Long-term forest composition and its drivers in taiga forest in NW Russia

Understanding the processes behind long-term boreal forest dynamics can provide information that assists in predicting future boreal vegetation under changing environmental conditions. Here, we examine Holocene stand-scale vegetation dynamics and its drivers at the western boundary of the Russian taiga forest in NW Russia. Fossil pollen and conifer stomata records from four small hollow sites and two lake sites are used to reconstruct local vegetation dynamics during the Holocene. Variation partitioning is used to assess the relative importance of the potential drivers (temperature, forest fires and growing site wetness) to the long-term stand-scale dynamics in taiga forest. All the main tree taxa, including the boreal keystone species Picea abies (Norway spruce) and Larix sibirica (Siberian larch), have been locally present since 10,000 cal yr bp. The constant Holocene presence of L. sibirica at three small hollow sites suggests a fast postglacial immigration of the species in northern Europe. Picea was present but not dominant at all study sites until its expansion between 8,000 and 7,000 cal yr bp markedly changed the forest structure through the suppression of Betula (birch), Pinus (pine) and Larix. Our results demonstrate that in general, the Holocene forest dynamics in our study region have been driven by temperature, but during short intervals the role of local factors, especially forest fires, has been prominent. The comparison between sites reveals the importance of local factors in stand-scale dynamics in taiga forests. Therefore, the future responses of taiga forest to climate change will be predominantly modulated by the local characteristics at the site.     

六种温带森林类型凋落物量长期动态及其环境驱动

阐明凋落物动态及其环境控制机制,可以为森林生态系统生产力及碳汇功能的维持提供重要的数据支持和理论依据。以长白山系余脉张广才岭西坡林龄相近但立地条件不同的4种天然次生林（即硬阔叶林、杨桦林、杂木林和蒙古栎林）和2种人工林（落叶松人工林和红松人工林）为研究对象,对其地上凋落物产量及其组分以及相关环境因子进行了14年（2008-2021年）的连续测定,旨在揭示森林凋落物量及其组分的时空变化（林型间和年际变异）及其环境驱动机制。结果表明：6种森林类型的凋落总量（TL）无显著差异,波动范围为500.5-556.1 g m^-2 a^-1;但其叶凋落量（LL）、繁殖组织凋落量（RT）和其他组织凋落量（OT）均存在显著差异,波动范围依次分别为333.9-391.8 g m^-2 a^-1、8.43-69.93 g m^-2 a^-1和93.4-185.9 g m^-2 a^-1。6种森林类型的TL均存在显著的年际变化;其中LL和OT年际变化的显著性因森林类型而不同,而RT的年际变化不显著。除落叶松人工林外,其余5种森林类型的LL与生长季平均气温、日最低气温均值、土壤10 cm深度处的平均温度、最低温度（Ts_min）和土壤5 cm含水量（Ms）均呈显著正相关。杂木林、硬阔叶林和红松人工林的RT与Ms呈显著负相关;杂木林、杨桦林和硬阔叶林的OT与Ts_min呈显著负相关。样地水平的LL与土壤10 cm处含水量存在显著的正相关关系,而RT和OT则与其呈现显著负相关关系。这些结果表明林龄相似的温带森林地上凋落物总量有趋同趋势,但其通过改变组分分配格局来适应立地条件的变化;土壤湿度和温度变化会引起凋落物量的年际变化,但不同森林类型的凋落物量对环境波动的敏感性不同。     

Contribution of winter processes to soil nitrogen flux in taiga forest ecosystems

