Cambodia’s cut
An ITTO fellowship
helped estimate asustainable yieldfrom logged-overforests in Cambodia
By Dana Kao1,Nobuya Mizoue2 andShigejiro Yoshida2
Dr Dana Kao (Cambodia) received
an ITTO fellowship in 2008 toundertake a Doctoral Program inForest Management at theDepartment of Forest and Forest
Products Sciences, Faculty ofAgriculture, Graduate School ofBioresource and Bioenvironmental
Sciences, Kyushu University,
Japan. This article is based on his
doctoral research.

Stand of foresters: One of the inventory teams. Photo: D. KaoTropical forests host a large majority of the earth’s
biodiversity, representing an invaluable asset bothglobally and for local communities (see Top et al.
2009). Forests are also important for their role in the carbon
and water cycles (Clark et al. 2001), and well-managed
forests can be an ecotourism attraction.
One of the tasks of foresters is to ensure that the extractionof forest products such as timber does not exceed thesustainable capacity of the forest ecosystem, thus ensuringthat forests are able to perform their many functions. To
assess the sustainability of commercial timber harvesting,estimates are needed of forest increment—that is, the rate at
which the forest grows. However, reliable data on commercial
tree growth are very limited in the natural tropical forests ofSoutheast Asia.

1Forest Management Office,Department of Forest andForestry Community
Management, Forestry
Administration of Cambodia
kaodana@gmail.com

2

Department of Forest and Forest
Products Sciences, Faculty ofAgriculture, Kyushu University,
Japan

In 1998 over 7 million hectares of Cambodia’s forests wereavailable for harvesting in forest concessions. In 2001 thegovernment suspended all logging activities in concessions
and this ban remains mostly in place, although illegal
logging is thought to be widespread (ITTO 2011). Should
legal logging resume it is important to know growth andyield characteristics so that a sustainable harvest can becalculated and imposed. Little is known, however, about thegrowth dynamics of Cambodian forests. Therefore, wecarried out a study to estimate forest increment of logged
and unlogged tropical evergreen forests in northern
Cambodia.

Study site and method
The study area is located at longitude 104º58’E to 105º82’E
and latitude 13º48’N to 14º89’N within a forest concession in12ITTO Tropical Forest Update 21/1

Preah Vihear province (Figure 1), with various (logged andunlogged) forest formations covering a total area of 103 058
hectares. In 20 sample plots in logged (1998) and unlogged
forests, the diameter at 1.3 m (dbh) and height of each live
tree (commercial, non-commercial and non-timber forest
product—NTFP) were measured, first in March 2001 andthen in October 2008. Immature trees and NTFPs with dbh
10–29 cm were measured in subplots (20×20 m), whilemature trees with dbh greater than 30 cm were measured inthe main plots (40×60 m).
All measured trees were classified by diameter and tree
density, volume and basal area were estimated. The averagetree volumes of dipterocarps and non-dipterocarps wereestimated based on equations reported in Forest Authority(2004). The periodic annual increment (PAI) was estimatedby comparing the densities, volumes and basal areas oflogged and unlogged sites in 2001 and 2008.
The structural change in the first three years after logging
was estimated by comparing analogous unlogged evergreen
forest (UNFE) with the 2001 measurement of evergreen
forest that was logged in 1998 (LGFE). The change over ten
years was estimated by comparing the 2008 measurementsof the UNFE and the LGFE. The annual change in structure
was estimated by comparing measurements in 2001 and2008.
The PAI was assumed to constitute net growth because theremaining live trees and newly recruited trees wereconsidered as live trees in the second measurement. Vanclay(1994) defined yield as Vn = V2 – V1 + Vc, where V2 and V1
are the live stand volume at measurements 2 and 1,
respectively, and Vc is the cut volume. Vanclay (1994) definedLogged and unloggedFigure 1

Plot locations

Note: UNFE = unlogged evergreen forest and LGFE = logged evergreen forest.

the net growth of initial volume as Vni = Vn – Vi, where Vi
is the ingrowth volume. This study considers only V2 – V1 ofeach forest type.

Results
In 2008 the density, volume and basal area (for trees withdbh ≥ 10 cm) of the LGFE were 431.7 trees/ha, 202.6 m3/haand 26.0 m2/ha, respectively; those of the UNFE were 483.3
trees/ha, 199.7 m3/ha and 22.2 m2/ha (Table 1). The averageannual recruitment of trees with dbh ≥ 10 cm in the LGFE
(5.7%) was higher than that in the UNFE (3.3%), due to theopen canopy created by harvesting (Table 2).
For trees with dbh ≥ 50 cm the PAI of commercial tree
volume was 1.1 m3/ha in the LGFE and 0.2 m3/ha in theUNFE, while the PAI of basal area was 0.6 m2/ha and 0.2 m2/
ha, respectively (Table 2). About 2.4% of trees with dbh ≥ 10cm were assessed as dead in the LGFE in 2008, comparedwith 5.5% in the UNFE (Table 1). The annual growth rate oftree density (all stems with dbh ≥ 10cm) was higher in theLGFE (5.7%) than in the UNFE (3.3%), as was the annual
volume increment (3.5% compared with 1.6%) (Table 2).

