Publications by A.L. Orchansky

Carbon, water, and energy exchanges of a hybrid poplar plantation during the first five years following planting. 2011. Cai, T.; Price, D.T.; Orchansky, A.L.; Thomas, B.R. Ecosystems 14(4):658-671.

Tue, 03 May 2011

Eddy covariance was used to measure above-canopy exchanges of CO2 and water vapor at an operational plantation of hybrid poplar (variety ‘‘Walker’’) established on marginal agricultural land in east central Alberta, Canada. Winter ecosystem respiration (Re) rates were inferred from seasonal changes in the normalized respiration rate at 10C (R10) for the growing season and observations of soil CO2 concentration measured with solid-state probes. Over five consecutive growing seasons following planting, gross ecosystem production (GEP) increased each year, ranging from 21 g C m-2 y-1 in year 1 to 469 g C m-2 y-1 in year 5. During this period, the annual carbon balance shifted from a net source of greater than 330 g C m-2 in year 1 to approximately C-neutral in year 5. Total carbon (C) release over 5 years likely exceeded 630 g C m-2. Intra- and interannual variations in temperature and soil water availability greatly affected annual C balance each year. GEP and Re were particularly sensitive to temperature during spring and to soil water availability in summer: year 5 was notable because a cold spring and accumulating drought caused growth and carbon uptake to fall well below their potential. Annual evapotranspiration (ET) increased slightly with leaf area, from 281 mm in year 1 to 323 mm in year 4, but in year 5 it declined, while exceeding total precipitation (P). This trend of increasing annual ET/P suggests that annual GEP could become increasingly water-limited in years with below normal precipitation, as the plantation achieves maximum leaf area. Measured canopy albedos did not change appreciably over three winters, suggesting that estimates of increased radiative forcing resulting from afforestation in high latitudes could be exaggerated in regions where fast-growing deciduous plantations are managed on short (~20-year) rotations.

The effect of post-fire stand age on the boreal forest energy balance. 2006. Amiro, B.D.; Orchansky, A.L.; Barr, A.G.; Black, T.A.; Chambers, S.D.; Chapin III, F.S.; Goulden, M.L.; Litvak, M.; Liu, H.P.; McCaughey, J.H.; McMillan, A.; Randerson, J.T. Agricultural and Forest Meteorology 140: 41-50.

Fri, 08 Dec 2006

Photosynthetic light use efficiency of three biomes across an east–west continental-scale transect in Canada. 2006. Schwalm, C.R.; Black, T.A.; Amiro, B.D.; Arain, M.A.; Barr, A.G.; Bourque, C.P-A.; Dunn, A.; Flanagan, L.B.; Giasson, M-A; Lafleur, P.M.; Margolis, H.A.; McCaughey, J.H.; Orchansky, A.L.; Wofsy, S.C. Agricultural and Forest Meteorology 140(1-3): 269-286.

Fri, 08 Dec 2006

Late-summer carbon fluxes from Canadian forests and peatlands along an east-west continental transect. 2006. Coursolle, C.; Margolis, H.A.; Barr, A.G.; Black, T.A.; Amiro, B.D.; McCaughey, J.H.; Flanagan, L.B.; Lafleur, P.M.; Roulet, N.T.; Bourque, C.P-A.; Arain, M.A.; Wofsy, S.C.; Dunn, A.; Morgenstern, K.; Orchansky, A.L.; Bernier, P.Y.; Chen, J.M.; Kidston, J.; Saigusa, N.; Hedstrom, N. Can. J. For. Res. 36(3): 783-800.

Tue, 05 Dec 2006

Net ecosystem productivity (NEP) during August 2003 was measured by using eddy covariance above 17 forest and 3 peatland sites along an east-west continental-scale transect in Canada. Measured sites included recently disturbed stands, young forest stands, intermediate-aged conifer stands, mature deciduous stands, mature conifer stands, fens, and an open shrub bog. Diurnal courses of NEP showed strong coherence within the different ecosystem categories. Recently disturbed sites showed the weskest diurnal cycle; and intermediate-aged conifers, the strongest. The western treed fen had a more pronounced diurnal pattern than the eastern shrub bog or the Saskatchewan patterned fen. All but three ring were clearly afternoon C sinks. Ecosystem respiration was highest for the young fire sites. The intermediate-aged conifer sites had the highest maximum NEP (NEP_MAX) and gross ecosystem productivity (GEP_MAX), attaining rates that would be consistent with the presence of a strong terrestrial C sink in regions where these types of forest are common. These results support the idea that large-scale C cycle modeling activities would benefit from information on the age-class distribution and disturbance types within larger grid cells. Light use efficiency followed a pattern similar to that of NEP_MAX and GEP_MAX. Four of the five recently disturbed sites and all three of the peatland sites had low water use efficiencies.

