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Soil Organic Matter (SOM) in agroecosystems and intact cloud forest in The Monteverde area, Costa Rica J. T. Metten Department of Natural Resource s, Colorado State University ABSTRACT Properly managed agroecosystems have great potential for sequestering carbon as Soil Organic Matter (SOM) (Brown et al. 2002; Lal 2005). I measured % SOM, Bulk Density, Total SOM, and Root Biomass in two agroecosystems, forest fragment, and intact cloud forest in Caitas and Monteverde, Costa Rica. These data were analyzed to see if agroecosystems and forests differ in carbon sequestering abilit y. I found significant differences in % SOM and Bulk Densities between agroecosystems but when Total SOM was calculated, results were not significant. Analysis on Total SOM alone suggests that agroecosystems and forest in Monteverde ha ve an equal ability to sequester SOM. However, root biomass may have an important role. When significant data from Average Root Biomass was added to Total SOM to cal culate an estimate of belowground carbon data became significant. Intact forest was si gnificantly higher in combined Root Biomass and Total SOM than the agroecosystems and forest fragment. Though the data suggests that agroecosystems in Monteverde are capab le of sequestering considerable amounts of Total SOM, including Root Biomass illustrates the importance of conserving intact forest to maximize carbon sequestration. Resumen Los agroecosistemas apropiadamente manejados tienen gran potencial para el embargar del carbn como Materia Orgnica de Tierra (MOT) (Brown et al. 2002; Lal 2005). Med % MOT, la Densidad del Bulto, SOM Tota l, y la Biomasa de Races en dos agroecosistemas: el fragmento del bosque, y el bosque nuboso intacto en Caitas y Monteverde, Costa Rica. Estos datos fueron anal izados para averigar si agroecosistemas y bosques difieren en la habilidad de el embargar el carbn. Encontr las diferencias significativas en % MOT y las Densidades del Bulto entre agroecosistemas pero cuando MOT Total fue calculado, los resultados no fueron significativos. El anlisis de solamente MOT Total sugiere que estos agro ecosistemas y el bosque en Monteverde tienen habilidades iguales para embargar MOT. Sin embargo, la biomasa de races puede tener un papel importante. Cundo datos signif icativos del Promedio de la Biomasa de Races fueron agregados al MOT Total para calcular una estimacin de carbn bajo la tierra los datos llegaron a ser significativos. El bosque inta cto tuvo apreciablemente ms Biomasa Combinada de Races y MOT Total que los agroecosistemas y el bosque fragmentado. Aunque los datos sugieren que los agroecosistemas en Monteverde son capaces del embargar unas cantidades consid erables de SOM Total, incluyendo la Biomasa de Races ilustra la importancia de conservar el bosque inta cto para llevar al mximo el secuestro del carbn. 1
INTRODUCTION The impact of human activities on climate change is clear; since CO2 emissions first spiked at the beginning of the industrial ag e, atmospheric carbon has increased by 30% (Vitousek et al. 1997). Warming has led to a 10% decrease in snow cover and ice extent since the 1960s and th is trend is likely to contin ue. The recently released Stern Review on the economics of climate change identified many more negative impacts of global climate change such as increased flood risk from glacial melti ng, lowered crop yields, and widespread increases in disease out breaks (Stern 2006). From an ecological standpoint climate change has been implicat ed in global species declines, including the loss of 67% of Atelopus spp. (Pounds et al. 2006). While the largest producer of greenhouse gasses, the United States, still remains unwilling to ratify the Kyoto Protocol, numerous methods have been identified to either reduce emissions or sequester carbon on a globa l scale. By extrapolating the amount of land needed to sequester sufficient atmos pheric carbon Wright and colleagues (2001) identified forests as the only realistic method. However, poverty and high demand for land makes implementation unlikely. A plausibl e alternative with great potential is the use of various agroecosystems including second ary forest agroforestry, plantations, and improved pastures to increase the Soil Organic Matter (SOM) pool (Lal 2005). Under proper management, the top 48 tropical and subtropical developing countries could sequester 2.3 billion tones of carbon in the ne xt 10 years alone, and for a profit of 16.8 billion dollars a ccording to one estimate (Nile s et al. 2002). Recovering