Effect of Improved Planting Stock on Tree Growth, Wood Properties, and Soil Fertility of Teak Plantations 10 Years After Planting

Abstract

Teak (Tectona grandis Linn. f.) is one of the most economically valuable types of tropical forest because teak wood has high durability, resilience and good aesthetic qualities. Teak tree improvement in Indonesia was initiated in 1983 producing planting stock for reforestation, i.e. clonal seed orchards (CSO) to produce seedling as sexual reproduction (referred to seedling), and hedge orchards to produce shoot cuttings as asexual (vegetative) reproductive (referred to shoot cuttings). Teak plantations established using seedling and shoot cuttings should improve forest productivity. The objectives of this study were to compare the growth rate, wood properties, and soil fertility of teak plantations propagated using seedling and shoot cuttings. Three square plots of 100 trees (10 × 10 trees; 1,000 m²) were established on both types of plantation and tree growth characteristics, wood properties, and soil fertility were monitored. The tree growth characteristics were diameter at breast height (DBH), tree height (H), clear bole height (CB), and volume of standing stock (Vss), and the wood properties included pilodyn penetration (PP) and stress wave velocity (SWV). Soil fertility was assessed from soil samples collected from three soil depths, with three replicates in each plot: 0–5 cm (top layer), 6–30 cm (middle layer), and 31–60 cm (bottom layer). Soil samples were analysed for total nitrogen, total phosphorus, total potassium, total calcium, and total magnesium. The results showed that the mean DBH, H, CB, and Vss differed significantly between the type of planting stock. The DBH, H, CB, and Vss values were 28.4%, 46.8%, 49.1%, and 130.1% higher, respectively, in teak plantations from shoot cuttings than from seedling. Moreover, the SWV of shoot cuttings planting stock plantation was 3.6% higher than from seedling. The mean PP did not differ significantly between teak plantations from shoot cuttings (22.00 mm) and seedling (21.80 mm). Furthermore, the planting stock did not affect soil fertility, which was highest in the top layer in all treatments. Our results suggest that teak plantations from shoot cuttings would increase growth, forest productivity, maintaining wood quality and soil fertility. Thus, it can maintain sustainable teak forest plantations.

Keywords:

• Growth
• planting stock
• soil fertility
• wood properties

1. Introduction

Teak (Tectona grandis Linn. f.), a member of the Lamiaceae (Li et al. 2016; Li and Olmstead 2017), is one of the most economically valuable tropical forest species in Asia (Kollert and Walotek 2015) and is naturally distributed in the monsoon forests of India, Myanmar, Thailand, and Laos (Kaosa-ard, 1989; Kollert and Kleine 2017). Teak is known for its good dimensional stability and its natural hardiness against termites, fungi, and weather (Lukmandaru and Takahashi 2008; Miranda et al. 2011). Therefore, this species has been introduced and domesticated outside its natural distribution, including on Java Island, Indonesia between the fourteenth and sixteenth centuries (Verhaegen et al. 2010; Kollert and Kleine 2017).

The main teak wood production came from natural teak forests, which cover an area of about 29 million ha (Kollert and Kleine 2017). However, since the late 20^th and into the early 21^st century, the production in the global wood market of premium teak wood from natural forests has been declining because of over-exploitation and unsustainable forest management, land-use change, and deforestation of natural teak forests (Pandey and Brown 2000; Mon et al. 2012; Kollert and Walotek 2015; Kyaw et al. 2020). This trend has led stakeholders in the global teak industry to divert their dependency from the natural teak forest supply to more sustainable teak forest plantations (Midgley et al. 2015). The establishment of teak forest plantations has been successful in 65 countries involving outside of the tree’s natural distribution, and there is approximately 7 million ha of plantations worldwide (Kollert and Kleine 2017; Midgley et al. 2015).

In lowland monsoon forests in Indonesia, the establishment of teak forest plantations is usually differentiated by two types of planting stocks: sexual (i.e. clonal seed orchards/CSO) and asexual reproductions (hedge orchards to produce shoot cuttings as vegetative propagation). Both types have been produced from a long series of teak improvement programs initiated since 1983 (Naiem 2001; Naiem 2014). The seeds have been produced from a clonal seed orchard (CSO), which is derived from clones of selected plus trees for genetic improvement (Mathew and Vasudeva 2003). The vegetative planting stock was produced from shoot cuttings from selected plus trees through a series of clonal tests (Naiem 2001). Thus, both types of planting stocks were genetically improved.

