Field evaluation of stump and root trainer grown teak(Tectona grandish L.f.) plantations

Abstract

Teak (Tectona grandis L.f.) stands out to be the most popular commercialtimber species in the tropics by virtue of its matchless combination of properties. Over a century, root- shoot cutting (stump) has been the common nursery productiontechnology for teak across the world. However, the recent decade has seen unprecedented decline in the productivity of teak plantations which could be attributed to diverse reasons. In this context, the efficiency of the stump based planting method for teak hence assume close scrutiny by virtue of the limitation in the root spread and consequent belowground resource acquisition. In this backdrop, a field study entitled “Field evaluation of stump and root trainer grown teak (Tectona grandis L.f.) plantations” was conducted on teak plantations established at Karakkad, Kalady range, Malayattoor forest division, Kerala during 2017-18, to evaluate the influence of planting material viz. stump and root trainer on growth aspects, soil physio-chemical properties and root distribution separately in five and seven-year-old teak plantations. The teak plantations selected for study included; five-year-old (2012 establishment) stump and root trainer grown stands at 3x3 m spacing, seven-year-old (2010 establishment) stump and root trainer based stands at 2x2 m initial spacing. Attempt were also made to study the effect of planting spacing on the growth of teak that was raised from root trainers and managed separately at 2x2 and 3x3 m spacing. Nine random plots of size 20x20 m were demarcated for each of the treatments such that there were 45 experimental plots for observation. Altogether there were three treatment combinations for comparison viz. stump vs root trainer at 3x3 m spacing and five-year-old; stump vs root trainer at 2x2 m spacing and seven-year-old; five-year-old root trainer based teak stands at 3x3 m vs at 2x2 m spacing. Each treatment combinations were analyzed separately with independent t- test. Biometric observations on teak growth showed considerable difference with variable planting material and spacing. Root trainer grown teak stands showed better performance in total tree height (6.68 m at seven-years of age), DBH (9.04 cm at seven-years of age), and mean tree volume (0.031 m3 at seven-years of age) as compared to stump origin stand both at five and seven-years of stand ages. The basal area and bole height showed marginal improvement in root trainer grown stand at five-years of age. Initial spacing showed only marginal influence on total height and bole height with an advantage for stands at 2x2 m spacing as compared to 3x3 m spaced stands. However, DBH, basal area and volume showed discernible improvement in the stands at 3x3 m spacing. Crown diameter showed a nominal increase in the root trainer grown stand than stump grown stand at both ages. However, spacing had great influence on the crown diameter with more spread (2.7 m) by widely spaced stands (3x3 m). Stand LAI also was better for root trainer stand while spacing had poor influence on LAI. Persistence of stem axis and straightness of stem showed limited advantage for stump grown teak origin stand. Also closely spaced teak stands (2x2 m) developed from root trainer stands showed slightly better performance than teak at wider spacing (3x3 m). Attempts to analyze the influence of planting material and spacing on plant leaf nitrogen and soil physio-chemical properties suggested that plant leaf nitrogen concentration was modestly better for root trainer grown trees than stump grown trees. However effect of spacing indicated that widely spaced trees (3x3m) showing significantly higher nitrogen up take than narrow spaced trees. Soil physical and chemical properties were found to be less influenced by the planting material. However, all teak stands irrespective of planting material showed considerable improvement in soil organic carbon and nitrogen concentration and reduction in soil bulk density as compared with respective treeless open plots. Also there was consistent reduction in carbon content and nitrogen with increase in soil depth up to one meter soil depth. The average soil carbon concentration values were 1.15 % and 1.55 % for the root trainer and stump grown teak stands at seven-years of stand age. The corresponding soil carbon stocks were 24.60 Mg ha-1 and 32.85 Mg ha-1 for teak stands at seven-years of stand age. Investigations on root distribution among stump and root trainer grown teak trees revealed obvious advantage in root spread and root intensity for root trainer raised teak stands. Teak trees grown from stump had smaller roots confined to the base of the tree at shallow depths which drastically reduced with increase in lateral distance of soil depth. The presence of prominent multiple tap root systems could be the reason for the high root spread observed with root trainer based teak trees. The trends were the same for small, medium and larger root intensity. Yet another noteworthy observation was that teak trees at closer spacing showed reduction of root spread and restricted the root system at proximal lateral distance while widely spaced trees showed wider root distribution.