Sustainable site productivity and nutrient management in a short rotation plantation of Gmelina arborea in East Kalimantan, Indonesia
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New Forest 28: 277–285, 2004. # 2004 Kluwer Academic Publishers. Printed in the Netherlands.
Sustainable site productivity and nutrient management in a short rotation plantation of Gmelina arborea in East Kalimantan, Indonesia CAHYONO AGUS1,2,*, OKA KARYANTO1, SATOSHI KITA2, KIKUO HAIBARA2, HIROTO TODA2, SURYO HARDIWINOTO1, HARYONO SUPRIYO1, MOHAMAD NA’IEM1, WAHYU WARDANA3, MAURIT S. SIPAYUNG3, KHOMSATUN4 and SUHARTONO WIJOYO3 1 Faculty of Forestry, Gadjah Mada University, Yogyakarta, Indonesia; 2Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan; 3PT Sumalindo Lestari Jaya, Samarinda, Indonesia; 4PT ITCI-KU, Balikpapan, Indonesia; *Author for correspondence (e-mail: itto-gmu@ yogya.wasantara.net.id.
Received 5 April 2003; accepted in revised form 10 December 2003
Key words: Land use change, Legume cover crop, Short-rotation plantation, Site quality, Sustainable forest nutrient management, Tropical forest Abstract. Sustainable Forest Management (SFM) requires information on plant growth and nutrient dynamics in forest ecosystems. To obtain fundamental information for SFM in short-rotation plantations in tropical regions, a serial study was conducted on: (i) land use changes and effects on soil chemical properties in tropical forestland, (ii) site index and nutrient dynamics in Gmelina arborea Roxb. (yemane), (iii) stand age and nutrient cycles in the first rotation of a yemane plantation on a moderately productive site, and (iv) biomass and N2-fixation of legume cover crops (LCC) for soil amelioration. Land use change from natural stands to plantations was linked to a decrease in electric conductivity (EC), cation exchange capacity (CEC), total carbon (T-C), carbon to nitrogen ratio (C=N ratio) and exchangeable ca. Three sites classified by productivity (poor, moderate and good) were examined using annual inventory data from 3 to 4% sampling intensity of yemane plantations in the Sebulu site, PT Sumalindo Lestari Jaya. The growth of yemane was very rapid during the first 6 years and was strongly influenced by site quality. The differences in average stand height between the site classes at 6 years were 3 m, representing stand volume differences of approximately 40 m3 ha1. Whole-tree harvesting removed 50% of the aboveground biomass and nutrients. The good site had greater amounts of total phosphorus (T-P), total calcium (T-Ca), total magnesium (T-Mg), available P, and exchangeable Ca and Mg in the soil than moderate and poor sites. There were no significant differences in nutrient amounts in the soil at different stand ages (4, 6 and 8 years of age). The effects of site class on the topsoil characteristics were greater than those for land use change and stand age. Yemane plantations in tropical regions are supported more by nutrient cycling rate than by the amount of nutrient availability in soil. Nitrogen and phosphorus were the limiting nutrients for yemane growth and regeneration in East Kalimantan. Legumes can promote sustainable site productivities in shortrotation plantations in tropical forests by supplying N to the soil through N2-fixation and organic matter. Annual N2-fixation from the atmosphere by LCC was 10–60 kg N ha1 yr1. Application of fertilizer needs to be considered for development of yemane on very poor soils. Palabras clave: Cambios del use de la tierra, Cultivos de leguminosas, Plantacio´n de corta rotacio´n, Calidad de sitio, Manejo de nutrientes en bosques sustentables, Bosque tropical Resumen. Para un Manejo Forestal Sostenido (MFS) se necesita informacio´n acerca del crecimiento de las plantas y la dina´mica de los nutrientes en los ecosistemas forestales. Para obtener informacio´n fundamental para el MFS en regiones tropicales de plantaciones de corta rotacio´n, se condujeron estudios en
