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Comprendiendo los efectos de la sucesin secundaria en la concentracin de nutrientes del suelo y los macro-invertebrados
Understanding the effects of secondary succession on soil nutrient concentration and soil macro-invertebrates
When agricultural land is abandoned, secondary succession is known to occur within the plant community, but little is known about the effects of regeneration on the soil. Since plant richness and productivity is tightly correlated with nutrient availability, I investigated the effect of time after regeneration on nutrient
levels and macro-invertebrate richness. I sampled six sites ranging in age of regeneration (0 years, 7 years, 11 years, 19 years, 45 years, and primary) measured at the concentration (lb/acre) of potassium,
phosphorous, iron, and nitrate nitrogen and counted the morpho-species richness. Potassium and phosphorous concentrations were significantly correlated with age of regeneration; iron concentration was
marginally significant when correlated with age of regeneration; but, nitrate nitrogen was not significantly correlated with age of regeneration. Morpho-species richness was positively correlated to regeneration time as well. Differences in trends in potassium, phosphorous, and iron may be due to differences in nutrient cycling on a geological scale and movement of water across surfaces. Lack of significance with
nitrate nitrogen may signify a difference in the distribution of nematodes. Morpho-speices may or may not ever return to primary levels, however they do increase compared to pasture levels. In conclusion,
secondary succession has an effect on soil in terms of both abiotic and biotic conditions.
Cuando la tierra usada para la agricultura queda abandonado, la vegetacin secundara empieza a crecer. Pero hay poca informacin sobres los efectos de la vegetacin secundara en el suelo. Debido a que hay una correlacin entre la diversidad en la comunidad de plantas y los nutrientes del suelo, mir los cambios en los nutrientes del suelo a travs del tiempo. Tom una muestra del suelo, en seis lugares, con aos diferente de vegetacin secundara (0, 7, 11, 19, 45 y bosque primario). Med la concentracin de potasio, hierro, fosforo y hierro. Tambin, cont la diversidad de morfo-especies. Las concentraciones de fosforo y potasio tuvieron una correlacin significativa con el tiempo. El hierro fue marginalmente significativo con el tiempo. El nitrgeno no tuvo una correlacin significativa con el tiempo. Es posible que las diferencias entre los nutrientes fuera el resultado de los ciclos de nutrientes y el movimiento del agua en el suelo. Tambin el nitrgeno podra ser un resultado del nmero de nematodos. Es posible que la diversidad de morfo-especies nunca vaya a regresar a los nmeros que se pueden ver en un bosque primario. En conclusin, la vegetacin secundara tiene un efecto en el suelo.
Text in English.
Costa Rica--Puntarenas--Monteverde Zone--Cerro Plano
Composicin del suelo
Invertebrados del suelo
Costa Rica--Puntarenas--Zona de Monteverde--Cerro Plano
Tropical Ecology Fall 2009
Ecologa Tropical Otoo 2009
t Monteverde Institute : Tropical Ecology
Understanding the effects of secondary succession on Soil Nutrient Concentration and soil macro invertebrates Rebecca Goldstein School of Public and Environmental Affairs, Indiana University ABSTRACT When agricultural land is abandoned, secondary succes sion is known to occur within the plant community, but little is know about the effects of regeneration on the soil. Since plant richness and productivity is tightly correlated with nutrient availably, I investigated the effect of time after regeneration on nutrient levels and macro invertebrate richness. I sampled six sites ranging in age of regeneration (0 years, 7 years, 11 years, 19 years, 45 years, and primary) measured at the concentration (lb/acre) of potassium, phosphorous, iron, and nitrate nitro gen and counted the morpho species richness. Potassium and phosphorous concentrations were significantly correlated with age of regeneration Iron concentration was marginally significant when correlated with age of regeneration but nitrate nitrogen was no t significantly correlated with age of regeneration. Morpho species richness was positively correlated to regeneration time as well. Differences