The grazing impacts of four barren ground caribou herds (Rangifer tarandus groenlandicus) on their summer ranges: An application of archived remotely sensed vegetation productivity data

Rickbeil, Gregory J. M.; Coops, Nicholas C.; Adamczewski, Jan

doi:10.1016/j.rse.2015.04.006

Cited by 17 publications

(12 citation statements)

References 51 publications

(83 reference statements)

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“…In the SE model, we hypothesized that large herds of caribou could reduce the plant biomass by browsing. However, contrary to previous studies ( 7 , 16 , 19 , 20 ), we found no evidence of a “top-down” effect of caribou on the vegetation biomass. Our results indicated a weak positive effect of herd size on the May NDVI.…”

Section: Discussioncontrasting

confidence: 99%

Arctic greening from warming promotes declines in caribou populations

et al. 2017

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Section: Discussioncontrasting

confidence: 99%

Arctic greening from warming promotes declines in caribou populations

et al. 2017

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“…A central challenge in arctic ecology is understanding the potential effects of a changing climate on caribou and reindeer (Rangifer tarandus), the most widespread terrestrial herbivore in the Arctic (Hummel and Ray 2008). The centrality of caribou to high latitude ecosystems is reflected in their high circumpolar abundance, their strong impacts on tundra vegetation (V€ ais€ anen et al 2014, Rickbeil et al 2015, Bichet et al 2016, Br athen et al 2017, Schmitz et al 2018, their importance as prey species for predators and scavengers (Reynolds et al 1987, Bergerud 1996, Young and McCabe 1997, Legagneux et al 2014, and their importance to the subsistence and culture of human groups throughout the Arctic (Burch 1972, Wolfe and Walker 1987, Hummel and Ray 2008. In North America, the most numerically abundant ecotype of caribou are the migratory barren-ground caribou, which undertake long-distance movements of several hundred kilometers between wintering, calving, and post-calving summer ranges (Fig.…”

Section: Introductionmentioning

confidence: 99%

Tactical departures and strategic arrivals: Divergent effects of climate and weather on caribou spring migrations

et al. 2019

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The Arctic has been warming rapidly, affecting ecological processes across the region. Caribou and reindeer (Rangifer tarandus) is a keystone Arctic species undergoing declines in many parts of its range, but definitive links between climate and populations remain elusive. The conspicuous and dramatic mass migration of many caribou populations, during which nearly all pregnant females move from wintering ranges to calving grounds shortly before giving birth, may be an important link between climate and caribou populations. The drivers of migration, however, are similarly mysterious. It is unknown, for example, whether caribou respond to immediate phenological cues, anticipate conditions on calving grounds, or are driven by lagged effects related to physical condition. To investigate the drivers of migration, we analyzed movement data from over 1000 individual caribou from seven major herds, spanning 3000 km across Alaska, Yukon, Northwest Territories (NWT), and Nunavut in Canada, from 1995 to 2017. We developed a hierarchical model to estimate migration departure and arrival times, and analyzed these variables against global climate indices and local weather conditions, exploring immediate and lagged effects, as well as snowmelt timing and vegetation indices. We discovered a continent‐wide synchrony in spring migration departure times, driven mainly by large‐scale, ocean‐driven climate indices (Pacific Decadal Oscillation, Arctic Oscillation, and North Atlantic Oscillation). However, we also found that the speed of migration was highly plastic with later migration departure times followed by shorter migration durations. This plasticity made arrival timing independent of departure timing and its respective drivers. Rather, arrival timing depended strongly on weather conditions from the previous summer: cooler and windier summers generally led to earlier arrival at calving grounds the following year. We suggest that maternal body condition, mainly influenced by conditions that limit insect harassment, is a major factor for earlier spring migration arrival timing, and therefore earlier calving and higher survival rates. We place these results in the context of mechanistic links between climate and caribou population dynamics. Long‐term and large‐scale observations of migratory animals can provide insights into the mechanisms by which long‐distance, collective migrants may adapt to dynamic and unpredictable environments.

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“…The TS analysis calculated all pairwise slopes for the LVE through time for each pixel throughout the image stack (1984–2012), returning the median slope as the estimate of yearly LVE change. TS slopes are less sensitive to outliers than traditional linear regression and, as a result, are becoming more commonly used in time series analyses at the pixel level [ 18 , 50 ]. Slope significance was determined using non-parametric Mann-Kendall tests ( Fig 2D ) [ 22 , 51 ].…”

Section: Methodsmentioning

confidence: 99%

Estimating changes in lichen mat volume through time and related effects on barren ground caribou (Rangifer tarandus groenlandicus) movement

et al. 2017

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Lichens form a critical portion of barren ground caribou (Rangifer tarandus groenlandicus) diets, especially during winter months. Here, we assess lichen mat volume across five herd ranges in the Northwest Territories and Nunavut, Canada, using newly developed composite Landsat imagery. The lichen volume estimator (LVE) was adapted for use across 700 000 km2 of barren ground caribou habitat annually from 1984–2012. We subsequently assessed how LVE changed temporally throughout the time series for each pixel using Theil-Sen’s slopes, and spatially by assessing whether slope values were centered in local clusters of similar values. Additionally, we assessed how LVE estimates resulted in changes in barren ground caribou movement rates using an extensive telemetry data set from 2006–2011. The Ahiak/Beverly herd had the largest overall increase in LVE (median = 0.033), while the more western herds had the least (median slopes below zero in all cases). LVE slope pixels were arranged in significant clusters across the study area, with the Cape Bathurst, Bathurst, and Bluenose East herds having the most significant clusters of negative slopes (more than 20% of vegetated land in each case). The Ahiak/Beverly and Bluenose West had the most significant positive clusters (16.3% and 18.5% of vegetated land respectively). Barren ground caribou displayed complex reactions to changing lichen conditions depending on season; the majority of detected associations with movement data agreed with current understanding of barren ground caribou foraging behavior (the exception was an increase in movement velocity at high lichen volume estimates in Fall). The temporal assessment of LVE identified areas where shifts in ecological conditions may have resulted in changing lichen mat conditions, while assessing the slope estimates for clustering identified zones beyond the pixel scale where forage conditions may be changing. Lichen volume estimates associated with barren ground caribou movement metrics in an expected manner and, as such, show value for future habitat assessments.

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The grazing impacts of four barren ground caribou herds (Rangifer tarandus groenlandicus) on their summer ranges: An application of archived remotely sensed vegetation productivity data

Cited by 17 publications

References 51 publications

Arctic greening from warming promotes declines in caribou populations

Arctic greening from warming promotes declines in caribou populations

Tactical departures and strategic arrivals: Divergent effects of climate and weather on caribou spring migrations

Estimating changes in lichen mat volume through time and related effects on barren ground caribou (Rangifer tarandus groenlandicus) movement

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