Historical forest succession and disturbance dynamics in Coastal Douglas-fir forests in the southern western Cascades of Oregon

Coastal Douglas-fir (Pseudotsuga menziesii var menziesii) forests are extensive west of the crest of the Cascade Mountains in Oregon and Washington and are renowned for their productivity, biodiversity, and the ecosystem services they provide. Increasing wildfire activity in recent years including the extensive 2020 Labor Day fires, and a warming climate have raised concerns about the resistance and resilience of Coastal Douglas-fir forests. At the same time federal land managers are now tasked with restoration of natural successional and disturbance processes including fire to maintain biodiversity and ecosystem services given natural and anthropogenic stressors. However, we lack information that precisely describes historical fire regimes and successional dynamics in Coastal Douglas-fir forests sufficient to guide reintroduction of wildfire, in the context of restoration and adaptation of forest conditions and successional dynamics that are resilient to climate change. This gap in information exists because rigorous dendrochronological research methods have been sparsely used in Coastal Douglas-fir forests due to the challenges of sampling intact fire-scarred trees and the expectation that historical fires were infrequent and often severe. This dissertation provides the first extensive annually resolved dendrochronological reconstruction of historical (1600-1910 CE) fires and forest development in Douglas-fir forests of the southern western Oregon Cascades. Reconstruction sites covered an ecological gradient where Douglas-fir is the dominant tree species from low elevation warm-dry Douglas-fir forests to high elevation cool-wet Pacific silver fir (Abies amabilis) forests. In Chapter 2, I used multiple lines of evidence to reconstruct historical fire events. A frequent mixed-severity fire regime historically influenced tree establishment and successional dynamics across the broad warm-dry to cool-moist climatic gradient that I sampled. The majority of fire intervals prior to the early 19th century were 50 years long in both warm-moist and cool-moist microclimates, predominantly in the 19th century. Fire extent and frequency varied at fine spatial and temporal scales with small isolated fires occurring at approximately the same frequency as extensive fires. Most (94%) of historical fires were reconstructed from crossdated fire scars. Although the majority of tree establishment cohorts (90%) were associated with fire, tree establishment cohorts provided evidence of only 26% of historical fires evidenced by fire scars because historical fires did not always provide an opportunity for tree establishment or tree cohorts were killed by subsequent fires. Chapter 2 demonstrates the importance of crossdated fire records for quantifying fire history in these forest types, providing more nuanced and precise understanding of tree establishment and the development of old-growth forest conditions than previously known in Douglas-fir forests with a mixed-severity fire regime.. In Chapter 3, I quantified annual fire-climate relationships, identified variability in fire frequency over time, and evaluated how fire occurrence and frequency are related to climate, biophysical setting, people, and forest succession. I found no evidence that historical fires occurred preferentially in drought conditions prior to European settlement in 1830. After 1830 fires were significantly associated with drought. The increased fidelity of fire to drought years occurred at approximately the same time that fire frequency declined at most sites in my study area, and these declines in fire frequency occurred 50 - 100 years before fire suppression efforts began in the early 20th century. These unexpected