Table 1.
Woody encroachment levels, age of enclosure, soil and livestock population density characteristics of the research sites in the Yabello and Dire districts of Borana zone.
Geological information was summarized from the Borana land use study project soil survey report (unpublished data).Woody encroachment levels:Low woody encroachment site (LE), moderate woody encroachment site (ME), severe woody encroachment site (SE), highest woody encroachment (HE).
Table 2.
Mean values (± SE) of vegetation characteristics of the grazing regimes for each encroachment level in the Yabello and Dire districts of Borana, southern Ethiopia.
Low woody encroachment site (LE), moderate woody encroachment site (ME), severe woody encroachment site (SE), highest woody encroachment site (HE). Open = open access grazing land, enclosure = areas of livestock exclosure, reserved for heifers and calves only in the dry season. N = number of plots sampled in each grazing regime.
Fig 1.
Study sites: low woody encroachment site (A), moderate woody encroachment site (B), severe woody encroachment site (C), highest woody encroachment site (D) in the semi-arid rangelands of Yabello and Dire districts, Borana, southern Ethiopia.
Pictures taken by Hasen-Yusuf in 2011.
Fig 2.
Schematic map of the location of the four levels of woody encroachment (panel A: Low woody encroachment site (LE), moderate woody encroachment site (ME), severe woody encroachment site (SE), highest woody encroachment site (HE), transects and plots in the open and enclosure grazing regimes (B) and their replications (R1, R2 and R3) and soil sampling location at each sub plots(C).
Table 3.
Mean (± SE) herbaceous root biomass carbon (HROC) and herbaceous aboveground biomass C (Hag OC) in enclosures and open grazing land across four levels of woody encroachment.
Encroachment levels: Low woody encroachment site (LE), moderate woody encroachment site (ME), severe woody encroachment site (SE), highest woody encroachment site (HE). N, grazing regime replicates per site. Different lowercase letters represent statistical differences determined by the interaction of grazing regime and woody encroachment terms in the mixed Model andTukey’s means comparisons (P < 0.05).
Fig 3.
Means and standard errors by levels of woody encroachment and grazing regime (grey bars = enclosure, black bars = open grazing land) for soil organic carbon (A), total soil nitrogen content (B), and soil organic carbon to total soil nitrogen ratio (C).Low woody encroachment site (LE), moderate woody encroachment site (ME), severe woody encroachment site (SE), highest woody encroachment site (HE).
Different lowercase letters represent statistical differences determined by woody encroachment by grazing interaction term in themixed model and Tukey’s means comparisons (P < 0.05).
Table 4.
Mean (x SE) soil bulk density (BD), percent soil organic carbon (SOC %), soil organic carbon stocks (SOC), percent total soil nitrogen (TSN %), total soil nitrogen stock (TSN) for two soil depths in enclosures and open grazing land across four levels of woody encroachment (for characteristics see also Table 1).
Encroachment levels: Low woody encroachment site (LE), moderate woody encroachment site (ME), severe woody encroachment site (SE), highest woody encroachment site (HE). N, grazing regime replicates per site. Different lowercase letters represent statistical differences determined by the grazing regime and woody encroachment interaction term in the mixed Model andTukey’s means comparisons (P < 0.05).
Fig 4.
Regression of soil organic carbon fraction (% SOC) against total soil nitrogen fraction (TSN; A), cation exchange capacity (CEC; B), soil bulk density (C), sand fraction (% sand; D) and soil pH (E) within a depth of 0–20 cm.
r2 and P values are given for each plate.