in trends in potassium, phosphorous, and iron may be due to diffe rences in nutrient cycling on a geological s cale and movement of water across surface. Lack of significance with nitrate nitrogen may signify a difference in the distribution of nematodes. Morpho speices may or may not ever return to primary levels, however they do increase compared to pasture leve ls. In c onclusion, secondary succession has an effect on soil in terms of both abiotic and biotic conditions . RESUMEN Cuando tierra usada para agricultura queda abandonado la vegetaciÃ³n secundarÃa empieza a crecer. Pero hay poca informaciÃ³n sobros los efectos de la vegetaciÃ³n secundarÃa en el suelo. Debido que hay un a correlaciÃ³n entre la diversidad en l a c omunidad planta y los nutritentes del suelo, mirÃ© los cambios en nutrientes del suelo a traves del tiempo. TomÃ© una muestra de suelo, en seis lug ares, con aÃ±os diferente de vegetaciÃ³n secundarÃa (0, 7, 11, 19, 45 y bosque primero). MedÃ concentraciÃ³n de potasio, hierro fosforo y hielo . Tambi Ã©n, contÃ© la diversidad de morf o species. Las concentraciones de fosforo y potasio tuvo un a correlaciÃ³n sig nifica con el tiempo. El hierro fue marginalmente significativo con el tiempo. Nitrogen o no tuvo un correlaciÃ³n significativa con el tiempo. Es posible que diferencias entre los nutritivos fue resultado de ciclos de nutrientes y movimiento de agua en el suelo. Tam biÃ©n el nitrogen o podrÃa ser un resueltado de l numero de nematodos. Es po sible que la diversidad de morf o e species nunca vaya a regresar a los numeros que se puede n ver en un bosque primario. En conclusiÃ³n, vegetaciÃ³n secundarÃa tiene un efect o a suelo. INTRODUCTION The Neotropics have a common theme throughout history; humans have destroyed primary forest for agriculture, abandoned the land when agriculture fails, thus allowing new growth to slowly occur on the farmland (Arnold & Bryan 1 997). This makes the all destroyed or damaged land will pass through certain stages to return to a climax community, a stable community that is optimal for the region (Merchant 2007). This implies that one should be able to see abandoned farmland slowly change from weedy
grasses, to herbaceous plants, to softwood trees and finally return to a climax community of hardwood tree (Merchant 2007). In studies of secondary fo rest succession in Puerto Rico, Brazil, Venezuela, and Columbia, agricultural land eventually returned to climax community tree species at sapling stage, although the rate of reforestation varied depending on the intensity of the agricultural practice (Aid e et al. 1995). Clements predicted the recovery stages that plants pass through, but he did not predict anything about changes in the soil. Nevertheless, succession theory should apply to soil, since plant growth and productivity are strongly correlated wi th soil nutrient levels (Guariguata & Ostertag 2001). In past studies in the tropics, significant differences were found between soil nutrient levels in primary and pasture, but not between pasture and secondary forest or secondary forests and primary fore st (Camargo et al. 1999, Fox 2001). Another study found that soil organic matter (SOM) depended on how quickly the secondary stand reproduced biomass, but generally the older the site the more SOM, indicating more fertile soil. (Guggenberger & Zech 1999). These studies imply that nutrients are accumulated during secondary forest succession; therefore there may be succession in soil nutrients. If there is succession in nutrient levels, then overtime the soil should return to concentrations similar to that of primary forest (Guariguata & Ostertag 2001). Secondary forest succession may also affect the soil macro invertebrates. In a study in Brazil, it was found that the macro invertebrate community was significantly less species rich in recently deforested areas than in primary forest. It was also found that in fallow fields, the longer the field was left fallow, the greater the species richness (Mathieu et al. 2005). This implies that deforestation and time after deforestation have an effect on macro inve rtebrate presence and diversity. In a different study, higher macro invertebrate biomass was found in high quality soils (in this case defined by neutral pH, high organic matter and Ca content) (DecaÃ«ns 