Bio‐mitigation of carbon following afforestation of abandoned salinized farmland

Abstract

As the global demand for food continues to increase, the displacement of food production by using agricultural land for carbon mitigation, via either carbon sequestration, bioenergy or biofuel is a concern. An alternative approach is to target abandoned salinized farmland for mitigation purposes. Australia, for example, has 17 million ha of farmland that is already or could become saline. At a representative, salinized, low rainfall (350 mm yr À1 ) site at Wickepin, Western Australia, we demonstrate that afforestation can mitigate carbon emissions through either providing a feedstock for bioenergy or second generation biofuel production and produce salt-tolerant fodder for livestock. A range of factors markedly affect this mitigation. These include hydrological conditions such as salinity, site factors such as slope position and soil properties and a range of silvicultural factors such as species, planting density and age of the planting. High density (2000 stems ha À1 ) plantings of Eucalyptus occidentalis Endl. produced a mean total biomass of 4.6 t ha À1 yr À1 (8.5 t CO 2 -e ha À1 yr À1 ) averaged over 8 years. Atriplex nummularia Lindl. produced a mean total biomass of 3.8 t ha À1 yr À1 (6.9 t CO 2 -e ha À1 yr À1 ) averaged over 4 years and approximately 1.9 t ha À1 yr À1 of edible dry matter annually to 8 years of age. With differences in salt tolerance between E. occidentalis and A. nummularia, we propose an integrated approach to treating salinized sites that takes salinity gradients into account, replicates natural wetland ecosystems and produces both fodder and biomass. Continued mitigation is expected as the stands mature, assuming that growth is not affected by the accumulation of salt in the soil profile. Such carbon mitigation could potentially be applied to salinized farmland globally, and this could thus represent a major contribution to global carbon mitigation without competing with food production.

Seasonal Timing for Estimating Carbon Mitigation in Revegetation of Abandoned Agricultural Land with High Spatial Resolution Remote Sensing

“…Details of seedling production and planting have been described previously [7]. At the time of field measurement in December 2011 (dry season), the low-and high-density stands had average heights of 2.17 and 1.68 m, and average canopy diameters of 2.66 and 1.52 m, respectively.…”

“…The study site (32°43′34.33′′S, 117°39′55.27′′E) was located near Wickepin, Western Australia, and was established to investigate carbon stocks following revegetation of abandoned salinized farmland [7,28]. The region has a semi-arid Mediterranean climate, with a seasonal drought from November to April, and a mean annual rainfall of 357 mm·year −1 (2000-2011, Wickepin weather station No.…”

“…Bunting and Lucas [16] where the images are of sufficiently fine spatial resolution. Sochacki et al [7] and Walden et al [11] both found that aboveground biomass of A. nummularia followed a strong linear trend (R 2 = 0.81) in relation to a crown volume index (CVI), calculated from crown width, length, and height. Walden et al [11] also found that canopy diameter measurements were only slightly less predictive (R 2 = 0.68) compared to CVI, and could be used to estimate aboveground biomass (AGB).…”

“…Alternative mitigation approaches have been advocated, such as using low value or otherwise abandoned farmland to avoid competitive effects of vegetation [7].…”

“…One option for salt-affected land is revegetation with salt-tolerant grazing plants such as Atriplex spp. [7]. Revegetation is a specific category of mitigation activity within the United Nations Framework Convention on Climate Change and is defined as the establishment of vegetation that does not meet the definitions of afforestation or reforestation.…”