Cover Single.cdr BIOTROPIA Vol. 27 No. 2, 2020: 125 - 133 DOI: 10.11598/btb.2020.27.2.1176 SOIL PROPERTIES AND TREE COMPOSITION IN A 27-YEAR OLD Acacia mangium Willd. PLANTATION ON ABANDONED MINING AREA AT PHANGNGA FORESTRY RESEARCH STATION** JETSADA WONGPROM1', ROONGREANG POOLSIRI2, SAPIT DILOKSUMPUN2 AND CHATCHAI NGERNSAENGSARUAY3 1Faculty of Forestry, Kasetsarf University', Bangkok 10900, Thailand 2F)epartment ofSilviclture, Faculty of Forestry, Kasetsart University, Bangkok 10900, Thailand department of Botany, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand ^Corresponding author, e-mail: fforjdw@ku.ac.th Received 19 December 2018 / Accepted 04 April 2019 ABSTRACT In order to validate the important role of Acacia mangium plantation in mining rehabilitation, a study was conducted on the soil properties and tree composition in a 27-year-old A. mangium plantation growing on sandy (S27) and clay (C27) soil types, as well as a mixed plantation (MP) growing on clay soil type. The results were compared with those grown on an abandoned mining area (AB), a secondary forest (SF) and a primary forest (PF), at the Phangnga Forestry Research Station, Thailand. Three 40 x 40 m permanent plots were established and soil samples were randomly collected from depths of 0-10, 10-20, 20-30, and 30-50 cm, in each of the S27, C27, MP, AB, SF, and PF. The bulk density values in the S27, C27, and MP were lower than that in AB and was similar to those in SF and PF, particularly, the top soil. Total nitrogen, available phosphorus, organic matter, exchangeable potassium, and magnesium contents in the S27, C27, and MP were higher than that in AB, but were lower than those in SF and PF, indicating that the soil development in the S27, C27, and MP was slower than in the SF and PF. This lower bulk density values and higher soil nutrient contents were positively contributed by the A. mangium plantation. The Shannon-Wiener index obtained for S27 (1.43), C27 (2.51), and MP (2.77) were lower than that for the SF (3.86). The similarity indices of the tree species found in S27, C27, MP, and PF were low, ranging from 5.83 - 8.00, indicating that the development of the forest community was slow compared to SF (31.03). Enrichment planting with poorly dispersed shade tolerant trees has increased the diversity and improved the forest structure in the mined out areas and other similarly degraded lands. Keywords: Acacia mangium, mining area, soil properties, tree composition INTRODUCTION Ever since mining has been widely operational all over Thailand, the local environment and ecosystem conditions have been severely impacted by the mining activities (Macdonald et al. 2015). Vegetations were destroyed and soil properties were changed from ^Corresponding author, e-mail: fforjdw@ku.ac.th **This paper was presented at the 3rd International Conference on Tropical Biology 2018, 20-21 September 2018, Bogor, West Java, Indonesia the originally rich to currently poor soil. Soil textures have become unsuitable for planting (Oktavia et al 2015). In some areas, the soil has turned extremely acidic and the soil moisture went very low during the dry season (Tripathi et al. 2016). As a result, soil improvement and forest restoration in mining areas has taken a long time. Invariably, changes in such important factors as soil properties like soil texture, organic matter, pH, nitrogen, phosphorus and potassium have negatively affected the development of a forest community in 125 BIOTROPIA Vol. 27 No. 2, 2020 previously mined areas (Zhao et al. 2013; Lei et al. 2015). Oftentimes, nitrogen limits the growth and reestablishment of forest seedlings. As such, natural regeneration using native trees was applied to accelerate plantation establishment. However, restoration