No description available.

Eddy-covariance (EC) CO₂ flux data were analysed and annual carbon (C) balances estimated for a four-year period (2004-2007) following clearcut harvesting of a boreal jack pine stand in northern Saskatchewan. The site was a source of C to the atmosphere for all years, with annual net ecosystem productivity (NEP) increasing from -153 g C m⁻² yr⁻¹ in 2004 to -63 g C m⁻² yr⁻¹ in 2007. This increase was mainly due to gross primary productivity (GPP) increasing significantly from 78 to 200 g C m⁻² yr⁻¹ , while ecosystem respiration (R) increased only slightly from 231 to 263 g C m⁻² yr⁻¹ over the same period. In the 2006 growing season (GS), a field campaign was conducted to investigate the relationships between monthly destructive measurements of leaf area index (LAI) and daily measurements of the normalized difference vegetation index (NDVI) and photosynthetic capacity (Amax). The latter was derived from 5-day, 16-day, 30-day and annual Michaelis-Menten light response analyses using daytime measurements of NEP and incident photosynthetically active radiation. Digital-camera data were used to evaluate the potential of using the rectilinear-lens vegetation index (RLVI) as a surrogate for NDVI of a young forest stand. Results showed that LAI was linearly related to NDVI and RLVI, which was largely the result of changes in the deciduous vegetation component across the GS. These results indicate that RLVI could be used as a surrogate for NDVI up to a GS maximum LAI of 0.91 m2 m⁻² observed in 2006. Measured mean (± 1 S.D.) GS LAI was 0.67 (± 0.24) m² m⁻² in 2006. LAI accounted for the majority of the variability in Amax at the 30-day time scale, while at shorter time scales air temperature was the dominant control. For 2004 to 2007, mean spring estimates of LAI were 0.25, 0.29, 0.38 (compared to 0.40 m² m⁻² from measurements) and 0.41 m² m⁻², respectively. Results suggest that a steady increase in the jack pine LAI component accounted for the annual increases in GPP and hence NEP over the four years.

Climate change will pose increasing challenges to forest managers working to achieve sustainable forest management in the boreal forest. A logical starting point for climate change adaptation is to proactively identify management practices and policies that have a higher likelihood of achieving management objectives across a wide range of potential climate futures. This research implemented an approach to identifying such measures by tapping into the experiential knowledge base of local forest practitioners. The assessment was organized according to a structured decision-making (SDM) approach. Northern forest practitioners consider the goals of climate change adaptation to be synonymous with those of sustainable forest management indicating that the criteria for the conservation and sustainable management of boreal forests as defined by the Montréal Process are suitable objectives against which the performance of alternative adaptation options can be assessed. The case study area for this research was the Champagne and Aishihik Traditional Territory of southwest Yukon where a climatically-driven, large-scale spruce bark beetle disturbance has been driving forest management planning yet climate change considerations have not been directly addressed in the planning process. Twenty-four adaptation options were identified as being important to implement in forest development areas to achieve regional goals and objectives of forest management across three scenarios of climate change. In addition, the performance of alternative strategies to re-establish forests was assessed. Results indicate that the applicability of alternative forest renewal adaptation strategies is strongly related to the objectives of forest management which differed across the forest management planning area. However, since none of the strategies were judged to perform highly across any of the scenarios of climate change, additional work is needed to explore whether a threshold of acceptability can be met even with the adoption of adjustments to forest management policies and practices. If not, management objectives themselves may need to be revised. An extensive list of research and monitoring needs were also identified, an indication that climate change is providing the imperative for a more comprehensive research and monitoring program to support the sustainable management of forest resources in this region. The next steps in a SDM approach are to implement adaptation options and strategies deemed appropriate and to monitor their performance in achieving management objectives within an adaptive management context.

