Environmental Factors influencing Productivity of Planted Shorea macrophylla (de Vriese) P.S. Ashton in Rehabilitated Riparian Forest along Kayan Ulu River, Sarawak

Aina Nadia Najwa, Mohamad Jaffar (2019) Environmental Factors influencing Productivity of Planted Shorea macrophylla (de Vriese) P.S. Ashton in Rehabilitated Riparian Forest along Kayan Ulu River, Sarawak. Masters thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

Rehabilitation is essential in preventing further land degradation and loss of biodiversity especially under the tropical ecosystem. Plant survivorship and productivity depends on environmental factors that vary within an ecosystem. The objectives of the study area to determine the (i) survival, growth performance and biomass productivity of planted Shorea macrophylla (de Vriese) P.S. Ashton at different age stands after enrichment planting, (ii) species composition, soil compaction, relative light intensity (RLI) as well as canopy leaf area index (LAI) and, (iii) effects of soil compaction and RLI on the productivity of S. macrophylla in the rehabilitated riparian forest along Kayan Ulu River, Sarawak. The study sites were stands rehabilitated in different years (1996: SPD96; 1997: SPD97; 1998: SPD98; 1999: SPD99). The survival, growth performance, biomass production, species composition, soil compaction, RLI and LAI were determined. SPD96 trees had the highest survival (84%) and showed the most favourable growth in mean annual increment diameter with 0.83 cm year-1. Average height (20.6 m), mean annual increment in height (1.07 m year-1) and RLI (27.3%) were highest in SPD97. LAI, Shannon-Wiener diversity, Species Evenness and mean annual increment in volume were highest in SPD98. In rehabilitated forest, species composition of Hypericaceae shows the highest number of tree density with 141 tree ha-1, followed by Verbenaceae with 115 tree ha-1 and Anacardiaceae with 64 tree ha-1. Although there was significant difference found at both surface soils (0-20 cm depth) and subsurface soils (20-40 cm depth) on planting line, but it was observed that there was no significant difference on soil penetration resistance between planting line. Soil compaction in SPD98 and SPD99 was harder as compared to SPD96 and SPD97 at shallow depth. The soil penetration resistance in SPD96 and SPD97 shows 2.5 J cm-1 followed with SPD99 with 3.4 J cm-1 and SPD98 with 3.7 J cm-1 at shallow depth. This was due to the compacted soils caused by anthropogenic activities and natural causes (wet soils) in the riparian forest at shallow depth. High survival and favourable productivity of S. macrophylla was influenced by the edaphic factor with special reference to less compacted soils and high RLI. Stepwise multiple regression demonstrated significant effects of soil penetration resistance at the depth of 0-30 cm and RLI on mean annual increment in diameter. Further ecological studies on other environmental factors should be implemented to draw up a Dipterocarp planting scheme in rehabilitation of riparian ecosystem. Moreover, the release of carbon dioxide as stored carbon should be accounted to generate information associated with carbon sequestration potential towards fulfilling the ecosystem carbon sink in enrichment planting sites. Keywords: Shorea macrophylla, productivity, rehabilitated riparian forest, environmental factors

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