Secondary phloem traits in mature stems of Betula ermanii in stressful environments of volcanic activity

This research summarizes the results of study of structural peculiarities of Betula ermanii growing around Baransky Volcano close to the thermal Golubye Ozera. We have performed statistical analysis of parameters of the secondary phloem of multiyear shoots and stems and found some features tied to extreme environmental conditions. We have found that structural reaction of the secondary phloem of multiyear shoots and stems of B. ermanii to the extreme conditions of post-volcanic activity of Baransky Volcano manifests itself as changes in the geometry of the conductive elements and dilatation of the radial parenchyma in the non-conductive phloem. We believe these changes to be adaptive in nature due to the need for increased conductivity in volcanic landscapes.

Forest fire survival in young, dense Betula ermanii stands on soil scarification sites

A forest fire in a cool-temperate broad-leaved forest in northern Japan, from 26 May to 19 June 2019, provided an opportunity to examine its effects on young and dense birch (Betula ermanii Cham.) stands in soil scarification sites. To characterise post-fire responses (survival and resprouting) of birch, we set up two plots, 6 months post fire. We investigated trunk diameter at breast height and burn marks on tree trunks (scorch height and charring percentage around the tree bole) of all B. ermanii trees in both plots. Survival and resprouting of each tree were monitored over 2 years (6 and 16 months post fire). To quantify post-fire vegetation recovery in the forest floor, we manually mapped the dominant understory plant, dwarf bamboo (i.e. Sasa kurilensis (Rupr.) Makino et Shibata), from orthomosaic images obtained by an unmanned aircraft vehicle, and estimated the recovery rate in the second year post fire. Additionally, seedlings of woody species were counted in both plots. Size-dependent survival rates of plants in both plots were similar in the first year post fire. All B. ermanii trees died without resprouting in the second year post fire, indicating the lethal effects of fire on young birch trees. Moreover, a high recovery rate of dwarf bamboos over 2 years in both plots and limited seedling establishment of woody plants suggest that the fire resulted in regeneration failure of young stands in the scarification sites. On the basis of these findings, we propose future management of stands in soil scarification sites post fire, considering the vulnerability of young trees and the rapid change in vegetation from young forest to dense birch cover post fire.

Microsite Effects on Physiological Performance of Betula ermanii at and Beyond an Alpine Treeline Site on Changbai Mountain in Northeast China

The alpine treeline demarcates the temperature-limited upper elevational boundary of the tree life form. However, this treeline does not always occur exclusively as a sharp “line”, outposts of tree groups (OTG) with a height of at least 3 m are often observed in microsites up to several hundred meters beyond the line of continuous forest on some mountains. This suggests that other factors such as microenvironment may play a significant role in compensating for the alpine tree facing growth-limiting low temperature conditions. To test the microenvironment effects, this study compared the differences in growing conditions (climate and soil properties) and ecophysiological performance of Erman’s birch (Betula ermanii Cham.) trees growing in a continuous treeline site (CTL, ~1950 m above sea level, a.s.l.) and OTGs (~2050 m a.s.l.) on Changbai Mountain in northeastern China. The results show the average 2-m air temperature for OTG was slightly lower in the non-growing season than which at the CTL (−10.2 °C < −8.4 °C), there was no difference in growing season air temperature and soil temperature at 10 cm depth between CTL and OTG. The contents of focal soil nutrients in CTL and OTG were similar. Difference in K and Mn contents between sites were detected in leaves, difference in K, Mn, and Zn in shoots. However, comparing similarity of ecophysiological performances at an individual level, trees at CTL and OTG show no significant difference. Our study reveals that mature trees at the CTL and OTG experience generally similar environmental conditions (climate and soil properties) and exhibit similar overall ecophysiological performance (reflected in carbon reserves and nutrients). This might provide insight into how mature trees might be able to survive in areas higher than the continuous treeline, as well as the importance of microclimatic amelioration provided by protective microsites and the trees themselves.

Decreased Temperature with Increasing Elevation Decreases the End-Season Leaf-to-Wood Reallocation of Resources in Deciduous Betula ermanii Cham. Trees

Global air temperature has increased and continues to increase, especially in high latitude and high altitude areas, which may affect plant resource physiology and thus plant growth and productivity. The resource remobilization efficiency of plants in response to global warming is, however, still poorly understood. We thus assessed end-season resource remobilization from leaves to woody tissues in deciduous Betula ermanii Cham. trees grown along an elevational gradient ranging from 1700 m to 2187 m a.s.l. on Changbai Mountain, northeastern China. We hypothesized that end-season resource remobilization efficiency from leaves to storage tissues increases with increasing elevation or decreasing temperature. To test this hypothesis, concentrations of non-structural carbohydrates (NSCs), nitrogen (N), phosphorus (P), and potassium (K) during peak shoot growth (July) were compared with those at the end of growing season (September on Changbai Mt.) for each tissue type. To avoid leaf phenological effects on parameters, fallen leaves were collected at the end-season. Except for July-shoot NSC and July-leaf K, tissue concentrations of NSC, N, P, and K did not decrease with increasing elevation for both July and September. We found that the end-season leaf-to-wood reallocation efficiency decreased with increasing elevation. This lower reallocation efficiency may result in resource limitation in high-elevation trees. Future warming may promote leaf-to-wood resource reallocation, leading to upward shift of forests to higher elevations. The NSC, N, P, and K accumulated in stems and roots but not in shoots, especially in trees grown close to or at their upper limit, indicating that stems and roots of deciduous trees are the most important storage tissues over winter. Our results contribute to better understand the resource-related ecophysiological mechanisms for treeline formation, and vice versa, to better predict forest dynamics at high elevations in response to global warming. Our study provides resource-related ecophysiological knowledge for developing management strategies for high elevation forests in a rapidly warming world.