woodlandheritage.org

CONTINUOUS COVER FORESTRY GROUP
STUDY TOUR: LINGST, AUSTRIA
Hosted by Professor Josef Spoerk. 16-18 September 2003

We would like to begin by sincerely thanking Woodland Heritage for generously providing our Garthwaite Bursaries, enabling four foresters to travel to Austria and gain a valuable insight into continuous cover forestry and target diameter management.

As in the UK, continuous cover is the exception rather than the rule, and the vast majority of forests are still managed as even-aged plantation. The use of target diameter thinning to improve stand quality and provide conditions where natural regeneration can establish has become more widespread in recent years. The concept of Potential Natural Vegetation (PNV) is an integral part of forest management, and a strong emphasis is placed toward working with natural processes.

The forests of Furstenfeld, Hebalm and Sommereben, where the study tour took place, are situated in south-east Austria at the foot of the Alps near Ligist. These forests are owned by the Knights of Malta, and have been managed in succession by Josef’s father, Josef, and most recently by his son. All the sites were originally even-aged plantations managed on a clearfell system. In the 1970s the owners accepted Josef’s proposal to initiate transformation of the estate to continuous cover on the grounds of increasing profitability.

Frame Tree Marking and Structure Thinning in Norway Spruce Stands.

This sub-montane forest (1000- 1300m a.s.l, 1500ha) is comprised of spruce and beech, with a smaller component of rowan. Previous management dates back to the 1920’s when large scale clearcut systems were used, these gradually progressed into strip felling systems employed until the 1970s.

The economic output of the forest under the old system was particularly poor and the cost of restocking high, made worse by severe Hylobius infestation. There were also concerns about the biodiversity of the forest, specifically capercaillie which at the time were under threat because of the absence of old growth trees.

Since the early 1970s, the focus has been on the application of single tree and group selection systems. As a result, a 10% reduction in harvesting costs has been achieved. Costs fall and level out as production increases, underlining the importance of maintaining the forest’s productivity. The reliance on natural regeneration eliminates the cost of restocking. Natural regeneration, although reliant on careful manipulation of the canopy, occurs readily in the right conditions. This increased economic productivity more than compensates for the increased management costs associated with this type of system.

The focus for the day was the marking of a stand of spruce in the earlier stages of transformation.

Photo 1: From the left – Paul Schofield, Scottish Native Woodlands; Ian Barrington, Pryor & Rickett Silviculture; Ilia Osepashvili, PHD Student, Norwich; Mike Chapman, North York Moors National Park.

The criteria for selection were as follows:

• Selection of ‘F1’ trees. Dominant or co-dominant trees of the highest quality (but not necessarily diameter), which will reach marketable maturity first. Density: 150-200/ha
• Selection of ‘F2’ trees. Sub-dominant trees of high quality and potential, successors to the F1 trees on their removal. Density: 100-150/ha
• Removal of trees of a profitable dimension, trees that are of poor health or those that are likely to compete with the development of F1 trees or would begin to suppress F2 trees, in particular, the removal of ‘wolf trees’.
• Avoiding clusters of F1 or F2 trees, in order to maintain the high diversity level in canopy structure.

The graph above shows a diameter distribution of recorded diameters of: a) F1 and F2 trees, b) unmarked trees, c) trees to be felled.

Photo 2: Regeneration of oak, silver fir and beech marked beneath 120yr old spruce stand. Note the amount of side light caused by sanitation felling and windblow clearance (visible in the background).

This example highlights the overall distribution of diameters, which is near to being a normal distribution. The selection of trees to be felled seeks to favour those trees identified as F1. This is comparable to crown thinning, or thinning from above. It should be noted that the removal of F1 would only occur when the tree reaches its maximum marketable value, and that they would not all be removed in one intervention. Felling F1 trees any earlier than their maximum economic potential was compared to removing the best machines from a factory. Following the thinning, the diameter distribution would shift toward to the typical ‘J’ curve associated with uneven-aged stands. Although the diameter distribution approximates that in a selection or ‘plenterung’ system this is not a particular objective. The trees selected for felling in the larger diameter classes are typically wolves or damaged trees. Few trees in the smaller classes were selected because they don’t represent competition with the F1 and F2 trees and their extraction would be uneconomical. Within the marked area it was interesting to note that there was very little ground vegetation, and only very occasional signs of regeneration. When selecting trees, it was important to ensure that too much light didn’t enter the stand, in order to prevent excess ground vegetation which would limit the success of future regeneration.

In order to allow repeated interventions every 6-8 years, a comprehensive system of roads (50m/ha) and tracks (100m/ha) was considered essential. With such a road system in place it becomes possible to concentrate on the promotion of the best individual trees through the rebuilding phase.

Marking for Multiple Objectives and Stand Enrichment.

At Sommereben the forest (800-1000m a.s.l, 1000ha) is dominated by Norway spruce, following clearfelling and replanting that took place in the early twentieth century. The potential natural vegetation includes spruce, fir, larch and beech, with the composition of species varying by the altitude. Namely, the lower slopes are predominantly occupied by oak, with beech and silver fir being more prevalent at higher elevations.

