... 22 2. Aims of the research ......................................28 3. Description of the study area .................................29 4.Ecological preferences of Campylopus introflexus in the North York Moors National Park 4.1 Introduction ....................................... 35 4.2 Methods ......................................... 36 Thefuzzy c-means algorithm ........................ 39 Evaluation of the associations ........................ 43 Desiccation survival of the moss carpets ................ 44 4.3 Results .......................................... 45 Vegetationanalysis ............................... 45 Assessment of moss associations ...................... 49 Carpetthickness ................................. 51 Mosscarpets survival ............................. 55 4.4 Discussion ........................................ 57 5.Impact of a Campylopus introflexus carpet on Calluna vulgaris germination and growth 5.1 Introduction .......................................61 5.2 Methods .........................................65 5.3 Results ..........................................67 5.4 Discussion ........................................79 6. Establishment of Cailuna seedlings on carpets of Campylopus introflexus under field conditions 6.1 Introduction .......................................84 6.2 Methods .........................................87 6.3 Results ..........................................88 6.4 Discussion .......................................101 2 7. Impact of Campylopus introflexus on the regeneration of a Callunetum 7.1 Introduction ......................................104 7.2 Methods ........................................106 7.3 Results .........................................111 Amountof Calluna seedlings ....................... 113 Lengthof heather seedlings ........................117 Growthof Calluna seedlings ........................119 Association analysis at the grid-square level .............122 7.4 Discussion .......................................127 8. General discussion and conclusions 8.1 Discussion .......................................131 8.2 Conclusions ......................................137 9. References ............................................139 10. Appendix ............................................148 3 Acknowledgements I would like to express my gratitude to Dr. M.B. Usher for his continuous support and guidance throughout the development of this project and his very constructive criticism to my manuscripts. My appreciation also to Dr. R. Brown and the authorities of the North York Moors National Park Department for making possible the conditioning of the experimental site at Kildale Moor. P.T. Harding, Esq. (Biological Records Centre, JTE, Monks Wood) kindly provided the data and the distribution map on Campylopus introflexus. R.C. Palmer, Esq. (Soil Survey and Land Research Centre, University of York) kindly provided soil and climatological data of the area, and helped to obtain the corresponding interpolation values for the sampled sites. Thank you to C. Abbot and K. Patrick for so kindly looking after my heathers and my mosses in the greenhouse. To Dr. S. Gardner for her suggestions to some of the chapters and her friendship. Thank you to L. Mynto, S. Jones, J. Perrins, R. Toy, G. Shepherd, S. Sgardelis, J. Field, H. West, and J. Williams and all the people in the 'lab' for their friendship that contributed so much to make the whole experience of living abroad such an enjoyable one. Thank you to Griselda for her help in the field work during those cold-windy days and, together with Julián and Ana, for tolerating my bad moods and altogether helping me, with their love and support, to come to the end of this road. To my father, Luis Equihua and my brothers Luis, Fernando, Alberto and my sister Clementina, for being with us, despite the distance, lending me continuous support. To my mother, Clementina Zamora, because her strong soul sowed in me the enthusiasm for living. During the development of this project I received the financial support of the Mexican Council of Science and Technology (CONACYT). I also want to acknowledge the effort made by the 'Instituto de EcologIa A.C., Mexico' that grant me leave of absence during the development of this project and especially to M. en C. P. Reyes-Castillo and M. end C. M. Maury for their support. 4 Abstract Campylopus introflexus is one of the rare examples of invasive biyophytes worldwide. This moss has recently spread, outside its original distributional range in the Southern Hemisphere, into Europe (first recorded in 1941) and into North America (in 1975). C. introflexus invasion is important because of its capability of spreading aggressively within newly colonized habitats. The main goals of the thesis were: (1) to determine the factors controlling the distribution of C. introflexus in the North York Moors National Park and (2) to evaluate the potential impact of the moss on the dynamics of the moorland communities, specifically on Calluna, its dominant component. It was hypothesised that the interaction should take the form of modifications to the regeneration niche of Calluna. A vegetation survey of the National Park was conducted to analyze the association of C. introflexus with the vegetation and other environmental factors. It was found that C. introflexus has a wide distribution among Calluna dominated communities, but the preferred habitat is where Calluna has, on average, 43% cover and 9 cm in height. The carpets of C. introflexus tend to fragment producing loose blocks which may provide the moss with an additional form of propagation contributing to its ability to retain colonised territory. The results of laboratory experiments demonstrated that, despite inducing lower germination, C. introflexus has no direct inhibitory effect on Calluna. Heather plants growing on moss carpets performed better than those growing on open ground. 5 A field experiment showed that, although Calluna is able to germinate on top of carpets of C. introflexus, the seedlings failed to establish themselves. Therefore, heather cover regeneration may be delayed if a carpet of C. introflexus more than 1 cm thick develops in the vegetation gaps. Another field experiment showed that C. introflexus colonizes, after tire, practically at the same time as the other main components of the moorland. The small moss carpets showed mostly a positive association with the occurrence of Calluna seedlings. Although it is possible for the moss to delay the development of the Callunetum, eventually Calluna will outcompete the moss. How does an obviously inferior competitor manages to remain in the community? Disturbance is obviously paramount in this regard but in addition, it is argued, a non-equilibrium rationale to understand the dynamics of the community is useful in this case. 6 1. Introduction 1.1 The invader: Campylopus introflexus Campylopus introflexus (Hedw.) Brid. is a species that has recently spread outside its original distributional range in the Southern Hemisphere, where it is found from subantarctic islands to subtropical regions (Frahm 1984). Initially, C. introflexus was considered to be an almost cosmopolitan species, but Giacomini (1955) demonstrated that there were in fact two species: C. pilifer Brid. (=C. polytrichoides DeNot.) and C. introflexus. Some of the characteristics used by Giacomini to differentiate the two species have been questioned by other authors (Richards 1963, Barkman and Mabelis 1968 and Jacques and Lambinon 1968). However, Frahm (1972, 1974 and 1975) and Gradstein & Sipman (1978) have shown that the two species can be differentiated both anatomically and ecologically. The aim of this chapter is to provide a review of the information available on the biology of C. introflexus and to examine its role as an invasive plant. The invasion of the Northern Hemisphere The first record of C. introflexus in Europe dates from 1941, from a locality in Britain (Washington, Sussex). From that date onwards it has been reported with increasing frequency from new localities in the British Isles (Richards 1963, Richards & Smith 1975). By