Assessment of land use change and its effect on soil carbon stock using multitemporal satellite data in semiarid region of Rajasthan, India

Background:Land use change plays a vital role in global carbon dynamics.Understanding land use change impact on soil carbon stock is crucial for implementing land use management to increase carbon stock and reducing carbon emission.Therefore,the objective of our study was to determine land use change and to assess its effect on soil carbon stock in semi-arid part of Rajasthan,India.Landsat temporal satellite data of Pushkar valley region of Rajasthan acquired on 1993,2003,and 2014 were analyzed to assess land use change.Internal trading of land use was depicted throughmatrices.Soil organic carbon(SOC)stock was calculated for soil to a depth of 30 cm in each land use type in 2014 using field data collection.The SOC stock for previous years was estimated using stock change factor.The effect of land use change on SOC stock was determined by calculating change in SOC stock(t/ha)by deducting the base-year SOC stock from the final year stock of a particular land use conversion.Results:The total area under agricultural lands was increased by 32.14%while that under forest was decreased by 23.14%during the time period of 1993–2014.Overall land use change shows that in both the periods(1993–2003 and 2003–2014),7%of forest area was converted to agricultural land and about 15%changes occurred among agricultural land.In 1993–2003,changes among agricultural land led to maximum loss of soil carbon,i.e.,4.88 Mt C and during 2003–2014,conversion of forest to agricultural land led to loss in 3.16 Mt C.Conclusion:There was a continuous decrease in forest area and increase in cultivated area in each time period.Land use change led to alteration in carbon equity in soil due to change or loss in vegetation.Overall,we can conclude that the internal trading of land use area during the 10-year period(1993–2003)led to net loss of SOC stock by 8.29 Mt C.Similarly,land use change during 11-year period(2003–2014)caused net loss of SOC by 2.76 Mt C.Efforts should be made to implement proper land use management practices to enhance the SOC content.

Natural forests in New Zealand–a large terrestrial carbon pool in a national state of equilibrium

Background:Natural forests cover approximately 29%of New Zealand’s landmass and represent a large terrestrial carbon pool.In 2002 New Zealand implemented its first representative plot-based natural forest inventory to assess carbon stocks and stock changes in these mostly undisturbed old-growth forests.Although previous studies have provided estimates of biomass or carbon stocks,these were either not fully representative or lacked data from important pools such as dead wood(coarse woody debris).The current analysis provides the most complete estimates of carbon stocks and stock changes in natural forests in New Zealand.Results:We present estimates of per hectare carbon stocks and stock changes in live and dead organic matter pools excluding soil carbon based on the first two measurement cycles of the New Zealand Natural Forest Inventory carried out from 2002 to 2014.These show that New Zealand’s natural forests are in balance and are neither a carbon source nor a carbon sink.The average total carbon stock was 227.0±14.4 tC·ha^(−1)(95%C.I.)and did not change significantly in the 7.7 years between measurements with the net annual change estimated to be 0.03±0.18 tC·ha^(−1)·yr^(−1).There was a wide variation in carbon stocks between forest groups.Regenerating forest had an averaged carbon stock of only 53.6±9.4 tC·ha^(−1) but had a significant sequestration rate of 0.63±0.25 tC·ha^(−1)·yr^(−1),while tall forest had an average carbon stock of 252.4±15.5 tC·ha^(−1),but its sequestration rate did not differ significantly from zero(−0.06±0.20 tC·ha^(−1)·yr^(−1)).The forest alliance with the largest average carbon stock in above and below ground live and dead organic matter pools was silver beech-red beech-kamahi forest carrying 360.5±34.6 tC·ha^(−1).Dead wood and litter comprised 27%of the total carbon stock.Conclusions:New Zealand’s Natural Forest Inventory provides estimates of carbon stocks including estimates for difficult to measure pools such as dead wood and roots.It also provides estimates of uncertainties including effects of model prediction error and sampling variation between plots.Importantly it shows that on a national level New Zealand’s natural forests are in balance.Nevertheless,this is a nationally important carbon pool that requires continuous monitoring to identify potential negative or positive changes.