Collapse of an iconic conifer: long-term changes in the demography of Widdringtonia cedarbergensis using repeat photography. Issue 1 (December 2016)

• Record Type: Journal Article
• Authors: White, J.; Jack, S.; Hoffman, M.; Puttick, J.; Bonora, D.; Visser, V.; February, E.
• Is Part Of: BMC ecology. Volume 16:Issue 1(2016)
• Page Start: 1
• Page End: 11
• Publication Date: 2016-12
• Subjects: Temperature -- Conifer -- Repeat photography -- Population change -- Climate change -- Fire -- Cederberg; Ecology -- Periodicals; 577.05
• DOI: 10.1186/s12898-016-0108-6
• Languages: English
• ISSNs: 1472-6785

Abstract

Abstract Background Conifer populations appear disproportionately threatened by global change. Most examples are, however, drawn from the northern hemisphere and long-term rates of population decline are not well documented as historical data are often lacking. We use a large and long-term (1931–2013) repeat photography dataset together with environmental data and fire records to account for the decline of the critically endangeredWiddringtonia cedarbergensis. Eighty-seven historical and repeat photo-pairs were analysed to establish 20th century changes inW. cedarbergensis demography. A generalized linear mixed-effects model was fitted to determine the relative importance of environmental factors and fire-return interval on mortality for the species. Results From an initial total of 1313 live trees in historical photographs, 74% had died and only 44 (3.4%) had recruited in the repeat photographs, leaving 387 live individuals. Juveniles (mature adults) had decreased (increased) from 27% (73%) to 8% (92%) over the intervening period. Our model demonstrates that mortality is related to greater fire frequency, higher temperatures, lower elevations, less rocky habitats and aspect (i.e. east-facing slopes had the least mortality). Conclusions Our results show thatW. cedarbergensis populations have declined significantly over the recorded period, with a pronounced decline in the last 30 years. Individuals that established in open habitats at lower, hotter elevations and experienced a greater fire frequency appear to be more vulnerable to mortality than individuals growing within protected, rocky environments at higher, cooler locations with less frequent fires. Climate models predict increasing temperatures for our study area (and likely increases in wildfires). If these predictions are realised, further declines in the species can be expected. Urgent management interventions, including seedling out-planting in fire-protected high elevation sites, reducing fire frequency in higher elevation populations, and assisted migration, should be considered.