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Annona glabra L. (Annonaceae) commonly known as pond apple or monkey apple is
considered as an alien invasive species in Sri Lanka. It has been introduced possibly
in the 19th century, and the purpose of introduction is not known. This species is seen
growing as clusters in many wetlands, particularly in the wet-zone of the country, and
its spreading has identified as a serious threat to the survival of the wetland
ecosystems.
Biology of this species has not been studied in Sri Lanka, and therefore this study was
designed to conduct preliminary investigation on the biology and invasive
characteristics of the tree.
Bellanwila-Attidiya wetland is one of the wetlands, which has been recognized as a
wetland of international importance. Annona glabra is seen spreading rapidly in this
wetland as well.
In the present study some invasive characteristics of Annona glabra have been studied
for a period of 7 months. These include seed germination and vegetative propagation
experiments. In addition observations on phenology (flowering, fruiting & flushing)
and pollination were made to understand the life cycle of the species. Apart from the
above studies, distribution pattern & the cover percentage of pond apple has been
studied, and the average number of seeds in a fruit is also established.
Distribution pattern of Annona glabra varies with the habitat condition. Clumps with
more mature trees, comprising large crown diameters can be seen at the edge of the
marshland, while different sizes of clumps were seen in the open marshland area. The
average cover percentage of Annona glabra in the study area of Bellanwila- Attidiya
wetland is found to be around 35.6%. Although seed germination trails conducted
under ex-situ condition did not give satisfactory results, the seedling count in the field
showed that wet shady conditions are necessary for seedling establishment.
Vegetative propagation experiments have proved that leaf sprouting is possible in
both young & mature branches grown in the field. However damp soil with almost
100 percent moisture is needed for leaf sprouting
A remarkable increase in flushing and flowering was observed in March 2001-,
However prolong observations are necessary to establish the fluctuation patterns of
phenological characters. Average number of seeds in a fruit is found to be around 78
Experiments conducted using pollination bags revealed that Annona gfabra flower has
the capacity to self-pollinate or produce fruits without pollinating (apomictic)
Control further spreading of the plant is seemed to be somewhat difficult. Uprooting
of seedlings and saplings and periodic cutting of stems are expected to be fruitful as
control measures. Mechanized removal of fully-grown trees may be possible in dry
areas. Use of herbicides may be useful in destroying the tree, but careful thought is
necessary if herbicides are used in natural ecosystems.
