Forest and woodland replacement patterns following drought-related mortality

Forest vulnerability to drought is expected to increase under anthropogenic climate change, and drought-induced mortality and community dynamics following drought have major ecological and societal impacts. Here, we show that tree mortality concomitant with drought has led to short-term (mean 5 y, range 1 to 23 y after mortality) vegetation-type conversion in multiple biomes across the world (131 sites). Self-replacement of the dominant tree species was only prevalent in 21% of the examined cases and forests and woodlands shifted to nonwoody vegetation in 10% of them. The ultimate temporal persistence of such changes remains unknown but, given the key role of biological legacies in long-term ecological succession, this emerging picture of postdrought ecological trajectories highlights the potential for major ecosystem reorganization in the coming decades. Community changes were less pronounced under wetter postmortality conditions. Replacement was also influenced by management intensity, and postdrought shrub dominance was higher when pathogens acted as codrivers of tree mortality. Early change in community composition indicates that forests dominated by mesic species generally shifted toward more xeric communities, with replacing tree and shrub species exhibiting drier bioclimatic optima and distribution ranges. However, shifts toward more mesic communities also occurred and multiple pathways of forest replacement were observed for some species. Drought characteristics, species-specific environmental preferences, plant traits, and ecosystem legacies govern post drought species turnover and subsequent ecological trajectories, with potential far-reaching implications for forest biodiversity and ecosystem services.Peer reviewe

Cambios en la porosidad edáfica bajo siembra directa por la introducción de raphanus sativus l. (nabo forrajero)

Los objetivos del trabajo fueron evaluar la capacidad del nabo forrajero (Raphanus sativus L.) para regenerar porosidad edáfica a corto plazo bajo siembra directa (SD) continua y explorar la factibilidad de introducirlo en la rotación agrícola predominante en la región Pampa Ondulada. Se ensayó el efecto del nabo sobre algunas propiedades físicas edáficas en un lote con bajo nivel de degradación (A). Luego, se evaluó su introducción a la rotación agrícola en un lote con alto nivel de degradación edáfica (B). Los tratamientos consistieron en nabo y testigo, con barbecho químico. En A, las raíces de nabo produjeron cambios en la porosidad mayor a 30 mm de los horizontes A y BA que mejoraron la circulación del agua. En B, el nabo redujo la porosidad total del horizonte A, amortiguó el efecto degradante de las lluvias sobre la macroporosidad y la porosidad estructural del horizonte BA e incrementó un 70% la estabilidad estructural a 0-5 cm (efecto de corta duración). La introducción de nabo a la rotación se presenta como una alternativa viable para contribuir al desarrollo de sistemas sustentables bajo SD continu

Host spatial structure and disperser activity determine mistletoe infection patterns

What processes and factors are responsible for species distribution are long-standing questions in ecology and a key element for conservation and management. Mistletoes provide the opportunity to study a forest species whose occurrence is expected to be constrained by multiple factors as a consequence of their life form. We studied the mistletoe Tristerix corymbosus (Loranthaceae) on its most common hosts species in northwest Patagonia. The seeds of this mistletoe are almost exclusively dispersed by the small arboreal and endemic marsupial Dromiciops gliroides (Microbiotheridae). We assessed the underlying causes of plant spatial patterns through point pattern analysis and we used different variables that characterize the neighborhood around each host to analyze the relative effect of host availability, potential for disperser movement and canopy light conditions. We found that potential hosts were strongly aggregated and that the three most common host species were distributed independent of each other. Considering all host species together, infected and non-infected host were individually aggregated but segregated from each other. The aggregated pattern of infected hosts could be explained in part by the template of potential hosts distribution, but was subsequently modulated by the activity of the mistletoe disperser. Potential for disperser movement, the proximity to reproductive mistletoes and habitat complexity, increased mistletoe infection probability. However, neighboring host availability decreased mistletoe infection probability, and tree DBH (used as surrogate for light conditions) had no detectable effect. Our results suggested that the distribution of mistletoe infection was determined by the structure of potential host populations and by the marsupial disperser activity. Compared to bird dispersed mistletoes, the scale of the infection was smaller and the proximity to reproductive mistletoes and habitat complexity were important for seed arrival and infection. The interplay between landscape structure and disperser activity determine the spatial structure of mistletoe future generations