secondary forest on abandoned land has been found to recapture nearly all soil carbon lost from historical forest within 50 years (Brown and Lugo 1990). Effective shade coffee plantations can sequester 46.7-236.7 t ons C/HA (Dejong et al 1995). Pasture, while lacking in above ground biomass, has th e capacity for great (SOM) sequestration, comparable or even greater than surroundi ng native forest (Lugo 1986). Other studies have further identified the effectiveness of pasture for restoring so il carbon to degraded ecosystems (Neill et al. 1997; R hoades 2000; Trumbore et al. 1995). The significance for SOM in carbon seque stration, productivity, and sustainable use is great, both globally and in the tropics espe cially. Seventy-five percent of terrestrial carbon is found in soils and of that 14% (216 Pg) is found in the tropics (Houghtan et al. 1985; Lal 2005). Higher temperatures can increase the rate of carbon decomposition in the tropics to four times that of temperate areas, but greater biomass accumulation in the tropics makes content equal (Jenkinson a nd Ayanaba 1977; Sanchez 1982). This has implications for effective management to maximize carbon sequestration, as biomass accumulation needs to be maximized and decomposition minimized. For instance, Nestel (1995) found that increased sun exposure in sun coffee monocultures leads to increases in soil temperatures, decreased water, which can cause soil degradation. Root biomass has been shown to directly increase C in pastur e through depth and prolif eration (Chon et al. 1991). Though this is just a portion of total organic deposition contributing to SOM, root biomass can further influence SOM by stabiliz ing erosion, soil moisture, and temperature (Lal 2005). Under the current Kyoto protocol only one of the three agroecosystems discussed, agroforestry, is marketable for ecosystem service payments (UNFCCC 2002). Brown and colleagues argue that this is a mistak e and that there are numerous opportunities 2
through sustainable agriculture to sequester car bon (Brown, S. et al. 2002). The objective of this study is to address this issue by identifying if agroecosystems and forests differ in carbon sequestering ability. Furthermore, this study provides a first look on SOM sequestration in agroecosystems of Monteverde Costa Rica, and will thus provide a basis for further study. Based on past research illustrating high SOM sequestration in agroecosystems, I predict there will be no si gnificant differences between pasture, coffee, forest fragment, and intact forest. Methods Study Site Four sample sites were used in the M onteverde area, one at the Monteverde Biological Station (intact forest ) and the other three (coffee, pasture, and forest fragment) at the farm of Don Victor Torres, in nearby Caitas. The farm was chosen for access to agroforestry (secondary forest fragment), co ffee plantation, and past ure. It is assumed that these agroecosystems are at equilibriu m and are effectively sequestering carbon due to proper management. Bulk Density (BD) Bulk density measurement was adapted from Field and Laboratory Investigations in Agroecology (Gliessman 2000). Five composite samples to 15 cm were taken at each site using a 2 cm diameter soil core. The five composite samples were taken at 10 m, 30 m, 50 m, 70 m, and 90 m and consisted of th ree sub samples at each location. A drying oven was not available so samples were dried in the attic of the biological station for three days with an average temperature of 26.87 C. Once dried, samples were weighed and density was calculated. % SOM & Total SOM At each site, eight composite SOM samples were taken along a 100 m transect. Each sample was composed of 5 sub samples taken every 2.5 meters, from 0-10 m, 12.522.5 m, 25-35 m, 37.5-47.5 m, 50-60 m, 62.5-72.5 m, 75-85 m, and 87.5-97.5 m. At each sub sample, aboveground vegetation was removed and soil was excavated to 15 cm using a hand trowel. Soil was then mixed and put through a 2 mm sieve to remove rocks and roots. Samples were then sent to The Minist ry of Agriculture Soil Laboratory in San Jose for analysis. Total SOM (g/m3) was the percentage of Bulk density comprised of SOM and was calculated by multiplying % SOM with Bulk Density. Root Biomass (RB) A total of 40 samples were collected, 10 fr om each site, at 5 m, 15 m, 25 m, 35 m, 45 m, 55 m, 65 m, 75 m, 85 m, and 95 m. At each distance a total of 10 sub samples were collected from 0-10 m perpendicular to th e transect using a 2 cm diameter soil core at a depth of 15 cm. Samples were then wash ed using an adaptation of the Central Plains Experimental Range Root Washing Protocol, drie d in the attic of the biological station for 3 days, and weighed (Milchunas). Analysis All data were averaged and standard error calculated. Significant differences between data sets were identified using a Kruskal-Wallis test. Results 3
