congresos y reuniones científicas
The ghost of fragmentation past: habitat suitability models and genetic markers help unveil dry forest non-equilibrium landscapes in northern Patagonia
Campos de Jordao, Brasil
Congreso; 2009 Latin American IALE Conference; 2009
Institución organizadora:
&amp;amp;lt;!-- /* Font Definitions */ @font-face {font-family:SimSun; panose-1:2 1 6 0 3 1 1 1 1 1; mso-font-alt:&amp;amp;#23435;&amp;amp;#20307;; mso-font-charset:134; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:3 680460288 22 0 262145 0;} @font-face {font-family:"@SimSun"; panose-1:2 1 6 0 3 1 1 1 1 1; mso-font-charset:134; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:3 680460288 22 0 262145 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:SimSun; mso-ansi-language:ES; mso-fareast-language:ZH-CN;} @page Section1 {size:595.3pt 841.9pt; margin:70.85pt 85.05pt 70.85pt 85.05pt; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --&amp;amp;gt; Processes that shape most modern landscapes operate in realtime and thus are evident and quantifiable. Yet, most landscapes also carry legacies of past disturbance that are more subtle and difficult to unveil, but may explain a large percentage of current landscape structure, configuration, and composition.  Here we present a case study of a dryland forest landscape in northwestern Patagonia dominated by the xeric tolerant southern conifer Austrocedrus chilensis. Modern distribution of this species is restricted to the easternmost limit of austral South American temperate forests contacting the Patagonian steppe biome. While continuous A. chilensis forests dominate the landscape in mesic situations (c. 1000-1400mm/year), at precipitation levels below 700 mm/year the species occurs as numerous small forest fragments (most <0.5 ha).  Traditionally, this curtailing distribution has been interpreted as the response to declining rainfall patterns caused by strong rain shadow effect of the Andes on prevailing westerly moist air circulation. This equilibrium view has been recently challenged by retrospective studies that have demonstrated the dynamic nature of these patches in relation to major changes in fire and grazing regimes.  We hypothesized that the current forested landscape by A. chilensis is the result of fragmentation of a more widespread forest distribution induced by anthropogenic disturbance. To test this idea we conducted detailed mapping of A. chilensis fragments based on aerial photographs and Quickbird imagery and produced potential distribution extent of A. chilensis based on 5 bioclimatic and topographic variables using Mahalanobis typicality. In addition we performed genetic analyses on foliar tissue of 26 continuous forests and 41 forest fragments by means of isozyme elecrophoresis using eight putative loci.   We found that A. chilensis occupies a low fraction of the potentially suitable habitat based on bioclimatic / topographic variables and that forest fragments are highly associated with rocky/stony outcrops, suggesting that fire has retracted from historically larger widespread forests to fire-free refugia which have not yet reestablished back from those frgaments. A. chilensis fragments contained similar levels of polymorphism, rare alleles, and interpopulation divergence compared to the more westerly continuous forest, suggesting lack of founder effects expected under an equilibrium scenario of forest fragment origin based on long-distance dispersal. These results, in combination with previous fire history reconstructions and forest dynamics studies, strongly suggest that the current Austrocedrus forest landscape reflects a relict distribution not in equilibrium with current abiotic conditions that resulted from the paleofragmentation of a more widespread distribution during pre-European long-term (century to millennial-scale) period of high frequency of anthropogenic fires.