Reindeer eat to beat climate change

Reindeer are helping to slow down climate change by grazing on Arctic tundra and leaving vegetation that reflects more solar energy back into space.

Reindeer are best known – at least in much of the northern hemisphere – for pulling Santa’s sleigh, but a new study suggests they may have a part to play in slowing down climate change too.

A team of researchers, writing in the journal Environmental Research Letters, found that when reindeer reduce the height and abundance of shrubs on the Arctic tundra through grazing, the level of surface albedo – the amount of solar energy (shortwave radiation) reflected by the Earth back into space – is increased.

The study’s lead author, Dr Mariska te Beest, from Umeå University in Sweden, said: “Our theory was that heavy grazing by reindeer increases summer albedo, through a reduction in shrub height, abundance and leaf area index (LAI).

Regionally important finding

“The effect reindeer grazing can have on albedo and energy balances is potentially large enough to be regionally important. It also points towards herbivore management being a possible tool to combat future warming.

“Most of the Arctic tundra is grazed by either domesticated or wild reindeer, so this is an important finding.

“Of course, the impact the reindeer have will vary according to their densities and the subsequent effects on the vegetation levels across the whole tundra.”

“Our results show that reindeer
have a potential cooling
effect on climate”

The study combined land surface computer modelling with measurements of albedo and vegetation characteristics taken in the field. The team carried out their field measurements in Troms in northern Norway, in an area with four topographically-defined vegetation types that varied in shrub height and abundance.

They used a unique experimental method, with a fence over half a century old separating areas experiencing either light or heavy grazing by the reindeer.

Working through the summer season, the team estimated reindeer activity in the study areas by using vegetation trampling indicators, and through collecting dung.

They also measured the abundance of vegetation, its leaf area index, and the soil moisture and temperature levels, as well as the albedo levels.

Decrease in radiation

Dr te Beest says: “We found that high densities of reindeer changed Arctic tundra vegetation by decreasing shrub abundance. This resulted in corresponding shifts in leaf area index, canopy height and normalised difference vegetation index (NDVI) – the amount of live green vegetation.

“These pronounced changes in vegetation led in a substantial increase in albedo across the growing season. Our modelling results showed this increase in albedo would result in a corresponding decrease in net radiation and heat fluxes – indicating that heavily grazed sites absorbed less radiation.

“Our results show that reindeer have a potential cooling effect on climate, by changing the summer albedo. Although the estimated differences might appear small, they are large enough to have consequences for the regional energy balance.”

The reindeer on Norway’s mainland should perhaps count themselves lucky to have ample food available. On Svalbard, the Arctic archipelago administered by Norway, scientists have found the deer are losing weight because of the impact of climate change on the vegetation

The weight of the reindeer, over 16 years, has fallen by around 12%, from 55 to just over 48kg.

Frozen out

Professor Steve Albon, from the James Hutton Institute, UK, told the BBC that the weather on Svalbard, which lies about halfway between northern Norway and the North Pole, was becoming increasingly mild.

Precipitation which had formerly fallen as snow was often now replaced by rain, which froze and made it hard for the animals to reach through the ice for the food which has to sustain them through the islands’ eight-month winter.

The Svalbard reindeer are unique to the archipelago. Smaller than other sub-species, they are known locally, because of their compact build and generous girth, as “Svalbard pigs”.