Hastings Natural History Reservation

18 May, 05 AM - 14 Jul, 05 AM

Introduction Recently, there has been a call to join the disciplines of ecosystem and community ecology in order to understand the driving forces behind ecological phenomenon (Naeem, Loreau and Inchausti 2002; Naeem 2002). It is thought that to address one side and not the other is giving a biased view. Understandably, and like with so many disciplines, the members of each of these factions have very different ways of looking at nature. The community ecologist is interested in the abundance and distribution of species in space and time and how this can be affected by biotic (competition and predation) as well as abiotic and environmental influences(Wilson and Keddy 1986; Tilman 1987; Cornell and Karlson 1996). On the other hand, the ecosystem ecologist is trained to compartmentalize aspects of an ecosystem to understand the overall patterns of nutrient cycling and energy flow through the system (DeMazancourt, Loreau and Abbadie 1998). However, it has been shown that these ideas are intimately linked and that the species composition of a system has huge impacts on the functioning of the ecosystem (Hobbie 1992, Chapin et al 1997). Disturbance has been shown to play an integral role in the maintenance of species co-existence (Denslow 1980). It has been shown that in some communities disturbance is a necessary mechanism for the maintenance of species diversity (Connell 1978; Vandermeer et al 2000). By effectively reseting the system in which it operates and changing the previous competitive interactions it lessens the chances for competitive exclusion and increases the probabilities of co-existence (Hutchinson 1961). Disturbance has also been shown to change resource availability as well as decomposition and mineralization of nutrients (Canham and Marks1985). These changes can then, in turn, change the patterns of plant species coexistence by allowing species that were previously excluded to perhaps establish and become a viable member of the assemblage (Grubb 1977; need other sources). These new species then feed back into ecosystem cycles such as the nitrogen and carbon cycles by the processes such as decomposition or nutrient uptake and could potentially change the overall dynamics of a system (Hobbie 1992; Chapin et al 1997; Symstad et al 1998). This study is of the utmost importance because it takes and integrated approach by combining aspects of ecosystem and community ecology to determine the effects of disturbance by a novel disturbing agent. By combining analysis of different communities in the matrix of communities which is Central Coastal California, we can come up with generalizations about how disturbance effects plant species and ecosystem processes for the entire system. The purpose of this project is two-fold: I. Determine the direct effects of disturbance on ecosystem processes such as nitrogen availability and decomposition. II. Determine the direct effects of disturbance on patterns of germination and plant species assemblages. The Study System Central-coastal California has a gradient of plant communities that range from closed canopy oak forest comprised mainly of live oaks with a sparse understory to oak savanna comprised of deciduous blue oaks with an annual grassland in the understory to an annual grassland with no canopy. These different plant communities have proven to be quite stable and the boundaries between them remain distinct (Griffin 1988). With the introduction of invasive pigs, Sus scrofa, they have brought with them a pattern of disturbance that is new to the system. Sus scrofa are native to Eurasia and North Africa, but are now distributed throughout most of the world as feral animals (Kotanen 1995). In the United States, they are found in the Great Smoky Mountains, parts of Texas and California (Howe and Bratton 1975; Kotanen 1995). The pigs have been successful as feral animals because of their high reproductive potential, omnivorous feeding habits and the freedom from native predators (Howe and Bratton 1975). Pigs search for food by grubbing for roots, bulbs, rhizomes and other below ground material. Grubbing activity involves breaking through the surface layer of soil (5-15cm) while simultaneously displacing vegetation (Kotanen 1995). This ?rototilling? activity can be large scale (up to a hectare) but is characteristically of smaller scale, about 1 m2, but with many sporadic small disturbances in one location. In other systems, the invasion of pigs and their subsequent foraging damage has shown to have impacts on, not only, plant species composition but on patterns of resource availability macro-nutrients and also cation concentrations which lend to the idea that this disturbance could be changing larger ecosystem processes such as nitrogen and carbon cycling (Singer et al 1984). Disturbance and Ecosystem Properties Objective 1: Determine spatial extent of pig damage The spatial extent of disturbance needs to be quantified for