Saturday, December 1, 2012
Forest management group – a long weighted requirement in Sri Lanka Forestry Sector has been fulfilled
Wednesday, August 29, 2012
Yield table is one of the useful ways of predicting yield and growth of forests which shows expected volume and other important parameters per unit area by the combination of measurable characteristics of the forest stand. Although the yield and growth of trees can be predicted using more advanced modelling tools in forestry, the information contained in traditional yield tables is still considered valuable.
Eucalyptus torelliana is one of the eucalyptus species planted in Sri Lanka especially in the low country wet zone. Due to the unavailability of growth prediction methods for E. torelliana in Sri Lanka, a complete yield table and a two parameter volume table was constructed for this species using height and age relationships.
Five E. torelliana plantations from Matara and Rathnapura districts were used for this study. These plantations are 10 to 14 years old at the time of measurements taken and vary in extent from 1.14 to 20.00 ha. In order to represent the whole area of each plantation, stratified random sampling was used and 5 to 10 circular plots of 0.02 ha were used.
For the trees located in the plots, total height and dbh were initially measured. For the volume determination, each tree stem was divided into sections and sectional volumes were separately calculated using Newton's formula. The stem volume was determined by adding section volumes together.
Due to the unavailability of re-measured data, it was decided to to develop a relationship between height and tree age. In order to build that relationship, it was assumed that the tree produces one node per year. This concept was statistically tested later on in the present study and proven to be correct.
For the construction of the yield table in the present study, three relationships were mathematically constructed, i.e., height with age, dbh with height, volume with height and dbh. For the development of height age relationship, 10 trees were selected from each plantation and number of inter-nodes was counted using a high-quality binocular and the distance between consecutive nodes were accurately measured.
All three relationships were mathematically built using regression analysis and for each relationship over 15 models were tested. The best modes were selected based on R2 values and distribution of standard residuals. The selected best model for height-age relationship was non-linear. The selected linear models to predict dbh and volume had 75.9% and 73.9% R2 values respectively.
By using the finally selected models, a complete yield table and a two-parameter volume table was constructed. As it was found that there were no significant difference among the selected sites for this study, it was decided to construct one yield table for all site types with the planting density of 1,100 trees per ha.
Sunday, January 29, 2012
Analysis of mangrove vegetation cover and the present status of aquaculture in Puttlam District of Sri Lanka
Abstract of a research study
conducted by Supun Nigamuni, Upul Subasinghe and Chandani Edussuriya
Mangrove forests are complex ecosystems that occur along intertidal accretive shores in the tropics. Mangroves play a significant role in both ecology and economy. In Sri Lanka many estuaries and lagoons are fringed with vastly diverse mangrove forests. The northwestern coastline represent all three major climatic zones in Sri Lanka. It also has the largest mangrove forest patch which is located in Puttlam – Kalpitiya lagoon. From the recent past the mangrove forest cover in Puttalam District is experiencing severe pressures from the adjoining settlements, the fishery industry, aquaculture and other activities in the catchment. An abrupt decline in the forest cover is evident due to being converted into industrial shrimp farms.
An attempt was made in the present study to analyze the spatial pattern of mangrove destruction related to shrimp farm development and to analyze the distribution of mangrove species. For this purpose, shrimp farms of 2008 were mapped using IRS – LISS III image (2008) to identify the operational and abandoned shrimp farms. The results were verified by using Google Earth. In order to study the mangrove species distribution, a total of 40 sampling sites were selected to cover the whole study area. Data collection was done at each sampling point by a 10 m traverse established from the water level to the edge of the mangrove vegetation at the landside. Species and the number of individuals in each traverse were recorded during this survey.
According to the findings of the study in 2008 there is a total of 5355 ha of land is used for shrimp farms but only 3872 ha is in operation and others are abandoned. These barren lands could be cultivated with mangroves if suitable restoration programme is implemented while natural regeneration is also evident in some areas.It was evident that Chilaw lagoon area is the richest when it comes to mangrove diversity. Rhizophore mucronata, Avicennia marina and Lumnitzera racemosa were the most dominant species in the study area. The most significant finding was the recording of Scyphiphora hydrophyllacea Gaertn. f. from Udappwa (854883.4 N 366900.8 E) which has now become very rare species in Sri Lanka. Only a few trees were previously recorded to be restricted to one locality on the Kalpitiya Peninsula in Puttalam lagoon.