Impact of progressive and retrogressive land use changes on ecosystem multifunctionality: Implications for land restoration in the Indian Eastern Himalayan region.

Land use change, anthropogenic exploitation and climate change have impacted the flow of services in the Himalayan region. The dominant land uses in the region including natural forest, degraded forest, rubber (Hevea brasiliensis) plantations, Areca catechu plantations, Areca agroforestry and Piper agroforestry were considered for the study. A progressive shift in land use was defined as the conversion and restoration of a less productive system like degraded land to plantations or agroforestry systems. A land use shift was considered retrogressive when it entails the establishment of plantations after clearing natural forests or anthropogenic disturbance of natural forests resulting in forest degradation. The objectives of the current study were to estimate changes in soil properties, stand structure, tree biomass, fine root production and carbon storage following a progressive and retrogressive shift in land usage. The aboveground biomass (105.9 Mg ha-1) was highest in the natural forest, followed by Areca agroforestry (100.2 Mg ha-1) and least in the degraded forest (55.3 Mg ha-1). The aboveground biomass carbon (47.1 Mg ha-1) of Areca agroforestry was comparable with that of natural forest (51.3 Mg ha-1). The highest proportion of passive carbon concentrations was observed under Areca agroforestry, whereas the lowest (4.13 g kg-1) was found under Areca plantations in the 0-25 cm soil depth. With the progressive shift in land use from degraded forest to agroforestry, SOC stocks increased by 27.6 % and 3 % under Piper and Areca agroforests, respectively. SOC stocks decreased by 8.5 % with a shift in land use from natural forests to Areca plantations. The production of fine roots was maximum in the Areca agroforest (13.2 Mg ha-1) and lowest under rubber plantations (4.2 Mg ha-1). The results show that progressive shifts from degraded forest to agroforestry can considerably increase carbon stocks, plant species diversity and multifunctionality than shifts to monoculture plantations thereby supporting improved biodiversity and mitigation of climate change.

Modelling habitat suitability for Moringa oleifera and Moringa stenopetala under current and future climate change scenarios.

Moringa oleifera Lam and Moringa stenopetala (Baker f.) Cufod are being widely promoted as multipurpose trees across the tropics for their nutritional, medicinal and soil health benefits. Different parts of these species are edible, have therapeutic values and their seeds are used for water purification. Although the two species are similar in many ways, they have contrasting distributions. However, their current promotion is not guided by adequate knowledge of the suitability of the target areas. Information is also scanty on the suitability of habitats for these species under the current and future climate change scenarios. Therefore, the objective of this study was to predict the habitat suitability of M. oleifera and M. stenopetala under current and future climate change scenarios using an ensemble of models assuming four shared socio-economic pathways, namely, SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 for 2050 and 2070. The results suggest that areas that are highly suitable for M. oleifera will increase by 0.1% and 3.2% under SSP1-2.6 to SSP5-8.5 by 2050, respectively. By 2070, the area suitable for M. oleifera would likely decrease by 5.4 and 10.6% under SSP1-2.6 and SSP5-8.5 scenarios, respectively. The habitat that is highly suitable for M. stenopetala was predicted to increase by 85-98% under SSP3-7.0 and SSP5-8.5 scenarios by 2050 and by 2070, while suitable areas could increase by up to 143.6% under SSP5-8.5. The most influential bioclimatic variables for both species were mean diurnal temperature range, mean temperature of driest quarter, precipitation of wettest month, and isothermality. Additionally, soil pH, elevation and water holding capacity were influential variables in the distribution of M. oleifera, while soil pH, soil salinity and slope were influential in M. stenopetala distribution. This study has provided baseline information on the current distribution and possible future habitat suitability, which will be helpful to guide formulation of good policies and practices for promoting Moringa species outside their current range.

Trees outside forests as climate change mitigation champions: evaluating their carbon sequestration potential and monetary value in Maharshi Dayanand University, Rohtak (Haryana), India.