We measured annual net nitrogen (N) mineralization, nitrification, and amino acid production in situ across a primary successional sequence in interior Alaska, USA. Net N mineralization per gram dry soil increased across the successional sequence, but with a sharp decline in the oldest stage (black spruce). Net N mineralization expressed per gram soil organic matter exhibited the opposite pattern, suggesting that soil organic matter quality decreases significantly across succession. Net N mineralization rates during the growing season from green-up (early May) through freeze-up (late September–early October) accounted for approximately 60% of the annual inorganic N flux, whereas the remaining N was released during the apparent dormant season. Nitrogen release during winter occurred primarily during October–January with only negligible N mineralization during early spring in stands of willow, alder, balsam poplar and white spruce. By contrast, black spruce stands exhibited substantial mineralization after snow melt during early spring. The high rates of N mineralization in late autumn through early winter coincide with high turnover of fine root biomass in these stands, suggesting that labile substrate production, rather than temperature, is a major controlling factor over N release in these ecosystems. We suggest that the convention of restricting measurements of soil processes to the growing season greatly underestimate annual flux rates of inorganic nitrogen in these high-latitude ecosystems.     

A comparison of taiga flora in north-eastern Russia and Alaska/Yukon

Aim To understand the similarities and differences between the taiga floras of far north‐eastern Asia and north‐western North America in the light of their Tertiary and Quaternary histories. Does the taiga flora follow the tundra pattern (Asian–American commonality of species as a result of continuity through the Quaternary), the temperate forest pattern (distinct species because of late Tertiary disjunction), a combination of these two patterns, or some pattern unique to the taiga? Location The taiga regions of interior Alaska and the Yukon in North America (the ‘Alaskan taiga’), and the Kolyma and eastern Indigirka River basins in Russia (the ‘Kolyma taiga’). The study areas include both forested and unforested habitats below elevational treeline. The two regions have similar climate and topography and were linked via the Bering Land Bridge in the Tertiary and for several extended periods during Quaternary cold periods. Methods Systematic comparison of the vascular floras of the two regions from published sources; and review of palaeoecological literature for the region. Results Of the 796 species found in the study areas, 27% occur only in the Alaskan taiga, 35% occur only in the Kolyma taiga, and 38% occur in both the regions. The following subsets of species show a high proportion of species in common between the study areas (subsets are not mutually exclusive): plants that occur on the tundra and the taiga, non‐flowering plants, abundant taiga understory plants, and wetland and aquatic plants. A lower proportion of shared plants was noted for warm, south‐facing steppe communities. No tree species are common to both areas. Main conclusions The Bering Strait region in the Quaternary has acted as a biogeographical filter for taiga plants. Significant divergence between northeast Asia and northwest North America has developed among the more southerly ranging fraction of the flora (e.g. trees), while the more cosmopolitan and the most cold‐adapted elements of the taiga flora are common to both areas. Many plants in the former group have been disjunct between Asia and North America for millions of years, while many plants in the latter group have probably maintained continuity between the study areas via the Bering Land Bridge through much of the late Tertiary and Quaternary periods. Repeated extirpation of the less cold‐adapted species from both study areas during Pleistocene cold periods has probably enhanced floristic differences between the two regions.     

Community of dark-spored myxomycetes in ground litter and soil of taiga forest (Nizhne-Svirskiy Reserve,Russia) revealed by DNA metabarcoding

The diversity of dark-spored myxomycetes in forest ground litter and soil from four study plots across a fire chronosequence in Nizhne-Svirskiy Nature Reserve (northwest of Russia) was assessed by a DNA metabarcoding approach. The history of fire disturbances and the season of sampling influenced the composition of myxomycete assemblages. Several species showed substrate preferences different from what is known from fruiting body records. A high abundance of nivicolous species in the majority of the samples suggests that this ecological group constitutes a common element of soil microbial communities in lowland taiga forests. Four species are reported for the Leningrad region for the first time. Our results support the hypothesis that amoebae populations of myxomycetes may have much wider ecological niches than indicated by records of fructifications, and further environmental studies may provide valuable new insights on myxomycete ecology and distribution.     