Current forest management in boreal northeastern Ontario results in young, even-aged forests; however, fire history research has found old stands with multiple cohorts of trees are common, supporting the value of Multi-cohort Management. I investigated relationships between insect communities and stand live-tree diameter distribution, cohort class and structure. Results showed that variation in abundances of Carabidae, Diapriidae, Diptera and Hymenoptera were not strongly predicted by cohort class. The concept showed greater strength when parameters of live-tree diameter distributions were used. Forest structure, not age, was important for all communities, including heterogeneity of understory and/or overstory vegetation. Trap height was a strong predictor of aerial insect community structure, with insect abundance higher in the understory than in the canopy. In summary, a more diversified classification approach which includes important habitat features in addition to simple characterization of diameter distributions should be considered to better assess forest structural variation and management.

Current forest management in boreal northeastern Ontario results in young, even-aged forests; however, fire history research has found old stands with multiple cohorts of trees are common, supporting the value of Multi-cohort Management. I investigated relationships between insect communities and stand live-tree diameter distribution, cohort class and structure. Results showed that variation in abundances of Carabidae, Diapriidae, Diptera and Hymenoptera were not strongly predicted by cohort class. The concept showed greater strength when parameters of live-tree diameter distributions were used. Forest structure, not age, was important for all communities, including heterogeneity of understory and/or overstory vegetation. Trap height was a strong predictor of aerial insect community structure, with insect abundance higher in the understory than in the canopy. In summary, a more diversified classification approach which includes important habitat features in addition to simple characterization of diameter distributions should be considered to better assess forest structural variation and management.

No description available.

El presente trabajo de investigación analiza la fitogeografía, fitosociología y ecología de la vegetación de los saladares en el Chaco Boreal, Paraguay. El estudio hace hincapié en las características florísticas, ecológicas y estructurales de la vegetación a lo largo del gradiente salino desde zonas bajas con suelos fuertemente salinos hasta zonas con un relieve elevado y una influencia salina moderada. El área de estudio se encuentra ubicado en la franja de salinización que aparece en la zona de transición entre el Chaco húmedo y el Chaco central seco. Debido a las características geológicas y climáticas se desarrollan en esta zona fenómenos de salinzación en lagunas, riachos y cauces. Estos fenómenos de salinización son en gran parte naturales y se encuentran ligados a la napa freática salada y elevada en la zona. Los relevamientos fitosociológicos se realizaron en 14 lugares de muestreo durante los meses de verano de 2010-2012. Con un muestreo aleatorio estratificado fueron realizados 162 inventarios en las estepas salinas y 236 inventarios en la vegetación leñosa adyacente. Los inventarios fitosociológicos en vegetación fisionómicamente homogénea fueron acompañados de caracterizaciones ecológicas del hábitat. En coincidencia con inventarios florísticos en otros saladares continentales de Sudamérica, el área de estudio se caracteriza por una diversidad baja de especies. De las especies vegetales presentes en el Chaco paraguayo, fueron encontrados 18,9 % en el área de estudio y sólo 2,6 % en las estepas salinas. En la vegetación analizada dominan los géneros pantrópicos y neotrópicos. A nivel de especies se puede observar una marcada predominancia de especies con distribución neotrópica en sentido amplio. Las especies típicas de la provincia fitogeográfica chaqueña juegan en este sentido un rol especial en la composición florística. El espectro de las formas de vida y la distribución geográfica a lo largo del gradiente de precipitación de las especies en el área de estudio fueron comparados con la checklist de la flora vascular del Chaco paraguayo preparada y publicada recientemente por el autor. En el Chaco paraguayo y también en el área de estudio predominan las fanerófitas, mientras que las estepas salinas se encuentran dominadas