Drivers of non-native plant success in drylands are poorly understood. Here we identify functional differences between dryland native and non-native perennial plants and assess how biotic, abiotic and anthropogenic factors shape the success of the latter. On the basis of plant community and functional trait data from 98 sites across 25 countries, we report a total of 41 non-native plant species at 31 sites. Non-natives tend towards faster growth strategies than natives. Non-native plant richness is higher at sites with greater grazing pressure and under environmental conditions associated with higher soil fertility, decomposition and fungal richness-conditions that tend to occur in less arid regions-and lower where native plant and herbivore richness are greater. Non-native plant cover correlates positively with grazing pressure and negatively with native plant richness. Taken together, our results suggest that non-native plant success in drylands is facilitated when high grazing pressure coincides with elevated resource availability. Such context-dependence of non-native plant success and linkages with native plant and herbivore diversity highlight the need for managing grazing and conserving biodiversity across the world's drylands.

In Southern Argentine Patagonia, meadows are wetland ecosystems that require integrated grazing management, in which water dynamics, climatic components, and soil and vegetation characteristics are crucial factors for maintaining ecosystem functionality. The objectives of this study were to characterize and relate the productive parameters of the wet and dry meadow sectors to soil moisture and thermal time. Plant height, accumulated aerial biomass (AAB), live biomass (LB), dead biomass (DB), live AAB, daily vegetation growth rate (DGR), daily vegetation regrowth rate (DRR), soil moisture (SM), water table depth (WTD), and thermal time (TT) were determined monthly from October to April during three consecutive growing seasons in two extra-Andean meadows. AAB was analyzed using a factorial arrangement in a completely randomized design with three replications. Plant height and biomass were related to TT and SM by polynomial regressions, while DGR, DRR, and LB were related to SM and TT using multiple regression models. AAB in the wet sector was higher than in the dry sector from December to April, whereas biomass in both sectors was associated with TT and SM. In the wet sector, DGR, DRR and LB varied with SM, which was negatively associated with WTD. Overall, across both wet and dry meadow sectors, soil moisture emerged as the most relevant variable for guiding optimal management recommendations.

Questions Biological invasions significantly impact plant communities, affecting and threatening biodiversity at regional and local scales worldwide. The invasion process may be influenced by climate change, particularly by the increasing frequency of extreme droughts. Here we evaluate (1) the level of exotic plant invasion along an aridity gradient and its relationship with environmental variables, and (2) the cumulative effect of prolonged droughts on native plant communities and the invasion of exotic species.Location Rangelands located along an aridity gradient from the arid Patagonian steppe to the humid Pampa region in Argentina, South America. The study sites (11) encompass a wide range of mean annual precipitation (170-950 mm year-1) and diverse vegetation physiognomic characteristics.Methods We conducted floristic surveys to assess plant community composition, diversity, and the cover of native and invasive exotic species in (1) 11 sites located along an aridity gradient, and (2) a 4-year drought simulation experiment established in nine sites. At each experimental site, rain-out shelters intercepted 50%-60% of incoming rainfall to simulate drought conditions. We then used linear mixed models to analyze the effects of drought on the cover, richness, and dominance of the plant community.Results Our findings reveal (1) a positive relationship between plant invasion and rangeland humidity at the regional scale. In the humid extreme, invasive exotic species dominated the plant community, whereas in the arid extreme native species were more abundant than invasive exotic species. (2) Experimental droughts reduced native plant cover in arid and semi-arid rangelands and promoted the cover, dominance, and richness of invasive exotic species in humid counterparts, reducing native species richness.Conclusions This study suggests a potential intensification of biological invasions in response to increased occurrences of droughts predicted by climate change. Management strategies for invaded humid rangelands are imperative, and early warnings are crucial during dry years in arid and semi-arid rangelands, where droughts could enhance the abundance of invasive exotic species.

Mineral-associated organic carbon (MAOC) constitutes a major fraction of global soil carbon and is assumed less sensitive to climate than particulate organic carbon (POC) due to protection by minerals. Despite its importance for long-term carbon storage, the response of MAOC to changing climates in drylands, which cover more than 40% of the global land area, remains unexplored. Here we assess topsoil organic carbon fractions across global drylands using a standardized field survey in 326 plots from 25 countries and 6 continents. We find that soil biogeochemistry explained the majority of variation in both MAOC and POC. Both carbon fractions decreased with increases in mean annual temperature and reductions in precipitation, with MAOC responding similarly to POC. Therefore, our results suggest that ongoing climate warming and aridification may result in unforeseen carbon losses across global drylands, and that the protective role of minerals may not dampen these effects..