each species so that I can ascertain just how big of an impact these species are having on the reserve. On two hills in 3 plant communities (grassland, oak woodland, and closed canopy oak forest) 4 fifty meter transects will be laid out with 25 m between each. I will walk along these transects and any pig damage that intersects the transect will be quantified by measuring the diameter of the disturbance. This data can then be extrapolated to get a measure of total damage per area for the entire reserve. This disturbance may likely vary between years and so must be quantified for multiple seasons. Objective 2: Determine effects of damage on soil erosion. Along these transects in random damaged locations and adjacent undamaged locations, channels made of metal flashing will be positioned downhill of the damage. In 2m x 2m area of the damage or undamaged site, 5 liters of water will be poured over the plot to simulate a rainfall event. Collection containers will be placed at the base of these channels to collect any runoff and soil that has eroded. I will construct 5 erosion experiment plots in 3 different sites for a total of 15 plots. Objective 3: Determine direct effects of pig disturbance on Nitrogen and Carbon cycling Disturbance can have direct impacts on soil nitrogen and carbon dynamics (Hobbs 1996; Steudler et al 1991; Canals, Herman and Firestone 2003). In agricultural experiments, it has been shown that tillage decreases soil carbon pools through increased decomposition rates. It has also been shown that immediately after tillage there is a pulse in nitrogen availability due to the death of soil microorganisms (Rasse and Smucker 1999; Allmaras et. al 2000;Yamulki and Jarvis 2002). The damage by pigs is comparable to small scale soil tillage. If rates of decomposition are increased then there will be less plant material incorporated in the soil carbon pool. Methods: Soil CO2 flux will be measured in a disturbed patch and in an adjacent undisturbed patch. Soil CO2 flux is a measure of microbial activity. The more active the microorganisms are, the more decomposition will be taking place and there will be more CO2 released. I will take these measurements along the transects in damaged and adjacent undamaged locations as well as in all the experimental plots and then compare the soil CO2 rates to estimate differences in decomposition between the damaged and the control plots. Along with the soil CO2 measurements I will also bury 2 common substrate litter bags in each plot. One will be harvested at 6 months post disturbance and the other at a year. Mass loss of the litter bags will give another estimate on the rates of decomposition due to disturbance. Ammonium nitrate will be measured to attempt to quantify changes in nitrogen availability. I will bury resin bags in all the experimental plots and will retrieve them after 2 months. These samples will then be sent to the Ecosystem Analysis Lab, Lincoln, NE. and analyzed for ammonium nitrate concentrations. I will also measure total nitrogen and total carbon in the same locations to be used as covariates with ammonium nitrate. Predictions for Ecosystem Properties: I predict that pig disturbances will have major impacts on soil and therefore direct effects on ecosystem processes such as decomposition and soil nitrogen availability. Because of soil turnover and addition of live plant matter to the soil, decomposition should increase because microbes are coming into contact with a previous unavailable food source. Nitrogen availability should also increase because with the turn over of soil, microbe communities die and the assimilated nitrogen that was in the cell structure of these microorganisms is released. Because the plants that would have formerly taken up this newly available nitrogen have been uprooted due to the soil turnover, there is an increase in the available nitrogen pool. Disturbance and Community Properties Objective 1: Evaluation of abiotic conditions pre and post disturbance A critical component to understanding the distribution and abundances of species is the knowledge of the abiotic or environmental requirements of germination termed the ?regeneration niche?(Grubb 1977; Coomes and Grubb 2003; Forbis, Larmore and Addis 2004). Disturbance of the soil can change or create regeneration niches and therefore affect the types of species that are germinating and their subsequent competition for resources post germination (Forbis, Larmore and Addis 2004). Studies of pig disturbance have shown that there is an impact on soil properties and resource availability in the deciduous forest of the Great Smoky Mountains National Park (Singer et al 1984). These changes could in turn affect the regeneration niche of plants and in turn change the species that may be able to germinate and mature to adults in each community (Grubb 1977). It is important to know if these impacts are system specific or if they can be extended to other systems such as the savannas and annual grasslands of