Evaluating the impacts of the different types of planting stocks on the growth characteristics, wood properties, and soil fertility of the teak forest plantation is essential for further teak genetic improvements in Indonesia. Previous studies have reported that the difference in planting stock produced different patterns of growth (Moya and Calvo-Alvarado 2012; Moya and Tenorio 2021; Rahmawati et al. 2021) and the different patterns of tree growth subsequently occurred alteration in wood properties (Seta et al. 2021). Furthermore, studies on the physical environment showed that teak plantation was affected by physical soil properties and macronutrients, and favorable soil conditions could enhance teak growth (Watanabe et al. 2005; Fernández-Moya et al. 2015; Hardiwinoto et al. 2021; Kayama et al. 2021). These properties could be improved by increasing the amount of organic matter derived from litterfall decomposition, which could improve soil porosity, aggregate stability, water-holding capacity (Wehr et al. 2017), and soil fertility (Giweta 2020; Cavalcante et al. 2021). Meanwhile, the effects of different planting stocks on tree growth, wood quality, and soil fertility have not been unveiled. Our hypothesis is that the difference in planting stock would affect tree growth, wood quality and the soil fertility. Therefore, the goals of our study were to determine the effects of different planting stocks on the growth, wood quality, and soil chemistry of teak plantations. The study results would be used as a guideline for choosing the planting stock as material for reforestation in the lowland monsoon forest.

2. Materials and Methods

2.1. Study Site

The study was conducted in plantations owned by Perum Perhutani a state-owned forest enterprise in Indonesia. The planting stock of shoot cuttings and seedling was established in the compartment 61a, forest management resort (RPH) Sidalaju, sub-forest management unit (BKPH) Kedunggalar, Ngawi Forest Management Unit (KPH Ngawi), East Java Regional Division Perum Perhutani (Figure 1).

Figure 1. Research site.

Two types of teak forest plantations were used in this study, one was propagated by seed harvested from the CSO (referred to seedling), and another was vegetative reproductive materials using shoot cuttings from hedge orchards of the plus trees (referred to shoot cuttings). CSO is the seed orchard developed from selected clones and propagated by bud grafting for mass-producing genetically improved seeds based on an open pollinated system for operational forest plantation (Mathew and Vasudeva 2003; White et al. 2007). Our CSO was established with 25 clones from the best selected teak clone and each clone was propagated by bud grafting to produce the seedling. The spacing of CSO was 10 m x 10 m to produce the large crown and seed. After planting, the CSO is managed intensively to yield large quantities of seed, which is used for the large scale forest plantations (White et al. 2007). Furthermore, the seed produced by CSO was germinated and maintained in the nursery for 6 months to be ready for planting.

Furthermore, the hedge orchard is a method of providing juvenile materials for shoot cuttings. Vegetative propagation by shoot cuttings can enhance the number of planting stocks used for clonal forestry development. The two clones for hedge orchards (clone numbers 97 and 110) were the result of progeny and clonal tests established in 1997 and propagated and used for clonal teak plantation in lowland Java forest plantation area (Naiem 2001; Naiem 2014). Thus, the hedge orchard would produce juvenile materials for shoot cuttings. The shoot material was rooted in the nursery on propagation bed, after which the seedling was maintained for 6 months in the nursery as material for planting.

The seedling produced by hedge orchard and CSO was planted in 2011 with spacing of 3 m × 3 m and covered an area of 16 ha. Both plantations from the shoot cuttings and seedling were planted in the same compartment (61a). The site index of the compartment was 2.5 based on Wolff von Wülfing (WvW) of Opstandstafels Voor Djatiplantsoenan (Tectona grandis L. F) (Wulfing 1932). Furthermore, the forest maintenance (fertilizer, weeding frequency, etc.) has been properly conducted, and no difference between the plots. However, both plantation was not been thinned yet, as part of forest maintenace. Furthermore, the assessment of the both plantation was conducted in 2021 when the age of both teak plantation was 10 years after planting.

