POST-FIRE RESTORATION OF PLANT COMMUNITIES WITH PAEONIA TENUIFOLIA IN THE KHVALYNSKY NATIONAL PARK (RUSSIA)

The paper considers indicators of the dynamics of plant communities with Paeonia tenuifolia before and after fire impact. Studies were conducted in the Khvalynsky National Park (forest-steppe zone of Russia) in 2008–2018. The authors conducted a complex study in burned and unburned plant communities. An assessment of the effects of fire impact and the development of a post-fire action plan were considered in the Protected Area. The plant community Paeonia tenuifolia + Calamagrostis epigejos + Adonis vernalis – Potentilla volgarica burned down in 2009. The plant community Paeonia tenuifolia + Stipa pennata + Adonis vernalis – Anemone sylvestris was unburned. To characterise plant communities with Paeonia tenuifolia and its coenopopulations, we used standard geobotanical description methods. Sixty seven vascular plant species were part of the post-fire phytocoenosis. Of them, 14 species are included in the Red Data Book of the Saratov region. Changes in the post-fire plant community have occurred in the following order: 1) Paeonia tenuifolia + Calamagrostis epigejos + Adonis vernalis – Stipa pennata (in 2008) → 2) Paeonia tenuifolia + Elymus repens + Stipa pennata + Adonis vernalis + Thalictrum simplex (in 2010) → 3) Paeonia tenuifolia – Stipa pennata – Calamagrostis epigejos + Festuca valesiaca +Phleum pratense + Poa bulbosa + Prunus tenella (in 2011) → 4) Paeonia tenuifolia + Adonis vernalis + Stipa pennata (in 2015, 2017, 2018). After the fire influence on a plant community, the following changes took place: 1) annuals and ruderal plant species appeared and increased their abundance; 2) the ratio of dominant species has changed. In 2012–2018, the phytocenotic role of Calamagrostis epigejos decreased, while the coverage and abundance of Stipa pennata increased at the same period. The abundance dynamics of Paeonia tenuifolia decreased in 2010, while in 2015–2018, its value gradually increased. The species richness of the post-pyrogenic plant community varied from 20 species in the first post-fire year to 38 species in the last study year. In the first post-fire year, the families Poaceae (six species), Leguminosae plants (three species), Rosaceae plants (three species) occupied the leading positions. During the post-pyrogenic succession, the dominant position of the listed families was not changing. Species of Compositae, Poaceae, Ranunculaceae families prevailed in the unburned plant community. Steppe plants dominated in the post-fire plant community: Stipa pennata, Adonis vernalis, and Paeonia tenuifolia. The leading ecologic-coenotic groups were steppe plants (70%), meadow plants (16%), forest plants (5%), and ruderal plants (9%). Weed-steppe plants were indicators of habitat disturbance by human activities. Among weed-steppe plants, there were Arenaria serpyllifolia, Viola rupestris, Erysimum canescens, Verbascum lychnitis. Gradient analysis of environmental conditions showed that the highest value of the vitality index (IVC = 1.15) corresponds to the best conditions for the growth and survival of the Paeonia tenuifolia population in the post-fire community. In the control site, the vitality index (IVC = 0.85) corresponded to unfavourable conditions for plant development. We studied the age spectra of the natural Paeonia tenuifolia populations in the burned and unburned communities. We showed that both populations were normal, complete, and young. The fire-damaged populations were younger than the populations in the unburned communities. We suggest the need of comprehensive monitoring studies to properly assess the fire effects and subsequent management actions for the vegetation restoration after fire influence.


Introduction
The factors of negative impact on ecosystems in Protected Areas (PAs) are well known. These are wildfires (Batista et al., 2018;Brooke et al., 2018), logging (Remis & Jost Robinson, 2012;Slaght & Surmach, 2016), pollution (Kataev, 2017;Rodríguez-Jorquera et al., 2017), mining (Ferreira et al., 2014;Armendáriz-Villegas et al., 2015), road network development and construction (Garriga et al., 2012;Slaght & Surmach, 2016). The pyrogenic effect is long-term and has had an adverse effect on biological diversity for decades. It changes the composition and ratio of the areas of natural complexes (Lukyanova & Lukyanov, 2004;Perevoznikova et al., 2007). It also affects the abundance of many plant and animal species (Kuleshova & Korotkov, 2010;Goud, 2017). Fires are often catastrophic phenomena. They cause the death of plant and animal populations, ecosystems as a whole (Stepanitskiy & Shestakov, 2005;Pereira et al., 2016;Batista et al., 2018). Fires pose especially a serious threat to rare and protected (i.e. included in Red Data Books) plant species, the number of which is usually small (Bystrushkin, 2018). For a long time, Russian programmes of environmental monitoring included the studies of the natural ecosystem dynamics and their separate components associated with wildfires in PAs. In particular, they focused on the populations of Red Data Book species. And this topic has not lost its relevance until the present days (Isaeva, 2000;Malysheva & Malakhovsky, 2000;Kuleshova & Korotkov, 2010;Ilyina, 2011;Maslennikov & Maslennikova, 2011). The fire-caused change of the ecosystem is a pyrogenic succession (Komarova, 1980(Komarova, , 2009Rozanov, 1999;Berezina & Afanasyeva, 2009). There are numerous studies focusing on the processes of pyrogenic succession of plant communities at different stages (Morozov, 1912;Curry & Fons, 1940;Korchagin, 1954;Belov, 1973;Rodin, 1981;Komarova, 1991Komarova, , 1999Komarova, , 2011Agee, 1993;Isaeva, 2000;Popov, 2000;Oparin & Oparina, 2003;Ishutin, 2004;Golubtsova, 2012;Dusaeva, 2017). There is a lack of published data on this issue. According to some authors (e.g., Smelyanskiy et al., 2015), a fire in the steppe ecosystems does not lead to pyrogenic succession, but only changes the coenotic activity. It also causes pyrogenic fluctuations of the plant community including the projective cover of some species. There is especially little information about the attitude to the fire impact on population status of certain plant species.