The annual average increase in carbon dioxide (CO2) concentration is touching new heights every year. Global climate change and warming are twin outcomes of record-breaking CO2 levels. The trees outside forests (TOF) are the most promising and suitable components in the ecosystem for combating global warming via carbon (C) sequestration. Urban university campuses are the hotspot regions of TOF. We have attempted to quantify the C stock, C sequestration potential, and C credit value of dominant tree species at Maharshi Dayanand University (MDU), Rohtak. Different volumetric and biomass equations were used for biomass computation. We assessed a total of 29,442 trees (top 10) for measuring phytosociological parameters like total tree count, age, height (H), and diameter at breast height (DBH) to quantify the amount of C stored. The total C stock, C sequestration rate, and monetary value were 78.67 (Mg C ha-1), 19.05 (Mg CO2 ha-1 year-1), and 23,101.59 $ year-1, respectively. Eucalyptus globulus is the most dominant tree species on the campus and topped almost all the quantitative characteristics like total tree count (~40 %), age (25 years), density (D) (55.35 trees ha-1), and total C stock (16.06 ± 9.90 ï»¿Mg C ha-1). Tree basal area (BA), D, diversity, and H positively affected the total C stocks. When the C market becomes operational, these C credits can be traded while generating additional income for the university. The results from this study can also help calculate the total C footprint of the campus.

Combinatorial impacts of elevated CO2 and temperature affect growth, development, and fruit yield in Capsicum chinense Jacq.

Hot chilli ('Bhut Jolokia') (Capsicum chinense Jacq.) is the hottest chilli widely grown in the North-Eastern region of India for its high pungency. However, little information is available on its physiology, growth and developmental parameters including yield. Therefore, the present research was undertaken to study the physiological responses of Bhut Jolokia under elevated CO2 (eCO2) and temperature. Two germplasms from two different agro-climatic zones (Assam and Manipur) within the North-East region of India were collected based on the pungency. The present study explored the interactive effect of eCO2 [at 380, 550, 750 ppm (parts per million)] and temperature (at ambient, > 2 °C above ambient, and > 4 °C above ambient) on various physiological processes, and expression of some photosynthesis and capsaicin related genes in both the germplasms. Results revealed an increase (> 1-2 fold) in the net photosynthetic rate (Pn), carbohydrate content, and C: N ratio in 'Bhut Jolokia' under eCO2 and elevated temperature regimes compared to ambient conditions within the germplasms. Gene expression studies revealed an up-regulation of photosynthesis-related genes such as Cs RuBPC2 (Ribulose biphosphate carboxylase 2) and Cs SPS (Sucrose phosphate synthase) which, explained the higher Pn under eCO2 and temperature conditions. Both the germplasm showed better performance under CTGT-II (Carbon dioxide Temperature Gradient Tunnel having 550 ppm CO2 and temperature of 2 °C above ambient) in terms of various physiological parameters and up-regulation of key photosynthesis-related genes. An up-regulation of the Cs  capsaicin synthase gene was also evident in the study, which could be due to the metabolite readjustment in 'Bhut Jolokia'. In addition, the cultivar from Manipur (cv. 1) had less fruit drop compared to the cultivar from Assam (cv. 2) in CTGT II. The data indicated that 550 ppm of eCO2 and temperature elevation of > 2 °C above the ambient with CTGT-II favored the growth and development of 'Bhut Jolokia'. Thus, results suggest that Bhut Jolokia grown under the elevation of CO2 up to 550 ppm and temperature above 2 °C than ambient may support the growth, development, and yield. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-023-01294-9.

Determinants of phytolith occluded carbon in bamboo stands across forest types in the eastern Indian Himalayas.

