The advancing timberline on Mt. Fuji: natural recovery or climate change?
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- Sakio, H. & Masuzawa, T. J Plant Res (2012) 125: 539. doi:10.1007/s10265-011-0465-3
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The alpine timberline on Mt. Fuji (central Japan) is at 2,400–2,500 m above sea level. Over a 21-year period (1978–1999), we tracked changes in this vegetation boundary on a transect at a site impacted by the 1707 volcanic eruption. The timberline advanced rapidly upwards during this time period. Dominant tree species at the timberline (Alnus maximowiczii, Salix reinii, and Larix kaempferi) colonized sites that were initially largely free of vegetation at higher altitudes. Seedlings of L. kaempferi were particularly abundant at the border of advancing vegetation. According to tree age, we found that this was the first canopy species in the colonized areas. L. kaempferi is drought resistant, and this probably contributes to its establishment capability in the high-altitude climate. Most seedlings of Abies veitchii invaded patches of herbs and shrubs. These vegetation patches in the upper kampfzone provide important shelter for seedlings of invading tree species. We predict that the upward advance of the alpine timberline is a recovery process following the volcanic eruption, and that climate change may accelerate this advance.
KeywordsAbies veitchiiAge structureAlpineClimate changeLarix kaempferiSeedling establishment
The alpine timberline is a vegetation boundary marking the forest limit on high mountains. The zone around the alpine timberline is termed the “kampfzone,” and trees struggle to survive there (Tranquillini 1979). In this zone, the timberline migrates upwards and downwards over time. The main plant-limiting factors at the timberline are low air and soil temperatures, carbon limitation, frost damage, winter desiccation, wind, and snow (Holtmeier 2009). Ecophysiological investigations in this harsh climate contribute greatly to our knowledge of plant adaptations to the environment, especially morphological adaptations.
It is thought that global warming effects will first become evident in polar and high altitude ecosystems (Grabherr et al. 1994; Kullman 2001; Sanz-Elorza et al. 2003; Sturm et al. 2001; Wardle and Coleman 1992). Grabherr et al. (1994) demonstrated significant ecological impacts of global warming in the upwards advance of alpine-nival flora. Hence, long-term ecological research on alpine timberline dynamics is likely to provide integrated warning signals of climate change.
Has the alpine timberline of Mt. Fuji advanced over time?
What is the mechanism by which the timberline advances?
Materials and methods
The timberline climate on Mt. Fuji is cold, very windy, and with little snow cover (ca. 30 cm in depth from November to February). Annual mean air temperature is 1.1°C, with the highest and lowest monthly means of 11.8°C in August and −9.5°C in February (Masuzawa 1985). Annual precipitation is about 4,500 mm (Ito, 1964). Precipitation levels are high year-round, especially during the summer growing season. Relative humidity is high from May to October, and particularly high from June to September (mean >80%) when afternoons are frequently foggy (Masuzawa 1985).
The surface substratum consists of basalt scoria from the volcanic eruptions of Hoei in 1707. This scoria is easily moved by the freeze–thaw cycle and by strong wind; the ground surface is very unstable (Oka 1980). The nitrogen and carbon content of the soil is very low, 0.02 and 0.3%, respectively, at the upper timberline (Masuzawa 1985).
Increment cores were taken with a borer from three canopy tree species, i.e., L. kaempferi, A. veitchii, and P. jezoensis var. hondoensis. The largest tree (measured in DBH) of each species in each plot was selected to estimate its age. The increment borer was screwed into trunks about 40 cm above ground level, as close as possible to the substratum. Tree age was estimated from the sum of the number of annual rings in each core and the mean age of 40-cm-tall saplings. When the borer missed a tree center, the number of annual rings in the missing part was extrapolated from mean radial growth data.
We recorded seedling establishment in the eight uppermost plots (1–8). Data were used to investigate the upwards advance of vegetation. The number, diameter, and height of new seedlings established between 1978 and 1999 was measured in each plot in 1999. We recorded the shortest distance between each seedling and the edge of vegetation patches containing dwarf trees and herbs.
The advance rate of the alpine timberline before 1978 was estimated from the age of the largest L. kampferi tree in each plot because this is the dominant species of the timberline. The colonized age of this tree on each plot was estimated from the relation between largest age and distance. The advance rate was calculated from the difference in age between plot 5 and plot 22. The rate from 1978 to 1999 was estimated from the newly established seedlings over 130 cm in height.
