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Suelos altitudinales continuos de los andisuelos, en la vertiente atlntica de la Cordillera de Tilarn
Altitudinal soil continuums of andisols on the Atlantic slope of the Tilaran Mountain Range (Costa Rica)
Presently, little is known about soils along an altitudinal gradient on the Atlantic Slope of the Tilarn Mountain Range in Costa Rica, so soil samples were taken and horizons were measured, on altitudinal transects from 1700m to 1300m in elevation. Precipitation patterns, decomposition rates, litterfall rates, temperature, and soil parent material depth, are recognized as playing important roles in the % soil root mass and nutrient cycles of tropical
mountain soils. This study looks to find trends between these soil formation and maintenance factors, and altitude. These data present significant positive correlations of soil Nitrate-N and Phosphorus concentrations with elevation,
and significant negative correlation of Potassium concentrations and pH with elevation. No significant correlation
was found between % root mass and elevation due to high local and regional ecosystem heterogeneity. These discoveries lay the ground work for future comparative studies that will likely show the effects of climate change and land alteration practices on mountain rainforest soils.
En la actualidad, poco se sabe acerca de los suelos a lo largo de un gradiente altitudinal en la Vertiente Atlntica de la Cordillera de Tilarn en Costa Rica, por lo que se tomaron muestras de suelo y se midieron los horizontes, en trayectos altitudinales de 1700 a 1300m de altitud. Los patrones de precipitacin, las tasas de descomposicin, la temperatura y el material parental del suelo, son reconocidos en jugar un papel importante en el porcentaje de masa de races y los ciclos de nutrientes en los suelos montaosos tropicales. Este estudio busca encontrar tendencias entre esta formacin de suelos y el mantenimiento de los factores, y la altitud. Estos datos sugieren una correlacin positiva en las concentraciones de Nitrato-N y fosforo con la elevacin y una correlacin negativa en la concentracin de Potasio y el pH con la elevacin. No se encontraron correlaciones significativas entre el porcentaje de masa de races y la elevacin debido a la gran heterogeneidad local y regional. Estos descubrimientos abren una puerta para futuros estudios comparativos que muestren el efecto del cambio climtico y la alteracin de la tierra en suelos del bosque tropical.
Text in English.
Costa Rica--Puntarenas--Monteverde Zone
Composicin del suelo
Costa Rica--Puntarenas--Zona de Monteverde
Tropical Ecology Fall 2009
Ecologa Tropical Otoo 2009
t Monteverde Institute : Tropical Ecology
Altitudinal Soil Continuums of Andisols on the Atlantic slope of the TilarÃ¡n Mountain Range (Costa Rica) Tyler Reynolds Natural Resources and Environmental Science Program, Purdue University ABSTRACT Presently, little is known about soils along an al titudinal gradient on the Atlantic Slope of the TilarÃ¡n Mountain Range in Costa Rica, so soil samples were taken and horizons were measured, on altitudinal transects from 1700m to 1300m in elevation. Precipitation patterns, decomposition rates, litterfall rates, temperature, and soil parent material depth, are recognized as playing important roles in the % soil root mass and nutrient cycles of tropical mountain soils. This study looks to find trends between these soil formation and maintenance factors, and altitude. These data present significant positive correlations of soil Nitrate N and Phosphorus concentrations with elevation, and significant negative correlation of Potassium concentrations and pH with elevation. No significant correlation was found betw een % root mass and elevation due to high local and regional ecosystem heterogeneity. These discoveries lay the ground work for future comparative studies that will likely show the effects of climate change and land alteration practices on mountain rainfor est soils. RESUMEN Actualmente, poco es conocido sobre suelos a lo largo de un gradiente altitudinal a lo largo de la costa AtlÃ¡ntica en la Cordillera de TilarÃ¡n en Costa Rica, asÃ que se tomaron muestras de suelo y se midieron los horizontes, en un tr ansecto altitudinal desde los 1700 m hasta los 1300m de altura. Patrones de precipitaciÃ³n, tasas de descomposiciÃ³n, temperatura y el material parental del suelo, son reconocidos en jugar un papel importante en el porcentaje de masa de raÃces y los ciclos de nutrientes en suelos montaÃ±osos tropicales. Este estudio busca encontrar tendencias entre esta formaciÃ³n de suelos y el mantenimiento de factores, and altitud. Estos datos sugieren una correlaciÃ³n positiva en las concentraciones de Nitrato N y fosfor o con la elevaciÃ³n y una correlaciÃ³n negativa en la concentraciÃ³n de Potasio y el pH con elevaciÃ³n. No se encontraron correlaciones significativas entre el porcentaje de masa de raÃces y la elevaciÃ³n debido a la gran heterogeneidad local y regional. Esto s descubrimientos abren una puerta para futuros estudios comparativos que muestren el efecto del cambio climÃ¡tico y la alteraciÃ³n de la tierra en suelos del bosque tropical. INTRODUCTION From the top of a mountain to the base of its foothills, a change i n physical variables, on a landscape level, takes place on a continuous gradient that elicits different abiotic and biotic responses (Vannote 1980). Soils, and soil forming factors, are also subject of change on a continuous gradient. This means that the c ombinations of all the relationships between soil forming factors and soil characteristics can be used to predict the way soils attributes will change as physical variations that are associated with elevation, change. This concept is defined as the soil al titudinal continuum theory. This paper seeks to form the baseline understanding of several relationships between soil forming factors and soil compositions that will provide a better model for the way soils change as altitude changes.