The flora of the Saratov region consists of 1741 species of vascular plants (Elenevskiy et al., 2008). Of them, 285 species are listed in the Red Data Book of Saratov region (2006), including 42 species included in the Red Data Book of the Russian Federation (2008). Plant communities, which include Red Data Book species, are unique, sometimes one of a kind. Paeonia tenuifolia L. is one of the rare and protected species. This is a tuberiferous short-rhizome herbaceous perennial plant, optional calciphile, and a representative of Mediterranean steppe vegetation (Red Data Book of Saratov region, 2006). It is included in the Red Data Book of Saratov region (2006) with category 2 (V) -vulnerable, and listed in the Red Data Book of the Russian Federation (2008) with category 2B -declining in number. The species is also listed in the Appendix 1 of the Bern convention (Belousova et al., 2008). Paeonia tenuifolia has a discontinuous distribution area (Nosova, 1973). In the southeast of European Russia, its natural range is limited by the River Volga. In the south, its range borders with the North Caucasus and the Crimean peninsula. In the west, the distribution area is interrupted, and Paeonia tenuifolia can be found in Ukraine and Central Europe (Romania, Bulgaria), in the southwest of Eurasia, in Asia Minor and Iran. The peculiarities of the ecological-phytocenotic organisation and the island character of the range indicate its relictness.
Along the southern limits of the forest-steppe on the right bank of the River Volga, the species inhabits open areas, pine (Pinus sylvestris L.) forests on the limestone outputs, chalky-covered sods on slopes with a northern exposure (Nosova, 1973). In the Saratov region, Paeonia tenuifolia is distributed in some districts located on the right bank of the River Volga: Atkarsky district, Balashovsky district, Volsky district, Kalininsky district, Krasnoarmeysky district, Khvalynsky district, Saratovsky district. The most significant localities of this Red Data Book species are known on the Volsky-Khvalynsky ridge (Red Data Book of Saratov region, 2006;Elenevskiy et al., 2008). Paeonia tenuifolia grows in Stipeta pennatae -Festucosa valesiaca -Herbosa plant communities, steppe meadows, forest edges, shrub communities and on the sides of valleys, and on sandy steppes and hills (Red Data Book of Saratov region, 2006).
One of the necessary measures for the Paeonia tenuifolia protection is the study of its population status, implemented through the monitoring programme of plant communities in the Khvalynsky National Park. Since 2007, in the Khvalynskiy district, the studies of the status of Paeonia tenuifolia populations have been carried out (Suleymanova, 2010).
The aim of this current study was to identify the post-fire restoration patterns of plant communities with Paeonia tenuifolia. The following tasks were to be solved: 1) to characterise the natural plant communities after fire impact; 2) to analyse the plant community dynamics in 2008-2018; 3) to investigate the morphological traits of Paeonia tenuifolia individuals, floristic and coenotic composition of the plant community, age structure of the Paeonia tenuifolia population; 4) to estimate the conservation significance of the studied firedamaged communities in comparison to the similar unburned plant community.

Material and Methods
Field studies have been carried out in 2008-2018. In order to characterise plant communities with Paeonia tenuifolia and its coenopopulations ( Fig. 1), we used standard methods of geobotanical description (Tarasov, 1981;Matveev, 2006;Mirkin & Naumova, 2012). The Khvalynsky National Park is located in the northern part of the Saratov region in Khvalynsky district at the border of the Middle Volga region and Lower Volga region. It occupies the remnant massif of Khvalynskye hills of the Volga Upland and part of the River Tereshka Valley in the vicinity of the town of Khvalynsk (Makarov, 2008). In accordance with the botanical-geographical division, the region under the study belongs to the Central Russian (Upper Don) subprovince of the Eastern European forest-steppe province of the Euro-Asian steppe region. Zonal vegetation types are deciduous forests and meadow steppes (Tarasov, 1977). Forests are confined to the highlands, on the plains yielding to the meadow steppes. The National Park area is 260.37 km 2 . It is covered mainly by forests. The buffer zone of the National Park «Khvalynsky» is 1148.0 km 2 .
