R.S. Tripathi

Regeneration and survival of tree seedlings and sprouts in tropical deciduous and sub-tropical forests of Meghalaya, India

Abstract Species composition, regeneration status and survival of seedlings and sprouts of tree species were studied in tropical and subtropical forests of Meghalaya State in northeast India. The subtropical humid semi-evergreen forests at Upper Shillong and Mawphlang are dominated by Manglietia insignis, Pinus kesiya, Quercus dealbata, Q. griffithii, Rhododendron arboreum, Schima khasiana and Prunus undulata whereas the tropical deciduous forest lying at lower altitude (Burnihat) is dominated by Artocarpus chaplasa, Duabanga sonneratoides and Shorea robusta. The species composition of the tree community at the periphery is different from that of the forest stand at the centre. In the forests at Upper Shillong and Burnihat 40% of the tree species regenerated through both seedlings and sprouts, whereas the percentage of such trees in the undisturbed forest at Mawphlang was only about 22%. Survival of seedlings and sprouts was higher at the forest periphery than under the dense canopy, signifying the role of light in forest regeneration. Although the seedling mortality occurred throughout the year, it was particularly high during winter season due to prevailing low temperature and high soil moisture stress. The sprouts, however, were less susceptible to adverse environmental conditions.

Seasonal dynamics of microbial biomass C, N and P during regrowth of a disturbed subtropical humid forest in north-east India

Abstract Seasonal dynamics of microbial biomass C, N and P were studied in 7-, 13- and 16-year-old regrowths of a disturbed subtropical humid forest in north-east India. Microbial biomass C, N and P were highest during the winter and lowest during the rainy season at both the 0–10 and 10–20 cm sample depths. The surface soil layer (0–10 cm) had significantly higher microbial biomass C, N and P than the subsurface layer (10–20 cm). Microbial biomass C, N and P were highest in the 16-year-old regrowth and lowest in the 7-year-old regrowth, coinciding with highest and lowest clay content and nutrient status of the soil in the 16- and 7-year-old regrowths, respectively. The C/N and C/P ratios in microbial biomass showed a similar trend. Microbial biomass was negatively correlated with soil temperature and pH in all three regrowths.

Nitrogen mineralization as influenced by climate, soil and vegetation in a subtropical humid forest in northeast India

Abstract Nitrogen mineralization was studied in 7-, 13- and 16-year old regrowing forest stands by determining ammonium-N, nitrate-N, ammonification and nitrification rates during different seasons for two annual cycles. Mean concentrations of ammonium and nitrate-N were highest in the 16-year old stand, and lowest in the 7-year old stand. Inorganic-N (ammonium+nitrate) was highest during winter and lowest during rainy season in the three stands, whereas net ammonification, nitrification and N mineralization rates showed reverse seasonal trend. The net ammonification and mineralization rates were significantly higher (P

Fine root decomposition and nutrient mineralization patterns in a subtropical humid forest following tree cutting

Decomposition dynamics of fine roots (< 2 mm in diameter) and N and P mineralization pattern were studied in forest regrowths of three different ages in a humid subtropical region of India. The roots decomposed in a three-phased manner. The initial slow rate of decay up to 60 days was followed by a period of rapid weight loss until 120 days and then again by a phase of slow decay rate in all the three forest regrowths. A composite linear regression equation showed a good fit for the observed decay pattern of fine roots. The annual dry matter decay constants (k) for fine roots (1.62–1.74) increased with the increase in the regrowth age. The mean daily weight loss was positively correlated with rainfall, air temperature, soil moisture and soil pH, and negatively correlated with initial lignin concentration. Nutrient release from decaying fine roots was influenced by seasonal cycle of mineralization and immobilization processes. Winter was the period of active N and P immobilization, while mineralization was rapid during rainy season when N and P concentrations in the decomposing fine roots recorded 45.5–57.6% decrease from the preceding season. The net annual mineralization of N decreased from 50.9% in the 7-year-old regrowth to 46.4% in the 16-year-old regrowth, while P showed a reverse trend by registering an increase from 37.3 to 51.4%.

The impact of disturbance on detrital dynamics and soil microbial biomass of a Pinus kesiya forest in north-east India

Abstract Detrital dynamics and microbial nutrient flux due to disturbances such as treefall and tree cutting were studied in a subtropical Pinus kesiya Royle Ex. Gordon forest in north-east India. Disturbance has substantially altered community structure, and therefore soil nutrient status. Natural gap formation has not resulted in significant changes in dry matter, C and N accumulation in litter and fine roots, or in microbial nutrient concentrations. However, there was a significant reduction in all functional parameters in the selectively logged site and soil heap. Soil microbial C, N and P were maximum in the understorey and minimun in the heap. Fine roots and microbial biomass contributed more to nutrient recycling in the ecosystem. N-mineralization was generally higher in the disturbed sites.

