Floristic composition, tree growth and aboveground biomass along an altitudinal gradient thirty years after selective logging at Payeh Maga Highland, Sarawak, Malaysia

The tropical mountain forests ecosystem is a hotspot of biodiversity and provides a significant contribution to the humans’ livelihoods and is vital for global carbon cycle. However, there is still a lack of information regarding floral diversity and their altered biomass impact on how it has been affected due to a logging operation in Sarawak. A study was conducted to determine vegetation recovery, tree growth rate, above ground biomass (AGB) on the Payeh Maga Highland, Sarawak, Malaysia of logged and unlogged forests at different elevations: 750–1200 m (S1), 1200–1500 m (S2) and >1500 m (S3) in 30 plots (20 × 20 m). Tree height and dbh of tree with dbh of 10 cm and above were tagged with numbered metal plates and measured. The stand and growth dynamics were assessed for a 12 month duration. A total of 891 trees were enumerated. The trees comprised 55 families, 98 genera and 203 species. The lowest elevation site, S1, contained the highest number of species (117) and families (42), while the highest elevation site, S3, contained the lowest diversity (25 families and 59 species). The most speciose families in S1 were Dipterocarpaceae (11 species) and Lauraceae (10species), while Lauraceae and Fagaceae were the dominant tree families at S2 and S3. Secondary tree species are still abundantly found in the logged plots, especially at S2 (45.5%), indicating that after 30 years, these stands are still in the recovery stages. Significant increments in diameter at breast height (dbh), height, basal area and AGB were observed in the S3 between logged-over and primary plots. As elevation increases, diameter at breast height (dbh), basal area, height and stand AGB are decreasing. Lower concentrations of soil nutrients, especially N, may be the main reason for the slow recovery. Basal area and AGB exhibited negative relationships with elevation and rainfall but positively correlated with temperature, soil P and K. In conclusion, the results suggested that the selectively logged forest at the Payeh Maga Highland equired more than three decades to recover. Meanwhile stand dynamic variations favored recruitment and increases in density and basal area as well as AGB indicated that the Payeh Maga Highland community is experiencing the construction phase.

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