Cushion Shrubs Encroach Subhumid Rangelands: Fertility Islands in Fragile Soils Along a Grazing Gradient in Patagonia

PurposeThis work assesses changes in soil and vegetation structure associated with grazing intensity (GI) in subhumid grasslands. We conducted the study in the Subandean district of Patagonia, Argentina. Non-degraded Subandean grass steppes have extremely erodible volcanic soils and are valuable grazing ranges. However, nowadays vast portions exhibit a heterogeneous cover that is mostly of cushions shrubs, with big eroded soil patches.MethodsWe selected four study sites along a GI gradient and one grazed-excluded site. Soils, vegetation cover and patches structure were characterised. We took soil samples beneath grass and shrub patches and their interpatches and in undisturbed spots. ResultsSoils in undisturbed spots had the highest chemical fertility. Soils in grazing areas showed high heterogeneity associated with plant life-form and GI. Results also showed that medium and fine sand particles remobilised from bare soil to vegetated patches. Total nitrogen and organic matter increased in the same direction. Grass cover decreased as GI increases, while shrubs cover and total richness increased, until a collapse at the highest intensity. Relative cover of cushion shrubs and bare soil grow steadily with GI. ConclusionsThe fertility island effect was associated with cushion shrubs. Grazing caused cushion shrub encroachment regardless of its intensity. Notwithstanding this, the same disturbance -grazing- which promoted cushions prevalence also favoured the collapse of fertile islands when reached to maximum intensity. Ecosystem services provision from a range management standpoint decreased. However, the increases in richness under moderate GI could represent an enhancement in system functionality.

Dating the origins of persistent oak shrubfields in northern New Mexico using soil charcoal and dendrochronology

Megafires in dry conifer forests of the Southwest US are driving transitions to alternative vegetative states, including extensive shrubfields dominated by Gambel oak ( Quercus gambelii). Recent tree-ring research on oak shrubfields that predate the 20th century suggests that these are not a seral stage of conifer succession but are enduring stable states that can persist for centuries. Here we combine soil charcoal radiocarbon dating with tree-ring evidence to refine the fire origin dates for three oak shrubfields (<300 ha) in the Jemez Mountains of northern New Mexico and test three hypotheses that shrubfields were established by tree-killing fires caused by (1) megadrought; (2) forest infilling associated with decadal-scale climate influences on fire spread; or (3) anthropogenic interruptions of fire spread. Integrated tree-ring and radiocarbon evidence indicate that one shrubfield established in 1664 CE, another in 1522 CE, and the third long predated the oldest tree-ring evidence, establishing sometime prior to 1500 CE. Although megadrought alone was insufficient to drive the transitions to shrub-dominated states, a combination of drought and anthropogenic impacts on fire spread may account for the origins of all three shrub patches. Our study shows that these shrubfields can persist >500 years, meaning modern forest-shrub conversion of patches as large as >10,000 ha will likely persist for centuries.

Ant Guild Identity Determines Seed Fate at the Post-Removal Seed Dispersal Stages of a Desert Perennial

Ants play a dual role in their interaction with plant seeds. In deserts, the consumption of seeds by granivorous ants is common, whereas mutualistic seed dispersal, often associated with scavenging ants, is rarely documented. We evaluated the contribution of both ant guilds to efficient seed dispersal of an ant-dispersed plant, Sternbergia clusiana, in a desert ecosystem. We presented seed to colonies of three species of desert ants from the Cataglyphis (scavengers) and Messor (granivorous) genera. We recorded seed consumption, ejection from the nest, and seed transportation to potentially beneficial microhabitats. We evaluated microhabitat quality by testing the association between habitat types and the plant at various life stages. As expected, granivores mainly consumed the seeds, whereas scavengers consumed the elaiosome (seed appendage serving as a reward), but left the seeds intact. Moreover, scavenging ants relocated the seeds much further than granivores, mainly to shrub patches. The disproportional distribution of the plant under shrubs at several life stages suggests that this microhabitat is beneficial for the plant. Overall, while granivores seem to mainly harm seed dispersal, we provide the first evidence for the beneficial contribution of scavenging ants in deserts, showing they exhibit the same suite of characteristics that render them efficient seed dispersers in other ecosystems.

Channel geomorphology and riparian vegetation interactions along four anabranching reaches of the Upper Yellow River

The fluvial biogeomorphic succession (FBS) phase model is used to appraise biogeomorphic interactions along four anabranching reaches of the Upper Yellow River. Geomorphic features and vegetation distribution patterns are combined to assess the dominant FBS phase. A notable increase in shrub and tree cover and a decrease in sedges occur with decreasing elevation from 4200 to 2200 m asl. The Maduo reach (4185 m) is characterized by the biogeomorphic phase, while the Dari (3960 m) reach is at the pioneer phase, with short shrubs playing a prominent role. Both the Maqu (3450 m) and the Guide (2117 m) reaches are ecological phase dominated (the Guide reach has been impacted by flow regulation in recent decades). Reaches other than the Maduo have experienced an increase in post-pioneer vegetation (woody plants) in recent decades, with a decrease in pioneer plant communities (grass and sedges). The Dari reach experienced the most dynamic channel planform changes, with a marked increase in short shrub patches from 2007 to 2017. An increase in woody vegetation underpinned increasingly stable geomorphic dynamics in the Maqu reach. Human activities have restricted geomorphic impacts of expanded areas of woody riparian vegetation in the Guide reach. Variability in dominant FBS phases exerts a primary control upon channel behavior and evolutionary traits in the four study reaches.

Forest land-cover changes 2012-2018 in hunting grounds in Vojvodina

Deforestation could influence land cover ecological significance in hunting grounds on a big scale. This research examines changes of forest and shrub patches in the Vojvodina region by a set of landscape metrics. The study area includes 154 hunting grounds from which hunting organizations are managing with 134 hunting grounds, PC "Vojvodinasume" with 17, Serbian Armed Forces with two, and National Park "Fruska gora" with one hunting ground. The results show that in the National Park and Serbian Armed Forces hunting grounds the broad-leaved forest areas occurred on the surfaces that were under the transitional woodland-shrub and vice versa. A similar situation is in the hunting grounds managed by PC ''Vojvodinasume'' where there is not only the most intensive logging of broad-leaved and coniferous forests but also the most intensive afforestation of mixed forests and transitional woodland-shrub. On the other hand, in the hunting grounds managed by hunting organizations, there is the highest area growth under the broad-leaved forest.