Restoration ability of seasonal exclosures under different woodland degradation stages in semiarid Chaco rangelands of Argentina

BRASSIOLO MIGUEL; COTRONEO SANTIAGO; GOLUSCIO ROBERTO; JACOBO ELIZABEHT

JOURNAL OF ARID ENVIRONMENTS

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2018 vol. 158 p. 28 - 34

0140-1963

Exclosures are widely used for rangeland restoration in semiarid woodlands. However, grass recovery could be hampered if degradation exceeded certain thresholds. We hypothesized that the overstory degradation stage of the woodland control the effectiveness of seasonal exclosures in restoring understory vegetation, being restoration higher in such woodlands where less overstory degradation determines a higher availability of resources, and lower in those woodlands where a high overstory degradation would impose major abiotic constrains. We assessed four years effects of seasonally grazed exclosures -vs. open rangelands- on lower layer cover (grasses, low shrubs and litter) and productivity in three increasing degradation stages ?mature forests, secondary forests and shrublands? in arid Chaco woodlands. We found that grass cover and productivity increased tenfold in four years in mature and secondary forests but remained virtually null in shrublands. In rested forests, the grass cover increments remained relatively constant regardless the annual rainfall amount, both in the driest year 2013 (531 mm) and the wettest year 2015 (924 mm). Only in an extraordinarily wet year (2015) did grass productivity increased in rested shrublands. In that wet year, low shrubs cover ?higher at higher overstory degradation? decreased in all woodlands. Our results suggest that shrublands may constitute a new steady state unable to recover by grazing exclusion itself, but probably by its combination with wet periods.