278 serie acerca de (i) los cambios en la utilizacio´ n de los terrenos y sus efectos en las propiedades quı´micas del suelo en terrenos forestales tropicales (ii) el ´ındice de sitios y la dina´ mica de los nutrientes en la Gmelina arborea Roxb. (yemane) (iii) la edad de los rodales y el ciclo de los nutrientes en la primera rotacio´ n de una plantacio´ n de yemane en un sitio moderadamente productivo (iv) y estudios sobre la biomasa y fijacio´ n del N2 en cultivos con leguminosas para mejorar el suelo. El cambio en el uso de sitio bosque natural a plantaciones forestales, se relaciono´ con una disminucio´ n en la conductividad ele´ ctrica, capacidad de intercambio de cationes, carbo´ n total, tasa de carbo´ n a nitro´ geno (C=N) y el Ca intercambiable. Se examinaron tres sitios clasificados por su productividad (baja, moderada y buena), utilizando datos de un inventario anual con una intensidad de muestreo del 3-4 % de las plantaciones de yemane en el sitio Sebulu, de PT Sumalindo Lestari Jaya. El crecimiento del yemane durante los seis primeros an˜ os fue muy ra´ pido y estuvo fuertemente influenciado por la calidad del suelo. Las diferencias en la altura promedio del rodal entre las distintas clases de sitios fue de 3 m, lo cual representa diferencias en el volumen del rodal de aproximadamente 40 m3 ha1. La cosecha total de los a´ rboles removio´ el 50% de la biomasa y de los nutrientes en la capa superior del suelo. En el sitio de buena calidad, el suelo tenı´a mayores cantidades de fo´ sforo total (T-P), calcio total (T-Ca), magnesio total (T-Mg), fo´ sforo disponible y calcio y magnesio intercambiables, que en los sitios de calidad baja o moderada. No se encontraron diferencias significativas en la cantidad de nutrientes en el suelo a las diferentes edades de los rodales (4, 6 y 8 an˜ os de edad). Los efectos de la clase de sitio en las caracterı´sticas de la capa superficial del suelo fueron mayores que los efectos debido a los cambios de uso del terreno y por la edad del rodal. Las plantaciones de yemane en regiones tropicales, utilizan ma´ s los nutrientes reciclados que la cantidad de nutrientes disponibles en el suelo. El nitro´ geno y el fo´ sforo fueron los nutrientes limitantes en las plantaciones del oriente de Kalimantan. En plantaciones de corta rotacio´ n en bosques tropicales, las leguminosas pueden promover una productividad sostenida del sitio, al suministrarle N al suelo por medio de la fijacio´ n del N2 y de la materia orga´ nica. La fijacio´ n anual de N2 de la atmo´ sfera en los cultivos con una cobertura de leguminosas fue del 10 a 60 kg N=ha=an˜ o. Para el desarrollo de plantaciones de yemane en suelos de muy baja calidad, se debe considerar la aplicacio´ n de fertilizantes.
Introduction Forest degradation is one of the main environmental problems that affect global ecosystems. This is because it reduces the environmental benefits of forest cover such as protection against soil erosion and maintenance of water quality. Forest loss is also detrimental to the maintenance of biological diversity and lessens agricultural productivity and sustainability, and reduces carbon sequestration and mitigation of global warming. Indonesia has forestland totaling 120.35 million ha which covers 68% of its territory and represents over 60% of Asia’s tropical forests (Lee and Park 2001). Degraded areas total 43 million ha (including 6.5 million ha in East Kalimantan) which consist of 24 million ha for forest and 19 million for non-forest uses. Rate of degradation is approximately 1.6–2.1 million ha yr1, while rate of rehabilitation is only approximately 500,000 ha yr1 (Baplan 2000). Typic Hapludult are strongly weathered soils and represent 60% of the type found in East Kalimantan. Due to the high rate of weathering under constant warm and humid climate of the region, these soils consist mainly of kaolinite, an easily weathered clay mineral composed mostly of silica, aluminum, hydrogen and oxygen (Jordan 1985). As a result, these soils are acidic and have low potential for both holding and supplying mineral nutrients through weathering. These soil properties are recognized as one of the most outstanding features of moist tropical
279 forest soils in East Kalimantan. Understanding the soil characteristics that influence site productivity in forest ecosystems is important for sustainable development of both secondary forests (SF) and plantations of species like yemane. Short-rotation plantations in the tropics are not only a source of timber and pulp, but also serve to take pressure off natural forests (NF) (Reddy 2002). Beginning in 1992, PT Sumalindo Lestari Jaya (total land base 198,000 ha) and PT ITCI-KU (total land base 250,000 ha) have established plantations of Gmelina arborea (yemane) on 6- to 8-year rotations in parts of their land areas in order to supply the raw materials for pulp and medium density fiber (MDF). This paper reports on the effects of land use change on the chemical properties of forest soil in yemane plantations, nutrient dynamics by site index and stand age, and the role that legume cover crops (LCC) have in soil amelioration in East Kalimantan, Indonesia. Our main objective was to determine the primary characteristics that influence site productivity and nutrient management in short-rotation yemane plantations.
