Nelder wheel experiments at Luang Prabang Province · 2018-06-16 · Nelder wheel experiments at...

Progress Report: Nelder Wheel Experiments

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Progress Report: Nelder wheel experiments at Luang Prabang Province

Project Teak-based agroforestry systems to enhance and diversify smallholder livelihoods in Luang Prabang province of Lao PDR

Project component Investigate impacts of teak stocking on production of companion crops.

Project number FST/2012/041

Authors / Co-Authors Dr Mark Dieters, Dr. A. Nahuel A. Pachas


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Table of Contents

1. Introduction / Background............................................................................................................. 3

2. Objectives ...................................................................................................................................... 3

3. Materials and Methods ................................................................................................................. 4

3.1 Location .................................................................................................................................. 4

3.2 Design of treatments ............................................................................................................. 5

3.2.1 Nelder wheel experiment at the Agriculture and Forestry College ............................ 5

3.2.2 Nelder wheel experiment at Souphanouvong University .......................................... 11

3.2.3 Nelder wheel experiment at Thong Khan Research station ..................................... 12

3.3 Statistical Analysis ............................................................................................................... 13

4. Results ..................................................................................................................................... 13

4.1 Nelder wheel at the Agriculture and Forestry College ...................................................... 13

4.2 Agroforestry experiment at the Agriculture and Forestry College ................................... 20

4.3 Nelder wheel at Souphanouvong University ..................................................................... 21

5. Observation, problems, and opportunities ................................................................................ 25

6. References................................................................................................................................... 27


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1. Introduction / Background Teak (Tectona grandis L.) is a subtropical hardwood timber and its indigenous distribution is limited to the Southeast Asian countries of Myanmar, Northern Thailand and northwest of Lao PDR (Koasa-ard, 1989). There is approximately 20,000 ha of teak plantation in Laos PDR and there is not doubts that plantation of teak is a valuable resource of income for smallholders in Luang Prabang Province (Newby et al. 2012). Smallholder who early has planted teak had experienced the benefit to harvesting mature teak, which generated a substantial capital contribution to their family. Householder considers the teak plantation as a substantive economic resource that they can use in a particular situation, for example, if they need money for children education, buying a motorbike or tractor, or afford health cost (Midgley et al. 2007).

Traditional management of teak smallholders is not intensive and the silvicultural practice with the aim of maximizing high-quality timber productivity is not being adopted by farmers. The practice of using high stand density (>1,500 trees/ha), poor quality germplasm, lack of pruning and thinning management, entails to overstocked plantation stand resulting in trees of small diameters due to a high level of intraspecific competition and delaying merchantable timber harvest. The lack of implementation of silvicultural practices has been identified as a major constraint to the growth and qualities of the trees (Hansen et al. 2005; Midgley et al. 2007).

With the aim to evaluate and demonstrate the effect of plant density on growth of teak plantation, were established three Nelder wheel experiments in Luang Prabang under the ACIAR project FST/2004/057 which finished in 2012. These experiments were maintained and evaluated under the project FST/2012/041 with the aim of assessing the effect of planting density on tree growth and the establishment of intercropping experiments. The use of agroforestry systems, which involve much lower stocking rates, has the advantage of enabling the production of companion crops for a large proportion of time. Although low tree density results in producing less volume per unit area compared to high tree density, the quality of timber that is obtained per tree have much more value which offset this limitation.

The aim of this report is to summarize the finding of the Nelder wheel experiments on the effect of plant density on teak productivity and production of companion crops. The Nelder wheel design (Nelder, 1962) is widely used in agroforestry systems where trees are arranged in a circular layout contained concentric rings.

2. Objectives The objectives of the Nelder wheel experiments are:

- Demonstrate the potential of improved tree growth through reduced planting density.

- Investigate the interaction of teak on companion crops at a range of plant densities

- Provide data to model the changes in tree growth and form across a wide range of plant densities.


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- Determine plant density which will optimize financial returns from teak and paper mulberry plantations.

3. Materials and Methods Nelder (1962) proposed four systematic design and the layout of the three Nelder wheels established in Luang Prabang correspond to the design, which maintains a rectangular shape of space between trees that increases with radius length.