Earth harbours an extraordinary plant phenotypic diversity(1) that is at risk from ongoing global changes(2,3). However, it remains unknown how increasing aridity and livestock grazing pressure-two major drivers of global change(4-6)-shape the trait covariation that underlies plant phenotypic diversity(1,7). Here we assessed how covariation among 20 chemical and morphological traits responds to aridity and grazing pressure within global drylands. Our analysis involved 133,769 trait measurements spanning 1,347 observations of 301 perennial plant species surveyed across 326 plots from 6 continents. Crossing an aridity threshold of approximately 0.7 (close to the transition between semi-arid and arid zones) led to an unexpected 88% increase in trait diversity. This threshold appeared in the presence of grazers, and moved toward lower aridity levels with increasing grazing pressure. Moreover, 57% of observed trait diversity occurred only in the most arid and grazed drylands, highlighting the phenotypic uniqueness of these extreme environments. Our work indicates that drylands act as a global reservoir of plant phenotypic diversity and challenge the pervasive view that harsh environmental conditions reduce plant trait diversity(8-10). They also highlight that many alternative strategies may enable plants to cope with increases in environmental stress induced by climate change and land-use intensification.

Increases in the abundance of woody species have been reported to affect the provisioning of ecosystem services in drylands worldwide. However, it is virtually unknown how multiple biotic and abiotic drivers, such as climate, grazing, and fire, interact to determine woody dominance across global drylands. We conducted a standardized field survey in 304 plots across 25 countries to assess how climatic features, soil properties, grazing, and fire affect woody dominance in dryland rangelands. Precipitation, temperature, and grazing were key determinants of tree and shrub dominance. The effects of grazing were determined not solely by grazing pressure but also by the dominant livestock species. Interactions between soil, climate, and grazing and differences in responses to these factors between trees and shrubs were key to understanding changes in woody dominance. Our findings suggest that projected changes in climate and grazing pressure may increase woody dominance in drylands, altering their structure and functioning.

Semiarid Patagonia represents 25% of the rangeland area in Argentina, and sheep overgrazing has degraded about a third of it in the past. In this century, depleted domestic stocks have mostly stabilized, but Guanaco populations have grown. These native camelids share habitat and diets with sheep, but their effect on vegetation is poorly understood and has long been debated. We set up an exclusion experiment in Monte León and Cañadón Vaca, a semiarid shrubland grassland in southern Patagonia, currently grazed only by guanacos. Vegetation baselines were studied in 2016 in twelve plots, and half of them were protected from guanaco grazing. Thirty-six plots were cleared to study revegetation. Vegetation was reassessed in 2021, and changes were evaluated using a paired t-test. Within protected plots, vegetation cover increased, bare soil diminished, and vegetated patches grew in size, but the density of the patch-interpatch arrangement did not change. Biodiversity, measured by richness and the Shannon-Wiener (SW) index, grew significantly. Nutrient recycling increased, as did the Stability and Infiltration Land Function indexes, although these last differences were not significant. Vegetation cover under guanaco grazing also increased, mainly due to the growth of dwarf shrubs, a typical tendency in sheep grazing-induced transitions in the region. Vegetated patches under grazing fragmented, resulting in smaller patches and denser patch structures, while diversity and land function indexes remained unchanged. Young plants established in cleared plots without guanacos showed higher cover density and individual size. These effects are similar to those observed in numerous experimental sheep exclosures. Guanaco grazing may thus prevent restoration and contribute to the generalized land degradation processes that overgrazing has been causing in Patagonia for over a century.