Phytoliths are known to play a significant role in the global carbon cycle by sequestering atmospheric carbon dioxide as phytolith-occluded carbon (PhytOC) for a long time. Given the resistant nature of phytolith to decomposition, PhytOC can represent up to 82 % of total carbon in some soil and sediments even after 2000 years of litter decomposition. Hence, forests with high PhytOC sequestration rates could play a critical role in increasing terrestrial carbon storage. In this study, we quantified the variation in PhytOC concentrations in bamboo leaves, branches and culms with forest types in the Eastern Indian Himalayas as bamboos are efficient accumulator of phytolith and PhytOC due to their fast growth and high biomass accumulation rates. Using nine different machine learning techniques, we also investigated the determinants of PhytOC production in bamboo stands in the study area in India. The results revealed that the PhytOC concentrations in bamboo stands were in the order of leaf (3.0 g kg-1) > culm (1.0 g kg-1) > branch (0.2 g kg-1) across forest types. The highest PhytOC stock (53.8 kg ha-1) was found in bamboo stands in the subtropical pine forests (1900-3500 m elevation), while the lowest (28.0 kg ha-1) was in the tropical evergreen forests (<900 m elevation). Machine learning techniques established a positive correlation of PhytOC content in leaf and total PhytOC content with soil available phosphorus, elevation, total nitrogen, exchangeable potassium, atmospheric humidity, SOC content, CEC and pH. Numerical evaluation criteria and graphic methods identified artificial neural network (ANN) and support vector regression as the superior techniques with a root mean square error value of 0.52 kg ha-1 and 0.59 kg ha-1 respectively. The results of these two models were found to be better among all the nine machine learning algorithms used. The high PhytOC storage in the bamboo stands in the Indian Himalayan region suggests that forest management could secure a stable carbon sink on a millennial scale.

The Shifting Cultivation Juggernaut: An Attribution Problem.

Shifting cultivation entails clearing a delimited land and transforming it into arable land. Owing to its complexity, this system has been a subject of debate and intervention since the colonial-era, and is often considered as the "tropical deforestation culprit." Shifting cultivators are often labeled as "forest eaters" and are considered backward and primitive. Opponents of shifting cultivation often attribute the loss of forest cover to shifting cultivation, and favor intensification, claiming that commercial plantations are more productive. However, attempts to replace it have often failed due to inadequate understanding of the system and the decision-making processes involved. On the other hand, a growing body of literature provides evidence that shifting cultivation is an ecologically and economically efficient practice. After a careful review of the literature, the authors conclude that the dichotomy of opinions is the consequence of the attribution problem. The authors also argue that the management of forest ecosystems will be challenging if policy and practice are not based on careful understanding of the power of this age-old practice. Hence, there is a need for a careful diagnosis of this system and a rethink before claiming that the system is unsustainable and attempting to replace it with practices such as plantations.

Tree diversity and carbon important species vary with traditional agroforestry managers in the Indian Eastern Himalayan region.

Traditional agroforestry systems, one of the time tested and dominant land use from tropical to sub-tropical regions, were recognized for their contributions to food production, biodiversity conservation, and atmospheric carbon sequestration. Their management often varies from region to region. However, these systems frequently mimic economically managed land uses due to increased pressure on the monetary requirement of their managers. The present study aims to evaluate (i) tree density, (ii) tree diversity indices, and (iii) identify the biomass carbon important tree species managed by different communities of the Indian Eastern Himalayan region. We found that the Mizo community harbored the highest number of tree species (35) in the traditional agroforestry system with the highest tree diversity index (3.47). Total biomass carbon of tropical agroforestry systems managed by different communities ranged between 4.72 Mg ha-1 (Meitei) and 29.26 Mg ha-1 (Bengali). Similarly, in the sub-tropical traditional agroforestry system, the highest and the lowest biomass carbon was observed in Mizo- (10.93 Mg ha-1) and Angami- (6.05 Mg ha-1) managed systems. Of the 31 biomass carbon, important species found across the traditional agroforestry systems, Artocarpus heterophyllus, had the highest occurrence (50%), followed by Parkia timoriana (37.5) and Amoora rohituka, Delonix regia, Mangifera indica, and Toona ciliata (25% for each species). Farmers' preference to cash return of a species, trees density, and basal area were the determinant factors in the carbon stock potential of these systems. The present study suggests that the farmers' preferred and dominant species in their agroecosystems have a limited scope of enhanced biomass carbon storage. Therefore, improvement of traditional agroforestry systems through selective incorporation of biomass carbon important tree species is recommended to enhance the carbon sink capacity of these systems.