Materials and methods The effects of land use changes on the characteristics of chemical soil properties (0–10 cm and 10–30 cm depth) were studied in three plots of NF, three plots of SF, four plots of clear cut and burned areas (CB), two plots of degraded forest (DF), four plots of yemane plantations on sites with moderate productivity (Ga), and five plots of yemane plantations that were derived from coppice (Co). The study sites used were Sebulu Camp (008150 S to 008150 N, 1168530 to 1178000 E, owned by PT Sumalindo Lestari Jaya, Kenangan Camp (008200 S to 018000 S, 1168300 E to 1178000 E, owned by PT ITCI-KU), Wanariset (008500 S, 1178100 E, Samboja), and Bukit Bengkirai (008500 S, 1178110 E, owned by PT INHUTANI I), and Mulawarman University forest (008500 S, 1178100 E, owned by Mulawarman University). All research sites are located in East Kalimantan and ranged in altitude from 20 to 60 m above sea level. The site productivity classes of yemane plantations were divided into three general classes (poor, moderate and good) based on dominant tree height. Three permanent plots were established in triplicate on the poor, moderate and good sites of 6-year-old yemane plantations beginning in October 1998 to study the nutrient dynamics among site classes. The effects of stand age on nutrient dynamics were studied in 2-, 4-, 6- and 8-year-old yemane plantations established on sites with moderate productivity. The traits assessed included nutrient amounts aboveground, belowground, understory biomass, soil nutrient amounts, litter fall, leaf decomposition, and characteristics of N-mineralization and nutrient movement in soil solution (also see Agus 2003). The role of LCC in soil amelioration was studied by planting Crotalaria anagyroides Mucuna chochuchinensis and Calopogonium caeruleaum on the poor site, and Styloxanthes quionensis, Flamengia congesta, M. chochuchinensis and Mimosa pudica on the site with moderate productivity. Nutrient amounts in aboveground
280 and belowground biomass, topsoil (0–10 cm depth) and N2 fixation were studied 6 months after planting. Soil pH(H2O), pH(KCl), electric conductivity (EC), Total (T)-C, T-N, T-P, T-K, T-Ca, T-Mg, T-Na, T-Fe, T-Al, NH4-N, NO3-N, available P, exchangeable K, Ca, Mg, Na and Al, and free Fe concentrations, cation exchange capacity (CEC), base saturation (BS), soil microorganism biomass of C (MBC) and microorganism biomass of N (MBN) were determined by the method detailed in Page et al. (1982).
