H. N. Pandey

Community composition and tree population structure in a sub-tropical broad-leaved forest along a disturbance gradient

Floristic composition, diversity, dominance and distribution pattern of species and tree population structure were studied in three stands of a sub-tropical wet hill broad-leaved forest of Meghalaya, India, along a disturbance gradient. Tree species diversity declined with increasing disturbance. Disturbed stands showed low equitability or high dominance and the undisturbed stand exhibited high equitability or low dominance. Contagious distribution among the tree species increased with increasing intensity of disturbance. Species showing regular distribution were restricted only to the undisturbed stand. Effect of disturbance on tree population structure was analysed using density-diameter curves. In the disturbed stands tree species showed reverse J-shaped and/or negative exponential curves, while those in the undisturbed stand exhibited sigmoid to bimodal mound shaped curves.

EFFECTS OF ANTHROPOGENIC DISTURBANCE ON PLANT DIVERSITY AND COMMUNITY STRUCTURE OF A SACRED GROVE IN MEGHALAYA, NORTHEAST INDIA

This study analyses the effects of anthropogenic disturbance on plant diversity and community attributes of a sacred grove (montane subtropical forest) at Swer in the East Khasi Hills district of Meghalaya in northeast India. The undisturbed, moderately disturbed and highly disturbed stands were identified within the sacred grove on the basis of canopy cover, light interception and tree (cbh ≥ 15 cm) density. The undisturbed forest stand had >40% canopy cover, >50% light interception and a density of 2103 trees per hectare, whereas the highly disturbed stand had <10% canopy cover, <10% light interception and 852 trees per hectare. The moderately disturbed stand occupied the intermediate position with respect to these parameters. The study revealed that the mild disturbance favoured species richness, but with increased degree of disturbance, as was the case in the highly disturbed stand, the species richness markedly decreased. The number of families of angiosperms was highest (63) in the undisturbed stand, followed by the moderately (60) and highly disturbed (46) stands. The families Rubiaceae, Asteraceae and Poaceae were the dominant families in the sacred forest. Rubiaceae was represented by 11, 14 and 10 species in the undisturbed, moderately disturbed and highly disturbed stands, respectively, whilst the family Asteraceae had 16 species in the moderately disturbed stand and 14 species in the highly disturbed stand. The number of families represented by a single species was reduced significantly from 33 in the undisturbed stand to 23 in the moderately and 21 in the highly disturbed stand. The similarity index was maximum (71%) between the undisturbed and moderately disturbed stand and minimum (33%) between the undisturbed and highly disturbed stands. The Margalef index, Shannon diversity index and evenness index exhibited a similar trend, with highest values in the moderately disturbed stand. In contrast, the Simpson dominance index was highest in the highly disturbed stand. There was a sharp decline in tree density and basal area from the undisturbed (2103 trees ha−1 and 26.9 m2 ha−1) to the moderately disturbed (1268 trees ha−1 and 18.6 m2 ha−1) and finally to the highly disturbed (852 trees ha−1 and 7.1 m2 ha−1) stand. Density–girth curves depicted a successive reduction in number of trees in higher girth classes from the undisturbed to the moderately and highly disturbed stands. The log-normal dominance–distribution curve in the undisturbed and moderately disturbed stands indicated the complex and stable nature of the community. However, the short-hooked curve obtained for the highly disturbed stand denoted its simple and unstable nature.

Microenvironmental variability and species diversity in treefall gaps in a sub-tropical broadleaved forest

Microenvironmental variability and species diversity in gaps and forest understorey were studied to assess the role of treefall gaps in maintaining composition and patchy distribution in a broad-leaved sub-tropical climax forest, Mawphlang, Meghalaya, India. Photon flux density was higher in gaps than in the surrounding understorey. Relative humidity was low and the litter layer was relatively thin in gaps throughout the year. Soil moisture and photon flux density in the gaps significantly varied between seasons and gaps of different sizes. Relative humidity significantly varied between seasons but difference among gaps was insignificant. Among-gap and among-season variations in soil and air temperature were insignificant. The number of tree species in the gaps was positively correlated with gap area, and tree species abundance showed higher equitability in larger than in smaller gaps. In gaps, α-diversity was highest for herbs and lowest for shrubs. β-diversity was highest for shrubs and lowest for tree seedlings. α-diversity of tree seedlings was higher in the gaps than in the forest understorey. Conversely, β-diversity was higher in the understorey than in the gaps. Low species similarity for tree seedlings among the gaps could be an effect of patchy distribution of parent tree species in the forest. Thus a significant change in light and moisture regimes along the gap size gradient played an important role in influencing the composition and abundance of shade tolerant and intolerant tree species in gaps on one hand, and affected the overall species diversity of the forest, on the other.

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.

Vascular plant diversity in the sacred groves of Jaintia Hills in northeast India

Diversity of vascular plants was studied in three sacred groves of the Jaintia Hills, in northeast India. About 395 species, 250 genera, and 108 families comprising pteridophytes, gymnosperms and angiosperms were found in the groves. Orchidaceae, Rubiaceae, Asteraceae and Lauraceae were dominant families and Ficus was the largest genus, with nine species. About 160 tree species were distributed in canopy, subcanopy and under canopy strata of the forest. Concentration of tropical and temperate elements of the neighbouring Sino-Himalayan and Burma-Malayan regions, and endemic (54 species), rare (31 species) and primitive taxa (38 species) due to favourable climatic conditions and prolonged protection have contributed to the high species richness of the groves. Their better management and protection is important for the conservation of plant diversity in the region and also for the benefit of indigenous tribes of the state.

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

Tree diversity in sacred groves of the Jaintia hills in Meghalaya, northeast India

Biodiversity of woody species was investigated in Ialong and Raliangsacred groves of the Jaintia hills in Meghalaya, northeast India. These grovesrepresent the climax subtropical broad-leaved forest of the area. A total of 738individuals belonging to 82 species, 59 genera and 39 families was identified ina 0.5 ha plot of the Ialong sacred grove, whereas the same area in theRaliang sacred grove had 469 individuals of 80 species, 62 genera and 41families. About 32% species were common to both groves. Lauraceae, with10–17 species, was the dominant family. The canopy and subcanopy stratawere respectively composed of 28 and 33% of the total tree species in theforest. The number of species as well as stem density were greater for the treesof lower dbh (5–15 cm) class compared to the higher (> 66cm) dbh class. The majority of the species showed a contagiousdistribution pattern and low frequency. The basal area varied from 57.4 to 71.4m2 ha−1. Species richness within theforest varied from 3 to 15 per 100 m2 in Ialong and 3 to 12 per 100m2 in Raliang. The dominance–distribution curves showed highequitability and low dominance in both groves.

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.