Light climate related performance and management options for enrichment planting in bach ma...

Light Climate Related Performance and

Management Options for Enrichment Planting

in Bach Ma National Park in Vietnam

By M.W. Wieggers BSc.

Utrecht, October 2007

Supervion: Drs. M. Van Kuijk

Dr. Ir. N.P.R. Anten

Light Climate Related Performance and Management Options

for Enrichment Planting in Bach Ma National Park in Vietnam

Outline

1 Introduction

2 Material and Methods

3 Results

4 Discussion and

Recommendations

Here I am standing in the trails of

the 4 km plot in Bach Ma National Park



1.1 Secondary Tropical Rain Forest

Q: What is secondary forest?

A: Forest that develops after a disturbance, which can be natural or human-induced.

Typical causes of disturbances are; timber activities, agriculture, fire and wind. In

optimal conditions the biodiversity of secondary forest can reach a high level, but

never level a primary forest.

Because the decreasing area of primary forest worldwide, secondary forest is of

increasing importance for nature conservation and economy.

After the Vietnam war and the increasing human population of the last decades,

secondary tropical rain forest is of great importance to Vietnamese nature

conservation and economy. That is the reason why Vietnam established many national

parks like Bach Ma.



1.2 Succession and Enrichment Planting

Q: What is the most essential need for trees during succession?

A: Light.

After a disturbance in a forest a gap is created. The high light density gives several

plants the opportunity to grow fast, like grasses, herbs and bushes. Trees need to build

up wood for their stems, which is taking more valuable time. For trees it is hard to

profit from disturbances.

A possible management option could be an enrichment planting. That means that

saplings from nurseries are planted in man-made gaps. This management option gives

the opportunity to increase the biodiversity and reintroduce indegious original species.



1.3 Ecological Models

To optimize the enrichment planting it is important to know what the optimal light

condition is for a tree species. That is were the scientific models come in.

Pholiage is such a model, developed by Oomen in 2007. The model calculates the daily

light capture and the daily photosynthesis. Pholiage is based on Beer’s Law which

calculates the photon flux density (PFD);

I = I0 exp(-KF)

I = PFD

I0 = PFD above the cannopy

K = extincion coefficient of light in the vegetation

F = cumulative Leaf Area Index (LAI)



1.4 Aim and Research Questions

Aim of this research is to determine the extent to which Pholiage can be applied to

analyze tree growth in enrichment planting.

Fundamental ecological perspectiveQ1: Do the plant saplings have optimal crown dimensions such that light capture per unit

crown mass is maximized?

Management perspectiveQ2: How is light capture of planted saplings influenced by width of the gap opened

around them, cutting the lower branches of the surrounding vegetation or by the height

of the forest in which they are planted



2.1 Site Descriptions

The research took place in Bach Ma National Park. Bach Ma

National Park is located in central Vietnam in Thua Thien

Hue Province. The province is located between Lao and

South China Sea and its capital city is Hue.

Because of the diversity in altitude and the northern and

southern climate zone which are be bounded by each other.

The rain season is from September to December. This

makes the biotical factors for this province unique and the

biodiversity potentially extremely high.

Sadly this is not the case.




There are two locations at the Bach Ma Mountain where the research took place, at 4

km and 8 km from the entrance. At the two plots is enrichment planting taking place.

When the saplings in the nursery were about 40 to 50 centimeters tall they were

planted in these plots. These saplings are measured during the research.




The 4 km plot was an open secondary forest with trails where the saplings were

planted in 2003 and 2004. The trails did vary in width between one and three meter and

were cut parallel every several meters from the road into the forest. For three years

these trails maintained open and free from light competition for these saplings. After

the three years the saplings were expected to be competitive enough to be able to

compete against the surrounding vegetation. The forest was about five meter high and

dense from the soil upwards except for the trails which were cut free for the saplings

of the enrichment planting.

The second plot, the 8 km plot, near the Pheasant Trail, was a higher secondary forest

than the 4 km plot. The vegetation reached a height of fifteen meters. The saplings were

not planted in trails but under the vegetation which was open at soil level in 2001.



2.2 Field and Lab Work Methods

Non-Destructive Field Work MethodsThe non-destructive measures were taken in the Bach Ma National Park, some for

biomass estimations and some for light capture estimations. For the biomass

estimations were the stems, branches, petioles, subpetioles and the leaves measured.

