NewForests 5: 61--66, 1991. © 1991 KluwerAcademic Publishers. Printed in the Netherlands. Research note Effect of compaction of soils on growth of Acacia mangium Wilid. under glasshouse conditions K. JUSOFF Faculty of Forestry, UniversitiPertanian Malaysia, 43400 UPM Serdang, Selangor, Malaysia (present address: CranfieM Institute of Technology, Silsoe, Bedford MK45 4D T, UK) Received 30 January 1990; accepted 18 February 1991 Key words: Acacia rnangium Willd., compaction, glasshouse Application. A glasshouse study showed that there were significant differences in the initial height and diameter growth of A. mangium seedlings over a range of increased soil bulk densities. Losses in tree growth as found in this study could have a significant impact on the economic value of timber grown under similar field conditions. Abstract. A glasshouse study was conducted to observe the initial height and diameter growth of Acacia mangium Willd. seedlings over a period of 24 weeks in pots with soil at bulk densities of 0.8, 1.0, 1.2, 1.4, 1.6, 1.8 and 2.0 g/cm 3. Height and diameter growth increased significantly with decreasing soil bulk density. Significant differences in seedling diameter appeared during the tenth to twelfth week after transplanting and continued to increase until harvesting at week 24. The interaction between site water stress and com- paction is discussed. A better understanding of these processes and the influence of site/soil factors on them is essential to the development of effective stand manipulation programs. Introduction Ground-based logging systems are important in the extraction of logs from dipterocarp forests of Malaysia. On the hilly terrain found in much of central Pahang, Malaysia, ground skidding machines are the dominant equipment used for logging operations (Jusoff and Majid 1987). However, their effects on soil properties through compaction can lead to significant reductions in site productivity and site quality (Jusoff 1988). Several studies have shown that compaction affects seedling establish- ment and root growth by altering the basic physical properties of the soil that control root penetration: moisture, nutrient uptake, and water and gaseous fluxes through the soil. These changes in tum affect root growth and proliferation which directly affects shoot growth (Taylor et al. 1972). Pomeroy (1949) found that the greatest loss in seedling establishment occurred when the surface soil structure was destroyed by puddling. Foil and Ralston (1967) reported as much as a 34% reduction in seedling