Results and discussions The destruction of NF stands through conversion to SFs through selective cutting did not affect nutrient status in the topsoil, excluding Ca. Land use change that produced DFs tended to cause a decrease in exchangeable base cations (Ca and Mg). Carbon stocks in soils of NF decreased sharply following conversion to other land uses. The land use change that resulted from the clearcut-and-burn approach seemed to stimulate an increase of nutrient amounts (T-N, exchangeable K, Ca and Mg) in surface soil over a short time. Decreasing the nutrient supply or interrupting the nutrient cycle through the removal of nutrients by clearcutting of forests might adversely affect the growth of artificial regeneration of yemane. Land use changes from NF to plantations were linked to a decrease in EC, CEC, T-C, C=N ratio and exchangeable Ca. Three site productivity classes (poor, moderate and good) were discerned using annual inventory data (with 3–4% sampling intensity) of represented yemane plantations in the Sebulu site, PT Sumalindo Lestari Jaya. The differences in average stand height between the site classes at 6 years of age were 3 m, and differences in stand volume were approximately 40 m3 ha1. The height growth of the stand slowed down after 6 years, but stem diameter continued to increase with stand age. Therefore, yemane can be planted more densely than 3 3 m. The difference in volume growth among the site classes represented a difference of about two years of growth at differing site classes. Annual increments of stand volume reached a maximum at approximately 6 years in the good site and 8 years in the moderate and poor sites. Therefore the optimum age for clearcutting should be prolonged from 6 to 8 years in the moderate site. There was a high allometric relationship (y ¼ 0.074 x0.922) between D2H (DBH2 cm height m) and aboveground biomass regardless of the site class (also see Agus 2003 for other tree components). These equations can also be used in other regions of East Kalimantan. The nutrient dynamics in the 6-year-old yemane on a site with moderate productivity is shown in Figure 1 (also see Agus 2003). The ratio of biomass in the poor:moderate:good sites were 1:2:3. The same ratios were also found for some nutrients (N, P. K, Ca and Mg) amounts. The site with good productivity had greater amounts of T-P, T-Ca, T-Mg, available P, and exchangeable Ca and Mg in the soil available for circulation in the ecosystem than did the moderate and poor sites. The ratio of nutrient amounts in the topsoil (0–10 cm depth) to that in 0–100 cm soil depth was 70–80% for N and 40–50% for Ca and Mg. Free Fe and exchangeable Al
281
Figure 1. Nutrient circulation in 6-year-old yemane plantation in the moderate site.
amounts in the 0–10 cm soil depth on the good site were less than those on the moderate and poor sites, with less than 3% of the amount in the 0–100 cm soil depth. There were no significant differences in nutrient amounts in the soil among stand ages (4, 6 and 8 years old). The effect of site class on the nutrient amounts of the topsoil was greater than that of land use change and stand age. The ratio of soil available=exchangeable nutrient to total nutrient was less than 3% for N, P, K, Al, and approximately 30–40% for Ca and Mg. The amount and the ratios of main nutrient availability were very low regardless the site class. Microbial biomass C (MBC) and N (MBN) on the good and moderate sites (800 and 350 kg ha1, respectively) were two to three times the amount of that on the poor site (300 and 130 kg ha1, respectively). Even though there were differences by site class, there were no significant differences among stand age. Large amounts of inorganic C and N were dissolved from microbial biomass into soil water in the good and moderate sites every year due to the short lifespan of microbes (2–3 years). The litterfall of yemane plantations was evenly distributed throughout all months during the year, because the precipitation is well distributed and the temperature fluctuates little throughout the year in wet tropical rain forest regions. Annual litter fall was 8–9 Megagram ha1 yr1 on the moderate site, and 12 Megagram ha1 yr1 on the good site regardless of stand age (4, 6 and 8 years old). Generally, yemane plantations seemed to close their crowns at approximately 4 years of age in East Kalimantan. The rate of nutrient cycling in yemane tree biomass was greater than
