Natalia Hoyos

Este trabajo presenta el perfil de Gerardo Botero Arango (1911-1986) desde sus múltiples facetas como científico, docente, ingeniero, colega, amigo y miembro de familia, a partir de su correspondencia académica y personal, así como de recuerdos de su familia más cercana, en conmemoración de los 60 años de la publicación de su trabajo “Contribución al conocimiento de la geología de la zona central de Antioquia” (Botero, 1963). A pesar de que su educación formal fue la de ingeniero civil y de minas, sus intereses científicos abarcaron diversas ramas de las ciencias naturales, tales como la paleontología, estratigrafía, petrografía y geología regional, investigaciones que publicó a lo largo de medio siglo (1934-1983) con colegas nacionales y extranjeros. Tanto en su faceta profesional como en su trato personal se destacan su visión, conocimiento, pragmatismo y rectitud inquebrantable, enmarcados en una personalidad alejada de toda búsqueda de protagonismo.

Aim: Multiple abiotic and biotic factors, mainly the amount and seasonality of precipitation, fire regime, soil properties and species adaptation strategies, have been invoked to explain the existence of the tropical savanna–humid forest transition. We explored the rainfall variables that influence the probability of forest or savanna occurring in north‐west South America, specifically monthly precipitation and the mean and maximum duration of wet and dry spells, defined as the number of consecutive wet (dry) days.Location: North‐west South America.Time period: 1980–2017.Major taxa studied: Savanna and humid forest.Methods: We used a set of logistic generalized linear models to assess the effect of multiple variables on the probability of occurrence of forest. Predictor variables included monthly precipitation, mean monthly dry and wet spells and maximum monthly dry and wet spells.Results: The probability of forest (savanna) occurrence depends mostly on the average duration of dry and wet spells and the interaction between these two variables, whereas the effect of total monthly precipitation is marginal. Dry spell duration had the largest effect on the probability of forest occurrence, which decreased by 7.5% for each additional consecutive dry day. For wet spells, the probability of forest occurrence increased by 4.1% for each additional consecutive wet day. Our model shows that the savanna–forest transition takes place under an average combination of dry spells lasting 8–10 days and wet spells lasting 1–3 days during the dry season (December–February). This combination changes to dry spells lasting 1–3 days and wet spells lasting 4–6 days during the wet season (May–July).Main conclusions: This study reveals the importance of using precipitation data with a fine temporal scale to investigate forest–savanna distribution and indicates the limited explanatory power of aggregated precipitation variables (e.g., monthly and annual values). Models that assess the effect of climate change should therefore incorporate precipitation variables acquired at finer temporal resolution.

Dry biomes occupy ~35% of the landscape in the Neotropics, but these are heavily human‐disturbed. In spite of their importance, we still do not fully understand their origins and how they are sustained. The Guajira Peninsula in northern Colombia is dominated by dry biomes and has a rich Neogene fossil record. Here, we have analyzed its changes in vegetation and precipitation during the Neogene using a fossil pollen and spore dataset of 20 samples taken from a well and we also dated the stratigraphic sequence using microfossils. In addition, we analyzed the pollen and spore contents of 10 Holocene samples to establish a modern baseline for comparison with the Neogene as well as a study of the modern vegetation to assess both its spatial distribution and anthropic disturbances during the initial stages of European colonization. The section was dated to span from the latest Oligocene to the early Miocene (~24.2 to 17.3 Ma), with the Oligocene/Miocene boundary being in the lower Uitpa Formation. The early Miocene vegetation is dominated by a rainforest biome with a mean annual precipitation of ~2,000 mm/yr, which strongly contrasts with Guajira's modern xerophytic vegetation and a precipitation of ~300 mm/yr. The shift to the dry modern vegetation probably occurred over the past three millions years, but the mechanism that led to this change is still uncertain. Global circulation models that include the vegetation could explain the ancient climate of Guajira, but further work is required to assess the feedbacks of vegetation, precipitation, and CO₂.