En Patagonia austral el sobrepastoreo provoca cambios irreversibles en los pastizales.La sucesión secundaria en pasturas comerciales podría promover parcialmente la recuperación de especies nativas.Se estudiaron lotes laboreados y sembrados con pasturas perennes, sobre pastizales de Festuca gracillima con suelos franco-arenoso (sitio Fg) y arbustales de Lepidophyllum cupressiforme con suelos salino-sódicos (sitio Mv).Las pasturas (100-500 ha) fueron: nuevas (1 año desde la siembra sitio Fg; 7 años sitio Mv), intermedias (11) y antiguas ( 16).Se evaluó la vegetación con 3 transectos de 500 puntos por lote y las características químicas del suelo (0-20 cm).Un análisis de correspondencia canónica ordenó las transectos de vegetación según las propiedades del suelo y en el sitio Fg se agruparon además por antigüedad, esto no ocurrió en Mv.En Fg, la sucesión inició con especies introducidas (Agropyron sp.y Dactylis glomerata), luego se instalaron gramíneas y hierbas nativas (Poa spiciformis, Deschampsia patula y Carex andina) y; finalmente, gramíneas psamófilas nativas (Pappostipa chrysophylla y Pappostipa ibarii).Como resultado los dos sitios recuperaron parcialmente cobertura y diversidad de nativas, lo que aporta evidencia de resiliencia y potencial de regeneración natural en estos pastizales semiáridos luego del laboreo y siembra.

Grazing represents the most extensive use of land worldwide. Yet its impacts on ecosystem services remain uncertain because pervasive interactions between grazing pressure, climate, soil properties, and biodiversity may occur but have never been addressed simultaneously. Using a standardized survey at 98 sites across six continents, we show that interactions between grazing pressure, climate, soil, and biodiversity are critical to explain the delivery of fundamental ecosystem services across drylands worldwide. Increasing grazing pressure reduced ecosystem service delivery in warmer and speciespoor drylands, whereas positive effects of grazing were observed in colder and species-rich areas. Considering interactions between grazing and local abiotic and biotic factors is key for understanding the fate of dryland ecosystems under climate change and increasing human pressure.

Water is the main control of biological processes in arid and semiarid sytems. A rain interception experiment was conducted in order to evaluate changes in water availability of the superficial soil in a grass steppe of the Dry Magellanic Steppe (South Patagonia, Argentina). Treatments included: 50% interception (dry year simulation), control and 50% more rain added through watering during summer (wet year simulation). Three replications were available in each treatement. Each plot had a MPS-6 soil matrix water potential and a ECRN-100 temperature probe. Rain was recorded using a Decagon device ECRN - 100 pluviometer. Data was recorded hourly using a Decagon EM50 logger. Grazing was excluded in all plots. The hypothesis was that watering during summer would prevent the soil from drying and that rain interception would generate a long and intense drought during summer. Results indicate that the soil remained humid most of the time in the watered treatment, but nevertheless some short dry periods were registered when plots did not receive rain pulses between watering events. As hypothesized, soils in the interception plots showed longer and more intense drought periods, but this happend only during fall. At the beggining of winter soils reached field capacity in all plots and remained so until spring. In this way, drought in the superficial soil occured in brief periods during the warm season and depended on summer rains.

En ambientes áridos y semiáridos la disponibilidad de agua es el factor principal que controla los procesos biológicos. En un pastizal de la Estepa Magallánica Seca, sur de Santa Cruz, se instaló un ensayo de intercepción de lluvias con el fin de evaluar los cambios en la disponibilidad hídrica en la superficie del suelo. Se realizaron tres tratamientos: sequía con intercepción del 50% (simula año seco), testigo y un tratamiento con riego (50% más de lluvia en el verano). Cada tratamiento tuvo tres repeticiones y en todos los casos se excluyó el pastoreo. El experimento contó con sensores de potencial hídrico mátrico (MPS-6) y temperatura de suelo (un sensor Decagon ECT por parcela a 10 cm de profundidad), y un pluviómetro (Decagon device ECRN – 100), todos conectados a un logger Decagon EM50 con frecuencia de registro horaria. La hipótesis de este trabajo fue que el riego durante el verano evitaría que el suelo se seque y que la intercepción de lluvia generaría un período seco más intenso y prolongado durante esta estación. En general, el suelo estuvo húmedo en el tratamiento irrigado, aunque se generaron breves períodos secos en los casos de lluvias escasas entre riegos. Las parcelas de intercepción tuvieron un período seco más intenso y más prolongado en el tiempo tal como se supuso, pero esto ocurrió solamente en el otoño. A principios de invierno el suelo alcanzó valores de capacidad de campo y permaneció así durante la primavera. Los períodos secos en la superficie del suelo fueron breves, ocurrieron en la estación cálida y dependieron de las lluvias estivales.

