Abstract
Manual collection of accurate phenology data is time-consuming and expensive. In this study, we investigate whether repeat colour digital photography can be used (1) to identify phenological patterns, (2) to identify differences in vegetation due to experimental warming and site moisture conditions, and (3) as a proxy for biomass. Pixel values (RGB) were extracted from images taken of permanent plots in long-term warming experiments in three tundra communities at a high Arctic site during one growing season. The Greenness Excess Index (GEI) was calculated from image data at the plot scale (1 × 1 m) as well as for two species, Dryas integrifolia and Salix arctica. GEI values were then compared to corresponding field-based phenology observations. GEI and Normalized Difference Vegetation Index (NDVI) values from a paired set of true colour and infrared images were compared with biomass data. The GEI values followed seasonal phenology at the plot and species scale and correlated well with standardized observations. GEI correlated well with biomass and was able to detect quantitative differences between warmed and control plots and the differences between communities due to site-specific moisture conditions. We conclude that true colour images can be used effectively to monitor phenology and biomass in high Arctic tundra. The simplicity and affordability of the photographic method represents an opportunity to expand observations in tundra ecosystems.
Highlights
Plant phenology is controlled by climatic conditions and is an important indicator of climate change impacts in terrestrial ecosystems (Badeck et al 2004; Cleland et al 2007; Høye et al 2013; Inouye 2008; IPCC 2007; Schwartz et al 2006)
Observational and experimental warming studies have shown that vegetation phenology is sensitive to climate warming (Arft et al 1999; Oberbauer et al 2013; Walker et al 2006; Wolkovich et al 2012)
The objective of this study was to determine the effectiveness of colour digital photography in monitoring tundra vegetation at multiple scales
Summary
Plant phenology is controlled by climatic conditions and is an important indicator of climate change impacts in terrestrial ecosystems (Badeck et al 2004; Cleland et al 2007; Høye et al 2013; Inouye 2008; IPCC 2007; Schwartz et al 2006). The rapid warming at high latitudes over the past five decades (IPCC 2007) has caused changes in vegetation abundance and composition (Elmendorf et al 2012a) as well as tundra plant phenology in many sites (Høye et al 2013; Oberbauer et al 2013), similar to results from warming experiments (Arft et al 1999; Elmendorf et al 2012b). Hudson et al (2011) demonstrated the variability in response of traits of five species in three different vegetation communities to 16 years of experimental warming. The variability in responses at the site and species level to environmental change highlights the need for a greater number of studies of phenology and vegetation dynamics in order to better understand and predict patterns of responses
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