Advantageous development of buttresses displayed in Quercus spp.

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Advantageous development of buttresses displayed in Quercus spp.

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Advantageous development of buttresses displayed in Quercus spp.
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Desarrollo ventajoso de gambas que se muestran en Quercus spp.
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Platt, Mariel
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Trees--Growth
Buttresses
Monteverde Biological Station (Costa Rica)
Costa Rica--Puntarenas--Monteverde Zone--Monteverde
Tropical Ecology Spring 2003

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Abstract:
The many hypotheses aimed at describing the physiological, morphological, environmental forces contributing to buttress development have not clearly shown definitive evidence regarding what selective forces are responsible for buttress formation. One hypothesis that has little documented research available is that the presence of buttresses allows for an increased abundance of organic matter and inhibits nutrient leaching from the soil, thus providing the tree with a greater quality soil for localized growth. Twenty-five different soil samples were collected and analyzed for potassium, nitrogen, phosphorus, and pH from both the base of buttressed Quercus spp. and a control site in the cloud forest of Monteverde, Costa Rica. No significant difference was found in the relationship between the presence of buttresses and an increased amount of N, P, K, or a more suitable pH. Results found may be due to nutrient use by the roots of buttressed trees or a slower rate of decomposition due to decreased temperatures in lower montane wet forests verses lowland tropical forests. ( ,,,,,, )
Abstract:
Hay muchas hipótesis que pretenden describir las fuerzas fisiológicas, morfológicas y ambientales que contribuyen al desarrollo de gambas, pero no se ha mostrado evidencia definitiva acerca de cuál fuerza selectiva es responsable de su formación. Una hipótesis poco investigada predice que con la presencia de gambas aumenta la abundancia de materia orgánica e inhibe la lixiviación de nutrientes de la tierra, y de ahí proporcionan al árbol con un suelo de mayor calidad para el crecimiento localizado. Se analizaron veinticinco muestras diferentes de suelos con pruebas del contenido de potasio, nitrógeno, fósforo, y pH, tomadas en el bosque nuboso de Monteverde, Costa Rica de la base de árboles del género Quercus con gambas y de un sitio control cercano. No se encontró ninguna diferencia significativa sobre la relación entre la presencia de gambas y algún aumento de N, P, K, o niveles de pH más adecuados. Los resultados encontrados se pueden deber al uso de nutrientes por los raíces de los árboles con gambas o a una tasa más lenta de descomposición debido a las temperaturas bajas en el bosque premontano húmedo, comparadas con las de los bosques de bajuras tropicales.
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Student affiliation - Department of Environmental Science, University of Oregon

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PAGE 1

Advantageous Development of Buttresses displayed in Quercus spp. Mariel Platt Department of Environmental Science, University of Oregon, Eugene, Oregon 97401, U.S.A. _____________________________________________________________________________________ ABSTRACT The many hypotheses aimed at describing the physiological, morphological, environmental forces contributing to buttress development have not clearly shown definitive evidence regarding what selective forces are responsible for buttress formation. One hypothesis that has little documented research available is that the presence of buttresses allows for an increased abundance of organic matter and inhibits nutrient leaching from the soil, thus providing the tree with a greater quality soil for locali zed growth. Twenty five different soil samples were collected and analyzed for potassium, nitrogen, phosphorus, and pH from both the base of buttressed Quercus spp . and a control site in the cloud forest of Monteverde, Costa Rica. No significant difference was found in the relationship between the presence of buttresses and an increased amount of N, P, K, or a more suitable pH. Results found may be due to nutrient use by the roots of buttressed trees or a slower rate of decomposition due to decreased temper atures in lower montane wet forests verses lowland tropical forests. RESUMEN Hay muchas hipótesis que apuntan a describir las fuerzas fisiológicas, morfológicas y ambientales que contribuyen al desarrollo de gambas, pero no se ha mostrado evidencia definitiva con respecto a que fuerza selectiva es responsable de su formación. Una hipótesis que ha sido poco investigada predice que con la presencia de gambas se aumenta la abundancia de la materia orgánica e inhibe la lixiviación de nutrientes de la tierra, así proporciona al árbol con un sustrato más nutritivo para el crecimiento. Ve inticinco muestras diferentes de tierra fueron analizadas en el contenido de potasio, nitrógeno, fosforo, y de pH en la base de árboles de Quercus y un sitio control cerca, en el bosque nuboso de Monteverde, Costa Rica. Ninguna diferencia significativa se encontró en la relación entre la presencia de gambas y el aumento de N, P, K, o de un pH más adecuado. Los resultados encontrados pueden estar relacionados al uso de nutrientes por las raíces de las gambas o a una tasa más lenta de descomposición debido a la baja humedad y temperaturas en el bosque montano bajo comparado con los bosques de bajura tropicales. INTRODUCTION Buttresses are structures that develop at the base of tree trunks from strip like regions of enhanced cambial activity that extends from the trunk to the upper side of certain roots Fisher 1982. The degree of cambial activity determines the height and plank like form or relative thickness of the buttress Fisher 1982. General characteristics of trees that display buttresses are: emergen t trees of 30 m in height or more, trees on flood plain

