A. Arunachalam

Influence of gap size and soil properties on microbial biomass in a subtropical humid forest of north-east India.

We examined the effects of treefall gap size and soil properties on microbial biomass dynamics in an undisturbed mature-phase humid subtropical broadleaved forest in north-east India. Canopy gaps had low soil moisture and low microbial biomass suggesting that belowground dynamics accompanied changes in light resources after canopy opening. High rainfall in the region causes excessive erosion/leaching of top soil and eventually soil fertility declines in treefall gaps compared to understorey. Soil microbial population was less during periods when temperature and moisture conditions are low, while it peaked during rainy season when the litter decomposition rate is at its peak on the forest floor. Greater demand for nutrients by plants during rainy season (the peak vegetative growth period) limited the availability of nutrients to soil microbes and, therefore, low microbial C, N and P. Weak correlations were also obtained for the relationships between microbial C, N and P and soil physico–chemical properties. Gap size did influence the microbial nutrients and their contribution to soil organic carbon, total Kjeldhal nitrogen and available-P. Contribution of microbial C to soil organic carbon, microbial N to total nitrogen were similar in both treefall gaps and understorey plots, while the contribution of microbial P to soil available-P was lower in gap compared to the understorey. These results indicate that any fluctuation in microbial biomass related nutrient cycling processes in conjunction with the associated microclimate variation may affect the pattern of regeneration of tree seedlings in the gaps and hence be related with their size.

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

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.

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.

Evaluation of bamboos in eco-restoration of ‘jhum’ fallows in Arunachal Pradesh: ground vegetation, soil and microbial biomass

With a view to identify potential bamboo species that can help in soil nutrient binding during restoration of abandoned shifting agricultural lands (jhum fallows), we analyzed the ground vegetation, soil and microbial properties under the canopy of three bamboo species viz., Bambusa nutans, Bambusa arundinacea and Dendrocalamus hamiltonii growing in a 9-year old jhum fallow in the ecologically fragile north-eastern hilly region of India. The results were compared with a grassland to evaluate the role of bamboos in soil nutrient dynamics. Species diversity of ground vegetation was highest under B. nutans canopy. Soil pH was neutral and the soil organic matter did not vary significantly between different species growing in the jhum fallow and grassland. Available forms of nitrogen and phosphorus in the soil showed variations among species. Soil microbial carbon and phosphorus were greater in grassland (control site), while microbial nitrogen was in B. nutans soil. Significant correlations existed amongst microbial carbon, nitrogen and phosphorus. The study indicates that B. nutans could help in rehabilitating the jhum fallows with special respect to soil nutrient enrichment.

Leaf litter decomposition of dominant tree species of Namdapha National Park, Arunachal Pradesh, northeast India

Rates of weight loss and nutrient (N and P) release patterns were studied in the leaf litter of the dominant tree species (Ailanthus grandis, Altingia excelsa, Castanopsis indica, Duabanga sonneriatioides, Dysoxylum binectariferum, Mesua ferrea, Shorea assamica, Taluma hodgsonii, Terminalia myriocarpa and Vatica lancefolia) of a tropical wet evergreen forest of northeast India. Nitrogen and phosphorus mineralization rate and decay pattern varied significantly from species to species. In general, the decay pattern, characterized by using a composite polynomial regression equation, exhibited three distinct phases of decay during litter decomposition—an initial slow decay phase (0.063% weight loss day−1), followed by a rapid decay phase (0.494% weight loss day−1) and a final slow decay phase (0.136% weight loss day−1). The initial chemical composition of the litter affected decomposition rates and patterns. Species like D. sonneriatoides, D. binectariferum, and T. hodgsonii with higher N and P content, lower carbon and lignin content, and lower C:N ratio and lignin:N ratio exhibited relatively faster decomposition rates than the other species, for example M. ferrea, C. indica and A. grandis. A slow decay rate was recorded for species such as M. ferrea, C. indica, and A. grandis. The initial N and P content of litter showed significant positive correlations with decay rates. Carbon and lignin content, lignin:N, and C:N showed significant negative correlations with decay rates. Soil total N and P, and rainfall, soil temperature, and soil moisture had positive correlations with decay rates. The rapid decomposition rates observed in comparison with other different forest litter decay rates confirm that tropical wet evergreen forest species are characterized by faster decomposition rates, indicating a faster rate of organic matter turnover and rapid nutrient cycling.