results suggest that Native America traditional burning and changes in the flammability of Douglas-fir forests that occur with succession may have historically been important drivers of fire frequency. For example, there was strong evidence of traditional burning at one of my reconstruction sites where extremely frequent historical fires (mean fire interval 2.9 years) regularly occurred in years with wet spring and summer conditions. Declines in fire frequency in warm-dry forests coincided with disease epidemics and the disruption of Native America lifeways brought by European settlement. Decreases in fire frequency occurred several decades earlier across cool-moist western hemlock and Pacific silver fir forests at two of my study sites. These decreases in fire at cool-moist forest sites coincided with a cool-wet climatic period in the early 19th century and the development of mature Douglas-fir forest structure that resists burning. Younger early successional Douglas-fir forests developing after high-severity fire in the 19th century continued to burn frequently until fire suppression in the early 20th century. Chapter 3 demonstrates that fires historically burned under a broader range of climatic conditions, and this means that fire occurrence and frequency were likely mediated by fine scale endogenous drivers including topography, fuel moisture and structure, and the timing and distribution of ignitions. In Chapter 4, I use forest structure and composition, tree establishment records, and fire records to identify forest types and fire-mediated development types and precisely illustrate how fire frequency and severity historically contributed to diversity in forest development, structure, and composition. I identify how forest types and fire-mediated development types are uniquely related to biophysical environment to determine if forest types are indicative of a distinct historical fire regime, and to refine our understanding of how fire influenced forest development in different parts of the landscape. Old-growth forest conditions (composition and structure; forest type) varied at broad scales with microclimate. In contrast, forest development history (development types) varied at finer scales with slope and heatload, and even-aged, two-aged, many-aged, and multi-aged development types occurred across xeric, warm-dry, and cool-moist microclimates. Many-aged stands with continuous tree establishment over several decades to centuries developed almost exclusively on gentle slopes. Even-aged, two-aged, and multi-aged forests with distinct tree establishment cohorts that establish after moderate- to high-severity fire were usually located on steep slopes. Overall, the influence of fire on forest successional dynamics was partitioned at fine scales by topography, and this created a mosaic of distinct forest ages and development histories across warm-dry to cool-moist forest types in Douglas-fir forests in the southern western Cascades. This dissertation provides a uniquely detailed and precise characterization of frequent mixed-severity fire regimes in Douglas-fir forests in the southern western Cascades. A mixture of frequent low-, moderate-, and high-severity fire created the mature and old-growth forests that land management aims to protect today. Removing fire from these Douglas-fir forests has altered successional dynamics, forest structure and composition, and may have intensified drought and wildfire effects at the same time as drought severity and frequency are increasing across forests of the western United States. This research can inform future dendroecological reconstruction in Douglas-fir forests, guide reintroduction of fire, contribute to conservation and land planning, and inform response to contemporary wildfires as we adapt to a warmer and drier climate in the Pacific Northwest

