Evaluation of tree performance, site conditions and silvicultural procedures in forest plantations at high altitude sites in Lesotho.

Abstract

The permanent sample plots (PSP) and silvicultural trial plots established by the Forestry Research Section of the Forestry Department of the Ministry of Forestry and Land Reclamation in Lesotho were used as a source of information for this study. The study area is located in the forest plantations on high altitude sites in Lesotho which have the aim to determine important aspects of timber production for commercial use and to address the problem of fuel wood scarcity and energy crisis. The major objective of the study was to describe performance (survival, growth and timber volume) of exotic tree species introduced in Lesotho. The height and diameter relationships for trees in the 33 plots of Eucalyptus rubida and 44 plots of Pinus radiata were determined by a simple linear regression. There are four plots of Eucalyptus macarthurii, three plots of Pinus halepensis, one plot of Eucalyptus nitens and one plot of Pinus pinaster. The permanent sample plots data were analysed with the use of a statistical package Genstat (7th edition). Categorical analysis were used to detect the number of live and dead trees. The correlation analysis was used to study association between site and performance variables, while multiple regression analysis was utilised to analyse relationships between site index and site variables. The growth curves developed for E. rubida and P. radiata tended to indicate a sigmoidal shape. Analysis of variance was utilised to analyse the performance of species in terms of survival and growth (HT and DBH) for the four species and provenance trials. The early mortality rate was 2% for E. macarthurii, 14% for E. rubida, 0% for E. nitens. Later, it was found that the percentage of dead trees is as follows: 7% for E. macarthurii, 15% for E. rubida, 29% for E. nitens. It was detected that the mortality rate for eucalypts was 14% at last assessments. Similarly, it was detected that the final mortality rate for P. halepensis, P. pinaster and P. radiata was 2%, 19% and 20% respectively. The mean diameter for P. radiata ranged between 1,87 cm at age 3,75 years and 24,49 cm at age 18 years. The mean height ranged from 1,51 m at age 0,75 yrs and 13,51 m at 16 years. It was discovered that the mean diameter is found between 8,0 cm at age 4,83 yrs and 14,41 cm at age 8,83 yrs for P. halepensis. The mean height was 2,1 m at age 4,83 years and 16,48 m at age 13,50 years. The mean diameter ranged from 7,41 cm at age 6,42 years and 15,92 cm at age 10,42 years for P. pinaster. Similarly, the mean height was detected to be between 5 m at age 6,42 years and 7,75 m at age 12,42 years for P. pinaster. It was noted that the mean diameter for E. rubida ranged from 2,04 cm at age 2,25 years to15,87 cm at age 11,75 years. On the same line the mean height started at 4,55 m at age 2,42 years and ended at 16,15 m at age 11,75 years. The mean diameter for E. macarthurii was noted to be 13,64 cm at age 10 years. It was noticed that mean height is found between 3,8 m at age 2,17 years and 16,03 m at age 10 years. It was also detected that the mean diameter started from 4,45 cm at age 2,50 years and 10,78 cm at age 6,50 years for E. nitens. The mean diameter ranged from 5,98 cm at age 2,50 years and from 12,05 m at age 6,50 years for E. nitens. The mean annual increment (MAI) for P. radiata is found between 0,15 m3/ha/yr at age 2,25 years and 21,91 m3/ha/yr at age 6,50 years. The MAI ranged from 0,58 m3/ha/yr at age 3,42 years and 10,81 m3/ha/yr at age 10,42 years for E. rubida. It was determined that the MAI started from 0,25 m3/ha/yr at age 2,17 years to 9,99 m3/ha/yr at age 4,17 years for E. macarthurii. The MAI started from 1,59 m3/ha/yr at age 2,50 years and to 7,54 m3/ha/yr at age 6,50 years for E. nitens. It was noted that the MAI for P. halepensis began from 0,01 m3/ha/yr at age 4,83 years and 3,52 m3/ha/yr at age 13,50 years. Similarly, the MAI began from 0,73 m3/ha/yr at age 6,42 years and 2,70 m3/ha/yr at age 10,42 years for P. pinaster. The Site indices for E. rubida and P. radiata were calculated. They ranged from 6,72 to 14,40 m and from 12,05 to 18,43 m for E. rubida and P. radiata at age 6 years and 15 years respectively. The MAI and SI of different species justify that a viable commercial forestry can be implemented in Lesotho, if advanced selection of genetic material, improved silviculture and appropriate site species matching can be followed. It was noticed that various silvicultural practices like proper land preparation methods, weed management and deep planting have a large impact on tree performance. Based on these results, larger afforestation projects for commercial timber production and bioenergy are recommended.