1998). This study implicated that the highest biomas s of soil macro invertebrates will always be found in the most pristine community, which is the climax community. The following study investigates the relationship between the years regeneration has occurred and soil nutrient concentration. I predict tha t as the number of years of regeneration increases, nutrients will move closer to their primary levels because the forest is regenerating. As well, I will investigate the relationship between the number of years of regeneration and the richness of soil mac ro invertebrate community I predict that morpho species richness will increase as the years of regeneration increase because as the forest regenerates there are more niches for macro invertebrates to fill. METHODS Study Sites This study took place bet ween October 23 rd 2009 and November 20 th 2009. I chose all my soil sites within 1.5 km of the Hotel Belmar in Cerro Plano, Puntarenas, in Costa Rica. All sites other than primary forest either currently are or once were cattle pastures. I chose one pastu re site (age of regeneration 0 years), four secondary forest sites (ages of regeneration: 7, 11, 19, 45 years), and one primary forest (age approximated at >100). The pasture sample was taken at the cattle farm across from el Centro Panamericano de Idioma s (CPI). The 7 year
house. The 11 year year old sample came from the piper patch near the Estacion Biologica. The 45 year old sample came fr om the forest behind the Estacion Biologica on the Sendero Cariblanco . The primary forest sample also came from the forest behind the Estacion Biologica along the Sendero principal. Ages for the pasture sites and secondary forest ages seven and eleven w ere determined by talking to Alan Masters. Marvin Hidalgo, the station manager of the Estacion Biologica, helped me determine the 19 year old forest and the 45 year old forest. Since no one knew the exact age of the primary forest, I estimated it to be g reater than 100 years of regeneration without disturbance. This measure was made to be conservative since using 100 years or 250 years made little difference in the statistics, and I knew there had been at least 100 years without disturbance. From ea ch site, four soil samples and three macro invertebrate samples were taken from different parts of the area to obtain a better representation. All samples were taken at least three meters away from any roads or paths. At each site, I dug a hole 15 cm deep with a trowel, and then took a thin, vertical slice of the first 15 cm of soil . Once I returned to the lab, I separated the soil samples from the macro invertebrate samples and prepared them for various tests. Soil Chemistry I mixed the soil samples from the same site together to form a homogenous sample, and then filtered the homogenous sample through a mesh screen to remove rocks, roots, and large annelids. The sample was dried for 24 hours and then tested according to the STH series soil kit by La MOTTE. I tested potassium, nitrate nitrogen, phosphorous and iron. function. Soil Macro Invertebrate Sampling I used the Berlese Tullgreen funnel method and 50 g of soil fr om each of the macro invertebrate bags. I created the funnels by inverting the top of a 1.5 liter bottle and placed a paper towel soaked in ethanol in the bottom half to kill the insects. I used three layers of mesh screen as barriers between the soil an d the ethanol. About 10 cm above the top of the funnel, I hung a 25 watt light, which decreased moisture and increased temperature in the soil. This forced the macro invertebrates to move downward seeking moisture, leading them to the ethanol. The sampl es remained under the light for three days. The funnels and lights were covered by mosquito netting to keep out nocturnal insects. Any nocturnal insects found in the sample were not counted as morpho species. The samples were counted under a stereoscope . The macro invertebrates were identified to class, order, and morpho species. Data Analysis All data was analyzed using regression analysis. Years since regeneration began were recorded on the x axis and scaled logarithmically (log base 10). This was done to ensure that nutrients and macro invertebrate reached an asymptote. An asymptote was important because in primary forest nutrients concentrations and species richness remain constant. A logarithmic scale allows this to be factored into the model. The logarithmic scale also