Post-fire restoration of land under shifting cultivation: A case study of pineapple agroforestry in the Sub-Himalayan region.

Access to the knowledge associated with traditional and/or indigenous land-use systems can help develop adaptive strategies, more productive systems and, design sustainable development models and technologies. This article describes the evolution of traditional pineapple (Ananas comosus) agroforestry systems (PAFS) developed by the ethnic Hmar communities as a strategy for the restoration of land under slash-and-burn agriculture in the Sub-Himalayan region. We critically examine the social and ecological perspectives on rural livelihoods and environmental management, and documented the native tree species managed under different age groups of PAFS. We also interviewed farm managers to gain insights into the traditional farming practices and the uses and services of the different multipurpose tree species (MPTs) along with their traditional management. The study showed that PAFS are an integral part of the rural landscape in the study region exemplifying unique agroforestry systems that have evolved as a strategy to improve land under slash-and-burn on hilly landscapes. PAFS are post-fire sedentary systems evolving as a by-product of shifting agriculture. The system combines pineapple crops with remnant fallow vegetation and subsequent plantations of cash-oriented MPTs in the same farmland. MPTs such as the critically endangered Aquilaria malaccensis and the economically important tree bean (Parkia timoriana), which is no longer found in the wild are largely conserved in the PAFS. Our study demonstrates that PAFS can play a vital role in post-fire restoration of land under slash-and-burn agriculture, which is still practiced among many tribes in the Indian Eastern Himalayas.

Assessing tree diversity and carbon storage during land use transitioning from shifting cultivation to indigenous agroforestry systems: Implications for REDD+ initiatives.

Indigenous agroforestry systems are important reservoirs of biodiversity, and ecosystem services with a potential contribution for conservation of biodiversity while sustaining the livelihood of the rural populace. Pineapple (Ananas comosus) agroforestry systems (PAFS) form an essential constituent of the rural landscape in the Indian Eastern Himalayas and other parts of Asia. The traditional PAFS management in southern Assam is unique in that it involves shifting cultivation transitioning from native forests to a PAFS. Scarcity of information on the functioning and services in terms of species diversity and carbon storage potential in the traditional PAFS has restricted the opportunities for consideration under the nature-based solutions of climate action including REDD+. Therefore, the present study assessed the tree diversity and ecosystem carbon storage in a chronosequence from swidden agriculture through different phases of PAFS establishment. The result demonstrated that basal area in the PAFS increased with age. The most dominant species in the native forests was Palaquium polyanthum, while agricultural land use and PAFS aged <5, 11-15 and > 15 years old were dominated by Gmelina arborea, Albizia procera, Areca catechu and Hevea brasiliensis, respectively. The highest value of Shannon-Wiener diversity index (H) was recorded in native forests (2.71), and lowest in 5-10 years old PAFS. The ecosystem carbon storage declined from 261.43 Mg ha-1 in native forests to 181.07 Mg ha-1 in <5-years old PAFS. In <5 years old PAFS, the ecosystem carbon storage was 30 % lower than the native forest; while at >15 years it was merely 5 % less than the native forests. The traditional PAFS maintains a steady ecosystem carbon stock while reducing land use related carbon emission and providing additional co-benefits to the communities. Therefore, the traditional PAFS constitute a good opportunity for REDD+.

A global review of rubber plantations: Impacts on ecosystem functions, mitigations, future directions, and policies for sustainable cultivation.