3.1 Location The following Nelder wheel experiments were established at Luang Prabang Province:

- Nelder wheel experiment located at the Agriculture and Forestry College (Plate 1) (19.98983 N, 102.24369 E).

- Nelder wheel experiment at Soupanouvong University (19.927343 N, 102.191691 E)

- Nelder wheel experiment at Thong Khang NAFReC (19.582896 N, 101.984158 E)

Plate 1: Aerial view of the College Nelder wheel experiment (6 November 2017) at 9.3 year-old.


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3.2 Design of treatments

3.2.1 Nelder wheel experiment at the Northern Agriculture and Forestry College

The experiment was conducted in the Northern Agriculture and Forestry College (NAFC) at Luang Prabang district, Luang Prabang province, Lao PDR (19.98983°N, 102.24369°E). The soil was an alluvial floodplain of the Mekong River characterized as a black clay loam. The climate is tropical (Köppen-Geiger classification- Aw-), with an average rainfall of 1,615 mm per annum and distributed following a monsoon pattern, with more than 90% occurring in the six-month period from May to October. The average maximum and minimum temperatures of 36.6 and 22.4°C occurs in the hottest month (April) and 26.7 and 12.7°C in the coolest month (January) (Lao Statistics Bureau, Vientiane; http://www.nsc.gov.la).

Site preparation Prior to planting the trees, the site was prepared by slashing weeds and followed by conventional ploughing applied using a 4WD tractor and seven disc plough. Teak was planted on 29 July 2008 using stumps (15-month-old seedlings) produced from seeds sourced locally from two provenances one “Luang Prabang” collected in nearby plantations of teak and the second from a small plantation of Myanmar provenance established at the old teak experiment station at Kien Ben .

Experimental design Ten concentric rings of trees with radii of 6, 7.9, 10, 12.5, 16, 20, 25, 32, 40 and 50 m were planted. Each ring contained 24 trees located equidistantly around the circumference, giving a range of densities from 106 at the outside of the wheel to 2,424 trees/ha at the inside of the wheel (Table 1, Figure 1, Photo 1). In this design, the angles between spokes have been set at 15° (0.2617 radians) generating 24 spokes. Each quadrant contained six spokes, and each provenance was planted along alternate spoke (Figure 1). The Nelder experiment occupied an area of 0.78 ha and contained a total of 240 trees. The inner and outermost rings were used as guards (or isolation) trees.


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Table 1: Radial length (spoke), ring tree spacing, equivalent tree density and potential growing space of the Nelder wheel experiment

Radius Radius length

(m)

Tree density

(trees/ha)

Growing space (m2)

Spacing between rings (m)

Spacing between spokes

(m) 1 6 ----- ----- ----- ----- 2 7.9 2,424 4.1 2.1 2.1 3 10 1,659 6 2.5 2.6 4 12.5 1,020 9.8 3.5 3.3 5 16 637 15.7 4 4.2 6 20 423 23.6 5 5.2 7 25 255 39.2 7 6.5 8 32 159 62.8 8 8.4 9 40 106 94.5 10 10.4

10 50 ----- ----- ----- -----

Figure 1: Schematic representation of Nelder wheel experiment established at the Northern Agriculture and Forestry College at Luang Prabang, Laos. Teak trees provenances from Luang Prabang and Myanmar are shown in different colours.


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Agroforestry Experiments (NAFC Nelder) Maize (Zea mays), cassava (Manihot esculenta) and peanut (Arachis hypogaea) were planted in June 2013. Each crop was planted in the alley between the spokes of the Nelder wheel experiment (Figure 2a) at the Northern Agriculture and Forestry College. Twelve spokes were sown using the standard plant density used in the region of Luang Prabang for each crop and each crop was replicated four times (Table 2).

Before planting, the spokes were cleared of weeds and grasses by hand-chipping. Crops were hand sown on June 27, 2013 (Table 2). Due to the high level of shade in the inners ring of the Nelder experiment, the crops were sown along the spokes from radius five (equivalent to 637 trees/ha) to radius 10 (Table 3).