There are both true steppes and meadow steppes in the buffer zone of the Khvalynsky National Park. The steppe component dominates (60%) in the forest-steppes of the Khvalynsky National Park. Forests and meadow steppes extend from the northeast to the southwest of the Protected Area. In meadow steppes, zonal plant communities are phytocoenoses with domination of Stipa pennata L., Stipa capillata L. These plant communities are Stipeta pennatae -Bromopsisosa riparia -Pluriherbosa, Stipeta capillatae -Festucosa valesiaca -Herbosa, and Stipeta pennatae -Festucosa valesiaca -Herbosa. They form the narrow belts, which are almost always located directly near the forest areas, occupying dry ecotopes along slopes on chernozems. Sometimes they are distributed along small areas in the lower parts of the slopes. Meadow steppes have a rich species composition (60-70 species). These plant communities have a complex horizontal and vertical structure. Shrubs play a significant role in some of these plant communities. However, they usually do not form a layer. The main coenose-forming species are Stipa pennata and Stipa capillata and rhizomatous cereals (Bromopsis riparius Rehmann, Poa angustifolia L.). There are the following steppe cereals: Festuca valesiaca Schleich. ex Gaudin, Koeleria pyramidata P. Beauv., Phleum phleoides (L.) H. Carst., but their role is not high in formation of plant communities. The meadow-steppe herbaceous species (Fragaria viridis Weston, Securigera varia (L.) Lassen, Galium verum L., Salvia nemorosa L.) are widely represented (Malysheva & Malakhovsky, 2008).
The climate of the Khvalynsky National Park is continental. The summer is warm and dry. The winter is moderately cold and snowless. Daily, seasonal and annual fluctuations in the temperature of air and soil are typical for the weather conditions. The average annual temperature ranges from 5.2°C to 7.9°C. The average January isotherm is -13°С. The average July temperature is +20.5°C. The relative humidity is 70%, the average annual precipitation is 425-450 mm (Anikin, 2013). To study pyrogenic changes, the following plant communities were selected: 1) Paeonia tenuifolia + Calamagrostis epigejos (L.) Roth + Adonis vernalis L., with Potentilla volgarica Juz. microgroups occupied the middle and lower parts of the southern slope of the mountain Piche-Panda in the vicinity of the village Staraya Lebezhayka,Khvalynsky district (52.65478 N,47.86317 E), 185 m a.s.l. The total projective cover was 70%. The projective cover of Paeonia tenuifolia was 40%. The species number in the plant community was 67. The phytocoenosis was polydominant. The following co-dominants were found: Stipa pennata, Paeonia tenuifolia, Adonis vernalis. The soil is sod-calcareous.
On 8 May 2009, 3 km west of the village Staraya Lebezhayka (Khvalynsky district of the Saratov region), a fire broke out in the forest. The cause of the ignition was an unextinguished picnic campfire. A crown fire lasted for several hours and spread over an area of 0.5 km 2 . It reached the height of about 20 m. The wildfire was also caused by steady dry weather conditions for almost two weeks, as the last precipitation (1.3 mm) before the fire dates back to 22 April. The average daily air temperature on 7 May was +16.7°C. The maximum value reached +22.7°C. The wind was 6-12 m/s. It also contributed to the fire spread. The consequences of the fire impact were catastrophic. The forest on the west of the mountain Piche-Panda (Volskoe forestry) was burned down. The fire spread to the east was stopped by the field road and the guard service of the Khvalynsky National Park. A botanical description of the burned steppe area was made a week later. Since 2008, a permanent study plot has been located on this site to monitor the status of the plant community with Paeonia tenuifolia. Therefore, we had an opportunity to compare its status before and after fire influence.
2) Unburned plant community Paeonia tenuifolia + Stipa pennata + Adonis vernalis -Anemone sylvestris L. is located on a site 300 m from the forest of the Sosnovo-Mazinskoe forestry (52.32602 N, 47.92722 E). The fire break was located from the north of the plant community. The total projective cover was 80%, including up to 30% projective cover of Paeonia tenuifolia. The plant community consisted of 69 species. This plant community is polydominant with the following co-dominants: Stipa pennata, Paeonia tenuifolia, Adonis vernalis, Anemone sylvestris. The soil is sod-carbonate. The unburned plant community was located under similar physical-geographical conditions with the unburned one. Therefore, we used these data for its comparison with the burned plant community vegetation.
We studied the plant communities according to the standard methodics (Yaroshenko, 1969;Voronov, 1973;Mirkin & Rosenberg, 1983;Mirkin & Naumova, 2012). We estimated the species participation in each plant community by indicating the percentage of projective cover (Tarasov, 1981). To estimate the frequency of occurrence/coverage of a species, we used the scale of Drude (1890). The symbols are as follows: soc (socialis) -dominant species, frequency of occurrence/coverage exceeds 90%; cop 3 (copiosus)abundant species, frequency of occurrence/coverage is up to 80%; cop 2 -species is represented by numerous individuals, frequency of occurrence/coverage is up to 20%; cop 1 -frequency of occurrence/coverage is up to 4%; sp (sparsus) -frequency of occurrence/ coverage about 0.8%; sol (solitarus) -scanty individuals, frequency of occurrence/coverage not exceeds 0.16%; un (unicum) -single individual.
