Two nearly homogenous 60 acre watersheds near Heber, Arizona, within the Apache-Sitgreaves National Forest, were burned at moderate and high severities during the 2002 Rodeo-Chediski wildfire. Each watershed had 30 permanent plots located on it from earlier studies. In 2011, nearly 10 years following the fire, the plots were re-measured…
Two nearly homogenous 60 acre watersheds near Heber, Arizona, within the Apache-Sitgreaves National Forest, were burned at moderate and high severities during the 2002 Rodeo-Chediski wildfire. Each watershed had 30 permanent plots located on it from earlier studies. In 2011, nearly 10 years following the fire, the plots were re-measured to determine how fire severity affects the long term vegetative recovery of this ecosystem; specifically herbaceous production and tree regeneration and density. Canopy cover, litter depth, herbaceous weight, herbaceous cover and shrub cover are vital indicators of herbaceous production, and were found to be significantly different between the sites. Canopy cover and litter depth were found to be significantly higher on the moderate site while herbaceous weight, herbaceous cover and shrub cover were found to be significantly higher on the high site. Tree densities of the three present tree species, ponderosa pine, alligator juniper, and gambel oak, were measured and divided into five size classes to distinguish the diversity of the communities. The mean densities for each species and size class were analyzed to determine if there were any statistically significant differences between the sites. Ponderosa pine saplings (regeneration) were found to have no significant differences between the sites. Juniper and oak saplings were found to be significantly higher on the high site. The remaining four ponderosa pine size classes were found to be significantly higher on the moderate site while the remaining four size classes for juniper and oak were found to have no statistical differences between the sites. Further analysis of the tree proportions revealed that the ponderosa pine species was significantly higher on the moderate site while juniper and oak were significantly higher on the high site. Species specific proportion analysis showed that the ponderosa pine size classes were significantly different across the sites while the juniper and oak size classes showed no significant differences between the sites. Within the ponderosa pine size classes, saplings were found to be significantly higher on the high site while the remaining four classes were significantly higher on the moderate site.
Leonard Hayflick studied the processes by which cells age during the twentieth and twenty-first centuries in the United States. In 1961 at the Wistar Institute in the US, Hayflick researched a phenomenon later called the Hayflick Limit, or the claim that normal human cells can only divide forty to sixty…
Leonard Hayflick studied the processes by which cells age during the twentieth and twenty-first centuries in the United States. In 1961 at the Wistar Institute in the US, Hayflick researched a phenomenon later called the Hayflick Limit, or the claim that normal human cells can only divide forty to sixty times before they cannot divide any further. Researchers later found that the cause of the Hayflick Limit is the shortening of telomeres, or portions of DNA at the ends of chromosomes that slowly degrade as cells replicate. Hayflick used his research on normal embryonic cells to develop a vaccine for polio, and from HayflickÕs published directions, scientists developed vaccines for rubella, rabies, adenovirus, measles, chickenpox and shingles.
Although best known for his work with the fruit fly, for which he earned a Nobel Prize and the title "The Father of Genetics," Thomas Hunt Morgan's contributions to biology reach far beyond genetics. His research explored questions in embryology, regeneration, evolution, and heredity, using a variety of approaches.
