Earlywood vessel area analysis of Quercus macrocarpa tree rings at the Cedar Creek Ecosystem Science Reserve in Minnesota

Abstract

Quantification of various wood anatomical characteristics in annually resolved tree rings has been shown to reveal environmental information on seasonal or shorter timescales that is often not present in ring width alone. The genus Quercus is particularly important to dendroclimatology, and Q. macrocarpa tree rings are particularly useful for studies of regional climate. Further, the ring-porous anatomy of this species positions it as a prime candidate for quantitative wood anatomy. To date, the majority of dendroclimate studies involving Q. macrocarpa have been based purely on ring width. Very few quantitative wood anatomy studies have been conducted in North America, and virtually none in the Western Great Lakes states. Measurement of earlywood vessel area may provide an avenue for extracting information on past environmental conditions, even at forest interior locations which fall outside the typical schema of dendrochronology site selection. When related to tree height measurements, earlywood vessel area can provide key insights into the hydraulic properties of individual plants, water use strategies, and the history of tree height throughout ontogenesis.This study examines the interannual variability in mean vessel area as well as the reliance of vessel area on tree height in savanna and woodland habitat types at the Cedar Creek Ecosystem Science Reserve, in Minnesota. The relationship between vessel area and tree height is statistically and practically significant, and far stronger at this site than the relationship between inter-annual mean vessel area variability and climate, for which no clear process-based relationships were detected. This finding holds true when other metrics than mean vessel area are explored, including percentiles of mean vessel area, hydraulic diameter, and vessel area variance. The overall positive trend in vessel area throughout ontogenesis and the adherence of this trend to a functional allometric power curve further support the body of literature showing that tree height is a deterministic driver of vessel size in these individuals. Given the clear dependence of hydraulic characteristics on tree height, and the possible role of tree height as a factor in plant vulnerability to myriad factors associated with global environmental change, I advocate for tree height to become a standard datum in dendrochronological sampling, and encourage future studies involving quantitative wood anatomy to further examine the role of tree height on individual trends in xylem size through time.