Relationships between the abundance and site conditions of Abies sachalinensis juveniles in...

Relationships between the Abundance and Site Conditions of Abies sachalinensis Juveniles in Selection Forests in Central Hokkaido, Japan

Dr. Toshiaki Owari The University of Tokyo Hokkaido Forest, Japan

Selection Forests Forests managed with the

uneven-aged system called ‘selection system,’ in which trees are removed individually from a large area periodically (Zingg et al., 1999)

The whole area is continuously

covered, and trees with all size-classes/species are intermixed over a small area (Zingg et al., 1999)

A steady state of structure and

functions can be maintained over time as compared with even-aged forest management (O’Hara et al., 2007)

2012/03/17 FORMATH RYUKYUS 2012 (Owari, T.) 2

Selection System in Hokkaido, Japan … has been used since the early

20th century as a major option to manage natural forests (Yoshida et al. 2006)

Lack of natural regeneration after recurrent selection harvests in some areas (Ishibashi et al. 1993; Kitabatake et al. 2003; Yamamoto et al.1997)

… should be applied to the stands, in which natural regeneration is expectable (Takahashi 2001)


Abies sachalinensis (Sakhalin fir) … is a main species of selection

forests in Hokkaido (Kitabatake et al. 2003)

… forms a majority of produced timber from selection forests (The Tokyo University Forest in Hokkaido 2007)

Previous studies examined the influences of site conditions on Abies natural regeneration: Stand level (<1 ha) (Nakagawa et al. 2001;

Noguchi and Yoshida 2004)

Enterprise level (102-103 ha) (Hosaka et al. 2008)

Regional level (>104 ha) (Ishibashi 1993)


Purpose

To identify the sites where a sufficient number of natural regeneration are expectable after selection harvests, this study examined relationships between the abundance of Abies sachalinensis juveniles* and site conditions at the enterprise scale (103–104 ha) *height ≥ 1.3 m; DBH < 5 cm

A case analysis was conducted at the University of Tokyo

(UT) Hokkaido Forest, northern Japan

This is a verification study of Hosaka et al. (2008), who previously examined the same topic


Scope of This Study … affects abundance of Abies

sachalinensis juveniles Hosaka et al. (2008)*

(207 ha) This study (5,111 ha)

Dwarf bamboo coverage - Overstory Abies BA + x Slope + x HLI: heat load index + Elevation x Curvature x Solar radiation x TWI: topographic wetness index x


* Hosaka, T., Owari, T., Goto, S. (2008) Relationships between the distribution and site conditions of Abies sachalinensis seedlings, saplings and juveniles in selection cutting stands of natural forests in central Hokkaido, Japan. J. Jpn. For. Soc. 90: 357-363

Study Site: The UT Hokkaido Forest

Location: central Hokkaido (43º 10-20´ N, 142º 18-40´ E, 190-1460 m asl)

Area: 22,715 ha Mean annual temperature: 6.3 ˚C Mean annual precipitation: 1,210 mm Snow cover: late Nov. – early Apr. Substrate: welded tuff Soil type: dark and brown forest soil Forest type: conifer-broadleaved

mixed forest Floor vegetation: dwarf bamboo

(Sasa senanensis, Sasa kurilensis)


Data

A total of 1,382 inventory plots established in selection forests (5,111 ha) during 1995 – 2004 Plot size: typically 0.25 ha (50 m × 50 m)

Tree measurement: species and DBH (≥ 5 cm) for all live trees

Juvenile measurement: the number of juveniles* by tree species

* ≥ 1.3 m in height and < 5 cm in DBH

Single-tree selection cutting had been conducted in the

study site 1–3 times before the measurements



Fig. Location of selection forests and inventory plots

(5,111 ha)

Data Analysis

General characteristics of each variable: Density of Abies sachalinensis juveniles

Basal area (BA) of the overstory Abies (DBH ≥ 5 cm)

Topographic conditions >spatial analyses using the ArcGIS

Relationships between the variables: Correlation between site conditions – juvenile density >Kendall's τ

Determining site factors affecting the abundance of Abies juvenines

General linear mixed model (GLMM) analysis using R 2.14.1 with the ‘glmmML’ package

Number of juveniles per plot (response variable), site conditions (fixed effects), plot (random effect), plot size (offset)

Poisson with log link, variable selection by a stepwise AIC method


Topographic Conditions

Elevation (m a.s.l.) 10-m grid digital elevation models (GISMAP terrain Ver. 2.00)

Slope (deg.) The rate of maximum change in z-value from each cell

Curvature The second derivative of the surface: convex (+), concave (-)

Solar radiation (kWh m-2 yr-1) Insolation across a landscape or for specific locations

TWI: topographic wetness index 𝑇𝑇𝑇 = ln 𝐴𝐴

𝑡𝑡𝑡𝛽 As: catchment area; β: 𝑙𝑙𝑙𝑙𝑙 𝑠𝑙𝑙𝑠𝑠


Results


General Character of Each Variable

Juvenile density of Abies sachalinensis

Site conditions Overstory Abies BA

Elevation

Slope

Curvature

Solar radiation

Topographic wetness index (TWI)