Although the stand appeared to be of excellent quality we were informed that the condition of some parts of the forest was sub-optimal. It was explained that the impact of previous management, primarily the dominance of spruce and prolonged sheep grazing, has resulted in a lower soil pH with a consequent loss of increment over the life of the stand. Current management has provided conditions that favour the natural regeneration of silver fir, sycamore, beech and larch and reduce the regeneration of Norway spruce by keeping light levels low. Another priority is to retain a certain number of poor-quality broadleaved trees and dead wood to promote biodiversity. Increasing the proportion of broadleaves and moving closer to the PNV (Potential Natural Vegetation) of the site will also lead to increased fertility through higher rates of nutrient cycling leading to improved long-term productivity.

The marking took place in a predominantly evenaged stand of spruce approximately 90 years old. The range of species diameters was ‘normal’ in distribution, though the number of trees standing per hectare was only 340. In the exercise, the median DBH for all trees was 37cm. This meant that the goals of marking included harvesting larger material, maintaining a species mixture and promoting F2 trees. Of the trees that were marked for felling, the median DBH was higher than the average, at 42cm. The primary focus on selection was to (further) improve the quality of the stand by removing trees of ill health, damaged stems or crowns in order to allow space for further increment on the potentially most valuable trees. At the same time, an attempt was made to maintain small canopy gaps (through the removal of limited volumes of wood) to promote the regeneration of silver fir.

There was more regeneration on the ground here (10000 spruce/ha; 7000 fir/ha, 4000 rowan/ha, 2000 beech/ha) than at Hebalm, which had established ahead of Deschampsia flexuosa (which had become quite dense in place and less penetrable to seed). In those locations where the number of trees/ha was greater (and light levels lower), the regeneration was almost entirely silver fir – being too dark for spruce to become established.

The size and quality of the trees available for selection is reflected in the financial performance of the estate. By selecting trees of larger diameters, fewer trees per hectare are removed and harvesting costs are reduced. For the period 1996-2000, the yield averaged 16000m3 for the whole estate, of which 80% was sawlog (20cm), 17% small round wood and 3% firewood. For comparison, clearfelled forests in the region typically produce some 10% more pulp. Since 1980, the average log diameter has increased by some 19% to 23.6cm. In 2002, the net profit of the estate was 27% of the turnover, considerably more than other private forests in the region managed on the clear fell system. This is an interesting and somewhat sobering statistic when one considers that the total return for UK forestry in the same year was minus 4.6% (IPD UK Forestry Index 2003). The annual cut in one section of the forest rose from 4,000m3 to 6,500 m3 between 1971 and 2002, an increase of 64%. This highlights the importance of the promotion of F1 type trees to provide a consistent volume at a consistent dimension, and consequently maximising the financial return from the stand.

Both the stand types and history of previous management seen in Austria provided useful comparisons with forest conditions encountered in the UK. The approach outlined by Professor Josef Spoerk during the tour was based on the premise that the achieving economic success was determined by understanding the forest ecology of the location. The strategies employed allowed maximum choice and by having inbuilt flexibility the systems were both economically and ecologically robust. The success of this approach was demonstrated by sustained financial returns and increases in profit, increment and forest productivity.

Photo 3: Spruce regenerating beneath openings in the canopy.	Photo 4: Norway spruce planted in 1910. Average standing volume is 550m3/ha.

During the conversion of a plantation, the primary driving force should be the promotion of high quality and good health in trees with the greatest potential, and not necessarily the release of natural regeneration that may be establishing beneath. Trees of little marketable value that do not pose a threat to the development of F1 and F2 trees and regeneration and are uneconomical to harvest should be left. In the long term, their retention may contribute to an increased deadwood resource. Manipulation of light will play a key role in the species that will regenerate. It is also critical not to allow too much light into a stand too soon, and certainly not before regeneration has begun to appear, in order to prevent the competition from ground vegetation. Only after the natural regeneration has apparently succeeded, can the canopy be opened.

The acceptance of a wider range of species in regeneration will make the conversion process easier, as there is the scope to re-space some regeneration at a later stage to promote desired species. External factors such as wind, insect attack and deer can still provide an opportunity for conversion (and reduce associated costs), but may restrict conversion in terms of range of species or density of regeneration.Supplementary planting should be seen to be of benefit in providing a wider species distribution.

In the UK, we often hear continuous cover justified in terms of the obvious landscape and bio-diversity benefits. The economic advantages, however, are often less well understood. The Austrian experience clearly indicates that economic factors are often equally as important as ecological ones when making the conversion to continuous cover forestry. In this case, one of the main factors that has contributed to improved economic performance is the improved quality that has been achieved using the single tree selection system. The best trees are felled when they reach a suitable target diameter and earlier interventions concentrate on promoting the growth of these trees.

The approach and methods that we were shown were of course tailored to the particular conditions of that region. Clearly, transforming plantations in the UK will have its own particular challenges, some not always obvious, but the Austrian tour demonstrated how impressive results can be achieved in a relatively short period of time from a starting point not entirely dissimilar from our own.

Ian Barrington, Mike Chapman, Paul Schofield and Ilia Osepashvili