por las hemicriptófitas. En las estepas salinas fueron clasificadas nueve comunidades vegetales con secuencias bien definidas y generalmente sin transiciones graduales entre ellas. La mayoría de las comunidades se caracteriza por una sola especie diferencial respectivamente. Las comunidades diferenciadas se encuentran ubicadas a lo largo de un gradiente de disponibilidad de agua, desde la comunidad hidrohalófila de Ruppia maritima y la comunidad higrófila de Setaria geminata en suelos húmedos y salobres hasta la comunidad xerohalófila de Heterostachys ritteriana. El contenido de sodio y la materia orgánica en los horizontes superiores del suelo tienen una influencia significativa en la distribución de las especies en las estepas salinas. Setaria geminata se desarrolla en suelos húmedos con cierto porcentaje de materia orgánica y muy bajo contenido de sodio. En los suelos con alto contenido de sodio predominan generalmente Heterostachys ritteriana y Sarcocornia ambigua. Pequeñas diferencias del relieve juegan además un importante rol en la distribución de las especies porque influyen en forma decisiva las sedimentaciones, la disponibilidad de agua y la duración de la inundación. Acumulaciones de sedimentos arenosos reducen la humedad y la salinidad y facilitan el crecimiento de especies pioneras como Sesuvium portulacastrum y Sporobolus pyramidatus. Las diez comunidades vegetales diferenciadas en la vegetación leñosa de los saladares del Chaco paraguayo se encuentran ubicados a lo largo de un gradiente de humedad y salinidad. A lo largo de este gradiente aumenta la diversidad estructural y de las especies y disminuye el procentaje de especies halófilas. El contenido de sodio y el porcentaje de arena y limo en el suelo tienen una influencia significativa en la distribución y composición de las especies en las comunidades arbustivas y boscosas. Altos contenidos de sodio y pH están positivamente correlacionados y caracterizan suelos salinos. En estos hábitats se desarrollan principalmente especies halófilas, entre ellas varios arbustos como Cyclolepis genistoides, Lophocarpinia aculeatifolia, Lycium americanum, Lycium boerhaaviaefolium y Prosopis rojasiana. Altos porcentajes de limo y arcilla en el suelo caracterizan suelos mal drenados e influyen significativamente la composición de las especies en una comunidad determinada. Este efecto se pudo observar especialmente en las comunidades de Parkinsonia aculeata-Copernicia alba, Prosopis ruscifolia-Sporobolus pyramidatus, Prosopis ruscifolia-Evolvulus convolvuloides y Prosopis ruscifolia-Tabebuia nodosa. Mediante mediciones estructurales de los troncos con un DAP ≥10 cm fueron calculados la abundancia, frecuencia, dominancia y el índice de valor de importancia (IVI) para las especies leñosas presentes en cada comunidad. En las comunidades arbustivas la especie más abundante y frecuente es Prosopis ruscifolia, mientras que la especie con mayor abundancia y frecuencia en las comunidades boscosas es Salta triflora. En el presente trabajo se comparan las comunidades vegetales diferenciadas en los saladares del Chaco paraguayo con otros estudios similares en el contexto sudamericano y se presenta una esquema sintaxonómico de las mismas. Las comunidades vegetales de las estepas salinas y tambien de la vegetación leñosa pueden ser clasificadas en tres clases sintaxonómicas respectivamente. Teniendo en cuenta las alteraciones climáticas y el constante aumento del uso de la tierra en el Chaco paraguayo se realiza al final del trabajo una discusión acerca de las consecuencias y posibles pronósticos de desarrollo en los saladares. Además se presentan algunas recomendaciones para futuras investigaciones, usos alternativos y medidas necesarias para la conservación de los saladares estudiados. / Die vorliegende Arbeit befasst sich mit der Pflanzengeographie, Pflanzensoziologie und Ökologie der salzbeeinflussten Vegetation im Chaco Boreal von Paraguay. Im Mittelpunkt der Betrachtungen stehen die floristischen, strukturellen und ökologischen Merkmale der Vegetation entlang eines Gradienten von stark salzhaltigen bis zu mäßig salzbeeinflussten Standorten und die daraus resultierende vegetationsökologische Charakterisierung. Das Untersuchungsgebiet liegt in der Übergangszone von den regelmäßig überschwemmten Flächen des feuchten Ostchaco zum trockenen Zentralen Chaco, in der als Folge der klimatischen und geologischen Verhältnisse großflächige Salzstandorte vorkommen. Versalzungen, die in dieser Zone auf natürliche Weise