Mixed-conifer forests of central Oregon : structure, composition, history of establishment, and growth

The structure and composition of mixed-conifer forest (MCF) in central Oregon has been altered by fire exclusion and logging. The resulting increased density, spatial contagion, and loss of fire resistant trees decrease the resiliency of this ecosystem to fire, drought, and insects. The historical and current composition and structure of MCF are characterized by steep environmental gradients and a complex mixed-severity fire regime. This inherent variation makes it difficult to determine the magnitude of anthropogenic effects and set objectives for restoration and management. As a result, there is a lack of consensus regarding how MCF should be managed and restored across the landscape. My primary research objectives were to: (1) Characterize the current structure and composition of MCF and how these vary with environmental setting; and (2) Characterize establishment and tree growth patterns in MCF in different environmental settings. To address these objectives, I collected field data on structure and composition and increment cores across a range of environmental conditions in MCF of the eastern Cascades and Ochoco Mountains. I used cluster analysis to identify four stand types based on structure and composition in the eastern Cascades study area and four analogous types in the Ochoco Mountains study area. Variation in understory composition and the presence of large diameter shade tolerant species distinguish each type. Stand types occupied distinct environmental settings along a climatic gradient of increasing precipitation and elevation. At relatively dry PIPO sites understories were dominated by ponderosa pine. At wetter PIPO/PSME and PIPO ABGC sites understories were dominated by shade tolerant species, but ponderosa pine was dominant in the overstory. At the coolest and wettest PIPO/PSME/ABGC sites understories were dominated by grand fir and shade tolerant species were common in the overstory. In the eastern Cascades current density of all live trees and snags was 432, 461, 570, 372 trees per hectare (TPH) for the four stand types identified. Stand types in the drier Ochoco Mountains were currently less dense at 279, 304, 212, and 307 TPH. Current MCF densities in both areas are 2-3 times higher than densities estimated for the late 19th and early 20th centuries from other studies in those two areas. Reconstruction of cuts in each stand type indicates that the density of large diameter ponderosa pine has been reduced by approximately 50% in all stand types in both study regions. Age histograms demonstrate that current density and composition of MCF stand types is a product of abrupt increases in tree establishment following fire exclusion in the late 19th century. The number of trees established increased after 1900 in all stand types, but the timing and composition of changes in establishment varied with climate. At dry PIPO sites increases in establishment were delayed until the 1920s and 1930s and were composed of ponderosa pine. At PIPO/PSME and PIPO/ABGC sites with intermediate precipitation, establishment was dominated by ponderosa pine prior to 1900, but after 1900 establishment was dominated by a large pulse of Douglas-fir and grand fir. At the wettest PIPO/PSME/ABGC there was less evidence of changes in structure and composition over time. My results indicate that compared to dry pine and dry-mixed conifer sites, relatively productive moist mixed-conifer sites were characterized by large changes in structure and composition. Such sites could be considered more ecologically altered by lack of fire than drier forest types that had high fire frequencies but slower rates of stand development and less plant community change. Radial growth patterns of cored ponderosa pines differed between the eastern Cascades and Ochoco Mountains. In the eastern Cascades mean growth rates and variance decreased during favorable climatic periods after 1900. This is likely related to increased competition, and provides evidence that current stand density lacks a temporal analog in the 18th and 19th centuries. Sensitivity of growth to climate and harvest suggest competition for water in the denser forest of the eastern Cascades, and indicates thinning will increase the diameter growth rate of large old pines. In the Ochoco Mountains, ponderosa pine tree growth was less responsive to climate prior to fire exclusion in the late 1800s, and growth did not respond to fire events. This suggests competition among trees was historically low in this region. After fire exclusion growth became more responsive to wet and dry climatic cycles, which may indicate that increased density and competition made trees more responsive to climate variability. Patterns of slow and fast growth appeared to differ between study regions and likely differ at the sub-regional scale. Further analysis of the relationship between growth and climate in different environmental settings is needed to distinguish where stand development has been modified by disruption of fire regimes

Stand Structure of Old Growth Dry Mixed Conifer Forests in the Deschutes and Ochoco National Forests

Old-growth dry-mixed conifer forests are valued as habitats for late seral forest species, for the ecosystem services and landscape diversity they provide, and for their aesthetic appeal. The structure of these forests has been heavily altered by historic logging of overstory ponderosa pine and Douglas-fir. Additionally, changes in fire regime have altered understory density in these forests to an unknown extent. Conserving remaining stands and facilitating old-growth development in disturbed stands are objectives of the Deschutes and Ochoco National Forests. This investigation addressed these objectives with two separate analyses. The first analysis was an accuracy assessment of the GNN forest vegetation map’s ability to predict old-growth drymixed conifer structure at a site scale and at a landscape scale. This analysis determined that the GNN map is an adequate tool for identifying old-growth stands at a site scale, and was highly accurate at predicting dry-mixed conifer forest vegetation at a landscape scale. The second analysis characterized present day and historic stand structure of old-growth dry-mixed conifer forests, and described how stand structure varied across the Deschutes and Ochoco National Forests. The second analysis determined future research should investigate the growth rate of understory ponderosa pine and Douglas-fir under varying density levels

Ganzheitliche Untersuchungsmethoden zur Erfassung und Prüfung der Qualität ökologischer Lebensmittel: Stand der Entwicklung und Validierung

