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Richard A. Armstrong - One of the best experts on this subject based on the ideXlab platform.
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A review with new data from Iceland
2016Co-Authors: Tom Bradwell, Richard A. ArmstrongAbstract:This article reviews evidence from previous growth-rate studies on lichens of the yellow-green species of Subgenus Rhizocarpon – the family most commonly used in lichenometric dating. New data are presented from Rhizocarpon section Rhizocarpon thalli growing on a moraine in southern Iceland over a period of 4.33 years. Measurements of 38 lichen thalli, between 2001 and 2005, show that diametral growth rate (DGR, mm yr-1) is a function of thallus size. Growth rates increase rapidly in small thalli (<10 mm diameter), remain high (c. 0.8 mm/yr) and then decrease gradually in larger thalli (>50 mm diameter). Mean DGR in southern Iceland, between 2001 and 2005, was 0.64 mm yr-1 (SD = 0.24). The resultant growth-rate curve is parabolic and is best described by a third-order polynomial function. The striking similarity between these findings in Iceland and those of Armstrong (1983) in Wales implies that the shape of the growth-rate curve may be characteristic of Rhizocarpon geographicum lichens. The difference between the absolute growth rate in southern Iceland and Wales (c. 66 % faster) is probably a function of climate and micro-environment between the two sites. These findings have implications for previous lichenometric-dating studies; namely, that those studies which assume constant lichen growth rates over many decades are probably unreliable
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lichenometric dating lichenometry and the biology of the lichen genus Rhizocarpon challenges and future directions
Geografiska Annaler Series A-physical Geography, 2016Co-Authors: Richard A. ArmstrongAbstract:Lichenometric dating (lichenometry) involves the use of lichen measurements to estimate the age of exposure of various substrata. Because of low radial growth rates and considerable longevity, species of the crustose lichen genus Rhizocarpon have been the most useful in lichenometry. The primary assumption of lichenometry is that colonization, growth and mortality of Rhizocarpon are similar on surfaces of known and unknown age so that the largest thalli present on the respective faces are of comparable age. This review describes the current state of knowledge regarding the biology of Rhizocarpon and considers two main questions: (1) to what extent does existing knowledge support this assumption; and (2) what further biological observations would be useful both to test its validity and to improve the accuracy of lichenometric dates? A review of the Rhizocarpon literature identified gaps in knowledge regarding early development, the growth rate/size curve, mortality, regeneration, competitive effects, colonization, and succession on rock surfaces. The data suggest that these processes may not be comparable on different rock surfaces, especially in regions where growth rates and thallus turnover are high. In addition, several variables could differ between rock surfaces and influence maximum thallus size, including rate and timing of colonization, radial growth rates, environmental differences, thallus fusion, allelopathy, thallus mortality, colonization and competition. Comparative measurements of these variables on surfaces of known and unknown age may help to determine whether the basic assumptions of lichenometry are valid. Ultimately, it may be possible to take these differences into account when interpreting estimated dates.
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the use of the lichen genus Rhizocarpon in lichenometric dating with special reference to holocene glacial events
2015Co-Authors: Richard A. ArmstrongAbstract:Lichenometry is one of the most widely used methods of dating the surface age of substrata including rock surfaces, boulders, walls, and archaeological remains and has been particularly important in dating late Holocene glacial events. Yellow-green species of the crustose genus Rhizocarpon have been the most useful lichens in lichenometry because of their low growth rates and longevity. This review describes: (1) the biology of the genus Rhizocarpon, (2) growth rates and longevity, (3) environmental growth effects, (4) methods of estimating lichen age, (5) the methodology of lichenometry, (6) applications to dating glacial events, and (7) future research. Lichenometry depends on many assumptions, most critically that if the lag time before colonisation of a substratum is known and lichen age can be estimated, then a minimum surface age date can be obtained by measuring the size of the largest Rhizocarpon thallus. Lichen age can be estimated by calibrating thallus size against surfaces of known age (‘indirect lichenometry’), by constructing a growth rate-size curve from direct measurement of growth (‘direct lichenometry’), using radio-carbon (RC) dating, or from lichen ‘growth rings’. Future research should include a more rigorous investigation of the assumptions of lichenometry, especially whether the largest thallus present at a site is a good indicator of substratum age, and further studies on the establishment, development, growth, senescence, and mortality of Rhizocarpon lichens.