Population and conservation of Sapria himalayana Griffith. in Namdapha national park, Arunachal Pradesh, India

Sapria himalayana Griffith. (Rafflesiaceae), a root parasitic plant, is one of the lesser known and poorly understood taxons, which is at the brink of extinction due to incessant human interventions in the natural forest environment. This note deals with the population of Sapria in the buffer zone of Namdapha national park in Arunachal Pradesh, northeastern India. The host plant was a woody climber, Tetrastigma sp. Two patches of Sapria were observed at Hornbill (primary and relatively undisturbed forest) and four patches in Zero camp (disturbed secondary forest). Presently the species is prone to extirpation due to habitat loss through encroachments and massive NTFP extraction in the park area. All attempts to reintroduce or translocate the species will be in vain due to its phytogeographical limitations and host-specificity. A viable approach could be in situ conservation by effective protected area management.

Agricultural Practices in Northeast India and Options for Sustainable Management

The north east part of India has seven states comprising an area of 255,083 km2 with hills, valley and plateau. This region is inhabited by 100 major tribes and immigrant communities. Due to topographical and environmental conditions this region is rich in biodiversity and is one of the hot spots of the world. Altitude ranges from 150 to 7,300 m a.s.l and temperature varies from freezing point to 37°C. Mostly tribal people and immigrant communities depends on farming and forest products for their food and livelihood. Local people have been maintaining traditional agricultural practices, agro-biodiversity and knowledge. Generally farmers practice jhum or shifting agricultural system with other sedentary agricultural practices. About 400,000 families practice jhum cultivation covering land area approximately 386,300 ha annually. Other agricultural system are wet rice cultivation which is practiced in valley land and Aji system where rice and millet are cultivated with fish in deep water. In valley land mono cropping as well as mixed cropping is practiced by farmers. Terrace land cultivation system introduced by government could not get wide acceptability by farmers due to high input of labour and fertilizers. Farmers also have cultivation systems such as homegardens and agroforestry that link their families to the forest ecosystem. Recently government and non governmental organization have introduced agri-horti-silvipastoral system for good harvest and yield. The population density of the region is 324 person per km2 that is lower than the whole country. However, the growth rate during 1991–2001 has been recorded 31.2 person/km2, which is higher than the national rate of 21.4 person/km2. If population growth continues at this rate then a serious threat may occur to the sustainability of agroecosystem and rich biodiversity of the region. An attempt is made here to focus on agricultural practices, their productive capability and viable sustainable land use strategies for people of the region.

Hill Agricultural Response to Climate Variability: A Case Study from Uttarakhand Himalaya

Uttarakhand offers a vast scope for cultivation of diverse agricultural crops including certain wild edible species. Agriculture has been the primary occupation of people since ages. In Uttarakhand, the livelihood depends more or less on agriculture. Being, an indispensable part of the dayto-day life of the people, agriculture in the villages of northwest Himalayas is losing grounds and people are migrating to the towns in search of occupation. One of the major reasons for migration is the problems faced by the farmers in agriculture in the due course of time. The changing climate is also affecting the livelihood of people in the hills. The present study is focused on the impacts of climate variability on the cropping systems in the north-west Himalayas. The study has been conducted in a few villages across the altitudinal gradient (600–2,200 m) covering important hill districts of Uttarakhand. It has been observed that climate change has impacts almost in all the sites. Though in some areas, the change has been found to be beneficial, yet, the major study reveals that the adverse impacts of climate change have compelled the farmers either to bring some change in their cropping systems or migrate to some other place. The study guarantees policy intervention and inductive R&D for development of climate resilient agriculture to ensure livelihoods in the ecologically fragile mountain ecosystem.

Distribution, ecophysiology and medicinal and nutraceutical usage of Perilla frutescens (L.) Britton

Perilla frutescens is one of the important crops grown in Garhwal and Kumaon hills of Uttarakhand, India. Traditionally the seeds of the plant are eaten raw by people and oil extracted from seeds are used for cooking purposes. Medicinally, it is used in treating cough, bronchitis, uterine ailments and rheumatic arthritis. Most of the research on P. frutescens in India in general and Uttarakhand in particular have focused on characterization of its chemical constituents, genetic relationship between the wild and cultivated variety, its uses, and how cultivation practices have changed over the years. Here we envisaged on the R&D gaps for comprehensive understanding of its formulations as health food and nutraceuticals.