0029-B1

Temporal Pattern of Dry Matter and Nutrient Dynamics in Young Teak Plantations

Kaushalendra Kumar Jha^[1]

Abstract

Teak, a natural species of Southeast Asia, is one of the most widely introduced exotics in tropical countries. Recently this species has been promoted as short rotation and high investment plantation in several countries. As such it would be of paramount importance to study the species and utilize this knowledge for maximization of return. In this paper it has been attempted to provide vital information about structure and functioning of young teak plantations. Major parameters selected for the study in chronosequence of young age series plantations raised in Tropical Moist Deciduous Forest of India were stand basal area, biomass, net annual productivity, litter production, leaf litter decomposition rate, nutrient storage, nutrient uptake and nutrient return. These were estimated to be in the range of 1.20-18.52 m²/ha, 3.1-141.3 t/ha, 2.08-13.93 t/ha/year, 1.71-6.45 t/ha, 0.239-0.317 % per day, 20.3-586.6 (N); 5.3-208.8 (P) kg/ha, 18.15-125.21 (N); 3.2-20.20 (P) kg/ha/year and 25.8-91.3 (N); 2.74-10.19 (P) kg/ha/year, respectively. These findings were compared to earlier studies, mainly on teak and a few other species. Basal area, biomass and nutrient storage were found to be directly proportional to age. Annual productivity showed a decreasing trend while litter production showed an increasing trend with age. Results were found to be comparable to other edaphoclimatic regions, ecological zones, and species. As such linear regression equations derived for biomass could be used to assess growing stock in other teak plantations of comparable edaphoclimatic conditions. Although the paper mainly relates to the Indian context, it has much wider usage especially in all those countries that harbour extensive plantations of teak.

Introduction

Teak (Tectona grandis), a worldwide well known woody species, is particularly suitable for rapid production of large volumes of timber, poles and fuel wood and is widely used as lumber for shipbuilding and general carpentry. It is naturally confined to Southeast Asia and is one of the most widely introduced species out side its natural zone. Around fifty African, Caribbean, Central American and other tropical countries have witnessed successful introduction of teak. Today, teak ranks among the top five tropical hardwood species in terms of plantation area established worldwide (Krishnapillay 2000).

Changing demand and utilization technology have influenced teak management strategies in past. Commercial rotation age in natural teak stands was as high as 120 years. In plantation teak, it varied between 50 to 90 years in natural zone and between 40 to 60 years in the zones outside its natural range (Pande and Brown 2000). Most plantations are managed with far shorter rotations, usually from 20 to 30 years in tropical America (Centeno 1997) and India (Balooni 2000), and 15-16 years in Malayasia and Thailand (Keh 1997). A number of factors such as global decline of tropical timber supply from natural forests, increasing reliance on plantations to meet the growing demand for hardwood, involvement of private sectors in plantation activities, growth in international timber trade etc. are responsible for this drastic reduction in exploitation age (Nair and Souvannavong 2000).

There has been an increasing worldwide interest in short rotation and high capital investment plantations (Isebrands and Burk 1992). However, there is a general lack of data on dry matter and nutrient dynamics of teak plantations. This paper attempts to delve upon the following issues related to young teak plantations.

(a) What is the amount of biomass and productivity?
(b) What is the magnitude of litter fall and rate of litter decomposition?
(c) What is the quantum of uptake, retention, retranslocation and return of important nutrients?

Materials and Methods

Study site: Pure teak plantations (1, 5, 11, 18, 24 and 30 year old) raised in Moist Deciduous forests in Northern India (29^o3' - 29^o12' N latitude, 79^o20' - 79^o23' E longitude, 230-280 m MSL altitude) were selected for study. General details of edaphoclimatic condition of these plantation sites are given in earlier publication (Jha and Singh 1999).

Biomass: "Complete tree harvesting" technique was used for biomass assessment. First of all diameter at breast height (dbh) of all the trees was measured and grouped into 5 cm diameter classes e.g., 0-5, 5.1-10, 10.1-15, 15.1-20 and so on. In one-year old plantation 50cm above ground height was selected for diameter measurement instead of breast height. Tree density (number of trees per ha) and stand basal area (pr² density) were calculated. Three representative trees of each diameter class were harvested. Leaves, twigs, branches, boles, stump roots, and lateral roots were separated. Total green weight and sample green weight of each component were measured on site. The samples were dried in the laboratory and their constant weight was recorded. Sample green weight was converted into total dry weight diameter class wise. They were summed up to get tree biomass of the stand.