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Polyols in the crustose lichen Rhizocarpon geographicum
Environmental Research Journal, 2014Co-Authors: Richard A. ArmstrongAbstract:A lichen is an intimate association between an alga and a fungus and is regarded as one of the best examples of ‘mutualism’ or ‘symbiosis’ involving microorganisms. In lichens which have Trebouxia as the algal partner, photosynthesis by the algae results in the production of the soluble polyol ribitol which is then transported to the fungus where it is converted to arabitol and mannitol. Within the fungus, arabitol may act as a short-term carbohydrate reserve while mannitol may be involved in stress resistance. The crustose lichen Rhizocarpon geographicum (L.) DC., has an unusual thallus structure consisting of discrete granules (areolae) containing the algal component growing in association with a non-lichenised fungal hypothallus that extends beyond the areolae to form a marginal ring. The concentrations of ribitol, arabitol, and mannitol were measured, using gas chromatography, in the central areolae and marginal hypothallus of the crustose lichen Rhizocarpon geographicum (L.) DC. growing on slate rocks in north Wales, UK. The concentrations of all three polyols were greater in the central areolae than in the marginal hypothallus. In addition, the ratios of polyols in the marginal hypothallus to that in the central areolae varied through the year. The concentration of an individual poyol in the hypothallus was correlated primarily with the concentrations of the other polyols in the hypothallus and not to their concentrations in the areolae. Low concentration of ribitol, arabitol, and mannitol in the marginal hypothallus compared with the central areolae suggests either a lower demand for carbohydrate by the hypothallus or limited transport of polyols from areolae to hypothallus, and may explain the low growth rates of this species. In addition, polyols appear to be partitioned differently through the year with an increase in mannitol compared with arabitol in more stressful periods.
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the biology of the lichen Rhizocarpon geographicum symbionts growth ecology and lichenometry
2012Co-Authors: Richard A. ArmstrongAbstract:Rhizocarpon geographicum (L.) DC. is one of the most widely distributed species of crustose lichens. This unusual organism comprises yellow-green ‘areolae’ that contain the algal symbiont which develop and grow on the surface of a non-lichenized, fungal ‘hypothallus’ that extends beyond the margin of the areolae to form a marginal ring. This species grows exceptionally slowly with annual radial growth rates (RGR) as low as 0.07 mm yr-1 and its considerable longevity has been exploited by geologists in the development of methods of dating the age of exposure of rock surfaces and glacial moraines (‘lichenometry’). Recent research has established some aspects of the basic biology of this important and interesting organism. This chapter describes the general structure of R. geographicum, how the areolae and hypothallus develop, why the lichen grows so slowly, the growth rate-size curve, and some aspects of the ecology of R. geographicum including whether the lichen can inhibit the growth of its neighbours by chemical means (‘allelopathy’). Finally, the importance of R. geographicum in direct and indirect lichenometry is reviewed.
Irene A Garibotti - One of the best experts on this subject based on the ideXlab platform.
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nuevos datos de referencia para la tasa de crecimiento de Rhizocarpon subg Rhizocarpon en patagonia
Magallania (punta Arenas), 2014Co-Authors: Karen Borrazzo, Irene A GaribottiAbstract:This paper presents the results from lichen size survey of genus Rhizocarpon subgenus Rhizocarpon performed on surfaces exposed during last century in arid Patagonian environments (Santa Cruz, Argentina). We surveyed the cemetery of Puerto Deseado City and rock surfaces exposed by the retreat of Tunel Glacier in Los Glaciares National Park, providing eight new reference sites to estimate the growth rate of these lichens. Growth rate estimations for subgenus Rhizocarpon are between 0,125 to 0,061 mm per year. These values agree with previous estimations for other portions of Patagonian steppe and exhibit significant difference with available estimations for wetter regions in the Patagonian Andes.
