Livestock grazing in subtropical pastures: steps in the analysis of attribute response and plant functional types

McIntyre, S Lavorel, S

S. Mcintyre et S. Lavorel, Livestock grazing in subtropical pastures: steps in the analysis of attribute response and plant functional types, J ECOLOGY, 89(2), 2001, pp. 209-226

39

INGLESE

Article

Environment/Ecology

JOURNAL OF ECOLOGY

0022-0477 → ACNP

89

2

2001

209 - 226

ISI

0022-0477(200104)89:2<209:LGISPS>2.0.ZU;2-F

1 In order to investigate the use of plant functional types as an alternati ve to floristic descriptions of response to grazing, we analysed plant comm unities from a cattle grazing experiment conducted in grassy eucalypt woodl and in subtropical Queensland, Australia. The two variables analysed (lands cape position and stocking rate) accounted for similar proportions of varia tion in the vegetation ground layer, although forbs were more sensitive to slope position and perennial grasses were more sensitive to stocking rate. 2 As grazing pressure increased, perennial grasses declined, while the rela tive proportion of forbs and annual grasses increased. Detailed functional group analyses were conducted for the perennial grass and forb life-forms. Annual grasses were represented by only two species, preventing identificat ion of functional types within this life-form. 3 We conducted a five-step analysis for both perennial grasses and forbs as follows: (i) defining grazing-related species response groups; (ii) defini ng species groups based on natural attribute correlations; (iii) identifyin g attributes that changed significantly with grazing; (iv) identifying synd romes by relating (ii) and (iii); (v) describing functional types from (iii ) and (iv), and assessing them against actual species response. 4 Eight grass and eight forb functional types were identified. Of the taxa that had an observed response to grazing, 54% of the grass taxa and 57% of the forb taxa corresponded to one of these functional types in terms of mee ting both grazing response and trait criteria. The five-stage analysis prov ided a comprehensive but complex approach to functional type identification . 5 The functional types identified can be summarized as follows. Low levels of grazing were associated with more medium-sized, moderately leafy perenni al grasses with wind-dispersed or adhesive seeds, and more erect or twining forbs with large to medium sized seeds. High levels of grazing were associ ated with: more annual grasses; low-growing leafy perennial grasses with sm all seeds having no dispersal appendages; mat-forming large-seeded forbs; a nd low-growing, scrambling, small-seeded forbs.