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 Woodpeckers Dendrocopos 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 Woodpeckers Dryocopus 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 Woodpecker Dendrocopos major (juvenile) feeding on charred black pines Pinus nigra.|
|Black Woodpecker Dryocopus martius (female) feeding on charred black pines Pinus nigra.|
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 Redstarts Phoenicurus ochruros and Spotted Flycatchers Muscicapa 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 Great Parus major, Blue Cyanistes caeruleus and Coal Tits Periparus ater, Nuthatches Sitta europaea and Short-toed Treecreepers Certhia brachydactyla, plus locally also larger flocks of Chaffinches Fringilla coelebs feeding on the ground. In some places we also observed Marsh Poecile palustris and Crested Tits Lophophanes cristatus, while among the other interesting birds there was also a Goshawk Accipiter 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 Flycatcher Muscicapa striata in burned pine forest.|
|Great Tit Parus major 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 Beetles Ips sexdentatus. Other unusual insects were also present on the trunks, including the impressive shiny-blue bark-gnawing beeetles Temnoscheila caerulea (Trogossitidae) that feed by predating on bark beetles! For more on these interesting beetles see here & better photos here.
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
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!
|Dropwort Filipendula vulgaris on the burned ground near Brestovica pri Komnu. May 2023.|
|Dittany Dictamnus albus on the burned ground near Brestovica pri Komnu. May 2023.|
|White Laceflower Orlaya 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 Mullein Verbascum phoeniceum on the burned ground near Brestovica pri Komnu. May 2023.|
|Amethyst Eryngo Eryngium amethystinum (with Trichodes apiarius) on Renški vrh in July 2023.|