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areas where drainage is poor, and trees growing where shallow soils primarily made up of clay occur Smith 1979; Richards 1996. As altitude increases, the presence of buttresses usually decreases, ho wever, buttresses can still be found at higher elevations, but are less abundant. Many tree species in the tropics display buttressed roots. In Monteverde 1500 m elevation, Costa Rica, along the Tilarán Mountain Range in the province of Puntarenas the m ost abundant species exhibiting buttresses is Quercus spp . Mauricio Garcia, pers. com.. Quercus spp . Fagaceae are large canopy trees 20 35 m, common on ridges and peaks in the cloud forest Haber et al. 2000. Trunks of Quercus spp . are usually buttr essed with twisted branches and are covered in epiphytes Haber et al. 2000. The four species of Quercus found in the Monteverde are: Q. brenesii , Q. insignis , Q. corrugata , and Q. seemannii Hartshorn 1983; Haber et al. 2000. A theory widely excepted in the scientific community is that buttresses are an adaptation to wind or gravitational forces acting upon the tree Smith 1979; Hartshorn 1983; Richards 1996. In this case the buttress would be offering the tree increased struc tural support especially where poor drainage and shallow soil were a factor. Buttress development may be selected for as a competitive mechanism, which inhibits other trees from establishing themselves nearby. Thus, using nutrients valuable to the buttress ed species Black and Harpe 1979. A less researched idea is that buttresses provide the tree with more nutrients, which is a limited resource in tropical soils. By creating cavities for litter, water, and a hospitable habitat for soil organisms, buttresse s presumably would supply the tree with more organic matter, thus creating the availability of a higher quality soil. Phosphorus, nitrogen, and potassium are elements that most frequently limit plant production Brady and Weil 1996. Soil pH affects the p lants ability to use what elements are available in the soil; therefore it is an important factor to analyze when looking at P, N, and K Killham 1994. A good supply of N stimulates root growth and development as well as the uptake of other nutrients Tai ze and Zeiger 1991. Nitrogen is available for plant uptake through two different ways: one being through the breakdown of atmospheric dinitrogen gas by microorganisms and the other being through the soil organic matter present on the forest floor. Potassi um plays an important role in reducing the amount of water lost from leaf stomata and increasing the ability of root cells to take up water from the soil. Animal waste and plant residues are primarily responsible for potassium elements found in the soil B rady and Weil 1996. Potassium is normally abundant in soils, but in highly acidic soils, K is especially prone to loss by leaching, erosion and runoff. Phosphorus aids in photosynthesis, N fixation, and root growth; particularly development of lateral roo ts and fibrous rootlets. Phosphorus compounds are released when organic residues and humus decompose Brady and Weil 1996. Adaptations to nutrient poor environments occur in any region soils are infertile, but because poor soils are common in the tropics , nutrient conservation mechanisms are often associated with tropical species. A common plant adaptation to nutrient poor soils is the production of a large root biomass, often with the concentration of root biomass on or

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near the soil surface. However, bu ttress development might be an additional adaptation to nutrient poor soil Jordan 1985. I hypothesize that tree buttress presence on Quercus spp . is an adaptation to poor tropical soils. Trees that display buttresses do so because they allow for more or ganic matter to accumulate in an area optimal for nutrient capture by the roots. Buttresses may also limit the amount of nutrients lost due to leaching, by funneling the nutrient rich water towards the tree for uptake. I hypothesize that an increase in are a between the buttress planks may yield an increase in soil quality. Also, I am proposing that the greater the slope of the ground that a Quercus spp . reside on the lesser amount of N, P, and K will be found due to a higher rate of nutrient leaching. MATE RIALS AND METHODS Twenty five buttressed Quercus spp . were sampled from a plot of forest in the Estación Biológica Monteverde in Puntarenas, Costa Rica. For each tree the slope was measured using a clinometer. The area of ground, upslope from each Quercus spp ., between the buttress planks collecting area was measured. This was done by taking two measurements: first, the distance between the terminal ends of the two planks was measured, and second, the distance from the trunk to the center point between the t erminal measurements assuming a triangular form. Once organic matter was cleared from the collecting area a soil sample 150 ml was taken from the top layer 0 5cm deep directly in the middle of the triangular formation of the collecting area. A contro l sample was then taken to the left of the tree sample directly parallel on the same slope to it, 1.5 m away from the site of the buttress sample outside the buttress area. The availability of N, P, and K were then measured, in the control and the tree sample, using the LaMotte soil analysis kit. The pH was measured using an Okatun pH meter after mixing three parts distilled water and one part soil for each sample. A paired t test was conducted looking for differences between pH, P, K, and N in the but tress sample and the control sample. Regressions were done between area and the soil elements, slope and area, and slope and the soil elements. All statistical test ran were done with Statview 5.0. RESULTS There was no significant difference found in the pH level between the buttress and the control Paired t test, p = 0.7698 Fig. 1. The amount of N found in the buttress samples was not significantly different from the control Paired t test p = 0.7955 Fig. 2. There was no significant difference in P between the buttress samples and the control Paired t test, p = 0.2543 Fig. 3. The amount of K found in the buttress samples was not significantly different from the control Paired t test, p = 0.2413 Fig. 4. Slope did not show a significant relationship to, area Simple regression, p = 0.2544; R 2 = 0.056 Fig. 5, N Simple regression, p = 0.4188; R 2 = 0.029 Fig. 6, P

PAGE 4

Simple regression, p = 0.5283; R 2 = 0.018 Fig. 7, or K Simple regression, p = 0.1058; R 2 = 0.11 Fig. 8 in the butt ress samples. Slope did not show a significant relationship to the control samples Simple regression, N, p = 0.1969; R 2 = 0.071; P, p = 0.8172; R 2 = 0.002; K, p = 0.0306; R 2 = 0.118. Slope did not have a significant effect on the pH level of buttress s amples Simple regression, p = 0.2292; R 2 = 0.062 or the control samples Simple regression, p = 0.8172; R 2 = 0.002. Area did not have a significant effect on N Simple regression, p = 0.1125; R 2 = 0.071, P Simple regression, p = 0.4980; R 2 = 0.02, o r K Simple regression, p = 0.0816; R 2 = 0.126. Area did not have a significant effect of pH Simple regression, p = 0.2700; R 2 = 0.053. DISCUSSION For nutrients to be available for uptake they must be in a soluble form and must be located at the root s urface. The existing supply of nutrients in contact with the root eventually becomes depleted and more nutrients are needed to replenish the depleted portion. This is done in three ways: root interception roots continually grow into new undepleted soils, mass flow dissolved nutrients are carried along with the flow of soil water towards the root, and by diffusion nutrient ions continually moving from areas of greater concentration towards the nutrient depleted areas of lower concentration Brady and W eil 1996. As a result the similar levels of N, P, and K Fig. 2 4 measured from the collecting area of buttresses in comparison to the control might be due to a significant amount of nutrient uptake being done by the roots. The control samples were all t aken from an area of ground where no apparent vegetation was growing, therefore, the amount of nutrients present wasn€t being depleted by plant uptake whereas the buttress samples were all taken in close vicinity to the roots and amount derived could possi bly be lower due to the active depletion and use of the nutrients Brady and Weil 1996. Temperature in Monteverde is lower compared to lowland tropical areas. When temperature is present in greater amounts it acts as a catalyst for decomposition Brady and Weil 1996. Plants rely on N, P, and K to release ions in a form that is available for uptake by the decomposing of organic matter. In tropical areas of higher temperatures and humidity you would expect to find a higher decomposition rate and thus a hi gher value of N, P, and K availability Jordan 1985. While sampling it was noticed that much of the organic matter collected in the buttresses was not well decomposed. Sampling was done toward the end of the dry season, which, could contribute to the slow rate of decomposition. Sampling during the rainy season, when more moisture was available for decomposition, or sampling done from lowland tropical area might have resulted in different findings. Nitrogen Simple regression, p = 0.4188; R 2 = 0.029 Fig. 6, P Simple regression, p = 0.5283; R 2 = 0. 018 Fig. 7, and K Simple regression, = p = 0. 1058; R 2 = 0.11 Fig. 8 all showed no significant relationship relating an increased slope with a