An important aspec t of neotropical ecology, processes associated with soils affect, to a degree, flora and fauna on a landscape scale. Presently, few studies have been conducted on tropical soils, and of the publications that exist, almost none address the effects of elevat ion on % root mass, soil nutrient content, and horizon development. While many altitudinal continuum surveys have been completed for floral diversity, no such investigation has been undertaken to create a baseline description of tropical montane soils and their possible effects on forest structure, species diversity and distribution. An understanding of the interaction between climate, soils and biota along incremental elevation gradients is important for providing insights into the sensitivity of many eco logical processes to the changing climate (Silver 2000). The geology of the TilarÃ¡n mountain range in Costa Rica is described as being made up primarily of andesitic and basaltic tertiary volcanic rocks from lava flows, agglomerates, and breccias resultin g from the Aquacate and Monteverde Formation, which provides the parent material for the soils of the area (Janzen 1983; Clark 2000). Under the USDA soil classification system, the majority of these soils are defined as Andisols, and more specifically clas sified as Udands, which are formed under udic, or wet, moisture regimes (Clark 2000). Monteverde andisols, are typically made up the easily identifiable soil horizons: O, decomposing organic material accumulations; A, the darker upper soil profile layer wi th organic matter accumulations; B, the middle subsoil layer; E, the nutrient leached layer; and C, the lower part of the soil profile that extends to the parent material (Clark 2000). Area soils are described as having low to moderate, varying clay conten ts creating textures that are typically silt to sandy loams in the A horizon (Clark 2000). Additionally, increases in altitude, leading to a decrease in plant productivity and litterfall, coupled with decreasing rates of litter decomposition, have resulted in larger accumulations of organic matter in the A and B horizons as well as an increase in root masses and nutrient concentrations (Grubb 1977; Vitouseck and Sanford 1986; Marrs et al. 1988). This paper looks at the relationship between altitude and sev eral measureable soil properties. My objectives were to: (1) understand how elevation is related to soil properties and (2) collect baseline information of soil properties in the Monteverde area for future research that could relate soil properties to ecol ogical processes. METHODS Study Site The study was carried out from November 3 21, 2009 on the Atlantic slope of the TilarÃ¡n mountain range in the Reserva Santa Elena, Monteverde, Puntarenas, Costa Rica. The forest of the area is classified as primary lower montane and premontane rain forests with a local summit of 1744 masl in altitude. Regional climate is comprised of between 8000mm and 4000mm of mean annual rainfall with a dry season of approximately three months, usually beginning in March or April, and with a mean annual temperature between 12 24 o C (Haber 2000). Above 1400masl, the forest canopy becomes increasingly broken with a minimum height between 15 20m depending on wind exposure and slope. Below this altitude, a more complete canopy exists wi th large buttressed trees possibly reaching maximum heights of 50m.
