A narrower gap of grazing intensity. Reply to Fetzel et al., 2017. Seasonality constrains to livestock grazing intensity

IRISARRI, JORGE GONZALO NICOLA; AGUIAR, SEBASTIÁN; OESTERHELD, MARTIN; DERNER, JUSTIN D.; GOLLUSCIO, RODOLFO A.

GLOBAL CHANGE BIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2017

1354-1013

Fetzel, Havlik, Herrero, & Erb (2017) globally mapped the gap between observed and potential grazing intensity (GI): the ratio between consumption by livestock and aboveground net primary productivity (ANPP). Fetzel et al. (2017) estimated grazing land, forage production and livestock demand at a half-degree resolution. They mapped GI below 15% for most of the world. Here we present some independent tests of their predictions and show that observed GI reported in the literature is consistently higher than observed GI reported by Fetzel et al. (2017). Consequently, the gap between forage produced and consumed may be narrower.We present seven examples that show higher GI than Fetzel et al. (2017) (Table 1). The first two examples are global (Table 1; McNaughton, Oesterheld, Frank, & Williams, 1989; Milchunas & Lauenroth, 1993; Oesterheld, Loreti, Semmartin, & Paruelo, 1999). They show that livestock GI estimated by Fetzel et al. (2017) are within the range of GI in natural systems dominated by invertebrates and well below systems dominated by vertebrate herbivores or livestock (Table 1, see Fig. 1 by Fetzel et al., 2017). The other examples are regional and focus on livestock. Two regional compilations for South American livestock production systems (Irisarri, Oesterheld, Golluscio, & Paruelo, 2014; Oesterheld et al.,1999) had higher GI values than estimated by Fetzel et al. (2017) for the same region. The remaining three examples correspond to two of the most important rangeland areas of North America, the Northern Mixed Grass Prairie and the Short Grass Steppe. There, rangeland scientists have reproduced ranchers GI levels in long-term experiments (Biondini, Patton, & Nyren, 1998; Derner & Hart, 2007; Milchunas, Forwood, & Lauenroth, 1994). In all cases, the simulated GI (?40%) was higher than the maximum values by Fetzel et al. (2017) for those vast areas. Moreover, the maximum GI value from the long-term experiments almost doubled the maximum GI by Fetzel et al. (2017). In summary, most reports of GI in the literature are above the 0-15% GI reported by Fetzel et al. (2017) for most of the world.