Pigeon pea (Cajanus cajan), which is a perennial legume, was planted in double rows along the spokes, starting in the Nelder wheel experiment in 2014 (Table 2, Figure 2b). The double-row was replicated in nine spokes, and due to the high level of shade, they were placed from radius six to ten along spokes of the experiment.

In 2017, leucaena seedlings (Leucaena leucocephala) were planted in twelve spokes of the Nelder wheel experiment with the aim of evaluating the performance of three cultivars, two improved (Wondergraze and Tarramba) and local seeds from naturalized leucaena trees from Luang Prabang, at different teak tree densities. Double rows of legume tree were planted along the spokes (1 x 1 m apart) commenced from radius four to ten (Table 2, Figure 1c) and covering four spokes per cultivar (four replications).

With the aim of determining the relationship between the yield of annual and perennial crops growing at different teak tree densities, and considering that the crops were planted along the spokes, it was assumed that the performance of the companions crops was influenced by the trees growing in the adjacent rings. Therefore, the tree density was calculated as an average of density between rings of the Nelder wheel experiment (Table 3).

Table 2: Summary of plant density, date of planting and harvesting and replications of the companion crops tested in the Nelder wheel experiment from 2013 to 2015.

Companion

crop

Planting

density

Date of

planting

Date of

harvesting

Reps.

Maize 0.5 x 0.5 m 27/6/2013 27/9/2013 4

Cassava 1 x 1 m 27/6/2013 15/11/2013 4

Peanut 0.3 x 0.3 m 27/6/2013 03/10/2013 4

Pigeon pea 1.5 x 1.5 m 05/5/2014 16/4/2015 9


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a) b)

c)

Figure 2: Schematic representation of the agroforestry experiment carried out at the Nelder wheel experiment in 2013 with maize, cassava and peanut (a), and with pigeon pea during 2014-2015 (b), and 2017 (c).


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Table 3: Average tree density used in the agroforestry experiments.

Radius Tree

density (trees/ha)

Spacing between rings (m)

Average tree

density (trees/ha)

5 637 4 530 6 423 5 339 7 255 7 207 8 159 8 132 9 106 10 75

10 44 -----

Tree measurement The height of all trees was measured annually at 0.8 (2/05/2009), 1.5 (25/01/2010), 2.4 (12/12/2010), 3.5 (10/01/2012), 4.4 (29/12/2012), 5.7 (2/04/2014), 6.6 (20/02/2015), 7.5 (18/01/2016), 8.6 (20/02/2017) and 9.3 year-old (6/11/2017); due to marked wet/dry seasons these measurements correspond to the growth achieved after the first through to tenth growing seasons respectively. The height was measured using height measuring pole in the first and second years and a ultrasonic hypsometer (Haglof Vertex III) in the following years.

The diameter at breast height (DBH) (over the bark) was measured using diameter tape at 2.4 (12/12/2010), 3.5 (10/01/2012), 4.4 (29/12/2012), 5.7 (2/04/2014), 6.6 (20/02/2015), 7.5 (18/01/2016), 8.6 (20/02/2017) and 9.3 year-old (6/11/2017). The volume per tree was estimated using the calibration equation (Equation 1) fitted for teak in Luang Prabang Province (Dieters et al., 2014).

Vol (m3/tree) = (0.4230 π (DBH)2 Ht) / 40,000 (Eq. 1)

Where Vol is the volume of an individual tree (m3), DBH is diameter at breast height (cm); and Ht is tree height (m). The volume per unit area (m3/ha) and basal area (m2/ha) were calculated by multiplying the average individual tree volume (m3/tree) or basal area (m2/tree) at each stocking level by the equivalent stand density (trees/ha).

Merchantable timber volume was estimated using taper equation (Equation 2) suggested by Cordero and Kanninen (2003).

Volm = Vol (1-0.7839 (dm) 2.4149 (DBH) -2.4175 (Eq. 2)

Where, Volm is merchantable volume per stem (m3); Vol is total stem volume estimated using Dieters equation (Eq. 1); dm is upper stem merchantability limit express as a minimum diameter in cm (15 cm) and DBH is diameter at breast height (cm). The merchantable volume per unit area (m3/ha) was estimated multiplying merchantable volume per stem by the equivalent stand density (trees/ha).


