Cover Single.cdr BIOTROPIA Vol. 27 No. 2, 2020: 162 - 170 DOI: 10.11598/btb.2020.27.2.1199 SITE INDEX OF SIAMESE ROSEWOOD { Dalbergia cochinchinensis Pierre) IN PLANTATIONS OF THAILAND** TAENGMOO PHUNCHAISRI1, CHONGRAK WACHRINRAT'*, PONTHEP MEUNPONG1, SUWAN TANGMITCHAROEN2 AND NAWAPHONG KUASAKUN1 1Department of Silviculture, Faculty of Forestry, Kasetsart University, Bangkok 10900, Thailand 2Forest Research and Development Bureau, Royal Forest Department, Bangkok 10900, Thailand Received 07 January 2019 / Accepted 16 May 2019 ABSTRACT Currendy, decreased productivity of Siamese rosewood (Dalbergia cochinchinensis Pierre) is a problem due to illegal logging and the guidelines to manage this prevention being may be insufficient. Forest plantations should be promoted to achieve sustainable wood production for this species. Site index (SI) is a measure that can be used to predict forest productivity to identify appropriate sites for planting Siamese rosewood. The objective of the current study was to predict the SI for Siamese rosewood in Thailand. A sample of 78 temporary plots at 26 sites in 16 provinces of Thailand was selected to construct a site index curve with a base age of 30 years. The results showed that the mean age of Siamese rosewood was 28 years (between 13 and 55 years), the mean diameter at breast height (DBH) was 20.03 cm (between 7.99 and 33.80 cm), and the mean dominant height was 20.79 m (between 7.32 and 24.82 m). The SI equation was: SI = e(kiFU-12.476(A4-Ab-1)) with an R2 value of 0.406 at p < 0.0001 (chosen as 30 years in the present study). The equation indicated that 14, 18, 22, 26 and 30 m trees belonged to site classes I, II, III, IV and V, respectively. Although in natural forest, Siamese rosewood is distributed in dry evergreen and mixed deciduous forests, in the present study, several sites in areas under both in situ and ex situ conservation were in the good and very good site categories. Thus, both areas can be used to plant Siamese rosewood and increase its productivity. Keywords: Siamese rosewood, site index, temporary plot INTRODUCTION Siamese rosewood ( Dalbergia cochinchinensis Pierre) is generally found in the dry evergreen and mixed deciduous forests (Veesommai & Kavduengtain 2004) at elevations between 100 and 775 m above sea level (Eiadthong & Tangmitcharoen 2015). This species is native to Thailand, Cambodia, Laos, and Vietnam. Over the years, this species has been severely affected by illegal logging, due to the quality of its hardwood and high durability, leading to a gradual reduction in its numbers (Cadena 2014). It was under the ‘vulnerable” category and red listed as a threatened species by the International Union for Conservation of Nature ^Corresponding author, e-mail: fforcrw@ku.ac.th *Whis paper was presented at the 3rd International Conference on Tropical Biology 2018, 20-21 September 2018, Bogor, West Java, Indonesia (IUCN) (IUCN 2008), leading to a high demand of its wood and high price (Forest Research and Development Bureau 2010). This has been the prime reason affecting the numbers of Siamese rosewood trees. According to a survey by the Royal Forest Department of Thailand (2015), the price of Siamese rosewood heartwood was USD 30,000/m3 on the black market. Such a high price provided sufficient motivation for illegal logging in both natural forest and plantations. In 2014, 1,823 m3 of Siamese rosewood was seized by the Thai government. The lawsuits filed for illegal logging of Siamese rosewood have increased while productivity has decreased every year in Thailand (Department of National Parks, Wildlife and Plant Conservation 2015). A similar situation exists for other threatened species with similar hardwood characteristics, such as Dalbergia oliveri Gamble ex Prain and Tterocarpus 162 Site index of Siamese rosewood ('Dalbergia cochinchinensis Pierre) in Thailand — Phunchaisri et al macrocarpus Kurz (Internal Security Operations Command 2014). The diminishing number of individual trees of such species is of grave concern and needs to be dealt with urgently. Plantations can play an important role in the success of reviving these species. Several economically viable species, including Siamese rosewood, have been promoted in certain areas by the Thai government. Two distinct procedures have been applied: 1) in situ conservation areas (conservation of ecosystems and natural habitats and maintenance and recovery of the population that allows the species to exist in the natural environment and in the case of domesticated or cultivated plant species in an environment in which those species have developed special properties); and 2) ex situ conservation (conservation of plant genetic resources outside the natural habitat). The current methods being used for selecting areas where this planting Siamese rosewood need to be improved and implemented in the future (Tangmitcharoen 2013). Site index (SI) is one of the measures used to predict forest productivity, wood volume, and the potential rate of growth (Hanson et al. 2002). The relationship between dominant height and age was used to construct a site index curve by Mayhew & Newton (1998). There are several techniques for determining SI such as: (1) the proportion curve or guide curve method; (2) the parameter prediction method; and (3) the different equation method (Clutter et al. 1983). In Thailand, the proportion curve method has been used for assessing and predicting the site quality of Tectona grandis L.f. (Forestry Research Center 1996) and Eucalyptus camaldulensis Dehnh. plantations in the lower northeastern parts (Insaun et al 2009) and Acacia mangium Willd. plantation in Trat province (Jumwong 2006). Siamese rosewood research has also focused on other dimensions such as inventory, ecology, growth and yield. The prediction of SI for Siamese rosewood is yet to be undertaken. Thus, the objective of the current research was to summarize the growth characteristics and develop a SI for Siamese rosewood found in plantations in Thailand. MATERIALS AND METHODS Study Site and Data Collection Thailand is a tropical country located between 5°37M N and 20°27M N latitude and 97°22M E and 105°37M E longitude. The annual rainfall ranges between 1,200 and 1,600 mm and the mean annual rainfall is 1,587 mm. The mean annual temperature is around 27° C (Thai Meteorological Department 2014). The study was conducted in Siamese rosewood plantations owned by the Royal Forest Department of Thailand (RFD) and the Forest Industry Organization (FIO). Twenty-six sites were selected from 16 provinces distributed throughout Thailand (Table 1 and Fig. 1). Three temporary sample plots were selected per site (78 temporary sample plots in total). Each temporary plot was 0.16 ha in size and the diameter at breast height over bark (DBH) at 1.30 m above ground and total height (H), of all trees in the plot, were measured. Meteorological data from the Thai Meteorological Department for the sample sites are shown in Table 2. Table 1 Summary of 26 Siamese Rosewood study sites in Thailand used in the study No Plantation Province Region Code Latitude Longitude 1 Kam Phaeng Phet Silvicultural Research Station Kamphaengphet N KPP1 16° 33’ 99° 30’ 2 Kam Phaeng Phet Silvicultural Research Station Kamphaengphet N KPP2 16° 34’ 99° 30’ 3 Kam Phaeng Phet Silvicultural Research Station Kamphaengphet N KPP3 16° 33’ 99° 30’ 4 Phit Sa Nu Lok Silvicultural Research Station Phitsanulok N PNL 16° 50’ 100° 53’ 5 In Tha Khin Silvicultural Research Station Chiangmai N ITK 19° 9’ 98° 56’ 6 Tha Turn Silvicultural Research Station Surin NE TT 15° 18’ 103° 45’ 7 Nong Khu Silvicultural Research Station Surin NE NK 14° 41’ 103° 45’ 8 Huai Tha Silvicultural Research Station Sisaket NE HT1 14° 