California. Also, in order to understand the overall impact on the system we must understand the dynamics of the role that disturbance plays in each separate community. Below are the hypothesized environmental conditions of each community relative to one another (Table 1). In each community, disturbance could play a different role because of these different attributes. For example, in the closed canopy oak forest community there is a significant humus layer that, when undisturbed, can hinder the germination of seedlings. With disturbance, this humus layer will be turned over, mixed with the soil and previously unexposed soil will become exposed allowing for germination sites. Also, through mixing, the humus layer becomes more available to soil micro-organisms and could be decomposed faster, thereby freeing nutrients that could then be taken up by germinating plants. It seems that the dynamics of disturbance and its subsequent impacts on germination will be very different in the closed canopy oak forest than in the grassland simply due to differences in the environmental variables. Environmental Variables Closed Canopy Oak Forest Savanna Grassland Humus layer High Medium Low Soil Organic Matter High Medium Low Light availability Low Medium High Soil Moisture High Medium Low Soil Temperature Low Medium High Table 1. Hypothesized environmental variables in each distinct plant community relative to one another. Methods: In each community and replicated over 3 hills I will have 5 plots in each community for a total of 45 plots. 3 plots will be disturbed and 2 will be undisturbed. Pigs will be baited in each location so the disturbance will be natural and the time of the disturbance known. Each plot will be 4m x 4m and fenced so as to prevent any further disturbance. In each community, light levels will be taken with a light meter. Soil moisture will be measured in disturbed and undisturbed plots every 2 weeks for 3 months post-disturbance with a soil moisture probe. Soil bulk density, pH, ammonium nitrate, phosphorus and will be measured in each plot. Bulk density will be assessed with a coring method (Klute 1986), whereas pH, ammonium nitrate, and phosphorus will be quantified with resin bags and and analyzed in the Ecosystem Analysis Lab in Lincoln, Ne. Objective 2: Potential Germination Capabilities: Estimation of the seed bank The pre-disturbance and post-disturbance seed bank in each community will be quantified to determine the abundance and identity of species seeds in the seed bank that could potentially germinate in optimal conditions. Experiments have shown that species composition shifts post-disturbance can be related to the timing of the disturbance and how that coincides with the species seeding at that time (Lavorel et al 1994; Amiaud and Touzard 2004). The seed bank has not always been correlated to the vegetation present (Amiaud and Touzard 2004). This can also give indications on the dispersal capabilities of these plant species (Hobbs and Hobbs 1987; Roughgarden, Gaines and Pacala 1987). If the seeds are present in the seed bank and yet not present in the plant community from which the seed bank came from, the seeds would have had to have been dispersed from the population of reproducing mature plants. If these species are dispersal limited and that is why there is stability in these plant communities, there may not be a change in species composition with a disturbance event. Methods: In each community, closed canopy oak forest, savanna and grassland, 8 20cm x 20 cm x 5 cm deep soil samples will be taken. 4 samples will be from a recently disturbed area and 4 from and undisturbed area within the plant community. Any existing above-ground vegetation will be removed from the sample and it will be transported to a greenhouse. The samples will be spread in separate trays and then set at optimal light and moisture levels. The emerging seedlings will be counted and identified to species every 3 days and then removed from the soil. This will continue until there are no more emerging seedlings. Objective 3: Quantification of plant community and patterns of germination Studies in community ecology have shown that there can be a colonization-competition tradeoff in species that depends upon seed size. Smaller seeded species have been shown to be superior colonizers where as relatively larger seeded species have the resource reserves to be superior competitors once they become established (Coomes and Grubb2003). Studies have also shown that disturbance can have immediate effects by changing the abiotic conditions to facilitate germination of species (i.e. exposing new soil that was previously under a litter layer) that are shown in germination patterns and lasting effects by changing overall resource patterns that would determine mature plant competition (Calrton and Bazzaz 1998). Methods: This objective will be addressed both by assessing the natural patterns of germination and by a seed addition experiment. In the plots constructed to address the changes in abiotic conditions, percent cover will be assessed in 0.5 m x 0.5 m quadrats in each plot. Percent bare ground as well as the percent cover of all species will be assessed in each plot. I will then be able to assess changes in plant species composition as well as diversity in the disturbed and control plots. These estimates will be taken every year to quantify the temporal variation in these species assemblages. The seed addition experiment will be constructed in the 3 plant communities using common species that range in functional group (grasses, forbs, legumes) and also a range in seed size. 28 1m x 1m plots will be constructed in each of the plant communities. 