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With the aim of characterizing the form of the trees and canopy size, the crown diameter (CD), crown base height (CBH), stem straightness and roundness were measured in the whole experiment on 18th August 2017 as described below:

• Crown diameter was obtained by measuring the horizontal distance using a tape meter from the vertical projection of the edges of the canopy in two directions 90° apart.

• The crown base height was defined as the height above the soil surface to the first green branch in the crown and was measured using a height measuring pole.

• Stem straightness and roundness were assessed visually on a five point scale (Table 4).

Table 4: Visual score classification according to a schematic stem straightness and roundness.

Score Straightness Roundness

1- Very good

2- Good

3- Regular

4 -Poor

5- Very poor

Yield of the companion crops The height and canopy diameter of maize, cassava and peanut were measure after 33 and 120 days after sowing (DAS). The date of harvest varied according to crops, being maize, cassava and peanut harvested after 92, 110 and 98 days after sowing. On each spoke and for each density treatment, the total yield was recorded and expressed by unit area.

Pigeon pea was harvested in 2015 and the yield per unit area was estimated by harvesting subplots of 2 x 2 m (4 m2) on each treatment and replication.

Maize, cassava and peanut were harvested in 2013 after 92, 110 and 98 days after sowing (DAS). On each spoke and for each density treatment, the total yield was recorded and expressed by unit area (kg/m). Pigeon pea was harvested in 2015 after 346 DAS. The yield per


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unit area was estimated by harvesting subplots of 2 x 2 m (4 m2) on each treatment and replication.

3.2.2 Nelder Wheel Experiment at Souphanouvong University The Nelder wheel experiment at Souphanouvong University was planted on 2 June 2009 in an alluvial brown sandy clay soil. Similar to the experiment at the College, ten teak densities were tested from 106 to 2,424 trees/ha (Table 1). However, due to land limitation, trees were only planted in 14 spokes using a fan-shaped design. The angle between each spoke was fixed at 15° (0.2617 radians) and ten trees were planted per spoke. The inner and outmost rings and the outside spokes (1 and 10) were used as isolation trees. The area used for the Nelder experiment was 0.27 ha with 140 trees provenance from Luang Prabang.

Around the Nelder wheel experiment, four un-replicated blocks were planted using four spacing configuration of 2 x 2 m (2,500 trees/ha), 3.3 x 2 m (1,500 trees/ha), 5 x 2 m (1,000 trees/ha) and 5 x 4 m (500 trees/ha). The same spacing configurations were replicated at the west of the Nelder experiment.

Figure 3: Schematic representation of Nelder wheel experiment (fan-shaped) established at the at Souphanouvong University, Luang Prabang Province, Lao PDR.

Tree measurement The height of all trees was measured annually at 1 (15/05/2010), 1.5 (11/12/2010), 2.5 (15/12/2011), 3.6 (28/12/2012), 5.7 (20/02/2015), 7.7 (21/02/2017) and 8.4 year-old (6/11/2017). The height was measured using height measuring pole in the first and second years and an ultrasonic hypsometer (Haglof Vertex III) in the following years.


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The diameter at breast height (DBH) (over the bark) was measured using diameter tape at 3.6 (28/12/2012), 5.7 (20/02/2015), 7.7 (21/02/2017) and 8.4 year-old (6/11/2017).

The basal area (m2/ha), individual and stand volume were calculated using DBH and total height.

3.2.3 Nelder Wheel Experiments at Thong Khan Agroforestry Research Station

The nelder wheel experiment at Thong Khan research station was planted on July 30, 2008 using the same design as that planted at the College, but incorporating paper mulberry in alternate spokes. However, the planting was not successful, and due to the high rate of tree mortality, it was discarded after being replanted twice. In 2013, a new Nelder wheel experiment with teak trees on a nearby site using a similar configuration to that at Souphanouvong University; however despite use of more intensive silviculture and addition of fertilisers, the growth of the teak trees was poor. Therefore in June 20, 2016 the teak trees were replaced with acacia hybrid (Acacia mangium x A.auriculiformis). Fire in early 2017 killed many of the teak acacia hybrids, and two lines of lecauena were planted between the acacia hybrids on July 2017 (Figure 4).