Change in forest structure over time
Age structure of dominant tree species
Establishment of seedlings at the upper timberline
Number and height of Larix seedlings established from 1978 to 1999
No. of seedlings
Seedling height (cm)
12 ± 8
32 ± 38
52 ± 60
74 ± 79
77 ± 74
44 ± 23
11 ± 9
Distance from the edge of vegetation patch
No. of seedlings
Distance from patch (cm)
Picea jezoensis var. hondoensis
Advance rate of the alpine timberline
The vegetation on the mountain was displaced downwards by a volcanic eruption by Hoei-Zan in 1707, and our study site was bare ground 300 years ago. On Mt. Fuji, the timberline on the western slope that escaped the eruption in 1707 is at 2,800 m asl, with a limit at 2,900 m (Oka 1992). Hence, it is expected that vegetation near the study site will progress toward the same altitude as the timberline on the western slope. It might be argued that the recent advance upwards in our study site is part of a recovery process following the eruption. Indeed, the alpine timberline on the southeastern slope has advanced upwards for about 200 years (Fig. 7). Maruta and Masuyama (2009) also showed the advance of the timberline using aerial photography, and reached the conclusion that the cause of the advance of the timberline ecotone on the southern slope affected by the eruption of Mt. Fuji is natural recovery through succession. In this study site, the advance rate of L. kaempferi trees was 7.6 m per 10 years before 1978, while a rough rate estimate from seedling establishment after 1979 gave a figure of about 10 m in 10 years (Figs. 4, 8). Hence, the advance rate has not changed significantly.
However, the shape of L. kaempferi trees at our study site have changed. Maruta and Masuyama (2009) classified the form of this species on the south slope of Mt. Fuji into five categories. Table-shaped trees (formed by the continuous death of main shoots) occurred only in the upper kampfzone, whereas erect trees with symmetrical branches occurred in down-slope sections of the timberline. These changes in tree shape may represent the natural course of primary succession. Akasaka and Tsuyuzaki (2005) showed that stunted and branched stems with higher root allocation in L. kaempferi is an adaptation to bare ground for the effective acquisition of light, water, nutrients, and high tolerance to wind. At our study site 21 years ago, most L. kaempferi trees were table-shaped in the upper kampfzone. Most trees present in 1978 had reached a ceiling as table-shaped trees (Fig. 9). On the other hand, trees that colonized after 1978 were erect from the start, having retained their main stems, and table shapes were absent (Fig. 9). Slatyer (1976) demonstrated that low temperature kills Eucalyptus pauciflora at the timberline in the Snowy Mountains of Australia. Tranquillini (1979) argued, however, that tree death in winter at the timberline is attributable to desiccation stress. On Mt. Fuji, the primary factor causing winter desiccation damage and krummholz formation in timberline larch (L. kaempferi) is abrasion by fine, wind-blown volcanic gravel (Maruta 1996). It is expected that bark abrasion will be reduced and high plant water content will be maintained in mild winters, as found by Maruta (1996) for shoots of krummholz larches in the winter of 1985–1986. Measurements from the meteorological station at the summit of Mt. Fuji show that there has been a reduction in wind velocity during recent winters (Japan Meteorological Agency 2011).
The dominant high-altitude trees on Mt. Fuji (A. maximowiczii, S. reinii, and L. kaempferi) colonized upper sections of the timberline over our 21-year study period (Figs. 4, 8). A. maximowiczii and S. reinii are pioneer shrubs with many stems, and they tend to disappear from forests with tall trees due to shading. A. maximowiczii dwarf forest is highly productive (Sakio and Masuzawa 1987) and has a high nitrogen content in leaves (Sakio and Masuzawa 1992); therefore, this forest type could play an important role in nitrogen supply to soil below this forest. L. kaempferi was a particularly active dominant tall tree in this zone; tree age analysis (Fig. 7) and patterns of seedling establishment (Fig. 8) demonstrated that L. kaempferi was the first colonizer among canopy tree species to the high altitude zones, while A. veitchii was the last colonizer. S. reinii is particularly dominant in vegetation patches below 50 cm in height in the herb layer of upper sections of the timberline, and may provide important shelter for A. veitchii seedlings. L. kaempferi is drought resistant and is able to colonize very dry landscape areas. A. veitchii seedlings invaded existing herb and shrub patches, where climatic conditions are moderate. These vegetation patches in the upper kampfzone play important roles in tree seedling invasion, indicating that facilitative interactions among alpine plants increase with stress (Callaway et al. 2002). Yura (1988, 1989) suggested that L. kaempferi seedlings can avoid desiccation by extending roots deep into the soil faster than A. veitchii seedlings. This may help explain why L. kaempferi is able to become established in dry barren ground outside herb/shrub patches.
In conclusion, the timberline of Mt. Fuji at our study site will continue to advance upward in the future as a natural recovery process from the volcanic eruption of 1707. Although the influence of climate change on the advance of the timberline was not clear in this research apart from a change in tree shape, climate-related changes such as increases in air temperature and CO2 concentration may accelerate the advance of the timberline in the future. Therefore, long-term ecological monitoring is needed to elucidate the dynamics of the timberline ecotone on Mt. Fuji in relation to climate change.
The authors are indebted to Dr. F. Konta for his advice, and to members of the Laboratory of Plant Ecology, Shizuoka University, for their kind assistance during field work. A part of this investigation was financed by a Grant-in-Aid for Scientific Research (B) (No. 19310008) from the Ministry of Education, Culture, Sports, Science and Technology. We would also like to thank anonymous reviewers and an editor for very constructive comments and suggestions.