Contribution of cowberry transpiration to evapotranspirationin larch forest
Mie Miyahara1,Chisato Takenaka1, Takashi Kuwada2, Takeshi Ohta1,2,T.C.Maximov3(1:Graduate School of Agriculture, Nagoya University,
2:CREST, Japan Science and Technology Agency,
3:Institute for Biological Problems of the Cryolithozone, SDRA)
Graduate School of Agriculture, Nagoya University, Japan, 464-8601, Furo-cho,
Chikusa Nagoya, Japan. e-mail: i031038@mbox.nagoya-u.ac.jp
Abstract
To demonstrate the contribution of cowberry transpiration to evapotranspiration in eastern Siberia larchforests, cowberry transpiration rate was measured from May to September 2004. Just after larch leaf
developed, cowberry transpiration rate came considerably down, in spite of relatively high temperature
and VPD. These results suggest that it may be caused by competition of water with larch. Thus, it is
supposed that cowberry transpiration rate depends on phenology of larch. And we found that the latent
heat by transpiration of cowberry occupied nearly 100% in the early stage of leaf development of larch,and 35 to 60% during the growing season, by analyzing the seasonal variation of latent heat flux. Theseresults indicate that cowberry plays a very important role in water cycles in larch forest, and the effects
for water cycles may be most conspicuous before growing season of larch.

Keyword: cowberry, transpiration, evapotranspiration, phenology of larch

1.

Introduction

Forests in Eastern Siberia are dominated byunderstory

deciduous conifer tree, Larch (Larix cajanderi),important to understand the role of understory

known as light taiga. In mature larch forest, thevegetation in various substance cycles in a forest

overstory is so sparse that the forest floor isecosystem. Recently, an interest in energy andcovered with cowberry (Vaccinium vitis-idaea)

water cycles in Siberian boreal forests has been

due to its light environment. From many studies,growing, and many studies on these subjects haveit was found that understory vegetation, covering

been conducted. Hamada et al. (2004) reported

forest floor, have various effects on forestthat the contribution of understory to entire

ecosystems.

thatevapotranspiration of larch forest was quite

understory vegetation affect soil characteristics,

significant and was estimated 25% to 50%. Since

and growth and physiology of overstory such as

cowberry is evergreen species, it is supposed thatroot biomass, transpiration rate, and net primary

cowberry transpiration plays an important role inproduction (Sanada et al., 1996, Robert et al.,water cycle in larch forest. However, field

2003, Busse et al., 1996, Kelliher and Black., 1986,

observation data on the role of cowberry in larch

Kari et al., 2003). Moreover, Kelliher and Black

forest have been little. The purpose of this study(1986) and Miller et al. (1998) reported thatis to quantify the contribution of cowberry

understory evapotranspiration is considerable,transpiration to larch forest evapotranspiration,

especially when trees are spaced with littleand to reveal its seasonal contribution.

Somestudies

reportedshading.

Therefore,

itisvery2.

Study site and Methods

environmental factors during the observation

Study site was a larch forest at Spasskaya Pad

period are showed in Fig.3. Temperature and(62°14’29”N, 129°39’2” E), located about 20km

VPD had highest values on July 2 and soil

north of Yakutsk in eastern Siberia. The standmoisture showed the lowest values in the samedensity is 840 trees ha-1, and the mean annualday. These environmental factors could nottemperature and the annual precipitation are−explain the two-peak shaped transpiration rate of

10.2℃ and 188mm, respectively.

cowberry.

We measured transpiration rate of cowberry
using an infrared gas analyzer, LI-6400. Threeplots (1m×1m) were chosen in a larch forest, andmeasurement. To obtain LAI (Leaf Area Index) ofcowberry, all of shoots in five small plots (0.1m×0.1m) were cut and the total leaf area weremeasured by scanning. The transpiration rate perunit area was calculated using LAI, and was

mmol H2Om-2s-1

4 shoots of cowberry from each plot were used forconverted to latent heat flux. Soil moisture at
10cm depth was monitored using TDR. The

9/2
8/16
7/2
6/13
6/5
5/21

1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0Fig.

