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Grazing intensity elicits changes in the composition of plant functional groups in both shortgrass steppe (SGS) and northern mixed‐grass prairie (NMP) in North America. How these grazing intensity‐induced changes control aboveground net primary production (ANPP) responses to precipitation remains a central open question, especially in light of predicted climate changes. Here, we evaluated effects of four levels (none, light, moderate, and heavy) of long‐term (>30 yr) grazing intensity in SGS and NMP on: (1) ANPP; (2) precipitation‐use efficiency (PUE, ANPP : precipitation); and (3) precipitation marginal response (PMR; slope of a linear regression model between ANPP and precipitation). We advance prior work by examining: (1) the consequences of a range of grazing intensities (more grazed vs. ungrazed); and (2) how grazing‐induced changes in ANPP and PUE are related both to shifts in functional group composition and physiological responses within each functional group. Spring (April–June) precipitation, the primary determinant of ANPP, was only 12% higher in NMP than in SGS, yet ANPP and PUE were 25% higher. Doubling grazing intensity in SGS and nearly doubling it in NMP reduced ANPP and PUE by only 24% and 33%, respectively. Increased grazing intensity reduced C₃ graminoid biomass and increased C₄ grass biomass in both grasslands. Functional group shifts affected PUE through biomass reductions, as PUE was positively associated with the relative abundance of C₃ species and negatively with C₄ species across both grasslands. At the community level, PMR was similar between grasslands and unaffected by grazing intensity. However, PMR of C₃ graminoids in SGS was eightfold higher in the ungrazed treatment than under any grazed level. In NMP, PMR of C₃ graminoids was only reduced under heavy grazing intensity. Knowing the ecological consequences of grazing intensity provides valuable information for mitigation and adaptation strategies in response to predicted climate change. For example, moderate grazing (the recommended rate) in SGS would sequester the same amount of aboveground carbon as light grazing because ANPP was nearly the same. In contrast, reductions in grazing intensity in NMP from moderate to light intensity would increase the amount of aboveground carbon sequestrated by 25% because of increased ANPP.

Drylands cover about 41% of Earth's land surface, and 65% of their area supports domestic livestock that depends on the above‐ground net primary productivity (ANPP) of natural vegetation. Thus, understanding how biotic and abiotic factors control ANPP and related ecosystem functions can largely help to create more sustainable land‐use practices in rangelands, particularly in the context of ongoing global environmental change. We used 311 sites across a broad natural gradient in Patagonian rangelands to evaluate the relative importance of climate (temperature and precipitation) and vegetation structure (grass and shrub cover, species richness) as drivers of ANPP, precipitation‐use efficiency (PUE) and precipitation marginal response (PMR). Climatic variables explained 60%, 52% and 12% of the variation in grass cover, shrub cover and species richness, respectively. Shrub cover increased in areas with warmer, drier and winter rainfall climates, while the response observed for both grass cover and species richness was the opposite. Climate and vegetation structure explained 70%, 60% and 29% of the variation in ANPP, PUE and PMR, respectively. These three variables increased with increasing vegetation cover, particularly grass cover. Species richness also increased with ANPP, PUE and PMR. ANPP increased, and PUE decreased with increasing mean annual precipitation, whereas PMR increased with the proportion of precipitation falling in spring–summer. Temperature had a strong negative effect on ANPP and PUE, and a positive direct effect on PMR. Standardized total effects from structural equation modelling showed that vegetation structure and climate had similar strengths as drivers of ecosystem functioning. Grass cover had the highest total effect on ANPP (0.58), PUE (0.55) and PMR (0.41). Among the climatic variables, mean annual precipitation had the strongest total effect on ANPP (0.51) and PUE (−0.41), and the proportion of the precipitation falling in spring–summer was the most influential on PMR (0.36). Synthesis. Vegetation structure is as important as climate in shaping ecosystem functioning Patagonian rangelands. Maintaining and enhancing vegetation cover and species richness, particularly in grasses, could reduce the adverse effects of climate change on ecosystem functioning in these ecosystems.