We defined phenophases and phenological events (Haggerty & Mazer, 2008) using the BBCHscale (Zadoks et al., 1974;Meier, 2001;Meier et al., 2009;Polikarpova & Makarova, 2016). This system is used in Europe for a uniform coding of phenologically similar plant growth. For each Paeonia tenuifolia individual, we determined the following morphological parameters: plant height, corolla diametre, number of leaves, leaf length.
The statistical analysis has been processed by conventional methods using Statistica 6.0 software. We used Maevskiy (2014) for identifying plants. Scientific names of the plant species are given according to The Plant List (2019).

Results and Discussion
During the fire on 8 May 2009, dry grass, dead ground cover and aboveground parts of shrubs got burnt. It seemed that the fire caused irreparable damage to the plant community. On 15 May 2009, we found that an aspect was black with bright-green large dots represented by vegetative and flowering plants on the study plots. These were mainly represented by short-rooted perennials Thalictrum simplex L., Vincetoxicum hirundinaria Medik., Potentilla incana P. Gaertn., B. Mey. & Scherb., and Potentilla volgarica. The floristic composition of the plant community Paeonia tenuifolia + Calamagrostis epigejos + Adonis vernalis before the fire impact is demonstrated in Table 1.  Table 1 shows that the species richness of the plant community was 26-28 species before the fire impact. The species density was not exceeding 7-12 species ( Fig. 2A). Paeonia tenuifolia was the most abundant species. Its projective cover was 40-50%. Calamagrostis epigejos made an aspect with a projective cover of 15-20%. The remaining species had a low abundance and projective cover ( Table 1). The general aspect was bright-green. We determined three layers in the plant community (Fig. 2B).
In 2009, single vegetative shoots of Potentilla volgarica, Thalictrum simplex, Vincetoxicum hirundinaria, and flowering shoots of Potentilla incana were found on this study site seven days after the fire impact. The projective cover was 3%. The aspect was black with bright-green spots of vegetating herbs.
One year later, the plant community had recovered. However, the weather conditions in 2010 were extreme for the steppe and forest vegetation (Chub, 2011;Lewis et al., 2011a,b;Report, 2011;Solovyov et al., 2011;Polyakova & Melankholin, 2013). Table 2 provides a description of the burnt site one year after the fire.
The plant community showed a greenish aspect with strawy hue and burgundy spots of Paeonia tenuifolia. In general, the flora of the plant community consisted of 20 species. There were no annual plants, despite the fact that the fire impact stimulated their germination, and the substrate was updated (Malysheva & Malakhovsky, 2008). The floristic composition decreased quantitatively and changed qualitatively. The shrubs (e.g. Prunus tenella) and semishrubs (e.g. Onosma simplicissima) recovered. At the same time, the Volga-Don endemic Asperula tephrocarpa Czern. ex Popov & Chrshan. appeared. We found that rhizomatous plants, bulbous plants and seeds of annual plants are fire-resistant, with a density of 7-8 species per 1 m 2 . The dominant Paeonia tenuifolia and codominant Elymus repens (L.) Gould had a maximum projective cover. Other plant species have low values of both abundance and projective cover. The newly formed vegetative cover was fairly uniform. The vertical structure of the plant community was on an initial development stage. The total projective cover was 60%.  Thus, the first post-fire restoration stage was manifested by the change of the 2008 plant community Paeonia tenuifolia + Calamagrostis epigejos + Adonis vernalis -Stipa pennata into the 2010 plant community Paeonia tenuifolia + Elymus repens + Stipa pennata + Adonis vernalis + Thalictrum simplex. However, this phytocoenosis was not richer in species richness and had all the features contributing to the formation of a more productive plant community. However, further 2011 observations demonstrated a start of changes in this phytocoenosis. So, in 2011 the species composition of the fire-damaged plant community increased to 31 species (Table 3).