PAGE 5

decreased amount of nutrient availability in the buttress sa mples. No significance was found in the control samples relating increased slope to decreased nutrient availability Simple regression, N, p = 0.1969; R 2 = 0.071; P, p = 0.8172; R 2 = 0.002; K, p = 0.0306; R 2 = 0.118. This result may also be due to samplin g during the dry season. Leaching rates are highest when the soil is saturated with water and runoff is a occurring regularly Jordan 1985. The collecting area of the trees sampled did not show a relationship of increasing nutrients with increasing area, as originally hypothesized. This could be due to the lower temperatures in higher elevational tropical areas compared to lowland tropical areas, where decomposition allows for a greater nutrient availability Brady and Weil 1996. Other existing hypothes es propose that buttressing is strongly selected for as a means of achieving support. It has been noticed that trees growing on poor substrate often have buttresses, but in extra tropical areas buttress presence isn€t as prevalent even in swampy areas wher e the substrate offers almost no support Smith 1972. Mechanical stain and tension could also be stimuli for buttress production, producing asymmetrical growth and strengthening of the roots Smith 1972; Richards 1996. In a study done by Young and Perkoc ha 1994 , buttresses formation was greatest on the side of the tree away from the direction of crown asymmetry; suggesting that buttresses formation is at least partly due to tensile pressure acting on the tree. Numerous studies have been done on the effe cts wind force has on buttress development. In some reports buttress formation has been noticed to be pronounced on the leeward side. This hypothesis is often disputed due to the contradicting elevational and latitudinal gradient, where buttress presence d ecreases with increasing latitude and increasing elevation temperate and high elevational areas have higher wind velocities Smith 1972. It is possible that buttress growth is a competitive mechanism; deterring other plants from establishment. An obvio us increase in individual space occupied at ground level inhibits available space for rooting by other plants Black and Harpe 1979. Buttressed trees provide defense against soil rooted woody vines more energy is expended to establish on a buttressed tree vs. an unbuttressed tree which when established in large numbers can lead to tree damage and possible mortality Black and Harpe 1979. Numerous studies have been done trying to describe which factors cause buttress formation. Evidence, for, and agains t many of these factors exists in scientific literature; therefore, further studies need to be done before a consensus can be reached. It is most likely that a multitude of factors are responsible for buttress presences and it is doubtful that a definitive answer will ever be fully realized or accepted. ACKNOWLEDGEMENTS I would like to thank Mauricio Garcia for all his guidance and prudent knowledge. Andrew was a savor and helped me locate seven more buttressed Quercus spp. when I thought there were no mo re to be found. I would like to thank Rick Smith for allowing me the use of his Creedance Clearwater CD, which kept soil analysis bearable after the fourth hour. And last but not least, I would like to thank my nerdery companions.

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LITERATURE CITED Black, H.L., and K.T. Harpe. 1979. The adaptive value of buttresses to tropical trees: additional hypotheses. Biotropica 11: 240. Brady, N.C., and R.R. Weil. 1996. The Nature of Properties of Soils. Prentice Hall, New Jersey. Fisher, J.B. 1982. A survey of buttresses and arial roots of tropical trees for presence of reaction wood. Biotropica 14: 56 61 Haber, W.A., W. Zuchowski, and E. Bello. 2000. An Introduction to Cloud Forest Trees Monteverde, Costa Rica. Mountain Gem Publications, Monteverde. Hartshorn, G.S. 1983. Plants. In D.H. Janzen. Costa Rican Natural History. University of Chicago Press, Chicago. 145pp. Henwood, K. 1973. A structural model of forces in buttressed tropical rain forest trees. Biotropica 5: 83 93. Jordan, C.F. 1985. Nutrie nt Cycling in Tropical Ecosystems. John Wiley and Sons, New York. Killham, K. 1994. Soil Ecology. Cambridge University Press, Cambridge. Richards, P.W. 1996. The Tropical Rain Forest. Cambridge University Press, Cambridge. 70pp. Smith, A.P. 1972. Buttressing of tropical trees: a descriptive model and new hypotheses. The American Naturalist 106: 32 45. Taiz, L., and E. Zeiger. 1991. Plant Physiology. Benjamin/Cummings Publishing Company, New York. Young, T.P., and V. Perkocha. 1994. Treefalls, crown asymmetry, and buttresses. Journal of Ecology 82: 319 324.



