Agroforest Syst (2013) 87:857–870 DOI 10.1007/s10457-013-9602-4 Allometric relationships of frequently used shade tree species in cacao agroforestry systems in Sulawesi, Indonesia Nina Tiralla • Oleg Panferov • Alexander Knohl Received: 10 July 2012 / Accepted: 17 February 2013 / Published online: 3 March 2013 Ó The Author(s) 2013. This article is published with open access at Springerlink.com Abstract Shade trees play an important role within crown length relationship of the dicotyledonous tree agroforestry systems by influencing radiation and species’ A. moluccana and G. sepium with a coeffi- wind regimes as well as nutrient and hydrological cient of determination r2 = 0.925 and r2 = 0.738, cycling. However, there is a lack of quantitative respectively, and the height-crown length relationship assessments of their functions. One of the reasons is of the monocotyledonous palm C. nucifera with the rare information on structural characteristics of r2 = 0.663. The transferability tests ‘analysis of shade tree species. Therefore, the aim of this study is to covariance’ and ‘homogeneity of slopes’ have shown provide basic information on the structure of fre- that the obtained allometric functions are also appli- quently used shade tree species for the implementation cable to other cacao agroforestry systems of the of models simulating the ecosystem processes in region. agroforestry systems. The investigation of the shade trees was conducted at two cacao agroforestry sites on Keywords Tree allometry Á Aleurites moluccana Á Sulawesi, Indonesia. The measurements of the main Gliricidia sepium Á Cocos nucifera Á structural parameters: diameter at breast height, tree Cacao agroforestry system height, trunk height, crown length and crown radius were carried out for the shade tree species Aleurites moluccana, Cocos nucifera and Gliricidia sepium. For data collection, the National Forest Inventory Field Manual Template by FAO (2004) was applied. Based Introduction on this information allometric functions were derived for the correspondent shade tree species. The best Within the context of conservation of tropical rain- significant relationships were obtained for the height- forests, sustainable development of rural areas and afforestation and reforestation of degraded lands, agroforestry systems have become an increasingly & N. Tiralla ( ) Á O. Panferov Á A. Knohl successful approach as they reduce pressure on natural Department of Bioclimatology, Georg-August-Universita¨t Go¨ttingen, Bu¨sgenweg 2, 37077 Go¨ttingen, Germany forests while meeting economic as well as social needs e-mail: [email protected] of the local population (Michon and de Foresta 1996; O. Panferov Nair 1998; Rice and Greenberg 2000; Bhagwat et al. e-mail: [email protected] 2008; Jose 2009). Agroforestry systems consist of a A. Knohl low-density stratum of tall perennial woody plants e-mail: [email protected] i.e. shade trees, with a stratum of agricultural crops 123 858 Agroforest Syst (2013) 87:857–870 underneath, i.e. shade-bearers like cacao (Theobroma which should be measured (e.g. crown base). Hence, cacao), planted at the same land-management unit. measurements in at least two-storied cacao agrofor- Hence, an agroforestry system encompasses at least estry systems by means of standard inventory practices two different plant species, which allows a higher are often impossible for parameters containing crown productivity and more ecological stability (Lundgren elements. In such cases, the most facilely accessible and Raintree 1982). Shade trees, which provide shade parameter to measure is diameter at breast height for crops underneath, are a crucial component of (dbh). agroforestry systems as they modify radiation and Therefore, species-specific allometric functions wind regimes as well as nutrient and hydrological between different structural parameters are a useful cycling. Biological species composition, mass bal- tool allowing the deduction of inaccessible structural ance, and productivity of agroforestry systems are characteristics like height, crown length and crown influenced by intensity and distribution of shade (Beer radius from known or more easily measurable ones as 1987; Rice and Greenberg 2000; Mialet-Serra et al. dbh. However, information about structural features of 2001; Siebert 2002; Zuidema et al. 2005; Isaac et al. tropical tree species and their relations is rare (Thiollay 2007). However, the impact of shade trees on cacao 1995; Le Roux and Sinoquet 2000; Mun˜oz et al. 2006). crops is discussed controversially as it is not yet In Indonesian agroforestry systems, the typical shade evident in which aspects and how strong shade trees tree species are, inter alia, Gliricidia sepium, Erythrina favour or hamper cacao crops (Beer 1987; Somarriba spp., Inga spp., C. nucifera, Aleurites moluccana and and Beer 2011; Tscharntke et al. 2011). Durio zibethinus (Clough et al. 2009; Stenchly et al. To address this topic, models were developed 2012). They serve the purpose of shade and shelter, soil describing the