In dem wachsenden Markt ökologischer Lebensmittel werden Methoden zur produktorientierten Qualitätserfassung gefordert. Dabei geht es u.a. um die Unterscheidung von Produkten aus unterschiedlichen Anbauverfahren. Die Ziele des Projektes waren daher: 1. ausgewählte ganzheitliche Methoden gemäß ISO 17025 zu validieren, d.h. Laborprozesse festzulegen, sowie Einflussgrößen und Verfahrensmerkmale zu bestimmen, 2. zu testen, ob diese Verfahren eine Differenzierung von definierten Proben statistisch abgesichert zeigen können. . Diese Ziele konnten erreicht werden. Es wurde bestätigt, dass einige der Methoden auf Grundlage dokumentierter Prozeduren Lebensmittel aus definierten Anbauversuchen (u.a. aus dem DOK-Versuch am FIBL/CH) reproduzierbar unterscheiden können. Die Koordination und die Validierung der Kupferchlorid-Kristallisation sowie die Messung der Polyphenole lag bei der Universität Kassel, FG Ökologische Lebensmittelqualität und Ernährungskultur. Die KWALIS GmbH, Dipperz, validierte die Fluoreszenz-Anregungsspektroskopie und die Bestimmung des Physiologischen Aminosäurestatus, die EQC GmbH, Weidenbach die elektrochemischen Messungen. Dr. Kromidas, Saarbrücken übernahm die Beratung der Validierungsprozeduren. . An Blindproben wurde untersucht, ob die Verfahren für Weizen- und Möhrenproben aus definierten Anbau- und Sortenversuchen geeignet sind (Fragestellung der Validierung). Die Proben wurden von unabhängiger Stelle (OEL-FAL, Trenthorst) codiert. Die Proben wurden gleichzeitig an alle Partner versandt; dadurch konnten die Methoden auch untereinander verglichen werden. Die Methoden Kupferchlorid-Kristallisation, Fluoreszenz-Anregungsspektroskopie und Physiologischer Aminosäurestatus sind für die Fragestellung geeignet. Mit allen drei Methoden konnten die Proben differenziert und gruppiert werden. Darüber hinaus konnten mit der Fluoreszenz-Anregungsspektroskopie und über den physiologischen Aminosäurestatus die Proben auch den Anbauweisen richtig zugeordnet werden. Allerdings ist damit noch keine Aussage über die Fähigkeit dieser Verfahren möglich, generell Proben aus ökologischer und konventioneller Herkunft zu unterscheiden. Dafür sind weitere Untersuchungen sowohl an Proben definierter Herkunft als auch an Marktproben notwendig

Trace Metals and Their Isotopes in the Tropical Atlantic Ocean - Cruise No. M81/1, February 04 – March 08, 2010, Las Palmas (Canary Islands, Spain) – Port of Spain (Trinidad & Tobago)

Summary Meteor Cruise M81/1 was dedicated to the investigation of the distribution of dissolved and particulate trace metals and their isotopic compositions (TEIs) in the full water column of the tropical Atlantic Ocean and their driving factors including main external inputs and internal cycling and ocean circulation. The research program is embedded in the international GEOTRACES program (e.g. Henderson et al., 2007), which this cruise was an official part of and thus corresponds to GEOTRACES cruise GA11. This cruise was completely dedicated to the trace metal clean and contamination-free sampling of waters and particulates for subsequent analyses of the TEIs in the home laboratories of the national and international participants. Besides a standard rosette for the less contaminant prone metals, trace metal clean sampling was realized by using a dedicated and coated trace metal clean rosette equipped with Teflon-coated GO-FLO bottles operated via a polyester coated cable from a mobile winch that was thankfully made available by the U.S. partners of the GEOTRACES program for this cruise. The particulate samples were also collected under trace metal clean conditions using established in-situ pump systems. The cruise track led the cruise southward from the Canary Islands to 11°S and then continued northwestward along the northern margin of South America until it reached Port of Spain, Trinidad & Tobago. The track crossed areas of major external inputs including exchange with the volcanic Canary Islands, the Saharan dust plume, as well as the plume of the Amazon outflow. In terms of internal cycling the equatorial high biological productivity band, as well as increased productivity associated with the Amazon Plume were covered. All major water masses contributing the Atlantic Meridional Overturning Circulation, as well as the distinct narrow equatorial surface and subsurface east-west current bands were sampled. A total of 17 deep stations were sampled for the different dissolved TEIs, which were in most cases accompanied by particulate sampling. In addition, surface waters were continuously sampled under trace metal clean conditions using a towed fish

