Effect of woody vegetation clearing on nutrient and carbon relations of semi-arid dystrophic savanna

Abstract

Throughout the savanna biome, woody vegetation is cleared to increase productivity of herbaceous pasture. While clearing can result in increased pasture production of semi-arid dystrophic savannas in the short term, it is uncertain whether production is sustained in the long term. There is insufficient knowledge of how clearing affects soil nutrient and organic carbon (SOC) stocks. Using cleared-uncleared site pairs, we evaluated techniques for time-integrated assessment of nutrient and carbon relations in Australian savanna. Short-term in situ resin incubation showed that soil at cleared sites had a higher time-integrated availability of ammonium and nitrate, indicating that nitrogen (N) may turn over faster and/or is taken up slower at cleared sites than uncleared savanna. Nitrate and ammonium availability was approximately 2-fold higher in spring than in summer, likely due to greater uptake and/or loss of nitrate during summer rains. Nitrate was a prominent N source for evergreen trees, especially before summer rain, pointing to a role of trees as permanent N sinks. Stable isotope signatures of soil and vegetation indicate that N input occurs via N 2 fixing microbiotic crusts and Acacia species. 30 years after clearing, SOC contained more C 4 grass-derived carbon than uncleared savanna, but this shift in C source was not associated with the net C gain often observed in grasslands. Interactions between altered nutrient and C relations and composition of the understorey should be assessed in context of introduced buffelgrass (Cenchrus ciliaris) which had higher macronutrient concentrations than native grasses. Heterogeneity of the studied soils highlights the need for replication at several spatial scales to infer long-term dynamics with space-for-time chronosequences. We conclude that the techniques presented here are useful for gaining knowledge of the biogeochemical processes governing savannas and the systems that result from clearing.

Dynamics of component carbon fluxes in a semi‐arid Acacia woodland, central Australia

“…The soil is a heavily weathered red kandosol, which is typical of large portions of semi‐arid Australia and has a high potential for drainage [ Schmidt et al ., ; Morton et al ., ]. The soil characteristics of this site have been described in Eamus et al .…”

Carbon Sink Potency in Three Types of Savanna in Nusa Tenggara Timur

“…Savana tropis mencakup 15% dari permukaan daratan bumi dan merupakan suatu lanskap yang kompleks dimana rerumputan, perdu, semak dan pepohonan secara bersama-sama berada pada kondisi dinamika yang seimbang (Schmidt et al, 2010). Wilayah Nusa Tenggara Timur (NTT) memiliki hamparan savana yang luas dan mendominasi daratan pulau-pulau di provinsi ini.…”

Speculations on the application of foliar <sup>13</sup>C discrimination to reveal groundwater dependency of vegetation and provide estimates of root depth and rates of groundwater use

“…- Eamus et al, 2013), typical of large portions of semi-arid Australia, and has a high potential for drainage (Morton et al, 2011;Schmidt et al, 2010). Patches of hard siliceous soil are often observed and are likely surface expressions of the underlying hardpan (Cleverly et al, 2013), a common formation in the top 1-1.5 m in this type of soil (Cleverly et al, 2013(Cleverly et al, , 2016aMorton et al, 2011).…”