282 their availability in soil. The rate of nutrient cycling in tropical regions was also greater than in temperate regions (Agus 1995; Jug et al. 1999). Therefore, the contribution to nutrient loss of harvesting in East Kalimantan is higher than in temperate regions. The uptake and loss of N and P by whole-tree harvesting in yemane plantations were greater than their availability in the soil. The uptake and loss of K by harvesting were also greater than its availability, but because of K input from rain under tree crown (55–80 kg ha1 yr1, Tanaka et al. 2000), K deficiencies were not a major problem for yemane. In order to maintain the productivity of forest plantations, the rate of nutrient input must equal or exceed any losses that occur through leaching, erosion, fire, or harvesting. Nutrients are added to the soil through the processes of mineralization, weathering, symbiotic-N fixation, and atmospheric deposition. Considerable amounts of some nutrients should be supplied to substitute nutrient loss by harvest. Based on this study, approximately 250 kg of N, 40 kg of P, 150 kg of K, 100 kg ha1 of Ca and other nutrients should be maintained for the next rotation in order to sustain soil productivity on the site with moderate productivity. Priority should be given to adding organic matter and symbiotic microbes and developing sound fertilization programs. Leaf litter was almost completely decomposed after about one year, potentially supplying nutrients to the soil, regardless of site class and stand age. Nevertheless, because litter fall on the good site was greater than that on the moderate site, the amounts of nutrient released from decomposed litter on the good site were also greater. To be available for uptake, N must be present in the soil solution in an þ available form, either NO 3 or NH4 . Most N is stored in an organic form and is not available until the organic matter is broken down and decomposed through the biological processes. Ammonium-N produced by N-mineralization in yemane plantations was converted rapidly into nitrate (NO3-N) and was not affected by room incubation temperature (258C and 308C). Annual N-mineralization in the topsoil (0–10 cm depth) at the moderate and good productivity sites was 51 kg ha1 yr1 and 77 kg ha1 yr1, respectively. On the other hand, N input through litter fall on the moderate and good site was 86 and 181 kg ha1 yr1, respectively. N-mineralization in the 8-year-old plantation on the moderate site was relatively similar to that in the 6-year-old plantation on the good site. N-mineralization of forest soil at 5–10 cm soil depth was only about 50% of that at 0–5 cm soil depth. With N uptake at 190 kg ha1 yr1 on the moderate site and 320 kg ha1 yr1 on the good site, N is one of the limiting factors of tree growth in yemane plantations in tropical regions. Nitrogen and P were the limiting nutrients for yemane growth and regeneration, since these elements were absorbed and exported in an amount that exceeds their low availability in the soil. These nutrient imbalances in the soil will cause a decline in productivity of the next rotation. Alternatively, site productivity could be maintained by mineral fertilization, managing closed nutrient cycling or by practicing biological fertilization. The nutrient export from soils with poor nutrient pools in East Kalimantan causes deficiency of some elements for plant growth. Therefore, subsequent productivity
283 of the plantation might decline without the addition of amendments like fertilizer. Yemane plantations grown in tropical regions are influenced more by the nutrient cycling rate than by the amounts of nutrients available in the soil. Sites with good productivity had more rapid nutrient circulation than those on sites with moderate productivity. Nutrient input through litter fall on the good site was approximately 50–100% greater than that of the moderate site. Nutrients released through decomposition of leaf litter were 30–80% greater on the good versus moderate productivity sites, annual N-mineralization in topsoil (0–10 cm depth) was 60% greater, nutrient loss through total-tree harvesting were 30–50% greater, and the uptake on the good site was 50–70% greater than on the moderate site. We suggest that microorganisms play a key role in nutrient cycling in tropical forests. The rapid nutrient cycles and high microbial activity might be driven by high rainfall, moisture and temperature throughout the year in tropical regions. More information is necessary to clarify the role of microorganisms in nutrient cycles and site productivity. Coppice management for second-rotation yemane has been examined as a regeneration system on a research level in East Kalimantan. The growth of secondrotation yemane, as coppice, is rapid for the first 2 years, but growth stagnates by the third year. The rapid initial growth of coppice during the first 2 years might be the result of established root systems of the original tree stump. It is estimated that the mean growth of yemane in the second rotation using the coppice system will be lower than that in the first rotation. The inefficiency and dieback of old roots and nutrient loss by harvest removal will affect the growth of the next short rotation. A second rotation of yemane can be established by the coppicing method on sites with good productivity, and by artificial regeneration of yemane seedlings on sites of moderate productivity. Other more suitable species should be planted on poor sites. It should be noted that continued coppicing in the third generation is known to lead to decreased productivity because of the dieback of old root systems (Soerianegara and Lemmens 1993). Use of better genetic planting stock should be considered over rotations in combination with the development of well-adapted clones. Legumes could provide good soil