Meet the 2014 Undergraduate Research Fellows and view this year’s Center for Tree Science Undergraduate Research Symposium.
Ohio Wesleyan University
Title: Inferring the history of morphological diversification in sedges
Advisor: Dr. Andrew Hipp
Interns: Alexa Cotton & Kasey Pham
Abstract: Section Ovales, in the sedge genus Carex, exhibits a remarkable degree of morphological variation. The underlying processes explaining morphological diversification in sedges have gained momentum in recent publications. This study investigates the history of morphological diversification of sedges in Section Ovales in a phylogenetic context. Perigynium solidity and achene width are the most reliable predictors of phylogeny while culm width was the least reliable predictor. In general, trait differentiation within Section Ovales was found to vary at the subclade level, indicating much of the trait diversification is within the Eastern North American clade (ENA) and within the Western North American grade (WNA) rather than between the two. Conversely, a clean split between ENA clade and WNA grade is found in climatic niche space suggesting additional factors are important in explaining trait diversification. Strong phylogenetic tracking of some reproductive morphological traits may be constrained by phylogeny, while weak phylogenetic tracking of other traits may suggest functional significance in climatic and habitat adaptation. A general increase in the rate of morphological evolution was found at the base of the ENA clade, possibly co-occurring with the increase in rate in evolution of chromosome number. Increased rates in the evolution of morphological traits and the number of chromosomes may signify a shift in selection regimes at the base of the ENA clade. Further work is needed to determine the extent of convergent morphological evolution between the ENA clade and WNA grade to gain a better understanding of the trait variability observed within Section Ovales.
Title: Do oak species that are genetically associated with warmer climatic niches have greater isoprene emission rates?
Advisor: Dr. Mark Potosnak
Abstract: The hydrocarbon isoprene plays an important role in atmospheric chemistry, particularly in regards to air pollution and climate change. It is important to know why certain plant species emit isoprene and what factors affect its production in order to predict future air quality. Past research has indicated that isoprene aids in coping with heat stress, so I hypothesized that source latitude (a proxy for climate) would significantly impact isoprene production. 12 Bur Oaks collected from a latitudinal range (30-45°) were assayed for their isoprene emission rate. There was no significant effect of source latitude on isoprene emission rate. As an alternative explanation, I considered the influence of average daily temperature on isoprene emission rate, but there was also no significant effect. Future statistical analysis will be conducted to investigate the interactive effects of source latitude and daily average temperature.
University of Wisconsin - Stevens Point
Title: Assessing performance of volunteers to monitor the urban forest
Advisors: Dr. Bryant Scharenbroch & Dr. Lara Roman
Abstract: Utilizing volunteers to monitor the urban forest can reduce management costs, but is the data they collect accurate? To evaluate the effect of volunteer prior experience in data collection accuracy, six novice and six intermediate volunteers were provided the same level of training and tasked with collecting basic tree data in Lombard, IL. Results show that volunteer prior experience level does not impact data accuracy. Data accuracy was acceptable for all volunteers for identification to genus-level, measuring diameter of single-stemmed trees, and evaluating the mortality and dieback status of trees. Data accuracy was not acceptable for identification to species-level, evaluation of wood condition or assessing crown transparency.
Indiana University - South Bend
Title: Carbon storage and dynamics of The Morton Arboretum
Advisor: Emma Bialecki
Abstract: Due to disruptions in the carbon cycle, atmospheric CO2 is on the rise. Surface respiration is one of the main sources of atmospheric CO2 and is influenced by land use and change. Urbanization is rapidly increasing and more land is being altered to meet the needs of an increasing human population. Understanding and monitoring surface respiration and its drivers will help us better understand how urbanization may alter the carbon cycle. The objective of this study was to characterize the small-scale variability of surface respiration in three different land uses (park, developed, and forest) in The Morton Arboretum. These landscapes represent major types of land use and change associated with urbanization. Overall, we found surface respiration to be greater in developed and park landscapes compared to forested sites at The Morton Arboretum. We suspect surface respiration is lowest in the forest, because these soils are less disturbed and buffered by the forest canopy cover. Further research is needed monitor these parameters throughout the year and across more sites to give us a better understanding of the carbon dynamics of the landscapes of The Morton Arboretum.