gives more weight to changes that occur during the first 10 years, mirroring what is seen in a plant succession cycle (Merchant 2007). RESULTS Soil Chemistry I found a significant correlation between years of regeneration an d the potassium concentration within the soil (F = 10.49, df = 5, p < 0.05,Figure 1a). The general trend was negative, implying that over time, potassium levels became less concentrated in the soil. Potassium concentration was the same as primary concent ration when the secondary forest had reached 45 years of regeneration (220 lbs/acre). I also found a significant correlation between years of regeneration and phosphorous concentration within the soil, (F = 24.45, df = 5, p < 0.05, Figure 1b). The trend was positive; phosphorous concentration increased with time. However, the concentration at 45 years of regeneration (100 lbs/acre) was not the same as the primary concentration (150 lbs/acre). Iron concentration was marginally significantly correlated w ith years of regeneration (F=7.09, df=5, p = 0.05, Figure 1c). The overall trend was positive. This implied that iron concentration increases with years of regeneration. Iron concentrations returned to primary levels by 19 years of regeneration. I did n ot find a significant correlation between years of regeneration and nitrate nitrogen concentration (F= 0.77, df = 0.05, p > 0.05, Figure 1d). There was a general positive trend. However, at 11 years of regeneration the concentration of nitrate nitrogen ( 150 lb/acre) was higher than at primary levels (100 lb/acre). At 19 years of regeneration, the concentration dropped back down to 20 lb/acre, the same as found in the pasture. Soil Macro Invertebrates 63 individual macro invertebrates were collected r epresenting 49 different morpho species (Table 1). The maximum number of morpho species found at one site was ten and the minimum was seven. Morpho species richness was positively correlated with years of regeneration (F = 9.40, df = 5, p < 0.05, Figure 2 ). The morpho species richness found in the 45 year old secondary forest (8), was not the same as found in primary forest (10). The number of morpho species consistent from 7 years on to 45 years.
A B C D FIGURE 1. Correlations b etween the number of regeneration and soil nutrient concentration (Nutrient lb/acre). Six sites of different ages from Cerro Plano, Costa Rica were tested (0, 7, 11, 19, 45, and > 100). Figure 1a shows the regression of potassium concentration, modeled by the equation f(x) = 121.54log(age) + 484.78 (R 2 = 0.72, p < 0.05). Figure 1b shows the regression of phosphorous concentration, modeled by the equation f(x) = 59.61log(age) + 7.26, (R 2 = 0.86, p < 0.05). Figure 1c shows the regression of the iron conce ntration, modeled by the equation f(x)=22.03log(x)+7.45 (R 2 =0.64, p = 0.05) Figure 1d shows the regression of the nitrate nitrogen which was not significant (R 2 =0.16, p > 0.05)
TABLE 1 Morpho species of macro invertebrates found in each of the six sit e. Sites were chosen based on years of regeneration. All site were located in Cerro Plano, Costa Rica. Years of Regeneration at the Study Sites Morpho species 0 7 11 19 45 100 Araneae 1 1 Coleoptera 1 1 2 1 Coleoptera 2 1 Coleoptera 3 2 1 1 Coleoptera 4 1 2 coleoptera 5 1 1 coleoptera 6 1 coleoptera 7 1 2 coleoptera 8 1 Dermaptera 1 1 diplopoda 1 1 diplopoda 2 1 1 Diplopoda 3 1 1 diptera 1 1 diptera 2 1 diptera 3 1 diptera 4 1 Diptera 5 1 Hemiptera 1 1 1 2 1 Hemiptera 2 2 4 1 Hemiptera 3 1 1 1 Hemiptera 4 1 2 Hemiptera 5 1 1 Hemiptera 7 1 Hemiptera 8 1 Hempitera 6 3 Hymenoptera 1 1 Hymenoptera 2 1 Hym enoptera 3 1 Hymenoptera 4 1 Isopoda 1 2 Ixodida 1 1 S 7 8 8 8 8 10 Abundance 8 9 12 10 9 15