of several mined out areas is costly and is usually a long term process (Oktavia et al. 2015). The popularly known nitrogen fixing tree, Acacia mangium is a multipurpose fast-growing tree which plays an important role in restoring the soil quality of degraded lands. This species has been widely introduced in Southeast Asia (Nambiar & Harwood 2014). Its survival, growth rate and the aboveground biomass it produces are relatively high compared to other fast growing and native tree species found in abandoned mining areas (Martpalakorn 1990). A. mangium plantation has been established in degraded lands for wood production, forest restoration, as well as soil improvement (Wang et al 2010). Degraded land restoration using plantation is one approach for catalyzing the natural succession process and increasing the tree species diversity (Tripathi et al. 2016). Since native tree species have been introduced into plantations, resulting in an increased tree species richness and increased forest structure complexity, the restoration of previously mined areas using nitrogen fixing trees has been focused on soil improvement (Bohre & Chaubey 2014). Generally, after plantation establishment, the soil physical and chemical properties will improve (Zhao et al 2013; Bohre & Chaubey 2014), simultaneously with the ecosystem services such as litter supply, nutrient cycling, and biodiversity (Parrotta 1999; Celentano 2011). The objectives of this study were, firstly; to evaluate the soil properties, tree composition, and diversity of a 27-year-old A. mangium plantation located in Phangnga Forestry Research Station, Thailand and compare these with an abandoned mining area (AB), secondary forest (SF) and primary forest (PF) and secondly, to recommend trees, like A. mangium, that are suitable for this site restoration programs and for other mined out areas. MATERIALS AND METHODS Study Area The experiment was conducted on an abandoned tin mine at Phangnga Forestry Research Station, Takuapa District, Phangnga Province, Thailand. The area also includes a 27- year-old A. mangium plantation grown on sandy (S27) and, clay (C27) soil types, as well as mixed plantation (MP) of Eucalyptus camaldulensis, A. mangium, and Diptercapus alatus grown on a clay soil type. Phangnga Forestry Research Station is approximately 3 km away from a primary forest (PF) and is surrounded with rubber and oil palm plantations. The area receives a mean annual rainfall of 3,668.80 mm, with rainy season occurring from April to November and dry season from December to March. Its relative humidity is around 83% and its mean annual temperature is at 27.1 °C (Wongprom et al 2013). In addition, secondary forest (SF), primary forest (PF), and abandoned mining area (AB) were established as reference sites. The SF plot is approximately a 30-year-old protected forest, a tropical rainforest that was disturbed in the past by shifting cultivation. Soil Properties Soil samples were collected from the S27, C27, MP, AB, SF and PF sites at four soil depth series, 0 - 10, 10 - 20, 20 - 30 and 30 - 50 cm. Three soil pits were randomly established, while soil samples were collected from each plot using a split tube sampler for the soil physical and chemical analyses. For the chemical properties, the samples within each plot were mixed thoroughly to form a soil composite. Soil bulk density was analyzed by the core method, while the soil texture was analyzed by the hydrometer method. Soil pH was examined by a pH meter with 1:1 soil: water ratio. Total nitrogen (N) was measured using the Dumas method (Jackson 1965) by CHNS analyzer. Organic matter content (OM) was analyzed by the Walkley and Black rapid titration method. Available phosphorus (P) was extracted using the Bray II