Effect of management treatment and growing regions on wood properties of Gmelina arborea in Costa Rica

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1 New Forest 28: , # 2004 Kluwer Academic Publishers. Printed in the Netherlands. Effect of management treatment and growing regions on wood properties of Gmelina arborea in Costa Rica RÓGER MOYA ROQUE Technological Institute of Costa Rica (ITCR), Research Center for the Forestry Industry Integration (CIIBI), Apartado , Costa Rica ( rmoya@itcr.ac.cr) Received 5 April 2003; accepted in revised form 10 December 2003 Key words: Climate, Heartwood, Management, Specific gravity, Wood properties Abstract. Gmelina arborea (gmelina) was introduced into Costa Rica through reforestation programs with federal incentives. Two areas where gmelina planting were most abundant were the North Pacific and North regions of the country that are representative of dry tropical and humid tropical climatic zones, respectively. This distribution pattern has led to plantations with different management regimes, which still exist today, namely intensive, intermediate and no management treatment. This research looks at the type of wood being produced in both climatic regions and the effect of management intensity. Preliminary results indicate that gmelina wood from the dry region has a higher heartwood percentage, higher specific gravity, better mechanical properties and higher absorption of preservatives when pressure treated than does wood from the humid regions. With regards to management intensity, the results indicate that plantations with no management produced higher specific gravity wood with better mechanical properties than those with intensive or intermediate management. There were no differences between intermediate and intensive management regimes in relation to heartwood percent, decay resistance, and preservative absorption using the dip-diffusion system. Palabras clave: Clima, Duramen, Peso específico básico, Manejo, Propiedades de madera Resumen. La Gmelina arborea fue introducida en toda Costa Rica a través de los programas de reforestación con incentivos fiscales por parte del estado. Las dos áreas en particular, en donde se plantó gmelina ampliamente, fueron la Pacifico Norte y Norte de Costa Rica las cuales representan un clima tropical seco y un clima tropical húmedo respectivamente. Estos patrones de distribución en la reforestación, dieron como resultado diferentes grados de manejo, los cuales existen todavía, con áreas con manejo intensivo, intermedio y sin manejo alguno. Esta investigación examina los diferentes tipos de madera que se está produciendo en las dos regiones climáticas y el efecto que tiene la intensidad en el manejo de las mismas. Los resultados preliminares han indicado que la madera de gmelina proveniente del clima tropical seco presenta un mayor porcentaje de duramen, una mayor peso específico básico, mejores propiedades de resistencia y una mayor absorción de los preservantes, cuando se utiliza el método vacío-presión, que la madera proveniente de regiones húmedas. No se encontraron diferencias entre los regímenes de manejo intermedio y manejo intensivo, con relación al porcentaje del duramen, resistencia al ataque de los hongos, y la absorción de los preservantes cuando se utiliza el sistema de difusión (dip-diffusion system). Introduction Gmelina arborea (gmelina) has been used extensively in reforestation efforts in Costa Rica, representing approximately 60% of the total area planted or about

2 326 90,000 ha (Zamora and Arias 1999). The two regions that are most important in gmelina reforestation are the Northern region that is representative of the humid tropics and the North Pacific that is representative of the dry tropics. Reforestation in Costa Rica has been influenced by federal incentives, which have been applied in different manners, at different times, and under varying circumstances. One of the inconveniences caused by the incentive system has been the lack of management of the reforested areas because the government did not have the resources to apply silviculture to the plantation areas. This resulted in many plantations with little or no management. According to Meza (1999) one of the conclusions in evaluating the quality of the plantations in Costa Rica was,...there were big mistakes and deficiencies during the initial stages of the process, including lack of attention to origin of planting material and generalized delays in the application of pruning and thinnings. Lack of management has resulted in plantations of low quality... Meanwhile, basic properties of the species (physical and mechanical properties, anatomy, performance in industrial processes and utilization) are not yet clearly established for the local market. Of interest are the possible differences in wood properties that could arise in gmelina from one climatic region compared to another as well as the effects of different management regimes on plantation development and wood quality. Lack of knowledge about the effect of growing regions and management practices on the development of gmelina limits the integral use of this forest resource in Costa Rica. This research examines how wood properties in gmelina plantation change with age of the tree, at different locations within the tree, and under varying management regimes in different climatic regions of the country. Materials and methods The study was carried out in two geographic areas in Costa Rica, the North Pacific and North regions of the country (Figure 1). Each region is characterized by specific climate characteristics, the North Pacific zone is dry and the North region is very humid. Preliminary inspections were carried out in each zone to categorize management regimes (Table 1). Based on the categorization, 10 farms (plantations) for each of three management regimes (no management, intermediate, and intensive) were selected, for a total of 30 plantations uniformly distributed in each region (Table 1). The plantations chosen for the study were near their final harvest age of 12 years and were to be used to produce raw material for saw milling. At each plantation, an average tree representing the most frequent height and diameter class in the plantation was selected. This was done by visual inspection according to the plantation conditions. One log 1.25 m in length was cut from the base up to diameter breast height (DBH) and one disc was obtained every 1.25 m along the stem from the base up to the commercial height of the tree where the diameter was no less than 10 cm.