Root biomass was significant, and was highest in intact forest and lowest in coffee (Kruskal-Wallis: X2 = 29.44 DF = 3.00 p = 0.00). Coffee was significantly lower than the next lowest sites, pasture and intact forest which were statistically equal (Figure 1a). BD was also significant but followed opposite trends, highest in pasture and lowest in intact fore st (Kruskal-Wallis: X2 = 16.62 DF = 3.00 p = 0.00) (Figure 1b). Similar to RB, intact forest had the highest % SOM, but pasture was lowest instead of coffee (Kruskal-Wallis: X2 = 20.68 DF = 3.00 p = 0.00). Forest fragment % SOM was also significantly less than intact forest (Figure 2a). When Total SOM calculated, results were not significant and averages were statistically equal (KruskalWallis: X2 = 4.15 DF = 3.00 p = 0.25) (Figure 2b). Adding RB to Total SOM provided significant results with intact forest having the highest value (Kruskal(B)0.00 50.00 100.00 150.00 200.00 250.00 300.00 COFFEE PASTURE FOREST FRAGMENT FOREST INTACTB.D. (g/m^3) (A)0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 COFFEE PASTUREFOREST FRAGMENTFOREST INTACTRoot Biomass (g/m^3 ) (A)0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00COFFEE PASTURE FOREST FRAGMENT FOREST INTACT% SOM (B)0.00 10.00 20.00 30.00 40.00 50.00 60.00 COFFEE PASTURE FOREST FRAGMENT FOREST INTACTTotal SOM (g/m^3 ) Figure 2: Average % SOM (A ) and Average Total SOM (g/m3) with standard error bars at the Torres Farm in Caitas and the Biological Station in Montever de. While Avearage % SOM was significant, Average Total SOM (g/m3) was not. was 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 COFFEEPASTUREFOREST FRAGMENT FOREST INTACTTOTAL SOM (g/m^3) + RB (g/m^3 ) Figure 3: Average Co mbined Total SOM (g/m3) and Root Biomass (g/m3) with standard error bars at the Torres Farm in Caitas and the Biological Station in Monteverde. Data was significant, suggesting belowground carbon sequestration was greatest in intact forest. Figure 1: Average Root Biomass (g/m3) (A) and Average Bulk Density (g/m3) with standard error bars at the Torres Farm in Caitas and the Biological Station in Monteverde. Root Biomass and Bulk Density showed an inverse relationship. 4
Wallis: X2 = 9.32 DF = 3.00 p = 0.03) (Figure 3). Forest Fragment was significantly less than Intact Forest (Figure 3). Discussion The significant results from BD and RB show an invers e relationship between the two across all sites. Low BD in intact fore st is likely due to high litter fall and as a consequence has made root proliferation eas ier, which explains high RB occurring there (Figure 1a,b). BD was high in pasture and coffee which is explained by human and livestock compaction occurring at those sites (Figure 1b). Interes tingly, RB in pasture was much greater than coffee despite its BD. High BD in pasture did restrict roots to being very fibrous which explains why RB is so much less than it is in intact forest. Coffee RB may have been further reduced due to weed trimming and monoculture. While RB for forest fragment was statistically equal to pasture, it was significantly lower than intact forest. Much less understory wa s observed during sampling of forest fragment than intact forest, which may have contributed to this finding. Similar to RB, % SOM also showed an inve rse relationship to BD (2a,b). As soil is compacted, its composition of SOM decreases while inorganic matter increases. These data may also be supported by comparing RB to % SOM. Greater RB in intact forest suggests that there is also a greater amount of decomposing and already decomposed roots which would directly add to % SOM. Furthermore, indirect properties of roots, such as erosion, temperature, and moisture control could be further influencing % SOM. The inverse relationship between BD a nd % SOM equalized values for Total SOM, making differences between sites not significant. These data suggest that pasture, coffee, and forest fragment at the study site can sequester equal amounts of Total SOM (Figure 2b). Past research in pasture, secondary forest, and coffee all support these findings (Rhoades 2000; Lugo and Brown 1992; Dejong, et al. 1995). However, Total SOM is not a complete picture of belo wground carbon. Adding RB to Total SOM made data significant which show s the