We found a high projective cover for the dominant Calamagrostis epigejos. The impact of both fire and drought caused the elimination of the biennial Erysimum aureum M. Bieb., and the perennials Veronica spicata subsp. incana (L.) Walters, Salvia tesquicola, Plantago urvillei, Seseli libanotis, Polygala nicaeensis subsp. mediterranea Chodat, Psephellus marschallianus (Spreng.) K. Koch, and Alyssum lenense.  The monocarpic herbaceous Seseli libanotis has polycyclic monopodally growing shoots with vertical rhizomes. Due to the peculiarities of its life cycle, this species has a cyclical participation in the composition of plant communities (Rabotnov, 1972;Knapp, 1974). Perhaps, a fire destroyed a few virginile Seseli libanotis individuals, which would be consequently turn into a generative stage and produce seeds. So, the cycle of the Seseli libanotis development ended on the study site in 2011. Outside the study plot, Polygala nicaeensis subsp. mediterranea, Psephellus marschallianus, Alyssum lenense were found. Therefore, they are likely to recover on this study site. A sharp decrease in the competition caused by the fire impact, was contributing to an appearance of R-strategy plants (Grime, 1979) in the burnt area. They are the little competitive vegetatively mobile perennials (e.g. Euphorbia esula subsp. tommasiniana (Bertol.) Kuzmanov), annuals and biennials (e.g. Draba nemorosa, Androsace maxima, Alyssum linifolium Stephan ex. Willd., Verbascum lychnitis L.), as well as weeds, like Vincetoxicum hirundinaria and Taraxacum campylodes. The presence of R-strategy species indicated a habitat disturbance and possible subsequent changes in structure of the plant community toward reducing the number of R-strategy plants, and ratio of the main phytocoenosis components (Rabotnov, 1972). We also noted the appearance of the following perennials: Phleum pratense, Poa bulbosa, Festuca valesiaca, Eremogone longifolia (M. Bieb.) Fenzl, Potentilla incana, and Origanum vulgare L.. Layers were well distinguishable (Fig.  3B). The first layer consisted of Stipa pennata (60 cm in height), vegetative shoots of Calamagrostis epigejos, generative shoots of Paeonia tenuifolia (30-50 cm in height). The second layer was formed by Paeonia tenuifolia vegetative shoots and perennial herbs in both vegetation and flowering stages. The third layer consisted of leaf rosettes of perennials and ephemeral annuals. The total projective cover was 65-70%.
The competition strongly limited the participation of some species in the plant community. The firecaused competition reduction affected the increase of a coenose-forming role of Calamagrostis epigejos in the plant community. Table 4 shows the 2008-2018 plant community dynamics with indication of the species composition and their projective cover.
Over the study years, we found 67 plant species. In 2015, the total projective cover was 70%. The projective cover of Paeonia tenuifolia was 35%, while a value of this indicator for Adonis vernalis was 8%. The general aspect was whitishgreen with blooming spots of Paeonia tenuifolia. This plant community was named as Paeonia tenuifolia + Adonis vernalis + Stipa pennata (Herbosae -Stipa pennatae). In 2017, the total projective cover was 70%, whereas the projective cover of Paeonia tenuifolia was 37%. In 2018, the total projective cover of the plant community was 80%, including 35% of projective cover of Paeonia tenuifolia. The general aspect was green with a white mosaic of flowering Vincetoxicum hirundinaria. The species composition was the richest in 2017 with 38 plants. In 2018, the number of species in the plant community was 33.
Thus the fire was not so catastrophic, as we expected earlier. Moreover, it had rather positive consequences for the steppe vegetation. The fire impact caused the change from Paeonia tenuifolia + Calamagrostis epigejos + Adonis vernalis -Stipa pennata in 2008 to Paeonia tenuifolia + Elymus repens + Stipa pennata + Adonis vernalis + Thalictrum simplex in 2010. Then the plant community transformed into and the Paeonia tenuifolia -Stipa pennata -Calamagrostis epigejos + Festuca valesiaca + Phleum pratense + Poa bulbosa + Prunus tenella in 2011. The phytocoenotic role of Calamagrostis epigejos started decreasing from 2012 to 2018. In contrary, the projective coverage of Stipa pennata increased twice. Although the projective coverage of Paeonia tenuifolia decreased directly after the 2010 fire impact, in 2015-2018 both the projective cover and abundance of Paeonia tenuifolia increased. Thus, the Paeonia tenuifolia restoration was characterised by an increase in projective cover, abundance and vitality.
Xerophytic and mesoxerophytic plant species of different life forms turned out to be resistant to fire impact. Among them, there are Prunus tenella, Onosma simplicissima, Adonis vernalis, Astragalus buchtormensis Pall., Calamagrostis epigejos, Potentilla volgarica, Paeonia tenuifolia, Stipa pennata, Securigera varia, Thalictrum simplex, Vincetoxicum hirundinaria, and Verbascum lychnitis. These species have been present in the plant community both before and after the fire impact for ten years. These species are called pyrophytes.
Some species participated in the plant community structure from time to time, being present at certain years and being absent in other years. Among them, there are the xeromesophytic hemicryptophytes Psephellus marschallianus, Eremogone longifolia, and Galium octonarium (Klokov) Pobed.
Some species were eliminated from the plant community after the impact of the fire and drought. These are perennials (Salvia nemorosa, Polygala nicaeensis subsp. mediterranea, Plantago urvillei, Seseli libanotis, Veronica spicata subsp. incana), and the shrub Cerasus fruticosa. Most of them were meso-xerophytic and xeromesophytic hemicryptophytes.
The analysis of the coenotic groups showed the predomination of steppe plants (stepants) (60.85%) in the studied post-fire plant community. Among them, Stipa pennata, Adonis vernalis, Paeonia tenuifolia, Onosma simplicissima, and Galium verum had the highest projective cover. The meadow plants (pratants) were represented by 17.60% of the species in the plant community. Among them, there are cereals (Calamagrostis epigejos, Bromus inermis Leyss., Phleum pratense), herbaceous perennials (Securigera varia, Thalictrum simplex, Filipendula vulgaris Moench, Asparagus officinalis L.). The presence of forest species (sylvants) (6.21%) was to be expected, as the plant community was located near the forest massif. The forest species were represented by the shrub Prunus tenella, the herbs Erysimum aureum, Origanum vulgare, and Gagea bulbifera (Pall.) Salisb.