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lichenometric dating using Rhizocarpon subgenus Rhizocarpon in the patagonian andes argentina
Quaternary Research, 2009Co-Authors: Irene A Garibotti, Ricardo VillalbaAbstract:This study represents the first attempt to develop and apply lichenometric dating curves of Rhizocarpon subgenus Rhizocarpon for dating glacier fluctuations in the Patagonian Andes. Six glaciers were studied along the Patagonian Andes. Surfaces of known ages (historical evidences and tree-ring analyses) were used as control sites to develop indirect lichenometric dating curves. Dating curves developed for the studied glaciers show the same general logarithmic form, indicating that growth rate of subgenus Rhizocarpon decreases over time. The strong west–east precipitation gradient across the Andean Cordillera introduces statistically significant differences in the growth curves, with faster growth rates in the moist west sites than the drier eastern sites. Latitudinal difference among the studied glaciers does not appear to be a major factor regulating lichen growth rates. Therefore, we developed two lichenometric curves for dating glacier fluctuations in wetter and drier sites in the Patagonian Andes during the past 450 yrs. Application of the developed curves to moraine dating allowed us to complement glacial chronologies previously obtained by tree-ring analyses. A first chronosequence for moraine formation in the Torrecillas Glacier (42°S) is presented. Our findings confirm the utility of lichenometry to date deglaciated surfaces in the Patagonian Andes.
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tecnicas de liquenometria basadas en Rhizocarpon subgenero Rhizocarpon para datar depositos glaciares en los andes patagonicos
Boletín Geográfico, 2007Co-Authors: Irene A Garibotti, Ricardo VillalbaAbstract:La liquenometria es una tecnica de datacion que estima la edad de exposicion de una superficie a partir del diametro de los liquenes que crecen en ella. El objetivo de este estudio es calibrar la curva de crecimiento de Rhizocarpon subgenero Rhizocarpon en los Andes Patagonicos, y aplicarla para reconstruir las fluctuaciones glaciares durante los ultimos siglos. Para ello se investigaron seis glaciares, tres en el norte y tres en el sur de los Andes Patagonicos, en los cuales se realizaron mediciones del diametro de ejemplares del subgenero Rhizocarpon en sitios de edad conocida (sitios control) y sitios de edad desconocida. La edad de los sitios control se determino fehacientemente a partir de informacion historica. Los datos liquenometricos relevados en estos sitios control fueron utilizados para calibrar la curva de crecimiento. La relacion entre el tamano de los liquenes y la edad de la superficie (curva de crecimiento) es lineal, indicando que los liquenes del subgenero Rhizocarpon tienen una tasa de crecimiento constante a lo largo del tiempo. Esta curva se extiende por 270 anos. Aplicacion de la curva a los datos liquenometricos relevados en las morenas de edad desconocida permitio establecer la cronologia de la secuencia de morenas de los seis glaciares bajo estudio. Los datos liquenometricos fueron contrastados con datos dendrocronologicos, mostrando una gran concordancia entre los metodos. Los resultados obtenidos muestran dos periodos principales de formacion de morenas. El primer periodo se extiende desde la mitad del siglo XVII hasta finales del siglo XIX, y esta caracterizado por morenas muy prominentes. El segundo periodo se extiende desde mediados del siglo XIX hasta finales del siglo XX, y esta caracterizado por la formacion de un gran numero de morenas pequenas.
Ricardo Villalba - One of the best experts on this subject based on the ideXlab platform.
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lichenometric dating using Rhizocarpon subgenus Rhizocarpon in the patagonian andes argentina
Quaternary Research, 2009Co-Authors: Irene A Garibotti, Ricardo VillalbaAbstract:This study represents the first attempt to develop and apply lichenometric dating curves of Rhizocarpon subgenus Rhizocarpon for dating glacier fluctuations in the Patagonian Andes. Six glaciers were studied along the Patagonian Andes. Surfaces of known ages (historical evidences and tree-ring analyses) were used as control sites to develop indirect lichenometric dating curves. Dating curves developed for the studied glaciers show the same general logarithmic form, indicating that growth rate of subgenus Rhizocarpon decreases over time. The strong west–east precipitation gradient across the Andean Cordillera introduces statistically significant differences in the growth curves, with faster growth rates in the moist west sites than the drier eastern sites. Latitudinal difference among the studied glaciers does not appear to be a major factor regulating lichen growth rates. Therefore, we developed two lichenometric curves for dating glacier fluctuations in wetter and drier sites in the Patagonian Andes during the past 450 yrs. Application of the developed curves to moraine dating allowed us to complement glacial chronologies previously obtained by tree-ring analyses. A first chronosequence for moraine formation in the Torrecillas Glacier (42°S) is presented. Our findings confirm the utility of lichenometry to date deglaciated surfaces in the Patagonian Andes.