entstehen, treten hier im Bereich von Niederungen und Unterläufen periodisch wasserführender Flusssysteme auf und stehen in enger Verbindung zum hochanstehenden salzigen Grundwasser. An insgesamt 14 Untersuchungsorten wurden 162 stratifiziert-randomisierte Vegetationsaufnahmen in den Salzmarschen und 236 Aufnahmen in der angrenzenden salzbeeinflusten Gehölzvegetation durchgeführt. Den Bestandsaufnahmen in physiognomisch unterscheidbarer homogener Vegetation folgten Untersuchungen einiger Standortfaktoren. Die untersuchten Salzstandorte sind in Übereinstimmung mit Studien anderer Binnenlandsalzstellen in Südamerika artenarm. Von den im paraguayischen Chaco vorkommenden Arten wurden an den untersuchten salzbeeinflussten Standorten 18,9 % und in den Salzmarschen nur 2,6 % gefunden. Pflanzengeographisch wird die untersuchte salzbeeinflusste Vegetation von pantropischen und neotropischen Gattungen dominiert. Im weiteren Sinne neotropische Arten sind vorherrschend, wobei die direkte phytogeographische Umgebung des Chaco eine entscheidende Rolle in der Artenzusammensetzung spielt. Das Lebensformenspektrum und die lokale Verteilung entlang eines Niederschlagsgradienten der vorkommenden Arten im Untersuchungsgebiet wurde mit der vorab vom Verfasser angefertigten Checkliste der Gefäßpflanzen im paraguayischen Chaco verglichen. Sowohl im paraguayischen Chaco insgesamt als auch an den untersuchten salzbeeinflussten Standorten dominieren Phanerophyten, während in den Salzmarschen Hemikryptophyten vorherrschen. In den Salzmarschen wurde anhand originaler Vegetationsaufnahmen eine Abfolge von neun Pflanzengesellschaften unterschieden. Die in den meisten Fällen aus nur einer Differenzialart bestehenden Gesellschaften weisen nur selten allmähliche Übergänge auf und kommen entlang eines Gradienten unterschiedlicher Wasserverfügbarkeit vor. Der Gradient reicht von der hydrohalophilen Ruppia maritima-Gesellschaft und der hygrophilen Setaria geminata-Gesellschaft schwach salziger Standorte bis zur stark salz- und trockenresistenten Heterostachys ritteriana-Gesellschaft. Als signifikante Bodeneigenschaften, die die Verteilung der Arten in den Salzmarschen bestimmen, konnten der Natriumgehalt und die organische Substanz im Oberboden festgestellt werden. Setaria geminata kommt in Böden mit höherem Humusanteil vor, während in natriumreichen Böden Heterostachys ritteriana und Sarcocornia ambigua vorherrschen. Eine bedeutende Rolle spielen außerdem kleine Reliefunterschiede, die maßgeblich die Sedimentablagerungen, Wasserverfügbarkeit und Dauer der Überschwemmung beeinflussen. Sandige Sedimentaufschüttungen reduzieren die Feuchtigkeit und Salinität und erleichtern die Etablierung von Pionierarten, wie Sesuvium portulacastrum und Sporobolus pyramidatus. Die untersuchte salzbeeinflusste Gehölzvegetation konnte anhand originaler Vegetationsaufnahmen in zehn Gesellschaften klassifiziert werden, die entlang eines Wasserverfügbarkeitsgradienten vorkommen. Entlang dieses Gradienten nimmt die Arten- und Strukturdiversität zu und der Anteil an halophilen Arten ab. Die Bodenparameter, die signifikant die Artenzusammensetzung in den Gebüsch- und Waldgesellschaften beeinflussen, sind der Natriumgehalt und die Bodenart. Hohe Natrium- und pH-Werte im Oberboden sind in den untersuchen Probeflächen positiv korreliert und kennzeichnen salzreiche Standorte, die größtenteils von halophilen Arten besiedelt werden. Typische halophile Straucharten sind Cyclolepis genistoides, Lophocarpinia aculeatifolia, Lycium americanum, Lycium boerhaaviaefolium und Prosopis rojasiana. Die Bodenart im Oberboden spielt für die Artenzusammensetzung eine entscheidende Rolle, da hohe Schluff- und Tonanteile im Oberboden zu einer schlechten Dränage und somit zu stauwasserbeeinflussten Habitaten führen. Dieser Effekt kann ganz besonders an Standorten der Parkinsonia aculeata-Copernicia alba-Gesellschaft, der Prosopis ruscifolia-Sporobolus pyramidatus-Gesellschaft, der Prosopis ruscifolia-Evolvulus convolvuloides-Gesellschaft und der Prosopis ruscifolia-Tabebuia nodosa-Gesellschaft beobachtet werden. Anhand von Strukturmessungen aller Stämme mit einem BHD ≥10 cm wurden die Abundanz, Frequenz, Dominanz und der Bedeutungswert-Index (IVI) für alle Gehölzarten in den einzelnen Gesellschaften berechnet. Prosopis ruscifolia erreicht hohe Abundanz- und Frequenzwert in den Gebüschgesellschaften, während Salta triflora ein besonderer Stellenwert in den Waldgesellschaften zukommt. In dieser Arbeit werden die Untersuchungsergebnisse der salzbeeinflussten Vegetation im paraguayischen Chaco mit ähnlichen Studien aus dem südamerikanischen Kontext verglichen und syntaxonomisch eingeordnet. Sowohl die Vegetation der Salzmarschen als auch die Gehölzvegetation kann jeweils in drei unterschiedlichen syntaxonomischen Klassen eingeordnet werden. Abschließend werden die Auswirkungen und Entwicklungsprognosen hinsichtlich klimatischer Veränderungen und des immer stärker werdenden Landnutzungswandels diskutiert und Ansätze für zukünftige Nutzungs- und Naturschutzmaßnahmen sowie für weitere Untersuchungen empfohlen.

