The Karst region stretching bewteen southwestern Slovenia and northeastern Italy, on the edge of the Mediterranean, has long been characterised by summer wildfires. Due to its limestone terrain with virtually no surface water, the region is prone to prolonged summer droughts and therefore to forest fires. The extensive fire from July 2022 will be remembered as the largest wildfire in Slovenia's history (more details on this event here). The fire affected a total of 4500 hectares, stretching in the transboundary area between Slovenia and Italy. In Slovenia it burned an area of 3707 hectares, of which 2902 hecteres were forests. However most of the burned forest was composed of non-native stands of black pine Pinus nigra (planted extensively throughout the Karst in the 19th century) and areas of native thermophilous scrub of relatively low biodiversity importance (bushes, young trees). Therefore the damage done to the ecosystem is relatively low, compared to the economical damage on the value of timber. Fortunately firefighters also managed to keep the flames away from the numerous villages scattered within the wildfire area.
In spring 2023 we set a research group among colleagues and friends, to monitor birds in the burned trans-boundary area. The first breeding season of censuses is over and hopefully we'll be able to monitor the situation on the study plot also in the next couple of years. Results from this year's census are not yet analysed, but here in this post, we'd like to share some first impressions we noted in the field, in the most severely burned patches of forest. During a recent visit (July 2023) to the northern slopes of Renški vrh/Fajti Hrib/Cerje (above the lower Vipava valley between Miren and Renče) we were amazed by the number of birds using the charred black pines for feeding. Actually the forest that most people would term as "dead" is very much alive!
Burned stands of black pine Pinus nigra on the northern slopes of Renški vrh/Fajti hrib, July 2023.
Along a 3,5 km stretch of forest road we made 5 stops/points where we
listened and searched for (mostly) woodpeckers in the most fire-affected
patches of forest. The "count" was not very methodological and accurate
(also due to the time of visit & season), but still gave a rough idea of the importance of such severely burned forest for the local birds. Every point held at
least two Great Spotted WoodpeckersDendrocopos major, with the
highest number of Great Spots counted on one point being four
individuals. In the end we counted a total of 12 Great Spotted
Woodpeckers which were utilising the burned trees for feeding. In
addition we also observed two Black WoodpeckersDryocopus martius
feeding on the charred pines and found many signs of their bill strikes
on the bark. Great Spotted and Black are the commonest species of woodpeckers in forests of black pines in the Karst, so their presence was expected, however local aggregations occur, when feeding conditions are particularly favourable, such in the case of a forest stand damaged by fire. Other less common species of woodpeckers expected to utilise this burned forest include Lesser Spotted Dryobates minor, Grey-headed Picus canus and perhaps even Green Woodpecker Picus virids which was heard on site (the latter usually strictly linked to deciduous stands).
The bark removed from a black pine Pinus nigra by a hungry woodpecker.
Feeding signs of woodpeckers on the charred trunks of black pines Pinus nigra.
Black pines Pinus nigra first hit by the fire and then by woodpeckers.
Great Spotted WoodpeckerDendrocopos major (juvenile) feeding on charred black pines Pinus nigra.
Black WoodpeckerDryocopus martius (female) feeding on charred black pines Pinus nigra.
Great Spotted & Black Woodpecker feeding on burned black pines (video).
Apart from woodpeckers there were also lots of other small songbirds feeding in the burned pine stands. Unusual species for this type of forest (if the forest would be unaffected by fire) were the numerous Black RedstartsPhoenicurus ochruros and Spotted FlycatchersMuscicapa striata, both taking advantage of the more open space in the forest created by the fire and the infinity of suitable hunting perches. However the most numerically common were birds in mixed "gangs" such as GreatParus major, BlueCyanistes caeruleus and CoalTitsPeriparus ater, NuthatchesSitta europaea and Short-toed TreecreepersCerthia brachydactyla, plus locally also larger flocks of ChaffinchesFringilla coelebs feeding on the ground. In some places we also observed Marsh Poecile palustris and Crested TitsLophophanes cristatus, while among the other interesting birds there was also a GoshawkAccipiter gentilis that took off from a burned stand of pines. The latter is a typical breeder of pine stands in the Karst and is one of the species that could have been affected by the loss of nesting habitat. Many of the observed birds were juveniles, as it's typical for this season. And of course only some of them were cooperative enough to be able to photograph them.
Spotted FlycatcherMuscicapa striata in burned pine forest.
Great TitParus major in burned pine forest.
Short-toed TreecreeperCerthia brachydactyla in burned pine forest.
And what were all these birds feeding on in such a "dead" forest? A closer inspection of some burned pine trees revealed that they were alive with bark beetles (Scolytinae), most probably Six-toothed Bark BeetlesIps sexdentatus. Other unusual insects were also present on the trunks, including the impressive shiny-blue bark-gnawing beeetlesTemnoscheila caerulea (Trogossitidae) that feed by predating on bark beetles! For more on these interesting beetles see here & better photos here.
Six-toothed Bark BeetlesIps sexdentatus excavating in the bark of a black pine Pinus nigra.
Temnoscheila caerulea (a species of bark-gnawing beetle; familyTrogossitidae)
Bark beetle outbreaks usually occur as a consequence of natural disturbances in the
forest (fire, windfall, ice storm) that weaken the stands and
make the trees more vulnerable to the attacks of various "pests".
