Species Composition And Stand Structure Of Three Forest Types In Northern Cambodia
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Date
2014-07
Authors
Saret, Khorn
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Species composition and stand structure of evergreen (EF), semi-evergreen (SF) and deciduous (DF) forests were compared in permanent forest plots in Seam Riep province in Cambodia. The changes in the numbers of families, genera, species and stems ha-1 were recorded over the twelve-year period from 1998 to 2011 in those plots. At the time of their most recent measurements in 2011, there were 22 families, 34 genera, 37 species and 660 stems ha-1 in the EF plots; 23 families, 28 genera, 32 species and 343 stems ha-1 in the SF plots; and 11 families, 15 genera, 17 species and 259 stems ha-1 in the DF plots. Dendrograms developed from Cluster Analyses indicated that floristic composition varied across forest types, as well as life forms, which demonstrated a similar pattern of change. On the basis of Importance Values Index, Dipterocarpaceae was the most dominant family in the three forest types, followed by Euphorbiaceae, Guttiferae, Moraceae, and Ebenaceae and other families. Based on DBH class, nearly 50% of the trees were distributed in the lower diameter classes (15 cm – 35 cm). According to height life-form categories, 50 % of stems were small trees (7.5 cm < DBH < 15 cm). The densities of trees across all DBH classes were 660 stems ha-1 in the EF plots, 343 stems ha-1 in the SF plots and 259 stems ha-1 in the DF plots. The basal area measures were 244.90 m2 ha-1 in the EF plots, 34.95 m2 ha-1 in the SF plots and 10.07 m2 ha-1 in the DF plots. The lower species richness and density in the DF plots than in the EF and SF plots in trees with DBH > 7.5 cm is at least partially attributable to relative soil conditions and natural requirements for seedling establishment. Annualized mortality rates for trees in the 7.5 cm < DBH < 30 cm range were highest at 3.3 % ha-1 in the EF plots and lowest at
0.6% ha-1 in the SF plots. Annual recruitment rates were 2.65% ha,-1 0.26% ha-1 and 0.41% ha-1 in the EF, SF and DF plots, respectively. Annual diameter increment ranged from 34 to 61 mm yr-1among trees in the 10 cm < DBH >50 cm class. In the DBH class from 10 cm to 20 cm with the highest numbers of trees, the mean diameter increment was 35 mm yr.-1 Large trees, with a DBH > 80 cm, had an annual diameter increment of 6 mm yr.1 The ranges for the mean growth rate and standard deviations of the selected species in the EF plots were from 1.43 mm yr-1 to 4.09 mm yr.-1 Dipterocarpus alatus had the highest mean growth rate (5.24 ± 0.18 mm yr-1) in the SF plots and ranged from 2.43 to 3.24 mm yr-1, with a maximum growth rate of 4.94 mm year,-1 in the DF plots. The trends in biomass revealed declining levels from initial measures in 1998 of 760.88 Mg ha-1 in the EF plots and 210.85 Mg ha-1.in the DF plots. These measures had declined by 2005 to 578.82 Mg ha-1 in the EF plots and 167.81 Mg ha-1 in the DF plots and in 2011 to 329.93 Mg ha-1 in the EF plots and 144.56 Mg ha-1 in the DF plots. The above-ground, below-ground and total biomass in the SF plots were much higher than in the EF and the DF plots, reflecting the more continuous growth in the undisturbed SF plots. It is very probable that the differential biomass distribution patterns in the EF, SF and DF plots are attributable to past disturbance histories, age and soil conditions of these forests. In 2000, the highest carbon stocks were in the EF and the DF plots, but these had gradually declined to 140.35 Mg C ha-1 and 82.40 Mg C ha-1, respectively, by 2011. SF plots, where carbon stocks increased from 524.25 Mg C ha-1 (1998) to 613.31 Mg C ha-1 (2011). The contribution of the pools for total carbon stocks varied markedly between the EF and the DF plots. The results of this study will be especially useful in comparing species composition and stand structure, growth and biomass in other forests across Southeast Asia.
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Keywords
Permanent forest plots , in Cambodia