Impact of soil scarification on reindeer pastures

During recent years, soil scarification has become a standard procedure for improving seed beds after logging. Around 57 000 ha were treated, primarily through harrowing and ploughing, in the counties of Vâsterbotten and Norbotten during 1985. The positive effects of scarification, from a forestry point of view, are improved access to plant nutrients, raised soil temperatures and reduces surface moisture. The aim of the present study was to describe long-term changes in the ground vegetation following scarification. Harrowing affects 45-55% of the plant cover while ploughing affects 65-90%. 10 years after ploughing and harrowing about 20% of the surface is still without vegetation. Real long-term effects remain in dispute. It has been claimed that ploughing, at least, may lead to irreversible changes.


Introduction
All types of soil scarification after final felling of forest stands aim to support germination of tree seeds and establishment of tree plants and their further development.
The aim of this investigation was to study the long-term effects of harrowing and ploughing, especially on plant species that are grazed by reindeer.
Reindeer are herded over almost all of the two northernmost counties in Sweden, Norrbotten and Vasterbotten, and in a considerable  vardstyrelsen, 1987).Harrowing is by far the most common practise but mounding is increasingly used (Fig. 2).
During the last eight years the total annual scarification area in the northernmost county, Norrbotten, has totaled 27 000 ha.Of this area 20% is ploughed (Fig. 3).There is, however, a great variation between counties, different districts and ownership categories within counties (Fig. 2).

Study area
The study area is located between latitude N 63°and 68°in N Sweden.It belongs to the with an threshold value of + 5°C (Odin et al, 1983).The annual precipitation is 450-550 mm, of which 35-45% falls as snow (Atlas over Sverige, 1971).

Methods
Based on information from the National Forest Enterprises of Sweden, a number of regeneration stands were defined.The aim was to find as comparable areas as possible from biotic and abiotic viewpoints.
The scarification methods which so far have been studied are ploughing and harrowing.Because of the differences in construction, in the degree of disturbance capacity, ect., between the earlier and the existing scarifiers, we have concentrated on regeneration areas, which were cultivated with the most frequently used machines and models still utilized.
The soil moisture and the thickness of the humus layer primarily determine the method to be used.We decided to choose areas with me- As we could not study a limited number of sites over a long period of time we instead had to select our investigation areas in an age series, based on year of treatment.A number of control sites, i.e. mature forest stands comparable to the logged ones before logging and situated quite close to them, were also chosen and inventoried; accordingly we are using a static method (Austin, 1977).
In each investigation area the relative frequencies of the different subsections -tilt, shoulder, ditch bottom and intact ground -were recorded.The standing crop of the ground vegetation on each subsection was calculated.
A number of parallel transects, at a 45° angle to the dominating plough course, were distributed across the sites.A number of sample plots were systematically placed along these transects and in each plot the following measurements were made: 1.In the 1 m 2 plots the cover of each plant spe-cies or plant group, both in the whole plot and in the respective subsection within the plot, were estimated and the proportion of each subsection was estimated.
2. On every subsection a vegetation sample (500 cm 2 ) was taken in order to quantify the standing crop.The samples were brought to the laboraory, where they were dried, sorted and weighed.
3. From the centre of each plot a 10 m measuring tape was laid out at right-angles to the predominant plough course and along that tape the length each subsection occupied was measured.
4. The height differences between the intact ground level and the manipulated subsections, top of tilt and shoulder, and bottom of ditch, were measured.

Preliminary results and discussion
The material presented below is preliminary and, in many ways, also incomplete.Some data from an earlier pilot study are also included (Eriksson, 1985).

Physical features
The proportion of intact ground on recently ploughed areas varied between 13-22% and on harrowed areas between 48-56%.The values obtained on the ploughed areas agree well with those reported by Kellomaki (1971) and Ferm ÔC Pohtila (1981) from ploughed areas from different parts of Finland.Eriksson (1985) also obtained similar values in his investigation carried out near Jokkmokk in North Sweden.
The heights of the tilts varied form 17 to 27 cm on ploughed areas and from 14 to 15 cm on the harrowed areas in relation to the intact ground.There was, however, no clear reduction in height with time, probably because so few stands have been investigated.

Development of the vegetation
The proportion of litter, mineral soil and humus decreased from 48% to 17% during a period of eleven years on harrowed sites (

Fig. 1 .
Fig. 1.Areas of interest to forestry and to reindeer husbandry in northern Sweden (Mattson, L. 1981).part of the county of Jamtland (Fig. 1).Most of the winter range lies below and east of the cutting boundary for regeneration (Fig.l).In this part of Sweden, logging is the major industry.According to the Forestry Act, all logged areas have to be reforested either artificially by planting or sowing, or naturally from seed trees.(Only Scots pine, Pinus sylvestris, is left as a seed tree, because of the risk of wind-throws which would occur if spruce trees, Picea abies, were left solitary.The current trend is to treat the ground after logging in most sites (Skogs- northern boreal vegetation zone according to Ahti et al,(1968).The study objects are situated between 300 and 580 m a.s.l.The growing season lasts 130-150 days.The temperature sum for the whole region is less than 800°C

Fig. 2 .
Fig 3. Site preparation during the period 1980-87 in the county of Norrbotten (Source: The National Board of Forestry.)

Fig. 4 aGrFig. 4 .
Fig. 4. Harrowed sites of different age.Cover (%) of 7 different groups/ground cover categories on sites of different ages after soil scarification.A = harrowed sites, B=ploughed sites N=number of investigated stands.ploughed areas (Fig. 4 b) before the soil is covered by ground vegetation.The time period is probably a little shorter on harrowed areas (Fig. 4a).The total percentage cover of dwarfshrubs was lower than the mature stand 11 years after ploughing and 16 years after harrowing.The opposite effects were observed for the sum of grasses and herbs (Fig. 4 a,b).The dominant dwarf-shrubs in the study stands were Vaccinium myrtillus, Vaccinium vitis-idae Vaccinium uliginosum and Empetrum herma phroditum.Deschampsia flexuosa was the most common graminoid.Herbs such as Chamaenerion angustifolium, Linnea borealis, Solidago gaurea were quite rare.Pinus and Picea plants, Salix spp.and Betula pubescens were the most fr quent shrubs.Lichens in the study stands were of rare occurrence.