Vegetation changes in the Jornada Basin from 1858 to 1998

Notes made by land surveyors in 1858 were utilized to estimate cover of grasses and shrubs on the Jornada Experimental Range (JER) and the Chihuahuan Desert Range Research Center (CDRRC) in the northern Chihuahuan Desert in southern New Mexico, USA. Portions of these areas have been previously assessed for historical vegetation dynamics but the entire 84,271 ha assessed in the 19th century has not been examined in total. In 1858, fair to very good grass cover occurred on 98% and 67% of the JER and CDRRC, respectively. Shrubs were present throughout both properties but 45% of the JER and 18% of the CDRRC were shrub free. Reconnaissance surveys, made to determine carrying capacity for livestock were made in 1915–1916 and 1928–1929 on the JER and in 1938 on the CDRRC, show that shrubs had made large increases in area occupied at the time of the surveys. Vegetation type maps were made of both properties in 1998. Mesquite (Prosopis glandulosa) was the primary dominant on 59% of the JER in 1998 and creosotebush (Larrea tridentata) was the primary dominant on 27% of the area. On the CDRRC mesquite and creosotebush were primary dominants on 37% and 46% of the area, respectively. Grass cover has decreased greatly with the increase in shrubs and only shrub control efforts have maintained the once abundant black grama (Bouteloua eriopoda) as a primary dominant on 1% or less of the area on both properties.     

Climatic response of thick leaf spruce (Picea crassifolia) tree-ring width at different elevations over Qilian Mountains, northwestern China

Tree-ring cores of thick leaf spruce (Picea crassifolia) taken from four sites at different elevations, in the middle of the Qilian Mountains, in the arid and semi-arid region of northwestern China, were used to develop four tree-ring width chronologies using standard dendrochronological methods. Results indicate that with increasing altitude the chronologies’ year-to-year variations decreased. Hence, the sensitivity of the tree-ring chronologies to climate decreases with altitude. Further analysis showed that the significant limiting factor on tree growth is spring precipitation. Measurements of stomata density and leaf dry weight suggest the species’ ecological adaptation strategy changes with elevation. At high elevation the metabolic rate of thick leaf spruce decreases, thus showing the effect of the climate.     

Morphological and microtectonic analysis of Quaternary deformation from Puná and Santa Clara Islands, Gulf of Guayaquil, Ecuador (South America)

This paper presents the neotectonic study of Santa Clara and Puná Islands sited in the Gulf of Guayaquil eastern part. Both islands are located on the south-western segment of the fault zone bounding to the east the North Andean Block. Fault motion and morphostructural analysis were carried out from Pleistocene age terrain. A two step deformation characterises the South Puná tectonics. The first step involves the Zambapala Cordillera uplift that post-dates Pleistocene sediments and pre-dates a marine terrace correlated with the M.I.S. 11 or 13 (440–550 ka). The second step is the formation of a pull-apart that shows evidence of 2.9 km dextral offset since the M.I.S. 11 or 13, giving an offset mean rate of 5.3 to 6.6 mm/yr. This rate is higher than the one calculated on the Pallatanga Fault northeast of the study area, in the Western Andean Cordillera, suggesting that deformation is split in different fault segments from the Gulf of Guayaquil to the continent. The Zambapala Cordillera uplift and transpression deformation requires a compressive event that may have been induced by the subduction process during the early Pleistocene.