Five study sites were located on an altitudinal transect every 100m in elevation change from 1300 to 1700 masl. Based on the Holdridge life zone classification system, the study sites w ere located in the two life zones: Lower Montane wet forest (1550 1850masl) and Premontane rain forest (700 1400masl) (Holdridge 1966). At each site, eight locations were chosen for sampling[excluding the 1700m site with 6 locations], spaced between 10 and 20 meters apart. Sites were selected for similar slope and forest structure. Once an appropriate test location was determined, soil horizon thicknesses were made measureable by digging out a 60cm soil profile. A machete was used to precisely remove a samp le cross section of soil 1000cm 3 in volume from the surface layer of soil beneath the O1 horizon. In total, 38 samples were removed from the forest and transported to the lab where % root mass was determined for each sample by carefully dividing and weig hing the roots and soil. Nutrient composition analysis was conducted after combining and drying equal parts soil from samples, according to traditional soil sampling methods, at corresponding altitudinal test locations. Samples were then ground and nitrate N, Phosphorus, Potassium, and pH were determined using LaMotte soil testing kits. All soil analysis was carried out no more than 48 hours after soil had been removed from the test locations. Traditional soil nutrient testing techniques are such that indi vidual samples from each test location are not individually tested, but combined in equal parts and then tested only once to create a single average test result, for each nutrient variable at a single study site. This testing procedure makes standard devia tions impossible. One way ANOVAs were run to test for significant differences in % root mass, Nitrate N, Phosphorus, Potassium, and pH among the five elevations. Simple regressions were run for each study site to check for significant relationships betwee n altitude and soil nutrient contents. RESULTS Percent Root mass (%RM) found in the soil samples was not significantly different between altitudinal study sites (Fig 1., One way ANOVA, F 1,36 =0.018, p=0.89). An apparent trend of decreasing average %RM wi th increasing altitude exists, excluding the average %RM found at 1300m (5.63%) which showed a distict decrease from the %RM found at the adjacent 1400m site (9.88%). Standard deviations were large, sometimes greater than the means themselves and/or below 0. Average Nitrate N, Phosphorus, and Potassium concentrations (kg/h) were significantly different among the study sites at different elevations (Fig. 2, One way ANOVA, F 1,36 =106.62, p=<.0001; Fig. 3, One way ANOVA, F 1,36 =14.48, p=.0005; and Fig . 4,One way ANOVA, F 1,36 =5.57, p=.0238). Interestingly, simple regressions revealed significant, possitive relationships between average Nitrate N concentrations (kg/h) and increasing altitude, and average Phosporus concentrations (kg/h) and increasing alt itidue (Fig. 2, Simple Regression, R 2 =0.75, p=<.0001, n=38; and Fig. 3, Simple Regression, R 2 =0.29, p=.0005, n=38). This was different from the relationship between average Potassium concentrations (kg/h) and increasing altitude, which revealed a significa nt, negative relationship (Fig. 4, Simple Regression, R 2 =0.13, p=.0238, n=38). Average pH was significantly different among the study sites at different elevations (Fig. 5, One way ANOVA, F 1,36 =53.6842, p=<.0001) and a simple regression test s howed a
significant, negative relationship between average pH and increasing altitude (Fig. 5, Regression, R 2 =0.60, p=<.0001, n=38). Mean O, A, and E horizon thicknesses (cm) were not significantly different among the five study sites (Fig. 6, One way ANOVA, F 1,36 =1.36, p=.2686; Fig. 7, One way ANOVA, F 1,36 =1.78, p=.1571; and Fig. 8, One way ANOVA, F 1,36 =2.06, p=.1080). Predictably, average standard deviations of mean horizon thicknesses (cm) increased with depth (Fig. 6, mean SD=Â±1.34; Fig. 7, mean SD=Â±4.15; and Fig. 8, mean SD=Â±4.56). DISCUSSION The lack of significant differences in % root mass and the absence of any trends among study sites can be explained by the general heterogeneity of tropical forests, both above and below ground level , and limiting biotic and abiotic factors of the environment. High variation of %RM among test locations within each study site is likely the result of elevated floral distribution variability that occurs often in montane tropical forests (Ewel 1993; Tuomi sto 2003). The irregularity of floral species richness and abundance is not affected by soil nutrient cycling, but instead, is heavily influenced by rainfall patterns, (which are, strangely, are an effect of elevation) but more likely influenced by the deg ree of exposure, or direction, of slope faces and prominence of position among other adjacent slope faces (Tuomisto 2003). Local heterogeneity aside, a significant trend line cannot explain changes in %RM on an altitudinal gradient because the limitation o f the range of plant root stratagies by environmental filtering does not vary significantly as altitude changes, a fairly common occurrence on tropical montane landscape scales (Powers 2002). It is probable that the slope, precipitation patterns, substrate stability, and various other environmental characteristics select and limit the