52’ 104° 26’ 9 Huai Tha Silvicultural Research Station Sisaket NE HT2 14° 52’ 104° 26’ 10 Pha Nok Khao Silvicultural Research Station Khon Kaen NE PNK 16° 50’ 101° 56’ 11 Loei Forestry and Forest Products Research Center Loei NE LOEI 16° 52’ 101° 56’ 163 BIOTROPIA Vol. 27 No. 2, 2020 Table 1 (Continued) 12 Udon Tha Ni Forest Nursery Center Udon Thani NE UD 16° 50’ 102° 56’ Nakhon 13 Mu Si Silvicultural Research Station Ratchasima NE MSI 14° 30’ 101° 25’ Nakhon 14 Mu Si Silvicultural Research Station Ratchasima NE MS2 14° 30’ 101° 25’ 15 Ka La Sin Silvicultural Research Station Kalasin NE KLS 16° 28’ 103° 24’ 16 Dong LanSilvicultural Research Station Khon Kaen NE DL 16° 49’ 101° 59’ 17 Huai Rang Plantation Trat E HR 12° 26’ 102° 33’ 18 Tha Kum Noboru Umeda Plantation Trat E TK1 12° 22’ 102° 40’ 19 Tha Kum Noboru Umeda Plantation Trat E TK2 12° 23’ 102° 39’ 20 Tha Kum Noboru Umeda Plantation Trat E TK3 12° 23’ 102° 39’ 21 Rat Cha Bu Ri Silvicultural Research Station Ratchaburi C RBR 13° 34’ 99° 44’ 22 Central Silvicultural Research center Kanchanaburi C PK1 14° 24’ 98° 55’ 23 Central Silvicultural Research center Kanchanaburi c PK2 14° 24’ 98° 55’ 24 Thong Pha Phum Silvicultural Research Station Kanchanaburi c TPP 14° 42’ 98° 39’ 25 Southern Silvicultural Research center Songkhla s PT 7° 1’ o 0 Prachuap Khiri 10° 59’ 99° 27’26 Sai Thong Silvicultural Research Station Khan s ST Note: Regions as identified by the Thai Meteorological Department are: N” is north, “ NE” is northeast, “ E” is east, “ C” is central, and “ S” is south. Table 2 Meteorological data for the study sites Average Average relative No. Station name temperature (°Q humidity , (%) (nrim/year) Study site 1 Phitsanulok 28.1 74.2 1,399 PNL 2 Kamphaengphet 28.5 76.8 1,372 KPP1, KPP2, KPP3 3 Chiangmai 27.2 71.3 1,158 ITK 4 Pakchong Agromet 26.4 73.3 1,206 MSI, MS2 5 Thatom 27.9 74.1 1,313 TT 6 Surin 27.7 72.4 1,454 NK 7 Sisaket Agromet 27.7 74.8 1,420 HT1, HT2 8 Loei 26.9 73.2 1,310 LOEI 9 Kalasin 27.2 72.0 1,340 KLS 10 Khon Kaen 27.7 70.4 1,196 PNK, DL 11 Udonthani 27.5 71.1 1,338 UD 12 Trat 27.9 81.4 4,988 HR, TK1, TK2, TK3 13 Ratchaburi 28.6 78.1 1,067 RBR 14 Kanchanaburi 29.0 70.4 1,104 PK1, PK2 15 Thong Phaphum 28.1 78.5 1,827 TPP 16 Prachuap Khiri Khan 28.8 76.3 1,056 ST 17 Hatyai 28.3 79.4 1,793 PT Determination of SI Equation The height of the tree is important in the creation of the SI but the mean height of a stand is usually sensitive to age, site, class and stand density. Thus, the dominant height is normally used to represent a stand and specifically mean height of the 100 tallest trees/ha is most widely used to construct an SI (Alder 1980). In this case, the SI equation was constructed using the top 16 tallest trees per plot (plot size of 0.16 ha). There are several techniques for determining the SI. However, the current study only had access to data derived from temporary plots and consequently, the guide curve method was used (Alderl980) based on equation (1) and the SI equation was constructed using equation (2). In (Hdo) = Inb0+biA-k (1), SI = e (In (Hdo)+bi (A-hAy1)) (2), where Hdo is the dominant height, In is the natural logarithm, bo and bi are regression coefficients, A is the stand age, k = 1, SI is the site index, e is the natural exponent, and Ab is 164 Site index of Siamese rosewood ( Dalbergia cochinchinensis Pierre) in Thailand — Phunchaisri et al. the base age (chosen as 30 years in the present study). Based on equation 2, 5 site classes were used (I, II, III, IV, and V) indicating very poor, poor, moderate, good, and very good sites, respectively. The upper and lower bounds for each SI class were determined using simple interpolation and extrapolation in the Excel software package (Microsoft Corp.; Redmond, CA, USA). RESULTS AND DISCUSSION The growth characteristics of Siamese rosewood, as determined from 26 sites, are presented