Environmental Consequences of Landscape Fires in Trans-Baikal Forests

Landscape fires play the leading role in the modern anthropogenic dynamics of forest ecosystems in south-eastern Siberia. Forest pyrologists consider them the most destructive manifestation of fires - an environmental factor that acts across wide areas to change the state of landscapes. Due to the insufficient knowledge of the nature of pyrogenic forest ecosystems, especially its dynamic aspects in the forestforming process, obtaining data on the pyrogenic dynamics of forest ecosystems belonging to various ranks is of broad scientific interest. A new aspect of this study is assessing ecosystem transformations under various pyrological regimes that determine the pyrogenic successions of plant communities, the hydrothermal regime of soils, a post-fire runoff, etc. The history of catastrophic landscape fires in the Baikal and Trans-Baikal regions began after the construction of the Trans-Siberian Railway. At that time, a long strip of coastal hemiboreal small-leaved deciduous forests formed along the southern shore of Lake Baikal, in the area of indigenous dark coniferous taiga, as a result of the “selective” impact of a lingering series of fires that followed intense forest harvesting. It happened regardless of the average productivity of the pyrogenic stands being 30-40% lower vs. the potential level. The landscape fires of the 1930-1950s that arose during industrial development, especially in the areas of intense forest harvesting, caused heavy damage to forest ecosystems throughout Transbaikalia. Now, due to a regress in the Russian forest management, landscape fires have turned into an archaic alternative to the ecological progress as of the 1970s and 1980s. Therefore, the relevant goal of this article is to consider the transformation of forest ecosystems after landscape fires. The emergence and spread of landscape fires were studied during two fireintensive seasons through the air monitoring of the Trans-Baikal territory. Geographic coordinates: 49-57° N, 99-122° E. Regular pyrological studies of the seasonal dynamics of the forest fire danger implied the use of the method suggested by N.P. Kurbatsky (1970) [9]. The permanent trial plots were located on the Malkhansky and Khamar-Daban Mountain Ranges. The route studies covered the Selenga Highlands, as well as the basins of the Rivers Barguzin, Turka, Upper Angara, Muya, and Chara. Fig. 1 shows the schematic map of the sites. The pyrological regimes of vegetation complexes were established based on research data (see the table). The environmental consequences of landscape fires were studied in the forests of South-Eastern Baikal and Central Transbaikalia. The closest observations of the dynamics of burned (including through prescribed burning) and control stands were performed on permanent sample plots. There the researchers also ensured regular accounting of litterfall using special 1x1m collectors. The grain composition and physical and mechanical properties of the soils were determined via the common methods [21]. The pyrogenic variations of the forest-forming process after landscape fires were observed in different natural districts (Fig. 2). Pyrological regimes differ in the altitude-belt complexes (ABC) of vegetation and correspond to a wide range of atmospheric moistening. Forest-steppe vegetation prevails in the valleys of large rivers and low mountains in the conditions of extremely insufficient moistening. This vegetation is exposed to an extreme fire regime in the spring and in the early summer. The Scots pine (Pinus sylvestris L.) prevails in subtaiga-forest-steppe forests. There, an intense regime takes place even in a standard weather situation. The fire maturation of forests in the light-coniferous taiga belt with predominant larches (Larix sibirica Ledeb., Larix gmelini Rupr.) is approximately two times longer vs. forest-steppe and hemiboreal forests. Accordingly, the pyrological regimes vary from intense to moderate. Dark coniferous forests comprising the Siberian pine (Pinus sibirica Du Tour.), fir (Abies sibirica Ledeb.) and spruce (Picea obovata Ledeb.) are confined to wet belts with a moderate pyrological regime. A safe regime prevails in the subalpine ABC. The general fire danger is determined by ground fires, after which most burned forests retain their vitality at the level of their fire resistance, as well as depending on the actual intensity of fire in this area. Fig. 3 illustrates the typical dynamics of Scots pine stands established based on forest management data. In fact, diverse structural transformations of plant communities are observed after landscape fires - from a moderate fire damage to heavy thinning caused by an intense fire, and even complete death after head fires with probable local deforestation. Fig. 4 shows the comparative dynamics of the population of trees in normal and pyrogenic larch forests. Larch trees have an advantageous position vs. pines, as they are better protected from thermal damage by their thick bark. Besides, the crowns of larch trees are capable of regenerating needles and shoots damaged by fire. The duration of recovery to the pre-fire basal area increases exponentially with age, since forest stands inevitably face a growth decline as they become old. The pyrogenic digression of larch forests in permafrost areas with a burned peat horizon was followed by a tree fall, which was observed during the air monitoring of fires. Later thickets of birch and willow trees formed there. The fire damage to trees (trunks and crown), the ground cover, as well as the hydrothermal regime of soils are most comprehensively studied in the Scots pine forests of Central Transbaikalia where the ground cover and lower forest layers were explored not only at natural fire sites but also through prescribed burning. The integral picture of forest disturbance with landscape fires is complex and diverse. On mountain slopes, the strongest fire was observed when it was moving upwards. The speed and direction of the wind, as well as the daily temperature and humidity rhythm played a significant role in the spread of the fire line. Therefore, extensive landscape fires left behind a chaotic structure of damaged and dead stands. Later, a complex mosaic of uneven-aged stands modified by repeated fires formed during post-fire reforestation. After high-intensity fires, the forest plant communities were locally replaced by steppe ones, while reforestation took entire decades. Successions after fires were different. Extensive fires in the upper taiga ABC used to lower the upper boundary of the forest belt. Meanwhile, situations being destructive for the forest ecosystems of Transbaikalia regularly recurred, which was clearly seen based on the 200-year dynamics of the tree-ring width of the Scots pine in the River Turka valley. The tree diagram in Fig. 5 unambiguously shows a sharp decline in the width of tree rings at the turn of the 19th-20th centuries when the TransSiberian Railway was built. One may also identify drought periods in the 1930-1970s. The pyrogenic anomaly of 2015 that covered over 10% of the Baikal region turned out to be extremely dangerous. The article contains 5 Figures, 1 Table and 58 References. The Authors declare no conflict of interest.

