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 534 m to 638 m. The forests of the park are quite well preserved and cover great areas from approx. 400 m to nearly 1300 m 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 50 m tall and over 400 cm 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 ha 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 m and has average annual temperatures of about 6°C. The average annual precipitation is about 1900 mm, 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.
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 860 m. 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 900–1400 m 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 approx. 50 m, with cbh of fir up to 440 cm and spruce up to 410 cm. However, there are also records of a 58 m tall fir, as well as firs up to 170 cm in dbh (diameter at breast height). Currently the national park site lists a fir tree of 500 years old, 150 cm in dbh (probably measured from high slope), and a height of 58 m. 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 58 m 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 149 cm, 112 cm for spruce, and 193 cm 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 149 cm, but also a max height of 58 m belonging to another tree with a dbh of 148 cm. It is not impossible that the 149 cm and 148 cm tree are the same tree simply listed incorrectly as two different specimens. It is even possible that the supposed 58 m 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 170 cm and 150 cm 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 50 m in the best stands; while beech is often over 40 m. Tallest trees measured were a spruce of 53 m (photo right) and a beech of 44 m. The largest tree found was a spruce of over 500 cm 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.
DJ
References:
https://hrcak.srce.hr/file/48592
https://zir.nsk.hr/islandora/object/sumfak:1317/preview
https://np-plitvicka-jezera.hr/prasuma-corkova-uvala/