10 plots will be seeded with known amounts of each species and not disturbed. 10 plots will be seeded and disturbed 4 plots in each community will be controls in which there will be no seed addition and no disturbance and 4 will be no seed addition and disturbed. This is a total of 84 plots. The plots will be visited each year for 3 years to quantify the species composition of each plot. By starting with a known amount of seed and with knowledge of seed size generalizations can be made about the effects of disturbance on community composition and what traits such as seed size play into the resulting plant community. Disturbed and Seed AdditionN=10 Undisturbed and Seed AdditionN=10 Disturbed and No Seed AdditionN=4 Undisturbed and No Seed AdditionN=4 Table 2. Treatment combinations for the seed addition experiment. Predictions for Community Properties: I predict that there will be changes in the composition of the plant communities because of pig disturbance events. This could be due to changes in resource availability in disturbed patches and by creating new regeneration niches that were previously unavailable. The magnitude of the change may depend upon which community whether it be closed canopy oak forest, savanna, or grassland due to differences in the environmental variables in each community and the properties of the seed banks. Significance and Future Directions: This work is attempting to, not only, address the plant community assemblage effects that disturbance can have but also attempts to put it in an ecosystem ecology framework. By quantifying the spatial extent of disturbance the changes that I observe on the small scale such as changes in resource availability and plant species composition can then be extrapolated to determine overall system effects. This sort of integrated approach to understanding the impacts that disturbance can have on a system is rarely done and these set of experiments will attempt to show the merit of such an approach. Realistically, in order to understand the true species composition dynamics these plots will have to be followed for many years. However, with 3 years of data I expect to be able to determine, at the very least, the direct effects of disturbance on nutrient availability as well as the patterns of germination and how disturbance can affect the regeneration niches in each community. In essence, these questions are really only addressing one part of the puzzle of how disturbance can directly effect ecosystem cycles and species assemblages. Over years of observation, it may become apparent that pig disturbance is changing the plant species composition in these different communities. Plant species are known to mediate processes such as nutrient cycling (Hobbie 1992). Therefore, if disturbance is directly changing the plant community it not only has the direct ecosystem effects that are being addressed with my experiments, but it also has indirect effects mediated by the change in plant species composition that can effect the longer term patterns of nutrient cycling. These questions concerning indirect effects can only be addressed by long-term data and further experimentation once the short-term effects are quantified. Literature Cited. Allmaras, R.R., Schomberg, H.H., Douglas, C.L., and T.H. Dao. 2000. Soil organic carbon sequestration potential of adopting conservation tillage in US croplands. Journal of Soil and Water Conservation 55: 365-373. Amiaud, B. and B. Touzard. 2004. The relationships between soil seed bank, aboveground vegetation and disturbances in old embanked marshlands of western France. Flora 199:25-35. Methods of Soil Analysis Part 3: Chemical Methods. 1996. J.M Bartels (managing ed) American Society of Agronomy, Inc. and Soil Science Society of America. Inc. Publisher. Madison, Wi. Canham, C.D. and P.L. Marks. 1985. The response of woody plants to disturbance: patterns of establishment and growth. Pp. 197-216 in S.T.A. Pickett and P.S. White (eds). The Ecology of Natural Disturbance and Patch Dynamics. Academic Press, Inc. San Diego, Ca. Carlton, G.C., and F.A. Bazzaz. 1998. Resource congruence and forest regeneration following an experimental hurricane blowdown. Ecology 79: 1305-1319. Chapin III, F.S., B.H. Walker, R.J. Hobbs, D.U. Hooper, J.H. Lawton, O.E. Sala and D. Tilman. 