importance of RB in belowground carbon sequestration. Intact forest was significantly higher than the other three sites due to the direct and indirect contribution of RB (Figure 3). The results of this study have numerous implications and questions for further understanding of belowground carbon sequestra tion in the Monteverde area. Though intact forest is significantly different and greater in seque stration ability, the agroecosystems studied appear to be seque stering high amounts of SOM. Further research is needed to determine if this is a trend across Monteverde, if SOM is stable, and what management techniques are most effective at increasing SOM within agroecosystems. Additionally, unintended cons equences of management decisions which lead to the release of other greenhouse gases such as N2O or cause other environmental problems must be identified. The most im portant implication of this study is the importance of intact forest for carbon seque stration. Results sugge st that belowground carbon storage is greatest in forest; this st udy did not even discuss the great amounts of above ground biomass which exists in both understory and canopy of the Monteverde cloud forest. Furthermore, the value of intact forest for its ecosystem services such as watershed protection, biodiversity, air qualit y, and even tourism must be recognized. Diversity of forest vegetation may even be a contributing factor to increased SOM in intact forest. 5
Acknowledgements I would first like to thank mi familia Tica for an incredible experience on their farm in Caitas. Nery, you are an awesome cook, sorry I was late to meals so much! Thanks to Mauricio for taking me out harves ting coffee and all of th e kids for giving me a workout from so much playing. And many thanks to Don Victor for the use of his beautiful farm in my study. Thanks to Karen Masters for dealing with all my last minute questions and making this study possible. Ca m and Tom are the best TAs ever, props for not freaking out from so many ridicul ous questions from me and the other 29 students. Thanks to Aidee, Grant an d Katie L. for all the excellent help. Literature Cited Brown, S., and A.E. Lugo. 1990. Effects of forest clearing and succession on the carbon and nitrogen content of soils in Puerto Rico and US Virgin Islands. Plant and Soil 124: 53-64 Brown, S., I.R. Swingland, R. Hanbury-Tenison, G. T. Prance, N. Myers. 2002 Changes in the use and management of forests for abating carbon emissions: issues and challenges under the Kyoto Protocol. In: Philosophical Transactions: Mathematical, Physical and Engineering Sciences, 360:1797 19531605 Chon, T., F. Andreux, J. C. Correa, B. Volkoff, and C. C. Cerri. 1991. Changes in organic matter in an oxisol from the central Amazonian forest during eight years as pasture, determined by 13C composition. Pages 307-405 in J. Berthelin, editor. Diversity of environmental biogeochemistry Elsevier, New York, New York, USA. Dejong, B., G. Monoyagomez, K. Nelson, and L. Soto-Pinto. 1995. Community forest management and carbon sequestration-a feasibility study from Chiapas, Mexico. Interciencia 20:6. Gliessman, S.R. 2000. Field and Laboratory Investigations in Agroecology E. W. Engles, ed. Lewis Publishers, London. pp. 57-59 Griffith, K., D.C. Peck, J. Stuckey. 2000. Agriculture in Monteverde. In: Monteverde: Ecology and Conservation of a Tropical Cloud Forest Nadkarni, N.M. and N.T. Wheelwright, eds. Oxford University Press, Oxford. pp. 389-417 Houghton, R.A., R.D. Boone, J.M. Melillo, C.A. Palm, G.M. Woodwell, N. Myers, B. Moore, and D.L. Skole 1985. Net flux of carbon dioxide from terrestrial tropical forests in 1980. Nature 316:17-620 Jenkinson, D.S. and A. Ayanaba. 1977. Dcomposition of carbon-14 labeled plant material under tropical conditions. Soil Science Society of America Journal 41: 912-915 Jenkinson, D.S. and A. Ayanaba. 1977. Dcomposition of carbon-14 labeled plant material under tropical conditions. Soil Science Society of America Journal 41: 912-915 Lal, R. 2005. Soil Carbon Sequestration in Na tural and Managed Tropical Forest Ecosystems. Journal of Sustainable Forestry 21: 1-30. Lugo, A.E., M.J. Sanchez. 1986. Land use and organic carbon content of some subtropical soils. Plant and Soil. 96: 185-196 Milchunas, D. Monthly Root Harvest Washing Protocol. Accessed from : M. D. Lindquist. email@example.com Accessed: 11/20/06 6