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tecnicas de liquenometria basadas en Rhizocarpon subgenero Rhizocarpon para datar depositos glaciares en los andes patagonicos
Boletín Geográfico, 2007Co-Authors: Irene A Garibotti, Ricardo VillalbaAbstract:La liquenometria es una tecnica de datacion que estima la edad de exposicion de una superficie a partir del diametro de los liquenes que crecen en ella. El objetivo de este estudio es calibrar la curva de crecimiento de Rhizocarpon subgenero Rhizocarpon en los Andes Patagonicos, y aplicarla para reconstruir las fluctuaciones glaciares durante los ultimos siglos. Para ello se investigaron seis glaciares, tres en el norte y tres en el sur de los Andes Patagonicos, en los cuales se realizaron mediciones del diametro de ejemplares del subgenero Rhizocarpon en sitios de edad conocida (sitios control) y sitios de edad desconocida. La edad de los sitios control se determino fehacientemente a partir de informacion historica. Los datos liquenometricos relevados en estos sitios control fueron utilizados para calibrar la curva de crecimiento. La relacion entre el tamano de los liquenes y la edad de la superficie (curva de crecimiento) es lineal, indicando que los liquenes del subgenero Rhizocarpon tienen una tasa de crecimiento constante a lo largo del tiempo. Esta curva se extiende por 270 anos. Aplicacion de la curva a los datos liquenometricos relevados en las morenas de edad desconocida permitio establecer la cronologia de la secuencia de morenas de los seis glaciares bajo estudio. Los datos liquenometricos fueron contrastados con datos dendrocronologicos, mostrando una gran concordancia entre los metodos. Los resultados obtenidos muestran dos periodos principales de formacion de morenas. El primer periodo se extiende desde la mitad del siglo XVII hasta finales del siglo XIX, y esta caracterizado por morenas muy prominentes. El segundo periodo se extiende desde mediados del siglo XIX hasta finales del siglo XX, y esta caracterizado por la formacion de un gran numero de morenas pequenas.
Jeanpaul Bravard - One of the best experts on this subject based on the ideXlab platform.
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croissance du lichen Rhizocarpon geographicum l s sur le pourtour nord occidental de la mediterranee observations en vue d une application a l etude des lits fluviaux rocheux et caillouteux
Geomorphologie-relief Processus Environnement, 2002Co-Authors: Nicolas Jacob, Frederic Gob, Francois Petit, Jeanpaul BravardAbstract:Les applications de la lichenometrie en geomorphologie sont nombreuses; toutefois elles n'ont que rarement ete pratiquees en dynamique fluviale. Dans les lits rocheux et caillouteux de vallees en gorges, cette technique peut permettre de pallier l'absence de documents et d'observations historiques. On propose ici une etude de la croissance du lichen Rhizocarpon geographicum l.s. dans trois espaces de montagnes mediterraneennes. Le grand nombre des releves permet une reconstitution assez fiable de la croissance sur une duree d'un siecle et demi; la parente des courbes mediterraneennes autorise a proposer une courbe de synthese pour les trois espaces etudies.
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croissance du lichenRhizocarpon geographicum l s sur le pourtour nord occidental de la mediterranee observations en vue d une application a l etude des lits fluviaux rocheux et caillouteux growth curves of Rhizocarpon geographicum l s in granitic mountains of the french mediterranean application to bedrock and gravel river studies
Geomorphologie-relief Processus Environnement, 2002Co-Authors: Nicolas Jacob, Frederic Gob, Francois Petit, Jeanpaul BravardAbstract:Resume Les applications de la lichenometrie en geomorphologie sont nombreuses ; toutefois elles n'ont que rarement ete pratiquees en dynamique fluviale. Dans les lits rocheux et caillouteux de vallees en gorges, cette technique peut permettre de pallier l'absence de documents et d'observations historiques. On propose ici une etude de la croissance du lichen Rhizocarpon geographicum l.s. dans trois espaces de montagnes mediterraneennes. Le grand nombre des releves permet une reconstitution assez fiable de la croissance sur une duree d'un siecle et demi ; la parente des courbes mediterraneennes autorise a proposer une courbe de synthese pour les trois espaces etudies.
