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Projected global change will increase the level of land-use and environmental stressors such as drought and grazing, particularly in drylands. Still, combined effects of drought and grazing on plant production are poorly understood, thus hampering adequate projections and development of mitigation strategies. We used a large, cross-continental database consisting of 174 long-term datasets from >30 dryland regions to quantify ecosystem responses to drought and grazing with the ultimate goal to increase functional understanding in these responses. Two key aspects of ecosystem stability, resistance to and recovery after a drought, were evaluated based on standardized and normalized aboveground net primary production (ANPP) data. Drought intensity was quantified using the standardized precipitation index. We tested effects of drought intensity, grazing regime (grazed, ungrazed), biome (grassland, shrubland, savanna) or dominant life history (annual, perennial) of the herbaceous layer to assess the relative importance of these factors for ecosystem stability, and to identify predictable relationships between drought intensity and ecosystem resistance and recovery. We found that both components of ecosystem stability were better explained by dominant herbaceous life history than by biome. Increasing drought intensity (quasi-) linearly reduced ecosystem resistance. Even though annual and perennial systems showed the same response rate to increasing drought intensity, they differed in their general magnitude of resistance, with annual systems being ca. 27% less resistant. In contrast, systems with an herbaceous layer dominated by annuals had substantially higher postdrought recovery, particularly when grazed. Combined effects of drought and grazing were not merely additive but modulated by dominant life history of the herbaceous layer. To the best of our knowledge, our study established the first predictive, cross-continental model between drought intensity and drought-related relative losses in ANPP, and suggests that systems with an herbaceous layer dominated by annuals are more prone to ecosystem degradation under future global change regimes.

their construction, to a stable range condition, took from 14 years in the lightly grazed field to more than the length of the study in the A study was conducted to examine the effects of 4 stocking rates on the vegetation in a Rough Fescue Grassland vegetation in southwestern Alberta. Stocking at a light rate (1.2 AUM/ha) for 32 very heavily grazed field. The duration required for recovery was years did not affect range condition. However, a modest increase in stocking rate (1.6 AUM/ha) led to a marked decline in range related to the original range condition of the exclosures. condition. This was associated with a change in the composition of rough fescue from 38 to 21% of basal area. Rough fescue (FestzCQ ScQbreflQ) was nearly eliminated with a stocking rate of 2.4 AUM/ha. Rough fescue was repiaced by Parry oat grass (DQnthoni~ parryi) which increased from 24% at 1.2 AUM/ha to 48% at 2.4 AUM/ha. However, stocking at 4.8 AUM/ha resulted in severe deterioration of the grassland. This required annual adjustment of the stocking rate to avoid animal losses. The recommended stocking rate for good condition range in the area is 1.6 AUM/ha. Recovery of the vegetation within the exclosures, from the time of setting stocking rates. The stocking rate, expressed in this paper as animal unit months per hectare (AUM/ ha), defines the relative quantity of forage that will be harvested during the grazing period in a given year. The effect of increasing the stocking rate is to increase the proportion of forage utilized, which may lead to changes in species composition of grasslands (Ellison 1960). The species that increase because of an increased stocking rate are often subdominants in the plant community and are potentially less productive than the dominant species (Looman 1969). The purpose of this study was to examine the changes that occur in species composition of a Rough Fescue Grassland as a result of stocking with cattle at different rates. The work described is part of a final assessment of the study which was reported earlier (Johnston 1961, Peake and Johnston 1965). The Rough Fescue Grasslands (Festuca scabrella)t in western Canada are managed primarily for grazing by cattle. They are found on highly productive soils, but cultural practices are limited by steep terrain. Consequently, management of grassland vegetation is through management of grazing by cattle. This is normally accomplished using a continuous grazing system where the cattle are turned onto the range in spring and removed in autumn. The most critical management decision made, with this system, is in ing in elevation from 1,280 to 1,420 met&above sea level (Fig. i). Average precipitation at the substation, over a 30-year period from April to August, was 35 I mm. Average precipitation from April to Site Description August at 2 similar areas within 65 km (Pincher Creek and Pekisko) was 353 mm while the annual precipitation averaged 614 The study area was at the Agriculture Canada Research Substamm over the same 30-year period. Annual precipitation data a...