Conclusion
In 1998, the harvest of the LGFE site involved the removal of
3.0 trees/ha (dbh ≥ 50 cm), which resulted in a yield of 22.2
m3/ha by volume and 1.6 m2/ha by basal area (Kao and Iida2006). The volume and basal area increments for trees withdbh ≥ 50 cm can be used to set the sustainable yield(although logging damage, planned silvicultural treatments
and the forest’s capacity to provide ecosystem services suchas those related to biodiversity, carbon, water and aesthetic
values should also be taken into account).
The ITTO criteria and indicators for the sustainable
management of natural tropical forests (ITTO 2005) statethat forest resource assessments carried out periodically arevital for ensuring the sustainable production of forest goods
and services for society; this includes determining thesustainable yield. In the study area, the total volume
increment of trees with dbh ≥ 50 cm 25 years after logging
is estimated at about 27 m3/ha (i.e. 1.1 m3/ha x 25), which isgreater than the previously harvested volume. Therefore,
harvesting on a 25-year cutting cycle should be possible inthe LGFE. Since the initial logging was in 1998, the next
harvest could take place in 2023. However, we recommend

ITTO Tropical Forest Update 21/1

13

Showing their classes
Table 1Forest parameters, 2001 and 2008, by dbh class and logged and unlogged

dbh class(cm)

2008

2001

LGFE

UNFE

LGFE

UNFE

DeVolBADeVolBA

DeVolBA[dbh < 0.5 cm;
height >1 m]

9440

NANA7960

NANA5100NA0.5–9810

115.8

3.3

900.0

146.1

3.5

691.7

NANA

DeVolBA

3900

NANANA

712.5

NANA

10–19230

47.6

3.6

327.5

77.0

4.8

143.8

35.6

2.1

250.0

62.7

4.2

20–29120

50.2

5.4

87.5

28.4

3.3

62.5

29.3

2.8

62.5

23.9

2.8

30–39

37.1

18.8

2.6

25.4

13.7

2.0

22.9

18.2

2.0

17.2

11.3

1.5

40–49

12.9

12.8

2.0

13.3

13.1

1.9

2.8

3.5

0.4

10.9

11.7

1.7

>50

31.7

73.1

12.4

29.6

67.4

10.1

16.7

64.7

7.7

22.9

65.9

8.8

Total (dbh≥10cm)

431.7

202.6

26.0

483.3

199.7

22.2

248.6

151.4

15.1

363.5

175.6

18.9

Grand total

10682

318.4

29.2

9343.3

345.8

25.7

6040.3

151.4

15.1

4976.0

175.6

18.9

[Total dead]

40.4

54.6

[Total deaddbh≥10 cm]

10.4

24.6

Note: LGFE = logged evergreen forest, UNFE = unlogged evergreen forest, dbh = diameter at breast height (1.3 m); De = density (trees/ha); Vol = tree volume (m3/ha); BA = basal area (m2/ha); NA = data not available; TD ≥ 10 cm = total number of trees with dbh > 10 cm.

Growing back
Table 2

Periodic annual increment, by diameter class, logged and unlogged
Annual growth

Annual growth (% of dbh≥10 cm)

LGFE

UNFE

LGFE

dbh class (cm)

DeVolBA

De

Vol

BA

[dbh < 0.5 cm;
height >1 m]

578.7

NANA

541.3

NANA

0.5–915.8

NANA

25.0NANA

10–19

11.5

1.6

0.2

10.3

1.9

20–29

7.7

2.8

0.3

3.3

30–39

1.9

0.1

0.1

40–49

1.3

1.2

>50

2.0

Total (dbh≥10 cm)

24.4

UNFE

DeVolBADeVol

BA

0.1

2.7

0.8

0.82.11.0

0.4

0.6

0.1

1.8

1.4

1.3

0.7

0.3

0.3

1.1

0.3

0.1

0.4

0.0

0.3

0.2

0.2

0.3

0.2

0.3

0.2

0.0

0.3

0.6

0.8

0.1

0.1

0.1

1.1

0.6

0.9

0.2

0.2

0.5

0.6

2.4

0.2

0.1

0.8

6.8

1.5

16.0

3.2

0.4

5.7

3.4

5.6

3.3

1.6

2.0

See Table 1 for abbreviations.

that damage caused by logging should be studied in detail
before putting this conclusion into effect, as should theeffects of logging at this intensity on other forest values.
Long-term monitoring of yield, growth and regeneration isespecially important to ensure that harvest levels and themix of forest products are sustainable.

Acknowledgements
The authors thank H.E. Sokhun Ty, former Director Generalof the Cambodian Forestry Administration, for his approvalto enter the forests for setting up and measuring thepermanent sample plots; local authorities and indigenous
people who willingly contributed to the project through a
consultation process and gave the authors their trust;
reviewers, who gave valuable comments and suggestions on
the draft manuscript; and ITTO, which provided crucial
support through the ITTO Fellowship Program.

14

ITTO Tropical Forest Update 21/1

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