Tree cores of Fraxinus pennsylvanica were used in a dendrochronological analysis investigating the species' responses to climate and flooding. The objective was to develop a model that incorporates the effects of precipitation, temperature, and flooding on radial growth in this species in north-central Texas. The trees exhibited strong climatic signals. The study clearly shows that all three factors have significant impacts on tree ring growth both prior to and during growth; however, the nature and extent of these impacts are highly dependent on what time of year they occur. The large temporal variations in growth responses emphasize the importance of considering the timing of environmental events when studying tree growth responses.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

<p>This study is part of an ongoing project established in 2007 as an emerald ash borer (<em>Agrilus planipennis</em>) trapping study. The primary objective of this thesis was to assess how forests have changed following the loss of ash over a 15-year period, from 2007 to 2022. The study aimed to answer three key questions: 1) How has the loss of ash affected the regeneration and recruitment patterns of ash and other tree species? 2) Which specific species are driving forest regeneration and recruitment in the absence of ash? 3) Can the data be used to predict future changes in forest composition following the loss of ash? To achieve these objectives, I conducted analyses of 44 forests representing 19 different forest types in Indiana, Michigan, and Ohio. Forest composition was examined at the overstory, midstory and understory levels to capture the overall impact of ash loss on forest regeneration and succession. Despite the decline or total loss in overstory ash, ash regeneration continued at most sites from 2017 to 2022. However, ash regeneration was not observed at 15 sites, and competition from established shade-tolerant species, such as red maple and American elm, was identified as a primary factor hindering ash recruitment. The loss of ash did not lead to significant changes in forest types. Forest types at all sites remained stable, with only minor shifts in dominant species. Tree species that were already present in the overstory filled the space left by the lost ash, thereby maintaining the existing forest types. In terms of driving species, my findings demonstrated a rapid increase in red maple dominance across all sites, particularly in the absence of ash. Red maple exhibited vigorous growth, suggesting it plays a crucial role in shaping future forest composition following ash loss. Other species, including black cherry, American elm, and American basswood, also contributed to forest regeneration, with some sites showing a shift toward a higher abundance of these species. Although the loss of ash has led to changes in forest composition, existing species have shown resilience and adaptability in filling the niche left by the lost genus. The long-term effects of emerald ash borer infestation on forest ecosystems are complex and multifaceted. This study provides insights into the regeneration and recruitment patterns of ash and other tree species following ash loss. The data suggest that while forests have experienced loss of ash, the remaining understory and midstory individuals of this species may contribute to future overstory recruitment. Furthermore, the dominance of red maple highlights its potential as a key driver of forest composition in the wake of ash loss. </p>

