How threatened are plants? : assessing conservation status of plants to support global conservation targets

This thesis aims to gain a more quantitative answer to the question: ‘How threatened are plants?’ Plants make up a large component of the world’s biota but are suffering as a result of pressures from anthropogenic activities including land cover change, over-consumption of plant resources and stresses associated with a changing climate. Loss of plants, either in terms of reduction in abundance or in the extreme case, extinction of species, will reduce the stability of ecosystems, and will potentially cause the collapse of ecosystems. Insufficient resources are available to protect all plants and a process of prioritisation is therefore needed to stem the losses resulting from anthropogenic activities. To support prioritisation we need to know which are the most important species and sites to protect and this could be determined by the density of species in an area, the usefulness of a species, the functional role a species plays in an ecosystem as well as the costs likely to be incurred to undertake protection. However, we also need to know the urgency with which we need to act. By assessing the threat status of species we can better understand both the level of exposure to threatening processes and how sensitive a species is to these threats. Conservation planning that does not consider threat status can be compromised because long-term persistence of threatened species is not guaranteed. In this thesis, I discuss the assessment of threat status at the species level in the context of conservation narratives and target-setting. I then make a series of specific advances with respect to improving global knowledge of threats to plant species as follows. As well as directly supporting conservation prioritisation efforts, threat status and trends in threat status have been incorporated into global biodiversity and conservation targets. The IUCN Red List framework for assessing threat status, or more specifically, risk of extinction, has been used to respond to the 2010 Biodiversity Target. I applied the Red List methodology to a random sample of c. 4,000 plants from the monocot, gymnosperm and pteridophyte clades, and legume family, of which 21.5% were threatened with extinction. Using the Red List framework means this approach can be compared to other groups; this indicates that plants are as threatened as mammals, more threatened than birds, but not as threatened as amphibians. Furthermore, the status of species can be reassessed to determine trends in extinction risk over time in support of renewed conservation targets. Conservation targets have been set specifically for plants, such as the Global Strategy for Plant Conservation (GSPC), and threat status features heavily in a specific target (GSPC Target 2), as well as being incorporated into many other targets. A quantitative response to GSPC Target 2 had been lacking until now. Here I present the most comprehensive synthesis of plant threat status assessments, showing that as many as 30,000 plant species have been assessed as threatened at the global scale. Furthermore, with only about a quarter of plant species assessed, there is a large gap in the knowledge of threat status for plants. Acknowledging that gaps in plant threat status knowledge could limit conservation efforts, it is necessary to speed up the process of assessment, without compromising assessment quality. Despite little evidence that trends in assessment production have increased in recent years, I review recent developments and identify ongoing challenges to progress. I conclude that there are good opportunities, such as the exploitation of technological developments, to close the knowledge gap much more quickly. Overall, this thesis provides new information on the level of threats that plants face and sets baselines from which trends can be monitored. It includes a quantitative response to a key global conservation target (GSPC Target 2). Further work should now focus on closing remaining knowledge gaps, to ensure that opportunities for plant conservation are not lost.