Leaf litter decomposition and nutrient mineralization patterns in regrowing stands of a humid subtropical forest after tree cutting

Abstract Decomposition dynamics, and N and P mineralization patterns of leaf litter of Pinus kesiya, Quercus dealbata, Q. griffithii, Rhododendron arboreum and Schima khasiana were studied in forest of three different ages in a humid subtropical region of India. The decay pattern varied from species to species. The decay pattern, characterized using a composite linear regression equations, exhibited two to three distinct phases during leaf litter decomposition. Initial lignin, nitrogen (N) and lignin/N showed significant negative correlations with decay rate, whereas soil properties like pH, moisture and total Kjeldahl nitrogen (TKN) and climatic variables, e.g. rainfall and air temperature, showed positive correlations. The annual dry matter decay constants (k) varied from 0.77 in R. arboreum to 1.39 in Q. griffithii. Nutrient release from the decomposing litter was influenced by the seasonal cycle of mineralization and immobilization processes. Net mineralization was rapid during rainy season, as nitrogen (N) and phosphorus (P) concentrations in the decomposing leaf litter decreased by ca. 20–50% from the preceding season, while immobilization occurred during winter when nutrient concentration increased up to 60%. Annual dry matter decay, net N and P mineralization constants for Q. dealbata were higher in the 16-year old regrowth than in the 13-year old regrowth.

Influence of leaf litter quality on N mineralization in soils of subtropical humid forest regrowths

Abstract Laboratory net N mineralization as influenced by leaf litter quality of several subtropical tree species was studied in soils of forest regrowths of three different age groups. Concentrations of NH4+ and NO3– in the soil generally increased with age of forest regrowth. However, during incubation concentrations fluctuated markedly. In the “soil only” treatment, the cumulative N mineralization, ammonification and nitrification rates were highest in soils of the 13-year-old regrowth, followed by those of the 16- and 7-year-old regrowths. Soils from all three regrowths planted with Quercus dealbata had greater N mineralization rates than soils planted with Pinus kesiya. Overall, leaf litter of Schima khasiana showed the highest release of N, followed by leaf litter of Q. griffithii; greatest immobilization of N was recorded for Rhododendron arboreum leaves and P. kesiya needles. The percentage of N accumulated/depleted from the leaf litter correlated positively with the initial N concentration, and correlated negatively with the lignin content and C/N ratio.

Fine litterfall and nutrient dynamics during forest regrowth in the humid subtropics of north-eastern India

Fine litterfall and nutrient return patterns were studied in three subtropical humid forest stands (7-, 13- and 16-year old), regrowing after selective tree cutting in north-eastern India. The seasonality of fine litterfall was unimodal, with a peak during spring and a trough during rainy season in the forest regrowths of three different ages. The rate of fine litterfall increased with increasing basal area of the woody vegetation during forest regrowth. Leaf litter accounted for 83% of the total litterfall. N concentration was maximum during autumn and minimum during rainy season; nutrient concentrations were highest in the leaf litter. Seasonal variation in P concentration was small. Maximum and minimum input of N and P to the forest floor through fine litter coincided with the respective periods of litter production.

Tree Regeneration in a Disturbed Sub-Tropical Wet Hill Forest of North-East India: Effect of Stump Diameter and Height on Sprouting of Four Tree Species

Abstract The effect of diameter and height of stumps on sprouting and survival of sprouts of Alnus nepalensis, Quercus dealbata, Quercus griffithii and Schima khasiana was studied in a disturbed sub-tropical wet hill forest of north-east India. The study is based on observations of five diameter and four height classes of the stumps. Sprouting percentage of the stumps and number of sprouts per stump decreased with the stump diameter. Thickness of stump bark increased with the increase in stump diameter in all the four species. Number of sprouts per stump decreased with the bark thickness, whereas it increased with stump height. Production of sprouts was maximum in S. khasiana and minimum in Q. griffithii. In all species, the sprouts arising from the stumps of medium diameters (> 15–30 and > 30–45 cm) and heights (25–30 and 45–50 cm) survived better than those from the stumps of smaller or larger diameter and heights.

BIOMASS AND PRODUCTION OF FINE AND COARSE ROOTS DURING REGROWTH OF A DISTURBED SUBTROPICAL HUMID FOREST IN NORTH-EAST INDIA

Seasonal variation and depthwise distribution of dry matter in roots of different diameter classes and their annual production were studied using sequential core sampling. The investigations were carried out in three stands of a subtropical humid forest of north-east India representing different stages of regrowth after tree cutting. The mean annual standing crop of fine (<2 mm in diameter) and coarse (2–15 mm diameter) roots increased gradually from 5.4 Mg ha-1 and 0.7 Mg ha-1 in 7-yr old regrowth to 9.4 Mg ha-1 and 2.8 Mg ha-1 in 16-yr old regrowth, respectively. The contribution of fine roots to the total root mass declined from 88% in 7-yr old regrowth to 77% in both 13 and 16-yr old regrowths, while that of coarse roots increased from 12 to 23%. A major portion of fine roots (59–62%) was present in 0–10 cm soil layer, but the coarse roots were concentrated in 10–20 cm soil depth (38–48%). In all the three stands, biomass of both fine and coarse roots followed a unimodal growth curve by showing a gradual increase from spring/pre-rainy season to autumn/post-rainy season. Biomass to necromass ratio increased from 2.5 in the 7-yr old to 3.2 in the 16-yr old stand. The annual fine root production increased from 5.9 Mg ha-1 to 7.7 Mg ha-1 and total root production from 7.6 Mg ha-1 to 14.7 Mg ha-1 from 7-yr to 16-yr old regrowth.