Quantifying soil organic matter and young stand development in managed California forests

This dissertation focuses on quantifying managed forest ecosystems in northern California to assess C and energy stored in soil organic matter (SOM) and management practices that alter productivity and water relations in young planted stands.;Estimates of soil C pools across the landscape are uncertain due to intrinsic SOM variability at local spatial scales (m2 to hectare). Variability requires the collection and analysis of large sample sets, which are time (collect, handle & prepare samples) and cost (labor & analysis) intensive, and the primary barrier to accurate soil C quantification. Sample collection is unavoidable but new techniques, that reduce the time and cost associated with analysis, would greatly aid the development of soil C budgets at management scales (plot, field or soil series). In this study we developed predictive relationships between soil darkness and SOM/C demonstrating the value of quantitative soil color measurements to function as a proximal descriptor of soil C content. This simple low cost technique provides a new tool to produce soil C estimates and facilitate spatially explicit data development across diverse soils. Energetic properties of two forested Ultisols -thermal stability, energetic equilibrium and organo-metallic associations.;In this study we investigate the thermochemistry of two forest Ultisols in Northern California with TG-DSC and analytical modeling. Our results demonstrate the influence of substrate availability and mineral constituents on SOM TS & De with highly reactive poorly crystalline Fe-oxides drastically altering energetic properties compared to more crystalline Al-oxides. These findings provide an alternative interpretation of soil thermochemical data and illustrate the fundamental limitation of our current understanding of organo-metallic bond stability and energy dynamics in soil.;The establishment and growth of young conifer stands are essential components of resilient forested landscapes. In California, summer seasonal drought, combined with vigorous understory growth in disturbed or newly planted stands, can produce severe resource limitations (water and nutrients) that restrict productivity and can cause mortality (Powers and Ferrell, 1996). Common silvicultural practices, that reduce competition and enhance site nutrient availability, are effective at increasing productivity but the effects on young tree physiology are not well understood.;Physical and chemical analysis of tree rings provides insight to understand the interaction between growth, water relations and the environment (Andreu-Hayles et al, 2011) with isotopic analysis providing a powerful tool to study physiological responses over time (Maseyk et al, 2011). The analysis of δ13C in annual growth rings supports the calculation of intrinsic water use efficiency (iWUE), which integrates the effects of photosynthetic CO2 assimilation (A) and stomatal conductance (gs) in a simple ratio (A/gs). iWUE varies across time driven by environmental (Soule and Knapp, 2011; McDowell et a, 2010) and management influences (McDowell et al, 2003) but δ13C alone provides no indication if alteration of A or gs was the factor driving change (Scheidegger et al., 2000). Coupled analyses of δ13C and δ18O provide the resolution to detangle the influence of each factor in experimentally manipulated stands (Brooks and Mitchell, 2010) with δ18O capturing the combined effects of stomatal conductance and evaporative enrichment on water used during photosynthesis.;In the study we assessed the growth and physiology of early ponderosa pine stands across sites with varying precipitation and productivity to quantify the effects of reduced competition and enhanced nutrient availability. Our results show gs is the most important factor controlling iWUE during early growth and soils are generally nutrient limited at all sites. At drier sites, increasing plant available water or photosynthetic efficiency produced comparable growth. Combining reduced competition and fertilization produced synergistic growth and unexpeceted levels of maximum growth at each site. 9Abstract shortened by UMI.).