range of root mass strategies along the entire elevational gradient, preventing a trend of changing %RM values from forming. It is also possible that the lack of a relationshi p between altitude and %RM can be explained by the ratio of dead and live roots. Higher accumulations of dead root biomass prevail as elevation increases, indicating the possibility that a relationship may lie between live to dead root mass and altitude (H ertel 2003). In my study, Nitrate N concentrations increased as elevation increased. An increase in Nitrate N as elevation increases could be explained by the low rate of leaf little decomposition at high elevations, which results in an increase in organi c matter accumulation, a decrease in temperature, and a resulting decrease in microbial activity. (Silver 2000; Yavitt 1993). Increasing concentrations of average Nitrate N concentrations as altitude increases can also be the by product of the negative re lationship between soil age and decreasing nitrification rates (Hall 2004). An increase in Phosphorous as elevation increases could be due to heightened levels of precipitation, a relationship that can easily be acknowledged considering that precipitatio n rates and increasing elevation are positively correlated (Yavitt 1993). Additionally, the trend between increasing average Phosphorus concentrations and altitude, conceivably is the result of a relationship between the increasing proximity of soil parent material to the soil surface as altitude increases. This is imporant because Phosphorus is supplied to the soil surface from the soil parent material (Silver 2000). Potassium decreases as elevation increases. This trend could be explained by decreasing concentrations of wreathing micas which produce available potassium, and 2:1 clays which hold fixed K, both of which more commonly located at lower elevations (Brady 1996). Decreased
concentration levels of K at higher altitudes may also be the outcome of increased precipitation, and increased leaching, to which K is more susceptible to than other soil macronutrients (Brady 1996). The significant differences between average pH levels among study sites and the negative relationship between pH and increasing altitude is the result of increasing precipitation with increasing altitude (Yavitt 1993). The trend could also occur because as altitude increases, decomposition rates of rocks and minerals releasing base forming cations also decrease, creating more acid ic soils. (Brady 1996) Mean O, A, and E horizon thicknesses were not significantly different among the five study sites . Soil horizon creation factors are highly variable as a result of weathering due to slope face exposure, soil stability, and agents of horizon development (Silver 2000). Increases in standard deviation of soil horizons as depth increases is a result of increased soil age and level of subjection to extreme weather events that greatly alter biogeochemical processes for short periods of tim e moving and altering existing soil horizons as well as creating new ones (Silver 2000). Future studies, possibly comparatively testing the Pacific Slope of the TilarÃ¡n mountain range, and including plant surveys related to variation among soil samples c ollected along a single altitudinal transect could greatly advance the understanding of local variation of soil characteristics and their possible relationship with plant diversity. Also, studies conducted over longer periods of time, such as years, would undoubtedly show large changes in soil structure and nutrient cycling, at single locations, which could be used to create trends that could then be compared, as climate change and human induced land alteration affect biogeochemical and geologic soil proces ses and cycles. ACKNOWLEDGEMENTS Much deserved thanks goes to Anjali Kumar for helping me focus and develop a new idea, statistical analysis assistance, study site identification, and motivating concrete constructive criticism. Thanks also goes to Yime n Araya for help with statistical analysis. I would also like to thank the Reserva Santa Elena for use of their property and their lack of skepticism of a college kid rolling though forest wielding a machete and spade. Finally, thanks goes out to the rando m ticos that picked up a very tired and muddy researcher who had been walking for far too many hours with a pack full of soil samples. LITERATURE CITED BRADY, N. C., and WEIL, R. R. 1996. The Nature and Properties of Soils. Prentice Hall, New Jersey. C LARK K.L., LAWTON R. O., and BUTLER P. R., 2000. The Physical Environment. In: Monteverde Ecology and Conservation of Tropical Cloud Forest, Nadkarni, N. M., and Wheelwright, N. T. Oxford University Press, New York. pp. 27 29. EWEL, J. 1980. Tropical Suc cession: Manifold Routs to Maturity. Biotropica 12(2):2 7. GRUBB, P. J. 1977. Control of forest growth and distribution on wet tropical mountains: with special reference to mineral nutrition. Annual Review of Ecology and Systematics 8:83 107. HABER, W. A. 2000. Plants and Vegetation. In: Monteverde Ecology and Conservation of Tropical Cloud Forest, Nadkarni, N. M., and Wheelwright, N. T. Oxford University Press, New York. pp. 42. HALL, S.J., ASNER, G.P., KITAYAMA, K. 2004. Substrate, Climate, and Land Us e Controls over Soil N Dynamics and N Oxide Emissions in Borneo. Biogeochemistry 70(1):27 58.