amelioration in short-rotation plantations in tropical regions (Agus et al. 2003). The total biomass of the observed LCChad nutrient amounts similar to the 15–25% of nutrient losses caused by total tree harvesting in a short-rotation plantation of yemane (6 years old). Total biomass in the legumes assessed varied from 4 to 14 Mg ha1. The amount of nitrogen in the biomass of LCC was 140–463 kg ha1. The contribution of aboveground biomass to the total biomass in legumes was approximately 80%. The biomass of root nodules varied from 80 to 235 kg ha1 among the four legumes examined. Annual fixation of N2 from the atmosphere ranged from 10 to 60 kg N ha1 yr1. Legumes planted on a better site class in tropical forestland seemed to have lower N2-fixation rates compared to the poor-class sites, but had a greater biomass. The rate of fixed-N to N amounts in the legume biomass was 5–20%. Legumes could promote sustainable site productivity of short-rotation plantations in tropical forests by supplying N to the soil through N2-fixation and organic matter. Investigations into the possibility of
284 mixed planting methods of legumes with short-rotation plantation of yemane on soils with poor nutrient status are necessary. Conclusions Land use change from NF to plantations was linked to a decrease in EC, CEC, T-C, C=N ratio and exchangeable Ca. The difference in stand average height between the poor and good site classes at 6 years of age was 3 m, which represents a difference in stand volume of approximately 45 m3 ha1. Annual increments of stand volume reached a maximum at approximately 6 years in the good site and 8 years in the moderate and poor sites, therefore the optimum age for clear cutting should be prolonged from 6 to 8 years of age in the moderate site. There was a high allometric relationship between D2H (DBH2 cm height m) and components of aboveground or belowground biomass. The good yemane site had greater amounts of T-P, T-Ca, T-Mg, available P, exchangeable Ca and Mg in the soil than that on the moderate and poor sites. Nevertheless, there were no significant differences in nutrient amounts in soil among stand ages (4, 6 and 8 years old). The effect of site class on the properties of the topsoil was greater than that of land use change and stand age. Yemane plantation forests in tropical regions are influenced more by nutrient cycling rate than by amounts of nutrient availability in soils. Nitrogen and P are the limiting nutrients for yemane growth and regeneration in East Kalimantan. Legumes can promote site productivity in the short-rotation plantations in tropical forests by supplying N to soil through N2-fixation and organic matter. Mineral fertilizer applications also have to be considered. It is necessary to investigate the role of soil microorganisms on site productivity. The benefits of mixed planting of yemane with legumes need more study. References Agus C. 1995. Study on biogeochemical cycles of evergreen broad-leaved forest in northern limit region. M.Sc. Thesis, Tokyo University of Agriculture and Technology, Tokyo, 266 p. Agus C. 2003. Nutrient dynamics in short-rotation Gmelina arborea plantations in East Kalimantan, Indonesia. Ph.D. Thesis, Tokyo University of Agriculture and Technology, Tokyo, 141 p. Agus C., Karyanto O., Hardiwinoto S., Kita S., Haibara K. and Toda H. 2003. Legume cover crop as soil amelioration at a short-rotation plantation in a tropical region. Jpn. J. Forest Environ. 45 (1): 13–19. Baplan. 2000. Indonesian forest statistics. Ministry of Forest and Estate Crop, Republic of Indonesian, 233 p. Jordan C.F. 1985. Nutrient Cycling In Tropical Ecosystems. John Wiley and Sons, Chichester, 190 p. Jug A., Hofman-Schielle C., Makeschin F. and Rehfuess K.E. 1999. Short-rotation plantations of balsam poplars, aspen and willow on former arable land in the federal republic of Germany. II. Nutritional status and bioelement export by harvested shoot axes. Forest. Ecol. Manage. 121: 67–83. Lee D.K. and Park Y.K. 2001. Degradation issues in Southeast and Northeast Asia. Proceedings of 10th International workshop of BIO-REFOR. The University of Tokyo, Tokyo, pp. 3–24. Page A.L., Miller R.H. and Keeney R. 1982. Methods of Soil Analysis. Part 2– Chemical and Microbiological Properties. American Society of Agriculture, Inc. and Soil Science Society of America, Inc. Publishers. Madison, Wisconsin, USA, 1159 p.
285 Reddy M.V. 2002. Introduction. In: Reddy M.V. (ed) Management of Tropical Plantation-Forests and their Soil Litter System. Litter, Biota and Soil-Nutrient Dynamics. Science Publisher Inc, USA, pp. 1–40. Soerianegara S.S. and Lemmens R.H.M.J. 1993. Plant resources of Southeast Asia No 5(1). Timber trees: Major commercial timbers. Prosea, Bogor, 620 p. Tanaka N., Aksa D., Effendi S. and Ohta S. 2000. Vertical transportation of chemical elements through water movement in different vegetation. In: Guhardja E., Fatawi M., Sutisna M., Mori T., Ohta S. (eds) Ecological Studies, Vol. 140. Rainforest Ecosystems of East Kalimantan. El Nin˜ o, Drought, Fire and Human Impacts. Springer, Tokyo, pp. 59–67.
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