The growing global need for latex is driving rubber plantation (RP) expansion since the last century, with >2 Mha of cultivation area being established in the last decade. Southeast Asia is the hotspot for rubber cultivation at other land-use costs. Although rubber cultivation has improved the economic status of farmers, it has altered the habitat's ecology and ecosystem functions (EF). However, studies on the impacts of RP on EF are limited, and a clear overview is not available. To bridge this gap, we conducted an inclusive review of the EF of RP, including soil carbon storage, aboveground biomass (AGB) and belowground biomass (BGB), litter production and decomposition, respiration, and biodiversity (plants, animals, soil fauna, and microbes). We compared the EF in RP (monoculture) with those in forests because the conversion of forests to RP is prevalent in the tropics and because most RP studies used forests as reference ecosystems. We found RP generally have lower EF than forests. The impacts of RP on some EF are more severe (e.g., AGB, BGB, and plant diversity), causing decreases of >55%, and the effects are consistently negative irrespective of plantation age. However, including agroforestry or polyculture, integrated pest management, cover cropping, mulching, and composting can improve the EF in RP to some extent. We highlighted research gaps, particularly substantial research gaps concerning the influence of plant diversity treatments (i.e., agroforestry) performed in RP on EF. Additionally, more empirical data on the significance of spatial and temporal levels are required, such as how the impact on EF could vary with climate and RP age, as we showed some examples where EF differs spatially and temporally. More importantly, further research on plantation management to offset EF losses is needed. Finally, we emphasized knowledge gaps and suggested future directions and policies for improving EF in RP.

Patterns and driving factors of biomass carbon and soil organic carbon stock in the Indian Himalayan region.

Tree-based ecosystems are critical to climate change mitigation. The study analysed carbon (C) stock patterns and examined the importance of environmental variables in predicting carbon stock in biomass and soils of the Indian Himalayan Region (IHR). We conducted a synthesis of 100 studies reporting biomass carbon stock and 67 studies on soil organic carbon (SOC) stock from four land-uses: forests, plantation, agroforest, and herbaceous ecosystem from the IHR. Machine learning techniques were used to examine the importance of various environmental variables in predicting carbon stock in biomass and soils. Despite large variations in biomass C and SOC stock (mean ± SD) within the land-uses, natural forests have the highest biomass C stock (138.5 ± 87.3 Mg C ha-1), and plantation forests exhibited the highest SOC stock (168.8 ± 74.4 Mg C ha-1) in the top 1-m of soils. The relationship between the environmental variables (altitude, latitude, precipitation, and temperature) and carbon stock was not significantly correlated. The prediction of biomass carbon and SOC stock using different machine learning techniques (Adaboost, Bagging, Random Forest, and XGBoost) shows that the XGBoost model can predict the carbon stock for the IHR closely. Our study confirms that the carbon stock in the IHR vary on a large scale due to a diverse range of land-use and ecosystems within the region. Therefore, predicting the driver of carbon stock on a single environmental variable is impossible for the entire IHR. The IHR possesses a prominent carbon sink and biodiversity pool. Therefore, its protection is essential in fulfilling India's commitment to nationally determined contributions (NDC). Our data synthesis may also provide a baseline for the precise estimation of carbon stock, which will be vital for India's National Mission for Sustaining the Himalayan Ecosystem (NMSHE).

Variations in soil organic carbon content with chronosequence, soil depth and aggregate size under shifting cultivation.

