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Flammable Mexico

April 13th, 2016 No comments

Mexico is a megadiverse North American country with a wide range of climates (e.g., wet tropical, warm temperate, mediterranean, and arid) and a diverse topography (from sea level up to 5700 m asl). These characteristics together with its location in the transition toward Central America make this land a global biodiversity hotspot with species belonging to northern (Neartic) lineages co-occurring with others from southern (Neotropical) lineages. An important factor contributing to this biodiversity are the frequent disturbances in this region where volcanoes, hurricanes, and wildfires are common, together with droughts and floods. Fires occur mainly in April-May (Figure below, [1]); the natural sources of ignition being lightning, especially in mountains, and volcanoes (with clear evidence of fires ignited by volcanoes, e.g. from the Popocatépetl volcano). However, currently most fires are caused by human activities, as in many other countries. Hurricanes add fuel and increase the intensity and probability of fire [2].

Mexico is a center of diversification of pines (Pinus) and oaks (Quercus), two species groups strongly related to fire [3,4]. Mexico harbors about 50 species of pines and these incorporate all the fire strategies and traits observed in this genus [4]. For instance, there are many fire tolerant pines with thick barks, self-pruning abilities, and in some cases, with basal or juvenile resprouting capabilities; fire embracers (postfire seeders) with thin bark and serotinous cones; and fire avoiders that lack these traits. The country also harbors some 160 Quercus species, ranging from strongly resprouting shrubby species to many tree oaks with relatively thick bark that live in surface fire ecosystems, and including evergreen and drought-deciduous species with a large range of leaf morphologies. I was surprised to see some oaks with very large, and very thick leathery leaves that are deciduous, certainly an outlier in the leaf economics spectrum. More details in [1].

Flamable-Mexico
Figure: Recent fire activity in Mexico (2001-2015) estimated from the monthly number of active fires recorded by the Terra satellite (MODIS hotspots). Top: temporal variability (x-axis ticks indicate the begining of the year). Bottom left: fire seasonality– the flammable season is concentrated into four months (March-June), with a peak in April-May (the end of the dry season). Bottom right: proportion of active fires in each biome (TrDry: tropical dry broadleaf forests; TrConif: tropical coniferous forests: TrMost: tropical moist broadleaf forests; Desert: deserts and xeric shrublands; Others). From [1]

References
[1] Pausas J.G. Flammable Mexico. Int. J. Wildland Fire [doi | pdf]

[2] Fire-wind interactions, jgpausas.blogs.uv.es 30 Oct 2015

[3] He T, Pausas JG, Belcher CM, Schwilk DW, Lamont BB. 2012. Fire-adapted traits of Pinus arose in the fiery Cretaceous. New Phytol. 194: 751-759. [doi | wiley | pdf | suppl.]

[4] Pausas, J.G. 2015. Evolutionary fire ecology: lessons learned from pines. Trends Plant Sci. 20: 318-324. [doi | sciencedirectpdf]

Incendios forestales (de vegetación) en México

March 1st, 2016 1 comment

Recientemente se ha publicado un nuevo libro sobre incendios forestales. El libro describe la importancia y los regímenes de incendios en los diferentes ecosistemas de México, así como aspectos sobre historia y manejo del fuego [1]. Es un libro extenso, enciclopédico, con unas 1700 páginas publicadas en 2 volúmenes. El primer volumen (18 capítulos) representa un paseo por la gran variedad de paisajes de México (pinares, bosques de encinos, de oyamel, de galería, pastizales, matorrales, selvas, bosques mesófilos de montaña, sabanas, manglares, palmares, etc.), y en cada uno de ellos se explica el régimen de fuego y las respuesta de las especies y ecosistemas. El segundo volumen (11 capítulos) aborda cuestiones de comportamiento, prevención, y combate del fuego, así como una historia del fuego desde sus inicios (con los primeros ecosistemas terrestres [2]) hasta el uso del fuego en las culturas mesoamericanas y en el México actual. Si hay algo que se encuentra a faltar sería una visión evolutiva; quizá los lectores pueden encontrar esas visión en mi propio libro [3]. Más comentarios sobre el libro y sobre México en [6].