Figure 4: Schematic representation of Nelder wheel experiment (fan shaped) established at the Thong Khang Agroforestry Research Station, Luang Prabang Province, Lao PDR.


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3.3 Statistical Analysis The common methods for analysing data from Nelder wheel experiments has been regression models, mixed-effect models are also recommended for statistical analyisis of Nelder design experiments due to the hierarchical and spatial correlation of the data (Parrot and Lhotka, 2012). For this study, mixed model analysis was used to determine the effect of density on growth trait (DBH, total height, volume, basal area). Both experiments, at the College and Souphanouvong University were analyzed by mixed model apprach. At the College, a two-sample test was carried out with the aim to compare whether the provenance of teak trees from Myanmar and Luang Prabang had effects of diameter and total height at 9.3 years after planting. Due to there was no difference in diameter and total height of teak trees according to their provenance, the data were pooled and each quarter of the Nelder wheel analyzed as a block.

Regression analysis was used to determine the effect of tree density on volume per tree (m3/tree), per unit area (m3/ha), basal area (m2/ha), merchantable volume (m3/ha) and the relationship on yield of companion crops. All statistical analyses were carried out using GenStat 18.2 and figures developed in SigmaPlot 13.0.

4. Results

4.1 Nelder Wheel at the Northern Agriculture and Forestry College The average diameter per tree varied significantly according to tree density and age (P<0.05). Overall, the average DBH decreased with an increment of plant density. During the second and third years, there were no significant differences in diameter between the plant densities. However, in the following years, trees growing at lower densities had significantly larger diameters compared to teak trees growing at high densities (Figure 5). The maximum mean annual increment (MAI) at 9.3-year-old occurred at 159 trees/ha (2.93 cm/year), followed by 255, 106, 423 and 637 trees/ha that registered increments over 2 cm/years. The MAI of trees growing at 1020, 1659 and 2424 was 1.78, 1.54 and 1.32 cm/year respectively.


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Figure 5: Average diameter per tree growing at different tree densities. The error bars indicate LSD (P=0.05) based on the analysis of all density treatments.

The average total height of the trees increased with density and age (P<0.05) (Figure 6). Differences in total height between treatments were observed from the third year of growth, where trees growing at high densities were taller than trees at lower densities. At 9.3 years after planting, trees growing at densites of 106, 159 and 423 were significatively smaller than teak growing in other densitites. Maximum average high of 17.3 m was registered at stand density of 1020 trees/ha.


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Figure 6: Average total height per tree growing at different tree densities. The error bar indicates LSD (P=0.05) based on the analysis of all density treatments.

Individual volume per tree varied according to age and tree densities (P<0.01). During the first years after planting (2.4 – 4.4 years-old), the volume did not vary significatly with tree density. However, in the following years, the volume per tree significantly increased when trees were grown at wider spacings, following a similar pattern to that observed with tree diameter (Figure 7). For instance, trees growing at densities of 106 trees/ha had a three-fold increment in volume compared to trees growing at 2,424 tree/ha. However, the inverse relationship was observed when the volume was expressed per unit area (m3/ha) due to individual volume per tree decreased, while total volume per hectare increase with stand density (Figure 8). This relationship is critical for silviculture management and the decision of timber products, due to depending on the target market, the balance between the growth of individual tree and productivity per unit area (m3/ha) should be considered and analyzed.


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Figure 7: Relationship between the average volume per tree (m3/tree) and tree density at different ages after planting. Regression equiations were fitted for each age of measurement, and the estimated regression model and their coeficient of determinantion (R2) are shown only for trees of 9.3 years-old.

Figure 8: Relationship between the average total volume (m3/ha) and tree density at different ages after planting. Regression equations were fitted for each age of measurement, and the estimated regression model and their coefficient of determination (R2) are shown only for trees of 9.3 years-old. The error bar indicates LSD (P=0.05) based on the analysis of all density treatments.


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The basal area (m2/ha) had similar patterns that volume per unit area, which increased with the increment of tree density and age (P<0.05) (Figure 9).

Figure 9: Relationship between average basa area (m2/ha) and tree density at different ages after planting. Regression equations were fitted for each age of measurement, and the estimated regression model and their coefficient of determination (R2) are shown only for trees of 9.3 years-old. The error bar indicates LSD (P=0.05) based on the analysis of all density treatments.