2.2 Experimental Design

2.2.1. Evaluating teak forest plantation growth characteristics and wood properties

Three plots were established in teak plantations from the shoot cuttings and seedling, respectively, and their size of each plot was 1,000 m² (10 × 10 trees) (Figure 1). The parameters observed included the tree growth characteristics and wood quality. The tree growth characteristics were expressed by measuring diameter at breast height (DBH), tree height (H), clear bole height (CB), and volume of standing stock (Vss). DBH was measured using a diameter tape. H and CB were measured using a Haga altimeter. The volume of each tree (V) was calculated using the following formula: (1) $$V=\left(\frac{\left(\pi {\times \mathit{DBH}}^2\times \frac{1}{4}\right)}{10000}\right)\times H\times 0.64,$$(1) where 0.64 is a teak tree shape correction factor used in Perum Perhutani. Vss (m³ ha⁻¹) was calculated by extrapolating V (Wibowo et al. 2021)

The wood quality was represented by the pilodyn penetration (PP) and stress wave velocity (SWV). PP and SWV, which examine the mechanical properties, were assessed using non-destructive techniques. A pilodyn wood density tester (Pilodyn J6 type manufactured by PROCEQ, Zurich diameter with a pin, 2.5 mm) was used to estimate the PP value at DBH of three positions on each tree without debarking the stem, and the mean PP value was determined for each tree (Ishiguri et al. 2008; Wu et al., 2010; Hidayati et al. 2013; Widiyatno et al. 2020; Seta et al. 2021). SWV was determined using a stress wave timer (FAKOPP Microsecond Timer, FAKOPP Enterprise, Hungary). To evaluate SWV, a transmitter sensor (sensor 1) and receiver sensor (sensor 2) were placed on the stem of the tree at 150 cm and 50 cm from the soil surface, respectively (Hidayati et al. 2013; Seta et al. 2021). Then, sensor 1 was struck with a small hammer to propagate a stress wave, which was received by sensor 2. The stress wave propagation time (T_reading, µs) between the two sensors was recorded (Figure 2). The data of T_reading were recorded 10 times for each tree and the mean T_reading per tree was determined by averaging 10 data collected. We used the following formula to determine T_reading per length basis (Wang et al. 2000; Wang et al. 2004; Widiyatno et al. 2020; Seta et al. 2021): (2) $$T_m=\frac{T_{\mathit{reading}}}{LD},$$(2) where T_m (µs m⁻¹) is the T_reading per length basis and LD (m) is the distance between the transmitter and receiver sensor. Thus, SWV (km s⁻¹) was determined using the formula (Wang et al. 2000; Wang et al. 2004; Nakai et al. 2019; Widiyatno et al., 2020; Seta et al., 2021): (3) $$\mathit{SWV}=\frac{1\times 1000}{T_m}.$$(3)

Figure 2. Illustration of stress wave velocity assessments; θ = 45° (Source: Ishiguri et al. 2008; Proto et al. 2017; Seta et al., 2021).

2.2.2. Evaluating teak forest plantation soil fertility

Soil samples were collected at each teak forest plantation type with replication in three plots. Each plot's soil sample was collected from 3 different locations and taken from three depths of 0–5 cm (top layer), 6–30 cm (middle layer), and 31–60 cm (bottom layer). The soil sample from each plot and the same soil depth was composite and were air-dried and reduced to small particles using a 0.5-mm mesh sieve. Then, the composite soil samples from each soil depth of each plot were analysed to determine the soil's chemical characteristics including total nitrogen (N; %), total phosphorus (P; mg P₂O₅/100g), total potassium (K; mg K₂O/100g), total calcium (Ca; %), and total magnesium (Mg; %). The total N and P were analysed using H₂SO₄ (Eviati and Sulaeman et al. 2005), while K, Ca, and Mg were analysed by atomic absorption spectrometry (Shimadzu 2014).

2.3. Statistical Analysis

2.3.1. Growth characteristics and wood properties

An independent t-test (α = 0.05) was used to analyse the mean differences of growth characteristic variables (DBH, H, CB, and Vss) and wood properties of teak (PP and SWV) between the two types of teak plantations if the data distribution was normally distributed (Sheskin 2011). Meanwhile, the non-parametric tests would be utilized if the data were not distributed normally. The Mann-Whitney U test as one of non-parametric tests was used to assess differences in growth characteristic variables. Statistical analysis was performed using the IBM SPSS Statistics Version 25.0 (IBM Corp. 2017).