Destructive Field Work MethodsThe destructive measures took place at the nursery of Bach Ma National Park. These

saplings were used and measured according similar way as the non-destructive

measures for the biomass estimations. Two additional measures were carried out,

after cutting all different parts of the saplings the leaves were photographed and the

all the parts of the sapling were dried. From the photographs was the leaf area

calculated at the office with SigmaScan Pro 5. The dry weights of the sapling parts

were measured for each individual.



2.3 Pholiage Model

To calculate the light capture and the photosynthesis from the trees in Bach Ma

National Park a model designed by Oomen (2007) was used. The model is tested for the

first time during this research. As noted the model assumes the crown of a sapling to

have ellipsoid shape with the dimensions x, y and height z. Leaf inclination angles are

divided into three 30 degree classes: 0-30°, 30-60° and 60-90°. The leaves are

assumed to be homogeneous divided in the crown.

For the vegetation characteristics are the bottom height and the top height of the

vegetation, the gap radius and the Leaf Area Index (LAI) put in the model. Assumed is

that the leaves in the vegetation are randomly divided and that leaf elements are

infinitely small. The surrounding vegetation is assumed to have flat sides at the top,

bottom and at the gap side. In the model are parallel light beams from a free sky from

all the angles of the sky dome falling up the crown. This is called free sky light

distribution. The above canopy light intensity is set on 1000 umol s-1 m-2.



3.1 Ecological Runs

Optimal Crown VolumeThese runs are a simulation of what the

light capture per unit of leaf area would

be if the crown dimensions were a factor

smaller or larger. The crown dimensions

are multiplied with a factor in the range

of 0.25 to 4.00 while the amount of leaf

area remains constant. The leaf area

density varies due to this. In that way the

optimum crown dimensions to capture as

much light per leaf area as possible would

be simulated.



3.1 Ecological Runs

Optimal Crown Volume per Biomass InvestmentTo produce larger crown dimensions the sapling has to invest more biomass in the

production of additional branch and petiole length. To estimate the trade-off between

the increased light capture per leaf area and the extra supporting biomass

investments, light capture is divided by the crown biomass.



3.2 Management Runs

Variation in Trail WidthIn Bach Ma National Park was the trail

width approximately 2.5 meter, so the gap

radius was set as a standard on 1.25 meter

in Pholiage. Pholiage is not simulating a

trail but a gap, so the model simulates the

light capture of the sapling in a gap with a

radius of 1.25 meter. The following two runs

study the variation in gap radius between

0.0 and 5.0 meter. Both of the runs show

the light capture per leaf area of the

saplings in response to the variation in gap

radius.



3.2 Management Runs

Variation in Top Height of VegetationIn Bach Ma National Park were the heights of the

vegetation respectively 5 and 15 meter for the 4

km and 8 km plot. These management runs are

showing what would happen if the same saplings

are planted in a higher vegetation. The additional

height of the vegetation varies from 0.0 to 5.0

meter in the runs. The leaf area density of the

vegetation will kept constant so the LAI is

increased with the additional vegetation top

height. For both plots the light capture per leaf

area of the saplings in relation with the top

height of the vegetation is shown in graphs.



3.2 Management Runs

Variation in Bottom Height of VegetationIn the simulations of the two plots in Bach Ma

National Park, the vegetation bottom height is

set on 0.0 meter. A management tool to cut the

bottom vegetation up to 2.0 meter is run in

Pholiage. The bottom height of the vegetation

varies from 0.0 to 2.0 meter above soil level in

the next two graphs. For both plots the light

capture per leaf area of the saplings in relation

with the bottom height of the vegetation is

shown in graphs.



4.1 Ecological Aspects

In both plots Hopea and Tarrietia capture more light per leaf area than the other

species. This can be explained by the leaf area density of these species. Also the

amount of self-shading is the lowest for these two species.

In the 4 km plot is Sygyzium had the highest leaf area density and thus a much

stronger self-shading within its crown.

In the 8 km plot is Gymnocladus having the highest leaf area density and logical the

lowest light capture per leaf area for all species of the plot.