Threatened Alvar Grasslands in NW Russia and their Relationship to Alvars in Estonia

Alvar grasslands are thin-soil calcareous grasslands on Silurian and Ordovician limestone bedrock. They are considered unique plant communities for northern Europe and America with a high conservation value. Until now, European alvar grasslands have only been described in Sweden and Estonia. We described species-rich alvar grasslands on the Izhora plateau, NW Russia and compared this vegetation with that of Estonian alvar grasslands. Floristic composition and environmental conditions of Russian alvars were similar to Estonian alvar grasslands on thicker dry soil. Russian alvars are isolated from similar communities in Estonia, but extensive transport of domestic animals from Estonia to NW Russia in past centuries has probably enhanced species dispersal. Some characteristic Estonian alvar species were missing in NW Russia because it lies outside their natural ranges. Other differences in vegetation were explained by higher atmospheric nitrogen deposition and younger age of Russian sites. In NW Russia the alvar grasslands were small, but several red-listed plant species were present. In order to preserve European alvar vegetation effectively, Russian alvar grasslands need further study and conservation as an outpost of this threatened vegetation type.     

内蒙古森林火灾发生风险及其驱动因素

森林火灾是危害森林健康的主要灾害之一,科学预测森林火灾是预防森林火灾的重要依据。以中国新旧森林火灾政策作为分界线,将内蒙古森林历史火灾数据分为四个阶段,基于增强回归树模型建立内蒙古森林火灾发生模型,预测森林火灾发生情况,解释不同时期森林火灾和火灾风险变化的差异。预测结果表明:(1)4个时期建模精度AUC均大于0.94,表明BRT模型能够较好地预测研究区森林火灾的发生;(2)气温日较差、日最小相对湿度、上一年春防累计降水量、上一年秋防累计降水量、上一年春防最高地表气温海拔、距火点最近公路距离被确定为影响内蒙古森林火灾发生的重要驱动因素。(3)新旧《森林防火条例》实施前后森林火灾风险等级变化:1981-1988年3月14日,中、高和极高森林火灾风险区分布在呼伦贝尔的东部,而2009-2020年中、高和极高森林火灾风险区分布在呼伦贝尔南部和中部、赤峰市的西南部、锡林郭勒盟和呼和浩特市的中部、乌兰察布市和包头市的南部以及鄂尔多斯市的东部。有助于了解不同时期《森林防火条例》影响下的内蒙古森林火灾的驱动因素和火险等级的变化,为优化森林火灾管理政策及预测预报工作提供科学依据。     

俄罗期平原针—阔林过渡带森林群落组成结构与物种多样性的研究

俄罗斯平原针-阔林过渡带森林群落的物种多样性的研究表明,该地区的物种多样性类同于许多类型的过渡带,即群落的过渡带（针阔混交林）比相邻群落（针叶林和阔叶林）具有更高的多样性。针阔混交林群落的组成结构较好地反映了其特殊的过渡性。在该过渡带较高的物种多样性并不证明群落稳定性的增加。因此,在探讨多样性与群落稳定性关系时,综合包括均匀度在内的多个指数才可能作出较为客观的结论。     

俄罗斯平原针－阔林过渡带森林群落组成结构与物种多样性的研究

俄罗斯平原针－阔林过渡带森林群落的物种多样性的研究表明,该地区的物种多样性类同于许多类型的过渡带,即群落的过渡带 (针阔混交林)比相邻群落(针叶林和阔叶林)具有更高的多样性。针阔混交林群落的组成结构较好地反映了其特殊的过渡性。在该过渡带较高的物种多样性并不证明群落稳定性的增加。因此,在探讨多样性与群落稳定性关系时,综合包括均匀度在内的多个指数才可能作出较为客观的结论。     

Forest floor respiration in a black spruce taiga forest ecosystem in Alaska

A technique was developed for measuring respiration of virtually undisturbed forest floor samples, and used to follow seasonal changes in two black spruce forest stands in interior Alaska, In the laboratory, soil respiration showed a positive response to increasing temperature: however, respiration measured in the field was negatively correlated with air and soil temperature, but positively correlated with water content of the soil within the range (100–250% of dry weight) normally experienced in the field. Moisture levels above 250% inhibited respiration. Precipitation events usually stimulate forest floor respiration, but prolonged periods of dry and rainy weather lead to limitation of respiration by sub- and supraoptimal moisture, respectively. Long-term confinement of soil has significant effects upon soil arthropod densities, moisture content, temperature, and respiration, and should not be taken to represent the natural conditions of the forest floor.     

