Dag Bjerketvedt

The Hardangervidda wild reindeer herd: a problematic management history

The unique and internationally important wild reindeer Rangifer tarandus herd on the Hardangervidda plateau of southern Norwayxa0 has shown frequent and extreme fluctuations in harvest numbers for the past 60 years, despite considerable effort to stabilize the herd size at a winter carrying capacity ofxa0 9000 – 12 000 animals . In the absence of large mammalian predators, herd size is managed through hunting.xa0 Here we attempt to unravel the causes of the management problems related to this population by examining the relative roles of historical, biological and management-related processes. From 1900 - 1950 the population remained mainly low due to a combination of generous harvest quotas, poaching and competition from domestic reindeer.xa0 From 1950 - 2012 three extreme harvest peaks of between 4500 - 9500 animals occurred, followed by three equally extreme troughs including two shorter periods of total protection.xa0 This extreme harvest fluctuation contrasts with the estimated annual harvest of 2300 - 3000 needed to stabilize the winter herd between 9000 - 12 000 animals.xa0 We conclude that this population has been difficult to manage mainly because of 1) a management based on frequently unreliable population data on herd size (especially before 2001), 2) lack ofxa0 in depth analyses and evaluation of both recruitment and sex and age composition and 3) a low and highly variable harvest success (harvest/quota) due mainly to poor hunter mobility, a disadvantage when reindeer must be harvested from large flocks that constantly move upwind, seeking refuge on small areas with few hunters.xa0 More reliable population data to create better harvest models plus increased hunter mobility are necessary to attain a more sustainable herd size, implying an improvement of the current herd survey methodology available to local reindeer boards.xa0 Finally, a critical and independent evaluation of the scientific methodology employed to study and manage this herd is needed.

Estimation of lichen biomass with emphasis on reindeer winter pastures at Hardangervidda, S Norway

Quantification of lichen abundance is important for management of reindeer populations. We measured dry lichen biomass in 876 micro plots (16.5 cm × 16.5 cm) systematically sampled within 219 vegetation plots (2 m × 2 m) from 7 different areas in S Norway. Lichen biomass was quantified as: (a) dry weight in g m-2, (b) lichen height in cm, (c) lichen cover, and (d) lichen volume (lichen height × lichen cover). Lichen biomass decreased with increasing precipitation and increasing altitude. On local scale, the variation in lichen biomass varied strongly with snow conditions. The grazed parts of Hardangervidda had in general a low average lichen biomass (an average mostly lower than 150 g m-2). Lichen biomass was much higher in area where reindeer migration was interfered by human activity. Lichen height and lichen volume were strongly linearly correlated with dry lichen biomass. These proxy methods may therefore be used to predict lichen biomass, but deviations from exact measurements should be expected.

Experimental Study of Gas Explosions in Hydrogen Sulfide-Natural Gas-Air Mixtures

An experimental study of turbulent combustion of hydrogen sulfide (H2S) and natural gas was performed to provide reference data for verification of CFD codes and direct comparison. Hydrogen sulfide is present in most crude oil sources, and the explosion behaviour of pure H2S and mixtures with natural gas is important to address. The explosion behaviour was studied in a four-meter-long square pipe. The first two meters of the pipe had obstacles while the rest was smooth. Pressure transducers were used to measure the combustion in the pipe. The pure H2S gave slightly lower explosion pressure than pure natural gas for lean-to-stoichiometric mixtures. The rich H2S gave higher pressure than natural gas. Mixtures of H2S and natural gas were also studied and pressure spikes were observed when 5% and 10% H2S were added to natural gas and also when 5% and 10% natural gas were added to H2S. The addition of 5% H2S to natural gas resulted in higher pressure than pure H2S and pure natural gas. The 5% mixture gave much faster combustion than pure natural gas under fuel rich conditions.

Are trampling effects by wild tundra reindeer understudied

This journal is published under the terms of the Creative Commons Attribution 3.0 Unported License

Herbivore grazing—or trampling? Trampling effects by a large ungulate in cold high- latitude ecosystems

Abstract Mammalian herbivores have important top‐down effects on ecological processes and landscapes by generating vegetation changes through grazing and trampling. For free‐ranging herbivores on large landscapes, trampling is an important ecological factor. However, whereas grazing is widely studied, low‐intensity trampling is rarely studied and quantified. The cold‐adapted northern tundra reindeer (Rangifer tarandus) is a wide‐ranging keystone herbivore in large open alpine and Arctic ecosystems. Reindeer may largely subsist on different species of slow‐growing ground lichens, particularly in winter. Lichen grows in dry, snow‐poor habitats with frost. Their varying elasticity makes them suitable for studying trampling. In replicated factorial experiments, high‐resolution 3D laser scanning was used to quantify lichen volume loss from trampling by a reindeer hoof. Losses were substantial, that is, about 0.3 dm3 per imprint in dry thick lichen, but depended on type of lichen mat and humidity. Immediate trampling volume loss was about twice as high in dry, compared to humid thin (2–3 cm), lichen mats and about three times as high in dry vs. humid thick (6–8 cm) lichen mats, There was no significant difference in volume loss between 100% and 50% wetted lichen. Regained volume with time was insignificant for dry lichen, whereas 50% humid lichen regained substantial volumes, and 100% humid lichen regained almost all lost volume, and mostly within 10–20 min. Reindeer trampling may have from near none to devastating effects on exposed lichen forage. During a normal week of foraging, daily moving 5 km across dry 6‐ to 8‐cm‐thick continuous lichen mats, one adult reindeer may trample a lichen volume corresponding to about a years supply of lichen. However, the lichen humidity appears to be an important factor for trampling loss, in addition to the extent of reindeer movement.