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Topics of revegetation on Mount Usu (有珠山における植物群集動態)

Mount Usu / Sarobetsu post-mined peatland
From left: Crater basin in 1986 and 2006. Cottongrass / Daylily

[ volcanoes | volcanology | Mount Usu ]

Summit area before the 1977-78 eruptions
Forests dominated by Populus maximowiczii and Betula platyphylla var. japonica
Artificial meadows: grazed by cow
The effects of the 1977-78 eruptions
The summit area was covered with volcanic ejecta of which thickness was 1-3 m
→ the former vegetation was completely destroyed
After the eruptions, I have annually monitored vegetation succession on the summit areas, by using permanent plots, since 1983. The survey in 2015 was completed.

[plant community dynamics on volcanoes]

Table 1. Life form and seed dispersal type of vascular plants observed on the volcano Usu (number of species). I: Vegetatively recovering species, II: Immigrant species, III: Artificially introduced species, and IV: Buried-seed species (Tsuyuzaki 1987)
    Group                I  II III  IV  Total
    Annual               0   3   0   8    11
    Perennial           64   8   3   9    84
    Woody               31   7   2   0    40
        long distance    7  10   0   0    17
        short distance  49   3   4   7    63
    Gravity-dispersal   10   1   0   5    16
    Self-dispersal       8   2   0   5    15
    Animal-dispersal    21   2   1   0    24
    Total               95  18   5  17   135

Characteristics of succession after the 1977-78 eruptions (特徴)

Permanent pltos monitored for more than 30 years confirmed the following four topics Usu
  1. A rolling stone gathers no moss
    No moss stage in the succession (Tsuyuzaki 1987)
  2. You can't squeeze blood out of stone
    No annual plant stage in the succession (Tsuyuzaki 1994)

    → Exception: seedbank (埋土種子) in the former topsoil contained many annuals

  3. Unsung heroes in the plant community
    Perennial plants derived from vegetative reproduction were dominated soon after the eruption (Tsuyuzaki 1989)
  4. Fable of the hare and the tortoise
    Forestation was faster on slowly-recovered areas in the early stages than on areas recovered fast (Tsuyuzaki 2009)
    See the abstract of G8 symposium P

(Tsuyuzaki 2019)

Still increasing for 30 years
Fig. Yearly fluctuations of mean (a) species richness, (b) diversity and (c) evenness for 25 years from 1984 to 2008 in 2 × 5 m plots (shaded circles) and from 1994 to 2008 in 5 × 5 m plots (open circles) after the 1977 and 1978 eruptions of Mount Usu, northern Japan. Mean (circles) is shown with standard deviation (vertical bars). The statistical significances were examined by generalized linear mixed model

(Otaki & Tsuyuzaki 2016)

Litter decomposition

Changes in the fungal and bacterial biomass and community structure in litter after the volcanic eruptions of Mount Usu, northern Japan, were investigated using a chronosequence approach, which is widely used for analyzing vegetation succession. The vegetation changed from bare ground (10 years after the eruptions) with little plant cover and poor soil to monotonic grassland dominated by Polygonum sachalinense with undeveloped soil (33 years) and then to deciduous broad-leaved forest dominated by Populus maximowiczii with diverse species composition and well-developed soil (100 years). At three chronosequential sites, we evaluated the compositions of phospholipid fatty acids (PLFAs), carbon (C) and nitrogen (N) contents and the isotope ratios of C (δ13C) and N (δ15N) in the litter of two dominant species, Polygonum sachalinense and Populus maximowiczii. The C/N ratio, δ13C and δ15N in the litter of these two species were higher in the forest than that in the bare ground and grassland. The PLFAs gradually increased from the bare ground to the forest, showing that microbial biomass increased with the development of the soil and/or vegetation. The fungi-to-bacteria ratio of PLFA was constant at 5.3 ± 1.4 in all three sites, suggesting that fungi were predominant. A canonical correspondence analysis suggested that the PLFA composition was related to the successional ages and the developing soil properties (P < 0.05, ANOSIM). The chrono-sequential analysis effectively detected the successional changes in both microbial and plant communities.