Surface energy balances of Canadian boreal forests following fire. 2006. Sass, A.P.; Amiro, B.D.; Orchansky, A.L. Pages P.1.2-P.1.5 in Proceedings: 27th Conference on Agricultural and Forest Meteorology. May 22-25, 2006, San Diego, California, USA. American Meteorological Society, Boston, Massachusetts, USA.

Tue, 18 Jul 2006

Fire is an important stand renewing event in boreal forests that drastically changes the surface characteristics of the forest. As forests go through various stages of succession following fire, the surface energy fluxes will change. Data obtained from eddy covariance measurements at three post-fire boreal sites in central Saskatchewan of ages 27 years, 15 years, and 6 years were used to quantify the energy balances. Located in close proximity to one another, the sites are exposed to similar climate and weather conditions. Monitoring began at the site burned in 1989 (F89) and the site burned in 1998 (F98) in the spring of 2001. The site burned in 1977 (F77) has been monitored since the spring of 2003. Net radiation, sensible heat flux, latent heat flux, and soil heat flux were measured at all sites. Additional meteorological measurements were also taken. Significant differences among sites were observed in all fluxes during 2001 and 2002. By 2004, the fluxes at all sites became more similar. Latent heat flux best illustrates the changes in site characteristics that take place with time after fire. Summertime daily latent heat fluxes are twice as high at the F77 and F89 sites compared to the F98 site. This difference is likely due to the abundance and maturity of the vegetation at the two older sites compared to F98 where the vegetation is small and sparse. The amount of bare ground at F98 has a significant impact on soil heat flux which is illustrated during the summer and winter months when F98 has the highest soil heat flux. Understanding how the energy balance changes with time following disturbance is also important for predicting the effects that the possible increase in forest fires that may accompany climate change could have on local, regional and global climates.

A perspective on carbon dioxide flux measurements using an open-path infrared gas analyzer in cold environments. 2006. Amiro, B.D.; Orchansky, A.L.; Sass, A.P. Pages 4.7-4.11 in American Meteorological Society, Proceedings: 27th Conference on Agricultural and Forest Meteorology. May 22-25, 2006, San Diego, California, USA. American Meteorological Society, Boston, Massachusetts, USA.

Thu, 30 Mar 2006

Open-path infrared gas analyzers, such as the LI7500 (LICOR Inc, Lincoln, NE), offer tremendous promise for measuring fluxes of water and carbon dioxide. The advantage is fast frequency response, lower power requirements and simplified system design because a pump is not needed to flow air through the sensor. Hence, they have become a common instrument for measurements in remote locations where power requirements are a major consideration. Over the past few years, we have been puzzled by apparent downward fluxes of carbon dioxide during winter at our sites in northern forests. The observations are inconsistent with our knowledge of biological activity in frozen landscapes, and are different from measurements made with a closed path sensor, where small net respiration is observed. Several other researchers have also observed this at their sites, although there does not appear to be a problem at warmer sites, and summer-time comparisons between closed- and open-path sensors are usually satisfactory. Recently, scientists at LICOR have illustrated that the sensor head is temperature controlled and that the heating/cooling power increases with temperature deviations from an ideal condition of about 30C. We believe that this heating is causing air density fluctuations within the sensor head path during cold conditions, and these density fluctuations are not being accounted in the Webb/Pearman/Leuning (WPL) adjustment for density to determine the correct quantity in the eddy flux calculation. Although attempts are being made to resolve heat transfer calculations, it is possible that a full adjustment will be elusive. Here, we present a simplified bracketing of the problem to be used in quality control. We do this through a calculation of the local sensible heat flux density created by the heated sensor, which increases with decreasing temperature. We then apply the correction as an added heat flux term to the WPL adjustment to show the magnitude of potential error. This is less satisfactory than a full heat transfer correction, but allows for data quality control until a rigorous solution becomes available. We illustrate the effect using data through seasonal cycles from forested sites in central Saskatchewan, Canada, which clearly shows that the data are questionable through much of the winter.

Comparison of net ecosystem production at mature and disturbed forest sites, Saskatchewan, Canada 2001-02. 2004. Amiro, B.D.; Barr, A.G.; Black, T.A.; Iwashita, H.; Kljun, N.; McCaughey, J.H.; Morgenstern, E.K.; Murayama, S.; Nesic, Z.; Orchansky, A.L.; Saigusa, N. Pages 12.9-12.17 in Proceedings of the 26th Conference on Agricultural and Forest Meteorology, August 23-26, 2004, Vancouver, British Columbia. American Meteorological Society, Boston, Massachusetts, USA.

Wed, 01 Dec 2004

Net ecosystem productivity following fire in the Canadian boreal forest. 2004. Orchansky, A.L.; Amiro, B.D. Pages 1.16-1.18 in Proceedings 26th Conference on Agricultural and Forest Meteorology, August 23-26, 2004, Vancouver, British Columbia. American Meteorological Society, Boston, Massachusetts, USA.

Thu, 24 Jun 2004