Average crown diameter and crown base height were influenced by tree density (Table 5). The crown diamter measured at 2,424 trees/ha was 60% of the crown diamter of trees growing at 106 trees/ha. By contrast, the crown base height was greatest at the higher tree densities (Table 5).

In terms of straightness and roundness assessment, overall score indicated ‘regular’ score of both parameters evaluated. However, it was observed a slight trend of better stem straightness with an increase of tree density, but this effect was not significant.


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Table 5: Average crown diameter (CD), crown base height (CBH) and mean straightness and roundness score (1-5) at eight different planting density.

Radius Stocking (trees/ha)

CD (m) CBH (m) Straightness

Score

Roundness

score

1 ----- ----- ----- ----- ----- 2 2,424 2.31 ± 0.18 8.91 ± 0.32 3.1 3.4 3 1,659 2.65 ± 0.22 8.35 ± 0.32 3 3.2 4 1,020 2.98 ± 0.24 8.45 ± 0.34 3.3 3.4 5 637 3.73 ± 0.29 7.27 ± 0.43 3.1 3.4 6 423 4.35 ± 0.27 7.32 ± 0.32 2.9 3.2 7 255 5.26 ± 0.31 6.91 ± 0.17 3.2 3.2 8 159 6.26 ± 0.15 6.20 ± 0.18 3.4 3.8 9 106 5.87 ± 0.25 5.84 ± 0.24 3.6 3.4

10 ----- ----- ----- ----- -----

Although total volume (m3/ha) increase with tree density, it does not mean there is more merchantable timber volume per ha as timber market of teak depends on log size. The merchantable volume per unit area (m3/ha) is shown in Figure 10. At 9.3 years old, the maximum commercial volume per ha was obtained at 423 trees/ha (85.6 m3/ha), followed by 637 and 255 trees/ha that reached 77.9 and 72.5 m3/ha respectively. Trees growing at densities over 1,659 trees/ha did not reach volumes of 30 m3/ha.


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Figure 10: Average merchantable volume (m3/ha) over 15 cm diameter estimated at different teak tree densities at 8.6 years old. Regression equation was fitted and the estimated regression model and their coeficient of determinantion (R2) is shown in the figure.

The proportion of trees according to their girth class at 9.3 year-old is presented in figure 12.

Figure 12: Girth class distribution obtained at 9.3 year-old and simulated to 15 year-old at densities of 255, 423, 637 and 1020 trees/ha.


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4.2 Agroforestry Experiments at the Northern Agriculture and Forestry College

The yield of companion crops varied according to interaction between the cultivated species and tree density (P<0.05) (Figure 11). Overall, cassava had greater yield than both maize and peanut, when it was grown at lower tree density. At higher teak densities, maize registered larger yield, although, there was not a significant statistical difference with the yield of cassava. Maximum yield was registered by cassava (3.312 kg/ha) growing at 44 trees/ha. Meanwhile, at the same tree density, the yield of maize and peanut were 1.787 and 63 kg/ha respectively (Figure 11).

Figure 11: Relationship between yields of annual crops growing at different tree densities in the Nelder wheel experiment during 2013. Regression equation were fitted and the estimated regression model and their coeficient of determinantion (R2) are shown in the figure for each cultivated crop.The error bar indicates LSD (P=0.05) based on the analysis of all density treatments.

Yield of pigeon pea was negatively affected with increment of tree density in the Nelder wheel experiment (P<0.05) (Figure 12). Maximum yield of 2,625 kg/ha was obtained at 44 trees/ha, while yield drastically decreased to 62 kg/ha when the annual crops was cultivated at 339 trees/ha.


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Figure 12: Relationship between yields of pigeon pea growing at different tree densities in the Nelder wheel experiment during 2014-2015. Regression equation was fitted and the estimated regression model and their coeficient of determinantion (R2) is shown in the figure.The error bar indicates LSD (P=0.05) based on the analysis of all density treatments.