Shifting cultivation is a globally important form of agriculture covering over 280 million hectares in the tropics, but it has often been blamed for deforestation and forest degradation. In North East India (NEI) it has been practiced for millennia and it is an important element of the cultural identity of indigenous communities. It is often practiced on slopping lands with fragile soils (mostly Acrisols), which are prone to rapid degradation with cultivation. The shortened fallow cycle as practised currently is ecologically unsustainable and economically not viable. This study aimed to quantify (i) changes in soil bulk density, aggregate stability and compaction in relation to chronosequence and soil depth, (ii) changes in the proportion of macro, meso, and micro aggregates and associated soil organic carbon (SOC) content in relation to soil depth and fallow chronosequence, and (iii) determine the minimum fallow length that achieves SOC stocks comparable with adjacent intact forest land. The proportion of soil macro-aggregates and meso-aggregates significantly varied with land-use and soil depth as well as their interactive effects. Across all soil depths, forest land had the highest proportion of macro-aggregates (75.6%), while the currently cultivated land had the least proportion (51.1%). The SOC contents in macro-aggregates increased with fallow age and decreased with soil depth; the highest (1.95%) being in the top 10 cm soil of 20 years old fallows and the lowest (0.39%) in 21-30 cm depth of 5 years old fallows. Multivariate analysis identified bulk density and porosity as the most important variables to discriminate between land use practices. The analysis provided evidence for significant changes in soil compaction, aggregate stability and SOC content with the transition from undisturbed forest to slash-and-burn cultivation and fallow phases. It is concluded that a minimum of 20 years of fallow period is required to achieve SOC content and C stocks comparable with intact forest land.

Water stable aggregates and the associated active and recalcitrant carbon in soil under rubber plantation.

Rehabilitation of the degraded soil is imperative to minimize the effects of soil degradation. It is in this context that stable soil aggregates, essential to providing physical protection to the organic residues, are important indicators of soil restoration or degradation. Thus, the present study was aimed at determining the soil aggregate stability and associated carbon fractions under rubber (Hevea brasiliensis) plantations. The study was conducted on 10, 15, 25, and 34-year-old rubber plantation established on Imperata grassland. Soil samples were collected from 0 to 10, 10-20, 20-50, 50-100 cm depths from different aged rubber plantation and native forest (NF) using a soil core of 5.6 cm inner diameter. Soil aggregates from each depth were separated by the wet-sieving technique, and grouped into three fraction size classes: macro-aggregates (>2 mm), meso-aggregates (0.25-2 mm), and micro-aggregates (<0.25 mm), and analyzed for carbon concentrations. The results showed that macro-aggregates dominated soil under different plantation ages and decreased with an increase in soil depth. The Mean Weight Diameter (MWD) and the Geometric Mean Diameter (GMD) increased with an increase in the age of the plantation and decreased with increase in soil depth. The MWD was the highest in the forest soil (5.8 mm) and the lowest (3.0 mm) under 10-year-old rubber plantation. The highest GMD was found under 34-year-old rubber plantation (2.1 mm) and the lowest under 10-year (1.4 mm) plantation. The SOC concentration under the recalcitrant pool increased with the increase in plantation age, and the highest amount was observed under 34-year old plantation. The increase in aggregate stability, recalcitrant carbon pool, and SOC stock with age chronosequence suggests the ecological role of mature rubber plantations in soil rehabilitation by minimizing the process of soil degradation.

Net ecosystem productivity and carbon dynamics of the traditionally managed Imperata grasslands of North East India.

There have been few comprehensive descriptions of how fire management and harvesting affect the carbon dynamics of grasslands. Grasslands dominated by the invasive weed Imperata cylindrica are considered as environmental threats causing low land productivity throughout the moist tropical regions in Asia. Imperata grasslands in North East India are unique in that they are traditionally managed and culturally important in the rural landscapes. Given the importance of fire in the management of Imperata grassland, we aimed to assess (i) the seasonal pattern of biomass production, (ii) the eventual pathways for the produced biomass, partitioned between in situ decomposition, harvesting and combustion, and (iii) the effect of customary fire management on the ecosystem carbon cycle. Comparatively high biomass production was recorded during pre-monsoon (154 g m-2 month-1) and monsoon (214 g m-2 month-1) compared to the post-monsoon (91 g m-2 month-1) season, and this is attributed to nutrient return into the soil immediately after fire in February. Post fire effects might have killed roots and rhizomes leading to high belowground litter production 30-35 g m-2 during March to August. High autotrophic respiration was recorded during March-July, which was related to high belowground biomass production (35-70 g m-2) during that time. Burning removed all the surface litter in March and this appeared to hinder surface decomposition and result in low heterotrophic respiration. Annual total biomass carbon production was estimated at 886 g C m-2. Annual harvest of biomass (estimated at 577 g C m-2) was the major pathway for carbon fluxes from the system. Net ecosystem production (NEP) of Imperata grassland was estimated at 91 g C m-2 yr-1 indicating that these grasslands are a net sink of CO2, although this is greatly influenced by weather and fire management.