Characteristics of isolated Tilia nasczokinii Stepanov (Tiliaceae) populations near Krasnoyarsk

Tilia genus in Siberia is a relict element of flora which grows as isolated plots. Some authors consider Siberian lime as Tilia sibirica Bayer. Two small lime populations near Krasnoyarsk have been described as a separate species Tilia nasczokinii Stepanov. Both T. sibirica and T. nasczokinii retain the ambiguous status in the modern international nomenclature of plants. The facts concerning the presence of a number of relict nemoral species among T. nasczokinii satellites indicate the relict origin of its populations. Recent investigations have ascertained that T. nasczokinii species is essentially genetically removed both from T. cordata and T. sibirica. This confirms the relict origin of the populations. The aim of our investigation is to determine the number of lime plants and their sizes, to find out the ontogenetic structure and reproduction character of relict T. nasczokinii populations and to estimate the vitality of the plants. T. nasczokinii populations are located on different banks of the Yenisei River. The fist population is on the left bank (from 55°57'34''N, 92°28'07''E to 55°57'51''N, 92°30'10''E) and the second one is on the right bank (55°57'26''N, 92°46'41''E) (See Fig. 1). We made a general geobotanical description of phytocenosis. The ontogenetic status was determined for each T. nasczokinii plant. The sizes (height and diameter at 1.3 m) and the vital status were established for virginile and generative plants. In order to assess the contribution of vegetative and seed reproduction, we calculated the index of genotypic richness R (Dorken, Eckert, 2001) and clonal heterogeneity D* (Arnaud-Haond et al., 2007) using the GenClone v2.0 program (Arnaud-Haond and Belkhir, 2007) on the basis of genotype analysis of 11 polymorphic nuclear microsatellite loci (Ekart et al., 2021). Also, we determined the number of unique multy-locus genotypes (MLG) in every population. As a result of our research, 305 T. nasczokinii plants were found in the left bank population (39 of them are large trees, others belong to the undergrowth) and 196 plants (30 from them are rather large) on the right bank. T. nasczokinii is a part of pine and pine-birch forests with Carex macroura Meinsh. and other grasses which have the average closeness of crowns (0.55-0.65). On the right bank, all the lime trees grow on the area of 1.5 ha. On the left bank, they are located on the area of 370 ha as individual trees or as groups up to 7 big trees and 5-96 small plants. The distance between the groups is rather long: from 500 to 1000 m. It is demonstrated that both investigated populations have a similar ontogenetic structure (See Fig. 2). Juvenile and immature plants occupy the biggest part (84% on the left bank and 77% on the right). Not many current year sprouts were found both on the left (2%) and on the right bank (8%). As it is typical for the lime, senile plants were practically absent (only one plant was found on the left bank). The calculated indexes R and D* were rather high (0.731 and 0.987 in general for both populations). We showed that most of the analyzed plants are not the parts of clones but there are some clones with a few ramets. In the left bank population, from 77 analyzed individuals we recognized 61 unique MLG and 10 (16.4%) of them have 2-5 ramets. On the right bank, 32 individuals were analyzed and among 19 MLG there were 3 (15.8%) clones with 2, 5 and 9 ramets. The genotypic diversity of T. nasczokinii is higher than that of T. sibirica in Kemerovo region (R=0.661) but slightly lower than that of T. cordata (R=0.938). The high genotypic diversity demonstrates the significant role of seeds in the self-reproduction of T. nasczokinii populations. The contribution of vegetative reproduction is also considerable (33.8% on the left and 50% on the right banks). It turns out that the sizes of virginile trees in both populations are very close (See Table), the differences in the average values are insignificant at p=0.05. The generative trees in the left bank population are higher than in the right bank population, and they are rather close in diameter. In general, for both populations the virginile trees have the average height of 6.0±0.31 m and trunk diameter of 5.1±0.32 cm, with the generative trees being 13.7±0.71 m and 12.2±0.56 cm, accordingly. Individuals of these groups have the habitus of single-stemmed (56.4% on the left and 73.3% on the right bank) and bush-like trees (See Fig. 3). T. nasczokinii is much smaller than both T. sibirica and T. cordata. The large part (58% on the left bank and 77% on the right) of T. nasczokinii trees has the vitality status “healthy” (See Fig. 4). Thus, both T. nasczokinii populations are characterized by the normal ontogenetic structure with the complete left-handed spectrum. They are able to reproduce both by seeds and by vegetative organs. The existence of unique T. nasczokinii populations is possible only if the natural phytocenosis with its participation is preserved.

