Assessing the interaction between history of usage and plant invasions: Bamboo as a case study Dissertation presented for the degree of Doctor of Philosophy in the Faculty of Science at Stellenbosch University By Susan Canavan Supervisor: Prof. John R. Wilson Co-supervisor: Prof. David M. Richardson Co-supervisor: Prof. Johannes J. Le Roux December 2018 Stellenbosch University https://scholar.sun.ac.za Declaration By submitting this dissertation electronically, I declare that the entirety of the work contained therein is my own, original work, that I am the sole author thereof (save to the extent explicitly otherwise stated), that reproduction and publication thereof by Stellenbosch University will not infringe any third party rights, and that I have not previously in its entirety or in part submitted it for obtaining any qualification. This dissertation includes three articles published with me as lead author, and one article submitted and under review, one paper published as a conference proceeding, and one paper yet to be submitted for publication. The development and writing of the papers (published and unpublished) were the principal responsibility of myself. At the start of each chapter, a declaration is included indicating the nature and extent of any contributions by co-authors. During my PhD studies I have also co-authored three other journal papers, have one article in review, and published one popular science article; these are not included in the dissertation . Susan Canavan ___________________________ December 2018 Copyright © 2018 Stellenbosch University All rights reserved ii Stellenbosch University https://scholar.sun.ac.za Abstract Studies in invasion science often focus on the biological or environmental implications of invasive alien species. However, biological invasions are inherently due to the human- mediated dispersal of species; this means that there needs to be a greater focus on the socio- economic context of why species have been introduced by humans, and how humans have created environments or situations to foster the success of alien taxa. This dissertation explores the interaction of human usage and plant invasions using bamboos as a case study, with the intention of answering the following questions: Why are some species selected by humans over others? How does this influence invasion success, impacts, and the cultural role of alien species in receiving environments? I found that, like many other alien taxa, the transfer of bamboos globally has been non- random. Large-statured Asiatic species and those with a greater number of cultivars are more likely to have been introduced outside of their native ranges. The species with high introduction rates are the bamboos that are found to be invasive; this supports the notion that propagule pressure is a universally important factor in facilitating invasions. However, in contrast to many other studies, biogeographic status (the native status) of bamboo was not a strong predictor of the type and magnitude of impacts. Impacts are rather explained by certain human activities (disturbance such as logging and clearing, increasing temperatures related to climate change, and the promotion of bamboo monocultures in mixed forests for commercial purposes). As such, the management of highly competitive native species should be considered in conjunction with the management of invasive alien species in forest ecosystems where bamboos are present. The competitive nature of bamboos that leads to impacts can be applied to other tall-statured grasses. Specifically, rapid growth rate and the capacity to accumulate biomass (a function of height) allow many tall grasses to form monospecific stands, accumulate dense and deep litter mats, reduce light availability and alter fire and nutrient-cycling regime. Naturalisation rates are greater in tall-statured grasses compared to other grasses, and the pathways of introduction are generalizable (e.g. for addressing environmental problems). Tall-statured grasses are a useful functional group for predicting high-risk taxa and for making generalised management plans. iii Stellenbosch University https://scholar.sun.ac.za Looking at South Africa as a case-study, I found 26 alien species of bamboo recorded as introduced, with populations of several species widely naturalised around the country. I also found bamboos to be an inherently difficult group to identify to the species level, emphasizing the caution that must be taken with regard to future introductions. Amongst the public there is a complex tapestry of perceptions towards bamboos related to (1) a long history of introduction, and multiple introduction events, where bamboos have become culturally significant for some groups of people, and (2) the realisation that