Vegetation composition and soil nutrients status from polyculture to monoculture
The study was conducted on status of nutrients in three major types of forests namely, broad-leaved, mixed pine and pine forests in Meghalaya, considering altitude and seasonality as variables. The findings revealed that the change in micro-environmental conditions as influenced by attitude and seasonality has marked effect on status and release of nutrients in the soil of representative forest stands at markedly difference. The ambient and soil temperature was sharply greater at high altitude (Upper Shillong) and values were decreased from broad-leaved to pine forests. The soil temperature was lower than air temperature in all cases. The soil temperature at low altitude (Umroi) during postmonsoon season was higher than pre-monsoon season; however, on the contrary, it was higher during pre-monsoon season in other cases. The light interception decreased from broad-leaved to pine forests, and greater values were recorded at high altitude. The light interception and temperature played a key role in determining relative humidity, and as a result more relative humidity was recorded at high altitude and the values were decreased from broad-leaved to pine forests. The litter thickness and litter accumulation on forest floor at high altitude was about two fold greater than representative forest at low altitude. The values were higher during post-monsoon season, except that more litter thickness was noticed during pre-monsoon season at high altitude; this could be linked with high litter production and low rate of litter decomposition. Soil moisture content was always higher in top-soil, and post-monsoon season showed greater values. Soil pH ranged from 4.6 to 5.8 in top-soil, and from 4.8 to 6.3 in sub-soil. High rate of litter decomposition leads to greater soil pH in top-soil during postmonsoon season. The organic carbon, total nitrogen and available phosphorus contents were more in top-soil, with exception that the phosphorus content was generally higher in sub-soil during postmonsoon season. The values for soil moisture, organic carbon, nitrogen, and phosphorus were markedly higher at high altitude with respect to forest types and seasonality. Normally, the nutrient poor soil has high C:N ratio, and on account of this fertility of soil decreased from polyculture to monoculture. The finding reveal that the C:N ratio was increased from broad-leaved to pine forests, and more values were observed in sub-soil.
Key words: Altitude, monoculture, nutrient release, polyculture, seasonality, top-soil and sub-soil, vegetation.