Browsing by Subject "oak"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
  • Thumbnail Image
    Item
    Earlywood vessel area analysis of Quercus macrocarpa tree rings at the Cedar Creek Ecosystem Science Reserve in Minnesota
    (2021-07) Crawford, Daniel
    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.
  • Thumbnail Image
    Item
    Fire and vegetation effects on productivity and nitrogen cycling across a forest-grassland continuum
    (Ecological Society of America, 2001) Reich, Peter B; Peterson, David W; Wedin, David A; Wrage, Keith
    Mixed tree–grass vegetation is important globally at ecotones between grasslands and forests. To address uncertainties vis-à-vis productivity and nitrogen (N) cycling in such systems we studied 20 mature oak savanna stands, ranging from 90% woody dominated to 80% herbaceous dominated, growing on comparable soils in a 32-yr-old fire frequency experiment in Minnesota, USA. Fire frequencies ranged from almost annual burning to complete fire protection. Across all stands, aboveground net primary productivity (ANPP) ranged from 2 to 12 Mg·ha−1·yr−1, decreased with fire frequency (r2 = 0.59), increased with woody canopy dominance (r2 = 0.83), and increased with soil net N mineralization rates (r2 = 0.79), which varied from 25 to 150 kg·ha−1·yr−1. ANPP was positively related to total biomass (r2 = 0.95), total canopy leaf N content (r2 = 0.88), leaf area index (LAI; r2 = 0.87), annual litterfall N cycling (r2 = 0.70), foliage N concentration (r2 = 0.62), and fine root N concentration (r2 = 0.35), all of which also increased with increasing tree canopy cover. ANPP, soil N mineralization, and estimated root turnover rates increased with woody canopy cover even for stands with similar fire frequency. ANPP and N mineralization both decreased with fire frequency for stands having a comparable percentage of woody canopy cover. Fine root standing biomass increased with increasing grass dominance. However, fine root turnover rate estimated with a nitrogen budget technique decreased proportionally more with increasing grass dominance, and hence fine root productivity decreased along the same gradient. Via several direct and indirect and mutually reinforcing (feedback) effects, the combination of low fire frequency and high tree dominance leads to high rates of N cycling, LAI, and productivity; while the opposite, high fire frequency and high grass dominance, leads to low rates of N cycling, LAI, and productivity. Carbon and N cycling were tightly coupled across the fire frequency and vegetation type gradients.