they can cause problems. In conclusion, many bamboos can be classified as synanthropic species in that they have benefited from human activity or the habitats that humans create around them. Studying bamboos has provided further insights into how social and economic imperatives are shaping a new biota at a global level. iv Stellenbosch University https://scholar.sun.ac.za Opsomming Die implikasies op die omgewing en ander biologiese sisteme is gewoonlik die fokus van meeste indringer studies. Tog is hierdie biologiese indringing die gevolg van menslik- bemiddelde verspreiding van spesies. Daar moet dus meer fokus wees op die sosio-ekonomiese konteks van waarom spesies deur mense ingebring word, en ook op hoe mense situasies en omgewings geskep het om hierdie uitheemse taksa te bevorder. Bamboes word as gevallestudie gebruik om die interaksie van menslike gebruik en plantindringing te ondersoek. Die tesis poog om die volgende vrae te beantwoord: Waarom word sommige spesies bo ander gekies? Hoe beïnvloed dit die sukses van die indringing, die impak, en die kulturele rol van uitheemse spesies in die betrokke omgewings? Ek het gevind dat die inbring van bamboes wêreldwyd nie eweredig oor spesies versprei was nie, soos met baie ander uitheemse taksa. Groot Asiatiese spesies en dié met meer kultivars word meer gereeld buite hul natuurlikke streke aangeplant. Die bamboes spesies met ‘n hoë aanvraag vir invoer is die wat indringers geword het. Dit ondersteun die idee dat propagule druk 'n universeel belangrike faktor is vir indringers. In teenstelling met baie ander studies was bamboes se biogeografiese status (die natuurlikke streek van voorkoms se klimaat en omstandighede) nie 'n goeie voorspeller van die tipe en grootte van impak nie. Impakte word eerder verklaar deur sekere menslike aktiwiteite (versteuring soos afkap, klimaatsverandering se stygende temperature, en kommersiële bamboesmonokultures in gemengde woude). Daarom moet hoogs mededingende inheemse bamboes spesies se bestuur ook oorweeg word net soos vir indringer spesies. Hierdie mededingende aard van bamboes wat impakte veroorsaak, kan toegepas word op ander groot en lang (hoë) grasse. Spesifiek, die vinnige groeitempo en die kapasiteit om biomassa op te bou ('n funksie van hoogte) laat baie lang grasse toe om monospesifieke stande te vorm, digte en diep komposmatte op te bou, ligindringing te verminder en vuur- en voedingstof-siklusse te verander. Lang grasse se naturalisasie tempo is hoër in vergelyking met ander grasse, en die meganismes van inbringing is ook veralgemeenbaar wanneer daar bv. gekyk word na die aanspreek van omgewingsimpakte. Ek argumenteer dat lang grasse 'n nuttige funksionele groep is vir die algemene bestuur en risiko voorspelling van hoërisiko-grasse. v Stellenbosch University https://scholar.sun.ac.za Deur na Suid-Afrika te kyk as ‘n gevallestudie, het ek 26 uitheemse bamboespesies gekry, met populasies van verskeie spesies wat genaturaliseer het. Ek het ook gevind dat bamboes 'n inherente moeilike groep is om tot spesievlak te identifiseer, wat die waaksaamheid met verderre invoere beklemtoon. Die publiek het ‘n komplekse tapisserie van persepsies teenoor bamboes wat verband hou met (1) die besef dat hulle probleme kan veroorsaak, en (2) waar bamboes kultureel betekenisvol geword het vir sommige groepe mense vanwee 'n geskiedenis en gebruike. Ter afsluiting kan baie bamboes as sinantropiese spesies geklassifiseer word omdat hulle voordeel trek uit menslike bemiddeling, aktiwiteit en gewoontes rondom bamboes. Die studie oor bamboes het verdere insig gegee in hoe sosiale en ekonomiese behoeftes 'n nuwe biota op globale vlak vorm. vi Stellenbosch University https://scholar.sun.ac.za Acknowledgements I would like to thank my supervisors (John Wilson, Dave Richardson, and Jaco Roux) for their mentorship, support and constant encouragement. I acknowledge and thank my Funders for their financial assistance: The DST-NRF Centre of Excellence for Invasion Biology, South African National Department of Environment Affairs, Working for Water Programme, National Research Foundation (NRF). A thank you to those that helped with fieldwork, valuable input or providing information: Joubert Roux, Felix Sorour, Ingrid Nanni, Megan Mathese, Reshnee Lalla, Vusi Mkhize, Gerald Cebekhulu, Sharon Louwe, Menzi Nxumalo, Thabiso Cele, Adrian Sutton, Ludi Kern, Philip Ivey, William Radloff. The CIB & departmental staff team (Carla, Christy, Mathilda, Mari, Rhoda and Suzaan) for their help over the years. My examiners (Dr. Katharina Dehnen-Schmutz, Prof S Luke Flory, Prof Karen Esler) and all the reviewers along the way for helpful comments and suggestions. I would also like to thank the following people for general PhD guidance but also in contributing towards