Assessing the dendroclimatic potential of tropical tree species in northern Bolivia
The most biodiverse region in the world can be found in the tropical Andes (~5º-24ºS) between Venezuela and the Bolivian Altiplano, yet it is highly under-sampled in dendrochronology in part due to the prevalence of trees without rings (continuous growth) and the overall hyperdiversity of the ecosystems. The Madidi National Park (MNP) in northern Bolivia. (~14 ºS, -68°W) is a biodiversity hotspot with lowland rainforests and high montane environments that provide unique opportunities for tree-ring analyses. This study focuses on determining which climate factors limit radial growth, expressed by tree-ring width (TRW) data, in two tree species in the MNP: Juglans boliviana from a tropical wet forest (1400 m a.s.l.) and Polylepis pepei, a high elevation species (4400 m a.s.l.). To investigate the climate sensitivity of TRW, we conducted spatial analysis using mean monthly and daily temperature and precipitation data from nearby station and gridded reanalysis products for the period 1960-2015. We found that P. pepei TRW was influenced by precipitation during the onset of the austral summer wet season (November-December). This is different than the response of P. tarapacana from the southern Altiplano (prior-year growing season signal; see: Morales et al., 2012). The TRW variability in the J. boliviana chronology appears to have had a positive response to austral summer (DJF) temperature and precipitation since the 1970s. To our knowledge this is the first time that J. boliviana has been reported as suitable for dendrochronological studies. These newly developed chronologies in the northern altiplano are at least 150 years old and may be useful in a region where century-long climate data is not available.