Data from: Herbivory resistance in dwarf shrubs combines with simulated warming to shift phenology and decrease reproduction

Research focus on the phenology of plants has accompanied current trends
in climate warming, because the two are inextricably linked. Warmer
temperatures have led to advanced plant phenology in a range of systems,
although some responses are species specific. However, other stressors,
such as herbivory, can delay or advance plant phenology, and few studies
have addressed the combined impact of these drivers. We experimentally
warmed plots with open top chambers (OTCs) and simulated herbivory
resistance to insect outbreaks with Methyl jasmonate (MeJA), along an
elevational climatic gradient. We then recorded vegetative and
reproductive phenology in two functionally important dwarf shrubs, the
deciduous Vaccinium myrtillus (bilberry) and the evergreen V. vitis-idaea
(lingonberry), to test the responses to the combined treatments. Based on
earlier findings, we expected larger phenological responses at higher
elevations and for bilberry. We found that in the year after MeJA
application, both bilberry and lingonberry delayed vegetative and
reproductive phenology, although responses were stronger in bilberry.
Warming with OTCs weakly advanced phenology in both species, but combined
effects were not consistent. We further examined the consequences of this
altered phenology on reproductive output with multigroup piecewise
structural equation modelling and found that herbivory resistance driven
changes to phenology had a strong mediating effect on berry numbers,
particularly under warmed conditions and mainly in the year after MeJA
application. Synthesis: These results demonstrate the need to consider
combined pressures in understanding the impacts of global change on plants
and highlight that multiple drivers may have unidentified synergetic
effects on species phenology and reproduction.