FIGURE 2 Relationship between Macro Invertebrate Species Richness and years of regeneration began. Relationship modeled by 1.18log(age ) + 6.82 ( R 2 = 0.73, p < 0.05) DISCUSSION My results indicate that the number of years land was allowed to regenerate has a significant effect on potassium, phosphorous, and iron concentrations, but not nitrate nitrogen concentrations. To understand why nitrate nitrogen is not significantly correlated with regeneration time, better understanding is needed of the nutrient. Nematodes, along with bacteria and fungi, are responsible for the fixation of nitrate nitrogen, and there is a significant correlation that higher levels of nematodes indicate higher nitrogen. However, neither nematode richness nor abundance has been found to correlate with regeneration time. Instead, nematode distribution seems to be random (Hanel 1995). Therefore my individual sites m ay have had different nematode communities, which resulted in the non logarithmic results of nitrate nitrogen concentrationWithin the two significant trends (potassium and phosphorous), there were differences in the sign of the trend. These differences ma y be explained by nutrient cycling. Potassium concentration had a negative trend. In the potassium nutrient cycle, only 2% of the total potassium within the soil should be in solution and available to plants. Deforestation may change this balance, becau se less plants use less potassium, therefore the solution becomes more concentrated (Helmke & Sparks 1996). Concentration may also increase at low levels of vegetation because less vegetative cover increases the temperature of the soil. Higher temperatur es drive more potassium into the solution form from the exchangeable and non exchangeable form (structural form is usually not involved although it is possible). The decrease in soil temperature with more vegetation may drive this equilibrium to deposit m ore potassium in the exchangeable and non exchangeable forms and less in
(Helmke & Sparks 1996). The concentration of potassium stayed relatively even until 45 years, at which time it dropped. This time coinc ides with an increase in soft and hard wood trees and the beginning of a significant canopy.(Merchant 2005) The canopy cools the soil. This change in soil temperature combined with more vegetation is probably what causes the decrease in potassium. Phosp horous, however, increased with the regeneration of the forest. Phosphorous is found mostly in the top layer of the soil, under the humus layer. Like the humus layer, it is often affected by erosion and rain, which washing it away. (Jones & Jacobson 200 5). In pastures, there is little to no humus present and little vegetative cover, so rain and erosion wash away nutrients in the topsoil more often (Jones & Jacobson 2005). Although tropical rainforest contains less humus than deciduous forest, there is still more humus in a tropical primary forest than in a pasture (Guggenberger & Zech 1999). The more vegetation and humus in the area, the more likely phosphorous is to accumulate. Phosophorous will not accumulate indefinitely. At the equilibrium level i n the primary forest, phosphorous is being used and leeched at the same rate it is being renewed (Jones & Jacobson 2005). At 45 years of regeneration, the phosphorous may still be accumulating, even if its at a slower rate than during the first 10 years. Iron concentration is naturally high in tropical soil because the parent material is volcanic in nature (Loeppert & Inskeep 1996). Looking at Figure 1c, iron content increased overtime, with the major increase occurring at 19 years of reforestation. This increase may be caused by a decrease in water washing away topsoil. I ron occurs throughout the soil, yet iron in the topsoil, created by organic matter decomposition is easily washed away (Loeppert & Inskeep 1996). Changes in pH to a more neutral soil may bring more iron toward the surface. (Loeppert & Inskeep 1996) At 19 years, there are more understory and small woody plants, which would increase the amount of topsoil, decreasing iron leeching. ( Merchant 2005). The increase in plants may also help the soil become more neutral helping fulfill the second condition. (Loeppert & Inskeep, 1996) Like soil nutrients, soil macro invertebrate richness was significantly correlated with the amount of time regeneration had occurred. All secondary forests had the same richness of macro invertebrate; the difference occurred between the primary richness and the pasture richness. This same scenario was seen by Matheiu et al in 2005. Some morpho speices were only found in primary forest while others were found only in secondary sites or the pasture. For example, hemiptera 1, 2, and 3 were found in almost all the sites, while diptera 2, 3, and 4 were only found in primary forest. The composition of macro