Phosphorus (P) is an essential element for life on our planet. It is central in numerous biochemical processes in terrestrial and aqueous ecosystems including food production; and it is the primary growth-limiting nutrient in some of the world’s biomes. The main source of P for use as agricultural fertilizer is mining of non-renewable mineral phosphate. In terrestrial ecosystems the main source is soil P, where the largest fraction is organic P, composed of many species with widely differing properties. This fraction controls the utilization of P by plants and microorganisms and influences ecosystem development and productivity. However, there is only scarce knowledge about the molecular composition of the organic P pool, about the processes controlling its bioavailability, and about its changes as soils develop. Therefore, the aim of this thesis was to develop robust solution- and solid-state 31P nuclear magnetic resonance spectroscopy (NMR) methods to provide molecular information about speciation of the organic P pool, and to study its dynamics in boreal and tropical soils. By studying humus soils of a groundwater recharge/discharge productivity gradient in a Fennoscandian boreal forest by solution- and solid-state NMR, it was found that P speciation changed with productivity. In particular, the level of orthophosphate diesters decreased with increasing productivity while mono-esters such as inositol phosphates increased. Because the use of solution NMR on conventional NaOH/EDTA extracts of soils was limited due to severe line broadening caused by the presence of paramagnetic metal ions, a new extraction method was developed and validated. Based on the removal of these paramagnetic impurities by sulfide precipitation, a dramatic decrease in NMR linewidths was obtained, allowing for the first time to apply modern multi-dimensional solution NMR techniques to soil extracts. Identification of individual soil P-species, and tracking changes in the organic P pools during soil development provided information for connecting P-speciation to bioavailability and ecosystem properties. Using this NMR approach we studied the transformation of organic P in humus soils along a chronosequence (7800 years) in Northern Sweden. While total P varied little, the composition of the soil P pool changed particularly among young sites, where also the largest shift in the composition of the plant community and of soil microorganisms was observed. Very old soils, such as found Africa, are thought to strongly adsorb P, limiting plant productivity. I used NMR to study the effect of scattered agroforestry trees on P speciation in two semi-arid tropical woodlands with different soil mineralogy (Burkina Faso). While the total P concentration was low, under the tree canopies higher amounts of P and higher diversity of P-species were found, presumably reflecting higher microbial activity. / <p>I delarbete III har titel och författaruppgifter förändrats.</p>

Archaeological sites in the boreal forest are facing threats due to urban development, resource exploitation, vandalism, and infrastructure development, among others. In the context of archaeological site preservation as a public issue, I examine the perspectives of various publics towards the preservation and stewardship of archaeological sites in the boreal forest. Through a series of interviews, I examine the opinions of three publics involved in the archaeological process in Ontario: developers, First Nations, and archaeologists. I outline the participants??? opinions on the meaning and goals of preservation, the preservation of non-physical aspects of sites, such as oral history and site spirituality, preservation methods, site ownership and access, land use and development, involvement in the archaeological process, and funding. I also identify common themes which presented themselves throughout the interview process, such as the importance of education; the