Vegetation Response to Removal of Plant Groups and Grass Seeding in a Microphyllous Desert Shrubland: A 4-Year Field Experiment

Grazing is one of the most important land management activities worldwide, and cases of overgrazing increase erosion, land degradation, and plant invasion. The objective of this study was to assess the effect on individual species and species composition in response to groups of plants removals or grass seeding after four years of vegetation transformation in a microphyllous desert shrubland excluded from cattle grazing. Nine treatments involved (1) clearing of vegetation and seeding of Bouteloua curtipendula (BOCU), a native grass, (2) clearing and seeding of Chloris gayana (CHGA), an introduce grass from Africa, (3) clearing except for grasses (GRA), (4) clearing except for grasses and fodder shrubs (GRA-SHR), (5) free grazing by cattle (GRAZ), (6) clearing except fodder shrubs (SHR), (7) no modification (CON), (8) clearing of all plants (BARE), and (9) clearing except plants not eaten by cattle (UND). Treatments were replicated five times each in 10 m × 10 m experimental plots. Plots were surveyed for density, cover of all plants, and standing forage. Total plant cover was higher in CON and UND than the other treatments. Except for BOCU, where forage production was the highest, forage production ha−1 was low among all other treatments. Plant density was highest in SHR and lowest in CON. Results after four years of transformation indicate that seeded Chloris gayana failed to become established, but seeding of Bouteloua curtipendula was able to persist, and had the greatest influence on the vegetation restoration, which is what we consider the most appropriate restoration treatment.

Predicting changes in bee assemblages following state transitions at North American dryland ecotones

Drylands worldwide are experiencing ecosystem state transitions: the expansion of some ecosystem types at the expense of others. Bees in drylands are particularly abundant and diverse, with potential for large compositional differences and seasonal turnover across ecotones. To better understand how future ecosystem state transitions may influence bees, we compared bee assemblages and their seasonality among sites at the Sevilleta National Wildlife Refuge (NM, USA) that represent three dryland ecosystem types (and two ecotones) of the southwestern U.S. (Plains grassland, Chihuahuan Desert grassland, and Chihuahuan Desert shrubland). Using passive traps, we caught bees during two-week intervals from March – October, 2002 – 2014. The resulting dataset included 302 bee species and 56 genera. Bee abundance, composition, and diversity differed among ecosystems, indicating that future state transitions could alter bee assemblage composition in our system. We found strong seasonal bee species turnover, suggesting that bee phenological shifts may accompany state transitions. Common species drove the observed trends, and both specialist and generalist bee species were indicators of ecosystem types or months; these species could be sentinels of community-wide responses to future shifts. Our work suggests that predicting the consequences of global change for bee assemblages requires accounting for both within-year and among-ecosystem variation.

Cactus diversity in the Sierra del Rosario, Durango, Mexico

The Sierra del Rosario is a calcareous mountainous area located in the northeast region of the state of Durango, where xerophilous vegetation and chaparral predominate. The aim of this study was to determine cactus diversity and distribution in the region. A list of cacti was obtained from 15, 3 km transects covering the vegetation of microphyllous desert shrubland, rosetophyllous desert shrubland and chaparral. A total of 33 species and 13 genera were recorded, with the most representative genera being Coryphantha, Echinocereus and Mammillaria. There are six species in some category of risk according to NOM-059-SEMARNAT-2010, distributed in the genera Coryphantha, Glandulicactus and Peniocereus. No species was found at risk in the IUCN, while Coryphantha sneedii is in the CITES. Species richness estimators indicate that diversity ranges from 34 to 47 taxa. The greatest diversity is between 1 207 and 1 400 masl in the rosetophyllous desert shrubland.