invertebrates was different in each site, however a larger sampl e size would be needed to determine similarity. Similarity might give better insight to succession stages within macro invertebrates. It is also important to look at which nutrients have reached their primary concentrations by 45 years of regeneration. Both potassium and iron concentrations were at primary levels by in secondary forest age 45. Phosphorous seemed to be along a trend that within 100 years it would reach primary concentrations. However it is unclear from the data if nitrate nitrogen will return to primary concentration. Similarly, richness increases in the macro invertebrate population between a pasture and any secondary forest. However all secondary forest had the same richness, meaning that local extinctions or long colonization times may affect the biotic portion of the soil more than
previously thought. An old secondary forest may be primary in terms of soil nutrients, but not in terms of macro invertebrates. Regeneration has a significant effect on both the abiotic factors (soil nutrients) and the biotic factors (macro invertebrates). The extent of the effect changes depending the specific nutrient or the macro invertebrates, but the effect is significant. This is important to note for conservation because it implies that soil c an mostly regenerate to primary levels. In places such as Santa Rosa National Park in Guanacaste, Costa Rica, the park is currently made up of abandoned pastures. However, given 50 200 years, the soil and the soil community could return to what it was be fore agriculture. It may be that because of succession, tropical forests are more resilient than previously thought. Further studies could include looking for a connection between nitrate nitrogen and different types of macro and micro invertebrate in t he soil. Another study could look at the relationship between soil nutrients and nutrients with in the water nearby to determine the effect of water on nutrient leeching. ACKNOWLEDGMENTS I would like to thank my advisor, Pablo Allen for guiding me throu gh this project helping me add new components as problems occurred, and always being enthusiastic about the project. Thank you to Alan Masters and Marvin Hidalgo for helping me find my study sites. A special thank you to Alan for helping me develop my pr oject from an idea to a proposal. Thank you to Yimen Araya for always offering to help me, no matter what I needed. Thank you to my family in the US who supported me and were happy to hear ca family who always were happy when I came home and said that my project was working. . Lastly, thank you to Tyler Reynolds for searching through the computer room closet to find all the STH chemicals. LITERATURE CITED A RNOLD M. AND N. B RYAN 1997. What futures for people of the tropical forest. CIFOR. A IDE M. T., J.K Z IMMERMAN , L. H ERRERA , M. R OSARIO , AND M. S ERRANO 1995. Forest recovery in abandoned tropical pastures in Puerto Rico. Fores t Ecology and Management 77: 7 86 B RADY N. C. AND R.R. W EIL . 1996. The Nature and Properties of Soils. Prentice Hall. New York. C ARMAGO PB, S. E. T RUMBORE , L. M. M ARTINELLI , E. A. D AVIDOSON , AND R. V ICTORIA . 1999 Soil Carbon Dynamics in regrowing forests in eastern Amazonia. Global Change Biology. 5: 693 702. D E CAENS T., T. D UTOITB , D. A LARDB AND P. L AVELLE . 1998. Factors influencing soil macrofuanal communities in post pastoral succession of western France. Applied Soil Ecology. 9: 361 367. F OX , J. 2001 . Comparative soil study between primary forests, windbr eaks and pasture in Monteverde, Costa Rica. Tropical Ecology and Conservation. (Student Project Unpublished) G AURIGUATA M. R. AND R. O STERTAG . 2001. Neotropical Secondary Forest Succession: changes in structural and function characteristics. 148:185 206 G UGGENBERGER G. AND W. Z ECH . 1999. Soil organic matter composition under primary forest, pasture, and secondary forest succession, Region Huetar Norte, Costa Rica. Tropical Ecology and Management. 124: 93 104. H ANEL L. 2003 . Recovery of soil nematode po pulations from cropping stress by natural secondary succession to meadow land. Applied soil Ecology. 22:255 270. H ELMKE P. A. AND D. L. S PARKS . 1996. Lithium, Sodium, Potassium, Rubidum and
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