Species distribution models must balance the need for model generality with that for precision and accuracy. This is critical when modelling range-expanding species such as invasive species. Given the increased use of species distribution models to study invasive species-landscape relationships, a better understanding of the effect of spatial scales, sampling biases, model transferability and discrepancies between different models’ future predictions is necessary. This dissertation addresses these knowledge gaps using mute swans (Cygnus olor) as a case study species. I specifically examine mute swan’s distributions in parts of their native range of Britain and their non-native range of Ontario, Canada. I first investigate which environmental variables at which spatial scales best explain mute swan’s distribution in its non-native range. Second, I perform a sample selection bias study to examine predictive accuracy when species distribution models are built using varying ranges of environmental variables and applied to broader spatial extents. Third, I examine the potential for, and limitations of model transferability between native and non-native regions. Finally, I use two different modelling approaches and three different climate change and land use change scenarios to predict future mute swan habitat suitability. The results indicate that (1) models with better predictive accuracy include environmental variables from multiple ecologically-meaningful scales and measured at spatial extents that include a broad range of environmental variable values; (2) models can exhibit asymmetrical transferability; (3) climate change will facilitate mute swan range expansion in the future more than land use change; and (4) mute swans are often found near urban waterbodies. When modelling invasive species distributions, I suggest that ecologists consider: (I) spatial scale of the underlying landscape processes and species’ use of the landscape; (II) variability and range of each environmental variable used for building models; and (III) stage of establishment of the invasive species.

No description available.

Land use and cover change (LUCC) is increasingly recognised as one of the most visible impacts of humans on nature. In rural areas, most of the observed LUCC is associated with agricultural activities. This has traditionally been attributed to the interplay of the socio-economic and political milieu, and the opportunities and constraints arising from the climatic conditions and physical attributes of land. Although there is no doubt that these factors influence farmer decisions, the mosaic of farming systems suggests that farmers do not always behave uniformly, even in areas with comparable socio-economic and environmental conditions. While the multi-facetted and varying nature of farmer decision-making is considered to be established knowledge in rural sociology, it is often neglected in LUCC models that typically describe it as homogeneous and rational in economic terms. This thesis presents an application of mixed-method social survey which aims at improving the representation of the diversity and complexity of farmer decision-making process in LUCC models. Different data collection methods (in-depth, semi-structured interviews, questionnaire) and analyses (thematic analysis, principal components analysis, cluster analysis, choice-based conjoint analysis) were used complementarily to identify the factors that facilitate or constrain farmer participation in environmental management practices (a), to identify the dominant farmer profiles (b) and to assess farmer preferences that influence land use decisions (c). Data collection was conducted in a study area located in the Canton of Aargau, Switzerland, where there is limited knowledge about farmer decision-making drivers and actions. Research findings were used to empirically inform an agent-based model that simulates farmer decisions. Paremeterised storylines were used to explore farmer decisions in alternative futures. An advanced and context-specific representation of human agents in modeling frameworks can make LUCC models valuable tools both for landscape analysis and policy making. In the face of new policy reforms, this thesis contributes to the achievement of this objective, by presenting an approach to explore and organize the heterogeneity of farmer behaviour and to make this usable in agent-based modeling frameworks.

The unusual environmental conditions within caves provided unique opportunities for developing an understanding of ecosystem processes. However, relatively few studies have been conducted on the ecology of New Zealand cave systems. The primary aim of this research was to investigate changes in aquatic invertebrate communities along a longitudinal gradient from the surface into caves and investigate the fundamental drivers of cave communities. This study was carried out in three streams (two in pasture catchments and one in a forested catchment) flowing into caves in the Waitomo region, North Island, New Zealand. In order to address these aims I carried out a longitudinal survey of 12 sites in each stream, an experimental manipulation of food, and an isotopic study of a single stream. The longitudinal survey of the three cave streams revealed light intensity as well as algal and CPOM biomass all decreased significantly from outside the caves into caves. In contrast, water temperature, dissolved oxygen, stream width, depth, and velocity did not vary significantly with distance into caves. Benthic aquatic macroinvertebrate communities within the caves were a depauperate subset of surface communities, appearing to be structured by gradients in resources and colonisation through drift. However, some invertebrate taxa (primarily predators) were rarely found within caves, further suggesting that resource gradients were structuring cave communities. Surprisingly, the densities of some collector-browsers (primarily mayflies) increased within cave streams relative to surface densities. This may be due to a decrease in competition and predation, flexible feeding strategies, and high drift propensity. However, the benthic densities of most taxa within the caves appeared to be related to drift densities. Although surface forest and pastoral stream communities differed in community composition and density 32 meters within the caves invertebrate community diversity and density became similar, although specific taxa within communities varied. This convergence was attributed to similar environmental gradients within the caves. The resource addition experiment (adding leaf packs) indicated that cave streams were resource limited; the addition of leaves produced communities of similar richness and density across the environmental gradient. The isotopic survey suggested cave stream invertebrate communities were reliant upon similar basal resources to surface streams. However, within the cave epilithon appeared to be increasingly important while filamentous algae were absent. Cave aquatic invertebrates were also found to support terrestrial predators (spiders, harvestmen, and glow-worms), presumably increasing the abundance and diversity of terrestrial cave communities. In conclusion, aquatic cave communities were reliant upon surface derived resources and consequently strongly linked to surface land-use and managerial practices.