In their study of steppe plant communities with Hedysarum grandiflorum Pall. in the Volga Upland region, Lavrentiev & Boldyrev (2016) indicated the following species groups ratio: 64.05% of stepants (steppe plants), 7.84% of pratants (meadow plants), 9.15% of sylvants (forest plants), 18.96% of ruderants (ruderal plants), ruderants-stepants, ruderant-pratants, rudrants-sylvants. Hedysarum grandiflorum inhabited a chalky substrate, where disturbance factors were more pronounced and more complex than under intact conditions. These factors were wind and water erosion, soil freezing in winter due to the absence of dry grass remnants, possible soil salinisation.
The presence of ruderal species (16.80%) (Vincetoxicum hirundinaria, Viola rupestris F.W. Schmidt, Arenaria serpyllifolia L., and Nonea pulla (L.) DC.) in the studied plant community with Paeonia tenuifolia indicated a certain level of habitat disturbance. The latter resulted of the fire impact and its consequences, moderate grazing, and natural factors (water and wind erosion). The effect of these factors is reduced due to an increase in the general projective cover of the vegetation, soil fertilisation with ash elements, and the general mesophytisation of the Paeonia tenuifolia habitat.
In 2018, we found 14 more species new for the plant community: Alyssum tortuosum Willd., Asparagus officinalis, Euphorbia glareosa Pall. ex M. Bieb., Gypsophila volgensis Krasnova, Festuca valesiaca, Hedysarum grandiflorum, Filipendula vulgaris, Nonea pulla, Stachys recta L., Potentilla incana, Trinia multicaulis (Poir.) Schischk., Veronica austriaca L., Viola rupestris, and Verbascum orientale (L.) All. Although the floristic composition of the studied phytocoenosis had changed, the ratio of coenotic groups remains the same as it was in 2008, i.e. before the fire impact (Table 5). Semi-shrubs, tap-root perennials, short-root perennials, and long-root perennials determined the structure of the post-fire plant community for a number of years. Before the fire impact (i.e. in 2008), short-root perennials had a leading position (29.63%) in the plant community. They retained this position for a number of post-fire years: 25% in 2010, 26% in 2011, 35.14% in 2017, 36.36% in 2018. In 2015, tap-root perennials occupied a dominant position in the studied plant community with 33% of the total species number. In other years, they occupied the second position: 22% in 2008, 15% in 2010, 13% in 2011, 16% in 2017, 21% in 2018. Before the fire impact, the long-root perennials occupied the third position (11.11%). Subsequently, they demonstrated a resistance to pyrogenic effects, and an ability to quickly occupy the vacant space after the fire impact. In the 2010-2011 growing season, these plants, similarly to short-root and tap-root perennials, had a leading position in the plant community: 25% in 2010, 13% in 2011, 11% in 2015, 11% in 2017, 9% in 2018. Our results are in accordance with published data. For example, Marenina & Maslennikov (2014) demonstrated that in the Arsk forest-steppe (north of Ulyanovsk region, Russia), tap-root perennials (25.4%), long-root perennials (19.8%), and shortroot perennials (10.8%) domianted in the post-fire plant communities. The same authors also noted a fire-caused increase a the proportion of root-sucker perennials (14.5%) and biennials (8.4%) in the ratio of life forms in the plant community.
The analysis of the morphometric traits of the Paeonia tenuifolia population before and after the fire impact showed, that the least variability of the trait is typical for the height of its generative shoots.
The highest values of flowering shoot height were recorded in 2018 (47.13 cm). This is 36% more than in 2010. The smallest height of generative shoots was associated with unfavourable weather conditions of the spring and summer in 2017 (Syvorotkin, 2017). In general, the height of the vegetative and generative shoots of Paeonia tenuifolia remained at a constant level for a number of post-fire years (Fig.  4). Extremely low and high values of these parameters depend on meteorological factors.
The development of an action plan for fires in Protected Areas should be based on the results of the assessment of biological diversity and comprehensive studies over succession on the burnt areas in compare with undisturbed habitats. For comparison, we chose similar plant community with Paeonia tenuifolia, not fire-disturbed in the southwestern part of the Khvalynsky National Park (Sosnovo-Mazovskoe forestry).
