Impacts of climate and drought on tree radial growth in Neotropical dry forestsScaling up from short to long time-scales = Impactos del clima y las sequías en el crecimiento radial de los árboles en los bosques secos Neotropicales: Evaluación de sus efectos a diferentes escalas temporales

Resumen

This thesis analyzed the dynamics of tree radial growth at different tlrne-scales In relation to cllmate and drought in two tropical dry forests (TDFs) from ' Colombia (Tulua) and Bolivia (JNPA). The specific objectives were: (I) To assess Intra -annual patterns of radia l growth (radial-Increment dynamics and xylogenesls) In ten coexisting tree species from Tu lua and INPA and determine thelr relatjonshlp with climate and leaf phenology. (ii) To analyze the effects of climate and drought on long-term radial growth at different time-scales using dendrochronology in seven coexisting deciduous tree species from INPA. (Iii) To evaluate the long-term radial growth responses to changes In climate water balance and determine their relat10 11shlp with sapwood density in seven coexisting deciduous tree species from INPA. At Intra-annual scales It was found that: (i) cambium reactivation and xylem growtl1 of tree species occurred during the wet season, reflecting the influence of high precipltatfon and a positive water balance on the development of new xylem cells. (ii) In the semi-deciduous tree species from Tu lua the xylem growth period overlapped with the wet season, whereas, In the deciduous tree specJes from INPA, the growth period started at the mid ·wet season, when the tree crowns were fully developed. (Ill') Temperatu re, as a determinant factor in the hourly fluctuations of both the vapor pressure deficit (VPD) and the evapotranspiratlon rate, could exert a huge Influence on tree radial growth dynamics during the growing seasoh. In Tulua, the growing season was particularly associated with low temperatures and hence low VPD, while In INPA the growing season was related to high temperatures and VPD. Nevertheless, the high temperatures registered throughout the day at both TDFs negatively affected radial increment at hourly scales. Tree species could face the adverse dry conditions by restricting growth to periods of the day when temperatures are low. (Iv) Stem shrinkage and swelling occurred at hourly to dally scales In all tree spec es, and most INPA tree species registered strong reversible shrin kage at monthly scales. Particularly, the climate controls on radial-Increment dynamics varied between daily and monthly scales. At dally scales, there was a positive effect of high precipitation and positive water balance and a negative effect of VPD on the Increment phase, while at monthly scales the precipitation was the main variable qffectlng radial Increment positively. At Inter-annual scales It was found that: (I) The tree radial growth showed a positive relationship with precipitation and climate water balance and a negative association wi th temperature, indicating that the tree species studied share high common growth variability in response to local climate. Nevertheless, the strongest response of growth to climate was species-specific, Indicating that there was a differential sensitivity among tree species to these climate variables. (II) The radial growth of all tree species responded positively to water balance during the wet season, but such responses differed among species as a function of their stem sapwood density. Speciflcally, sapwood density was negatively related to growth variability explained by water balance. Tree species with lowdensity wood and high production of sapwood were the most sensitive to water balance, whereas species with the opposite characteristics were the least sensitive ones. (Ill) Tree species tolerated short-term droughts wl1lle they were partlcularly sensitive to long-lasting droughts. This Indicates that tree species from the INPA site are predominantly sensitive in terms of growth red uction to long-lasting droughts. The most temperature -sensitive tree species, also showed the highest growth sensitivity to long-lasting droughts. In contrast, growth of tt,e tree species with the lowest sensitivi ty to water balance, did not respond to longterm drougl1t varlablllty.