Productivity: After twelve months interval of the first dbh measurement all the trees were measured again. Using linear regression equation values derived from biomass data (y = a + bx, where y; x; a and b are biomass; diameter; intercept and slope, respectively) and diameters of first and second year, two sets of biomass data were obtained. By subtracting first year's biomass from the second year's the incremental biomass was found out. Annual foliage loss was added to calculate net annual productivity (NAP).

Litter fall: "Litter trap method" was used to assess litter production. Four litter plots (5m by 5m) were laid randomly in each sample plot. Litter was collected from these plots in every last week of the month for one year. The litter was separated into leaf, twig and fruits. Different fractions were weighed and samples were transported to laboratory. Oven dried fraction samples were weighed again and converted into total litter components.

Decomposition: The direct method of "Litterbag technique" was adopted to find out the rate of decomposition. Mature leaves were collected, dried, crumpled and packed in nylon mesh bags. Fifty pre-weighed litterbags were kept in each sample plots. Three bags from each plot were removed at monthly interval. Samples were dried, weighed and then stored. Average loss of litter mass from the bag was taken as decomposition per month. Stored samples were subjected to chemical analyses. Total nitrogen was estimated by "Microkjeldahl method" (Jackson 1958) and total phosphorus by "Phosphomolybdic blue method" (Singh and Singh 1991b)

Nutrient cycling: Samples of different tree components stored during biomass estimation were pooled together. Woody samples were sawn by power driven saw to get their sawdust. Sawdust samples were further mill ground in domestic mixer cum grinder to get powdered samples. Pooled litter samples were also mill ground to obtain powdered samples. Composite powdered samples were analysed by the methods adopted as in the case of litter samples.

Standing state, nutrient uptake and nutrient return were calculated by multiplying biomass, net annual productivity and total litter fall, respectively, with nutrient concentration of corresponding components. Retranslocation of nutrients was calculated following Ralhan and Singh (1987).

Results

Biomass: Age versus stand biomass showed linear relationship (Table 1). Total biomass ranged between 3.1 and 141.3 t/ha. In general, above ground contribution of biomass was 87.904 % (SD=0.366) while below ground was 12.084 % (SD=0.364) in all stands except one-year old plantation, where below ground contribution was 38% and above ground was 62%. Total foliage (0.475 to 2.896 t/ha) showed increasing trend but percentage contribution (1.06 to 15.3%) showed decreasing trend with age. Commercially utilizable biomass i.e., bole biomass ranged from 1.62 to 90.918 t/ha and showed similar trend with age as in the case of total biomass. Linear regression equations between biomass and average diameter were highly significant at all ages except at one year (Table 2).

Table 1: Magnitude of dry matter dynamics in teak

Table 2: Linear regression values in teak plantations

y₁ = biomass, x₁ = diameter, y₂ = litter weight, x₂ = time elapsed, ns = not significant, ** = significant at 1%

Productivity: As per the diameter record of two consecutive years 5-12% trees did not show any increase in diameter. Maximum increment was 1 cm/year while minimum was 0.1 cm/year. NAP ranged between 2.086 and 13.393 t/ha/year (Table 1). Percentage average contribution of above ground and below ground parts towards NAP was 93.96% (SD=1.008) and 6.02% (SD=1.009), respectively. Foliage contributed 50.56% (SD=2.66) in above ground productivity. However, in one year old plantation the above ground and below ground contribution were higher than the average of five other plantations while the amount of foliage was lower. Biomass accumulation ratio (BAR, biomass: productivity) and Production efficiency ratio (PER, productivity: foliage) varied between 1.4 to 18.1 and 1.17 to 2.12, respectively.

Litter fall: Annual litter production varied between 1.71 and 6.45 t/ha (Table 1). The bulk of litter was in the form of leaf (90.16%, SD=5.3) followed by wood (8.25%, SD=4.8) and reproductive part (1.56%, SD=1.2). Seasonal pattern of total litter fall indicated that winter was the peak while rainy season was the lean period.

Litter decomposition: Decomposition data of 180 days showed that 54% decay of leaf litter was possible. Assuming same trend of decomposition rate, extrapolated values were obtained with the help of linear regression analysis (Table 2). Thus generated set of data showed 355 days were required for 100% degradation of leaf litter.