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Advantageous Development of Buttresses displayed in Quercus spp. Mariel Platt Department of Environmental Science, University of Oregon, Eugene, Oregon 97401, U.S.A. _____________________________________________________________________________________ ABSTRACT The many hypotheses aimed at describing the physiological, morphological, environmental forces contributing to buttress development have not clearly shown definitive evidence regarding what selective forces are responsible for buttress formation. One hypothesis that has little documented research available is that the presence of buttresses allows for an increased abundance of organic matter and inhibits nutrient leaching from the soil, thus providing the tree with a greater quality soil for locali zed growth. Twenty five different soil samples were collected and analyzed for potassium, nitrogen, phosphorus, and pH from both the base of buttressed Quercus spp . and a control site in the cloud forest of Monteverde, Costa Rica. No significant difference was found in the relationship between the presence of buttresses and an increased amount of N, P, K, or a more suitable pH. Results found may be due to nutrient use by the roots of buttressed trees or a slower rate of decomposition due to decreased temper atures in lower montane wet forests verses lowland tropical forests. RESUMEN Hay muchas hipótesis que apuntan a describir las fuerzas fisiológicas, morfológicas y ambientales que contribuyen al desarrollo de gambas, pero no se ha mostrado evidencia definitiva con respecto a que fuerza selectiva es responsable de su formación. Una hipótesis que ha sido poco investigada predice que con la presencia de gambas se aumenta la abundancia de la materia orgánica e inhibe la lixiviación de nutrientes de la tierra, así proporciona al árbol con un sustrato más nutritivo para el crecimiento. Ve inticinco muestras diferentes de tierra fueron analizadas en el con tenido de potasio, nitrógeno, fó sforo, y de pH en la base de árboles de Quercus y un sitio control cerca, en el bosque nuboso de Monteverde, Costa Rica. Ninguna diferencia significativa se encontró en la relación entre la presencia de gambas y el aumento de N, P, K, o de un pH más adecuado. Los resultados encontrados pueden estar relacionados al uso de nutrientes por las raíces de las gambas o a una tasa más lenta de descomposición debido a la baja humedad y temperaturas en el bosque montano bajo comparado con los bosques de bajura tropicales. INTRODUCTION Buttresses are structures that develop at the base of tree trunks from strip like regions of enhanced cambial activity that extends from the trunk to the upper side of certain roots Fisher 1982. The degree of cambial activity determines the height and plank like form or relative thickness of the buttress Fisher 1982. General characteristics of trees that display buttresses are: emergen t trees of 30 m in height or more, trees on flood plain

PAGE 2

areas where drainage is poor, and trees growing where shallow soils primarily made up of clay occur Smith 1979; Richards 1996. As altitude increases, the presence of buttresses usually decreases, ho wever, buttresses can still be found at higher elevations, but are less abundant. Many tree species in the tropics display buttressed roots. In Monteverde 1500 m elevation, Costa Rica, along the Tilarán Mountain Range in the province of Puntarenas the m ost abundant species exhibiting buttresses is Quercus spp . Mauricio Garcia, pers. com.. Quercus spp . Fagaceae are large canopy trees 20 35 m, common on ridges and peaks in the cloud forest Haber et al. 2000. Trunks of Quercus spp . are usually buttressed with twisted branches and are covered in epiphytes Haber et al. 2000. The four species of Quercus found in the Monteverde are: Q. brenesii , Q. insignis , Q. corrugata , and Q. seemannii Hartshorn 1983; Haber et al. 2000. A theor y widely excepted in the scientific community is that buttresses are an adaptation to wind or gravitational forces acting upon the tree Smith 1979; Hartshorn 1983; Richards 1996. In this case the buttress would be offering the tree increased structural s upport especially where poor drainage and shallow soil were a factor. Buttress development may be selected for as a competitive mechanism, which inhibits other trees from establishing themselves nearby. Thus, using nutrients valuable to the buttressed spec ies Black and Harpe 1979. A less researched idea is that buttresses provide the tree with more nutrients, which is a limited resource in tropical soils. By creating cavities for litter, water, and a hospitable habitat for soil organisms, buttresses presu mably would supply the tree with more organic matter, thus creating the availability of a higher quality soil. Phosphorus, nitrogen, and potassium are elements that most frequently limit plant production Brady and Weil 1996. Soil pH affects the plants a bility to use what elements are available in the soil; therefore it is an important factor to analyze when looking at P, N, and K Killham 1994. A good supply of N stimulates root growth and development as well as the uptake of other nutrients Taize and Zeiger 1991. Nitrogen is available for plant uptake through two different ways: one being through the breakdown of atmospheric dinitrogen gas by microorganisms and the other being through the soil organic matter present on the forest floor. Potassium play s an important role in reducing the amount of water lost from leaf stomata and increasing the ability of root cells to take up water from the soil. Animal waste and plant residues are primarily responsible for potassium elements found in the soil Brady an d Weil 1996. Potassium is normally abundant in soils, but in highly acidic soils, K is especially prone to loss by leaching, erosion and runoff. Phosphorus aids in photosynthesis, N fixation, and root growth; particularly development of lateral roots and fibrous rootlets. Phosphorus compounds are released when organic residues and humus decompose Brady and Weil 1996. Adaptations to nutrient poor environments occur in any region soils are infertile, but because poor soils are common in the tropics, nutri ent conservation mechanisms are often associated with tropical species. A common plant adaptation to nutrient poor soils is the production of a large root biomass, often with the concentration of root biomass on or