La variación temporal del índice NDVI predice los cambios temporales de la cobertura vegetal en las tierras secas de la Patagonia argentina. En las tierras secas, la vegetación natural es una fuente importante de sustento para las comunidades que viven en ellas, dado que la utilizan como alimento, combustible y forraje para el ganado. Además de los bienes y servicios que brinda a las comunidades, la vegetación de las tierras secas también juega un papel importante en muchos procesos ecosistémicos, como por ejemplo el reciclaje de nutrientes o la protección del suelo frente a la erosión. Por lo tanto, el monitoreo a largo plazo de la cobertura vegetal es clave para la toma de decisiones en la gestión de estas regiones. En este estudio, analizamos la variación de la cobertura vegetal en 239 sitios de una red de monitoreo a largo plazo (red MARAS), en uno de los biomas de tierras secas más grandes del mundo: la estepa patagónica argentina. A continuación, la relacionamos con la variación de diferentes períodos del Índice de Vegetación de Diferencia Normalizada (Normalized Difference Vegetation Index, NDVI), obtenido del sensor MODIS, que sirve como variable predictora. El modelo empírico ajustado explicó hasta un 40% de la variación en la cobertura vegetal medida a campo. Con este sencillo modelo empírico hemos estimado y cartografiado los cambios temporales en la cobertura vegetal de un extenso bioma de tierras secas a bajo coste.

We compared animal and vegetation responses of a 13 600-ha area under holistic grazing management (HGM) with a similar area under continuous grazing (CGM) in a Patagonian station. Limitations were a dry 2012- 2016 experimental period, poorer soils, and grazing of native guanacos (Lama guanicoe) in the HGM area. Forage standing crop in this area before the experience was lower and remained so during the study: (194 +/- 31 HGM vs. 244 +/- 33 kg dry matter. ha(-1) CGM). Six monitoring sites showed similar and remarkable (though mostly nonsignificant) vegetation improvements in total cover (10.6% HGM vs. 10.9% CGM) and cover of short palatable grasses (21.4% vs. 23.9%, respectively). Species richness showed small changes (- 1 vs. - 6%), bare soil interpatches decreased (- 11.9 vs. - 5.4%), and land function indicators of Stability (5.4% vs. 9.9%), Infiltration (12.4% vs. 12.0%), and Nutrient recycling (4.2% vs. 20.6%) increased. Tussock cover changed significantly with grazing management, as it decreased - 6% (ns) in HGM and grew 42% (P = 0.03) under CGM, probably due to coarse tussock forage consumption in HGM. Sheep under HGM were 15% lighter (43.9 +/- 0.5 HGM vs. 51.7 +/- 0.5 kg. ewe(-1) CGM P < 0.001), ewes scored 28% lower body condition (1.60 vs. 2.25, P < 0.001), and lambing rates were 36% lower (48.3 +/- 2.1% vs. 74.2 +/- 1.9%). Rotation ended in 2015 as a consequence of low lambing rates, and sheep body condition and reproductive rates recovered to similar values in both areas. Positive vegetation changes in both areas may be driven by residual effects of destocking 3 decades ago and show that improvement is possible using moderate stocking rates. Although it could be argued that rest periods of HGM may be positive in the long term, its negative effects on animal production should be addressed, and fast regeneration using intense management in these severely restricted habitats should not be expected. Slow, persistent progress under careful management seems achievable under both grazing systems. (C) 2020 The Society for Range Management. Published by Elsevier Inc. All rights reserved.