5:00

7:00

9:00 11:00 13:00 15:00 17:00 19:00

1Diurnal

variationofcowberrytranspiration rate per leaf area.

measurements were conducted from May (earlystage of leaf development of larch) to September(early stage of leaf-fall of larch) in 2004.

1.2

Temperature and relative humidity in eachmeasurement day were measured at a flux tower,of cowberry transpiration. The relative humidity
was converted to vapor pressure deficit (VPD).

13:00

0.8mmol H2Om-2s-1

located about 300m east of the measurement plot

11:00

1.0

0.6
0.4
0.2
0.0

3. Results and Discussion
Figure 1 shows diurnal variation of cowberrytranspiration rate of all observation days in 2004.
Cowberry transpiration rate tended to reach a5/21

6/4

5/21

6/5 6/136/18

7/2

Leaf
development

Fig.

2

Seasonal

7/16

7/30

8/13

7/2

8/27

8/16

Growingseasonvariation

9/2
Leaf
fallofcowberry

peak at 11 a.m. or 13 p.m. The seasonal changetranspiration rate at 11:00 a.m. andof cowberry transpiration rate at 11 a.m. and 13

13:00 p.m.

p.m. during the observation period are shown in
Fig.2. It showed a two-peak shaped variation, andOn the other hand, from a viewpoint of larch

on

came

phenology, the date of snow disappearance wasconsiderably down. In plant physiology, it is wellMay 10, and leaf development of larch started

known that transpiration rate is controlled byfrom middle of May and ended on middle of June.

various

air

Therefore, the day of the lowest cowberry

temperature, VPD, or soil moisture, so on. Thesetranspiration (6/13) corresponded to the end ofJune13,

thetranspiration

environmental

factorsratesuchasleaf development. From these results, it iscowberry transpiration to evapotranspiration issupposed that the decrease of transpiration rate

more important before growing season thanon June 13 could be attributed to the competitionduring growing season of larch.

of water uptake with larch, because the wateruptake by larch may be vigorous at immediately
after

leaf

development.

Thatis,seasonal

variation of cowberry transpiration rate may

10080

3080
6060

40

40

2020

Soil moisture

250

5/21
1

6/5
2

6/13
3

7/2
8/16
45

9/2
60Fig. 4 Percentage of latent heat flux by

20transpiration of cowberry to entire

latent heat flux at 11 a.m. and eachflux.

155/21Fig.

VPD%℃, kPa

Temperature

100%

W m-2

depend on the phenology of larch.

20181614121086420%
CanopyCowberry120

6/5 6/13

7/2

8/13

9/2

3 Air temperature, vapor pressure deficit

4. Conclusionand surface soil moisture (10cm depth) at

It is suggested that cowberry transpiration rate

11 a.m. in each measurement day ofdepends on the phenology of larch, since itcowberry transpiration rate.

decreased significantly at immediately after leaf
development of larch. Contribution of cowberry

To make clear the contribution of cowberrytranspiration

toevapotranspiration

occupiedtranspiration to evapotranspiration, the latentnearlyintheofheat flux by cowberry was calculated usingdevelopment of larch, and even during thetranspiration rate. The LAI of cowberry is

growing season, it showed 35 to 60%. Therefore, itestimated at 2.1. Figure 4 shows percentages ofis demonstrated that cowberry plays a very

cowberry latent heat flux in the canopy flux inimportant role in water cycle in larch forests, andforest with each flux. Latent heat flux by

the effects may be most conspicuous before

cowberry accounted from 35% to 100% in entiregrowing season of larch.

100%

early

stageleaf

forest values. Especially before the larch leaf
development, almost all of latent heat flux wasReferences

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