method and was analyzed using a spectrometer. The exchangeable potassium (K), calcium (Ca) 126 Soil properties and tree composition in a 27-year old Acacia mangium Willd. plantation — Wongprom el al. and magnesium (Mg) were extracted with ammonium acetate (NhUOAc) 1 N pH 7.0 and analyzed by an atomic absorption spectrometer (Estefan et al. 2013). Tree Composition Three permanent plots of 40 x 40 m were established in each of the S27, C27, MP, SF, and PF sites. Each sample plot was divided into sixteen subplots of size 10 x 10 m plot. At the permanent plots, all tree species with diameter at breast height (DBH) > 4.5 cm were identified and recorded. The DBH and total height of a tree was measured using a diameter tape and Haga altimeter, respectively. Plant specimens were collected and identified, and the unidentified species were compared with the herbarium specimens deposited at the Forest Herbarium, Natural Parks, Wildlife and Plant Conservation Department. Data Analyses Soil physical and chemical properties, including bulk density, porosity, soil pH, total N, available P, OM, exchangeable K, Ca, and Mg were analyzed using a one-way analysis of variance (ANOVA) and the means were compared using Tukey’s test at 5% probability level. The importance value index (IVI), tree density, and basal area were also calculated. The IVI value was obtained as a relative density (RD), relative frequency (RF), and relative dominance (RDo) of a given tree species.The tree species diversity for each site was calculated using the Shannon-Wiener index (Shannon & Weaver 1949) using the formula: n H' =-S (pi*ln pi) n=l where, H? is the Shannon-Wiener index, Pi is the proportion of each species in the sample, In Pi is the natural logarithm of this proportion. Species evenness (E) was calculated as follows (Pielou 1966): E = H’ / In S where, H’ is the Shannon-Wiener index and S is total number of species in the sample. The similarity of plant composition was calculated using the Sorensen similarity index (Sorensen 1948) by the formula: S = 2c / (a + b) x 100 where, S is the Sorensen similarity index, a is the number of species found in site A, b is the number of species in site B, and c is the number of species shared by the two sites. Shannon- Wiener index and the Sorensen similarity index are the most widely used tools to evaluate plant community (Barrantes & Sandoval 2009; Martinez-Ruiz & Fernandez-Santos 2005; Zhang et al. 2014). RESULTS AND DISCUSSION Soil Physical Properties At the top soil (0 - 1 0 cm), the soil bulk density and soil particles were significantly different among the sites but not for porosity (Table 1). However, at soil depths of 10 - 20, 20 - 30 and 30 - 50 cm the bulk density, soil particles, and porosity of the subsoil significantly differed among the different sites. The bulk density was the highest (1.31 g/m3) in AB, while bulk densities of S27, C27 and MP were similar to SF and PF. The bulk density can be relatively lower in mining areas having a forest plantation (Bohre & Chaubey 2014). Soil development at AB was slow compared to those at S27, C27 and MP. Plantations have been known to markedly improve the physical properties of soil, vegetation cover and natural regeneration in post mining sites (Zhao et al 2013; Lei et al. 2015). The variations in soil bulk density, specific gravity, porosity, water holding capacity and soil aggregation in a reclaimed mine are mainly caused by variations in organic matter. As such, soil physical properties are largely related to the organic matter content (Charman & Roper 2000; Zhao et al 2013). 