La disponibilidad de agua es el factor principal que determina la producción primaria de los pastizales en zonas áridas y semiáridas. En noviembre de 2018, en el sur de Patagonia, Estepa Magallánica Seca, se instaló un ensayo de disponibilidad hídrica, con el fin de evaluar la productividad primaria aérea neta (PPAN) de gramíneas altas y bajas frente a distintos niveles de ingreso de agua. Los tratamientos fueron: sequía con interceptores de lluvia (reciben 50% menos de la precipitación anual), tratamiento húmedo (60mm de agua agregados en el periodo seco) y testigo, tres parcelas por tratamiento excluidas del pastoreo. En estas parcelas se instalaron sensores de potencial hídrico de suelo a 10cm de profundidad y un pluviómetro conectados a un logger con frecuencia de medición de una hora. La productividad anual se estimó por cosecha de biomasa en marcos de 0,6m2 y separación de material en verde y seco, los cortes se realizaron al final de la estación de crecimiento (marzo 2019). Los tratamientos de disponibilidad hídrica no afectaron la PPAN, pero si mostraron diferencias en los valores de humedad de suelo, el suelo en el tratamiento de riego estuvo más húmedo. Posiblemente se requiera de un periodo más extenso para que la sequía se manifieste en el suelo y en la vegetación.

Water is the main factor controlling the primary production in arid and semi-arid grasslands. A rainfall intercept experiment was installed in southern Patagonia in November 2018. In this trial we evaluated net primary aerial productivity (PPAN) of tussock and short grasses with different rainfall levels. The treatments were: drought with rain shelters (that received 50% of the annual precipitation), wet treatment (60mm of water added in the dry period) and control, that consisted in three plots per treatment. All plots were excluded from grazing, and were provided with soil water potential sensors at a 10 cm soil depth and connected to a logger together with a single rain gauge for the site. The measurement frequency was one hour. Annual productivity was estimated by harvesting biomass in 0.6 m(2) plot and we separated biomass in green and dry. Harvests were made at the end of the growing season (March 2019). The treatments did not affect the PPAN, but showed differences in the soil water potential, as soil in the irrigation treatment was more humid. It is possible that longer periods are required for drought to manifest in the soil water potential and in vegetation productivity.

We present the MARAS (Environmental Monitoring of Arid and Semiarid Regions) dataset, which stores vegetation and soil data of 426 rangeland monitoring plots installed throughout Patagonia, a 624.500 km 2 area of southern Argentina and Chile. Data for each monitoring plot includes basic climatic and landscape features, photographs, 500 point intercepts for vegetation cover, plant species list and biodiversity indexes, 50-m line-intercept transect for vegetation spatial pattern analysis, land function indexes drawn from 11 measures of soil surface characteristics and laboratory soil analysis (pH, conductivity, organic matter, N and texture). Monitoring plots were installed between 2007 and 2019, and are being reassessed at 5-year intervals (247 have been surveyed twice). The MARAS dataset provides a baseline from which to evaluate the impacts of climate change and changes in land use intensity in Patagonian ecosystems, which collectively constitute one of the world´s largest rangeland areas. This dataset will be of interest to scientists exploring key ecological questions such as biodiversity-ecosystem functioning relationships, plant-soil interactions and climatic controls on ecosystem structure and functioning.

Based upon primary productivity estimates, Oliva et al. (2019) concluded that, at the end of last century and after long periods of overgrazing, Patagonia's domestic stocks adjusted to regional-scale herbivore carrying capacity. Populations of guanaco, a native camelid, increased thereafter, driving combined grazing pressures once again over carrying capacity in some areas. Marino et al. (2020) argued that grazing is not really at equilibrium because domestic stocks are concentrated in areas that remain overgrazed. They support the ideas that guanaco density is auto-regulated by resource-defence territoriality, and that guanacos are weak competitors with domestic stock, occupying only marginal areas. In their view, Oliva et al. (2019) put guanacos in the role of scapegoats, leaving domestic stocks unchecked. Equilibrium at regional scale does not preclude overgrazing and under-grazing at local scales. By separating areas with and without domestic stocks, Marino et al. (2020) estimated overgrazing at 28% in Chubut Province and 73% in Santa Cruz Province. Our recalculations show 28% and 47% domestic overgrazing, respectively. However, when combined with guanaco densities, these increase to 48% for Chubut and 108% for Santa Cruz. We question the hypothesised lack of competitive value and efficient self-regulating mechanisms that would prevent guanaco populations from overshooting carrying capacity. A dataset of 13 sheep farms showed mean density of 26 +/- 3.8 guanacos/km(2)and high combined grazing pressures. This was also observed in a protected area of Chubut that reached 42 guanacos/km(2)and crashed during drought, with 60% mortality. Thereafter, guanacos increased to 70 guanacos/km(2), with recruitment rates that showed a complex response of density dependence but remained relatively elevated at densities above the estimated carrying capacity. Synthesis and applications. Marino et al. (2020) are right to question the apparent equilibrium of domestic stocks that are concentrated in areas that may be still overgrazed. But ground data show that guanaco populations have inefficient density population regulation and can reach densities well over carrying capacity, even in the presence of sheep. This does not mean that the main control should be on growing guanaco populations but it stresses our conclusion that joint management of the native-domestic herbivore system is urgently needed. Joint management can be effected through local plans, as current guanaco management permits can only be issued in areas that are not overgrazed by sheep. Farm management plans may in this way transform an apparent competitor into a valuable resource, complementary to sheep raising.