HERTEL, D., LEUSCHNER, C., and HOLSCHER, D. 2003. Size and Structure of Fine Root Systems in Old Growth and Secondary Tropical Montane Forests (Costa Rica). Bio tropica 35(2):143 153. HOLDRIDGE , L . R . 1966. The life zone system. Adansonia 6: 199 203 . JANZEN, D.H. 1983. Costa Rican natural history. University of Chicago Press, Chicago. MARRS, R. H., PROCTOR, J., HEANEY, A., and MOUNTFORD, M.D. 1988. Changes i n soil nitrogen mineralization and nitrification along an altitudinal transect in tropical rainforest in Costa Rica. Journal of Ecology 76:466 482. POWERS, J. S., and SCHLESINGER, W. H. 2002. Geographic and vertical patterns of stable carbon isotopes in tropical rain forest soils of Costa Rica. Geoderma 109:141 160. SILVER, W. L. 1998. The potential effects of elevated and climate change on tropical forest soils and biogeochemical cycling. Climate Change 39: 337 361. SILVER, W. L., NEFF, J ., MCGRODDY, M., VELDKAMP, E., KELLER, M., and COSME, R. 2000. Effects of Soil Texture on Belowground Carbon and Nutrient Storage in Lowland Amazonian Forest Ecosystem. Ecosystems 3(2):193 209. TUOMISTO, H., DALBERG POULSEN, A., RUOKOLAINEN, K., MORAN, R .C., QUINTANA, C., CELI, J., and CAÃ‘AS, G. 2003. Linking floristic patterns with soil heterogeneity and satellite imagery in Ecuadorian Amazonia. Ecological Applications 13(2):352 371. VANNOTE, R. L., MINSHALL, G. W., CUMMINS, K. W., SEDELL, J. R., and CUSHING, C. E. 1980. The River Continuum Concept. Can. J. Fish. Aquat. Sci. 37:130 137. VITOUSEK, P.M., and R. L. SANFORD, Jr. 1986. Nutrient cycling in moist tropical forest. In: Monteverde Ecology and Conservation of Tropical Cloud Forest, Nadkarni, N . M., and Wheelwright, N. T. Oxford University Press, New York. pp. 27 29. YAVITT, J.B., WIEDER, R.K., and WRIGHT, S. J. 1993. Soil Nutrient Dynamics in Response to Irrigation of a Panamanian Tropical Moist Forest. Biogeochemistry 19(1):1 25. APPENDIX FIGURE 1. Mean % root mass found at altitudinal study sites. % root mass was not significantly different among each of the five study sites . Very high variation was found among samples which was likely the result of local ecosystem heterogeneity.
FIGURE 2. Average soil Nitrate N (kg/h) found at altitudinal study sites. A significant, possitive relationship was found to exist between the Average Soil Nitrate N concentration (kg/h) and increasing altitude . There appears to be a marked increase d in average Nitrate N concentrations above 1400masl, an altitude which also is marked by a transition from one Holdridge classified life zone (Premontane rain forest) to another (Lower montane rain forest). FIGURE 3. Average Phosphorus (kg/h) f ound at altitudinal study sites. A significant, possitive relationship was found to exist between the Average Phosphorus concentration (kg/h) and increasing altitude .
FIGURE 4. Average Potassium concentration (kg/h) found at altitudinal study sites. A significant, negative relationship was found to exist between the Average Potassium concentration (kg/h) and increasing altitude . Interestingly, maximum concentrations of all nutrient compositions were found at 1500masl in elevation. Potassium does not deviate from this trend. FIGURE 5. Average pH found at altitudinal study sites. A significant,negative relationship was found to exist between pH and increasing altitude .
FIGURE 6. Mean O Horizon Thickness (cm) found at altitudinal study sites. Mean O Horizon Thickness was not significantly different among the five study sites . The average standard deviation of O horizon thicknesses(cm) was determined to be 1.34. FIGURE 7. Mean A Horizo n Thickness (cm) found at altitudinal study sites. Mean A Horizon Thickness was not significantly different among the five study site . The average standard deviation of A horizon thicknesses(cm) was determined to be 4.15.
FIGURE 8. Mean E Horizon Thickness (cm) found at altitudinal study sites. Mean E Horizon Thickness (cm) was not significantly different among the five study sites . The average standard deviation of E horizon thicknesses(cm) was determined to be 4.56. FIGURE 9. Topographic Map showing altitudinal study sites, every 100m in altitude change and individual test sample locations, 8 at each study site excluding the transect at 1700m that only resulted in 6 test sample locations.
FIGURE 10 . Soil horizon distribution and thickness at each test location within each altitudinal study site.