Browsing by Subject "RATES"

Now showing 1 - 4 of 4
  • Thumbnail Image
    ItemOpen Access
  • Thumbnail Image
    ItemOpen Access
    Deforestation risks posed by oil palm expansion in the Peruvian Amazon
    (Environmental Research Letters, 2018-11-01) Vijay, V; Reid, CD; Finer, M; Jenkins, CN; Pimm, SL
    Further expansion of agriculture in the tropics is likely to accelerate the loss of biodiversity. One crop of concern to conservation is African oil palm (Elaeis guineensis). We examined recent deforestation associated with oil palm in the Peruvian Amazon within the context of the region's other crops. We found more area under oil palm cultivation (845 km2) than did previous studies. While this comprises less than 4% of the cropland in the region, it accounted for 11% of the deforestation from agricultural expansion from 2007-2013. Patches of oil palm agriculture were larger and more spatially clustered than for other crops, potentially increasing their impact on local habitat fragmentation. Modeling deforestation risk for oil palm expansion using climatic and edaphic factors showed that sites at lower elevations, with higher precipitation, and lower slopes than those typically used for intensive agriculture are at long-term risk of deforestation from oil palm agriculture. Within areas at long-term risks, based on CART models, areas near urban centers, roads, and previously deforested areas are at greatest short-term risk of deforestation. Existing protected areas and officially recognized indigenous territories cover large areas at long-term risk of deforestation for oil palm (>40%). Less than 7% of these areas are under strict (IUCN I-IV) protection. Based on these findings, we suggest targeted monitoring for oil palm deforestation as well as strengthening and expanding protected areas to conserve specific habitats.
  • Thumbnail Image
    ItemOpen Access
    Links between physical and chemical weathering inferred from a 65-m-deep borehole through Earth's critical zone.
    (Scientific reports, 2019-03-14) Holbrook, W Steven; Marcon, Virginia; Bacon, Allan R; Brantley, Susan L; Carr, Bradley J; Flinchum, Brady A; Richter, Daniel D; Riebe, Clifford S
    As bedrock weathers to regolith - defined here as weathered rock, saprolite, and soil - porosity grows, guides fluid flow, and liberates nutrients from minerals. Though vital to terrestrial life, the processes that transform bedrock into soil are poorly understood, especially in deep regolith, where direct observations are difficult. A 65-m-deep borehole in the Calhoun Critical Zone Observatory, South Carolina, provides unusual access to a complete weathering profile in an Appalachian granitoid. Co-located geophysical and geochemical datasets in the borehole show a remarkably consistent picture of linked chemical and physical weathering processes, acting over a 38-m-thick regolith divided into three layers: soil; porous, highly weathered saprolite; and weathered, fractured bedrock. The data document that major minerals (plagioclase and biotite) commence to weather at 38 m depth, 20 m below the base of saprolite, in deep, weathered rock where physical, chemical and optical properties abruptly change. The transition from saprolite to weathered bedrock is more gradational, over a depth range of 11-18 m. Chemical weathering increases steadily upward in the weathered bedrock, with intervals of more intense weathering along fractures, documenting the combined influence of time, reactive fluid transport, and the opening of fractures as rock is exhumed and transformed near Earth's surface.
  • Thumbnail Image
    ItemOpen Access
    rbcL data reveal two monophyletic groups of filmy ferns (Filicopsida: Hymenophyllaceae).
    (American journal of botany, 2001-06) Pryer, KM; Smith, AR; Hunt, JS; Dubuisson, JY
    The "filmy fern" family, Hymenophyllaceae, is traditionally partitioned into two principal genera, Trichomanes s.l. (sensu lato) and Hymenophyllum s.l., based upon sorus shape characters. This basic split in the family has been widely debated this past century and hence was evaluated here by using rbcL nucleotide sequence data in a phylogenetic study of 26 filmy ferns and nine outgroup taxa. Our results confirm the monophyly of the family and provide robust support for two monophyletic groups that correspond to the two classical genera. In addition, we show that some taxa of uncertain affinity, such as the monotypic genera Cardiomanes and Serpyllopsis, and at least one species of Microtrichomanes, are convincingly included within Hymenophyllum s.l. The tubular- or conical-based sorus that typifies Trichomanes s.l. and Cardiomanes, the most basal member of Hymenophyllum s.l., is a plesiomorphic character state for the family. Tubular-based sori occurring in other members of Hymenophyllum s.l. are most likely derived independently and more than one time. While rbcL data are able to provide a well-supported phylogenetic estimate within Trichomanes s.l., they are inadequate for resolving relationships within Hymenophyllum s.l., which will require data from additional sources. This disparity in resolution reflects differential rates of evolution for rbcL within Hymenophyllaceae.