Three hunters rescued alive after their campsite was hit by an avalanche in Fiordland, New Zealand.

Three men on a hunting trip were rescued alive after their campsite was hit by an avalanche early in the morning of Saturday 20 October 2018. The men were on an expedition trapping Stoats (a highly invasive European predatory species that presents a threat to New Zealand's native Birdlife) near Lake Te Anau in the Fiordland Region of South Island, New Zealand, when the avalanche hit, sweeping away the campsite, and leaving the men uninjured but very cold and wet (potentially life-threatening in a remote area without survival equipment), but were rescued after about an hour by a Southern Lakes Rescue Helicopter alerted to the event by an emergency beacon carried by the men.

Two of the hunters on a Stoat-trapping expedition that was later hit by an avalanche in Fiordland, New Zealand, on 20 October 2018. Ben Collins/Stuff.

 
Avalanches are caused by the mechanical failure of snowpacks; essentially when the weight of the snow above a certain point exceeds the carrying capacity of the snow at that point to support its weight. This can happen for two reasons, because more snow falls upslope, causing the weight to rise, or because snow begins to melt downslope, causing the carrying capacity to fall. Avalanches may also be triggered by other events, such as Earthquakes or rockfalls. Contrary to what is often seen in films and on television, avalanches are not usually triggered by loud noises. Because snow forms layers, with each layer typically occurring due to a different snowfall, and having different physical properties, multiple avalanches can occur at the same spot, with the failure of a weaker layer losing to the loss of the snow above it, but other layers below left in place - to potentially fail later. In this instance the avalanche appears to have been caused by rain falling onto snow covered slopes, weakening the structure of the snowpack.

Diagrammatic representation of an avalanche, showing how layering of snow contributes to these events. Expedition Earth.

Stoats, Mustela erminea, were introduced to New Zealand in the 1880s, in an attempt to control Rabbits, which had been introduced a decade earlier as a food animal and rapidly become an agricultural pest due to a lack of native predators, despite the warnings of scientists concerned about the effect that these alien predators would have on native Bird populations. Unfortunately these warnings proved to be accurate, and within six years dramatic population losses had been recorded in many species of New Zealand Birds. In an attempt to protect these Birds many species were established on offshore islands in the Fiordland area, though in the early 2000s Stoats were found to be reaching some of these islands, devastating the Bird populations there and leading to increased efforts to control Stoats in the Fiordland Region.

 An introduced Stoat, Mustela erminea, with a Bird chick in New Zealand. Department of Conservation Te Papa Atawhai.

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Understanding the role of Bears in enabling a Cherry tree to migrate up mountains.

The Earth's climate is known to fluctuate over time, requiring animals and plants to move in order to find suitable habitats. For animals this is a fairly easy task, since most animals constantly move in search of the optimum environments during their lives, however for plants this is much more problematic, as they live the majority of their lives rooted to a single spot, with dispersal only occuring during the seed stage. One way to track optimum conditions in a changing climate without traveling vast distances is to move up and down slopes, since on average a 100 m rise in altitude coresponds to a -0.65 °C drop in temperature. However, while a seed can easily move downslope throgh gravity or water dispersal, seeds cannot fall upslope, requiring the plant to find more creative ways to move seeds uphill.

In a paper published in the journal Current Biology on 25 April 2016 a team of scientists led by Shoji Naoe of the Forestry and Forest Products Research Institute examine the dispersal of the seeds of the Hill Cherry, Prunus verecunda, in Central Japan via two animal vectors, the Asiatic Black Bear, Ursus thibetanus and the Japanese Marten, Martes melampus.

Oxygen isotope ratios in plant tissue can be closely related to altetude, enabling Naoe et al. to estimate the altitude at which the trees that produced Cherry stones found in Bear and Marten droppings had been growing. Surprisingly they found that both species preferentially moved the seeds upwards, with Bears moving them an average of 749.5 m upslope and Martens 460.5 m, close to the maximum distance a foraging member of each species would be expected to travel between eating the fruit and excreting their stones.

The Hill Cherry produces fruit in spring-to-summer, with trees lower on the slope producing flowers, fruit and leaves earlier in the season. Bears, which were responsible for moving 80.3% of the Cherry seeds, have previously been shown to move upslope over the season enabling them to access fruit throughout the season. Naoe et al. suggest that the preferential movement of Bears and Martend uphill between consuming Cherries and defacating may reflect a daily feeding cycle, with the animals feeding first on the fruit, then moving upslope to forrage on herbs and young vegetation that cannot be accessed beneath the canopy of fruiting trees.

Vertical seed dispersal toward the mountain tops by mammals that are following the springto summer plant phenology. The spring-to-summer plant phenology proceeds from the foot to the top of mountains. Cherry fruits and young vegetation are no longer available in low altitudes, ripe fruits are available but young vegetation is no longer available in middle altitudes, and ripe fruits are unavailable but young vegetation is available in high altitudes. Naoe et al. (2016).

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