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Die Verbreitung von gebietsfremden Arten in Gebiete außerhalb ihres natürlichen Verbreitungsgebietes kann zu einem Verlust der Biodiversität führen. Einst als produktionssteigerndes Mittel eingesetzt, wurden viele gebietsfremde Baumarten in Mitteleuropa und Deutschland eingeführt und verblieben dort in den Wäldern. Unter anderem wurde in den Hartholzauenwäldern der Mittelelbe in Sachsen-Anhalt die nordamerikanische Rot-Esche (Fraxinus pennsylvanica) eingebracht und sie nimmt heute rund 50 % der Fläche ein. Um die Fragen zum Einfluss der Etablierung von F. pennsylvanica auf die Vielfalt der Waldstrukturen und der Arten in der Krautschicht zu bearbeiten, wurden vergleichende Erhebungen in 20 Beständen durchgeführt, die sich hinsichtlich der Bestandsanteile von F. pennsylvanica im Oberstand unterscheiden. Die Bestände wurden hinsichtlich der Bestandsstruktur und Totholzaufkommen sowie auf kleineren Plots mit je einem Bezugsbaum (F. pennsylvanica oder Quercus robur als Referenz) das Bodenmikrobiom und Bodenvegetation sowie Naturverjüngung der Gehölze untersucht. Am deutlichsten scheint die Einflussnahme von F. pennsylvanica in Reinbeständen. Diese sind weniger stark strukturiert und weisen mehr Anfälligkeiten gegenüber Umwelteinflüssen auf. Für alle anderen Bestandsformen waren die Effekte eher gering und zum Teil konnte in Misch- oder Dominanzbeständen eine höhere Diversität als in Referenzbeständen festgestellt werden. Unabhängig von der gesetzlichen Lage zum Umgang mit Neophyten in Schutzgebieten wird F. pennsylvanica als in die Hartholzauenwälder der Mittelelbe eingegliederte Baumart eingeschätzt, die das Potenzial hat, ausfallende Arten, wie die heimische Gewöhnliche Esche (Fraxinus excelsior), zu ersetzen. / The spread of alien species in areas outside their natural range can lead to a loss of biodiversity. Once used as a tool of increasing production, many alien tree species were introduced into Central Europe and Germany and remained in the forests there. Among other, the north american Green Ash (Fraxinus pennsylvanica) was introduced into the hardwood floodplain forests of the Mittelelbe in the federal state of Saxony-Anhalt and today it occupies around 50% of the area. In order to address the questions about the influence of the establishment of F. pennsylvanica on the diversity of forest structures and species in the herbaceous layer, comparative surveys were carried out in 20 stands that differed in terms of the proportion of F. pennsylvanica in the upper stand. Investigations on stand structure and deadwood as well as, in smaller plots with a reference tree (F. pennsylvanica or Quercus robur as a reference), investigations on soil microbiome, ground vegetation and natural regeneration were examined. The influence of F. pennsylvanica appears to be clearest in pure stands. These are less structured and are more susceptible to environmental influences. For all other types of stands, the effects were rather small and, in some cases, a higher diversity was found in mixed or dominant stands than in reference stands. Regardless of the legal situation regarding the handling of neophytes in protected areas, F. pennsylvanica is considered to be a tree species integrated into the hardwood floodplain forests of the Mittelelbe, which has the potential to replace failing species such as the common ash (Fraxinus excelsior).

Recent research has challenged the long-standing hypothesis that forests in the Upper Midwest of the United States developed during wetter periods and retreated during dry periods. We explored this debate by examining patterns of tree establishment on an oak savanna in east-central Minnesota within the context of variable moisture availability and fire suppression. We used superposed epoch analyses (SEA) to evaluate the mean moisture conditions for a 21-year window surrounding tree establishment dates. Before effective fire suppression (1809–1939), 24 of 42 trees with pith dates (62%) grew to 30-cm height during dry years (Palmer Drought Severity Index < -1), versus only 5 of 42 (12%) that established in wet years (PDSI > 1). Significantly more trees established during dry periods (negative PDSI values) than would be expected with the proportion of wet-to-dry years (x²= 10.738, df = 1, p-value = 0.001). Twenty of the complete sample of 74 trees with pith dates (27%) established during drought in the 1930s. We hypothesize that dry conditions limited plant productivity, which in turn decreased competition between grasses and tree seedlings and reduced rates of accumulation of fine fuels, enabling seedlings to grow tall enough to resist subsequent fires. We recommend SEA as a methodological approach to compare historical climate conditions with the timing of regeneration success in other regions of forest expansion.

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Urban runoff continues to impair water quality and there is an increasing need for stormwater management within the limited confines of urban spaces. We propose a system of structural soil and trees that can be incorporated beneath pavement. Structural soil has a high load-bearing capacity yet is engineered to support tree root growth. Stormwater is directed into a structural soil reservoir below the pavement where tree roots can also thrive. Two container experiments evaluated tree function in this system. We examined whether tree roots can grow into compacted subsoils and if root penetration increases soil infiltration rate. Quercus velutina, Acer rubrum, and a no-tree variant were planted in 26.5 L (7 gal) containers and the rootballs surrounded by compacted clay loam. Roots grew into all layers of the compacted soil. Infiltration rate increased by 63% (+/-2%) compared to no-tree containers. A second experiment evaluated water uptake and tree development in fluctuating water tables. Quercus bicolor and Fraxinus pennsylvanica were planted in 94.6 L (25 gal) containers with structural soils (either Stalite or CU® Structural Soil). Trees were subjected to fluctuating water tables simulating infiltration rates of 2, 1, and 0.1 cm/hr for two growing seasons. Trees thrived in all infiltration regimes but roots were shallower in slowly drained treatments. Trees grew best and transpired the highest water volume with moderate infiltration. Even if trees uptake only small volumes of water, increased canopy size compared to conventional plantings (because of greater penetrable soil volume) allows greater rainfall interception thus decreasing runoff. / Master of Science