# Inter-Annual Variability of Peatland Vegetation Captured Using Phenocam- and UAV Imagery
## 5 Conclusions  
Vegetation phenology plays a strong role in the inter-annual variability of the peatland carbon balance [108; 109; 118], and will be affected by both long-term climate change and an associated increase in the frequency of extreme weather events [30]. As such, phenological monitoring is key to improving predictions of the future fate of peatland carbon stocks under climate change. However, the remoteness of many peatland ecosystems means that traditional phenological datasets are limited. Furthermore, due to the pronounced spatial heterogeneity of peatlands, satellite data products are unable to accurately capture variability in their phenology [62]. The present study examined the use of phenocam imagery and the novel approach of multi-temporal UAV surveying to monitor the phenology of peatland vegetation over a number of growing seasons. Both methods were suitable for characterising peatland phenology, although they differed in terms of their relative merits and weaknesses. The high temporal resolution of phenocam data (daily) was invaluable for identifying the different stages of phenological development. Such high temporal coverage was not feasible with manual UAV surveys, although these provided us with discrete time points of rich data to supplement the limited spatial and spectral resolution provided by phenocam imagery. We found that collection of spectral data in the red-edge and NIR bands was advantageous, in that VIs employing these bands were more sensitive to dry spells. Furthermore, we demonstrated the potential of UAV surveys for monitoring spatial heterogeneity in the phenology of peatland vegetation, which can be difficult to achieve with phenocam data (e.g., depending on site characteristics, camera viewing angle). Both datasets displayed a strong correlation with peatland GPP. For the UAV data, we found that VIs utilising the red-edge band (e.g., the reNDVI1) were best able to predict GPP at the site, partly because these indices were most sensitive to physiological changes such as drought. However, analysis of the high temporal resolution phenocam dataset was able to highlight a large amount of inter-annual and seasonal variability in the strength of this relationship. The years examined in the present study were unusual with respect to the long-term measurement record at the site, with frequent dry spells and a tendency for the peatland to function as a net source of CO\({}_{2}\). Our findings suggest that the seasonal timing of future weather anomalies will be a key factor determining their impact on the peatland carbon balance. Continued long-term monitoring of peatland ecosystems and their vegetation is crucial to improving our understanding of the current drivers of peatland CO\({}_{2}\) dynamics and how these may change in the future. Conceptualization--[PERSON] and [PERSON]; methodology--[PERSON], [PERSON] and T.W. ; data collection--[PERSON], [PERSON], [PERSON], [PERSON] and K.Y. ; formal analysis--[PERSON]; writing (original draft preparation)--[PERSON]; writing (review and editing)--all authors; visualization--[PERSON]; supervision--[PERSON] and [PERSON]; project administration, [PERSON] and C.H. ; funding acquisition--[PERSON] and C.H. All authors have read and agreed to the published version of the manuscript. [PERSON] was supported by a grant from the NERC Edinburgh Earth and Environment (E3) Doctoral Training Partnership (NE/L002558/1). For the purpose of open access, the author has applied a creative commons attribution (CC BY) licence to any author accepted manuscript version arising. The monitoring activities at Auchencorth Moss are supported by the Natural Environment Research Council by the UKCEH National Capability for UK Challenges programme (award number NE/Y006208/1), and previously by CEH's UK-SCAPE programme (award number NE/R016429/1). The data presented in this study may be made available on request from the corresponding author. The data are not publicly available due to ongoing analysis for publication.