127 BIOTROPIA Vol. 27 No. 2, 2020 Table 1 Soil physical properties on abandoned mining in the Phangnga Forestry Research Station and the reference sites DePth Site . Soil particle (%) Bulk density (g/m3) Porosity (%)(cm) Sand Silt Clay Soil texture 0-10 AB 91.23a 3.99c 4.77c Sandy 1.31a 56.99 S27 89.33a 2.24c 8.42bc Loamy sand 1.04ab 59.67 C27 17.70c 33.31a 48.99a Clay 0.94b 59.43 MP 20.15c 33.47a 46.38a Clay 0.90b 60.40 SF 31.45c 25.35ab 43.20a Clay 0.96ab 60.38 PF 67.73b 8.71bc 23.56b Sandy clay loam 0.92b 65.93 F-value 110.16* 16.72* 29.38* 4.08* 1.24ns 10-20 AB 91.14a 3.33c 5.56b Sandy 1.78a 32.86b S27 87.97ab 2.77c 7.76b Loamy sand 1.48b 44.92a C27 22.56c 26.93b 50.51a Clay 1.2L 53.46a MP 9.03c 38.95a 52.01a Clay 1.1lc 49.08a SF 18.09c 21.26b 60.65a Clay 1.09c 55.69a PF 67.1lb 7.24c 25.65b Sandy clay loam 1.22c 54.55a F-value 64.30* 64.89* 30.72* 45.57* 13.91* 20-30 AB 90.06a 3.37b 6.56c Sandy 1.71a 30.28c S27 84.33a 6.93b 10.07bc Loamy sand 1.69a 35.62bc C27 28.37bc 27.98a 43.65ab Clay 1.30b 46.12ab MP 17.70c 26.05a 56.25a Clay 1.17b 49.87a SF 26.37bc 19.19ab 54.44a Clay 1.21b 46.97ab PF 63.85ab 5.38b 30.77ab Sandy clay loam 1.33b 43.78ab F-value 13.13* 8.37* 10.29* 22.56* 7.97* 30-50 AB 90.57a 3.21c 6.22d Sandy 1.58a 38.14b S27 81.71ab 4.86c 13.43“ * Loamy sand 1.55ab 41.45ab C27 31.23cd 26.12ab 42.65ab Clay 1.12c 53.63a MP 8.44d 33.52a 58.04*b Clay 1.05c 52.14a SF 18.42d 18.93b 62.65* Clay 1.12c 52.78a PF 55.89bc 9.12c 34.98bc Sandy clay loam 1.30bc 42.92ab F-value 31.88* 53.83* 19.99* 17.34* 6.51* Note: * = Different superscripts along the same icolumn indicate significant differences at p < 0.05. Comparison between the rehabilitated sites, moderately to slightly acidic. These results S27, C27 and MP, and the reference sites, SF indicate that the A. mangium plantation had a and PF, indicate that the bulk density and significant influence in reducing soil pH, porosity were not significantly different, an observation similar to that of Yamashita especially at the top soil. Invariably, the forest et al (2008). Amounts of exchangeable plantation had a significant role in improving the bulk density. However, the restoration of soil texture at these sites to that of the levels of PF, and in particular the sandy area with a poor soil quality, can take a long time (Oktavia et al 2015). While soil bulk density and porosity in SF were similar to that in PF, degradation of the soil structure due to shifting cultivation in SF may be lesser in extent compared to that in the mined out area. Soil Chemical Properties K and Mg were significantly different among the sites at depths of 0 - 10, 10 - 20, 20 - 30, and 30 - 50 cm. Mining rehabilitation with A. mangium plantation resulted in increased K and Mg levels which were higher than those in AB. Nevertheless, K and Ca of S27, C27 and MP were lower than those in SF and PF. The levels of K, Ca and Mg were relatively high in the topsoil. Similarly, the available P, total N and OM were the highest at a depth of 0 - 10 cm, but was decreasing with the increasing soil depth. The topsoil was rich and higher in soil Soil pH was extremely acidic in S27, C27, MP and SF, while in PF it was strongly to moderately acidic. However, soil pH in AB was nutrient content, total N, OM, the available P, K, Ca and Mg in S27, C27 and MP than those in AB. In mining restoration, the soil nutrients 128 Soil properties and tree composition in a 27-year old Acacia mangium Willd. plantation — Wongprom et al. Table 2 Soil chemical properties in abandoned mining in the Phangnga Forestry Research Station and the reference sites DTh Site(cm) n T I Exchangeable (mg/kg) Available P Total N OM pH K Ca Mg (mg/kg) (%) (%) 0-10 AB 5.9a 6.33d 10.69 2.92c 5.90b 0.0L 0.67c S27 4.5bc 14.38cd 18.45 10.26bc 12.91b 0.11b 1.62bc C27 4.4C 35.37bc 23.98 33.56ab 15.16b 0.13ab 2.14b MP 4.7b 38.93b 27.46 35.34a 9.42b 0.10b 1.66bc SF 4.2C 82.27a 29.06 24.27abc 33.32a 0.17a 2.42ab PF 4.8b 