Managing India's small landholder farms for food security and achieving the "4 per Thousand" target.

The "4 per Thousand" initiative was launched at the 21st Conference of Parties (COP21) in December 2015 to address global climate change through the aspirational goal of increasing soil organic carbon (SOC) stock of the world to 40-cm depth by an average annual rate of 4%. Small landholders (SLHs), often faced with difficult bio-physical and socio-economic conditions, are the principal managers of soil in India. There are 117 million SLHs representing 85% of the total operational holdings, cultivating over 72 million ha of land, and meeting 50-60% of India's food requirement. The agricultural soils of SLHs are strongly depleted of SOC and nutrient reserves. Therefore, the challenge of feeding 1.7 billion people in India by 2050 will depend on increasing the current productivity levels by restoring the depleted soils of SLHs. According to our estimates, soils of SLHs currently contain 1370-1770 Tg C and, which can be increased to 2460-2650 Tg C by 2050 through large-scale adoption of best management practices (BMPs) including balanced application of nutrients, compost, agroforestry, and conservation agriculture. A wide spread adoption of these practices can enhance C sequestration by 70-130 Tg CO2e per annum and produce 410-440 million Mg of food grains accounting for 80-85% of the total requirement by 2050. In this paper we propose strategies for achieving the dual objectives of advancing food security, the "4 per Thousand" target and mitigating climate change in India.

Fired Bricks: CO2 Emission and Food Insecurity.

Fired bricks are used for construction purposes over the millennia, going back to the Indus Valley Civilization. The traditional brick-making process involves removal of agriculturally productive topsoil rich in clay and soil organic matter contents. In addition to the removal of the fertile topsoil and accelerated degradation by other processes, the traditional clay brick making process also emits CO2 and other gases into the atmosphere. Therefore, the present study aims to assess the impact of brick making in India on: (i) the magnitude of annual CO2 emission and (ii) the loss of agricultural production. Currently, 0.7 Mha (million hectare) of agricultural land is under brick kilns that produce ≈250 billion bricks annually. It is estimated that soil organic carbon lost through the firing process of 250 billion bricks is 5.58-6.12 Tg (teragram) (20.48-22.46 Tg CO2), and in conjunction with clay burning and coal combustion the process releases 40.65-42.64 Tg CO2 into the atmosphere per annum. Brick kiln also impacts quality of the exposed subsoil, and may also reduce 60-90% agronomic yield. Therefore, brick making from topsoil exacerbates food and nutritional insecurity by degrading soil quality, and increases risks of climate change through increase in gaseous emissions.

Impact of land use changes on the storage of soil organic carbon in active and recalcitrant pools in a humid tropical region of India.

Quantifying soil organic carbon (SOC) dynamics is important in understanding changes in soil properties and carbon (C) fluxes. However, SOC measures all C fractions and it is not adequate to distinguish between the active C (AC) and recalcitrant or passive C (PC) fractions. It has been suggested that PC pools are the main drivers of long term soil C sink management. Therefore, the present study was undertaken with the objective of determining whether or not SOC fractions vary with land use changes under a humid tropical climate in the North East India. A chronosequence study was established consisting of natural forest, Imperata cylindrica grassland and 6, 15, 27 and 34yr old rubber (Hevea brasiliensis) plantations to determine changes in the different fractions of SOC and total SOC stock. SOC stocks significantly varied with soil depth in each land use practice. SOC stocks increased from 106Mgha-1 under 6yr to 130Mgha-1 under 34yr old rubber plantations. The SOC stocks under 34yr old plantations were 20% higher than that under I. cylindrica grassland, but 34% lower than SOC stocks recorded under natural forest soil. The proportion of AC pools decreased with increase in plantation age, AC pools being 59% of SOC stock in 6yr old stands and 33% of SOC stocks in 34yr old plantations. In contrast, the proportion of PC pools increased from 41% of SOC stock in 6yr old plantation to 67% of SOC in 34yr old plantation. In the 50-100cm soil depth, the PC pool under 27-34yr old plantations was comparable with that under natural forest but much higher than in I. cylindrica grassland. Therefore, it is concluded that old rubber plantations can play a significant role in long term soil C sink management.