The tropical montane forest of Ecuador is one of the ‘hot spots’ of species diversity. Despite this great species diversity, there are forests in our study area, namely in the Zamora-Chinchipe province in southern Ecuador, which are being depleted at an alarming rate. For example, large areas are being permanently deforested for use as ‘pastureland ’. This development is typically characterized by intensive slash and burn activities for vegetation clearance. After clear cut and slash burning, pasture species are planted of which Setaria sphacelata and Melinis minutiflora, are the most common. However, forest clearing by slash burn for pasture production occurs in the region simultaneously with subsequent invasion of bracken fern (Pteridium arachnoideum) and re-colonization of secondary succession vegetation on abandoned pasture land. In this study, we will examine the effects that the above phenomena have on ecosystems, namely the effects associated with the conversion of natural forestland to pasture land, and the succession that occurs as a result. We will also examine how land use change affects the nutrient status of the soil. This study focuses specifically on the area called the ‘San Francisco Valley’, (3°58’ 30”S latitude, 79°4’ 25”W longitude), which lies between Loja and the Zamora-Chinchipe provinces in Ecuador. Field work for this study was carried out at 1,798 and 2,226 m a.s.l in the following sites: 1) the San Francisco Natural Forest (this area refers to the eastern part of Podocarpus National Park); 2) active pastures Type I (this area refers to the pastureland in front of the San Francisco Scientific Station ECSF, and are pastures that have existed for 50 years or more); 3) active pastures Type II (this area refers to the pastureland in Sabanilla sites, and are pastures that have existed for approximately 17 years); and 4) abandoned pastureland (affected by succession over a period of at least twenty years). Each land-use type consists of five plots of approximately 20 x 20m2. Five points in each plot were then chosen and later sampled (two sub-samples) according to the defined horizons and depth units, namely the organic layer and mineral top soil horizons. Organic layer (only on forest and succession sampling plots) were designated as LOf1, Of2/Oh1 and mineral top soil was sampled to a depth of a 0-10, 10-20, 20-30 cm. To quantify the effects of the impact that land use change has on the chemical characteristics of soil in the selected areas, we analyzed the following bio-elements: the pH value, soil organic carbon (SOC), the total nitrogen (TN), the effective cation exchange capacity (ECEC), as well as stocks of total and available macronutrients. In addition, we examined the biological characteristics such as carbon and nitrogen microbial biomass (MBC, MBN), basal respiration (BR), and nitrogen mineralization (Nmin) in organic layers and top mineral soils (0-30 cm) of the following: the San Francisco Natural Forest, ECSF pastureland, Sabanilla pastureland, and abandoned pastures affected by succession. The main results of this study can be summarised as follows: The soil pH value increased after forest-to-pasture conversion and tended to decrease with soil depth. Moreover, pastureland in the study that was fifty years or more, showed evidence of a decrease in pH values. This decrease in pH value of the soil can be attributed to the reduction in exchangeable cations . However, they still remained higher than the pH values for the forest sites in the study. After the abandonment of pastureland, we observed a re-acidification in the soil of succession sites. This resulted in a decrease of base saturation . On the other hand, the total exchangeable base cation stocks were significantly higher for pasture soils compared with forest and succession soils. This was because of the addition of basic cations by ‘slash and burn activity ’. In this study, we observed that the greater values of soil organic carbon stocks occurred in forest sites. This can be explained by their high SOC value in the organic layer (73.9 Mg ha-1). However, the mineral layer (0 to 30 cm depth) of forest had a lower value than pasture and succession sites. This higher SOC stock of the mineral layer of our pasture sites are partly a result of carbon input from the