1. Desertification is of critical concern because it may affect 40% of the global land area inhabited by more than 1 billion people. During the process of desertification, defined as land degradation in arid, semi‐arid and dry subhumid areas, drylands shift to a state of reduced biological productivity that may lead to widespread loss of human well‐being. Despite recent advances, we need a better understanding of the response of ecosystems to desertification to improve the assessment and monitoring of desertification. 2. We used a published physiognomic description, MODIS monthly NDVI data for 2000-2005 and rain gauge data to characterize the long‐term effects of degradation for an area of 128 000 ha located in western Patagonia. 3. We focused on three aspects of vegetation dynamics: radiation interception, precipitation use efficiency (PUE) and the sensitivity of vegetation to interannual changes in precipitation (i.e. the slope of the relationship between the above‐ground net primary productivity and precipitation, the precipitation marginal response, PMR). In particular, we analysed the response of PMR and PUE to long‐term changes in vegetation structure due to grazing. 4. On average, NDVI decreased by 28%, ranging between 35% (grass or grass-shrub steppes to semi‐deserts) and 22% (grass or grass‐shrub steppes to low cover grass steppes) suggesting that, in Patagonia, desertification may imply a reduction in the above‐ground net primary productivity. 5. Additionally, PMR and PUE captured the functional modifications associated with vegetation structure caused by desertification. In general, grass and grass‐shrub steppes had the highest average PUE and PMR. Shrub steppes and semi‐deserts had the lowest PMR and PUE. These results support the hypothesis that PUE is more sensitive to changes in total plant cover and PMR to changes in plant functional type composition. 6. Synthesis and applications. Our results indicate that the precipitation marginal response could complement current desertification assessments based only on precipitation use efficiency thereby improving our ability to monitor desertification. Enhanced monitoring programmes could provide an early warning signal for the onset of desertification allowing for timely management action.

Given the mandated increases in fuel production from alternative sources, limited high-quality production land, and predicted climate changes, identification of stress-tolerant biomass crops will be increasingly important. However, existing literature largely focuses on the responses of a small number of crops to a single source of abiotic stress. Here, we provide a much-needed review of several types of stress likely to be encountered by biomass crops on marginal lands and under future climate scenarios: drought, flooding, salinity, cold, and heat. The stress responses of 17 leading biomass crops of all growth habits (e.g., perennial grasses, short-rotation woody crops, and large trees) are summarized, and we identify several that could be considered “all purpose” for multiple stress types. Importantly, we note that some of these crops are or could become invasive in some landscapes. Therefore, growers must take care to avoid dissemination of plants or propagules outside of cultivation.

. A number of investigators have interpreted the slope of a linear production‐resource relationship as a measure of efficiency of resource utilization. However, this is rarely true and may lead to incorrect conclusions. Here, by means of simple mathematical equations and conceptual definitions, we point out the theoretical differences between slope and efficiency. While a slope represents the change in the dependent variable per unit change in the independent variable, efficiency expresses the amount of output produced by a unit amount of input. Practical implications of using slopes as indicators of resource‐use efficiency are less important as the resource amount increases. Slopes may be used as indicators of the sensitivity of production to changes in input, which is by itself an interesting property of biological systems. Finally, production function intercepts determine whether the efficiency will decrease, increase, or remain constant as resources increase.

A number of investigators have interpreted the slope of a linear production-resource relationship as a measure of efficiency of resource utilization. However, this is rarely true and may lead to incorrect conclusions. Here, by means of simple mathematical equations and conceptual definitions, we point out the theoretical differences between slope and efficiency. While a slope represents the change in the dependent variable per unit change in the independent variable, efficiency expresses the amount of output produced by a unit amount of input. Practical implications of using slopes as indicators of resource-use efficiency are less important as the resource amount increases. Slopes may be used as indicators of the sensitivity of production to changes in input, which is by itself an interesting property of biological systems. Finally, production function intercepts determine whether the efficiency will decrease, increase, or remain constant as resources increase.