By Michael
A. Bengwayan
Alnus
japonica or Japanese alder tree, when used as agroforest dominant
tree saves soil, food crops and biodiversity.
Alnus is a
non leguminous nitrogen fixing tree species. a deciduous or
semi-deciduous tree with a straight trunk, up to 30 m in height and
60 cm (rarely to 2 m) in diameter; twigs ribbed,
glabrescent;
bark dark grey, often with yellowish patches and slightly raised
lenticels. Leaves are alternate, elliptical, ovate to oblong,
yellow-brown scales; petiole strong.
It is
native to northeast Asia—Taiwan, Japan, Korea, Russia, and China.
Studies
suggest the stems, bark and leaves have antioxidant,
hepatoprotective, cytotoxic, anticancer, antiatherosclerotic,
antiviral, anti-trypanosomal, antiproliferative, pro-apoptotic
properties.
Alder
Gets to the Philippines
Alnus
japonica was introduced in the Philippines during the Second World
War particularly in Baguio City by the Japanese.
Alder
is now common on higher altitude. The climatic
conditions of the Cordillera favors the tree. it grows well in full
light but will also tolerate shade. At lower altitudes, it occurs in
moist sites, such as near rivers, but it will colonize in rocky sites
exposed by landslides or land abandoned after cultivation. It occurs
naturally in both pure and mixed stands and is common in streambeds,
near streams, in ravines and in drier forests. It is found naturally
in moist, cool,
subtropical
monsoon climates with a dry season of 4-8 months; it also grows in
humid, cool or subtropical mountain areas in tropical zones with high
rainfall.
.
Alnus
prefers moist and well-draied soils, including loam and loamy sand
gravel, sand and clay. It does not require high soil fertility but
prefers permeable soils. Grows well on soils with high water content
but not on waterlogged soils.
Restoring Poor Lands
Alnus restores soil
fertiliity through nitrogen fixation that takes place through a
symbiotic relationship between Alnus with nitrogen-fixing
actinomycetes of the genus Frankia and is therefore able to improve
degraded lands .
Symbiotic Frankia are
located in specialised structures, or nodules, along the root system
of the host plants. The root nodules are analogous to those induced
by Rhizobium in legumes, and they provide an environment, where
Frankia can grow and prosper, while providing the host-plant with
fixed nitrogen.
Unlike the
Rhizobium-legume symbiosis, where most of the host plants belong to a
single large family, Frankia can form root nodules in symbiosis with
actinorhizal plants distributed among eight families consisting of
over 200 species of angiosperms.
The value of alder tree
was recognized by the tribal farmers long back and more than 80 yrs
old trees can be seen in the area.
Agricultural crops,
together with alder trees forms a very remunerative agro-forestry
system and the ability of the tree to develop and retain soil
fertility has been fully utilized by the tribal
farmers of of the
Cordilleras.
Soil conservation
Soil erosion due to high
rainfall and hilly topography is very high in most of the Cordillera
provinces. There is great need to check the rate of soil erosion.
In this regard, the deep root system of alnus gives some stability to
slopes that tend to slip and erode. Its seeds have been
broadcast to stabilize landslides area effectively
used to reforest abandoned kaingin land areas.
Because
it grows as a pioneer in degraded habitats with low
fertility soils, alnus can also be planted to improve the stability
of slopes liable to erosion and landslides, and for forest
reclamation.
Considerable quantities
of nutrients are recycled through the litter of Alnus sp. Leaf and
twig litter of Alnus may produce 3-6 t/ha litter annually, containing
N 3.4-3.7 gm, P 0.08-0.1 gm, K 0.6-0.7 gm and Ca 0.2 gm per 100 gm
dry matter.
Intercropping
Cordi farmers can grow
paddy rice in Alder based agroforestry system. The high rate of
regrowth of Alder helps in supplying
good quantity of biomass
for nutrient enrichment the soil. It is a good crop for
intercropping. In some of horticulture crops coffee, , this is grown
as shade crop. On terraced slopes, the species is commonly pollarded
for poles and inter planted with crops like maize, beans, chili and
pumpkin.
Other Benefits
The foliage is of low to
moderate value as fodder for ruminants. It has a low calorific value
of 18,230 kJ/kg. It dries easily, burns well and is an important
source of firewood and charcoal. In the Philippines, kraft pulping of
wood of Alnus sp gives a pulp yield of 47.6%, and bleaching improves
the brightness to 76%. It is suitable for the manufacture of
high-quality paper.