40.25b 29.56 26.72abc 50.78a 0.17a 3.55a F-value 68.53* 28.60* 1.40ns 6.57* 70.22* 26.06* 15.38* 10-20 AB 6.0a 7.46b 11.17 3.21c 4.34c 0.0E 0.33b S27 4.7bc 9.76b 9.27 3.77bc 7.10bc 0.04c 0.91b C27 4.6bc 20.42b 11.81 15.91abc 7.67bc 0.04c 0.57b MP 4.8bc 24.07b 11.13 26.93a 5.32bc 0.04c 0.86b SF 4.4C 64.34a 12.83 17.38a 6.25bc 0.11b 1.49ab PF 4.9b 29.57b 12.00 16.34ab 14.52a 0.15a 2.53a F-value 35.03* 19.40* 1.45ns 11.08* 15.31* 73.57* 6.65* 20-30 AB 5.8a 5.18C 10.26 3.13b 3.22b 0.0L 0.25b S27 4.9b 8.17C 9.58 4.74b 7.32ab 0.02c 0.71b C27 4.6b 9.97bc 9.76 18.23b 7.36ab 0.03bc 0.36b MP 4.9b 19.07abc 9.59 35.42a 4.86ab 0.04bc 0.47b SF 4.6b 33.14a 14.21 9.87ab 5.65ab 0.07b 1.21ab PF 5.6a 24.08ab 10.59 16.45b 9.15a 0.13a 2.29a F-value 31.28* 11.44* 1.01ns 11.94* 4.81* 31.29* 6.84* 30-50 AB 6.1a 5.01c 9.12 2.85c 3.05 0.01b 0.19b S27 5.1b 6.19C 7.86 2.49c 5.54 0.01b 0.48b C27 4.8bc 10.75bc 12.41 18.53ab 7.12 0.02ab 0.54b MP 4.9bc 18.68ab 12.50 31.51a 2.62 0.02ab 0.41b SF 4.6C 20.12ab 9.94 5.94bc 3.59 0.04a 0.87b PF 5.7a 20.76a 5.03 17.23b 7.08 0.04a 2.16a F-value 43.13* 12.70* 3.21ns 15.41* 5.95ns 7.37* 8.95* Notes: * = significant difference; ns = non-significant difference; and a — c — different superscripts along a column indicate significant differences at p < 0.05. and organic matter contents usually increased with the age of the stand (Zhao et al 2013; Bohre & Chaubey 2014). Soil nutrients rapidly increased in plantations using a nitrogen fixing tree while natural succession increased gradually (Oktavia et al 2015). However, soil nutrients such as exchangeable K, available P, total N and OM levels at S27, C27 and MP were lower than those in both SF and PF at a depth of 0 - 10 cm. Overall, the soil properties in SF particularly, available P, total N and OM contents were improved faster than those in S27, C27 and MP. Although A., mangium was dominant in S27, C27 and MP, the level of total N was relatively low, particularly in the sandy area. These results indicate that mining activities highly impacted the soil properties and the restoration may take a longer time. Tree Composition and Ecological Characteristics There were 21, 34, 40, 81 and 94 tree species, 19, 29, 31, 62 and 68 genera, and 14, 26, 25, 33 and 38 families in the S27, C27, MP, SF and PF, respectively. The basal area, density and species diversity index in PF (3.91) was the highest, in contrast with those in S27 (1.43), which had the lowest density and species diversity index (Table 3). Soil characteristics showed a significant influence on the density, species diversity index, and natural regeneration (Lei et al 2015), especially in the S27. Soil texture in the area being sandy, has a low water holding capacity, and thus, has resulted in insufficient water supply during the dry season, a phenomenon causing high seedling mortality in the tropical rain forests (Li et al 2011). Soil properties play important roles on revegetation 129 BIOTROPIA Vol. 27 No. 2, 2020 Table 3 Ecological characteristics of the rehabilitated sites, S27, C27 and MP in the Phangnga Forestry Research Station, Thailand and the reference sites, SF and PF Ecological characteristics Sites S27 C27 MP SF PF Number of species 21.00 34.00 40.00 81.00 94.00 Basal area (m2/ha) 35.49 20.91 23.09 22.20 41.27 Density (stems/ha) 1,010.42 1,229.17 1,393.75 1,200.00 1,497.92 Shannon - Wiener index (FT) 1.43 2.51 2.77 3.86 3.91 Evenness of species 0.46 0.71 0.74 0.88 0.86 of native trees and forest community (Zhao et al. 2013; Lei et al. 2015). The number of species, tree diversity and density was significantly lower in S27 and C27, than those in MP, which consisted of A. mangium, E. camaldulensis and D. alatus. A mixed plantation of many tree species can facilitate a successful seedling