Sindora was also slightly taller and together with the lower leaf area density this

would lead one to expect that it captures more light per leaf area, than Homaliumdoes. But the reverse was the case. This can be explained in the differences in leaf

angles. The leaves of Homalium are placed more horizontal than from Sindora. This

difference is possible the reason why Homalium is capturing more light per leaf area

than Sindora.




The leaf area density is also explaining why Hopea and Tarrietia find their optimum

crown dimensions for light capture per leaf area per crown mass below the factor 1,

smaller than their actual crown dimensions.

The saplings light capture strategy seems to be to over invest in supporting biomass

for the crown to reduce self shading. That means that the plant is stretching its

supporting biomass more than needed. From an economic point a view is the plant

wasting energy.

For the other species is the gain in the amount of light captured per leaf area much

more when the crown dimensions are larger. With the actual crown dimensions the

volume is rather small compared to the amount of leaf area. This is causing self-

shading and has a negative effect on light capture.




The saplings with the variation in crown dimensions do decline in light capture per leaf

area close to factor 4. This is stronger the case with saplings with a huge crown

volume, because the crown of the sapling will probably grow into the surrounding

vegetation with a gap radius of only 1.25 meter. A large contribution of the differences

in light capture between the species is due to the leaf area density and leaf angles.

This is managed by spreading the leaves over a larger horizontal plane which is

supported by Sterck et al. (2001) and by Falster and Westoby (2003). Another large

contribution is due to the difference in leaf angles which is supported by Falster and

Westoby (2003).



4.2 Management Aspects

The light capture of all species is increasing with an increasing gap radius like

expected. This is quite logical; with a decreasing shade saplings capture more light. In

practice there is a trade-off between increasing the gap radius and preserving the

forest. Other researches already show that gap radius can have a positive effect on

light capture for some saplings and some saplings do need a shade from a canopy to

grow (Otsamo et al., 1997; Peña-Claros et al., 2002). This is due to the higher growth

rates of for example grasses which will overgrow the saplings in early succession

stages. That is why the gaps need to be cleared the first years.



4.2 Management Aspects

The additional vegetation height from the 4 km plot is showing different light capture of

saplings than the light capture from the saplings in plot 8 km. The saplings in the 4 km

plot are capturing much less light with the additional 5 meter of vegetation height than

the saplings in the 8 km plot without the additional height of the vegetation. In that

case is the vegetation of the 4 km plot is 10 meter and of the 8 km plot 15 meters high,

but the light capture in the 4 km plot is lower than in the 8 km plot. This does prove

that saplings do adapt to a different light climate (Sterck et al., 1999).

The cutting of the bottom height of the vegetation does not affect the light capture of

the saplings and therefore it is not of any use for the saplings. It is not advisable to

managers of enrichment plantings.



4.3 Concluding Remarks

The Pholiage model turned out to be working like expected. A model will always be

describing a systematic reflection of the reality. Pholiage did fulfill in the needs for

what it was made. The models of the Utrecht University were mostly applied for

fundamental science, but Pholiage is from my point a view also a very decent tool for

managers and can be applied world wide for enrichment plantings.



References

• Falster, D.S. and M. Westoby, 2003. Leaf size and angle vary widely across species: what

consequences for light interception? New Phytologist 158 (3): 509-525.

• Oomen, R.J., 2007. MSc Thesis (unpublished).

• Otsamo, A., G. Adjers, T.S. Hadi, J. Kuusipalo and R. Vuokko, 1997. Evaluation of reforestation potential

of 83 tree species planted on Imperata cylindrical dominated grassland. New Forests 14: 127-143.

• Peña-Claros, M., R.G.B. Boot, J. Dorado-Lora and A. Zonta, 2002. Enrichment planting of Bertholletiaexcelsa in secondary forest in the Bolivian Amazon: effect of cutting line width on survival, growth

and crown traits. Forest Ecology and Management 161, 159-168.

• Sterck, F.J., D.B. Clark, D.A. Clark and F. Bongers, 1999. Light Fluctuations, Crown Traits, and

Response Delay for Saplings in a Costa Rican Lowland Rain Forest. Journal of Tropical Ecology, Vol.

15, No. 1, pp. 83-95.

• Sterck, F.J., F. Bongers and D.M. Newbery, 2001. Tree architecture in a Bornean lowland rain forest:

intraspecific and interspecific patterns. Plant Ecology, 153: 279-292.

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