Influence of solar radiation factors on desert flora site selection.

摘要

This dissertation researches the influence of solar radiation factors on desert flora site selection. The study area is located at The Indio Mountains Research Station within the Chihuahuan Desert in southern Hudspeth County north of the Rio Grande near the Culberson County border. One of those mountains, Flat Top Mountain, meets the required characteristics for the research objectives of this dissertation. This mountain is located about 26 miles southwest of Van Horn, at 13R500209 and 3401417 UTM coordinates, with an elevations range of 1220–1390 m. Its vegetation is typical of the Chihuahuan Desert.; Field data consisted of measurements of slope, aspect, and shading angles, as well as the density of seven plants: Aloysia wrightii (Oreganillo), Ephedra aspera (Mormon Tea), Parthenium incanum (Mariola), Tiquilia greggii (Tiquilia) and Viguiéra stenoloba (Skeleton-leaf Goldeneye), Flouquieria splendens (Ocotillo) and Yucca torreyi (Torrey Yucca). Following eight transects from a fixed point on the top to the hills, a total of 2310 plants were recorded. The number of plots sampled along each radiation varied due to the topographical characteristics of the mountain. North radiation was sampled with 18 plots, northeast radiation with 37, east radiation with 12, southeast radiation also with 12, south radiation with 17, southwest radiation with 30, west radiation with 27, and northwest radiation with 24. In short, a total of 177 plots were sampled, and in 11 plots of them none of the 7 study plants were found.; A series of solar radiation parameters were calculated with a modified version of the SolPos. Statistical analysis was performed with Statistica and Canoco software. The main purpose of this research was to find the natural location preferences of the studied plants and the solar radiation parameters that can explain their site selection.; Through the principal component analysis the relationships between species and between solar radiation parameters (environmental variables) were found. Redundancy analysis explained 35% of the total variance based upon environmental variables. With the Generalized Linear Model under Poisson distribution, species responses to the environmental variables were evaluated. And finally, through a spatial analysis the distribution of plants and the solar radiation could be known.; Timing and amount solar radiation were found to be important in controlling plant distribution. Yucca, Aloysia, Parthenium, Ephedra, and Viguiéra were negatively associated with Winter Solstice, Seasonality, and Total annual radiation. Tiquilia, and to some extent, Flouquieria were positively associated.; Aloysia, Ephedra, Parthenium, Viguiéra and Yucca had a unimodal response to summer solstice radiation whereas Tiquilia had a monotonous response with peak growth at lower radiation levels.