Abstract
Plant phenology is strongly interlinked with ecosystem processes and biodiversity. Like many other aspects of ecosystem functioning, it is affected by habitat and climate change, with both global change drivers altering the timings and frequency of phenological events. As such, there has been an increased focus in recent years to monitor phenology in different biomes. A range of approaches for monitoring phenology have been developed to increase our understanding on its role in ecosystems, ranging from the use of satellites and drones to collection traps, each with their own merits and limitations. Here, we outline the trade-offs between methods (spatial resolution, temporal resolution, cost, data processing), and discuss how their use can be optimised in different environments and for different goals. We also emphasise emerging technologies that will be the focus of monitoring in the years to follow and the challenges of monitoring phenology that still need to be addressed. We conclude that there is a need to integrate studies that incorporate multiple monitoring methods, allowing the strengths of one to compensate for the weaknesses of another, with a view to developing robust methods for upscaling phenological observations from point locations to biome and global scales and reconciling data from varied sources and environments. Such developments are needed if we are to accurately quantify the impacts of a changing world on plant phenology.
Highlights
Change to phenological events may have implications for biogeochemical cycles, including that of carbon [32], and for may have implications for biogeochemical cycles, including that of carbon [32], and for the population dynamics of species connected at different trophic levels or in competitive the population dynamics of species connected at different trophic levels or in competitive and mutualistic interactions [33,34]
In Europe, climatic shifts in the Netherlands have caused an increase in the strength of asynchrony between the phenology of the Winter Moth (Operophtera brumata) and their host plant Oak (Quercus robur) [82], and drier conditions over a 17 year period in Spain resulted in higher asynchrony between pollinator butterfly species and their plants [83]
We examine how each method compares when considering key factors that influence the effectiveness of monitoring phenology: spatial resolution, temporal resolution, cost in terms of equipment, acquisition or labour, and data processing and interpretation requirements
Summary
Habitat Change—Anthropogenic pressures on the environment have caused unprecedented rates of habitat loss, fragmentation, and degradation over the last half-century [63,64,65,66,67,68,69,70]. Fragmentation, and the resulting edge effects produce fine-scale variations in light, temperature and humidity, that can in turn induce phenological changes. Individual flowers in fragmented forests were less likely to produce a mature fruit, at the scale of individual trees, the change in flowering and fruiting phenology in fragmented forest combined to increase reproductive capacity [74]. The phenology of 10 bee species from Northeastern North America has advanced by a mean of 10.4 days as a result of climate change altering the phenological timings of flowering plants [35]. In Europe, climatic shifts in the Netherlands have caused an increase in the strength of asynchrony between the phenology of the Winter Moth (Operophtera brumata) and their host plant Oak (Quercus robur) [82], and drier conditions over a 17 year period in Spain resulted in higher asynchrony between pollinator butterfly species and their plants [83]. Even in aquatic systems such as Argentinian lakes, zooplankton have undergone significant shifts in phenological metrics following temperature increases over the last decade [85]
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