Nadžak Bilo

Nadžak Bilo Old Growth Forest Reserve, Croatia

Croatia’s largest mountain range, Velebit, also still contains some of Croatia’s most fantastic old growth forest remnants. Among these virgin forests and reserves, many of which are a hundred hectares in area and some which are over a thousand, Nadžak Bilo covers only about 18 hectares. It is also situated by a high and seemingly exposed ridge. How then, has this small forest reserve produced one of Croatia’s greatest groves, perhaps even one of Europe’s? Despite the reserve’s size, Nadžak Bilo contains a great concentration of very large trees, as well as two giant record-breaking specimens. It seems there is no record of why Nadžak Bilo was created or even when, but it seems to be used as a protected forest for research due to its old composition. Nadžak Bilo is an example of how magnificent groves and record trees can be hidden in some of the most remote and seemingly unassuming sites, and it is particularly interesting for studying the generational cycles of virgin forests.

The primary old growth forest of Nadžak Bilo is unique not just on North Velebit but also in Croatia. It comprises several very large sinkholes, slopes, as well as ridges located just below high peaks above the Krasno Valley. Although the virgin forest is not very large it is quite remote, and displays a strong feeling of wilderness. The sinkholes are large enough to act as small valleys in how they influence forest composition, creating a diversity of environments. Within their confines there is deeper soil, greater humidity, and better shelter compared to the surrounding peaks and ridges. This is evident by the lush fern and butterbur (Petasites spp.) undergrowth as well as the moss cover. Because of the topography, highly productive groves of tall trees can be found below ridgetops with short and stunted trees, creating a great contrast. The virgin forest has no signs of human influence aside from research marks and is located at elevations of ~1300-1400m. Climate data from other similar sites on Velebit would put average annual temperatures at under 5oC, while average annual precipitation is over 2200mm, maybe more. Nadžak Bilo is unique for its trees and interesting stages of virgin forest development. Although all stages of forest growth can be observed, the shift from the late optimal and terminal stage to the regeneration stage is especially interesting. Certain parts of Nadžak Bilo have very large and old individual trees, which are also the largest and oldest surviving members of their generation. Immediately around these veteran trees, many of which are dead, there are many young beech trees. When the last giant trees at such sites fall and decay, the young beech forest will leave absolutely no indication that larger trees grew there in the past. Such generational dynamics show how deceiving forest compositions can be, and how current species dominance and age are influenced by the past characteristics of the forest. Studying such situations allows us to understand that human life is just a short glimpse into to the life cycle of a forest.

Cathedral grove with very large dead firs, also young beech trees. The only dead tree still standing as a snag was once the largest known tree in Croatia’s montane virgin forests. Most of the largest trees in the reserve fell or sustained damage within the past 30 years. Such forest composition is common in Nadžak Bilo due to the transition from the late optimal and terminal phase to the regeneration phase. Elevation is ~1350m

The most common trees in Nadžak Bilo are European beech (Fagus sylvatica), European silver fir (Abies alba), Norway spruce (Picea abies), and also sycamore maple (Acer pseudoplatanus). All these tree species reach large size. Expositions face in all directions, but north, east, and west are most common. Typical of karst topography, there are rock monoliths and cliffs scattered throughout the forest. Part of this virgin forest is not explored and there are almost no articles describing it. Perhaps other trees of great height and size may yet be discovered. Because of this, the information presented in this report is directly from personal exploration, as well as our guide who knows the forest well. To reach Nadžak Bilo, a guide should be found.

In nearly all lower mountain virgin forest reserves of Croatia, there are conifers of up to 500cm in cbh (circumference at breast height) and up to ~50m in height. Mountain reserves with favorable conditions comprise a relatively great area, and many of those reserves are about 100 hectares in area or more. And yet, both the tallest and the largest conifers of Croatia’s virgin forests were found within view of one another in Nadžak Bilo’s 18 hectares of virgin forest. One research article claimed that Nadžak Bilo was home to a fir which exceeded 185cm in dbh and over 500 years of age. However, other accounts claimed that this reserve did not in fact exist and was actually managed forest. Before visiting the real reserve, I had considered the possibility that the big fir tree was a misplaced record of the Tsar Fir or “Car Jela”. This tree grows in the same region of Velebit and it is claimed by some sources to be the largest fir in Europe. Truly, it is a giant tree with an almost taperless trunk, cbh of well over 630cm, estimated volume of 60 m3 or more, and a height of 48m with a heavily damaged top, probably struck by lightning in the past. The age was estimated at about 500 years, and judging by the width of the trunk at the break, the former height may have been about 55m or more. However, when I finally visited Nadžak Bilo reserve, it became clear that there were other giant firs in these mountains. The bumpy forestry roads and steep hikes lead to a seemingly insignificant forest covered ridge which seemed like the worst site to find large trees. And yet, upon reaching the ridgetop a large depression was revealed on the other side of the slope. There less than a hundred metres down into the sinkhole, are the remains of a titan among trees which may have been alive when Columbus landed in the Americas.