In the unburnt plant community, the height of generative shoots (36.47 cm) was slightly lower than in the post-fire plant community (47.13 cm). The probable reasons for this were the weakening of competition between plants caused by the fire impact and the soil fertilisation with ash elements. In contrary, in the unburnt plant community, the average plant height and the height of vegetative shoots were 3 cm larger than in the post-fire plant community (Table 6).  It is caused by a large number of pre-generative Paeonia tenuifolia individuals, the height of which reached 11-17 cm. Individuals of juvenile, immature, and virginile age clаsses have vegetative shoots. In the post-fire plant community, the fire-stratificated seeds of Paeonia tenuifolia germinated well. In subsequent years, we observed a large number of Paeonia tenuifolia juveniles (first year individuals) with an average height of 4.5 cm. The determination of age structure for the Paeonia tenuifolia population is of great importance, as it allows to a better understanding of the mechanisms of post-fire succession. The distribution of individuals along age groups and the completeness of population age structure contribute to the species sustainability in the plant community, since each group has its own specific relationship with the habitat (Bespalova & Popova, 1972). In addition, normal type populations are recognised as highly resistant (Rabotnov, 1983). If a plant population is incomplete or constist of indviduals of the same age, its resistance to unfavourable conditions decreases. There are three types of age classes of a population: growing population, stationary population, declining population (Zlobin, 1989). Maslennikov & Maslennikova (2011) noted that the natural Paeonia tenuifolia population is characterised as complete, stationary. At the same time, young individuals predominate as most of them will eliminate before reaching flowering and fruiting stages. Ilyina (2011) found that the pyrogenic effect changes the age structure of a threatened species population by shifting age class percentage towards old (senile) individuals. As a result, the initially mature normal populations could be gradually changed into populations of aging (regressive) type. And it thus can contribute to plant population extinction. However, based on comparison of the unburnt and post-fire Paeonia tenuifolia population in the study area, we showed that young pre-generative individuals dominated (67% of the total number of individuals) in the age spectrum of the postfire populations (Table 7).
We found Paeonia tenuifolia seedlings in the study plots in April. In the second decade of May, the plants passed into a juvenile age class. Within group of generative plants, middle-age generative (g 2 ) individuals prevailed (13% of total number of individuals) in the post-fire plant community. Subsenile (6%) and senile (2%) individuals were also represented in the populations. In the age spectrum of the unburnt Paeonia tenuifolia population, generative individuals predominated (43%). Among them, generative individuals (g 2 ) dominated (63%). The post-generative age classes were represented by a small number of individuals in the unburnt Paeonia tenuifolia population (Fig. 5).
Since the studies were carried out on sites with a different disturbance degree, we used recovery and replacement indices to compare the populations' status. In the post-fire plant community, the I recovery of Paeonia tenuifolia population was Ir = 2.70. It indicates that this population is stable, and the pre-generative individuals are able to replace generative individuals. In the unburnt plant community, the I recovery was lower (1.25). It indicates a less stability of this Paeonia tenuifolia population, as a large number of pre-generative individuals are being eliminated and thus cannot sufficiently replace generative individuals. Based on the age index (Δ) of Uranov (1975) and the efficiency index (ω) of Zhivotovsky (2001), the post-fire population of Paeonia tenuifolia was estimated as younger (ω = 0.36) than the P. tenuifolia population in the unburnt site (ω = 0.54). According to the classification of normal type populations (Zhivotovsky, 2001), both populations were recognised as young full-membered populations. The post-fire plant community contained remarkably more juvenile and virginile individuals, than the population on the unburnt site. Both the recovery and replacement rates were higher in the burnt site than in the unburnt area. Note: p -seedlings, j -juvenile, im -immature, v -virginile, g 0 , g 1 , g 2 , g 3 -generative, s -senile, ss -subsenile.
The gradient analysis of environmental conditions showed that the Paeonia tenuifolia population in the fire-damaged plant community was characterised by the highest value of the vitality index (IVC = 1.15). It corresponded to the best conditions for population development.
On the unburnt site, the vitality index (IVC) of the Paeonia tenuifolia population was 0.85. In indicated the unfavourable conditions for survival and development of this population. The index of species plasticity (ISP = 1.35) reflected a resistance of Paeonia tenuifolia to unfavourable conditions, in particular, to the fire effects. This is a low value in comparison with ISP values calculated for some other herbaceous plant species. For instance, the ISP of Tulipa gesneriana L. was 1.9 (Kashin et al., 2016(Kashin et al., , 2017. The ISP for Iva xanthiifolia Nutt. (as Cyclachaena xanthiifolia (Nutt.) Fresen.) was 4.95, and the ISP for Atriplex tatarica L. was 6.28 (Ishbirdin & Ishmuratova, 2004). The ISP value of Paeonia tenuifolia was within the limits of earlier obtained ISP values for perennial herbaceous plants (Ishbirdin & Ishmuratova, 2004). More specifically, its values are close to the ones calculated for Cephalanthera rubra (L.) Rich. with ISP = 1.31 (Ishbirdin et al., 2005), and Allium denudatum F.Delaroche (as Allium albidum Fisch. et Bieb.) with ISP = 1.38 (Tkhazaplizheva & Shkhagapsoev, 2008). This ISP value suggests that Paeonia tenuifolia is characterised by narrow limits of ecological preferences.
We considered the number of reproductive shoots on the study sites as an objective indicator of the status of Red Data Book plant populations (Table 8).
The positive effects of a fire impact were manifested by the higher number of Paeonia tenuifolia shoots in the post-fire plant community in comparison to the unburnt site. This is probably caused by the substrate renewal, improvement of lighting conditions, soil fertilisation with ash elements, and the reduced competition from other plant species.