former standing biomass. Likewise, in the mineral layers, we found that MBC content increases in a similar way to the SOC content. For example, when we compared the MBC content of forests with the pasture sites, we observed that pastures had approximately three times as much MBC. The results of nitrogen stored in the Microbial Biomass (MBN) showed the same tendency as the MBC values. Moreover, for organic layers, the total nitrogen stocks of forest were higher compared to succession sites. On the other hand, for mineral soil (0 to 30 cm depth), nitrogen stocks increased after forest to pasture conversion. This increase is partly due to the burning of aboveground biomass and the subsequent death of roots. Furthermore, the values of nitrogen stocks decreased again in succession sites (4.2 Mg N. ha-1), with similar values those of forests (4.4 Mg N. ha-1 ). Our results show that the slash-and-burn practice leads to a significant increase of P stock. We found that stocks of total phosphorus were significantly higher in the mineral topsoil (0–30 cm) of 50 year-old pastures (ECSF) than in the 17 year-old pastures (Sabanilla). It is important to note that the P stocks in the mineral soil of the abandoned pasture (20 year-old pasture sites) tend to return to forest values (399.9. Kg.ha-1). Nevertheless, the results show very low values of available P on both pastures and succession sites compared with forest sites. In the organic layers, our results show significant differences in the values of basal respiration between forest and succession sites. This indicates that the level of CO2 was greater in the selected forestland due to an increase of organic material. This essentially means that there was an increase of micro-organisms in the soil and subsequently an improved nutrient cycle . For the mineral soil, however, the results only showed a significant difference of 0-10 cm depth in the ECSF pastures and forests. In our study, we did not find any significant differences in the net nitrogen mineralization values in the four studied areas. Nevertheless, the results show that net nitrogen mineralization values decrease systematically according to the depth of the land uses. Summarizing, after the conversion of forest to pasture, there was an increase of the value of bio-elements in the mineral layers at both pasture sites. However, this increase was higher in 50 year old pastures (ECSF) than in the 17 year old pastures (Sabanilla). In addition, we noticed that after 20 years of the abandonment of pastures, most measured soil properties returned to the old-growth forest levels. / El bosque montano tropical de Ecuador es uno de los \"puntos calientes\" de diversidad de especies. Pero el bosque primario en el área de investigación (la provincia de Zamora Chinchipe al Sur de Ecuador) se está perdiendo a un ritmo alarmante. Grandes áreas están siendo permanentemente deforestadas para su uso como tierras de pastoreo. Este proceso se caracteriza por el uso intensivo de fuego para desmonte de la vegetación. Después de la quema y roza, se plantan especies de pastos entre las que Setaria sphacelata y Melinis minutiflora son las más comunes. Sin embargo, la quema y tala del bosque para la conversión a zonas de pastos ocurre simultáneamente con la subsecuente invasión del helecho común (Pteridium arachnoideum), produciéndose. La difusión de esta maleza y la decreciente productividad de los pastos (especialmente Setaria spacelata y Melinis minutiflora) conducen a que las tierras se utilizan en pastoreo hasta que la tierra se agota de nutrientes y luego se abandonan. En este estudio, se examinan los efectos que los fenómenos anteriormente mencionados tienen sobre los ecosistemas; a saber, los efectos asociados a la conversión de bosques naturales en tierras de pastoreo y la posterior sucesión de los pastizales; además de cómo el cambio de uso del suelo afecta el estado nutricional de los suelos del sur del Ecuador. El estudio se sitúa en la zona del valle de San Francisco (3°58’ 30”S latitud, 79°4’ 25”W longitud), entre Loja y Zamora Chinchipe, provincias que se encuentran en el sur de Ecuador. El trabajo de campo se llevó a cabo a una altura entre 1,798 y 2,226 m s.n.m.; en: 1) las áreas de bosque natural San Francisco (esta área se refiere a la parte oriental del Parque