PAGE 3

near the soil surface. However, buttress development might be an additional adaptation to nutrient poor soil Jordan 1985. I hypothesize that tree buttress presence on Quercus spp . is an adaptation to poor tropical soils. Trees that display buttresses do so because they allow for more organic m atter to accumulate in an area optimal for nutrient capture by the roots. Buttresses may also limit the amount of nutrients lost due to leaching, by funneling the nutrient rich water towards the tree for uptake. I hypothesize that an increase in area betwe en the buttress planks may yield an increase in soil quality. Also, I am proposing that the greater the slope of the ground that a Quercus spp . reside on the lesser amount of N, P, and K will be found due to a higher rate of nutrient leaching. MATERIALS AND METHODS Twenty five buttressed Quercus spp . were sampled from a plot of forest in the Estación Biológica Monteverde in Puntarenas, Costa Rica. For each tree the slope was measured using a clinometer. The area of ground, upslope from each Quercus spp ., between the buttress planks collecting area was measured. This was done by taking two measurements: first, the distance between the terminal ends of the two planks was measured, and second, the distance from the trunk to the center point between the t erminal measurements assuming a triangular form. Once organic matter was cleared from the collecting area a soil sample 150 ml was taken from the top layer 0 5cm deep directly in the middle of the triangular formation of the collecting area. A contro l sample was then taken to the left of the tree sample directly parallel on the same slope to it, 1.5 m away from the site of the buttress sample outside the buttress area. The availability of N, P, and K were then measured, in the control and the tree sample, using the LaMotte soil analysis kit. The pH was measured using an Okatun pH meter after mixing three parts distilled water and one part soil for each sample. A paired t test was conducted looking for differences between pH, P, K, and N in the but tress sample and the control sample. Regressions were done between area and the soil elements, slope and area, and slope and the soil elements. All statistical test ran were done with Statview 5.0. RESULTS There was no significant difference found in the pH level between the buttress and the control Paired t test, p = 0.7698 Fig. 1. The amount of N found in the buttress samples was not significantly different from the control Paired t test p = 0.7955 Fig. 2. There was no significant difference in P between the buttress samples and the control Paired t test, p = 0.2543 Fig. 3. The amount of K found in the buttress samples was not significantly different from the control Paired t test, p = 0.2413 Fig. 4. Slope did not show a significant relationship to, area Simple regression, p = 0.2544; R 2 = 0.056 Fig. 5, N Simple regression, p = 0.4188; R 2 = 0.029 Fig. 6, P

PAGE 4

Simple regression, p = 0.5283; R 2 = 0.018 Fig. 7, or K Simple regression, p = 0.1058; R 2 = 0.11 Fig. 8 in the butt ress samples. Slope did not show a significant relationship to the control samples Simple regression, N, p = 0.1969; R 2 = 0.071; P, p = 0.8172; R 2 = 0.002; K, p = 0.0306; R 2 = 0.118. Slope did not have a significant effect on the pH level of buttress s amples Simple regression, p = 0.2292; R 2 = 0.062 or the control samples Simple regression, p = 0.8172; R 2 = 0.002. Area did not have a significant effect on N Simple regression, p = 0.1125; R 2 = 0.071, P Simple regression, p = 0.4980; R 2 = 0.02, o r K Simple regression, p = 0.0816; R 2 = 0.126. Area did not have a significant effect of pH Simple regression, p = 0.2700; R 2 = 0.053. DISCUSSION For nutrients to be available for uptake they must be in a soluble form and must be located at the root s urface. The existing supply of nutrients in contact with the root eventually becomes depleted and more nutrients are needed to replenish the depleted portion. This is done in three ways: root interception roots continually grow into new undepleted soils, mass flow dissolved nutrients are carried along with the flow of soil water towards the root, and by diffusion nutrient ions continually moving from areas of greater concentration towards the nutrient depleted areas of lower concentration Brady and W eil 1996. As a result the similar levels of N, P, and K Fig. 2 4 measured from the collecting area of buttresses in comparison to the control might be due to a significant amount of nutrient uptake being done by the roots. The control samples were all t aken from an area of ground where no apparent vegetation was growing, therefore, the amount of nutrients present wasn€t being depleted by plant uptake whereas the buttress samples were all taken in close vicinity to the roots and amount derived could possi bly be lower due to the active depletion and use of the nutrients Brady and Weil 1996. Temperature in Monteverde is lower compared to lowland tropical areas. When temperature is present in greater amounts it acts as a catalyst for decomposition Brady and Weil 1996. Plants rely on N, P, and K to release ions in a form that is available for uptake by the decomposing of organic matter. In tropical areas of higher temperatures and humidity you would expect to find a higher decomposition rate and thus a hi gher value of N, P, and K availability Jordan 1985. While sampling it was noticed that much of the organic matter collected in the buttresses was not well decomposed. Sampling was done toward the end of the dry season, which, could contribute to the slow rate of decomposition. Sampling during the rainy season, when more moisture was available for decomposition, or sampling done from lowland tropical area might have resulted in different findings. Nitrogen Simple regression, p = 0.4188; R 2 = 0.029 Fig. 6, P Simple regression, p = 0.5283; R 2 = 0. 018 Fig. 7, and K Simple regression, = p = 0. 1058; R 2 = 0.11 Fig. 8 all showed no significant relationship relating an increased slope with a

PAGE 5

decreased amount of nutrient availability in the buttress sa mples. No significance was found in the control samples relating increased slope to decreased nutrient availability Simple regression, N, p = 0.1969; R 2 = 0.071; P, p = 0.8172; R 2 = 0.002; K, p = 0.0306; R 2 = 0.118. This result may also be due to samplin g during the dry season. Leaching rates are highest when the soil is saturated with water and runoff is a occurring regularly Jordan 1985. The collecting area of the trees sampled did not show a relationship of increasing nutrients with increasing area, as originally hypothesized. This could be due to the lower temperatures in higher elevational tropical areas compared to lowland tropical areas, where decomposition allows for a greater nutrient availability Brady and Weil 1996. Other existing hypothes es propose that buttressing is strongly selected for as a means of achieving support. It has been noticed that trees growing on poor substrate often have buttresses, but in extra tropical areas buttress presence isn€t as prevalent even in swampy areas wher e the substrate offers almost no support Smith 1972. Mechanical stain and tension could also be stimuli for buttress production, producing asymmetrical growth and strengthening of the roots Smith 1972; Richards 1996. In a study done by Young and Perkoc ha 1994 , buttresses formation was greatest on the side of the tree away from the direction of crown asymmetry; suggesting that buttresses formation is at least partly due to tensile pressure acting on the tree. Numerous studies have been done on the effe cts wind force has on buttress development. In some reports buttress formation has been noticed to be pronounced on the leeward side. This hypothesis is often disputed due to the contradicting elevational and latitudinal gradient, where buttress presence d ecreases with increasing latitude and increasing elevation temperate and high elevational areas have higher wind velocities Smith 1972. It is possible that buttress growth is a competitive mechanism; deterring other plants from establishment. An obvio us increase in individual space occupied at ground level inhibits available space for rooting by other plants Black and Harpe 1979. Buttressed trees provide defense against soil rooted woody vines more energy is expended to establish on a buttressed tree vs. an unbuttressed tree which when established in large numbers can lead to tree damage and possible mortality Black and Harpe 1979. Numerous studies have been done trying to describe which factors cause buttress formation. Evidence, for, and against many of these factors exists in scientific literature; therefore, further studies need to be done before a consensus can be reached. It is most likely that a multitude of factors are responsible for buttress presences and it is doubtful that a definitive answer will ever be fully realized or accepted. ACKNOWLEDGEMENTS I would like to thank Mauricio Garcia for all his guidance and prudent knowledge. Andrew was a savor and helped me locate seven more buttressed Quercus spp. when I thought there were no mor e to be found. I would like to thank Rick Smith for allowing me the use of his Creedance Clearwater CD, which kept soil analysis bearable after the fourth hour. And last but not least, I would like to thank my nerdery companions.