4.3 Nelder wheel at Souphanouvong University The DBH varied according to tree density and age (P<0.05) (Figure 13). At 8.4 year-old, the maximum diameter of 22.7 cm was registered at 255 trees/ha, followed by 159 and 106 trees/ha with average diameter of 21.9 and 21.2 cm respectively. The minimal average DBH was registered at 1,659 trees/ha (12.3 cm).


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Figure 13: Average diameter per tree (n=12) growing at different tree densities. The error bar indicates LSD (P=0.05) based on the analysis of all density treatments.

The average total height of trees increased with density and age (P<0.05) (Figure 14). At 8.4 years after plantation, the minimum average total heigth was registered at 106 trees/ha and the maximum average total heigth was observed at 255 trees/ha.

Age (years)

0 1 2 3 4 5 6 7 8 9 10

Dia

met

er (c

m)

0

5

10

15

20

25

106 trees/ha159 trees/ha255 trees/ha423 trees/ha637 trees/ha1,020 trees/ha1,659 trees/ha2,424 trees/ha


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Figure 14: Average total height per tree growing at different tree densities. The error bar indicates LSD (P=0.05) based on the analysis of all density treatments.

Maximum volume per tree was reached at 255 trees/ha (0.3 m3/tree) at 8.4 years after planting. Trees growing at tree densities of 106, 159 and 423 trees/ha, reached average stem volume of 0.2 m3/tree. Minimum average stem volume was observed at 1,659 and 2424 trees/ha (0.08 m3/tree) (Figure 15).

Age (years)

0 1 2 3 4 5 6 7 8 9 10

Tota

l hei

ght (

m)

0

5

10

15

20

25

106 trees/ha159 trees/ha 255 trees/ha423 trees/ha637 trees/ha 1,020 trees/ha1,659 trees/ha 2,424 trees/ha


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Figure 15: Average stem volume (m3/tree) measured at the Nelder wheel experiment at 3.6, 5.7, 7.7 and 8.4 year-old.

When, the volume was expressed per unit area (m3/ha), the average total volume increased with the increment of tree densities (Figure 16). At 8.4 years, maximum volume of 255 m3/ha was reached by trees growing at 2,424 trees/ha.Meanwhile, minimun total volume of 22.6 m3/ha was registered at 106 trees/ha.

Density (trees/ha)

0 500 1000 1500 2000 2500

Vol

ume

per t

ree

(m3/

tree)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

3.6 years5.7 years7.7 years8.4 years


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Figure 16: Relationship between the average total volume (m3/ha) and tree density at different ages after planting. Regression equiations were fitted for each age of measurement, and the estimated regression model and their coeficient of determinantion (R2) are shown only for trees of 8.4 years-old.

5. Observation, problems, and opportunities The Nelder wheel experiments at the Agriculture and Forestry College and Souphanouvong University showed that initial spacing has a strong influence on the individual growth of Tectona grandis. Overall, trees growing at wider spacing had a larger diameter compared to those grown at closer tree spacing, a trend that became more evident after the fourth year of growth due to increment on intraspecific competition. The effect of plant density on individual diameter growth was previously reported in several broadleaved and conifer species as results of increasing competition for light and water and lesser extent by nutrients (Cameron et al. 1989; Hummel, 2000; Ferrere et al. 2005; Erkan and Aydin, 2016 ). Initial spacing also affected total height, observing smaller trees at lower teak density, which could be associated with two factors. Firstly, trees growing at wider spacing were more exposes to canopy damage due to strong winds during storm seasons compared to trees growing at closer spacing. There is evidence that trees mechanically disturbed by wind affect shapes and mechanical properties of their trunk (Telewski and Jaffe, 1986), which tend to have smaller and conical stems that trees growing in crowded trees environments. Secondly, trees growing at high density tend to have larger height due to a physiological response that induces stem elongation to increase the chance of overtopping its neighbours (Holbrook and Putz, 1989). It is important to mention that in the


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Nelder wheel experiment, most of main stems of trees growing at lower densities (106, 159 and 255 trees/ha) were damaged at the top due to storm and strong wind events.