Nacional Podocarpus); 2) pasto activos Tipo I (esta área se refiere a los pastos en frente de la Estación Científica San Francisco ECSF, y son pastizales que tienen más de 50 años de edad); 3) pastos activos Tipo II (esta área se refiere a los pastos en los sitios de Sabanilla, y son pastizales que existen desde hace aproximadamente 17 años); y 4) pastos abandonados bajo vegetación de sucesión (más de 20 años de edad). Cada tipo de uso de la tierra consistió en cinco parcelas de aproximadamente 20 x 20 m2; se eligieron cinco puntos en cada parcela y se tomaron muestras (dos sub-muestras) de acuerdo con los horizontes orgánico y mineral. Las capas Orgánicas (solo presentes en el bosque y en los sitios de sucesión) se identificaron como LOf1, Of2/Oh1 y las capas minerales se muestrearon hasta los 0-30 cm de profundidad del suelo. Para cuantificar los efectos del impacto del cambio del uso de la tierra en las características químicas del suelo, se analizó los siguientes bio-elementos: pH, carbono orgánico del suelo (COS), nitrógeno total (Nt), la capacidad de intercambio catiónico efectiva (CICE), así como las reservas del contenido total y disponibilidad de los macro nutrientes. Además, las características biológicas, tales como el carbón (MBC) y nitrógeno (MBN) de la biomasa microbiana, la respiración basal (Rb) y la mineralización de nitrógeno (Nmin) en las capas orgánicas y en la capa mineral del suelo (hasta -30 cm) de los bosques naturales, pastos y pastizales abandonados bajo vegetación de sucesión. Los principales resultados del estudio se describen a continuación: El valor de pH del suelo indica una elevada acidez, después de la conversión de bosque a pastos y tiene una tendencia general a disminuir con la profundidad del suelo, cuando los pastos se hacen más viejos (más de 50 años de edad); los valores de pH del suelo disminuye como consecuencia de la lixiviación de cationes intercambiables, pero siguen siendo superiores a los valores de pH de los sitios del bosque. Tras el abandono de los pastos se observó una re-acidificación en el suelo de los sitios de sucesión, lo que resulta en una disminución de la saturación de bases. Los resultados además indican que las capas orgánicas, especialmente en los suelos de los bosques, almacenan una cantidad importante de potasio, calcio y magnesio. Sin embargo, las reservas totales de cationes básicos intercambiables fueron significativamente mayores en los suelos de los pastizales que en los bosques y que los suelos de sucesión, debido a la adición de cationes básicos producidos por la tala y quema usada en la conversión de bosques a pastizales. En este estudio, se encontró que los mayores valores de reservas de COS se producen en zonas forestales, que se corresponde con un alto valor en la capa orgánica (73,9 Mg C ha-1). Sin embargo, la capa mineral (hasta - 30 cm de profundidad) de los suelos del bosque tiene un valor menor en comparación con los valores de los pastos y sucesión. Este alto contenido de COS en los pastos, se debe en parte al ingreso de carbono desde la biomasa. Asimismo, en las capas minerales, se encontró que el contenido de carbono en biomasa microbiana (CBM) aumenta de una manera similar al contenido de carbono orgánico del suelo (COS). Por ejemplo, cuando comparamos el contenido de CBM de los bosques con los sitios de pastoreo, se observó que los pastos tenían aproximadamente tres veces más MBC. El resultado de nitrógeno almacenado en la biomasa microbiana (NBM) mostró la misma tendencia que los valores de CBM. En las capas orgánicas, las reservas totales de nitrógeno de los bosques fueron mayores en comparación con los sitios de sucesión. Por otro lado, en el suelo mineral (hasta -30 cm de profundidad) las reservas de nitrógeno aumentan después de la conversión de bosques a pastizales. Este incremento es parte debido a la quema de la biomasa superior y de la subsecuente muerte de las raíces. Además, los valores de las reservas de nitrógeno disminuyen de nuevo en los sitios de sucesión (4.2 Mg N. ha-1), a valores similares a las del bosque (4.4 Mg N. ha-1 ). Nuestros resultados muestran que las prácticas de quema y tala incrementan significativamente las reservas de fosforo, encontramos que las reservas de fosforo total fueron significativamente altas en las capas minerales (- 30 