Revegetation after farmland abandonment not only changes the aboveground biodiversity but also soil physicochemical properties and soil microbial biomass. However, how the revegetation after farmland abandonment influences soil properties and herb‐layer biodiversity remains unclear. In the present study, we examined the variation in soil chemical and biological properties (soil microbial biomass, stock, and stoichiometry), herb‐layer diversity indices, and aboveground biomass, their relationships in a chronosequence of 2, 5, 7, 11, 16, and 35 years following revegetation of abandoned farmland in the central Himalaya, India. Results revealed that the diversity indices, biomass, and soil properties significantly changed over successional stages. The species in the plant community shifted from the forbs in earlier stages to grasses and sedges in later stages. Our results indicated that the soil microbial carbon (C) and nitrogen (N) contents and stocks increased along the chronosequence and were highest at the 35‐year‐old fallow. However, soil microbial phosphorus (P) contents and stock generally decreased with time. The soil nutrient and microbial biomass were significantly correlated, which indicate close coupling between soil and microbial C, N, and P contents. Soil, microbial C/P, and N/P ratios were the lowest in 7‐ and 11‐year‐old fallows, indicating that middle‐aged fallows were more P‐limited. Our results suggest that revegetation changes the soil and microbial stoichiometry, potentially changing the vegetation composition and nutrient cycling of the abandoned farmland ecosystems.
Urban heat island (UHI) is developing in major cities of India due to increased urbanization and decreased vegetation cover. Urbanization induces substantial land use changes resulting in surface transformation and thermal emissions which modifies urban microclimate posing serious risk to human health, environment and ecology of the Himalayan ecosystems. Therefore, an improved understanding is required to mitigate UHI. The study illustrates the impact of urbanization on land surface temperature (LST) in the capital city- Shimla and Dehradun in the western Himalayan, India using satellite datasets. The process has been analyzed using urban cover patterns derived from Landsat 5, 7 and 8 with respective sensors of TM, ETM+, and OLI. Built-up and non-built-up areas were extracted and biophysical parameters NDVI, NDBI, NDWI and LST were computed to capture different characteristics of urban growth. The result indicated that during study period, built-up areas have increased from 32.19 Km2 (2000) to 68.37 Km2 (2016) for Dehradun and 12.38 Km2 (2000) to 29.47 Km2 (2016) for Shimla which has manifested an increase in NDBI and LST and decrease in NDVI and NDWI. The results revealed that temperature hotspots were maximum in built-up areas followed by vegetation and water body. We observed significant correlation (p < 0.05) between LST and biophysical parameters -NDVI, NDBI, NDWI. Spatial metrics at class and landscape-level has indicated that landscape has fragmented, became more heterogeneous from 2000 to 2016 because of increased urban growth. The trends identified for changes in landscape patterns and their ramifications in respective areas have prospective policy implications.
Urban heat islands (UHI) are developing due to increasing urbanization and loss of vegetation in major cities in India. Increased urbanization modifies the urban microclimate that leads to significant land-use changes resulting in surface conversion and heat release, which poses serious risks to human health, environment and the ecosystem of the Himalayan ecosystem. Hence, mitigating UHI becomes important and requires a better understanding of underlying associated biophysical processes. In the study an attempt has been made to demonstrate the impact of urbanization on land surface temperature (LST) in Shimla and Dehradun, capitals of the Western Himalayan states, India using satellite data and spatial metrics. The process was analyzed using urban coverage patterns obtained from Landsat 5, 7, and 8 and corresponding sensors from TM, ETM+, and OLI. The Built-up and Non-Built-up areas were extracted and the biophysical parameters NDVI, NDBI, NDWI and LST were calculated to capture different features of urban growth. The result indicated, that the built-up area increased from 32.19 km2 (2000) to 68.37 km2 (2016) in Dehradun and from 12.38 km2 (2000) to 29.47 km2 (2016) in Shimla during the study period, resulting in an increase in NDBI and LST and Reduction and NDVI and NDWI. Results showed that temperature hotspots were largest in urban areas, followed by vegetation and water bodies. A significant correlation (p < 0.05) was observed between LST and biophysical parameters -NDVI, NDBI, NDWI. Spatial metrics at the class and landscape levels show that increased urban growth from 2000 to 2016 has made the landscape fragmented and more heterogeneous. The Identified trends and changes in landscape patterns and their impact on heterogeneous urban areas suggest that the study is feasible to estimate LST, NDVI, NDBI and NDWI with reasonable accuracy that will likely have influence on policy interventions.
The leaf ecophysiological traits are expected to change with the leaf age, and tree age. Leaf phenology and tree age (seedling, sapling, and tree stages) was a stronger driver of changes in ecophysiological traits. In the present study, we measured effect of leaf phenophases (initiation stage, expansion stage, and senescence stages) and tree age (seedling, sapling, and tree stages) on the leaf physiological and morphological traits of nitrogen-fixing Alnus nepalensis (D. Don), a pioneer tree species in the central Himalaya. In fully expanded leaf and seedling stage demonstrate ecophysiological traits consistent with an acquisitive resource-use strategy. Results revealed that net photosynthetic capacity (A and A), leaf stomata conductance (gsw and gsw), transpiration rate (E and E), specific leaf area (SLA), pre-dawn and mid-day water potential (Ψ), leaf total chlorophyll concentration, photosynthetic N-, and P-use efficiency (PNUE and PPUE) were highest in seedling stage and sapling than trees. Seedling stage and sapling had significantly higher transpiration rates (E and E ) and stomatal conductance (gsw and gsw), therefore showing significantly lower water use efficiency (WUE) and intrinsic water use efficiency (WUE). Mass-based net photosynthetic capacity (A) were positively correlated with PNUE, PPUE, transpiration rate, stomatal conductance, SLA, and chlorophyll concentrations while negatively correlated with WUE and WUE. However mass-based leaf nitrogen (N), and phosphorus (P) concentrations were higher in fully expended leaf; they did not vary significantly, despite N concentration negatively correlated with SLA. Collectively, our results indicated that seedling A. nepalensis displayed characteristic values associated with a more acquisitive resource-use strategy. Consequently, this may explain their survival and replacement strategies during secondary succession and should be considered for the vegetation restoration model of degraded forest in the central Himalaya.
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