Dante-Rodriguez-Trejo_libroPortadas del volumen 1 (izquierda) y 2 (derecha)

A veces se ha considerado que el concepto de incendios forestales se refiere sólo a los incendios que ocurren en bosques, o incluso a incendios que ocurren en plantaciones forestales. Para evitar ese mal entendido, el autor titula el libro ‘incendios de vegetación‘, ese decir, para enfatizar que el libro se refiere a incendios en cualquier tipo de vegetación. En España, actualmente el término ‘forestal‘ se refiere a cualquier tipo de vegetación natural (también llamado monte), y en ese contexto es cómo a menudo usamos el concepto de incendios forestales [3]. Así es como lo explicaba yo en el prólogo del libro ‘Incendios forestales‘:

Los incendios son fuegos que se propagan sin control humano; cuando ocurren en la naturaleza se llaman incendios forestales. El término forestal está relacionado con una clasificación tradicional de los usos del suelo, donde el uso forestal incluye cualquier zona terrestre que no sea de uso urbano ni agrícola. De este modo, el término incendios forestales se refiere a los fuegos no controlados (sean de origen natural o antrópico) que ocurren en los ecosistemas terrestres, y que se propagan por la vegetación, sea ésta del tipo que sea (bosque, sabana, matorral, pastizal, humedal, turbera, etc.). Por lo tanto, incendios forestales, y por extensión este libro, no sólo hace referencia a bosques, como a veces se ha interpretado, sino a cualquier tipo de ecosistema terrestre” [3]

En inglés también hay una amplia nomenclatura para referirse a los incendios forestales, como por ejemplo, wildfires (principalmente utilizado en Norte América), forest fires (Europa), bush fires (Australia), vegetation fires, landscape fires, etc., todos ellos describen los incendios en cualquier tipo de vegetación.

Referencias:

[1] Rodríguez Trejo, D. A. 2015. Incendios de vegetación. Su ecología, manejo e historia. 2 vol. Ed. Colegio de Postgraduados, Biblioteca Básica de Agricultura, México.

[2] Pausas J.G. & Keeley J.E. 2009. A burning story: The role of fire in the history of life. BioScience 59: 593-601 [doijstor | pdfpost]

[3] Pausas J.G. 2012. Incendios forestales. Una visión desde la ecología. Ed Catarata-CSIC. Madrid. [libro]

[4] He T., Pausas J.G., Belcher C.M., Schwilk D.W., Lamont B.B. 2012. Fire-adapted traits of Pinus arose in the fiery Cretaceous. New Phytol. 194: 751-759. [doi | wiley | pdf | suppl.]

[5] Pausas, J.G. 2015. Evolutionary fire ecology: lessons learned from pines. Trends Plant Sci. 20: 318-324. [doi | sciencedirect | cell | pdf]

[6] Pausas J.G. 2016. Flammable Mexico. Int. J. Wildland Fire [doi | pdf]

 

Fire – wind interactions

October 30th, 2015 1 comment

I’ve just had the opportunity to see some of the consequences of the hurricane Patricia that affected Jalisco, Mexico, last weekend. Here is the effects on a Pinus dauglasiana forest in the Sierra de Manantlán biosfere reserve. Some parts of this forest had burned several years ago (< 10 years) mainly as understory fire, and some trees were injured at the base but most survived (as in any typical undertory fires); there were also some crowning in small patches. Fire killed many understory fire-sensitive broadleaved shrubs, and were replaced by a high density of the pine seedlings (Fig. 1); there were also some plants resprouting (e.g., Quercus, Arbutus, etc.). Now, the strong winds of the hurricane is interacting with fire in two ways: (1) the wind have killed some of the fire-injured trees that had survived the fire (Fig. 1); and (2) the wind has greatly increased the fuel in the forest floor, even in the places where trees were not blown down (Fig. 2), which implies an increase in the chance for a surface fire of high intensity during the next dry season. That is, this seems an opportunity to study the interaction between these two disturbances, fire and hurricanes.

Pinus dauglasianaFig. 1. Pinus dauglasiana forest after a fire (see the seedling regeneration) followed by an hurricane.

Pinus dauglasiana 2Fig. 2. The forest floor of the Pinus dauglasiana forest (unburned) has greatly increased the fuel after the hurricane even in the places where trees were not blown down; the whole forest has a carpet of recently fallen branches and leaves.

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