1997. Biotic control over the functioning of ecosystems. Science 277: 500-504. Connell, J.H. 1978. Diversity in tropical rain forests and coral reefs. Science 199:1302-1310. Coomes, D.A., and P.J. Grubb. 2003. Colonization, tolerance, competition and seed-size variation within functional groups. Trends in Ecology and Evolution 18: 283-291. Cornell, H.V. and R.K. Karlson, 1996. Species richness of reef-building corals determined by local and regional processes. Journal of Animal Ecology 65:233-241. DeMazancourt, C., Loreau, M., and L. Abbadie. 1998. Grazing optimization and nutrient cycling: when do herbivores enhance plant production? Ecology 79:2242-2252. Denslow, J.S. 1980. Patterns of plant species diversity during succession under different disturbance regimes. Oecologia 46: 18-21. Griffin, J.R. 1988. A natural history of hastings reservation. Report 1. Copyright by the Regents of the University of California. Grubb, P.J. 1977. The maintenance of species-richness in plant communities: the importance of the regeneration niche. Biological Review 52:107-145. Hobbie, S. 1992. Effects of plant species on nutrient cycling. Trends in Ecology and Evolution 7:336-339. Hobbs, R.J., and V.J. Hobbs. 1987. Gophers and grassland: a model of vegetation response to patchy soil disturbance. Vegetatio 69: 141-146. Hutchinson, G.E. 1961. The paradox of the plankton. American Naturalist 95: 137-145. Methods of Soil Analysis. Part 1: Physical and Mineralogical Methods. 1986. A. Klute (ed). American Society of Agronomy, Inc. and Soil Science Society of America. Inc. Publisher. Madison, Wi. Kotanen, P.M. 1995. Responses of vegetation to a changing regime of disurbance: effects of feral pigs in a Californian coastal prairie. Ecography 18: 190-199. Lavorel, S., Lepart, J., Debussche, M., Lebreton, J.D. and J.L. Beffy. 1994. Small scale disturbances and the maintenance of species diversity in Mediterranean old fields. Oikos 70: 455-473. Naeem, S. 2002. Ecosystem consequences of biodiversity loss: the evolution of a paradigm. Ecology 83:1537-1552. Naeem, S., Loreau, M. and P. Inchausti. 2002. Biodiversity and ecosystem functioning: the emergence of a synthetic ecological framework. S. Naeem, M. Loreau, and P. Inchausti (eds). Pp. 3-12. Biodiversity and Ecosystem Functioning Synthesis and Perspectives. Oxford University Press, New York. Rasse, D.P. and A.J.M. Smucker. 1999. Tillage effects on soil nitrogen and plant biomass in a corn-alfalfa rotation. Journal of Environmental Quality 28: 873-880. Roughgarden, J., S.D. Gaines, and S.W. Pacala. 1987. Supply-side ecology: the role of physical transport processes. Pp. 459-486 in P. Giller and J. Gee (eds). Organization of Communities: Past and Present. Blackwell Scientific Publications. Oxford. Singer, F.J., Swank, W.T., and E.E.C. Clebsch. 1984. Effects of wild pig rooting in a deciduous forest. Journal of Wildlife Management 48:464-473. Symstad, A.J., D. Tilman, J. Willson, and J.M.H. Knops. 1998. Species loss and ecosystem functioning: effects of species identity and community compsition. Oikos 81:389-397. Tilman, D. 1987. The importance of the mechanisms of interspecific competition. American Naturalist 129:769-774. Vandermeer, J., I. Graznow de la Cerda, D. Bourcher, I. Perfecto, and J. Ruiz. 2000. Hurricane disturbance and tropical tree species diversity. Science 290:788-791. Wilson, S.D. and P.A. Keddy. 1986. Species competitive ability and position along a natural stress/disturbance gradient. Ecology 67:1236-1242. Yamulki, S. and S. C. Jarvis. 2002. Short-term effects of tillage and compaction on nitrous oxide, nitric oxide, nitrogen dioxide, methane and carbon dioxide fluxes from grassland. Biology and Fertility of Soils 36: 224-231. Amy Kochsiek Understanding the Impacts of Disturbance: An Integrated Approach Summary The impacts of disturbance have been viewed by both ecosystem and community ecologists and conclusions made in each of the separate ecological camps. It is becoming increasingly well known that community ecology and ecosystem ecology are, in fact, intimately related and to simply study one aspect does not always give a clear picture of observed ecological patterns. In this study, I attempt to quantify the impact of disturbance by feral pigs in patterns of nutrient cycling and plant germination patterns in different plant communities in Central Coastal California. By incorporating aspects of both disciplines, I hope to show the merit of such an approach and to get an overall picture of the direct impacts of disturbance in the short-term as well as the potential for long-term indirect impacts.

Visit #5261 @Hastings Natural History Reservation

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Under Project # 4176 | Research

Understanding the Impacts of Disturbance

graduate_student - University of Nebraska

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Amy Kochsiek May 18 - Jul 14, 2004 (58 days)

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Ranch House 1 May 18 - Jul 14, 2004