However, from an ecological point of view, such outbreaks are important
events in the forest dynamics. All the invertebrates attacking the dead
and dying trees provide an important food source for
the local insectivorous birds. These in turn act as natural regulators
of the pests' populations. Woodpeckers in particular, such as the Three-toed Woodpecker Picoides tridactylus (absent from the Karst and only found in mountain coniferous forests in Slovenia)
are known to respond to such outbreaks by increasing their population
(up to 44x) in forests affected by bark beetles. In turn Three-toed
Woodpeckers can lower the populations of bark beetles even by 98% (check
this article).
In North America the Black-backed Woodpecker Picoides arcticus is
almost completely dependant on stands of severely burned forest (see here). In
Europe we don't really have such a specialised bird associated with
burned forest, although woodpeckers clearly benefit from beetle-infested trees and many other species benefit from areas opened
by the fire. In the Karst, this is the case for example with Natura 2000 species such as Ortolan
Bunting Emberiza hortulana, Nightjar Caprimulgus europaeus, Woodlark
Lullula arborea, Red-backed Shrike Lanius collurio and other species of endangered grassland habitats.
It remains to be seen (in the next
breeding seasons) if the burned forests are also important as nesting
places, or only as foraging areas for the local birds. However studying birds in the burned stands won't be easy, as few places will remain untouched. The Slovenian forestry is already making the most to remove the burned trees as soon as possible and to save the economical value of timber. Therefore now large areas already look like below...
(why is salvage logging wrong from an ecological point of view in this video).
Salvage logging of the burned black pine forest above the lower Vipava valley near Nova Gorica.
Earlier in spring (May 2023), during our bird censuses on the fire sites, we also came across some exceptional blooms of wildflowers in the more open areas, where the fire burned the thermophilous scrub interspersed with patches of grassland. From the biodiversity point of view this is the most "problematic" habitat in the Karst, as the scrubbing over of once open areas (grasslands & hay meadows) leads to biodiversity impoverishment (lower species richness). In terms of birds, we are losing all those species of conservation priority associated with open habitats that we already mentioned above. At the same time vast areas of impenetrable scrub (with dense bushes of Smoke-tree Cotinus coggygria) or overgrown meadows promote the quick spread of flames in the event of wildfires. Therefore managing open areas with a traditonal, low intensity type of agriculture (extensive grazing & mowing) would be beneficial for biodiversity and for fighting wildfires too!
DropwortFilipendula vulgaris on the burned ground near Brestovica pri Komnu. May 2023.
DittanyDictamnus albus on the burned ground near Brestovica pri Komnu. May 2023.
White LaceflowerOrlaya grandiflora on burned ground near Brestovica pri Komnu. May 2023.
Bloody Pink Dianthus sanguineus on the burned ground near Brestovica pri Komnu. May 2023.
Purple MulleinVerbascum phoeniceum on the burned ground near Brestovica pri Komnu. May 2023.
Amethyst EryngoEryngium amethystinum (with Trichodes apiarius) on Renški vrh in July 2023.
To learn more on the subject of fire ecology and species depending on wildfires, we recommend checking this informative website (and especially the videos) created by Dick Hutto, an emeritus professor in biology and wildlife biology at the University of Montana, who focused most of his research on conifer forests that have been restored by severe wildfires: Fire Ecology Story
Another biodiversity-rich and wildlife-filled year has gone by. Our routine field activities have brought us to many wonderful places, most of them close to home, in the Karst and the Notranjska region of Slovenia. However this year we also spent more time abroad. In April and May we censused rare woodpeckers in the primeval forests of Plitvice National Park in Croatia. In June we went to enjoy some Lammergeiers in the Austrian Alps. In mid August I (Domen) visited Norway on a work trip, with some amazing wildlife seen along the way. And finally in early September we made a road trip to Montenegro, visiting the country's national parks, enjoying great sceneries and finding lots of interesting stuff. However we still haven't found time for detailed trip reports...
As usual, most of early spring was dedicated to censusing woodpeckers, especially Middle Spotted and White-backed, but also Three-toed later in the season. In late spring and early summer, field activity was concentrated in the Karst's limestone grasslands, either counting breeding birds or monitoring rare species such as Ortolan Bunting. Surely one of the year's highlights was seeing seven Brown Bears in one day, while searching (unsuccesfully) for nests of White-backed Woodpecker!
Time for writing blogs this year has considerably shrunk, hence we also moved most of our regular (daily or so) posting to Twitter. Not sure what the new year will bring in terms of free time. Make sure to follow us, either here or there, also in the future. In the meantime, enjoy this selection from our field activities in 2022!
Red-rumped SwallowCecropis daurica, Karst, October.Pair close to an active nest (very rare breeder in Slovenia)
Middle Spotted WoodpeckerLeiopicus medius, Karst, October. A "km 0" Middle Spot! The first observation of the species in the woodland behind our house.
Autumn colours in the mountain beech forests of Snežnik in early October.
Tinder FungusFomes fomentarius, Snežnik, October.
Melanistic Ural OwlStrix uralensis, Kočevsko, November.Pics by Matteo Skodler.