Title: Oak seedling survival and growth in relation to canopy structure and understory competition
Advisor: Dr. Robert Fahey
Abstract: Prior to Euro-American settlement, oaks (Quercus) were the dominant genus in many forests across North America. However, the dominance of oaks has declined greatly in many forests due to changing climatic conditions, changes in fire regimes, increased browsing, exotic pests and vegetation, and logging. In addition, in many forests in which an oak component remains a transition is occurring to dominance by more shade-tolerant mesic species (e.g., sugar maple) and there is very little regeneration of oak species. Restoring oak dominance and promoting oak regeneration have become important goals for managers across a variety of forest types and locations. The principle goal of this project was to improve understanding of the relation between light environment and oak seedling success in a larger project focused on developing canopy thinning methods for promoting oak regeneration in urban natural areas. We analyzed how canopy openness, light transmittance, and understory competition varied among treatments (20% and 10% basal area removal and control) and how each affected oak seedling growth. We expected growth to be greatest with the most thinning; however, we also expected the negative effects of understory competition to be greatest in these locations. Seedling growth varied significantly among the thinning units, but growth only differed between the control and thinning treatments, not among the thinning intensities. Light availability was much greater at 2.5m in the 20% removal treatment, but this light was quickly attenuated by the understory layer and there was no difference in radiation at 0.5m (approximately the average seedling height). This effect illustrates the importance of the understory layer, but it is difficult to separate out the specific effect of this layer. A useful next step could be to manipulate understory vegetation within the experiment to isolate the impact of understory competition.
University of Illinois
Title: Towards a sustainable designer urban soil for trees
Advisors: Dr. Bryant Scharenbroch & Michelle Catania
Abstract: Growing healthy trees in artificial urban soils is challenging; these soils often constrain the establishment, growth, and longevity of urban landscape trees. These soils tend to drain well, but have low water-holding and nutrient supply capacities. The purpose of this study was to compare the performance of the current urban soil standard against a natural forest soil, as well as a new, intermediate specification (tree soil). Additionally, both mulched and non-mulched samples were studied to determine the effects of mulching on each soil type. Trees were watered for the first 65 days, after which watering was stopped to assess performance in drought conditions. Surface respiration and stomatal conductance were measured weekly. For each of these measurements, mulched pots consistently measured significantly higher than those with a bare surface. Respiration was significantly higher in the urban soil during the watering period, while the tree soil was significantly higher during the drought period. Stomatal conductance was not significantly different between soil types until the last week of measurements under drought conditions, in which the tree soil performed best. Overall, the tree soil may be best for urban trees. These trees must be relatively self-sufficient, and should not rely on heavy watering for survival. Future studies should assess the performance of these soils under multiple watering and fertilization levels to further understand their suitability for the urban environment.
Northern Illinois University
Title: Effects of urban trees and green infrastructure on water quality and runoff
Advisor: Dr. Bryant Scharenbroch
Abstract: In the late 1990’s, Morton Arboretum installed a permeable parking lot to improve the quality of water flowing into Meadow Lake. Integral to its design were 9’ wide bioswale medians, due to their ability to retain soil moisture. It is believed that healthier trees enhance the bioswale’s retentive capacity by transpiring extra water out of the system. This study analyzed the health and productivity of trees in Morton Arboretum’s bioswales. For 21 bioswale and 20 control trees, stomatal conductance, leaf greenness, and various soil parameters were catalogued over a five week period. Quercus macrocarpa was found to perform best compared to other species in both settings, while Cercis canadensis and Carpinus caroliniana were healthier in the control setting. Tolerance of various moisture conditions appeared to be a key trait for success of trees in bioswales.
University of California - Davis
Title: Assessing the use of morphological characteristics to predict branch attachment strength
Advisor: Dr. Jason Miesbauer
Abstract: Branch failure during storm events is a common problem experienced by urban trees, causing property damage, power outages, and human injury and fatality. Improving our knowledge of characteristics that affect branch attachment strength is crucial to help improve the resiliency of urban trees to storm damage. Previous research has shown that branch attachments with a low branch-trunk diameter ratio (aspect ratio) are stronger than attachments with a large aspect ratio. Included bark, which occurs when bark on the branch and trunk become embedded between them at the union, has also been shown to reduce the attachment strength of co-dominant stems (i.e. high aspect ratio). However, there is a lack of research investigating relationships between traits such as aspect ratio, included bark, and branch union shape and their effect on branch attachment strength. The objective of this project is to determine if outwardly observable characteristics, such as aspect ratio, included bark, union shape (U or V), and their interactions effect branch attachment strength in Norway Maple (Acer platanoides). Our findings suggest that trees with high aspect ratio will be more likely to fail during storms, and the presence of included bark and V-shaped unions may increase this likelihood. Results from this study could help arborists improve pruning techniques used on urban trees. While aspect ratio has been shown to be correlated with attachment strength, the influence of included bark on this relationship has not previously been shown. Further research on different tree species would help to further validate these results and help tree care professionals improve the resiliency of urban trees to storm damage.
Watch the 2014 Center for Tree Science Undergraduate Research Fellowship Symposium