cm) de los pastos de 50 años (ECSF), seguido de los pastos de 17 años de edad (Sabanilla). Es importante notar que las reservas de fosforo en las capas minerales de los suelos de pastos abandonados (20 años de edad) tienden a retornar a los valores del bosque (399.9. Kg.ha-1). Sin embargo, los resultados muestran valores muy bajos de fosforo disponible en ambos sitios de pastos y sucesión comparado con el bosque. En las capas orgánicas, los resultados revelan diferencias significativas en los valores de la respiración basal (potencial) entre el bosque y la sucesión. Esto indica que el nivel de CO2 fue mayor en el los sitios de bosque debido a un aumento de la materia orgánica. Esto implica un aumento de los microorganismos en el suelo y, posteriormente, una mejora en el ciclo de nutrientes. En el suelo mineral, los resultados sólo muestran una diferencia significativa en la profundidad de 0-10 cm entre los pastos ECSF con los bosques. En nuestro estudio, no se encontró diferencias significativas en los valores de mineralización neta de nitrógeno entre las cuatro áreas estudiadas. Sin embargo, los resultados muestran que los valores netos de mineralización del nitrógeno disminuyen sistemáticamente con la profundidad en todos los usos de los suelos estudiados. En resumen, después de la conversión de bosques en pastizales, se produjo un incremento del valor de los bio-elementos en las capas minerales de ambos sitios de pastoreo. Sin embargo, este aumento fue mayor en los pastos de 50 años de edad (ECSF) que en los pastos de 17 años de edad (Sabanilla). Además, los resultados muestras que después de 20 años del abandono de los pastos, la mayoría de los parámetros medidos retornan a valores similares a los de los sitios de bosque. / Im globalen Kontext stellt der tropische Bergregenwald in Süd-Ecuador ein „Hotspot“ der Biodiversität dar. Im Untersuchungsgebiet ist die enorme Artenvielfalt durch die massive Zerstörung der natürlichen Waldökosysteme gefährdet. Der Wald wird durch intensive Brandrodung großflächig in Weideland umgewandelt. Im Laufe der Weidenutzung kommt es auf den Weideflächen zu einer zunehmenden Ausbreitung und Dominanz des tropischen Adlerfarns (Pteridium arachnoideum). Die Farnausbreitung und die abnehmende Produktivität der Weidegräser insbesondere von Setaria sphacelata und Melinis minutiflora, führt zum Verlassen der Weiden und zur Etablierung neuer Weideflächen durch fortgesetzte Brandrodung des Naturwaldes. Aufgelassene ehemalige Weideflächen unterliegen einer sekundären Sukzession. Innerhalb dieser Studie wurden die Effekte der Umwandlung des Naturwaldes in Weideland, der Weidenutzung sowie der Wirkungen der sekundären Sukzession nach dem Verlassen unproduktiver Weideflächen auf die Nährstoffsituation der Böden untersucht. Die Untersuchung erfolgte im Gebiet des „San Francisco Tales“, (3°58’ 30”S, 79°4’ 25”W), welches sich zwischen den beiden Provinzen Loja und Zamora-Chinchipe in Ecuador befindet. Feldarbeiten innerhalb dieser Studie wurden in einer Höhe zwischen 1798 und 2225 m NN in den folgenden Bereichen ausgeführt: 1) Naturwald in San Francisco; 2) aktive Weidefläche Typ I (seit circa 50 Jahren in Nutzung); 3) aktive Weidefläche Typ II (seit circa 17 Jahren in Nutzung); und 4) verlassenes Weideland (bestimmt durch sekundäre Sukzession seit mindestens 20 Jahren). Jeder Landnutzungstyp besteht aus fünf Plots mit einer Ausdehnung von circa 20 x 20 m. Fünf Punkte innerhalb eines jeden Plots wurden zur Beprobung ausgewählt. Die organische Auflage (Naturwald, verlassenes Weideland) wurde nach Auflagehorizonten (LOf1 und Of2/Oh) und der Mineralboden nach Tiefenstufen (0-10 cm, 10-20 und 20-30 cm) getrennt beprobt. Um die Effekte und den Einfluss des Landnutzungswandels auf chemische Bodenkennwerte zu quantifizieren, wurden die folgenden Indikatoren untersucht: pH, organischer Kohlenstoffgehalt des Bodens (SOC), Gesamtstickstoff (TN), effektive Kationenaustauschkapazität (CECeff) sowie Vorräte der gesamten und pflanzenverfügbaren Makronährelemente. Zusätzlich wurden bodenbiologische Indikatoren wie Kohlenstoff und Stickstoff der mikrobiellen Biomasse (MBC, MBN), Basalatmung (BR) und Stickstoffmineralisation (Nmin) in den organischen Auflagehorizonten und dem mineralischen Oberboden (0-30 cm) wie folgt untersucht: Naturwald in San