3 327 Figure 1. Location of plantations. Table 1. Characteristics of the management regimes used for G. arborea plantations in the study Type of management Characteristics No management Intermediate Intensive Plantations that did not have any management, with more than 800 trees=ha at the sampling time. Plantations with 2 thinnings and a density between 400 and 800 trees=ha at the sampling time. Plantations with less than 400 trees=ha at the time of sampling. The traits that were assessed for the 60 trees gmelina trees were: General properties: pith, sapwood, heartwood, bark (amount and percentages) Physical properties: green density, specific gravity, shrinkage Mechanical properties: static bending, shear, hardness, compression Anatomical properties: intervascular pit diameter, vessel elements tangential diameter, number of vessels per mm 2, ray height, type of rays (uniseriate and multiseriate), number of rays per mm (tangential direction) and number of rays per mm 2 Decay resistance Preservative uptake Only characteristics related to heartwood percentage, specific gravity, static bending (modulus of elasticity and modulus of rupture), decay resistance and preservative uptake are presented in this paper.

4 328 Figure 2. Heartwood percentage in G. arborea for (a) two study regions and (b) different management treatments. Results and discussion Heartwood percentage is about 10% higher in trees growing in the dry tropical region than in trees growing in the humid tropical region in Costa Rica (Figure 2(a)). No significant differences were detected related to degree of management especially in the lower portions of the trees. Some visual differences were observed in the upper portions due mainly to a decrease in height in the trees with moderate or no management. Specific gravity ranged from 0.34 to The values obtained from the dry tropical region had an average specific gravity of and from the humid tropical region was 0.394, a difference of 4%, which was statistically significant. Gmelina wood produced in the dry tropical region has higher specific gravity than wood growing in the humid region. The same trend was observed in trees of different ages (Figure 3(a)). With regards to trends in specific gravity for different management regimes, it was observed that intensive management produced trees with lower specific gravity than for those with no management practices (Figure 3(b)). This behaviour has been observed in other species (Zobel and Van Buijtenen 1989). Mechanical properties of wood are directly related to specific gravity. This was seen in static bending within the different treatments. Plantations with no management presented the highest MOE and MOR values in bending (Figure 4). The other two management regimes were very similar with lower values than no management.

5 329 Figure 3. Behaviour of specific gravity of G. arborea for (a) two regions of Costa Rica and (b) different treatments of management. Figure 4. Behaviour of (a) Modulus of rupture (MOR) and (b) Modulus of elasticity (MOE) in radial direction for different treatments in G. arborea plantations. Figure 5. Weight loss due to the action of two decay fungi in G. arborea wood from (a) two different regions in Costa Rica and (b) three treatments of management. Decay resistance for G. arborea from plantations in Costa Rica was not affected by the origin of the wood or type of management. The trials carried out with two decay fungi species did not show significant differences among the variables analysed (Figure 5).

6 330 Table 2. Penetration and retention values for two preservation systems in G. arborea growing in two different regions in Costa Rica with three different management treatments Preservation system Parameter Dry tropic Humid tropic Type of management Intensive Intermediate No management Vacuum-pressure Penetration (mm) Retention (kg=m 3 ) Dip-diffusion Retention (kg=m 3 ) The heartwood of G. arborea, as many other species, was impermeable to pressure treatments which leads to low preservative penetration and retention compared to other species (Leandro et al. 2002). However, there were some differences between regions, due to the fact that trees growing in the dry tropical region produced higher heartwood percentage than those in the humid region (Figure 1). Retention and penetration values tended to be lower than the ones obtained for wood growing in the humid tropical region (Figure 2). Wood subjected to different types of management did not show differences for penetration and retention values. With the dip-diffusion system there were no differences between different regions or management treatment (Table 2), as expected since this method is applied to green wood under conditions which were very carefully controlled. References Leandro L., Moya R. and Canessa E Características de la preservación de la melina (Gmelina arborea) con el método de inmersión-difusión utilizando boro y el método vació presión utilizando CCA-C. Informe No. 6. Proyecto de Investigación FC : Evaluación de las características tecnológicas de la melina (Gmelina arborea) provenientes de plantaciones forestales de Costa Rica. Centro en Investigación en Integración Bosque Industria, Instituto Tecnológico de Costa Rica. Meza A Materia prima provenientes de plantaciones forestales. Curso práctico: Industrialización de la madera con énfasis en diámetros menores. COSEFORMA, Cartago, Costa Rica, 19 p. Zamora G. and Arias N Diagnóstico de las oportunidades o amenazas para el proceso de reforestación nacional que implicaría el tratado de libre comercio con Chile. COSEFORMA- CCF, San José, Costa Rica. Zobel B.J. and Van Buijtenen B Wood Variation, Its Causes and Control. Springer-Verlag, Berlin, Heidelberg, New York, USA, 363 p.