Since it seems people in general don't know too much about the subject, I google translated a piece of text from Reindyrsforvaltningen, which is basically a government agency responsible for most aspects of reindeer management in Norway.

The need for space

Reindeer herding is a land-intensive industry, and total industry uses about 40% of land area in Norway. Unlike other primary industries that can grow or planted new areas, the resource base for reindeer shrinking. This is due to various forms of intervention. Land protection is therefore a central area of ​​Reindeer Husbandry.

Below, we will try to explain why the reindeer are land-intensive and why land conservation is so important: Reindeer husbandry takes place largely in areas with low land productivity, ie the annual growth of pasture is low. This has the consequence that reindeer must travel long distances for overhead to find sufficient food. Especially in winter, reindeer barren pastures and other grazing animals would not have survived on.

Reindeer are the only domesticated grazing animals that depend on to even find pasture 365 days a year. This is in contrast to the sheep that usually do not graze in the outfield more than about 3 months a year.

Reindeer The year is divided into a number of seasonal pastures. There are basically three factors which determine this division: geology, rainfall and availability. Geology and amount of rainfall determines the plants that grow there, and the availability determines whether reindeer are able to utilize these plants. Especially in winter, this is crucial, because snow and ice can prevent the reindeer to dig through.

Rein in need of various grazing plants in different seasons. In the summer it needs protein-rich plants for growth and muscle growth, while the winter can survive on the protein diet. Different age groups of reindeer also have different needs.

Season pasturage may be located far apart, and it is therefore necessary to pull and move the tenant so that deer can utilize them. These hires follow ancient tracks determined by the topography, lakes and rivers, and infringement of these can have serious consequences.

Rein is a so-called semidomestisert or semi-tame animals. The consequence of this is that deer respond negatively to disturbance, and often do not use even good pasture because disturbances which are too large. Here too there are differences between different categories of reindeer, and females are particularly vulnerable in relation to calving in the spring. If pastures are locked during the winter, even small disruptions could have serious consequences.