Francisco, ECSF Weideflächen, Sabanilla Weideflächen und aufgelassene, von der Sukzession beeinflusste Weiden. Die hauptsächlichen Resultate der Untersuchung können wie folgt zusammengefasst werden: Der pH-Wert des Bodens erhöhte sich nach der Umwandlung von Wald zu Weide und zeigt mit zunehmender Tiefe einen abnehmenden Trend. Darüber hinaus nahmen die pH-Werte von der 17 Jahre alten zur 50 Jahre alten Weide ab. Diese Abnahme kann auf den Rückgang austauschbarer Kationen zurückgeführt werden. Dennoch verblieb der pH-Wert in den 50 Jahre alten Weiden oberhalb des pH-Wertes der im Wald beprobten Flächen. Nach dem Auflassen der Weiden wurde eine erneute Versauerung des Bodens im Stadium der Sukzession beobachtet. Dieser pH-Rückgang wird durch einen Abnahme der Basensättigung begleitet. Auf der anderen Seite waren die Vorräte an austauschbaren Basen der CECeff auf den Weideflächen signifikant über denen der Wald- und Sukzessionsflächen. Ursächlich dafür war die Freisetzung basischer Kationen während der Brandrodung des Naturwaldes. Innerhalb dieser Studie wurden die höchsten Vorräte an Bodenkohlenstoff im Naturwald ermittelt. Das kann durch hohe Vorräte an SOC in der organischen Auflage (73.9 Mg ha-1) erklärt werden. Allerdings waren die Vorräte im Mineralboden (0-30 cm) des Waldes geringer als auf den Weide- und Sukzessionsflächen. Diese höheren SOC-Vorräte im Mineralboden der Weideflächen sind teilweise das Resultat der höheren Kohlenstoffzufuhr durch Reste der oberirdischen Biomasse. Der Gehalt an mikrobiellem Biomassekohlenstoff nahm in ähnlicher Art und Weise wie der des bodenbürtigen organischen Kohlenstoffs zu. Beispielsweise wurde beim Vergleich von MBC und MBN-Gehalten des Waldes mit denen der Weide der dreifache Gehalt in der Weide gefunden. Außerdem waren die Stickstoffvorräte der organischen Auflagen im Wald höher als auf den Sukzessionsflächen. Andererseits nahmen die Stickstoffvorräte nach der Umwandlung von Wald zu Weide im Mineralboden (0-30 cm) zu. Diese Zunahme beruht zum Teil auf dem Abbrennen der oberirdischen Biomasse und dem anschließenden Absterben der Wurzeln. Des Weiteren verringerten sich die Stickstoffvorräte im Stadium der Sukzession (4.2 Mg N ha-1) und glichen sich wieder denen des Waldes (4.4 Mg N ha-1) an. Die Resultate zeigen, dass die Brandrodung zu einem signifikanten Anstieg der Phosphorvorräte führte. Vorräte des Gesamtphosphors waren in den mineralischen Oberböden (0-30 cm) der 50 Jahre alten Weide, gefolgt von der 17 Jahre alten Weide signifikant am höchsten. Zu betonen ist, dass die P-Vorräte im Mineralboden der aufgelassenen Weide dazu tendieren auf Werte des Waldes abzusinken (399.9 kg ha-1). Trotzdem zeigten die Ergebnisse sehr geringe Werte für pflanzenverfügbaren Phosphor in Weide und Sukzession im Vergleich zum Wald. In den organischen Auflagehorizonten wurden signifikante Unterschiede in der mikrobiellen Aktivität (Basalatmung) zwischen Wald und Weide gefunden. Das zeigt, dass das Niveau an C-Mineralisierung in der ausgewählten Waldfläche größer ist, was auf die erhöhte Verfügbarkeit der organischen Substanz zurückgeführt werden kann. Das bedeutet im Wesentlichen einen Anstieg der Mikroorganismen in den Böden und darauffolgend einen verbesserten Nährstoffkreislauf. Für den Mineralboden zeigten die Ergebnisse jedoch nur einen signifikanten Unterschied in einer Tiefe von 0-10 cm zwischen Wald und Weide. Signifikante Unterschiede in der Nettostickstoffmineralisation der vier untersuchten Gebiete konnten nicht gefunden werden. Nichtsdestotrotz zeigten die Ergebnisse, dass die Nettostickstoffmineralisation mit zunehmender Tiefe in den unterschiedlichen Landnutzungen abnimmt. Zusammenfassend kann festgestellt werden, dass nach der Brandrodung die Gehalte an Bioelementen im Mineralboden beider Weideflächen zunahmen. Dieser Anstieg war in den 50 Jahre alten Weideflächen (ECSF) sogar ausgeprägter als in den 17 Jahre alten Weideflächen (Sabanilla). Zusätzlich zeigte sich in den 20 Jahre alten Sukzessionsflächen, dass durch die Regeneration einer organischen Auflage ein positiver Effekt hinsichtlich erhöhter Vorräte an SOC und pflanzenverfügbarem Phosphor festgestellt werden konnte. Diese allmähliche Zunahme an Nährstoffen im Boden der Sukzession setzte sich fort, bis das Ausgangsniveau des Waldes wieder erreicht war.