cycle of organic matter and nutrients protection and fertilizer, pest and disease control, crop (Alpı´zar et al. 1986; Fassbender et al. 1988; Beer et al. health and economically and biologically enriched 1990; Dudley and Fownes 1992; Fuwape et al. 2001; fallows (Beer 1987; Rice and Greenberg 2000;McNe- Cole and Ewel 2006; Segura et al. 2006), the ely and Schroth 2006; Isaac et al. 2007). hydrological cycle (Imbach et al. 1989; Roupsard The aim of this study is, therefore, to provide basic et al. 2006;Ko¨hler et al. 2009) and radiative transfer in information on species-specific tree structural param- agroforestry systems (Dauzat and Eroy 1997; Mialet- eters of frequently used shade tree species in Indone- Serra et al. 2001; Leroy et al. 2005; Lamanda et al. sian cacao agroforestry systems and to develop 2008; Roupsard et al. 2008; Leroy et al. 2009; Quesada allometric relationships for the implementation in and Somarriba 2009). These models often require ecological investigations dealing with agroforestry information on species-specific structural features of ecosystem processes. Special attention is given to shade trees. For example, the model ‘ShadeMotion relationships between easily measurable parameters, 2.0’ by Quesada and Somarriba (2009) for the e.g. dbh, and parameters, which are more difficult to simulation of shading pattern of tree shades requires measure in dense cacao stands, e.g. crown radius. The information on trunk height, crown length, crown transferability of the obtained allometric relationships radius and crown shape to depict different tree species. to other agroforestry systems of that region is Some attempts to model the structure of tropical shade investigated. tree species as Acacia mangium, Cocos nucifera and Tectona grandis were made by Leroy et al. (2009) and Dauzat and Eroy (1997). Materials and methods However, the required structural parameters of shade trees are not always measurable directly. For Study sites instance, in cacao agroforestry systems, shade trees are usually growing amidst cacao plantations with Data collectionwas conducted in two cacao agroforestry their crowns above the cacao canopy. Therefore, the sites in the villages Omu (1°1706.700 S, 119°56051.200 E, dense cacao canopy often obscures a direct view on 188 m a.s.l.), subdistrict Kecamatan Kulawi, and Bulili their crown. Standard measurement techniques used in (1°10024.300 S, 120°5031.700 E, 588 m a.s.l.), subdistrict forest inventories presuppose a more or less unob- Kecamatan Palolo, located in Central Sulawesi, Indo- structed view on a tree or at least the part of the tree, nesia. Both sites are situated in a highly heterogeneous 123 Agroforest Syst (2013) 87:857–870 859 agricultural landscape with diverse small-scale land-use poor soils, drought and wind, and it has a natural systems varying between wet-field agriculture, slash- defence against insects and rodents, as all components and-burn cultivation and agroforestry systems in the of the tree are toxic (Barwick 2004; Elevitch 2006; rainforest fringe area along Lore Lindu National Park. Orwa et al. 2009). The appearance of this evergreen The study site Omu is a two-storied plantation with deciduous tree is bulky with a sprawling crown C. nucifera in the upper layer and cacao underneath (Stuppy et al. 1999; Lo Gullo et al. 2005; Elevitch whereas the study site Bulili is a cacao plantation with a 2006; Chen et al. 2009). In the open, A. moluccana has mixture of G. sepium, C. nucifera, A. moluccana, Durio a low crown base and naturally grows up to 20 m zibethinus and Persea americana as shade trees. Here, height with a crown diameter of 10–15 m with wide the crown of G. sepium was laterally pruned, implying a protruding or pendulous branches and foliage almost reduction of crown radius, after the trunk reached a dbh to the ground (Barwick 2004; Elevitch 2006;Orwa of about 20 cm. More precise statements about pruning et al. 2009). In dense stands, it has tall and mostly frequency and intensity could not be provided by the branchless trunks. The ‘Direktorat Hutan Tanaman farmers. Industri’ (1990) in Indonesia even mentioned a tree The spatial transferability of functions obtained for height of up to 35 m, with a branchless bole of Omu and Bulili was tested using inventory data 10–14 m and a trunk diameter of up to 1 m. The collected in the course of studies in 21 cacao palmately lobed silvery leaves are up to 30 cm long plantations distributed throughout the Kecamatan (Barwick 2004). It is assumed that A. moluccana is a Kulawi and Kecamatan Palolo (data: Yann Clough, moderately fast growing tree species with a growth Universty of Go¨ttingen, Germany, and Ramadhanil rate of 0.5–1.5 m in height per year; young trees can Pitopang, Tadulako University, Indonesia, pers. grow 1–2 m in height per year, whereas, for older com.). Only plantations containing the respective trees, the growth rate will decline over the years. shade tree species were selected for the test of However, direct information about the growth and transferability.