The condition of the epiphytic lichens of dark coniferous forest in the area of the outbreak of ips sexdentatus boern on the Maly Abakan site of Khakassky nature reserve

The study presents data on the condition of the t halli of epiphytic lichens, their occurrence and projective cover on the sample plots located in the area of the outbreak of Ips sexdenta tus Boern on the Maly Abakan site of Khakassky Nature Reserve.


Introduction
The Maly Abakan site of Khakassky State Nature Reserve is situated in the Tashtyp district of the Republic of Khakassia. In the territory, three main types of the landscape can be identified: the Alpine high-mountain landscape, the massive high-mountain landscape and the mid-mountain erosive landscape [2]. The study was conducted in the mountainous taiga vegetation belt represented by dark coniferous forest. The Siberian nut pine and the fir are the main trees of this forest.
Lichens represent one of the significant components of the forest communities. The species composition and the living forms of epiphytic lichens are closely connected with certain environmental factors and naturally vary as the environmental conditions change. For example, density and extension of the canopies of the trees described is one of such factors [1,[9][10].
For several decades, the reserve scientists have been investigating the impact of the bark beetle Ips sexdentatus Boern., which results in mass drying out of the trees [3][4][5].

Materials and methods
In 2019, we conducted a study of the species composition of the epiphytic lichens on the Maly Abakan site of Khakassky State Nature Reserve in the areas most infested by Ips sexdentatus [9][10]. Four permanent sample plots were selected (sized 20x20 m), located on two sites: near Nizhny post (further referred to as 'Nizhny' site and near the mouth of the Otkyl River ('Otkyl' site). Two sample plots were flawless (with trees not infested by the bark beetles), and two sample plots contained trees infested by the pest. On each site under study, 10 phorophytic trees selected belonged to Pinus sibirica Du Tour, and 5 -Abies sibirica Ledeb. [9][10]. Each tree was divided into zones: the lower part of the tree trunk, the trunk and the canopy. From all the sides, the projective cover of epiphytic lichens was determined for each tree using the method of line intersects [8]. The lichen thalli were studied on the intersection with the measuring tape (with millimeter graduation), applied horizontally to the tree trunk at a certain height (0.6 m; 0.9 m; 1.2 m; 1.5 m). The sum of the lengths of the thallus parts of lichens of a certain species divided by the length of the entire horizontal section was taken into consideration. The linear projective cover (PC) for the domineering species of epiphytic lichens was calculated as an integral value (average for all the trees and for all the heights).

Results and discussion
For two plots under study, 46 species of epiphytic lichens were identified, referring to 24 genera and 13 families. The small species variability of the epiphytic lichens in the dark coniferous forest may be caused to the high degree of canopy density in the territory under study (0.7-0.8) and by the other factors (the height and age of the phorophytic tree).
The total number of the identified lichen species on Pinus (on all the plots) was 34, and that on Abies was 32. Depending on the number of the infested phorophytes, the epiphytic lichens found on the plots could be divided into two groups: stenotopes -species found only on one phorophyte (26 species), and olygotopes -species found on Pinus and Abies (22 species).
Thus, foliose epiphytic lichens occur most widely in the said territories. On all the sample plots, the species Hypogymnia vittata is common. This epiphytic lichen has become well-adapted to the conditions of the locality under study. The occurrence and projective cover of the other types of epiphytic lichens are much lower.
Consider the composition of the domineering species of the epiphytic lichens and variation of their linear projective cover (PC) on the flawless sample plots and on the infested plots under study ( There is no clear regularity in the increase or decrease of the projected cover of lichens on the flawless and damaged sites in terms of the complex of the range of species. For instance, on the Nizhny site, the PC of Hypogymnia vittata (both on the Siberian nut pine and on the firs) was greater on the damaged plots with infested trees, while the inverse dependence was observed on the Otkyl site. In the damaged area of the Nizhny site, the increase of the average PC of certain lichen species was observed: Hypogymnia vittata, H. physodes, Tuckemanopsis chlorophylla, Usnea glabrescens. However, the total variety of the domineering species was found to be greater on the flawless sample plot.
The degree of the projective cover of the species Chaenotheca ferruginea rises in the damaged areas. The degree of the projective cover of such a species as Lobaria pulmonaria rises on the sample plots. This is definitely related to the fact that the thallus of this species is sensitive to the smallest fluctuations of atmospheric pollution, to fires, felling of the trees, and other limiting factors, but, in case these factors are absent, the species regenerates.
On the plots with infested phorophytes, the thallus of Lobaria pulmonaria turned dark brown, indicating its destruction. It is to be pointed out that the damaged thalli of epiphytic lichens were found also for Hypogymnia physodes, Parmelia sulcata and for single plants of Platismatia glauca. The damage was related to the presence of necroses on the thalli, manifested in the change of the color of the thallus (from gray to reddish-brown) and in the destruction of soralia (soredia).
Among the rare species (listed in the Red Books of the Russian Federation and of the Republic of Khakassia, respectively), the following species were found on the plots in question: Lobaria pulmonaria and Nephromopsis laureri (Kremp.) Kurok. [6,7]. The population of Nephromopsis laureri is in a stable condition, whereas that of Lobaria pulmonaria is suppressed.

Conclusion
In terms of the projective cover, foliose and fruticose lichens were found to prevail on the sample plots. The projective cover of crustose lichens rose on the sites infested by the bark beetle. Currently the influence of the bark beetle on the morphology of epiphytic lichens has been noted (the damage of lichen thalli), indicating the suppressed vital function of lichens on the infested territories.