<p>In this dissertation, I explored the effects of vegetation type on ecosystem services, focusing on services with significant potential to mitigate global environmental challenges: carbon sequestration and groundwater recharge. I analyzed >600 estimates of groundwater recharge to obtain the first global combined analysis of groundwater recharge and vegetation type. Using a regression model, I found that vegetation was the second best predictor of recharge after precipitation. Recharge rates were lowest under forests, intermediate in grasslands, and highest under croplands. The differences between vegetation types were higher in more humid climates and sandy soils but proportionately, the differences between vegetation types were higher in more arid climates and clayey soils. My extensive field estimates of recharge under paired vegetation types in central Argentina and southwestern United States provided a more direct test of the relationships between vegetation and recharge. The field data confirmed the strong influences of vegetation and its interactions with abiotic factors on recharge observed in the synthesis. The results indicate that vegetation shifts have a proportionately larger potential to affect recharge in more arid climates and clayey soils.</p><p>At the same study systems, I compared my field estimates of recharge to organic carbon stocks (in biomass, litter and soil) under the different vegetation types to evaluate tradeoffs between carbon sequestration and groundwater recharge as affected by vegetation shifts. To determine net values of vegetation shifts, I combined the changes in carbon and water with reported economic values of the ecosystem services. Based on physiological tradeoffs between photosynthesis and transpiration in plants, I hypothesized that vegetation promoting carbon storage would reduce recharge and vice versa. Changes in water and carbon services were inversely proportional, with rain-fed cultivation increasing groundwater recharge but decreasing carbon storage compared to the grasslands they replaced whereas woody encroachment did the opposite. In contrast, cultivated plots irrigated with ground water decreased both ecosystem services. Higher precipitation and clay content both exacerbated changes in carbon storage with grassland conversions, whereas higher precipitation accentuated, but higher clay content diminished, those in recharge. Regardless of the nature of vegetation shift, most of the net values of grassland conversions were negative, with the shifts representing increasing costs in the following order: woody encroachment, rain-fed cultivation and irrigated cultivation. Values of changes in carbon were greater in magnitude than those of recharge, indicating that establishment of carbon markets may drive land-use changes in grasslands over water markets.</p><p>Lastly, I examined the effects of changes in subsurface hydrology resulting from grassland conversion to croplands on soil inorganic carbon stocks in the same U.S. study system. I observed significantly lower inorganic carbon stocks under both rain-fed and irrigated croplands compared to the grasslands they replaced. The losses were visible to past 6 m depth in the soil profile and were uncharacteristically rapid for the carbon pool that is considered to be relatively inert. Based on the negative relationship between the inorganic carbon stocks and recharge rates and higher estimated exports of bicarbonates in recharge under croplands, I concluded that increased recharge with cultivation resulted in dissolution and leaching of grassland soil carbonates. Ecosystem services and their relationships to biotic and abiotic factors quantified here will further our understanding of the tradeoffs and interactions between the two services through vegetation shifts.</p> / Dissertation

Afforestation and stand development can significantly affect soil respiration and net ecosystem productivity (NEP). I studied 1) the effects of afforestation on NEP by comparing cropland previously planted to barley (on a barley-barley-alfalfa-alfalfa-alfalfa rotation) and that converted to a hybrid poplar (Populus deltoides Populus petrowskyana var. Walker) plantation and 2) the NEP along a chronosequence of stands aged 5-, 8-, 14-, and 16-year old in 2009 in central Alberta, Canada. Soil respiration and NEP decreased in the first two to three years after afforestation, while both generally increased with stand development. The ecosys model was used to simulate carbon dynamics in the plantations over a 20-year rotation under contrasting soil conditions. Soil conditions of the 14-year-old plantation accumulated the greatest amount of ecosystem carbon over the whole rotation. The research indicated that plantations could be a net carbon source in the first few years after afforestation and then became a net carbon sink, helping to mitigate net CO2 emissions for the remainder of the rotation. / Soil Science

This dissertation investigates three economic aspects of the climate change issue: optimal allocation of investment between adaptation and mitigation, impacts on a ground water dependent regional agricultural economy and effects on global food insecurity. This is done in three essays by applying mathematical programming. In the first essay, a modeling study is done on optimal temporal investment between climate change adaptation and mitigation considering their relative contributions to damage reduction and diversion of funds from consumption and other investments. To conduct this research, we extend the widely used Integrated Assessment Model?DICE (Dynamic Integrated Climate Economy) adding improved adaptation modeling. The model results suggest that the joint implementation of adaptation and mitigation is welfare improving with a greater immediate role for adaptation. In the second essay, the research focuses on the ground water dependent agricultural economy in the Texas High Plains Region. A regionally detailed dynamic land allocation model is developed and applied for studying interrelationships between limited natural resources (e.g. land and groundwater), climate change, bioenergy demands and agricultural production. We find out that the effect varies regionally across hydrologically heterogeneous regions. Also, water availability has a substantial impact on feedstock mix. In terms of biofuel feedstock production, the model results show that limited water resource cannot sustain expanded corn-based ethanol production in the future. In the third essay, a Computable General Equilibrium (CGE) model is applied in an attempt to study potential impacts of climate change on global food insecurity. Our results show that climate change alters the number of food insecure people in a regionally different fashion over time. In general, the largest increase of additional food insecure population relative to the reference case (no climate change) is found in Africa and South Asia, while most of developed countries will benefit from climate change with a reduced proportion of food insecure population. In general, climate change affects world agricultural production and food security. Integrated adaptation and mitigation strategy is more effective in reducing climate change damages. However, there are synergies/trade-offs between these two options, particularly in regions with limited natural resources.

