High Arctic plant phenology is determined by snowmelt patterns but duration of phenological periods is fixed: an example of periodicity

Abstract

The duration of specific periods within a plant's life cycle are critical for plant growth and performance. In the High Arctic, the start of many of these phenological periods is determined by snowmelt date, which may change in a changing climate. It has been suggested that the end of these periods during late-season are triggered by external cues, such as day length, light quality or temperature, leading to the hypothesis that earlier or later snowmelt dates will lengthen or shorten the duration of these periods, respectively, and thereby affect plant performance. We tested whether snowmelt date controls phenology and phenological period duration in High Arctic Svalbard using a melt timing gradient from natural and experimentally altered snow depths. We investigated the response of early-and late-season phenophases from both vegetative and reproductive phenological periods of eight common species. We found that all phenophases follow snowmelt patterns, irrespective of timing of occurrence, vegetative or reproductive nature. Three of four phenological period durations based on these phenophases were fixed for most species, defining the studied species as periodic. Periodicity can thus be considered an evolutionary trait leading to disadvantages compared with aperiodic species and we conclude that the mesic and heath vegetation types in Svalbard are at risk of being outcompeted by invading, aperiodic species from milder biomes.

Using Ordinary Digital Cameras in Place of Near-Infrared Sensors to Derive Vegetation Indices for Phenology Studies of High Arctic Vegetation

“…However, as reported from field observational studies [11,56,57], there were noticeable differences in these patterns between species/groups. For instance, vegetation plots containing graminoids reached a well-defined and short peak in index values before declining sharply, whereas plots containing C. tetragona and D. octopetala had broader mid-season peak values as well as increased values at the end of the growing season/study period.…”

“…A late season peak is also shown in Graminoid/Salix polaris vegetation plot (Figure 2a). Both graminoids and Salix are deciduous, normally changing colour and losing leaves around DOY 230 [11] so extended late-season growth for these plants may be an unlikely explaination for the second peak observed in Figure 2a.…”

“…The increased variation in vegetation index values observed towards the end of the season was likely due to senescence producing changes in leaf colouration, a process that occurs over a more prolonged period than green-up, and also has species-specific timing [11,57,61]. Although Richardson et al [22] found that RGB derived indices increased more slowly than NDVI values, we did not find this to be the case with High Arctic vegetation, thus suggesting that both NDVI and the GRVI used in this study captured the same vegetation attributes.…”

“…However, it has been argued that increased monitoring efforts should focus on polar regions [6], particularly as these areas have experienced greater than global-average increases in annual temperatures [7] and are intimately linked to other parts of the globe via complex atmospheric and oceanic cycles [8,9]. Field-based manual phenological observations in Arctic, Antarctic and alpine areas have been ongoing for a number of years at single sites [10,11] and multiple sites through coordinated networks such as the International Tundra Experiment [12,13]. However such traditional approaches can be problematic due to the time constraints imposed by short summer periods, the highly labour-intensive nature of the work, high financial costs and difficulties in accessing remote locations.…”

Disappearing green: Shrubs decline and bryophytes increase with nine years of increased snow accumulation in the High Arctic

“…At each fence location, areas were identified in 2006 in which the vegetation initially appeared visually similar, and to which three different snow regimes were applied: a fenceless, unmanipulated “ Ambient ” regime, where snow depth reached a maximum of roughly 35 cm; a “ Deep ” regime 3–12 m behind the fences, with maximum 1.5 m snow depth; and further on up to 20 m behind the fences, a “ Medium ” regime with 60–100 cm maximum snow depth (Semenchuk et al., ). Snowmelt timing is affected by snow regimes; even though there is large annual variation, the order of melting is the same every year, with average dates (for the six years 2008–2012 & 2015) being Ambient: 2 June, Medium: 12 June and Deep: 18 June (Semenchuk, Gillespie et al., ). Near‐surface soil temperature at 1 cm depth was recorded hourly using Tinytag data loggers model TGP‐4020 (Gemini) and soil moisture was measured twice a week throughout the summer at all four edges of the plots using a Theta ML 2× probe (Delta‐T Devices), and averaged to give a mean plot value.…”