Abundance and chronic anthropogenic disturbance at two vegetation types

Data for species abundance and chronic anthropogenic disturbance (CAD) in a semiarid grassland and a tropical dry forest. The file contains two sections, one for each vegetation type. All data correspond to abundances, except column labeled CAD. Semiarid grassland The semiarid grassland is in Concepción Buenavista, Oaxaca, southern Mexico, at an elevation of 2275 m a.s.l. Annual precipitation is 530·3 mm, and mean temperature is 16·3 °C. Data come from 21 0·5 ha sites. In each site, eight 1 × 1 m quadrats were randomly chosen, and in each one we randomly selected 20 0·1 × 0·1 m squares. In the latter, we quantified the abundance of all vascular plants. Tropical dry forest The tropical dry forest is located in La Cañada, Oaxaca. Its elevation ranges from 580 m a.s.l. to 850 m a.s.l. Precipitation ranges from 473 to 515 mm in annual precipitation and mean temperature ranges from 25·2 to 26·2 °C.Data comprise vascular plant abundances for 38 sites with 3 transects each, measuring 50 × 10 m for trees and 50 × 4 m for shrubs and small succulents. Chronic anthropogenic disturbance The chronic anthropogenic disturbance (CAD) index is based on 14 metrics that measure disturbance values for human activities, livestock, and land degradation, the sum of which provides an estimate of total CAD. The index runs from zero in pristine sites to slightly over 100 in extremely degraded communities where even soil has been almost completely lost. Metrics for human activities comprise fuelwood extraction, human trails density, human trail surface, settlement proximity, contiguity to activity cores, land use and wildfires. Metrics for livestock raising comprise goat droppings, cattle droppings, browsing, livestock trail density and soil compaction. Finally, land degradations metrics comprise erosion, presence of soil islands and totally modified surfaces. Each metric was measured in 3 different transects and averaged to obtain a single value for each site. See Martorell and Peters (2005, 2008) for more details.