influenced by both the sago palm type (folk variety) and its growing environment. In
Tebing Tinggi Island, Riau Islands, Indonesia where peat soils stretch, there are three
types of sago palm, namely (1) spineless with black band on the petiole and rachis:
identified as Mumai or Bemban, (2) sparse spine on the petiole and rachis: identified
as Sago berduri, and (3) very sparse spine: identified as Sanka (Ehara 1997; Ehara
et al. 1998). The names of spineless type, Mumai or Bemban, were used at different
sites on the island. The spine on the rachis and petiole of both Sago berduri and
Sanka is short and that of Sanka will disappear gradually along the progress of
growth. Despite having indefinite genetic background, the said types have different
morphological traits such as the presence or absence of spine and/or spine density. It
is unclear whether they can be recognized individually as folk variety or not (it has
been proposed at the eighth International Sago Symposium held in 2005 that various
types of sago palms classified depending on their morphological characteristics and
growth traits shall fall under folk varieties until the extent of genetic variation in
Metroxylon sagu is clarified (Ehara 2005).
Regarding the leaf emergence rate, Flach (1977) expressed that one leaf appears
per month. In the survey conducted by Yamamoto et al. (2000, 2006), the leaf
emergence rate was 8.4–10.3 leaves per year in Sulawesi Island, Indonesia and
5.8–7.0 leaves per year in Papua, Indonesia, which equals to 0.48 to 0.86 leaves per
month. On the other hand, Yamaguchi et al. (1997) reported leaf emergence rate of
12.0 leaves per year on trees growing in the thick peat horizons (increased up to
17.0–19.2 leaves per year, 3–4 years after the trunk formation) and 13.4–15.5 leaves
per year on trees growing in the thin peat horizons in Sarawak, Malaysia. Their
findings correspond to 1.0–1.29 leaves per month in peat soils. It is unclear how the
leaf emergence rate changes from the rosette stage to the trunk formation stage
(Nakamura et al. 2015b). Furthermore, the age of sago palms observed in the former
studies was uncertain and their genetic backgrounds were also different. Therefore,
the reported leaf emergence rates cannot be compared directly to one another.
Further investigation on leaf emergence in different soil conditions is needed.
17.3.2 Leaf Longevity
Kakuda et al. (2000) concluded in the report that peat soil provides more mineralization and nitrogen supply compared to mineral soil. According to the results of
analysis commenced by Kawahigashi et al. (2003) on peat soils and soil solutions in
Mukah, Malaysia, the peat soil horizon exhibits different characteristics depending
on the peat accumulation process. The leaf photosynthetic rate of sago palms reaches
a maximum 37–45 days after the unfolding of leaves and has 50% of the maximum
photosynthetic rate even about 70 days after unfolding of the leaves (Uchida et al.
1990). The lifespan of sago palm leaf was reported to be 8–13 months (Yamamoto
1998) or about 2 years (Flach and Schuiling 1989). Considering said information and
a report by Uchida et al. (1990), sago palm’s leaf development and deterioration
relating to the photosynthetic ability are slow compared to those of annual crops.
482
H. Ehara et al.
Tebing Tinggi Island, Riau Islands, Indonesia where peat soils stretch, there are three
types of sago palm, namely (1) spineless with black band on the petiole and rachis:
identified as Mumai or Bemban, (2) sparse spine on the petiole and rachis: identified
as Sago berduri, and (3) very sparse spine: identified as Sanka (Ehara 1997; Ehara
et al. 1998). The names of spineless type, Mumai or Bemban, were used at different
sites on the island. The spine on the rachis and petiole of both Sago berduri and
Sanka is short and that of Sanka will disappear gradually along the progress of
growth. Despite having indefinite genetic background, the said types have different
morphological traits such as the presence or absence of spine and/or spine density. It
is unclear whether they can be recognized individually as folk variety or not (it has
been proposed at the eighth International Sago Symposium held in 2005 that various
types of sago palms classified depending on their morphological characteristics and
growth traits shall fall under folk varieties until the extent of genetic variation in
Metroxylon sagu is clarified (Ehara 2005).
Regarding the leaf emergence rate, Flach (1977) expressed that one leaf appears
per month. In the survey conducted by Yamamoto et al. (2000, 2006), the leaf
emergence rate was 8.4–10.3 leaves per year in Sulawesi Island, Indonesia and
5.8–7.0 leaves per year in Papua, Indonesia, which equals to 0.48 to 0.86 leaves per
month. On the other hand, Yamaguchi et al. (1997) reported leaf emergence rate of
12.0 leaves per year on trees growing in the thick peat horizons (increased up to
17.0–19.2 leaves per year, 3–4 years after the trunk formation) and 13.4–15.5 leaves
per year on trees growing in the thin peat horizons in Sarawak, Malaysia. Their
findings correspond to 1.0–1.29 leaves per month in peat soils. It is unclear how the
leaf emergence rate changes from the rosette stage to the trunk formation stage
(Nakamura et al. 2015b). Furthermore, the age of sago palms observed in the former
studies was uncertain and their genetic backgrounds were also different. Therefore,
the reported leaf emergence rates cannot be compared directly to one another.
Further investigation on leaf emergence in different soil conditions is needed.
17.3.2 Leaf Longevity
Kakuda et al. (2000) concluded in the report that peat soil provides more mineralization and nitrogen supply compared to mineral soil. According to the results of
analysis commenced by Kawahigashi et al. (2003) on peat soils and soil solutions in
Mukah, Malaysia, the peat soil horizon exhibits different characteristics depending
on the peat accumulation process. The leaf photosynthetic rate of sago palms reaches
a maximum 37–45 days after the unfolding of leaves and has 50% of the maximum
photosynthetic rate even about 70 days after unfolding of the leaves (Uchida et al.
1990). The lifespan of sago palm leaf was reported to be 8–13 months (Yamamoto
1998) or about 2 years (Flach and Schuiling 1989). Considering said information and
a report by Uchida et al. (1990), sago palm’s leaf development and deterioration
relating to the photosynthetic ability are slow compared to those of annual crops.
482
H. Ehara et al.