Exoskeleton anomalies in taiga tick females from populations of the Asian part of Russia

Geographic variation of exoskeleton anomalies in females of the taiga tick Ixodes persulcatus Schulze, 1930 is described in populations of the Asian part of Russia. The total material examined comprised 3872 females collected by the flagging method from vegetation in the Far Eastern, Siberian, and Ural Federal Districts of Russia. Exoskeleton anomalies were found in all the populations studied, the “shagreen skin” anomaly of the scutum being prevalent in all the localities. Anomalies were significantly more frequent (63.4 ± 3.39%) in females collected north of 55°N than in those collected in more southern localities of the Siberian Federal District (33.1 ± 3.43%). At the same time, the frequency of anomalies was lower (24.4 ± 1.93%) in females from the Far Eastern Federal District than in specimens from territories with an extreme continental climate. The variation in the females’ exoskeleton structure observed in the Asian part of Russia may reflect the natural phenogeographic variability rather than result from anthropogenic impact.     

Long-term changes in forest response to extreme atmospheric dryness

Atmospheric dryness, as indicated by vapor pressure deficit (VPD), has a strong influence on forest greenhouse gas exchange with the atmosphere. In this study, we used long-term (10–30 years) net ecosystem productivity (NEP) measurements from 60 forest sites across the world (1003 site-years) to quantify long-term changes in forest NEP resistance and NEP recovery in response to extreme atmospheric dryness. We tested two hypotheses: first, across sites differences in NEP resistance and NEP recovery of forests will depend on both the biophysical characteristics (i.e., leaf area index [LAI] and forest type) of the forest as well as on the local meteorological conditions of the site (i.e., mean VPD of the site), and second, forests experiencing an increasing trend in frequency and intensity of extreme dryness will show an increasing trend in NEP resistance and NEP recovery over time due to emergence of long-term ecological stress memory. We used a data-driven statistical learning approach to quantify NEP resistance and NEP recovery over multiple years. Our results showed that forest types, LAI, and median local VPD conditions explained over 50% of variance in both NEP resistance and NEP recovery, with drier sites showing higher NEP resistance and NEP recovery compared to sites with less atmospheric dryness. The impact of extreme atmospheric dryness events on NEP lasted for up to 3 days following most severe extreme events in most forests, indicated by an NEP recovery of less than 100%. We rejected our second hypothesis as we found no consistent relationship between trends of extreme VPD with trends in NEP resistance and NEP recovery across different forest sites, thus an increase in atmospheric dryness as it is predicted might not increase the resistance or recovery of forests in terms of NEP.     

Exoskeleton anomalies in taiga tick males from populations of the Asian part of Russia

Variation of the exoskeleton is described for 2630 males of the taiga tick Ixodes persulcatus Schulze, 1930 collected by flagging from vegetation in the Far Eastern, Siberian, and Ural Federal Districts of Russia. Two types of conscutum anomalies were found to be prevalent in all the samples. Exoskeleton anomalies were less frequently recorded in the Far Eastern Federal District than in the Siberian and Ural Federal Districts: 6.5 ± 1.05, 29.7 ± 1.03, and 25.8 ± 3.93%, respectively. The observed phenotypic variation seems to be unrelated to anthropogenic impact. In the meridional direction, the taiga tick samples with different frequencies of exoskeleton anomalies correspond to two races of the species.     

大别山山核桃林植物组成与区系特征研究

大别山山核桃林植物组成与区系特征研究张旭东,黄成林（安徽农业大学,合肥２３００３６）叶志琪（合肥林业学校,合肥２３００３１）ＦｌｏｒｉｓｔｉｃｃｏｍｐｏｓｉｔｉｏｎａｎｄｉｔｓｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆＣａｒｙａｃａｔｈａｙｅｎｓｉｓｆｏｒｅ...