Čorkova Uvala | Europe's Virgin Forests

Čorkova Uvala Old Growth Forest Reserve, Croatia

Within the borders of Croatia’s most visited and famous national park, Plitvice Lakes, lie some of the largest areas of protected forest in Croatia. Of all these forests the grandest is the virgin forest of Čorkova Uvala. In this park karst geology and water phenomena meet, resulting in a river canyon containing 16 lakes of varying colors from deep blue to clear. But the true splendor of Plitvice are the waterfalls that connect these lakes, forming countless cascades of varying size in one of the most stunning and unique waterfall displays on Earth. The lakes range in elevation from 534m to 638m. The forests of the park are quite well preserved and cover great areas from ~400m to nearly 1300m in elevation. Despite the presence of only two true old growth forests, Čorkova Uvala and the beech virgin forest of Medvedak, the whole park is full of relatively old and natural forest. Some locations like Crna Rijeka even have spruce up to 50m tall and over 400cm in cbh (circumference at breast height).

Čorkova Uvala Reserve is the first old growth forest reserve declared in Croatia along with the old growth reserve of Štirovača Valley, back in the year 1965. Čorkova Uvala is the best researched out of all the old growth mountain forests of Croatia, as well as the most famous and undoubtedly among the most beautiful. It is a perfect example of a typical beech-fir forest which forms in depressions and on slopes. The virgin forest covers some 80 hectares of productive beech (Fagus sylvatica), fir (Abies alba), and spruce (Picea abies) forest. Sycamore maple (Acer pseudoplatanus) can be found occasionally. Čorkova Uvala comprises elevations of ~860 to ~1028 metres and has average annual temperatures of about 6°C. The average annual precipitation is about 1900mm, and terrain ranges from gentle slopes and sinkhole valley bottoms to steep slopes. Soil is deep in certain areas but may also be very shallow and rocky in places. Karst topography is well developed, with sinkholes, cliffs, and ravines. Slope expositions are mostly East or Northeast, but all expositions can be found. The name Čorkova Uvala comes from the meadow and former settlement in the larger valley nearby. The old growth forest occupies a section of this larger valley. The forest is very well preserved, with lots of deadwood and impressively tall and large trees. Only indications of human activity are research marks and a few individual stumps, reminders of the long-gone inhabitants of the nearby village. Access is almost impossible without a guide and would require a few hours of one way hiking to reach otherwise.

Old growth forest in Čorkova Uvala with large fir and spruce trees. Dense undergrowth and slope towards the lower parts of the reserve can be seen below. Elevation is ~950m

Čorkova Uvala probably has among the highest silver fir frequency of the virgin forests of Croatia, and therefore also has a great number of large firs. It is also one of the lowest elevation virgin forests to contain fir and spruce in Croatia at 860m. This is most likely due to its position further into the continent with colder climate. In contrast, virgin forests of similar compositions closer to the Adriatic Sea usually grow at 900m–1400m above sea level.

There are many studies done on Čorkova Uvala, but also many contradictions, mostly regarding tree dimensions. Perhaps this results from different measurement methods. Previously, the national park website listed the max height of spruce and fir trees at ~50m, with cbh of fir up to ~440cm and spruce up to ~410cm. However, there are also records of a 58m tall fir, as well as firs up to 170cm in dbh. Currently the national park site lists a fir tree of 500 years old, 150cm in dbh (probably measured from high slope), and a height of 58m. However, the validity of those measurements is not confirmed by this report, and the different dimensions may be separate maximum measurements belonging to several different trees. This fir is claimed to be the tallest tree of Croatia, but we measured a now broken Norway spruce in the virgin forest of Nadžak bilo which was several metres taller. There was also a spruce tree of similar height to this fir in the virgin forest of Štirovača. However, if this fir is in fact 58m tall, then it may be the tallest living tree in Croatia. Unfortunately, the confusing mix of different claims regarding Čorkova Uvala makes it difficult to determine which source is most accurate. One source even lists the max dbh for fir as 149cm, 112cm for spruce, and 193cm for beech! Beech is not known to reach such a dbh when it grows in a natural forest. Furthermore, larger spruce trees clearly exist like the one described on this report. Yet another study lists the max dbh for fir as 149cm, but also a max height of 58m belonging to another tree with a dbh of 148cm. It is not impossible that the 149cm and 148cm tree are the same tree simply listed incorrectly as two different specimens. It is even possible that the supposed 58m tall tree is not very wide at all or that the height is an old inaccurate measurement done without modern laser technology. The differences between the ~170cm and ~150cm dbh measurements may be due to the differences between mid-slope and high-slope measurements. Further exploration would help to confirm or disprove these claims.