2.3.2. Soil nutrients analysis

The soil's chemical characteristics were analysed by two-way analysis of variance (ANOVA) at the confidence level of 5% due to distributed normally data that was carried out with the IBM SPSS Statistics Version 25.0 (IBM Corp. 2017). The independent variables of the research were planting stock, and soil depth, while the dependent variables were total nitrogen, total phosphorus, total potassium, total calcium, and total magnesium. The variables showing significant differences according to ANOVA were tested by Tukey’s HSD test at p ≤ 0.05).

3. Results

3.1. Effects of Planting Stock on Tree Growth Characteristics and Productivity

The independent t-test showed that the different types of planting stock had significantly different mean DBH (t = −14.47; p < 0.0001). Meanwhile, the Mann-Whitney U test revealed that different types of planting stock had significantly different mean H (Z= −17.14; p < 0.0001), CB (Z = −-9.98; p < 0.0001), and Vss (t = −14.73; p < 0.0001) (Table 1).

Table 1. Result of t-test and Z-test for growth characteristics, pilodyn penetration, and stress wave velocity of two different planting stock of teak plantation.

Variable	t /Z value
DBH (cm)	−14.47**
H (m)	−17.14**
CB (m)	−9.98**
Vss (m^3)	−14.73**
PP (mm)	−0.42ns
SWV (km s^−1)	−2.42*

Note: DBH = diameter at breast height, H = tree height; CB = clear bole height; Vss = Volume of standing stock; PP = pilodyn penetration; SWV = stress wave velocity; ** significant at α = 0.01; *significant at α = 0.05; ns: not significant at α = 0.05.

The mean DBH was 28.4% higher in the clonal teak plantation from shoot cuttings (20.52 ± 0.19 cm) than in the teak plantation from the seedling (15.98 ± 0.25 cm). Furthermore, the mean of H, CB and Vss of shoot cuttings was higher than seedling (Table 2).

Table 2. Summary statistics of two different planting stock types of teak plantations.

Variable	A shoot cuttings		Seedling
	Mean	SE	Mean	SE
DBH (cm)	20.52a	0.19	15.98b	0.25
H (m)	17.43a	0.11	11.81b	0.13
CB (m)	14.57a	0.33	9.75b	0.24
Vss (m^3 ha^−1)	425.24a	9.68	182.65b	6.83
PP (mm)	22.00 ns	0.19	21.80 ns	0.45
SWV (km s^−1)	3.75a	0.03	3.65b	0.04

Note: different letter of mean indicates significant at α 0.05; ns: not significant at α = 0.05; DBH = diameter at breast height; H = tree height; CB = clear bole height; Vss = Volume of standing stock; PP = pilodyn penetration; SWV = stress wave velocity; SE = the standard error.

3.2. Effects of Planting Stocks on Tree Wood Properties Between Planting Stock

Contrary to the growth characteristic results, the t-tests for the wood characteristics showed different results that was pilodyn penetration (PP) did not differ significantly between the seedling planting stock (22.00 ± 0.19 mm) and shoot cuttings (21.80 ± 0.45 mm) (t = −0.42; p = 0.677; Table 1, Table 2). However, the mean SWV was significantly different between the seedling and shoot cuttings (t = −2.42; p < 0.020; Table 1). The average SWV value for both seedling and shoot cuttings were 3.65 ± 0.04 km s⁻¹ and 3.75 ± 0.03 km s⁻¹, respectively (Table 2).

3.3. Effects of Planting Stock and Soil Depth on Soil Fertility

The planting stock sources and the interaction between planting stock and soil depth (A × B) did not produce any significant differences in the soil’s chemical characteristic parameters (p > 0.05). However, the concentrations of N, P, and Ca differed significantly among the soil depths (N: F = 69.69, p < 0.0001; P: F = 92.24, p < 0.0001, and Ca: F = 7.24, p = 0.011). Soil depth did not affect the concentrations of K (F = 1.12, p = 0.36) and Mg (F = 0.57, p = 0.58) in the soil (Tables 3, 4, and 5).

Table 3. Two-way analysis of variance (ANOVA) for soil properties in different planting stock and soil depth of forest teak plantation at 10 years after planting.