PAGE 6

LITERATURE CITED Black, H.L., and K.T. Harpe. 1979. The adaptive value of buttresses to tropical trees: additional hypotheses. Biotropica 11: 240. Brady, N.C., and R.R. Weil. 1996. The Nature of Properties of Soils. Prentice Hall, New Jersey. Fisher, J.B. 1982. A survey of buttresses and arial roots of tropical trees for presence of reaction wood. Biotropica 14: 56 61 Haber, W.A., W. Zuchowski, and E. Bello. 2000. An Introduction to Cloud Forest Trees Monteverde, Costa Rica. Mountain Gem Publications, Monteverde. Hartshorn, G.S. 1983. Plants. In D.H. Janzen. Costa Rican Natural History. University of Chicago Press, Chicago. 145pp. Henwood, K. 1973. A structural model of forces in buttressed tropical rain forest trees. Biotropica 5: 83 93. Jordan, C.F. 1985. Nutrient Cycling in Tropical Ecosystems. John Wiley and Sons, New York. Killham, K. 1994. Soil Ecology. Cambridge University Press, Cambridge. Richards, P.W. 1996. The Tropical Rain Forest. Cambridge University Press, Cambridge. 70pp. Smith, A.P. 1972. Buttressing of tropical trees: a descriptive model and new hypotheses. The American Naturalist 106: 32 45. Taiz, L., and E. Zeiger. 1991. Plant Physiology. Benjamin/Cummings Publishing Company, New York. Young, T.P., and V. Perkocha. 1994. Treefalls, crown asymmetry, and buttresses. Journal of Ecology 82: 319 324.



PAGE 1

Advantageous Development of Buttresses displayed in Quercus spp. Mariel Platt Department of Environmental Science, University of Oregon, Eugene, Oregon 97401, U.S.A. ABSTRACT The many hypotheses aimed at describing the physiological, morphological, environmental forces contributing to buttress development have not clearly shown definitive evidence regarding what selective forces are responsible for buttress formation. One hypot hesis that has little documented research available is that the presence of buttresses allows for an increased abundance of organic matter and inhibits nutrient leaching from the soil, thus providing the tree with a greater quality soil for localized growt h. Twenty five different soil samples were collected and analyzed for potassium, nitrogen, phosphorus, and pH from both the base of buttressed Quercus spp. and a control site in the cloud for est of Monteverde, Costa Rica. No significant difference was found in the relationship between the presence of buttresses and an increased amount of N, P, K, or a more suitable pH. Results found may be due to nutrient use by the roots of buttressed trees or a slower rate of decomposition due to decreased temperature s in lower montane wet forests verses lowland tropical forests. RESUMEN Hay muchas hiptesis que apuntan a describir las fuerzas fisiolgicas, morfol gicas y ambientales que contribuyen al desarrollo de gambas, pero no se ha mostrado evidenci a definitiva con respecto a qu fuerza selectiva es responsable de su formacin. Una hiptesis que ha sido poco investigada predice que con la presencia de gambas se aumenta la abundancia de la materia orgnica e inhibe la lixiviacin de nutrientes de la tierra, as proporciona al rbol con un sustrato ms nutritivo para el crecimiento. Veinticinco muestras diferentes de tierra fueron analizadas en el co ntenido de potasio, nitrgeno, fsforo, y de pH en la base de rboles de Quercus y un s itio control cerca, en el bosque nuboso de Monteverde, Costa Rica. Ninguna diferencia significativa se encontr en la relacin entre la presencia de gambas y el a umento de N, P, K, o de un pH ms adecuado. Los resultados encontrados puede estar relacionado s al uso de nutrientes por las races de las gambas o a una tasa ms lenta de descomposicin debido a la baja humedad y temperaturas en el bosque montano bajo, comparado con los bosques de bajura tropicales.