The economic impacts of a government-funded, forest-based sequestration program were analyzed under two different payment schemes. The impacts were obtained by developing a regional, static CGE model built to accommodate a modified IMPLAN SAM for a determined region in the United States for 2008. The IMPLAN SAM was modified to accommodate the more conventional factors of production (labor, capital and land) and to account for land heterogeneity using the Major Land Resource Areas (MLRA). The regional aggregation considered included the Southern, Northeastern, Southwestern and Midwestern regions. The two policy scenarios considered consisted of two CO2-offset payment schemes: 1) the government compensates the generation of CO2-offsets only by the land converted to a carbon graveyard and 2) the government additionally compensates the CO2 offsets generated as a by-product by the existing commercial logging activity. By doing an analysis of the model with different budget magnitudes under the two scenarios, two different CO2-offset supply schedules were obtained with their respective CO2-offset price and quantity sets. For a budget allocation of $6.9 billion, approximately 1 billion metric tons of CO2 offsets (15% of U.S. 2008 total GHG emissions) were produced in the first scenario versus 0.8 billion metric tons (11% of U.S. 2008 GHG net emissions) in the second one. Fifty million acres were diverted out of agriculture and commercial forestry land to the carbon graveyard mainly in the Northern, Western and Central Great Plains in the first scenario. Twenty two million acres were diverted out of agricultural land to the carbon graveyard and commercial logging mainly in the Northern and Western Great Plains; and the Eastern and Western boundaries of the Appalachian Mountains in the second scenario. Both scenarios resulted in higher land and agricultural commodity prices, lower consumption of agricultural commodities by households, lower agricultural exports and higher imports. The payment structure of the second scenario benefited the commercial logging industry, increasing its production and exports, and decreasing its imports. The non-agricultural sectors mostly impacted by the two policy scenarios were the manufacturing, construction and government employment sectors.

Compreender o que impulsiona, catalisa ou impede a mudança de uso da terra na fronteira agrícola brasileira é uma condição para o desenho efetivo de políticas locais, o que por sua vez pode ter implicações para a produção de alimentos, a conservação ambiental e as emissões de gases de efeito estufa em todo o mundo. Analisou-se o processo de expansão agrícola em Mato Grosso, o maior produtor agrícola do País, mapeando e quantificando a incorporação de novas áreas de cultivo e a conversão das existentes em campos mecanizados de soja no nível de fazenda. Através de modelagem estatística, também se investigou a influência de variáveis econômicas, agronômicas e logísticas fundamentais nesse processo, considerando as recentes mudanças na legislação ambiental brasileira. Constatou-se que a área convertida para a produção de soja aumentou quase 1,5 milhão de hectares entre 2009 e 2013, porém mais de 70% ocorreram em fazendas que já possuíam soja em anos anteriores. Comparando o poder explicativo de oito modelos de regressão envolvendo diferentes grupos de variáveis, verificou-se que a expansão da soja está fortemente associada à própria presença de soja, bem como de armazéns dentro da distância de 50 a 100 quilômetros. De acordo com o modelo com os melhores resultados, a ampliação da soja também tem probabilidade de ocorrer em áreas de alto valor de conservação natural. Finalmente, a sensibilidade da expansão da soja aos preços correntes do período indicou que ainda há um grande potencial de crescimento agrícola em Mato Grosso, aumentando a importância estratégica de investimentos logísticos inteligentes que promovam o desenvolvimento regional aliado à proteção ambiental. / Understanding what drives, catalyzes or constraints land use change in the Brazilian agricultural frontier is a condition for effective policy design at the local level, which in turn might have implications for food production, environmental conservation and GHG emissions worldwide. We analyzed the process of agricultural expansion in the state of Mato Grosso, the country’s largest agricultural producer, by mapping and quantifying the incorporation of new farming areas and the conversion of existing ones into mechanized soybean fields at the farm-level. Through statistical modeling, we also investigated the influence of key economic, biophysical, environmental and logistics variables on this process while accounting for recent changes in the Brazilian environmental legislation. We found that the area converted to soybean production increased almost 1,5 million hectares between 2009 and 2013, but more than 70% of which in farms that already had some soybean in previous years. By comparing the explanatory power of eight regression models involving different groups of variables, we found that soy expansion is strongly associated with the presence of soybean fields and warehouses within a distance between 50 and 100 kilometers. According to the model with the largest explanatory results, soy expansion is likely to occur also in areas of high conservation value. Finally, the sensitivity of soy expansion to soy prices indicated the potential for further agricultural growth in Mato Grosso while highlighting how crucial smart logistics investments that promote regional development combined with environmental protection.