Globally, climate is a fundamental driver of plant species&am... more Globally, climate is a fundamental driver of plant species' geographical distributions, yet we still lack a good understanding of climatic variation on tropical mountains and its consequences for elevational floristic patterns. In a seasonally dry region of southern Mexico, we analysed meteorological patterns along a large elevational gradient (0-3670 m a.s.l.) and examined their relationship with changes in floristic richness. Meteorological patterns were characterised using two data sources. First, climatic information was extracted from cartography and records from a few existing meteorological stations. Additionally, air temperature and humidity were recorded hourly during 1 year with data loggers, at sites representing 200-m elevation increments. Floristic information was extracted from a database containing 10,124 records of plant collections, and organized in 200-m elevational belts. Climatic charts distinguished three climate types along the gradient, all with marked rainfall seasonality, but these bore little correspondence with the information obtained with the data loggers. Mean annual air temperature decreased with increasing elevation (lapse rate of 0.542 °C 100 m(-1)). Thermal oscillation was minimum around 1400 m and increased towards both extremes of the gradient. Relative humidity opposed this pattern, with maxima between 800 and 1800 m, decreasing towards the highest elevations. An analysis of temperature frequency distributions revealed meteorological features undetectable from the annual or monthly means of this variable; despite an overall gradual transition of the proportions of time recorded at different temperatures, some changes did not conform to this pattern. The first discontinuity occurred between 1000-1200 m, where dominant temperatures shifted abruptly; also noticeable was an abrupt increase of the proportion of time elapsed at 0.1-10 °C between 2400 and 2600 m. Air temperature appears to be the most influential climatic factor driving elevational variation of plant species richness in this region.
New localities are reported for three cycad species in Mexico. C eratozamia miqueliana was found ... more New localities are reported for three cycad species in Mexico. C eratozamia miqueliana was found in montane rainforest in western Chiapas and C. l1orsto,,?ii was found in dry tropical oak forest mixed with elements of seasonally dry tropical forest in eastern Oaxaca. Zamia splendens"was found on karstic topography in lowland tropical rainforest in the hills of southern Tabasco. The additional
ABSTRACT We examined general and family-specific patterns of vascular plant richness along a larg... more ABSTRACT We examined general and family-specific patterns of vascular plant richness along a large elevational gradient (0–3,670 m a.s.l.), assessed the continuity of these patterns and analysed their potential underlying causes in a high diversity region of the Sierra Madre del Sur, Oaxaca, Mexico. We used a vascular plant database constructed previously. The gradient was divided into 18 200-m elevation belts. To examine elevational patterns of richness, we used both observed and estimated (interpolated) species richness, as well as genus and family observed richness, for each belt. A generalised linear model (GLM) was used to assess the effect of altitude on area-corrected species richness (standard area = 100 km2), and a numerical classification of the elevational belts based on species richness was performed. Overall, richness at the three taxonomic levels decreased with elevation, but some individual families departed from this pattern. A sharp drop in species richness was observed at 1,800 m, and the dendrogram separated two elevational floristic groups at this elevation. The GLM revealed a significant negative effect of elevation on species richness. Despite this overall decreasing pattern for vascular plants along this extensive gradient, an examination of some family-specific patterns revealed the existence of other elevation–diversity relationships, indicating taxon-specific responses to elevation. The most noticeable discontinuity in species richness, at ca. 1,800 m, is likely related to a critical temperature isocline.
Dioon argenteum sp. nov. (Zamiaceae) is described from northern Oaxaca, México. Flat leaves, and ... more Dioon argenteum sp. nov. (Zamiaceae) is described from northern Oaxaca, México. Flat leaves, and persistently tomentose, slightly imbricate leaflets with marginal prickles characterize this species. The specific epithet argenteum was chosen to describe the silver appearance of the persistent tomentum covering the new leaves. D. argenteum appears to have affinities with D. purpusii and D. califanoi.
Resumen: La región de Zimatán, Oaxaca, cuenta con varios tipos de vegetación y una gran diversida... more Resumen: La región de Zimatán, Oaxaca, cuenta con varios tipos de vegetación y una gran diversidad florística, debido principalmente a un amplio intervalo altitudinal que varía desde el nivel del mar hasta 2,580 m. En 1991 está región fue propuesta como un área de gran importancia para la conservación en el estado de Oaxaca, sobre todo por las amplias superficies de selvas tropicales secas en excelente estado de conservación; sin embargo, la escasa información biológica disponible condujo a realizar a partir de 1997 una serie de estudios que sustentaran su conservación. En este trabajo se presenta la información florística de 8,063 colectas originales realizadas desde entonces. La lista florística incluye 1,384 especies, 668 géneros y 144 familias, lo que hace que la región de Zimatán sea una de las mejor colectadas y con mayor diversidad florística en la costa mexicana del Pacífico, junto con la Estación Biológica de Chamela en Jalisco. Palabras clave: Flora, vegetación, Costa del Pacífico, Oaxaca, México.
ABSTRACT We used higher taxonomic composition of 241 modern forest plots from across the New Worl... more ABSTRACT We used higher taxonomic composition of 241 modern forest plots from across the New World to identify the closest modern analog of the Florissant fossil flora and to infer Late Eocene paleotemperature for Florissant. Non-metric multidimensional scaling (NMS) based on both genus and family presence-absence placed Florissant in a no-analog taxonomic space surrounded by North American warm temperate broadleaved forests, Mexican humid pine-oak forests, and subtropical moist forests from Florida, Mexico, and Argentina. The most similar site to Florissant, as indicated by the mean of Euclidean distances in genus and family NMS space, was a subtropical moist forest in southern Florida, followed by the humid pine-oak forests of central and northeastern Mexico, and the broadleaved deciduous forests of eastern North America.