The Forest Observation System, building a global reference dataset for remote sensing of forest biomass

Forest biomass is an essential indicator for monitoring the Earth's ecosystems and climate. It is a critical input to greenhouse gas accounting, estimation of carbon losses and forest degradation, assessment of renewable energy potential, and for developing climate change mitigation policies such as REDD+, among others. Wall-to-wall mapping of aboveground biomass (AGB) is now possible with satellite remote sensing (RS). However, RS methods require extant, up-to-date, reliable, representative and comparable in situ data for calibration and validation. Here, we present the Forest Observation System (FOS) initiative, an international cooperation to establish and maintain a global in situ forest biomass database. AGB and canopy height estimates with their associated uncertainties are derived at a 0.25 ha scale from field measurements made in permanent research plots across the world's forests. All plot estimates are geolocated and have a size that allows for direct comparison with many RS measurements. The FOS offers the potential to improve the accuracy of RS-based biomass products while developing new synergies between the RS and ground-based ecosystem research communities.

Permafrost landslides promote soil CO2 emission and hinder C accumulation

Landslides are common in high-latitude forest ecosystems that have developed on permafrost. The most vulnerable areas in the permafrost territories of Siberia occur on the south-facing slopes of northern rivers, where they are observed on about 20% of the total area of river slopes. Landslide disturbances will likely increase with climate change especially due to increasing summer-autumn precipitation. These processes are the most destructive natural disturbance agent and lead to the complete removal of pre-slide forest ecosystems (vegetation cover and soil). To evaluate postsliding ecosystem succession, we undertook integrated ecological research at landslides of different age classes along the Nizhnyaya Tunguska River and the Kochechum River (Tura, Krasnoyarsk region, Russia). Just after the event (at the one-year-old site), we registered a drop in soil respiration, a threefold lower microbial respiration rate, and a fourfold smaller mineral soil carbon and nitrogen stock at bare soil (melkozem) plots at the middle location of the site as compared with the non-affected control site. The recovery of disturbed areas began with the re-establishment of plant cover and the following accumulation of an organic soil layer. During the 35-year succession (L1972), the accumulated layer (O-layer) at the oldest site contained similar C- and N stocks to those found at the control sites. However, the mineral soil C- and N stocks and the microbial biomass - even of the oldest landslide area - did not reach the value of these parameters in control plots. Later, the soil respiration level and the eco-physiological status of soil microbiota also recovered due to these changes. This study demonstrates that the recovery after landslides in permafrost forests takes several decades. In addition, the degradation of permafrost due to landslides clearly hinders the accumulation of soil organic matter in the mineral soil.

[Post-logging organic matter recovery in forest ecosystems of eastern Baikal region]

The dynamics of organic matter accumulated in the soil and main vegetation elements was analyzed for post-logging forest ecosystem succession series in eastern Baikal region. The phytomass was found to allocate up 63 and 50% of carbon in undisturbed Scots pine and fir stands, respectively. The post-logging phytomass contribution to the total carbon pool appeared to decrease down to 16% in Scots pine and 6% in fir stands. In Scots pine stands, carbon storage was determined to account for almost 70% of the initial carbon 60 years after logging. In 50- to 55-year-old fir stands, carbon recovered its initial pool only by 10%. Soil carbon recorded in recently logged Scots pine and fir sites appeared to be 5 and 16 times that accumulated in the phytomass, respectively. The ratio between phytomass carbon and soil organic matter recovered back to the prelogging level in Scots pine stands by the age of 50-60 years. While phytomass carbon also increased in fir stand of the same age, it did not reach the level of the control stand.