Fig. Spatial distribution of Abies juveniles

Plot Frequency of Juvenile Density

Mean: 162.1 trees ha-1 Median: 116 SD: 152.6 Skewness: 3.3 Kurtosis: 6.4 % occurrence: 99.3% (n=1,372)


Juvenile density (ha1)

Num

ber o

f plo

ts

0 200 400 600 800 1000 1200 1400

010

020

030

040

050

060

0

General Character of Each Variable

Juvenile density of Abies sachalinensis

Site conditions Overstory Abies BA

Elevation

Slope

Curvature

Solar radiation

Topographic wetness index (TWI)



Fig. Spatial distribution of overstory Abies BA


TWI

Plot Frequency by Site Condition


Abies BA

Basal area (m2 ha1)

Num

ber o

f plo

ts

0 10 20 30 40 50

010

020

030

040

0

Elevation

(m asl)0 200 400 600 800

010

030

050

0

Slope

(degree)0 10 20 30 40

050

100

200

Curvature

(m1)

Num

ber o

f plo

ts

-4 -2 0 2 4

020

040

060

080

0 Solar radiation

(kWh m2)600 800 1200

010

030

050

0

TWI

0 2 4 6 8

010

020

030

040

0

Mean: 12.8

Mean: 0.2

Mean: 1154.5 Mean: 3.4

Mean: 457.8

Mean: 16.6

Relationships Between the Variables

Correlation between site conditions – juvenile density

GLMM analysis to determine site factors affecting the abundance of Abies juvenines


Site – Juvenile Relationships


0 10 20 30 40 50

040

080

012

00

Abies BA

Abies BA (m2 ha1)

Juve

nile

den

sity

(/ha

)

300 500 7000

400

800

1200

Elevation

Elevation (m asl)0 10 20 30 40

040

080

012

00

Slope

Slope (deg.)

-4 -3 -2 -1 0 1 2 3

040

080

012

00

Curvature

Curvature (m1)

Juve

nile

den

sity

(/ha

)

600 800 1000 1200 1400

040

080

012

00

Solar radiation

Solar radiation (kWh m2)2 4 6 8

040

080

012

00

TWI

TWI

τ = 0.31** τ = -0.14** τ = 0.15**

τ = 0.12** τ = 0.11** τ = -0.16**

Relationships Between the Variables

Correlation between site conditions – juvenile density

GLMM analysis to determine site factors affecting the abundance of Abies juvenines


Results of The GLMM Analysis


Coefficient SE (Coef.) Z (Intercept) 1.796 0.273 6.586 Overstory Abies BA 0.035 0.004 8.314 Elevation -0.001 0.000 -4.112 Slope 0.032 0.003 10.316 Curvature 0.170 0.038 4.497 Solar radiation 0.002 0.000 10.193

AIC: 5594 TWI was not selected in the final model

Comparison with Hosaka et al. (2008)

Variable Hosaka et al. (2008)* (207 ha)

This study (5,111 ha)

Dwarf bamboo coverage - Overstory Abies BA + + Slope + + HLI: heat load index + Elevation - Curvature + Solar radiation + TWI: topographic wetness index ns


Note: ‘ns’ indicates that the variable was not selected in the final model.

Discussion

Consistent with Hosaka et al. (2008) Overstory Abies BA (+): seed dispersal (Uejima 1997), shading (Oda

1957), etc. Slope (+): less Sasa (Noguchi & Yoshida 2005; Hosaka et al. 2008),

Effects of other topographic conditions

Elevation (-): lower temperature > longer snow period? Curvature (+): faster snow melt? Solar radiation (+): slope aspect (Oda 1957; Ishibashi 1998) > faster

snow melt?

Longer snow period > More seeds damaged by snow blight (fungi)?


Managerial Implications

(A) (B) (C) Overstory Abies BA High Low Elevation Low High Slope Steep Gentle Curvature Convex Concave Solar radiation High Low


Forest managers are advised to employ the selection system at the sites where (A) is (B).

Forest managers should be careful to employ selection system at the site where (A) is (C). Silvicultural treatments (scarification, planting, etc.) may be considered.

Conclusions

This study was consistent with Hosaka et al. (2008), in which overstory Abies BA and slope positively affected the abundance of Abies juveniles

Results indicated that curvature and solar radiation had positive effects, while elevation had a negative effect on the abundance of Abies juveniles

Future research should include other site-specific factors (stand structure, substrate & soil type, disturbance history, etc.) and the regeneration of other tree species


Thank you!

I wish to thank current and former technical staffs at the University of Tokyo

Hokkaido Forest for their continuous and great efforts collecting field data.

This paper was partly supported by the Japan Society for the Promotion of

Science, Grant-in-Aid for Scientific Research (A), 22252002, 2010 – 2011.

(Corresponding address: [email protected])


mailto:[email protected]

Relationships between the abundance and site conditions of Abies sachalinensis juveniles in...

Documents

Transcript of Relationships between the abundance and site conditions of Abies sachalinensis juveniles in...