Table 3: Nutrient dynamics in young teak plantations

Nutrient cycling: Concentration of Nitrogen (N) was found highest in leaf and lowest in wood while Phosphorus (P) was recorded maximum in root and minimum in wood. Total retention or standing state of N and P in 1 to 30 year old plantations ranged between 20.3-586.6 kg/ha and 5.3-208.8 kg/ha, respectively (Table 3). This has direct relationship with age. Magnitude of gross uptake of N and P varied between 28.15- 125.21 and 3.32-20.20 kg/ha/year, respectively. After correction of retranslocated amount net uptake of these nutrients remained in the range of 19.42-80.05 (N) and 3.18-18.09 (P) kg/ha/year, respectively. Total nutrient return ranged from 25.8 to 91.3 kg/ha/year (N) and 2.74 to 10.19 kg/ha/year (P).

Discussion

Biomass: Biomass is the function of productive potential of a particular site or edaphoclimatic conditions. In tropical dry deciduous regime thirty year old teak plantation, above ground biomass was recorded between 11.34 t/ha (Singh and Gupta 1993) and 76.95 t/ha (Karmacharya and Singh 1992). In moist deciduous regime - the present study, above ground biomass production was much higher (123 t/ha) at thirty year. Negi et al. (1995) also estimated higher biomass (164.1 t/ha) at same age and regime, but this increase in biomass was due to higher density as compared to the stand selected for present study. However, this suggests that moist area is more suited to teak growth as compared to drier one. Ghosh and Singh (1981) have also stated that teak trees do not achieve large size in dry areas but put on better growth in moist locations. This is further supported by the report of Hase and Foelster (1983) from Venezuela, and Nwoboshi (1984) and Ola Adams (1993) from Nigeria where both rainfall and biomass production are higher than Indian conditions.

Biomass of teak has definite pattern of accumulation in different plant parts and crop measuring parameters. This provides the base of biomass calculation by regression method. This is very useful for the resource mangers and ecologist for planning and prediction purposes. Linear regression values, which were found highly significant, can be used for assessing growing stock of teak in other similar moist deciduous areas.

Productivity: Annual growth of the tree governs its productivity in that year. However, all the trees did not show annual increment in diameter in present study. This finding is in confirmation with earlier finding of Singh and Singh (1991a). Magnitude of NAP recorded at the age of thirty years (10.35 t/ha/year) is closer to the other findings on teak (Faruqui 1976, Karmacharya and Singh 1992 and Sharma and Naik 1989). Highest NAP (13.39 t/ha/year) recorded at five years declined eleven year onwards. This indicates that at younger age teak grows faster while it slows down afterwards. This pattern of productivity behaviour, was also suggested earlier by Lugo et al. (1988). Other similar reports of high NAP at lower age and then decline are also recorded at two different locations. Karmacharya and Singh (1992) estimated highest productivity at 4 year in dry locality while Faruqui (1976) estimated this at 5 year in moist locality. On both these sites decline in productivity was observed 14 year onwards.

BAR has been used to characterize the production condition of the stand. Like basal area BAR also increased with increase in age but PER showed decreasing trend. These findings confirm the earlier reports in poplar (Lodhiyal 1990) and teak (Karmacharya and Singh 1992). Decrease in production efficiency at higher age further corroborates faster growth at lower age while slower growth at higher age.

Litter fall: Litter production range in different climatic zones varies between 1.71 to 10.32 t/ha/year for 1 to 56 years old teak stands (Jha 2000). Total litter production in moist deciduous region (1.71 to 6.45 t/ha) is well within this range. Highest litter production in thirty years old plantation indicated maximum return of nutrients at this age.

Leaf litter, being the main contributor, regulates the quantum of the total fall in this species. Pande and Sharma (1986) have reported that in moist deciduous region concentration of leaf fall is during later half of the winter to earlier half of summer (February-March to April-May). Present study contradicts this finding as concentration of leaf fall is during the winter (November-February). This report is in agreement of other records in different localities (Egunjobi 1974, George et al. 1990, Rangarajan et al. 1997, Singh et al. 1993 and Sudheendra Kumar et al.1993). Rainy season was found to be the lean period of leaf fall. This pattern may be the result of moisture and temperature variation since high leaf fall in winter is associated with moisture stress and low temperature conditions. Sugur (1989) in Gmelina arborea and other species has also reported same pattern and has assigned same reasons. This was corroborated by sudden dip in leaf fall during December, a rainy month in the region of present investigation. This relates to the finding of Moore (1980) that water stress triggers de novo synthesis of abscissic acid in the foliage of the plants that can stimulate senescence of leaves and other parts.