establishment in the understory and native trees were also found more abundantly than in pure plantations, resulting in a high tree diversity (Wang et al. 2019). However, the rehabilitated sites in S27, C27 and MP had a low tree diversity compared to SF. The number of native tree species found in S27, C27 and MP were relatively less than that in SF, resulting in a low recovery of original tree species, forest structure, and forest function. In addition, species richness and evenness in SF was larger than those in S27, C27 and MP, resulting in high tree diversity. Tree diversity is related with species richness and evenness (Strong 2016). According to the Shannon- Wiener index of the old teak (Tectona grandis) plantation was higher when the evenness value of the plot was high (Koonkhunthod et al 2007). In addition, the Shannon-Wiener index in S27 (1.43), C27 (2.51) and MP (2.77) was lower than that in a 34-year-old A..mangium plantation (3.22) (Marod et al. 2013). A. mangium plantation can be highly effective to introduce native trees species (Van et al 2005). In this study, the native species were mostly shade intolerant trees. Therefore, accelerating the natural succession by enrichment planting with poorly dispersed shade tolerant trees, such as Swintonia floribunda, Dipterocarpus kerrii, Canarium patentinervium, Xanthophyllum virens, Mesua ferrea, Hopea gnffithii and Gluta elegans, may be considered in S27, C27 and MP for improving the forest structure and increasing the tree diversity. The high tree diversity and number of trees in SF could be due to various factors such as proximity to the forest fragment, rich soil nutrient content and organic matter. The vegetation composition and richness decrease with the increasing distance from the primary forest (Van et al 2005; Ruiz-Jaen & Aide 2005). Therefore, the distance from a natural forest and the surrounding mining area with oil palm and rubber plantations had largely obstructed on the process of natural forest succession in the S27, C27 and MP. This study, we showed top seven IVI in S27, C27, MP, SF and PF because they play ecological importance in ecosystem with high relative frequency, density and basal area. The dominant native trees in S27, C27 and MP included Vitex pinnata, Aporosa planchoniana, Carallia brachiata, Melicope lunu-ankenda and Bridelia tomentosa (Table 4). Most native species were identified as pioneers because of their various life forms such as very fast growth, frequent year-round flowering, production of a large number of small seeds, lighting demand for germination, and low wood density are often shade intolerant trees (Goosem & Tucker 2013; Elliott et al 2013). Similarly, the dominant trees in SF were also classified as pioneers, such as Eurya acuminata, Microcos paniculata, and Vitex pinnata. These trees are mostly found in disturbed areas (Sinbumroong 2009) and old plantation (Koonkhunthod et al. 2007). Pioneer trees are tolerant to adverse environmental conditions; therefore, these species can be considered for restoring other degraded areas. Twenty seven trees recorded were in both SF and PF, among which are Barringtonia macrostachya, Diospyros wallichii, Canarium patentinervium, and Garcinia cowa. However, these were only few small trees. Revegetation in SF was faster than in S27, C27 and MP, resulting in a complex forest structure and high tree diversity. The similarity index between PF and SF was 31.03%, PF with MP was 8.00%, PF 130 Soil properties and tree composition in a 27-year old Acacia mangium Willd. plantation — Wongprom et al. with C27 was 6.98%, and PF with S27 was 5.83% (Table 5). The similarity index between the rehabilitated sites in the mining area and PF was low suggesting that SF may be in a mid- successional