Summary
Diurnal and seasonal tree water storage was stud-
ied in three large Douglas-fir (Pseudotsuga menziesii [Mirb.]
Franco) trees at the Wind River Canopy Crane Research site.
Changes in water storage were based on measurements of sap
flow and changes in stem volume and tissue water content at
different heights in the stem and branches. We measured sap
flow by two variants of the heat balance method (with internal
heating in stems and external heating in branches), stem vol-
ume with electronic dendrometers, and tissue water content
gravimetrically. Water storage was calculated from the differ-
ences in diurnal courses of sap flow at different heights and
their integration. Old-growth Douglas-fir trees contained large
amounts of free water: stem sapwood was the most important
storage site, followed by stem phloem, branch sapwood,
branch phloem and needles. There were significant time shifts
(minutes to hours) between sap flow measured at different po-
sitions within the transport system (i.e., stem base to shoot tip),
suggesting a highly elastic transport system. On selected fine
days between late July and early October, when daily transpira-
tion ranged from 150 to 300 liters, the quantity of stored water
used daily ranged from 25 to 55 liters, i.e., about 20% of daily
total sap flow. The greatest amount of this stored water came
from the lower stem; however, proportionally more water was
removed from the upper parts of the tree relative to their water
storage capacity. In addition to lags in sap flow from one point
in the hydrolic pathway to another, the withdrawal and replace-
ment of stored water was reflected in changes in stem volume.
When point-to-point lags in sap flow (minutes to hours near the
top and stem base, respectively) were considered, there was a
strong linear relationship between stem volume changes and
transpiration. Volume changes of the whole tree were small
(equivalent to 14% of the total daily use of stored water) indi-
cating that most stored water came from the stem and from its
inelastic (sapwood) tissues. Whole tree transpiration can be
maintained with stored water for about a week, but it can be
maintained with stored water from the upper crown alone for
no more than a few hours.
Keywords: dendrometer, flow rate differences, heat balance
method, time shift, tissue free water content, vertical profile.
Introduction
Most analyses of plant water relations regard the soil as the
sole source of transpired water. Roberts (1976) reported that
the amount of free water from storage in Pinus sylvestris L.
trees and stands is insignificant relative to daily or seasonal
transpiration. Similarly, Tyree and Yang (1990) concluded that
stored water is not a significant source of water for transpira-
tion in most woody plants. Holbrook (1995) in her review of
stem water storage stated: “Its [Stem water storage] role in
maintaining high levels of photosynthetic carbon gain during
periods of drought, however, is limited to plants with inher-
ently low transpiration rates (i.e., CAM succulents and per-
haps large conifers).” However, Ladefoged (1963), Hinckley
and Bruckerhoff (1975), Waring and Running (1978), Waring
et al. (1979) and Èermák et al. (1976, 1982) have suggested
that internal water storage in both elastic and inelastic tissues
may be important in supporting diurnal and seasonal
transpiration of woody plants. In special situations, it has been
observed that internal storage can provide a significant propor-
tion of the total diurnal and even seasonal water use by a plant
(e.g., Èermák et al. 1982, 1984, Goldstein et al. 1984, 1998,
Borchert 1994). If storage is minimal in large trees, then water
loss would either result in severe water deficits or prolonged
stomatal closure. Either of these outcomes would have conse-
quences for growth and survival. Therefore, we contend, as
suggested by older work with trees, that stored water plays a
biologically significant role.
Water transport in large old-growth trees occurs over long
distances via conducting elements that may have low hydrau-
lic conductivities (Gartner 1995, Sperry 1995, Ryan and Yoder
1996). Even in short-stemmed woody plants, there may be a
Tree Physiology 27, 181–198
© 2007 Heron Publishing—Victoria, Canada
Tree water storage and its diurnal dynamics related to sap flow and
changes in stem volume in old-growth Douglas-fir trees
JAN ÈERMÁK,
1,2,3
JIØÍ KUÈERA,
4
WILLIAM L. BAUERLE,
5
NATHAN PHILLIPS
6
and
THOMAS M. HINCKLEY
3
1
Institute of Forest Ecology, Mendel University of Agriculture and Forestry, 61300 Brno, Czech Republic
2
Corresponding author (cermak@mendelu.cz)
3
College of Forest Resources, University of Washington, Seattle, WA 98195, USA
4
Environmental Measuring Systems Inc., 61300 Brno, Czech Republic
5
Department of Horticulture, Clemson University, Clemson, SC 29634, USA
6
Department of Geography, Boston University, Boston, MA 02215, USA
Received September 5, 2005; accepted April 1, 2006; published online November 1, 2006
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