Litter decomposition: Litter fall and decomposition are two primary mechanisms through which nutrient pool of forest ecosystem gets maintained (Mohan Kumar and Deepu 1992). The rate of decomposition plays a vital role in two of its major functions i.e., mineralization of essential elements and formation of soil organic matter. In moist deciduous regime or the sites under study average rate of decomposition is 0.291% (SD=0.031) per day. At this rate total decomposition of leaf litter takes around 12 months time. This finding is different from the reports of Pande and Sharma (1993), Singh et al. (1993) and Rangarajan et al. (1997) in the same species where only 70-75% litter gets decomposed in 12 months. However, there are certain reports in high rainfall regions that suggest that 6 months (Egunjobi 1974) to 8 months (Mohan Kumar and Deepu 1992) time is sufficient for complete mineralization. These variations can be related to temperature and moister availability on the ground. William and Gray (1974) have suggested that differences in temperature and moisture supply, their interaction and higher activity of decomposer at different locations explain the large variation in litter decomposition rate.

Nutrient cycling: Nutrient concentration controls the biochemical as well as biogeochemical cycles. Bargali et al. (1992), George and Verghese (1991) and Lodhiyal (1990) have reported that leaf contains highest concentration of nutrients in eucalypt, teak and poplar plantations, respectively. Present investigation agrees to these reports only to the extent that only nitrogen concentration is highest in the leaves while phosphorus is highest in roots. However, magnitude of concentration of N and P is 1.51% and 0.16%, respectively. This is comparable to the reports of George and Verghese (1992) where N and P concentration is 1.60% and 0.11%, respectively.

Final output of nutrient cycling is standing state of nutrients that has been defined as quantity of nutrient storage at a given time in a unit area. Standing state of nutrients increased with increase in age of the plantation and at the age of thirty years teak stored 586.6 kg/ha N and 208.8 kg/ha P. This kind of age versus storage relationship was also found in poplar (Bargali et al. 1992) and eucalypt (Lodhiyal 1990) in the same locality.

Magnitude of primary productivity is directly proportional to nutrient uptake. Since annual productivity was not affected by the age of stands nutrient uptake also did not show any relationship between uptake amount and age. At the age of 30 years gross uptake of N and P was 107.73 and 20.20 kg/ha/year, respectively. This report is well within the range of uptake (87-256 kg/ha/year for N and 4-134 kg/ha/year for P) in different forest types and plantations (Jha 2000). However, quantum of uptake for both N and P towards the lower range shows comparatively less nutrient demanding nature of the species.

Just before leaf fall plant conserves nutrients in the form of internal cycling. In the present study 32.63-59.97% N and 3.71-43.54% P got retranslocated in non-photosynthetic parts of the plant. This estimation does not agree to the investigation by Karmacharya and Singh (1992) where N and P retranslocation is 53-65% and 50-58%, respectively in 4-30 year old teak plantations. This may be due to site quality difference in these two localities, former being moist and nutrient rich area while latter dry and nutrient poor area. Eickmeir (1979) has also suggested that nutrient poor sites are more efficient in nutrient conserving mechanism.

Litter fall and its decomposition govern the nutrient return on forest floor. The range of nutrient return in different forest types and plantations is between 46-115 kg/ha/year N and 2-79 kg/ha/year P (Jha 2000). Return of nutrient in young teak plantations is highest (91.38 kg/ha/year N and 10.09 kg/ha/year P) at the age of 30 years. This magnitude of return falls towards the higher range for N while lower range for P. This reveals that nitrogen return is more efficient than phosphorus in teak.

Conclusion

Results and discussion have revealed that biomass production is not fully dependent on density of stands, rather growth rate plays significant role in it. It has also been revealed that though teak grows at faster rate during early years and growth rate slows down afterwards, at the age of thirty it produces considerably higher biomass at intermediate rate of annual productivity. As compared to other forest types and plant species teak is neither more nutrient demanding nor less nutrient conserving. However, greater accumulation of nutrients in older stands, as compared to younger ones, is an indication of locking up of nutrients resulting into their depletion in soil. This is further an indication that repeated raising and harvest of the crop on same land would result in fast depletion of nutrients from soil. Therefore, management intervention like, soil enriching intercropping or inter-rotational planting, manuring and composting, fertilizer application etc. would be useful. Nonetheless, keeping in view the economics hypothesis that time gained is money earned and above discussed ecological facts rotation of teak can be fixed at thirty years.

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