status and the rehabilitated sites at S27, C27 and MP were in early successional status, as indicated by their similarity index (Habich 2001). Table 4 Importance Value Index (IVI), Relative Density (RD), Relative Frequency (RF) and Relative Basal Areas (RDo) of the top seven trees in S27, C27, MP, SF and PF Site Tree species Family RD RF RDo IVI S27 Acacia mangium Fabaceae 63.85 35.60 95.15 194.60 Aporosa planchoniana Phyllanthaceae 16.45 15.15 1.21 32.81 Carallia brachiata Rhizophoraceae 4.33 9.85 0.54 14.72 Bridelia tomentosa Phyllanthaceae 3.25 7.58 0.38 11.21 Vitex pinnata Lamiaceae 1.95 6.06 0.74 8.75 Eitsea grandis Lauraceae 1.52 4.55 0.22 6.29 Morinda coreia Rubiaceae 1.73 3.03 0.38 5.14 Other species 6.92 18.18 1.38 26.48 C27 Melicope lunu-ankenda Rutaceae 18.19 15.11 26.59 59.89 Acacia mangium Fabaceae 38.83 6.22 6.55 51.60 Aporosa planchoniana Phyllanthaceae 5.65 7.11 17.73 30.49 Carallia brachiata Rhizophoraceae 8.74 9.33 11.56 29.63 Vitex pinnata Lamiaceae 5.61 8.89 6.17 20.66 Ilex cymosa Aquifoliaceae 1.92 8.00 6.36 16.28 Fagraea fragrans Gentianaceae 2.93 11.11 1.93 15.97 Other species 23.11 34.23 18.13 75.47 MP Eucalyptus camaldulensis Myrtaceae 10.23 9.45 47.12 66.80 Acacia mangium Fabaceae 15.27 8.54 20.78 44.59 Fagraea fragrans Gentianaceae 15.44 10.06 5.50 31.00 Ilex cymosa Aquifoliaceae 15.10 9.45 3.22 27.77 Dipterocapus alatus Dipterocarpaceae 6.21 6.71 1.73 14.65 Vitex pinnata Lamiaceae 2.18 3.96 8.56 14.70 Carallia brachiata Rhizophoraceae 4.19 6.10 1.47 11.76 Other species 31.38 45.73 11.62 88.73 SF Eurya acuminata Pentaphylacaceae 12.24 7.07 13.79 33.10 Gmelina arborea Lamiaceae 5.60 4.08 20.90 30.58 Microcos paniculata Malvaceae 5.39 4.62 10.21 20.22 Barringtonia macrostachya Lecythidaceae 5.81 6.25 1.63 13.69 Vitex pinnata Lamiaceae 3.11 2.99 4.86 10.96 Diospyros ivallichii Ebenaceae 4.77 4.08 1.94 10.79 Garcinia cowa Clusiaceae 2.28 2.72 4.27 9.27 Other species 60.80 68.19 42.40 171.39 PF Swintonia floribunda Anacardiaceae 5.93 4.56 19.72 30.21 Dipterocapus kerrii Dipterocarpaceae 4.17 4.36 13.64 22.17 Canarium patentinervium Burseraceae 7.37 4.77 2.05 14.19 Vanthophyllum virens Polygalaceae 4.17 4.56 5.26 13.99 Mesua ferrea Calophyllaceae 2.04 2.70 8.17 12.91 Hopea grijfithii Dipterocarpaceae 4.97 4.77 2.11 11.85 Gluta elegans Anacardiaceae 3.69 3.11 4.07 10.87 Other species 67.66 71.17 44.98 183.81 Table 5 Sorensen similarity index of tree species among S27, C27 and MP compared with SF and PF Site SF PF S27 17.48 5.83 C27 22.61 6.98 MP 23.53 8.00 SF 100.00 31.03 PF 31.03 100.00 131 BIOTROPIA Vol. 27 No. 2, 2020 CONCLUSION The A. mangium plantation in the abandoned tin mining area played a key role in the soil improvement particularly, the top soil. The bulk density and porosity of soil under the plantation remarkably improved. The level of soil nutrients, particularly, organic matter and total N, increased as a result of the presence of A. mangium trees. However, these quantities were lower than those measured in the secondary and primary forests. The tree diversity and number of species were low in the sandy soil type in S27 (1.43), clay soil type in C27 (2.51), and mixed plantation in MP (2.77). Moreover, the tree similarity indices in S27, C27, and MP, as well as in primary forest PF were relatively low (5.83 - 8.00). These results showed that plant development in S27, C27, and MP was slow and the dominant trees in the rehabilitated mining sites and the SF were mostly identified as belonging to the pioneer species group, suggesting that enrichment planting with poorly dispersed shade tolerant trees should be considered in improving tree diversity and forest structure and eventually, the ecosystem processes in these areas. 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