The North American tree-ring fire-scar network

Fire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree-ring fire scars provide valuable perspectives on fire regimes, including centuries-long records of fire year, season, frequency, severity, and size. Here, we introduce the newly compiled North American tree-ring fire-scar network (NAFSN), which contains 2562 sites, >37,000 fire-scarred trees, and covers large parts of North America. We investigate the NAFSN in terms of geography, sample depth, vegetation, topography, climate, and human land use. Fire scars are found in most ecoregions, from boreal forests in northern Alaska and Canada to subtropical forests in southern Florida and Mexico. The network includes 91 tree species, but is dominated by gymnosperms in the genus Pinus. Fire scars are found from sea level to >4000-m elevation and across a range of topographic settings that vary by ecoregion. Multiple regions are densely sampled (e.g., >1000 fire-scarred trees), enabling new spatial analyses such as reconstructions of area burned. To demonstrate the potential of the network, we compared the climate space of the NAFSN to those of modern fires and forests; the NAFSN spans a climate space largely representative of the forested areas in North America, with notable gaps in warmer tropical climates. Modern fires are burning in similar climate spaces as historical fires, but disproportionately in warmer regions compared to the historical record, possibly related to under-sampling of warm subtropical forests or supporting observations of changing fire regimes. The historical influence of Indigenous and non-Indigenous human land use on fire regimes varies in space and time. A 20th century fire deficit associated with human activities is evident in many regions, yet fire regimes characterized by frequent surface fires are still active in some areas (e.g., Mexico and the southeastern United States). These analyses provide a foundation and framework for future studies using the hundreds of thousands of annually- to sub-annually-resolved tree-ring records of fire spanning centuries, which will further advance our understanding of the interactions among fire, climate, topography, vegetation, and humans across North America

Correction: Kim et al. Assessing Role of Drought Indices in Anticipating Pine Decline in the Sierra Nevada, CA. Climate 2022, 10, 72

Author “David A [...

Appendix B. Dendrogram results of hierarchical cluster analysis.

Dendrogram results of hierarchical cluster analysis

Too hot, too cold, or just right: Can wildfire restore dry forests of the interior Pacific Northwest?

As contemporary wildfire activity intensifies across the western United States, there is increasing recognition that a variety of forest management activities are necessary to restore ecosystem function and reduce wildfire hazard in dry forests. However, the pace and scale of current, active forest management is insufficient to address restoration needs. Managed wildfire and landscape-scale prescribed burns hold potential to achieve broad-scale goals but may not achieve desired outcomes where fire severity is too high or too low. To explore the potential for fire alone to restore dry forests, we developed a novel method to predict the range of fire severities most likely to restore historical forest basal area, density, and species composition in forests across eastern Oregon. First, we developed probabilistic tree mortality models for 24 species based on tree characteristics and remotely sensed fire severity from burned field plots. We applied these estimates to unburned stands in four national forests to predict post-fire conditions using multi-scale modeling in a Monte Carlo framework. We compared these results to historical reconstructions to identify fire severities with the highest restoration potential. Generally, we found basal area and density targets could be achieved by a relatively narrow range of moderate-severity fire (roughly 365-560 RdNBR). However, single fire events did not restore species composition in forests that were historically maintained by frequent, low-severity fire. Restorative fire severity ranges for stand basal area and density were strikingly similar for ponderosa pine (Pinus ponderosa) and dry mixed-conifer forests across a broad geographic range, in part due to relatively high fire tolerance of large grand (Abies grandis) and white fir (Abies concolor). Our results suggest historical forest conditions created by recurrent fire are not readily restored by single fires and landscapes have likely passed thresholds that preclude the effectiveness of managed wildfire alone as a restoration tool