7Neill, C., J.M. Melillo, P.A. Steudler, C.C. Cerri, J.F. L. de Morales, M.C. Piccolo, M. Brito. 1997. Soil carbon and nitrogen stocks following forest clearing for pasture in the southwestern Brazilian Amazon. Ecological Applications 7: 1216-1225. Nestel, D. 1995. Coffee in Me xico: International market, agricultural landscape and ecology. Ecological Economics 15: 165-178 Niles, J.O., S. Brown, J. Pretty, A.S. Ball, J. Fay. 2002 Pote ntial Carbon Mitigation and Income in Developing Countries from Changes in Use and Management of Agricultural and Forest Lands. In: Philosophical Transactions: Mathematical, Physical and Engineering Sciences, 360:1797 1621-1639 Pounds, J.A, M.R. Bustamante, L.A. Coloma, J.A. Cons uegra, M.P.L. Fogden, P.N. Foster, E. La Marca, K.L. Masters, A. Merino-Viteri, R. Puschendorf, S.R. Ron, G.A. Snc hez-Azofeifa, C.J. Still, and B.E. Young. 2006. Widespread amphibian extinctions from epidemic disease driven by global warming. Nature. 439: 161-167. Rhoades, C.C. 2000. Soil Carbon Differences among Forest, Agriculture, and Secondary Vegetation in Lower Montane Ecuador. Ecological Applications. 10:2 497-505 Sanchez, P.A., M.P. Gichuru and L.B. Katz. 1982. Organic matter in major soils of the tropical and temperate regions. Translated 12th International Congress. Soil Science 1 (New Delhi). Sanchez, P.A., M.P. Gichuru and L.B. Katz. 1982. Organic matter in major soils of the tropical and temperate regions. Translated 12th International Congress. Soil Science 1 (New Delhi). Stern. 2006. Stern Review on th e economics of climate change. http://www.hmtreasury.gov.uk/independent_reviews/stern_review_ec onomics_climate_change/s tern_review_report.cf m Accessed. 11/20/06 Trumbore, S.E., E.A. Davidson, P.B. de Camargo, D.C. Nepstad and L.A. Martin elli. 1995. Below ground cycling of C in forests and pastures of eastern Amazonia. Global Biogeochemical Cycles. 9: 512-528 UNFCCC 2001 United Nations Framework Convention on Climate Change agenda items 4 and 7. In Proc. Conference of the Parties, 6th Session, Part 2, Bonn, 16-27 July 2001. (Available from http://www.climnet.org/cop7/FCCCCP2002L.7.pdf .) Vitousek, P.M., H.A. Mooney, J. Lubchenco, J.M. Melillo. 1997. Human Domination of Earths Ecosystems. Science 277: 494-499 Wright, D.G., R.W. Mullen, W.E. Thomason, W. R. Raun. 2001. Estimated land area increase of agricultural ecosystems to sequester excess atmospheric carbon dioxide. Commun. Soil Sci. Plant Anal. 32: 1803-1812.
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Metten, J. T.
Materia Orgnica del Suelo (SOM) en el agro ecosistema y el bosque nuboso intacto en el rea de Monteverde, Costa Rica
Soil Organic Matter (SOM) in agroecosystems and intact cloud forest in the Monteverde area, Costa Rica
Properly managed agroecosystems have great potential for sequestering carbon as Soil Organic Matter (SOM) (Brown et al. 2002; Lal 2005). I measured % SOM, Bulk Density, Total SOM, and Root Biomass in two agroecosystems, forest fragment, and intact cloud forest in Caitas and Monteverde, Costa Rica. These data were analyzed to see if agroecosystems and forests differ in carbon sequestering ability. I found significant differences in % SOM and Bulk Densities between agroecosystems but when Total SOM was calculated, results were not significant. Analysis on Total SOM alone suggests that agroecosystems and forest in Monteverde have an equal ability to sequester SOM. However, root biomass may have an important role. When significant data from Average Root Biomass was added to Total SOM to calculate an estimate of belowground carbon data became significant. Intact forest was significantly higher in combined Root Biomass and Total SOM than the agroecosystems and forest fragment. Though the data suggests that agroecosystems in Monteverde are capable of sequestering considerable amounts of Total SOM, including Root Biomass illustrates the importance of conserving intact forest to maximize carbon sequestration.
Los agro ecosistemas apropiadamente manejados tienen un gran potencial para retener el carbono en materia orgnica del suelo (SOM) (Brown et al. 2002; Lal 2005). Med el % MOT, la densidad del bulto, el total SOM, y la biomasa de las races en dos agro ecosistemas: el fragmento del bosque, y el bosque nuboso intacto en Caitas y Monteverde, Costa Rica. Estos datos fueron analizados para averiguar si los agro ecosistemas y los bosques difieren en la habilidad para retener el carbn.
Text in English.
Soils composition--Costa Rica--Puntarenas--Monteverde Zone
Cloud forest ecology--Costa Rica
Composicin del suelo
Suelos--Contenido de carbono
Ecologa del bosque nuboso--Costa Rica
Tropical Ecology 2006
Soil Organic Matter
Ecologa Tropical 2006
Materia orgnica del suelo
t Monteverde Institute : Tropical Ecology