The effect of teak initial planting density on volume had different patterns according to whether volume was expressed as individual volume per tree (m3/tree) or stand volume (m3/ha). When volume was expressed by individual stem, it followed a similar pattern that DBH and decreased with increments of teak densities. However, when the volume was expressed by unit area, stand volume was positively correlated with tree density. Similar results were reported for several authors in other Nelder wheel experiments (Ferrere et al. 2005; Erkan and Aydin, 2016). Zahabu et al. (2015), studied the effect of square spacing regimes (2, 3 and 4 m) on growth and yield of teak 14-year-old in Tanzania and they reported the DBH and volume increment increased significantly with increase of spacing. Additionally, their study showed that physical and mechanical properties such as basic density, heart wood proportion, modulus of rupture (MOR) and modulus of elasticity (MOE) were not significantly affected by planting spacing. Management decision on initial planting density needs to consider target market of timber product. For instance, woodlots plantation with the aim of supply paper or pulp mill will focus on maximise stand volume (m3/ha). However, if the aim of the teak plantation is to supply veneer or furniture sawmill industry, they will require that trees reach at least a minimal merchantable log size (e.g. 15 cm small end diameter). Therefore, teak silviculture needs to manage stand density that allows a right balance between individual growth, with the aim of obtain logs of large size, and tree density that maximized merchantable timber volume. Clearly, both Nelder wheel experiments, have shown that densities target to maximize the previous statement should be range between 423 and 637 trees/ha.

Regarding agroforestry systems, the Nelder wheel experiment at the College showed a high yield of companion crops (e.g. > 2 t of Cassava or maize) is still achievable five years after teak plantation at low tree density (<423 trees/ha), i.e. where the trees were 5m or more apart. The leucaena planted at the College during this year did not grow well due to excessive shade, and inability to effectively exclude goats.

As a recommendation, both Nelder wheel experiments should be continue to be measured every year. It is important to mention that the experiment at the College has frequently been visited by students (and less frequently by farmers), mainly due to its location, accessibility and condition. As a result, this trial has been successfully used for both research and extension proposes. Additionally, the data obtained from both experiment can be used for developing growth modelling. Also, would be important to investigate if physical and mechanical wood properties change with planting configuration.


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6. References Dieters M, Newby J, Cramb R, Sexton G, McNamara S, Johnson M, Vongphacsouvanh S,

Sakanphet S, Sodarak H, Singhalath K, Savathvong S, Soukkhy O, Souliyasack B, Midfley D (2014) Enhancing on-farm incomes through improved silvicultural management of teak in Luang Prabang Province of Lao PDR. Final report FST/2004/057, ACIAR.

Hansen P, Sodarak H, Savathong S (2007) Teak production by shifting cultivators in Northern Laos P.D.R. Voice from the forest. Integrating Indigenous Knowlodge into Suistainable Upland Farming. Ed. Malcom Cairns. Resources for the future.

Holbrook NM, Putz FE (1989) Influence of neighbors on tree form: effects of lateral shade and prevention of sway on the allometry of Liquidambar styraciflua (sweet gum) , American Journal of Botany :76, 1740–1749

Lao Statistics Bureau ( 2017) http://www.lsb.gov.la/en/Meteorology14.php visted 9/06/2017

Midgley S, Blyth M, Mounlamai K, Midgley D, Brown A (2007) Towards improving profitability of teak in integrated smallholder farming systems in Northern Laos. ACIAR technical reports 64. ACIAR, Canberra

Nelder JA (1962) New kinds of systematic designs for spacing experiments. Biometrics 18(3):283-307

Newby JC, Cramb RA, Sakanphet S (2012) Small-scale Forestry 11: 27–46 https://doi.org/10.1007/s11842-011-9167-x

Parrott DL, Brinks JS, Lhotka JM (2012) Designing Nelder wheel plots for tree density experiments. New Forests 43: 245–254. DOI: 10.1007/s11056-011-9278-4

Pérez Cordero LD and Kanninen M (2003) Above-Ground Biomass of Tectona grandis Plantations in Costa Rica. Journal of Tropical Forest Science, 15, 199–213.

Telewski FW and Jaffe M J (1986) Thigmomorphogenesis: Field and laboratory studies of Abies fraseri in response to wind or mechanical perturbation. Physiologia Plantarum, 66: 211–218. doi:10.1111/j.1399-3054.1986.tb02411.x

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