According to these authors, species of the families Poaceae (five species disappeared after fire), Rosaceae (three species), Rubiaceae (three species) were unstable to the fire factor under conditions of the South Ural steppes. On the contrary, the plant species number increased in the families Leguminosae (three species appeared after fire), Euphorbiaceae (two species), and Caryophylaceae (two species) after the fire impact in Ural steppes (Smelyanskiy et al., 2015). Our results showed that in the Khvalynsky National Park, the most unstable plants were assigned to the following families: Compositae (two species disappeared after fire), and Apiaceae (one species). After the fire impact, the species number increased in the families Poaceae (three species appeared after fire), Rubiaceae (two species appeared after fire), Rosaceae (one species appeared after fire) and Leguminosae (one species appeared after fire).
In the studied plant communities, we recorded the plant species (e.g., Anemone sylvestris, Adonis vernalis, Alyssum lenense, Asperula tephrocarpa) listed in the Red Data Book of Saratov region (2006) lousova et al., 2008). We found that the unburnt plant community had the highest value of the coefficient of conservation significance (K = 67.20) (Table 10).  (2006) It is well known that fires reduce the biodiversity of plant communities, and destroy the habitats of rare and threatened species (Ilyina, 2011;Bystrushkin, 2018). The fire impact caused remarkable damage to the populations of seven species of protected plants included in the Red Data Book of Saratov region (2006), three of which are listed in the Red Data Book of the Russian Federation (2008). The species represented by small populations with both small projective cover and abundance were in the most threatening situation. These plants are Alyssum lenense, Onosma simplicissima, Potentilla volgarica, Salvia nutans, and Stipa pennata. During the long-term monitoring, we found that four native plants of the studied plant community (Paeonia tenuifolia, Adonis vernalis, Potentilla volgarica, Onosma simplicissima) were pyrophytes. The semi-shrub Alyssum lenense disappeared from the plant community. The cereal Stipa pennata and tap-root perennial Salvia nutans recovered and strengthened their positions in the phytocoenosis structure as co-dominants. During the post-fire succession, we found six Red Data Book species (Alyssum tortuosum, Asperula tephrocarpa, Globularia punctata, Gypsophila volgensis, Hedysarum grandiflorum, and Polygala sibiri-ca L.) in the floristic composition of the studied plant community. Since the study site was at the edge of the burnt area at the time of a fire, most of the Red Data Book plants penetrated into the plant community from the surrounding unburnt vegetation. The perennial Paeonia tenuifolia turned out to be resistant to the fire impact. And the plant community with Paeonia tenuifolia had recovered ten years after the fire impact.

Conclusions
The species richness of the post-fire plant community varied from 20 species in the first post-fire year to 38 species in the last study year. In the first post-fire year, the families of Poaceae (six species), Leguminosae (three species), Rosaceae (three species) occupied the leading position. The dominant position of the listed families remained during the pyrogenic succession of the plant community. In the unburnt plant community, other families (Compositae, Poaceae, Ranunculaceae) were richest in number of species.
In the post-fire community steppe species dominated. In general, the full ecologicalcoenotical spectrum was represented by steppe plants (stepants) (70%), meadow plants (pratants) (16%), forest plants (sylvants) (5%), and ruderal plants (ruderants) (9%). At the same time, the ratio of coenotic groups remained the same before and after the fire impact. The only change was manifested in the appearance of new species in the studied phytocoenosis, most of which were steppe plants. During the post-fire succession, annuals and ruderals appeared and increased in abundance. This characterised an intermediate stage of pyrogenic transformation of the plant community with Paeonia tenuifolia.
The Paeonia tenuifolia populations in both the post-fire and unburned plant communities were normal, full-membered and young. Expectedfully, the age structure of post-fire Paeonia tenuifolia population was younger than its population in the unburnt plant community.
In the fire-damaged plant community, both the regeneration and growth processes of vegetative and generative shoots were more intense than in the unburnt plant community. This was caused by the substrate renewal and the decrease in species competition in the post-fire plant community Species saturation and stabilisation in species richness have become remarkable signs of a final restoration stage of the plant community affected by a fire.
Phytocoenoses with Paeonia tenuifolia are valuable botanical sites. In this area, they had grown for a long-time and were greatly adapted to local conditions under the influence of different factors. The presence of other Red Data Book species increases the conservation significance of the plant communities. The fire impact caused significant damage to the populations of Red Data Book plants in the post-fire community. Nevertheless, peculiarly, abiotic conditions contributed to the increased vitality of the Paeonia tenuifolia population and the restoration of the plant community after the fire impact.
The buffer zone of the Khvalynsky National Park contains mainly areas of meadow steppes with populations of Paeonia tenuifolia and other Red Data Book plant species. Therefore, it is necessary to include these areas with populations of protected plant species into the main area of the Khvalynsky National Park to ensure a reliable protection of intact habitats and populations of threatened species. To properly assess the fire effects on nature and its components and to subsequently create the correct recommendations for the ecosystem restoration, additional studies are needed.