Detecting early- warning signals of concern in plant populations with a Citizen Science network. Are threatened and other priority species for conservation performing worse?

Long-term monitoring of biodiversity is a fundamental part of environmental management, and Citizen Science (CS) approaches are increasing their contribution to such endeavour. CS plant monitoring programmes, however, almost exclusively report on the species presence, which can be used to detect changes in distribution or occupancy areas, but not to assess their local extinction risk. To anticipate the collapse of local populations, we need information on population sizes, trends, temporal fluctuations and threats. This is particularly important in the case of priority species (threatened, endangered and those that need special protection). Here we describe the working protocol of the 'Adopt a plant' programme, a collaborative network that is currently monitoring 332 populations of 204 plant taxa (threatened, of community interest, common, rare and habitat indicators) across a heterogeneous landscape in NE Spain. Coordinated by scientists, participants estimate population sizes, record disturbances and follow scientifically rigorous sampling methods to track plant abundances year after year in fixed representative areas within populations. Two simple indices are estimated from that information: the overall trend (mean population abundance change, as percentage; PAch) and temporal fluctuations (standard deviation of annual changes; PAch(sd)). The potential of this ongoing high-quality dataset is demonstrated through the analysis of 242 populations monitored over 3-10 years. Stability is the dominant trend (mean PAch: +0.14%), with priority species having similar PAch and lower PAch(sd) than non-priority ones. Regardless of the priority status, small populations performed worse than large ones. Only 8% of studied populations faced direct human threats. Synthesis and applications. The 'Adopt a plant' collaborative monitoring programme was launched in NE of Spain to produce standardized indices of abundance change and other early-warning signals of concern or risk of population collapse. Such information is crucial to report the conservation status of threatened plants, and plants of Community interest (Habitats Directive). By analysing hundreds of populations, we found that priority plants experienced few threats and did not perform worse than non-priority ones. This unexpected finding evidences the importance of gathering massive demographic information to refine conservation priorities and to achieve a more comprehensive assessment of flora's vulnerability.Diputacion General de Aragon, Grant/Award Number: RB-0.4075; OAPN, Grant/Award Number: 1656/2015; Diputacion Provincial de Huesca, Grant/Award Number: Decreto 1521; Spanish Research Agency, Grant/Award Number: CGL2017-90040-R; European Commission, Grant/Award Number: LIFE+12 NAT/ES/000180; Delegacion CSIC-Arago