Source	df	Mean Square					F
		N	P	K	Ca	Mg	N	P	K	Ca	Mg
Block	2	0.0006	6.10	308.91	0.05	0.51	2.31	16.89	8.44	1.93	2.27
Planting stock (A)	1	0.0001	0.09	40.05	0.05	0.13	0.33ns	0.25ns	1.09ns	2.29ns	0.57ns
Soil depth (B)	2	0.0187	33.34	41.14	0.17	0.13	69.69**	92.24**	1.12ns	7.24*	0.57ns
A x B	2	0.0005	0.55	2.26	0.03	0.20	2.00ns	1.52ns	0.061ns	1.26ns	0.87ns
Error	10	0.0003	0.36	36.61	0.02	0.23

Note: df = degree of freedom; ** = significant at α 0.01; * = significant at α 0.05; ns: not significant at α 0.05.

Table 4. The soil’s chemical characteristics in different planting stock of forest teak plantation at 10 years after planting.

Planting stock	N (%)	P (mg P2O5 /100g)	K (mg K2O/100g)	Ca (%)	Mg (%)
Shoot cuttings	0.17 ± 0.02	4.87 ± 0.70	29.31 ± 2.50	0.92 ± 0.15	0.74 ± 0.06
Seedling	0.17 ± 0.01	5.01 ± 0.82	26.33 ± 2.93	0.75 ± 0.18	0.63 ± 0.08

Note: Values are means + standard error.

Table 5. Soil’s chemical characteristics in different soil depths of forest teak plantation.

Soil Depth	N (%)	P (mg P2O5 /100g)	K (mg K2O/100g)	Ca (%)	Mg (%)
0-5 cm	0.22 ± 0.008a	7.51 ± 0.55a	30.80 ± 4.75ns	0.97 ± 0.13a	0.87 ± 0.02ns
6–30 cm	0.17 ± 0.005b	4.44 ± 0.41b	26.78 ± 2.52ns	0.68 ± 0.23b	0.65 ± 0.10ns
31-60 cm	0.11 ± 0.009c	2.87 ± 0.30c	25.89 ± 2.31ns	0.86 ± 0.24ab	0.54 ± 0.06ns

Note: Values are means + standard error; different letters indicate significant differences between plots (Tukey’s HSD); ns = not significant at α 0.05.

4. Discussion

4.1. Tree Growth Characteristics and Productivity of Teak Plantations Developed From Different Planting stock

The clonal teak plantation propagated from shoot cuttings had a 28.4%% higher mean DBH value than a teak plantation from a generative planting stock. Similar trends were also observed in the other growth traits, such as H, and Vss (Table 2). Furthermore, the standard error of all of variables of shoot cuttings were lower than in seedling because the shoot cuttings selected from the best growth clone and vegetative propagation had uniformity of growth characteristics. On the other hand, shoot cuttings has low genetic variation among the clonal offspring (White et al. 2007). Therefore, this study also showed that the shoot cuttings plantation had higher productivity than the teak plantation from the seedling, and establishing teak forest plantations through clonal forestry showed greater prospects for increasing forest productivity, which promises economical sustainability for teak forest management.

4.2. Impacts of Planting stock on Teak Wood Properties

Hidayati et al. (2013) reported an almost identical result in mean PP of clonal teak stands compared to the present study. The means of PP in clonal teak stands with three different thinning intensities (non-thinning, moderate thinning, and intensive thinning) were previously reported as 23.43 ± 1.71 mm, 24.63 ± 1.75 mm, and 26.28 ± 1.69 mm, representing (Seta et al. 2021). The mean PP value of the teak plantation from the seedling was almost the same as that from a 24-year-old teak provenance trial, which ranged from 20.4 mm to 25.9 mm (Hidayati et al. 2013). In general, PP has a strong negative correlation with wood basic density and modulus of rupture (Ishiguri et al. 2008; Seta et al. 2021). Wood basic density is an important characteristic determining the physical properties of wood, and it is strongly influenced by tree age and wood maturity (Bhat et al. 2001; Kumar et al. 2002). This study showed that the physical properties of the two teak plantations were almost same at the same age, irrespective of the difference in planting stock. It suggested that seedling and shoot cuttings wood did not differ significantly in the pilodyn penetration (PP) value (Table 2). PP was an indirect method for measuring wood basic density but it had some limitation to measure the wood density because it measured the outer section of stem tree (shallow penetration) and low sensitivity (Cown 1978; Wessel et al. 2011). However, PP was very economically efficient and precise for evaluating basic density of trees groups in one species, i.e. tree planted progeny test and trees planted in two different sites (Hidayati et al. 2013; 2015).

