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Frost-induced changes in aboveground biomass stocks in the northmost Neotropical dry forest
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  • Jesus Bojorquez,
  • Angelina Martinez-Yrizar,
  • Juan Alvarez-Yepiz,
  • Juan Alvarez-Yepiz
Jesus Bojorquez
Universidad Nacional Autonoma de Mexico, Universidad Nacional Autonoma de Mexico, Universidad Nacional Autonoma de Mexico

Corresponding Author:jabojorquezv@gmail.com

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Angelina Martinez-Yrizar
Universidad Nacional Autónoma de México, Universidad Nacional Autónoma de México, Universidad Nacional Autónoma de México
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Juan Alvarez-Yepiz
Instituto Tecnológico de Sonora
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Juan Alvarez-Yepiz
Instituto Tecnológico de Sonora, Instituto Tecnológico de Sonora
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Abstract

Climate-induced episodes of extensive tree mortality worldwide are leading to abrupt changes in forest carbon stocks. A severe frost in early February 2011 triggered widespread tree mortality in the lowland tropical dry forest (TDF) of northwestern Mexico. The studied landscape in southern Sonora is composed by a patchy matrix dominated by mature, secondary (originated in abandoned fields), and active agricultural fields. In this forest, we used allometric equations to assessed frost-induced changes in aboveground biomass (AGB) stocks in mature and secondary tropical dry forests. For AGB estimations we used 48 1-ha plots (24 plots per forest type) distributed within four distant subareas in our 83 230 ha study area. On each plot, we recorded all live/dead individuals, and a total of 11 205 woody plants were registered, of which 7 137 (with at least a stem DBH > 2.5 cm) were likely present before the frost, and the remaining smaller ones were considered as new recruits regenerated from seeds (4,068 individuals). From those plants present before the frost, 26 842 and 8 059 were live and dead stems, and 1 222 were dead individuals. All registered live and dead stems accounted for a total of 273.4 Mg of AGB in our study plots (4.8 ha). From this amount, 57.3 Mg was necromass (dead stems). Interestingly, only two out of a total of 74 registered species contributed with ca. 80% of this necromass. These highly sensitive species are the tree legumes Lysioma divaricatum and Acacia cochliacantha. On average, AGB in the studied mature and secondary TDF was 64.3 and 49.6 Mg ha-1, respectively. The corresponding necromass for these forests was 10.9 and 13 Mg ha, respectively. The 2011 frost induced a greater change from live biomass to necromass in secondary than mature forests, 26.2% and 16.9%, respectively, which can be explained by the higher abundance of individuals from sensitive species in secondary forests. Our results suggest that climate-induced shifts in carbon stocks are linked to previous land-use changes in tropical dry forests. Restoration plans of these degraded lands should consider the vulnerability of tropical dry forest species to climate extremes.