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Reduced Attack of Keora (sonneratia Apetala) by Stem Borer in Mixed-species Plantations in Coastal Bangladesh.

A. K. M. Wazih Ullah
Senior Research Officer
Bangladesh Forest Research Institute,Forest Economics & Statistics Division, Sholashahar, Chittagong.

S. Das
Field Investigator
Bangladesh Forest Research Institute,Forest Economics & Statistics Division, Sholashahar, Chittagong.

F. Rahman
Field Investigator
Bangladesh Forest Research Institute,Forest Economics & Statistics Division, Sholashahar, Chittagong.

S. S. Islam
Divisional Officer
Bangladesh Forest Research Institute,Forest Economics & Statistics Division, Sholashahar, Chittagong.

Abstract/ Executive Summary:

A survey was conducted in 1990-1992 on attack by the stem borer, Zeuzera conferta,, in mixed-species and mono culture plantation of keora (Sonneratia apetala) in four Coastal Afforestation Division and natural stands in the Sunbarban, Bangladesh. In mono culture stands, 51% of the keora trees were attacked by stem borers, where as 32% sustained attack in mixed-species stands. In the latter stands, infested trees comprised only 10.6% of the total stems. Infestation levels were similar in plantations and natural stands. Infestation frequency increased from the West coast to the East, with the least infestation in the Sundarban. There was a significant negative relationship (r=-0.98) between the numbers of kankra (Bruguiera conjugata) trees and the intensity of infestation in the mixed-species stands in all the coastal divisions. Soil salinity levels in the Sundarbans did not show any correlation (r=0.12) with infestation. We recommend that in the future keora should be planted with kankra in mixed culture in coastal areas of Bangladesh.

Keywords: Reduced attack of keora, Stem Borer, Mixed-species Plantations, Coastal area

Location: Chittagong, Noakhali, Barisal, Patuakhali and Sundarban

Start Date: 00-00-1990

End Date: 00-00-1992

Program Area: Pest Management

Commodity: Keora

Objectives:

To determine the effect of mixed-species plantations of keora on stem-borer attack throughout the coastal belt.

Methodology:

The survey covered the four Coastal Afforestation Divisions, constituting the man-made forests of Bangladesh as well as the natural forest of the Sundarban. At least 12 sample plots for each mixed-species and mono culture stands were laid out in each location (forest range or beat), providing 36 and 34 plots in Chittagong, 31 and 24 in Noakhali, 26 in Barisal, 24 in Patuakhali, and 20 and 29 in the Sundarban (total 112 plots for each type of stand). The locations of the sample plots were Chittagong Division (eight locations): Uttar Kattali, Bagachattar, Dhumkhali, Maghadfia, Teknaf, Damdamia, Zadimura and Urirchar; Noakhali (four locations): Hatia, Char Osman, D.C. Clerk and Head Quarters range; Barisal (four locations): Char Kukri Mukri, Dhal Char, Kalkinirchar and Char Patila; Patuakhali (three locations): Khajuria, Mohipur and Char Quashem; and the Sundarbans (five locations): Chandpai, Charkhali, Katka, Hiranpoint and Kobodak ranges. Sample plots were 0.02ha in size and were placed in the locations where mixed-species and mono culture plantations were side by side.The numbers of borer holes in stems of keora trees up to two meters from ground level were recorded (Bakshi 1977). Numbers of other species infested were recorded in the mixed plots. Soil samples were collected from five locations of the Sundarban to investigate any relationship between soil pH and infestation level.Percentages of infested Keora trees by division in both types of stand, as well as density of other species in the mixed-species stands, were calculated. Student’s t-tests compared the percentage of keora stems infested in mixed-species and mono culture stands in each division. Correlation coefficients (r) were calculated for infestation level in relation to frequency of baen, gewa and kankra in the mixed-species stands, and for the relationship between soil pH and percentage infestation in the Sundarban

Source of Information: Journal of Tropical Forest Science 8(4):476-480 (1996)

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

An average of 32% and 51% keora trees were attacked by stem borers in the mixed-species and mono culture plantations respectively. The significant difference indicates that the mono culture plantations are highly susceptible to stem borer attack. The infested keora tree represented only 10.6% of the trees in the mixed stands strikingly showing the impact of the stem borers. Similarly, the natural forests of the Sundarbans showed a 15% infestation in the mixed-species stands and a 27% infestation in the single-species stands, also a significant difference. There was no relationship (r=0.10) between infestation level and number of gewa trees. However, a significant negative relationship between the number of kankra trees and percentage infestation (r=-0.98) in all the divisions. On the contrary, for baen trees, percentage infestation rose to 42% with increasing density up to 331 trees per ha, and declined sharply to 17% with no baen trees (r=0.93). Therefore, optimal reduction of infestation level could probably be achieved by interplanting of keora with kankra.The trend of borer attack indicates an increasing rate of infestation from Patuakhali in the West coast to Chittagong in the east. The lowest infestation level was in the Sundarban, probably stabilized soil and a natural ecosystem.

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