in Table 3. The mean age was 28 years (between 13 and 55 years), mean DBH was 20.03 cm (between 7.99 and 33.80 cm), mean H was 16.48 m (ranging between 6.18 and 23.20 m), and the mean Hdo was 20.79 m (ranging between 7.32 and 24.82 m). The mean DBH, H and Hdo of the TT plantation were lowest (see Table 1 for identification of the plantation abbreviations used). Both the highest mean DBH and mean H were in the KLS plantation and the highest mean of Hdo was in the PNL plantation. The mean dominant heights for KLS and PNL were similar (24.18 and 24.82 m, respectively) despite their stand ages being rather different (42 and 27 years, respectively). This could be interpreted as the younger stand age alone indicating site suitability which is not necessarily correct. Thus, the methodology for assessing the appropriate site using the site index had to decrease the bias associated with the different-aged stands. «00000 1200000 i § Scale 1:8,000,000 0 75 150 300 450 600 I Kilometer! 600000 1200000 Figure 1 Location of Siamese rosewood study sites in Thailand Table 3 Growth characteristics of the Siamese rosewood in plantations located at the 26 sites in Thailand No Site code Age (years) DBH ± SD (cm) H ± SD (m) Hdo± SD (m) 1 TT 13 7.99 ± 3.94 6.18 ± 2.65 7.32 ± 2.22 2 RBR 22 23.42 ± 7.48 14.06 ± 3.30 14.55 ± 3.00 3 NIC 25 13.23 ± 5.66 10.78 ± 3.85 16.03 ± 2.40 4 HT1 25 18.38 ± 6.06 14.58 ± 3.56 17.55 ± 1.49 5 HT2 25 21.02 ± 8.27 16.64 ± 4.13 17.43 ± 3.03 6 PNK 54 31.59 ± 7.16 22.64 ± 4.83 22.92 ± 4.70 7 LOEI 55 18.34 ± 6.07 17.42 ± 4.68 22.14 ± 2.43 8 UD 20 14.18 ± 5.73 13.82 ± 4.95 17.50 ± 4.13 165 BIOTROPIA Vol. 27 No. 2, 2020 Table 3 (Continued) 9 KPP1 23 18.43 ± 7.30 16.72 ± 3.93 20.62 ± 1.90 10 MSI 28 21.15 ± 6.15 16.74 ± 3.18 20.02 ± 1.16 11 MS2 28 15.41 ± 6.29 13.96 ± 4.63 20.72 ± 2.38 12 HR 30 20.49 ± 7.92 16.21 ± 5.57 22.72 ± 2.61 13 TK1 32 25.06 ± 10.62 17.58 ± 6.16 23.53 ± 2.52 14 TK2 35 22.21 ± 8.48 15.82 ± 5.36 22.04 ± 1.74 15 TK3 36 25.40 ± 9.18 15.09 ± 5.25 21.38 ± 2.01 16 KLS 42 33.80 ± 9.92 23.20 ± 5.02 24.18 ± 4.94 17 PK2 18 18.39 ± 7.17 15.69 ± 4.64 20.71 ± 1.74 18 PK1 21 16.99 ± 7.65 15.09 ± 4.98 20.72 ± 1.53 19 KPP2 23 21.11 ± 7.07 19.47 ± 5.13 23.86 ± 2.38 20 KPP3 23 20.65 ± 9.55 17.54 ± 6.68 24.35 ± 1.96 21 PT 26 20.29 ± 8.14 18.24 ± 5.45 23.08 ± 0.90 22 PNL 27 15.97 ± 6.83 17.93 ± 5.45 24.82 ± 1.22 23 TPP 27 25.55 ± 11.14 20.01 ± 5.26 24.30 ± 1.28 24 ST 28 19.18 ± 7.67 19.64 ± 4.62 24.42 ± 1.15 25 DL 16 16.66 ± 5.68 16.06 ± 3.42 19.89 ± 1.92 26 ITK 20 15.85 ± 6.89 17.30 ± 5.16 23.60 ± 2.16 The SI equation for Siamese rosewood category. In this study, most of the measured obtained using the proportional curve method at sites were in either the moderate or good site a base age of 30 years was SI == e(lnHdo- classes. Even though thLHNK gEl •KL O MSI g M S Scale 1:3,500,000 0 30 60 120 160 240 Kilometers o 0 o 800000 1000000 1200000 750000 900000 g gI *- */ < § g o ft t-aKH K IX1r ‘ *• gTK3tk 2 Scale 1:2,000,000 0 15 30 60 90 120 Kilometen 750000 900000 Figure 3 In situ study sites of Siamese rosewood in northeastern and eastern Thailand 167 BIOTROPIA Vol. 27 No. 2, 2020 The natural distribution of Siamese rosewood is in the dry evergreen and mixed deciduous forests where located northeastern and eastern Thailand (Fig. 3). Both regions have in situ conservation areas in which were located the study sites HR, TK1, TK2 and TK3 in the eastern, and TT, NK, HT1, HT2, PNK, LOEI, UD, MSI, MS2, KLS and DL in the northeastern regions. Several sites in the in-situ conservation areas were not as appropriate as plantation sites as in the ex-situ conservation areas. The better ex situ sites were PK1, PK2, KPP1, KPP2, PT, PNL, TPP, ST and ITK were determined to be in the good and very good site classes (IV and V, see Fig. 4). Suanpaga & Boonyuan (2016) compared the growth of eight appropriate tree species for planting