Even in its decayed state, the snag of the Nadžak Bilo fir is still clearly larger than any other tree found in Croatia’s montane virgin forests. The cbh was nearly 700cm, and its volume was estimated to be about 60 m3 when alive based on what is left of the trunk. The height was never measured but other firs of smaller size and younger age nearby exceed 45m. Naturally, an even greater height could have been expected for such an old tree. Elevation is 1340m

This fir of Nadžak Bilo is now dead, but when alive it was certainly the largest tree of Croatia’s montane old growth forests. It was clearly far larger than any other trees in Nadžak Bilo, some of which are also of great dimensions. Judging from what is left of the giant snag, this tree was probably close to about 60 m3 in volume when alive. Its height was never measured but other far younger firs in the reserve can exceed 45m, so a tree of this age and size could have been well over 50m tall. It even appears to be wider than the Tsar fir at ~700cm in cbh, however this may be due to its position on a slope and the Tsar’s position on flat ground. The midslope cbh point of a tree growing on a steep slope is often measured slightly above the ground on the tree’s higher side. This seems to make the cbh of trees on slopes larger compared to trees on flat ground, even if they are of otherwise equal shape and trunk volume. When the cbh is measured from the highest ground level, it is about the same (over 630cm) for both firs.

Where there is one giant tree there will be another. Just slightly lower on the same slope, an old Norway spruce becomes visible, towering above the forest floor like a giant column with seemingly no end or sign of taper. However, looking high up through the canopy reveals it to have a broken trunk, rather than a distant top touching the sky. The spruce of Nadžak Bilo may have been the tallest native tree of Europe once, and it is still alive but presently its trunk is broken at around 35m. The upper half lies next to the base and was measured to be unbroken for another 24m all the way to the shattered top. Judging by the width of the top at the shatter, it was estimated to be at least 5m longer when unbroken by our experienced guide from the Velebit Nature Park. He had seen the whole tree in the past and remembers it towering above all the other tall specimens around it. This final estimate would result in a tree which would be at least 64m tall, making it the tallest of its species on record as well as the tallest native tree of Europe! The tree is also massive with almost no visible trunk taper and has a cbh of about 550cm. The trunk volume is estimated to be ~45 m3 before the break, and it may have also been the largest known spruce of Croatia, along with the largest specimens of Štirovača.

However, as this spruce’s trunk has broken and the true top is reduced to splinters, there is no way to confirm such precise measurements and find its exact height. Regardless, it is undoubtedly one of the tallest Norway spruce trees ever recorded, and certainly the tallest in Croatia. Along with this tree our guide mentioned another spruce of similar size which was uprooted by a storm, but we did not visit this site yet. Immediately next to the broken but still living Norway spruce, there is another huge fir whose trunk is also broken in half but the tree is still alive. It has a cbh of about 515cm and when intact it may have been up to 35 m3 in volume.

Beech, fir, and spruce forest with some very large conifers. In the foreground is the largest living fir found in Nadžak Bilo, while the large tree in the left background is the largest and tallest spruce. Both trees have had about half their trunk knocked off, but are still alive. The spruce has a cbh of about 550cm and was estimated at about 45 m3 of volume when intact. It was also estimated to be at least 64m tall when undamaged, and even today the standing tree and fallen trunk still amount to 59m. The fir has a cbh of about 515cm and was estimated at about 35 m3 of volume when intact. In-between these old trees are many young beech trees, signaling the regeneration which will take over once these old trees die and decompose. Elevation is ~1350m

Aside from these giant trees, other large fir and spruce can be 440–500cm in cbh and ~50m in height. The beech groves are fantastic, and some trees are over 350cm in cbh and 40m in height. Nadžak Bilo does not have quite the diversity of some other forests due to its small size. However, its remote location near the peaks, contrast between ridges and sinkholes, preservation, record trees, and incredible scenery mark it as one of Croatia’s greatest forest reserves.