PAGE 2

INTRODUCTION Buttresses are structures that develop at the base of tree trunks from strip l ike regions of enhanced cambial activity that extends from the trunk to the upper side o f certain r oots (Fisher 1982). The degree of cambial activity determines the height and plank like form or relative thick ness of the buttress (Fisher 1982). General characteristics of trees that display buttresses are: emergent trees of 30 m in height or more, trees on flood plain areas where drainage is poor, and trees growing where shallow soils primarily made up of clay o ccur (Smith 1979; Richards 1996). As altitude increases, the presence of buttresses usually decreases, however, buttresses can still be found at higher elevations, but are less abundant Many tree species in the tropics display buttressed roots. In Monteve rde (1500 m elevation), Costa Rica, along the Tilarn Mountain Range in the province of Puntarenas the most abundant species exhibiting buttresses is Quercus spp. (Mauricio Garcia, pers. com,). Quercus spp. (Fagaceae) are large canopy trees (20 35 m), comm on on ridges and peaks in the cloud forest (Haber et al. 2000). Trunks of Quercus spp. are usually buttressed with twisted branches and are covered in epiphytes (Haber et al. 2000). The four species of Quercus found in the Monteverde are: Q. brenesii, Q. i nsignis, Q. corrugata, and Q. seemannii (Hartshorn 1983; Haber et al. 2000). A theory widely excepted in the scientific community is that buttresses are an adaptation to wind or gravitational forces acting upon the tree (Smith 1979; Hartshorn 1983; Richards 1996 ). In this case the buttress would be offering the tree increased structural support especially where poor drainage and shallow soil were a factor. Buttress development may be selected for as a competitive mechanism, which inhibits other trees from establishing themselves nearby. Thus, using nutrients valuable to the buttressed species (Black and Harpe l979). A less researched idea is that buttresses provide the tree with more nutrients, which is a limited resource in tropical soils. By creatin g cavities for litter, water, and a hospitable habitat for soil organisms, buttresses presumably would supply the tree with more organic matter, thus creating the availability of a higher quality soil. Phosphorus, nitrogen, and potassium are elements that most frequently limit plan t production (Brady and Weil 1996 ). Soil pH affects the plants ability to use what elements are available in the soil; therefore it is an important factor to analyze when looking at P, N, and K (Killham 1994). A good supply of N s timulates root growth and development as well as tile uptake of other nutrients (Taize and Zeiger 1991). Nitrogen is available for plant uptake through two different ways: one being through the breakdown of atmospheric dinitrogen gas by microorganisms and the other being through the soil organic matter present on the forest floor. Potassium plays an important role in reducing the amount of water lost from leaf stomata and increasing the ability of root cells to take up water from the soil. Animal waste and plant residues

PAGE 3

are primarily responsible for potassium elements found in the soil (Brady and Weil 1996). Potassium is normally abundant in soils, but in highly acidic soils, K is especially prone to loss by leaching, erosion and runoff. Phosphorus aids in photosynthesis, N fixation, and root growth; particularly development of lateral roots and fibrous rootlets: Phosphorus compounds are released when organic residues and humus decompose. (Brady and Weil 1996) Adaptations to nutrient poor environments occur in any region soils are infertile, but because poor soils are common in the tropics, nutrient conservation mechanisms are often associated with tropical species. A common plant adaptation to nutrient poor soils is the production of a large root biomass, o ften with the concentration of root biomass on or near the soil surface. However, buttress development might be an additional adaptation to nutrient poor soil. (Jordan 1985) I hypothesize that tree buttress presence on Quercus spp. is an adaptation to poor tropical soils. Trees that display buttresses do so because they allow for more organic matter to accumulate in an area optimal for nutrient capture by the roots. Buttresses may also limit the amount of nutrients lost due to leachi ng, by funneling the nutrient rich water towards the tree for uptake. I hypothesize that an increase in area between the buttress planks may yield an increase in soil quality. Also, I am proposing that the greater the slope of the ground that a Quercus spp reside on the lesser amount of N, P, and K will be found due to a higher rate of nutrient leaching. MATERIALS AND METHODS Twenty five buttressed Quercus spp. were sampled from a plot of forest in the Estacin Biolgica Monteverde in Puntarenas, Costa Rica. For each tree the slope was measured using a clinometer The area of ground, upslope from each Quercus spp., between the buttress planks (collecting area) was measured. This was done by taking two measurements: first, the distance between the terminal ends of the two planks was measured, and second, the distance from the trunk to the center point between the terminal measurement (assuming a triangular form). Once organic matter was cleared from the collecting area a soil sample (150 ml) was taken from the top layer (0 5 cm deep) directly in the middle of the triangular formation of the collecting area. A control sample was then taken to the left of the tree sample directly parallel (on the s ame slope) to it, 1.5 m away from the site of the buttress sample (outside the buttress area). The availability of N, P, and K were then measured, in the control and the tree sample, using the LaMotte soil analysis kit. The pH was measured using an Okatun pH meter after mixing three parts distilled water and one part soil for each sample. A paired t test was conducted looking for differences between pH, P, K, and N in the buttress sample and the control sample. Regressions were done between area and the soi l elements, slope and area, and slope and the soil elements. All statistical test ran were done with Stat view 5.0.

PAGE 4

RESULTS There was no s ignificant difference found in th e pH level between the buttress and the control (Paired t test, p = 0.7698) (Fig. 1) The amount of N found in the buttress samples was not significantly different from the control (Paired t test p = 0.7955) (fig. 2). There was no significant difference in P between the buttress samples and the control (Paired t test, p = 0.2543) (Fig. 3). The amount of K found in the buttress samples was not significantly different from the control (Paired t test, p = 0.2413) (Fig. 4). Slope did not show a significant relationship to, area (Simple regression, p = 0.2544; R 2 = 0.056) (Fig. 5), N (Simple regression, p = 0.4188; R 2 = 0.029)(Fig 6), P (Simple regression, p = 0.5283; R 2 = 0.018) (Fig. 7), or K (Simple regression, p = 0.1058; R 2 = 0.11) (Fig. 8) in the buttress samples. Slope did not show a significant relationship to the control samples (Simple regression, N, p = 0.1969; R 2 = 0.071; P, p =0.8172; R 2 = 0.002; K, p = 0.0306; R 2 = 0.118). Slope did not have a significant effect on the pH level of buttress samples (Simple regression, p = 0.2292; R 2 = 0.062 ) or the control samples (Simple regression, p = 0.8172; R 2 = 0.002). Area did not have a significant effect on N (Simple regression, p = 0.1125; R 2 = 0.071), P (Simple regression, p = 0.4980; R 2 = 0.02), or K (Simple regression, p = 0.0816; R 2 = 0.126). Area did not have a significant effect of pH (Simple regression, p = 0.2700; R 2 = 0.053). DISCUSSION For nutrients to be available for uptake they must be in a soluble form and must be located at the root surface. The existing supply of nutrients in contact with the root eventually becomes depleted and more nutrients are needed to replenish the depleted portion. This is done in three ways: root interception (roots continually grow into new undepleted soils), mass flow (dissolved nutrients are carr ied along with the flow of soil water towards the root), and by diffusion (nutrient ions continually moving from areas of greater concentration towards the nutrient depleted areas of lower concentration) (Brady and Weil 1996). As a result the similar level s of N, P, and K (Fig. 2 4) measured from the collecting area of buttresses in comparison to the control might be due to a significant amount of nutrient uptake being done by the roots. The control samples were all taken from an area of ground where no app arent vegetation was growing, therefore, the amount of nutrients present wasn't being depleted by plant uptake whereas the buttress samples were all taken in close vicinity to the roots and amount derived could possibly be lower due to the active depletion and use of the nutrients. (Brady and Weil 1996) Temperature in Monteverde is lower compared to lowland tropical areas. When temperature is present in greater amounts it acts as a catalyst for decomposition (Brady