Vegetative and reproductive phenology of a floodplain tree species Barringtonia acutangula from North East India.

Vegetative and reproductive phenology of Barringtonia acutangula, a floodplain tree species was studied at Chatla floodplain, Assam North East India with the aim to investigate vegetative and reproductive phenology under stressful environment of seasonal submergence and to assess the impact of environmental variables (temperature and precipitation) on tree phenophases. Quantitative assessment was made at 15 day interval for all the phenophases (leaf initiation, leaf-fall, flowering and fruiting) by tagging 40 (forty) trees over aperiod of two years (2012-14).To test seasonal influence on the phenology of Barringtonia acutangula different phenophases were correlated with environmental variables and statistical spearman's rank correlation coefficient was employed. Aridity index was computed that delineate influence of rainfall and temperature together on any phenophases. Leaf initiation showed positively significant correlation with temperature (r(s) = 0.601, p = < .05) during the year 2012-2013 whereas it was significantly correlated with rainfall (r(s) = 0.583, p = < .05) and aridity index (r(s) = 0.583, p = < .05) during the year 2013-2014. Leaf-fall was significant negatively correlated with temperature (r(s) = -0.623, p = < .05), rainfall (r(s) = -0.730, p = < .01) and aridity index (r(s) = -0.730, p = < .01) for both the studied years. Flowering was significantly influenced by temperature (r(s) = 0.639, p = < .05), rainfall (r(s) = 0.890, p = < .01) and aridity index (r(s) = 0.890, p = < .01) while in one month lag flowering was significantly correlated with rainfall (r(s) = 0.678, p = < .01) in 2012-13. Fruiting was also positively significant with temperature (r(s) = 0.795, P < .05), rainfall (r(s) = 0.835, P < .01) and aridity index (r(s) = 0.835, P < .01) for both the years. During one month lag period fruiting was positively correlated with temperature, rainfall and aridity index in both the years. Temperature, rainfall and aridity index were major determinants of the various vegetative and reproductive phenology of B. acutangula and any changes in these variables in future due to climate change, might have profound effect on phenophases of this tree species.

Comparative study on growth performance of two shade trees in tea agroforestry system.

An attempt was made to study the stem growth of two native dominant shade tree species in terms of annual girth increment in three dominant girth size categories for two years in tea agroforestry system of Barak Valley, Assam. Fifty two sampling plots of 0.1 ha size were established and all trees exceeding 10 cm girth over bark at breast height (1.37 m) were uniquely identified, tagged, and annually measured for girth increment, using metal tape during December 2010-12. Albizia lebbeck and A. odoratissima were dominant shade tree species registering 82% of appearance of the individuals studied. The girth class was categorized into six different categories where 30-50 cm, 50-70 cm and 70-90 cm were dominating girth classes and selected for increment study. Mean annual girth increment ranged from 1.41 cm in Albizia odoratissima (50-70 cm girth class) to 2.97 cm in Albizia lebbeck (70-90 cm girth class) for the first year and 1.70 cm in Albizia odoratissima (50-70 cm girth class) to 3.09 cm in Albizia lebbeck (70-90 cm girth class) for the second year. Albizia lebbeck exhibited better growth in all prominent girth classes as compared to Albizia odoratissima during the observation period. The two shade tree species showed similar trend of growth in both the years of observation and significant difference in girth increment.