in the Songkhla province, southern Thailand (an ex-situ conservation area for Siamese rosewood). Based on their results, they recommended Siamese rosewood and three other species ('Dipterocarpus alatus Roxb, Xylia xylocarpa (.Roxb.) Taub. var. kerrii (Craib & Hutch.) I. C. Nielsen and Ayadirachta excelsa (Jack) Jacobs). Illegal logging has continued (Sudsakorn 2012) and so plans to increase sustainable productivity need to consider prevention and promotion. Chaipunya (2016) considered three aspects to maintain sustainable production from current stands: preventing illegal rosewood logging, preventing transportation, and preventing export of logs or wood products. In addition, Visaratana et al. (2016) presented a case to promote both forest management and silvicultural techniques via plantations located on good sites to provide increasing productivity and economic value. Siamese rosewood can fix nitrogen through Rhiyobium bacteria that can increase the health of ecological systems by fixing nutrients for use also by other species (Mungklarat 2001) and to improve soil fertility for reforestation purposes (So et al. 2010). With regard to the current study, several sites in the ex-situ conservation area belonged to either the good or very good site classes. Thus, both ex-situ and in-situ conservation areas can be used for plantation purposes to increase productivity. 400000 600000 " !i -» l s ITK STPP HM PK2PKPP sI Sfiit* 1:3,500,000 0 SO «0 120 ISO 2 Seal*1:4.000,000 45 90 180 21 -+! < " II I ' Figure 4 Ex situ study sites of Siamese rosewood in northern, central, and southern Thailand 168 Site index of Siamese rosewood (Dalbergia cochinchinensis Pierre) in Thailand — Phunchaisri et al. CONCLUSION A site index curve and equation are necessities for Thailand forestry to support Siamese rosewood plantations dating back more than 50 years; however, extensive research commenced only recently. As a result, knowledge is still lacking of the site requirements for plantations of this species. Based on the growth characteristic of Siamese rosewood from the Royal Forest Department of Thailand (RFD) and the Forest Industry Organization (FIO) plantations at 26 sites represented the age ranges between 13 and 55 years, the DBH ranges between 7.99 and 33.80 cm, the H ranges between 6.18 and 23.20 m and the Hdo ranges between 7.32 and 24.82 m. In addition, five SI classes were constructed with most sites in the moderate site class. The SI equation developed in this study can be applied to help avoid planting of Siamese rosewood on inappropriate lower quality sites and place more emphasis on identifying higher quality sites for plantation establishment. Several sites in the ex- situ conservation area belonged either to the good or very good site classes. Thus, both ex-situ and in-situ conservation areas can be used for plantation purposes to increase productivity. ACKNOWLEDGEMENTS This research was supported in part by a Graduate Program Scholarship from the Graduate School, Kasetsart University, Bangkok, Thailand. We thank the Royal Forest Department of Thailand (RFD) and the Forest Industry Organization (FIO) for helping with the supply of data and assistance with fieldwork. REFERENCES Alder D. 1980. Forest volume estimation and yield prediction vol. 2 yield production. Italy: Food and Agriculture Organization of United Nation. Cadena A [Internet], 2014. (Unprotected Areas: Rosewood poaching in Thailand’s Dong Phayayen- KhaoYai world heritage site: IUCN.com; [updated 2014 Feb 24; cited 2018 Jun 20]. Available from: https:/ /www.iucn.org/content/unprotected-areas- rosewood-poaching-thailand%E2%80%99s-dong- phayayen-khao-yai-world-heritage-site Chaipunya M. 2016. Monitoring of ad hoc plan's implementation on combating illegal logging of rosewood in Northeastern protected area 2013. 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