Carrying capacity is the maximum animal density an area can sustain without deterioration of its resources. Overgrazing has degraded Patagonia, but sheep stocks decreased and gave way to mixed systems with cattle, goats and guanacos (native wild camelids). The objective of this paper was to develop a method to estimate the carrying capacity based on the remotely sensed data, and to assess wild and domestic herbivore numbers in order to establish if grazing stocks have evolved to balance with carrying capacity. Net Primary Productivity (NPP) MOD17/A3 images and field Aerial Net Primary Productivity (ANPP) data of 66 sites were linearly regressed (R-2 = 0.83, p < 0.01), and the slope 0.236 used to convert MOD17/A3 NPP to ANPP. Harvest index (proportion of ANPP that may be sustainably consumed) was estimated as a function of ANPP and carrying capacity as a consumable forage/estimated annual consumption, set at 500 (sheep and goats), 3,200 (cattle) and 750 kg Dry Matter head(-1) year(-1) (guanacos). Regional ANPP +/- SD (2000-2015) was 758 +/- 52 kg Dry Matter ha(-1) year(-1) and Harvest index was 13.7 +/- 0.6%. Regional carrying capacity was 14.8 +/- 1.6 M sheep or goats, 2.3 +/- 0.3 M cattle or 9.9 +/- 1.2 M guanacos. Domestic stock was high from 1920 to 1980, but declined thereafter and remained mostly within 1 SD of mean 2000-2015 carrying capacity. In this century, annual provincial stocks and carrying capacity correlated well (R-2 = 0.94, p < 0.01) with a slope close to 1. Guanacos increased from 0.5 to 2 M between 2000 and 2015, driving linearly combined grazing pressures 36% and 62% above carrying capacity in southern Patagonia provinces in 2015. Synthesis and applications. From the year 2000, after decades of sheep overstocking, domestic stock has shown a regional trend towards a grazing equilibrium, but growth of guanacos might have upset that trend. Participation of guanacos as a critical excess in total grazing pressure is debatable, but management of these populations is necessary and may be increasingly attractive if combined production systems are developed to incorporate wild meat and fibre. Our method, MOD17/A3 enables a carrying capacity evaluation and stock adjustment in these unique mixed grazing systems, preventing further rangeland degradation and loss of ecosystem services.

Drylands contain 25% of the world’s soil organic carbon (SOC), which is controlled by many factors, both abiotic and biotic. Thus, understanding how these factors control SOC concentration can help to design more sustainable land-use practices in drylands aiming to foster and preserve SOC storage, something particularly important to fight ongoing global warming. We use two independent, large-scale databases with contrasting geographic coverage (236 sites in global drylands and 185 sites in Patagonia, Argentina) to evaluate the relative importance of abiotic (precipitation, temperature and soil texture) and biotic (primary productivity) factors as drivers of SOC concentration in drylands at global and regional scales. We found that biotic and abiotic factors had similar effects on SOC concentration across regional and global scales: Maximum temperature and sand content had negative effects, while precipitation and plant productivity exerted positive effects. Our findings provide empirical evidence that increases in temperature and reductions in rainfall, as forecasted by climatic models in many drylands worldwide, promote declines in SOC both directly and indirectly via the reduction in plant productivity. This has important implications for the conservation of drylands under climate change; land management should seek to enhance plant productivity as a tool to offset the negative impact of climate change on SOC storage and on associated ecosystem services.