PAGE 5

and Weil 1996). Plants rely on N, P, and K to release ions in a form that is available for uptake by the decomposing of organic matter. In tropical areas of higher temperatures and humidity you would expect to find a higher decomposition rate and thus a hi gher value of N, P, and K availability (Jordan 1985). While sampling it was noticed that much of the organic matter collected in the buttresses was not well decomposed. Sampling was done toward the end of the dry season, which, could contribute to the slow rate of decomposition. Sampling during the rainy season, when more moisture was available for decomposition, or sampling done from lowland tropical area might have resulted in different findings. Nitrogen (Simple regression, p = 0.4188; R 2 = 0.029)(Fig. 6 ), P (Simple regression, p = 0.5283; R 2 = 0.018) (Fig. 7), and K (Simple regression, p = 0.1058; R 2 = 0.11) (Fig. 8) all showed no significant relationship relating an increased slope with a decreased amount of nutrient availability in the buttress samples No significance was found in the control samples relating increased slope to decreased nutrient availability (Simple regression, N, p = 0.1969; R 2 = 0.071; P, p =0.8172; R 2 = 0.002; K, p = 0.0306; R 2 = 0.118). This result may also be due to sampling during the dry season. Leaching rates are highest when the soil is saturated with water and runoff is a occurring regularly (Jordan 1985). The collecting area of the trees sampled did not show a relationsh ip of increasing nutrients with increasing area, as originally hypothesized. This could be due to the lower temperatures in higher elevational tropical areas compared to lowland tropical areas, where decomposition allows for a greater nutrient availability (Brady and Weil 1996). Other existing hypotheses propose that buttressing is strongly selected for as a means of achieving support It has been noticed that trees growing on poor substrate often have buttresses, but in extra tropical areas buttress presen ce isn't as prevalent even in swampy areas where the substrate offers almost no support (Smith 1972). Mechanical stain and tension could also be stimuli for buttress production, producing asymmetrical growth and strengthening of the roots (Smith 1972; Rich ards l996). In a study done by Young and Perkocha (1994), buttresses formation was greatest on the side of the tree away from the direction of crown asymmetry; suggesting that buttresses formation is at least partly due to tensile pressure acting on the tr ee. Numerous studies have been done on the effects wind force has on buttress development In some reports buttress formation has been noticed to be pronounced on the leeward side. This hypothesis is often disputed due to the contradicting elevational and latitudinal gradient where buttress presence decreases with increasing latitude and increasing elevation (temperate and high elevational areas have higher wind velocities) (Smith 1972). It is possible that buttress growth is a competitive mechanism; deterr ing other plants from establishment. An obvious increase in individual space occupied at ground level inhibits available space for rooting by other plants Black and Harpe 1979). Buttressed trees provide defense against soil rooted woody vines (more energy is expended to establish on a buttressed tree vs. an unbuttressed tree) which when established in large

PAGE 6

numbers can lead to tree damage and possible mortality (Black and Harpe 1979). Numerous studies have been done trying to describe which factors cause buttress formation. Evidence, for, and against many of these factors exists in scientific literature; therefore, further studies need to be done before a consensus can be reached. It is most likely that a multitude of factors are responsible for buttress p resences and it is doubtful that a definitive answer will ever be fully realized or accepted. ACKNOWLEDGEMENTS I would like to thank Mauricio Garcia for all his guidance and prudent knowledge. Andrew was a savor and helped me locate seven more buttressed Quercus spp. when I thought there were no more to be found. I would like to thank Rick Smith for allowing me the use of his Creedance Clearwater CD, which kept soil analysis bearable after the fourth hour. And last but not least, I would like to thank my nerdery companions. Literature Cited Black, H.L., and K.T. Harpe. 1979. The adaptive value of buttresses to tropical trees: additional hypotheses. Biotropica 11: 240. Brady, N.C., and R. R. Weil. 1996. The Nature of properties of soils. Prentice Hall, New Jersey. Fisher, J. B. 1982. A survey of buttresses and arial roots of tropical trees for presence of reaction wood. Biotropica 14: 56 61. Haber, W.A., W. Zuchowski, and E. Bello. 2000. An Introdu ction to Cloud Forest Trees Monteverde, Costa Rica. Mountain Gem Publications, Monteverde. Hartshorn, G.S. 1983. Plants. In D.H. Janzen. Costa Rican Natural History. University of Chicago Press, Chicago. 145pp. Henwood, K. 1973. A structural model of force s in buttressed tropical rain forest trees. Biotropica 5: 83 93. Jordan, C.F. 1985. Nutrient Cycling in Tropical Ecosystems. John Wiley and Sons, New York. Killham, K. 1994. Soil Ecology. Cambridge University Press, Cambridge. Richards, P.W. 1996. The Trop ical Rain Forest. Cambridge University Press, Cambridge. 70pp. Smith, A.P. 1972. Buttressing of tropical trees: a descriptive model and new hypotheses. The American Naturalist 106: 32 45. Taiz, L. and E. Zeiger. 1991. Plant Physiology. Benjamin/Cummings Pu blishing Company, New York. Young, T.P. and V. Perkocha. 1994. Treefalls, crown asymmetry, and buttresses. Journal of Ecology 82: 319 324.


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