Regardless of the conflicting measurements and possible exaggerated claims, the trees in Čorkova Uvala can certainly grow quite large due to the favourable conditions, and the groves are well stocked, with nearly 800 m³ of living wood having been measured in a small plot. It is likely that some other hectare sized plots would yield over 1000 m³ of living wood. All regeneration and structural compositions of virgin forests can be found here, and there are open tall groves as well as dense sapling regeneration. The forest displays both dense undergrowth and clean forest floor depending on site conditions. Stony outcrops and sinkholes create diverse and interesting terrain, causing variations in tree development. Tree maximums are probably comparable to what can be found in other productive mountain forests of Croatia listed on this site. Unfortunately, most of Čorkova Uvala’s area has not yet been fully explored for this article.

Generally, Čorkova Uvala’s landscape is one of relatively dense and tall groves with occasional large trees interspersed between lush sinkholes and stony ridges. Most notable is a great variation in growth conditions depending on soil and terrain. Where there is deep soil and level or gentle terrain the forest develops into an archetypal example of a towering cathedral typical of the best growing sites for this zone in Europe. Spruce and fir regularly reach up to 50m in the best stands; while beech is often over 40m. Tallest trees measured were a spruce of 53m (photo right) and a beech of 44m. The largest tree found was a spruce of over 500cm in cbh with an estimated volume of over 30 m³. Due to its position within the national park, Čorkova Uvala is surrounded by relatively intact wilderness areas, making it the crown jewel of one of the largest and wildest protected forest ecosystems in Croatia.

References:

https://hrcak.srce.hr/file/48592

https://zir.nsk.hr/islandora/object/sumfak:1317/preview

https://np-plitvicka-jezera.hr/prasuma-corkova-uvala/

Cathedral groves of large conifer trees and lush undergrowth are characteristic of the best groves of Čorkova Uvala. The largest tree next to the person is a fir of ~440cm in girth; the other trees are spruce and beech. Elevation is ~950m

Dense collections of towering trees occupy the gentler sites of the reserve where terrain is less rugged. Some of the spruce and fir in this stand reach 50m in height. Abundant fir regeneration can be seen around the large spruce in the foreground. Elevation is ~850m

Old spruce trees often form imposing groves in Čorkova Uvala. Despite literature recording fir as the largest species of the reserve, the largest trees personally measured for this report were spruce. Elevation is ~850m

Cathedral grove dominated by large spruce trees and a few firs. Dense undergrowth of ferns. Elevation is ~960m

Shady grove with large fir and spruce trees, also a few beech trees. For scale, the man in the photo is about 193cm tall. Elevation ~950m

Large fir growing on the stony edge of a sinkhole, with a girth of ~440cm and height of ~40m despite a heavily damaged top. Undergrowth of the left foreground is hart's-tongue fern (Asplenium scolopendrium), which is abundant in Čorkova Uvala. It is interesting to note that this fern appears to be very rare in coastal beech, fir, and spruce virgin forests of Croatia. Elevation is ~900m

Two large spruce trees growing on a small ridge between two sinkholes. This type of topography is typical for Čorkova Uvala. The larger of the two is seen to the left with a notable corkscrew shaped lightning scar running down its wavy trunk. It is the widest tree recorded for this report. Elevation is 830m

Dense undergrowth below a grove of beech trees. The large tree shown right is the tallest beech measured with a height of 44m. Elevation is ~900 m

Large trees from left to right are fir, spruce, and beech. Elevation ~960m

Large firs of nearly 50m tall growing on gentle slopes at the edge of a small valley at ~850m

Dense stand of large conifers with abundant fir and spruce regeneration at ~850m

Steep stony slopes give way to lush undergrowth at the bottom of sinkholes. This stark contrast and variation between growing sites is a relatively common feature of karst bedrock, however the phenomenon is especially well developed in Čorkova Uvala. Elevation is ~850m

Large spruce tree, deadwood, and fir regeneration. Elevation is ~970m

Large mossy fir tree in the center, also the bark of spruce tree to the left. Elevation ~950m

Small windthrow with fallen trunks on the edge of a sinkhole. Cliff outcrops like the one on the right are especially common on ridgetops or hills. Elevation is ~900m

Young beech trees and the decaying snags of large fir trees. Each of the snags can be seen in a progressively greater state of decomposition from left to right. Elevation is ~900m

Large examples of hart's-tongue ferns. Also a sycamore maple in the center of the photo. Elevation is ~900m

Largest recorded spruce of Čorkova Uvala. Girth is ~500cm and volume is estimated at up to 30 cubic meters. Height is only 43m as lightning appears to have damaged the top. Elevation is 830m

The largest spruce tree measured, as well as the largest tree measured in this part of Čorkova Uvala. It has a cbh of about 470cm and an estimated volume over 30 cubic meters. Elevation is ~970m

The tallest measured spruce (53 m)

Čorkova Uvala valley and meadow. This meadow was the site of the former village of Čorkova Uvala from which the old growth reserve got its name. The old growth forest is in the near vicinity of this meadow. The highest peak visible to the far left is named Cigelj, and it is also the second highest peak in Plitvice National Park at 1252m

Čorkova Uvala meadow at 830 m in July. Cigelj peak rises above the valley