A study was conducted to explore the mechanism that emissions of volatile organic compounds (VOC) from heated needles and twigs (200°C, within 15 min) of Pinus pumila affect fire behaviours using the technology of Thermal Desorption — Gas Chromatography — Mass Spectrometry (TD-GC-MS). The results indicated that the main components of VOC from heated needles and twigs are terpenoids. Most of these terpenoids are monoterpenes. Terpenoids account for 72.93% for the needles and 92.40% for the twigs of the total VOC, and their emission ratios are 61.200 μg·g−1 and 217.060 μg·g−1 respectively. Heated twigs can emit more terpenoids than heated needles because twigs had more volatile oils than needles. In actual fires, these large amounts of terpenoid emissions, especially the monoterpene emissions, have strong effects on fire behaviors that are not only in the initial stage but also in the fast propagation stage of fires. These flammable gases are capable of causing violent combustion and creating crown fires. In addition, if these gases accumulate in an uneven geographical area, there will be a possible for eruptive fires and/or fires flashover to occur.

Emissions of volatile organic compounds from heated needles and twigs of Pinus pumila

Differences in tree and shrub growth responses to climate change in a boreal forest in China

We examined the effects of different life history strategies and tree competition on species coexistence in a northern coniferous forest. We investigated the growth and demography of trees with stems ≥1 cm dbh in a 2-ha study plot in the Taisetsu Mountains of northern Japan. Three species, Abies sachalinensis, Piceajezoensis, and Piceaglehnii, were found to be dominant in the forest. A. sachalinensis was the most dominant species in the understory, while the two Picea spp. were more abundant in the larger dbh size classes. The turnover rate of A. sachalinensis was about twice that of the Picea spp. The relative growth rate of understory trees in each species did not differ between different canopy conditions (closed canopy or canopy gap). The competitive advantage between A. sachalinensis and P. glehnii switched as they grew from understory (A. sachalinensis superior competitor) to canopy trees (P. glehnii superior competitor). Meanwhile, A. sachalinensis and P. jezoensis exhibited different environmental preferences. We propose that reversal in competitive superiority between different growth stages and trade-off between longevity and turnover are more important factors to promote their coexistence than regeneration niche differentiation related to canopy gaps in this sub-boreal coniferous forest.

Effects of life history strategies and tree competition on species coexistence in a sub-boreal coniferous forest of Japan

Recent temperature rise caused by human activities has led to profound changes in the forest ecosystem. Shrubs play an important role in the boreal forest. However, it is not clear how shrub growth responds to climate change, especially whether there is a difference in the response of shrub at different altitudes to climate change. Here, we developed three ring-width chronologies of Pinus pumila along an altitudinal gradient in the Aokelidui Mountains, northeast China, then analyzed the relationship between the growth of P. pumila and climate at different altitudes. The results showed that the radial growth of P. pumila at low altitude had more prominent climate signals than those at medium and high altitude and was more sensitive to climate change. The chronological similarity was the highest in low and middle altitudes (72.5%, p < 0.01). Summer temperature had a significant negative effect on the growth of shrubs, and summer precipitation was conducive to the formation of wider rings at medium altitude. The warmer winter of the previous year favored P. pumila growth at low and medium altitudes but just the opposite at high altitudes. After rapid warming, the negative correlation between temperature and P. pumila growth in the growing season changed to a positive correlation at high altitude. On the contrary, the relationship between precipitation and P. pumila growth in the growing season changed from a positive to a negative correlation. We also found that the sensitivity of the growth of P. pumila to the Standardized Precipitation Evapotranspiration Index (SPEI) has gradually increased at medium-altitude since the 1980s. Therefore, in recent decades, the effect of moisture on the radial growth of shrub has become more and more important at medium altitudes. At the same time, the temperature rise was beneficial to the growth of P. pumila at low altitude. Our results suggest that the treeline advancement in this area is unlikely to occur in the near future since the shrub at high altitudes is not sensitive to climate warming.

Climatic controls of Pinus pumila radial growth along an altitude gradient

The carbon (C) cycle in alpine ecosystems is sensitive to climate change, but information about the C storage in its undergrowth is scarce. In October 2017, a total of 6231 Pinus pumila (Pall.) Regel trees were investigated for above-ground growth and density in 60 sub-plots (10×10 m) from 12 stands (50 × 50 m) along the altitudinal gradient (800-1500 m a.s.l.) in Great Khingan Mountains, Inner Mongolia, Northeast China. Sites were characterized by different crown densities (CDs) from 20% to 90%. Height and root-collar diameter (RCD) were higher in stands with CDs of 40-70% than CDs of 20-30%. Stem density (SD) and crown area (CA) had a positive correlation with altitude and CD. Equations from local shrub models were used to adapt the allometric growth models for estimation. There were variations in estimated above-ground C density depending on the model and the involvement of the canopy area. Above-ground C storage in P. pumila individuals ranged from 0.05-2.46 kg tree-1, which corresponds to C storage density ranged from 0.17-37-ton ha-1. The C density in P. pumila increased with crown density instead of stem density along increasing altitudinal gradients and increasing RCD. Hence, the crown density and diameter of a P. pumila plant can be used to predict the above-ground C density of its natural population.

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Above-ground carbon storage in Pinus pumila along an alpine altitude in Khingan Mountains, Inner Mongolia of China

We investigated the spatial distribution and growth of the Siberian dwarf pine (Pinus pumila) in a valley–foothill larch–birch (Larix cajanderi–Betula platyphylla as canopy trees) mixed forest of fire origin located in central Kamchatka with the aim of elucidating the ecological features of P. pumila when it is an undergrowth species in a forest. The spatial distribution of all individuals of all tree species was clumped, and the spatial distribution of the two canopy tree species did not repulsively affect that of P. pumila (i.e., its establishment site). These results suggest that the regeneration of P. pumila does not depend on canopy gaps. However, the analysis using a growth model indicated that the canopy trees negatively affected the growth of P. pumila and that the negative effect of L. cajanderi on P. pumila growth was stronger than that of B. platyphylla. The direction of the crown extension of P. pumila was weakly related to the open-space direction. Our results suggest that, although the spatial pattern of establishment of P. pumila is not repulsed by the distribution of canopy trees, the crown can spread horizontally toward the more sparsely populated areas of the canopy trees where they may have higher growth rates.

Masaki Okuda

Papers

Establishment and growth pattern of Pinus pumila under a forest canopy in central Kamchatka