necessity for communication, collaboration, and cooperation; the problem of artifact curation; the perceived lack of genuine government involvement; and the publication of cultural resource management (CRM) archaeology???s ???grey literature???. Finally, I present suggestions on the preservation of archaeological sites which take into account the participants??? perspectives uncovered during the interview process. I conclude that preserving archaeological sites can be done using three techniques: education; communication, collaboration, and compromise; and using one of three general methods to preserve sites and artifacts. Education can be used to create public issues, teach people about the importance of archaeology and archaeological sites, and teach the involved publics about the goals and methods of CRM archaeology in Ontario. Encouraging communication, collaboration, and compromise between the interested publics includes the perspectives of formerly neglected parties, builds relationships between publics, and creates newly vested interests in site preservation. Three methods to preserve archaeological sites include site stabilization and monitoring, allowing sites to decay naturally, and excavating sites and curating the artifacts and oral histories for the long-term.

Soils of Northern Hemisphere forests contain a large part of the global terrestrial carbon (C) pool. Even small changes in this pool can have large impact on atmospheric [CO2] and the global climate. Soil respiration is the largest terrestrial C flux to the atmosphere and can be divided into autotrophic (from roots, mycorrhizal hyphae and associated microbes) and heterotrophic (from decomposers of organic material) respiration. It is therefore crucial to establish how the two components will respond to changing environmental factors. In this thesis I studied the effect of elevated atmospheric [CO2] (+340 ppm, 13C-depleted) and elevated air temperature (2.8-3.5 oC) on soil respiration in a whole-tree chamber (WTC) experiment conducted in a boreal Norway spruce forest. In another spruce forest I used multivariate modelling to establish the link between day-to-day variations in soil respiration rates and its δ13C, and above and below ground abiotic conditions. In both forests, variation in δ13C was used as a marker for autotrophic respiration. A trenching experiment was conducted in the latter forest in order to separate the two components of soil respiration. The potential problems associated with the trenching, increased root decomposition and changed soil moisture conditions were handled by empirical modelling. The WTC experiment showed that elevated [CO2] but not temperature resulted in 48 to 62% increased soil respiration rates. The CO2-induced increase was in absolute numbers relatively insensitive to seasonal changes in soil temperature and data on δ13C suggest it mostly resulted from increased autotrophic respiration. From the multivariate modelling we observed a strong link between weather (air temperature and vapour pressure deficit) and the day-to-day variation of soil respiration rate and its δ13C. However, the tightness of the link was dependent on good weather for up to a week before the respiration sampling. Changes in soil respiration rates showed a lag to weather conditions of 2-4 days, which was 1-3 days shorter than for the δ13C signal. We hypothesised to be due to pressure concentration waves moving in the phloem at higher rates than the solute itself (i.e., the δ13C–label). Results from the empirical modelling in the trenching experiment show that autotrophic respiration contributed to about 50% of total soil respiration, had a great day-to-day variation and was correlated to total soil respiration while not to soil temperature or soil moisture. Over the first five months after the trenching, an estimated 45% of respiration from the trenched plots was an artefact of the treatment. Of this, 29% was a water difference effect and 16% resulted from root decomposition. In conclusion, elevated [CO2] caused an increased C flux to the roots but this C was rapidly respired and has probably not caused changes in the C stored in root biomass or in soil organic matter in this N-limited forest. Autotrophic respiration seems to be strongly influenced by the availability of newly produced substrates and rather insensitive to changes in soil temperature. Root trenching artefacts can be compensated for by empirical modelling, an alternative to the sequential root harvesting technique.