Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title><jats:p>Forest ecosystems depend on their capacity to withstand and recover from natural and anthropogenic perturbations (that is, their resilience)<jats:sup>1</jats:sup>. Experimental evidence of sudden increases in tree mortality is raising concerns about variation in forest resilience<jats:sup>2</jats:sup>, yet little is known about how it is evolving in response to climate change. Here we integrate satellite-based vegetation indices with machine learning to show how forest resilience, quantified in terms of critical slowing down indicators<jats:sup>3–5</jats:sup>, has changed during the period 2000–2020. We show that tropical, arid and temperate forests are experiencing a significant decline in resilience, probably related to increased water limitations and climate variability. By contrast, boreal forests show divergent local patterns with an average increasing trend in resilience, probably benefiting from warming and CO<jats:sub>2</jats:sub> fertilization, which may outweigh the adverse effects of climate change. These patterns emerge consistently in both managed and intact forests, corroborating the existence of common large-scale climate drivers. Reductions in resilience are statistically linked to abrupt declines in forest primary productivity, occurring in response to slow drifting towards a critical resilience threshold. Approximately 23% of intact undisturbed forests, corresponding to 3.32 Pg C of gross primary productivity, have already reached a critical threshold and are experiencing a further degradation in resilience. Together, these signals reveal a widespread decline in the capacity of forests to withstand perturbation that should be accounted for in the design of land-based mitigation and adaptation plans.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Unprecedented modern rates of warming are expected to advance boreal forest into Arctic tundra<jats:sup>1</jats:sup>, thereby reducing albedo<jats:sup>2–4</jats:sup>, altering carbon cycling<jats:sup>4</jats:sup> and further changing climate<jats:sup>1–4</jats:sup>, yet the patterns and processes of this biome shift remain unclear<jats:sup>5</jats:sup>. Climate warming, required for previous boreal advances<jats:sup>6–17</jats:sup>, is not sufficient by itself for modern range expansion of conifers forming forest–tundra ecotones<jats:sup>5,12–15,17–20</jats:sup>. No high-latitude population of conifers, the dominant North American Arctic treeline taxon, has previously been documented<jats:sup>5</jats:sup> advancing at rates following the last glacial maximum (LGM)<jats:sup>6–8</jats:sup>. Here we describe a population of white spruce (<jats:italic>Picea glauca</jats:italic>) advancing at post-LGM rates<jats:sup>7</jats:sup> across an Arctic basin distant from established treelines and provide evidence of mechanisms sustaining the advance. The population doubles each decade, with exponential radial growth in the main stems of individual trees correlating positively with July air temperature. Lateral branches in adults and terminal leaders in large juveniles grow almost twice as fast as those at established treelines. We conclude that surpassing temperature thresholds<jats:sup>1,6–17</jats:sup>, together with winter winds facilitating long-distance dispersal, deeper snowpack and increased soil nutrient availability promoting recruitment and growth, provides sufficient conditions for boreal forest advance. These observations enable forecast modelling with important insights into the environmental conditions converting tundra into forest.</jats:p>

<jats:title>Abstract</jats:title><jats:p>A fundamental gap in the study of the origin of limbed vertebrates lies in understanding the morphological and functional diversity of their closest relatives. Whereas analyses of the elpistostegalians <jats:italic>Panderichthys rhombolepis</jats:italic>, <jats:italic>Tiktaalik roseae</jats:italic> and <jats:italic>Elpistostege watsoni</jats:italic> have revealed a sequence of changes in locomotor, feeding and respiratory structures during the transition<jats:sup>1–9</jats:sup>, an isolated bone, a putative humerus, has controversially hinted at a wider range in form and function than now recognized<jats:sup>10–14</jats:sup>. Here we report the discovery of a new elpistostegalian from the Late Devonian period of the Canadian Arctic that shows surprising disparity in the group. The specimen includes partial upper and lower jaws, pharyngeal elements, a pectoral fin and scalation. This new genus is phylogenetically proximate to <jats:italic>T. roseae</jats:italic> and <jats:italic>E. watsoni</jats:italic> but evinces notable differences from both taxa and, indeed, other described tetrapodomorphs. Lacking processes, joint orientations and muscle scars indicative of appendage-based support on a hard substrate<jats:sup>13</jats:sup>, its pectoral fin shows specializations for swimming that are unlike those known from other sarcopterygians. This unexpected morphological and functional diversity represents a previously hidden ecological expansion, a secondary return to open water, near the origin of limbed vertebrates.</jats:p>