The shoot cuttings teak plantation of our research had a 2.7% higher mean SWV (3.75 ± 0.03 km s⁻¹) than the teak plantation from the seedling (3.65 ± 0.04 km s⁻¹; Table 2). The mean SWV of the shoot cuttings plantation in this study was about 22% higher than the value obtained in a study of 14-year-old clonal teak plantation in Gunung Kidul, Indonesia (Seta et al. 2021). Moreover, the mean SWV of the teak plantation from the seedling in this study was about 11% higher than that of a 24-year-old teak provenance trial in Gunung Kidul, Indonesia (Hidayati et al. 2013). It suggested that SWV did not have a strong correlation with growth characteristics (Hidayati et al. 2013; Seta et al. 2021). However, SWV was reported to have strong positive correlation with Young’s modulus of the wood (Ishiguri et al. 2011; Wang et al. 2013). The Young’s modulus is an important determinant of the mechanical properties of wood; therefore, a higher SWV indicates higher quality in terms of mechanical properties. Because teak is cultivated primarily for construction timber, a higher SWV is desirable, making clonal teak forest plantations from shoot cuttings promising in teak forest plantation management.

4.3 Effects of Planting Stock and Soil Depth on Teak Plantation Soil Fertility

No clear difference in soil fertility in N, K and P was detected between the two teak plantations originated from different planting stock sources, which may hinder to detect effects of soil fertility on the growth and wood property of the two types of teak plantations (Table 4). This probably occurred because the planting stock of the shoot cuttings and seedling produced a similar biomass product that was converted to soil fertilizer through litter decomposition, where teak litter decomposition rates indicated that approximately 54% of teak litter decay occurs in the first 6 months (Jha 2010). Furthermore, the N and K concentrations of both teak forest plantations were classified as low and medium, respectively, whereas the P, Ca, and Mg concentrations were classified as very low. The research area was likely susceptible to leaching because of the high precipitation in the area (Fernández-Moya et al. 2015; (Al-Mahmud et al. 2018). This result indicated that nutrient availability could be improved by supplying essential nutrients (fertilization) to improve teak growth, i.e. crown growth, tree height, and diameter, through better light absorption and plant diameter development via the plant respiration and photosynthesis processes (Wang et al. 2013; Thuynsma et al. 2016; Hardiwinoto et al. 2021). Thus, we recommend improving the nutritional status of soils in both types of teak forest plantations by adding inorganic or organic fertilizers (Abod and Siddiqui 2002; Zhou et al. 2012; Hardiwinoto et al. 2021).

In the different soil depth of teak plantation, the N, P, K, Ca, and Mg concentrations were highest in the top layer (0–5 cm), followed by the middle (6–30 cm) and bottom (31–60 cm) layers (Table 5). Our results were similar to previous studies reporting that nutrient content decreased with soil profile depth (Adekunle et al. 2011; Widiyatno et al. 2017). The N, P, and K concentrations in the top layer were classified as moderate, whereas the Ca and Mg concentrations were very low and low, respectively. Fine teak roots are distributed in the 20-cm soil-depth layer in teak plantations, and diminish with increasing soil depth (Srivastava et al. 1986; Takahashi et al. 2012). Because of the higher nutrient availability in topsoil layers, fine teak roots absorb most of the nutrients for growth. This suggests that maintaining the availability of soil nutrients in the top layer through teak biomass management could contribute to better teak growth.

5. Conclusions

Differences in teak growth characteristics (diameter at breast height, height, clear bole height, and volume of standing stock) were significantly related to the plantation planting stock. The shoot cuttings had higher productivity than the seedling teak plantation. Furthermore, the planting stock did not significantly affect pilodyn penetration value. However, the mean stress wave velocity differed significantly between plantations from different planting stocks. Moreover, the planting stock of the teak plantations did not affect soil fertility, but soil fertility was higher in the top layer than at other soil depths. Our results suggest that developing large-scale of teak plantations by shoot cuttings has prospects to maintain the quantity and quality of teak wood and enhance forest productivity to achieve sustainable forest management in the future.