Perućica Nature Reserve, Bosnia and Herzegovina

Perućica (14 km²) is a part of Sutjeska National Park and is known as one of the best primeval forests in Europe because of its size, intactness and beauty. The national park forests outside Perućica are unfortunately still logged by national park staff, but most of Perućica itself is old-growth forest. There are a few small patches of meadow and young forest where grazing occurred in the past¹; the virgin forest begins immediately beside these patches, with no signs of human activities. The preservation of the virgin forest is a result of the lack of road connections until recent times². A bumpy road running through Perućica near its upper boundary was constructed in the 1950s ³. The alpine pastures above the reserve are still grazed by cattle and sheep but they only use the forest edges under very dry conditions³.

The reserve consists of almost the entire Perućica Creek catchment at approx. 600–1800 m elevation (photo below). Average annual temperature is 8.6°C at 700 metres and 5.9°C at 1300 m. Annual precipitation is 1400 mm at 700 metres and 1900 mm at 1300 m, 15 % of which falls during the three summer months². Soils are fertile and deep, derived from limestone and dolomite on the upper slopes and sandstone and shale at lower elevations ³. In the centre of Perućica there is a 75 m high waterfall Skakavac. The area below the waterfall in the northwestern end of the reserve is a steep gorge which is currently almost impossible to enter: the only entry point, with slightly gentler slopes, would be through Sutjeska Canyon, but this is the only part of Perućica suspected of having land mines from the Bosnian War⁴. Above the waterfall from the elevation of approx. 1000 m upwards, gentler and steeper slopes alternate; there too, Perućica Creek and its biggest tributary Prijevorski form steep gorges in places. The highest summit of Bosnia-Hertsegovina, Maglić (2386 m), rises above Perućica.

European silver fir (Abies alba) dominates the uppermost canopy perhaps more heavily than in any other old-growth forest, which can well be seen from the ridges above the forest limit (photo above). Here and there, patches of European beech (Fagus sylvatica) forest can be seen. Beech also grows in the fir dominated forest but does not become particularly large and straight-trunked there. The third most common tree is Norway spruce (Picea abies). Since the 1950s, the share of beech has increased and that of spruce has decreased⁵. Other canopy species include sycamore maple (Acer pseudoplatanus), wych elm (Ulmus glabra) and European ash (Fraxinus excelsior). Closer to the forest limit, Heldreich’s maple (A. heldreichii) gradually replaces sycamore maple. Unlike in many other forests, including Central Europe’s old-growth forest remnants, silver fir regenerates well in Perućica due to healthy predator populations⁴ and consequently low densities of large herbivores (roe deer (Capreolus capreolus), red deer (Cervus elaphus) and Balkan chamois (Rupicapra rupicapra balcanica)). The forest is heavily stocked; as much as 1870 m³/ha of living wood have been measured in a small research subplot², though this figure does not apply to the entire area. When measured over a larger area the growing stock is 937 m³/ha ⁵. Dead wood is abundant, 406 m³/ha ⁶. The oldest beech trees are as old as >500 years ³. Undergrowth is variable and abundant: sanicle (Sanicula europaea), sweet woodruff (Galium odoratum), wild garlic (Allium ursinum), wood sorrel (Oxalis acetosella), blackberries (Rubus spp.), greater wood-rush (Luzula sylvatica), ferns etc. In the steep lower-elevation gorge, in addition to beech, more drought resistant trees dominate, e.g. hop hornbeam (Ostrya carpinifolia), Oriental hornbeam (Carpinus orientalis), manna ash (Fraxinus ornus), Cornelian cherry (Cornus mas), common aspen (Populus tremula) and black pine (Pinus nigra). Perućica’s forest landscape of is very variable: there are smaller and larger windfall gaps, stands with many layers and abundant regeneration, but also cathedral groves with little or no regeneration. This, combined with the rich undergrowth, makes Perućica a very aesthetic forest.

Many European dendrologists remember Perućica as the place where the tallest Norway spruce (63 m) and European silver fir (65 m) are said to have been measured. These trees were measured by Prof. Hans Leibundgut and Prof. Konrad Pintarić in 1954. The measurements are so old that they must have been made using the tangent method, which often results in over-measurement⁷. In addition to this uncertainty, the reliability of their data is weakened by the fact that it varies in their several reports on the tallest trees:

These inconsistencies seem to suggest old men looking back on their youthful adventures without notes! The measurements by Jeroen Philippona***, Michael Spraggon and KR in 2012, by Jeroen in 2013, and by KR and TM in 2019 with Nikon 550 and TruPulse 200X laser instruments, gave the maximum height of Norway spruce as 57.8 metres and that of silver fir as 54.8 metres. Norway spruce of about 55 metres are not rare in favourable sites, with silver fir being regularly a few metres lower. Of course, it is possible that we have failed to find the tallest trees. Leibundgut and Pintarić did not publish the locations of the tallest trees and unfortunately both professors have already passed away. Nor does the national park administration know the tallest trees. Currently, the tallest reliably measured Norway spruce is 62.7 m and is located in Slovenia⁸. The tallest reliably measured European silver fir was 59.7 m and grew in Biogradska Gora National Park in Montenegro.

*** Jeroen’s www-site: bomeninfo.nl/english1.htm

KR & TM

References:

1. Nagel, T. A. & Svoboda, M. (2008): Gap disturbance regime in an old-growth Fagus-Abies forest in the Dinaric Mountains, Bosnia-Herzegovina. Can. J. For. Res. 38: 2728-37.
2. Leibundgut, H. (1982): Europäische Urwälder der Bergstufe. Haupt.
3. Nagel, T. A., Svoboda, M. & Kobal, M. (2014): Disturbance, life history traits, and dynamics in an old-growth forest landscape of southeastern Europe. Ecological Applications 24(4), 2014, pp. 663–679.
4. Sutjeska National Park, pers. comm. (2012)
5. Keren, S. et al. (2014): Comparative Structural Dynamics of the Janj Mixed Old-Growth Mountain Forest in Bosnia and Herzegovina: Are Conifers in a Long-Term Decline? Forests 5(6), 1243–1266.
6. Motta, R. et al. (2014): Development of Old-Growth Characteristics in Uneven-Aged Forests of the Italian Alps. Eur. J. For. Res.
7. Bragg, D. C., Frelich, L. E., Leverett, R. T., Blozan, W. & Luthringer, D. J. (2011): The Sine Method: An Alternative Height Measurement Technique. The Forest Service, United States Department of Agriculture, Research Note SRS-22.
8. https://www.monumentaltrees.com/en/