Globally, climate is a fundamental driver of plant species&am... more Globally, climate is a fundamental driver of plant species' geographical distributions, yet we still lack a good understanding of climatic variation on tropical mountains and its consequences for elevational floristic patterns. In a seasonally dry region of southern Mexico, we analysed meteorological patterns along a large elevational gradient (0-3670 m a.s.l.) and examined their relationship with changes in floristic richness. Meteorological patterns were characterised using two data sources. First, climatic information was extracted from cartography and records from a few existing meteorological stations. Additionally, air temperature and humidity were recorded hourly during 1 year with data loggers, at sites representing 200-m elevation increments. Floristic information was extracted from a database containing 10,124 records of plant collections, and organized in 200-m elevational belts. Climatic charts distinguished three climate types along the gradient, all with marked rainfall seasonality, but these bore little correspondence with the information obtained with the data loggers. Mean annual air temperature decreased with increasing elevation (lapse rate of 0.542 °C 100 m(-1)). Thermal oscillation was minimum around 1400 m and increased towards both extremes of the gradient. Relative humidity opposed this pattern, with maxima between 800 and 1800 m, decreasing towards the highest elevations. An analysis of temperature frequency distributions revealed meteorological features undetectable from the annual or monthly means of this variable; despite an overall gradual transition of the proportions of time recorded at different temperatures, some changes did not conform to this pattern. The first discontinuity occurred between 1000-1200 m, where dominant temperatures shifted abruptly; also noticeable was an abrupt increase of the proportion of time elapsed at 0.1-10 °C between 2400 and 2600 m. Air temperature appears to be the most influential climatic factor driving elevational variation of plant species richness in this region.
New localities are reported for three cycad species in Mexico. C eratozamia miqueliana was found ... more New localities are reported for three cycad species in Mexico. C eratozamia miqueliana was found in montane rainforest in western Chiapas and C. l1orsto,,?ii was found in dry tropical oak forest mixed with elements of seasonally dry tropical forest in eastern Oaxaca. Zamia splendens"was found on karstic topography in lowland tropical rainforest in the hills of southern Tabasco. The additional
ABSTRACT We examined general and family-specific patterns of vascular plant richness along a larg... more ABSTRACT We examined general and family-specific patterns of vascular plant richness along a large elevational gradient (0–3,670 m a.s.l.), assessed the continuity of these patterns and analysed their potential underlying causes in a high diversity region of the Sierra Madre del Sur, Oaxaca, Mexico. We used a vascular plant database constructed previously. The gradient was divided into 18 200-m elevation belts. To examine elevational patterns of richness, we used both observed and estimated (interpolated) species richness, as well as genus and family observed richness, for each belt. A generalised linear model (GLM) was used to assess the effect of altitude on area-corrected species richness (standard area = 100 km2), and a numerical classification of the elevational belts based on species richness was performed. Overall, richness at the three taxonomic levels decreased with elevation, but some individual families departed from this pattern. A sharp drop in species richness was observed at 1,800 m, and the dendrogram separated two elevational floristic groups at this elevation. The GLM revealed a significant negative effect of elevation on species richness. Despite this overall decreasing pattern for vascular plants along this extensive gradient, an examination of some family-specific patterns revealed the existence of other elevation–diversity relationships, indicating taxon-specific responses to elevation. The most noticeable discontinuity in species richness, at ca. 1,800 m, is likely related to a critical temperature isocline.
Dioon argenteum sp. nov. (Zamiaceae) is described from northern Oaxaca, México. Flat leaves, and ... more Dioon argenteum sp. nov. (Zamiaceae) is described from northern Oaxaca, México. Flat leaves, and persistently tomentose, slightly imbricate leaflets with marginal prickles characterize this species. The specific epithet argenteum was chosen to describe the silver appearance of the persistent tomentum covering the new leaves. D. argenteum appears to have affinities with D. purpusii and D. califanoi.
Resumen: La región de Zimatán, Oaxaca, cuenta con varios tipos de vegetación y una gran diversida... more Resumen: La región de Zimatán, Oaxaca, cuenta con varios tipos de vegetación y una gran diversidad florística, debido principalmente a un amplio intervalo altitudinal que varía desde el nivel del mar hasta 2,580 m. En 1991 está región fue propuesta como un área de gran importancia para la conservación en el estado de Oaxaca, sobre todo por las amplias superficies de selvas tropicales secas en excelente estado de conservación; sin embargo, la escasa información biológica disponible condujo a realizar a partir de 1997 una serie de estudios que sustentaran su conservación. En este trabajo se presenta la información florística de 8,063 colectas originales realizadas desde entonces. La lista florística incluye 1,384 especies, 668 géneros y 144 familias, lo que hace que la región de Zimatán sea una de las mejor colectadas y con mayor diversidad florística en la costa mexicana del Pacífico, junto con la Estación Biológica de Chamela en Jalisco. Palabras clave: Flora, vegetación, Costa del Pacífico, Oaxaca, México.
ABSTRACT We used higher taxonomic composition of 241 modern forest plots from across the New Worl... more ABSTRACT We used higher taxonomic composition of 241 modern forest plots from across the New World to identify the closest modern analog of the Florissant fossil flora and to infer Late Eocene paleotemperature for Florissant. Non-metric multidimensional scaling (NMS) based on both genus and family presence-absence placed Florissant in a no-analog taxonomic space surrounded by North American warm temperate broadleaved forests, Mexican humid pine-oak forests, and subtropical moist forests from Florida, Mexico, and Argentina. The most similar site to Florissant, as indicated by the mean of Euclidean distances in genus and family NMS space, was a subtropical moist forest in southern Florida, followed by the humid pine-oak forests of central and northeastern Mexico, and the broadleaved deciduous forests of eastern North America.
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