Garibotti, Irene Adriana - One of the best experts on this subject based on the ideXlab platform.
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Colonization of mid- and late-Holocene moraines by lichens and trees in the Magellanic sub-Antarctic province
'Springer Science and Business Media LLC', 2017Co-Authors: Garibotti, Irene Adriana, Villalba RicardoAbstract:Understanding the process of primary succession is a relevant topic in restoration and global change ecology, and provides the basis for classic dating methods in geomorphology, such as lichenometry and dendrochronology. The aim of this study is to investigate the colonization by lichens and vascular plants of two pro-glacial chronosequences encompassing the late- and mid-Holocene periods in the sub-Antarctic sub-region of South America. We use this information to address questions related to the pattern of Magellanic forests recovery after disturbance and the applicability of lichenometry for developing glacier retreat chronologies. Progression of succession to a state with high vascular plant cover was slow, and some moraines remained unforested for about 2000 years. Our results contrast with previous reports indicating a quick development of mature forest states on disturbed terrains, suggesting large regional variability on the course of succession. Environmental conditions seem propitious for lichens that colonize immediately after moraine formation. Lichens grow at relatively high rates in comparison to other world areas, but half as fast as in Antarctica and sub-Antarctic islands. Growth rates for the Rhizocarpon Ram. em. Th. Fr. sub-gen. Rhizocarpon group increase with lichen sizes up to ca. 50 mm and decrease in larger thalli, leading to a sigmoidal lichenometric growth curve that extends the applicable range of lichenometry to the last 5700 years in dry sites in the Magellanic province of the sub-Antarctic sub-region. Our results suggest that lichenometry is an effective technique in multi-proxy approaches for reconstructing glacier fluctuations, and agree with early studies in Antarctica suggesting that lichen annual growth rate is a sensitive attribute for the biomonitoring of climate changes.Fil: Garibotti, Irene Adriana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Villalba, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin
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Nuevos datos de referencia para la tasa de crecimiento de Rhizocarpon subg. Rhizocarpon en Patagonia
'Universidad de Magallanes Instituto de La Patagonia', 2014Co-Authors: Borrazzo, Karen Beatriz, Garibotti, Irene AdrianaAbstract:Se presentan los resultados obtenidos en el relevamiento del tamaño de líquenes pertenecientes al género Rhizocarpon subgénero Rhizocarpon realizado en superficies expuestas durante la última centuria en ambientes áridos de la Patagonia (Santa Cruz, Argentina). Se relevó el cementerio de la ciudad de Puerto Deseado y superficies expuestas por el retroceso del Glaciar Túnel en el Parque Nacional los Glaciares, proveyendo ocho nuevos sitios de referencia para estimar la tasa de crecimiento de estos líquenes. La tasa de crecimiento para el subgénero Rhizocarpon en estos sitios se estima entre 0,125 y 0,061 mm por año, siendo concordante con los valores obtenidos en otros sectores de la estepa patagónica, y difiriendo significativamente de las tasas de crecimiento estimadas para regiones más húmedas de los Andes Patagónicos.This paper presents the results from lichen size survey of genus Rhizocarpon subgenus Rhizocarpon performed on surfaces exposed during last century in arid Patagonian environments (Santa Cruz, Argentina). We surveyed the cemetery of Puerto Deseado City and rock surfaces exposed by the retreat of Túnel Glacier in Los Glaciares National Park, providing eight new reference sites to estimate the growth rate of these lichens. Growth rate estimations for subgenus Rhizocarpon are between 0,125 to 0,061 mm per year. These values agree with previous estimations for other portions of Patagonian steppe and exhibit significant difference with available estimations for wetter regions in the Patagonian Andes.Fil: Borrazzo, Karen Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto Multidisciplinario de Historia y Ciencias Humanas; ArgentinaFil: Garibotti, Irene Adriana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin