Caribou and reindeer (Rangifer ssp.) are widely distributed in the circumpolar Arctic and sub-arctic regions and have adapted to survive a wide range of conditions. General characteristics of the regions they inhabit are the short period of the year when the primary production of vascular forage plants takes place, and the considerably longer one when only perennial living plants and dead plant material are available as forage. This naturally becomes more extreme and demanding for the animals, the further north one goes. In the High Arctic regions vascular plants, in particular grasses and sedges, are essential dietary components during the entire year. In more southerly latitudes, terrestrial and arboreal lichen constitute an important part of the winter diet.

Among the apparent adaptations of Rangifer to Arctic conditions is a distinct seasonality, when the food demanding functions of their life cycles are concentrated to the growing season of the plants, while the rest of the year is devoted to survival on a minimum of food. Provided that winter conditions do not cause excessive deaths, their productivity is strongly determined by summer conditions.

Caribou and reindeer are ruminants. Just like other cervids they are more dependent on high quality forage than for example the muskox which lives in a similar environment. Forage quality is predominantly connected to the digestibility of the plant material. If there is a low degree of digestibility, the animals obtain less energy and protein from the food they ingest. In addition, it lowers their rate of food passage and thus their total food consumption. This adversely affects their ability to rebuild body reserves prior to winter and undermines their physical condition, in turn affecting both their survival and their reproductive success, and ultimately the dynamics of the herbivore population.

Low digestibility of vascular forage plants relates to a high cell wall content, i.e. a lower portion of highly digestible cell contents in the plant material, and to the occurrence of tannins which reduce digestion of the plant material. Although the cooler climate of these regions and the weather in general lead to a shorter growing season and less forage being available, they are at the same time expected to enhance forage quality by decreasing the cell wall portion in plants. Better forage quality may therefore be expected to compensate for less availability at higher latitudes. However, our knowledge in quantitative terms in this area is very limited.

In addition Arctic weather is highly variable, which means there is considerable annual variation as regards the timing of green up and the amount and quality of growth.

Our understanding of how the interaction between forage availability and quality affects the ability of Rangifer to cope with different conditions and the impact on population dynamics is limited as well. This renders quantitative assessments of e.g. future climatic changes very difficult. Better knowledge in this area would also facilitate understanding conditions in subarctic areas, for example the dynamics of reindeer on reindeer herding ranges in Scandinavia. The aim of this project is to contribute a little to this knowledge by relating the chemical composition and digestibility of various forage plants to different phenological stages and the climatic conditions they grow in. The general climatic gradients, which may have influenced the adaptations and phenological patterns of the plants, and the particular conditions of the year, are characterized by latitude, distance from the tree-line on the continent, length of growing season and total degree days for each sample collected this year. The results are to be evaluated together with similar information collected in Scandinavia, representing considerably warmer climatic conditions, in order to gain know ledge of Rangifer strategies in different climatic environments.

Field-work and sample preparations on board

Main efforts concentrated on collecting samples of potential forage species for chemical analyses and in vitro measurements of digestibility. The first sites were visited early in the season (beginning of July) when only a few species bad new shoots or leaves and were abundant enough to enable collection of new green in sufficient amounts. The number of sampled species varied between 4 and 15 at the different sites and included 39 species in total. In a few cases both old and new material was collected for possible later separation. Colleagues collected a few additional samples on the second leg of the expedition.

Quantitative assessments of forage productivity were excluded from the field-work at an early stage of planning since the difficulties involved in sampling an area representative of one a caribou, with its highly mobile grazing behaviour might use, were obvious. It also appeared that the majority of the sites visited were on ranges only occasionally used by caribou and then often during a different season. Observations of caribou pellets, made when compiling pellet inventories in parallel with the sampling, confirmed that caribou did not currently use the sites visited to any large extent.

Work on board included sorting the material to obtain samples of pure species or plant parts. The samples were then dried at 40°C for approximately 48 hours.

Preliminary results

The samples have not yet been analysed and any results concerning plant quality are not currently available.

Because of the expedition route, sampling from sites l to 5 covers a parallel increase of time from 1-17 July and of latitude from 62 to 76 degrees N, southward distance to the tree-line ranges from approximately 590 to 1850 km and the shortest (south-west) distance from approximately 580 to 1500 km. From sites 6 to 9 latitude is fairly constant, around 70 degrees N, while time progresses a further 12 days and the distance to the tree-line decreases from the 1850 km at site 5 to approx. 400-600 km for the last three sites. The phenological stages of the material collected vary more irregularly but with a gradual common pattern of increasing stages from site 1 to 9. The data should therefore allow statistical separation of the effects of northerliness and phenological stage at least to some extent. Use of meteorological data and simultaneous analyses with Scandinavian data will probably facilitate this further.