Migratory goose arrival time plays a larger role in influencing forage quality than advancing springs in an Arctic coastal wetland

Abstract

With warmer springs, herbivores migrating to Arctic breeding grounds may experience phenological mismatches between their energy demands and the availability of high quality forage. Yet, how the timing of the start of the season and herbivore arrival influences forage quality is often unknown. In coastal western Alaska, approximately one million migratory geese arrive each spring to breed, where foliar %N and C:N ratios are linked to gosling survival and population growth. We conducted a three-year experiment where we manipulated the start of the growing season using warming chambers and grazing times using captive Pacific black brant (Branta bernicla nigricans) to examine how the timing of these events influences the quality of an important forage species. Our results suggest that grazing timing plays a much greater role than an advanced growing season in determining forage quality. All top models included grazing timing, and suggested that compared to typical grazing timing, early grazing significantly reduced foliar %C by 6% and C:N ratios by 16%, while late goose grazing significantly reduced foliar %N by 15% and increased foliar C:N ratios by 21%. While second-ranking top models included the effect of season, the advanced growing season effect was not significant and only reduced %N by 4%, increased %C by <1%, and increased C:N ratios by 5% compared to an ambient growing season. In summary, in years where geese arrive early, they will consume higher quality forage when they arrive and throughout the season, while in years that geese arrive late they will consume lower quality forage when they arrive and for the remainder of the season. When the growing season starts has only a minor influence on this pattern. Our findings suggest that cues determining migration and arrival times to breeding areas are important factors influencing forage quality for geese in western Alaska.

Snowier winters extend autumn availability of high‐quality forage for caribou in Arctic Alaska

“…Warmer weather during the growing season may decrease leaf‐level nitrogen (N) and increase concentrations of anti‐herbivory compounds in spring and summer forage (Jonasson et al 1986, Turunen et al 2009, Zamin et al 2017). Warmer temperatures may also result in phenological mismatch (Post and Forchhammer 2008, Beard et al 2019). Though caribou exhibit significant physiological and behavioral resilience to phenological mismatches (Mallory et al 2020), shift of the growing season earlier into the spring could decouple annual caribou physiological stages like parturition and lactation from both the timing and seasonality of critical nutrients on the landscape (Walsh et al 1997, Fauchald et al 2017).…”

Response of forage plants to alteration of temperature and spring thaw date: implications for geese in a warming Arctic

“…Person et al (1998) and Beard et al (2019) argued that grazing response delayed senescence and maintained peak nitrogen content longer into the season than for ungrazed plots. It may be that a similar response does not occur after the peak and during the seasonal decline in nitrogen content (Beard et al 2019). Alternatively, we may not have had sufficient grazing pressure to stimulate a detectable response in the plants.…”

“…At the Colville River Delta, Alaska, USA (150 km east of our study area), Sedinger et al (2001) and Hupp et al (2017) found very little grazing offtake, similar to what we measured at the Smith River. Person et al (1998) and Beard et al (2019) argued that grazing response delayed senescence and maintained peak nitrogen content longer into the season than for ungrazed plots. It may be that a similar response does not occur after the peak and during the seasonal decline in nitrogen content (Beard et al 2019).…”

“…Whereas recent warming in the Arctic is associated with an increase in plant primary productivity (Bhatt et al 2010, Epstein et al 2012), there likely exists a temperature‐induced threshold beyond which the foliar ratio of carbon to nitrogen exceeds what is suitable for goose digestibility. The relationship between warming and overall plant response as it relates to goose populations is complicated because timing of herbivory has been shown to have a larger influence on plant nutrient concentration than timing of spring thaw (Post and Pedersen 2008, Olofsson et al 2009, Beard et al 2019).…”

Phenological mismatch between season advancement and migration timing alters Arctic plant traits

“…plant resources; Figure ; Nakazawa & Doi, ). Thus far, empirical studies in terrestrial systems investigating phenological mismatch at the lower trophic level have focused on the reductions in forage quality for herbivores (Beard et al, ; Doiron, Gauthier, & Lévesque, ; Lameris et al, ; Zamin, Côté, Tremblay, & Grogan, ), and how mismatches between plants and pollinators influence seed production (Forrest, ; Kudo & Ida, ). An often‐overlooked component is how phenological mismatches influence the producer itself (i.e.…”