Flood-pulse disturbances as a threat for long-living Amazonian trees

Abstract

The long-living tree species Eschweilera tenuifolia (O. Berg) Miers (Lecythidaceae) is characteristic to oligotrophic floodplain forests (igapo) influenced by a regular and predictable flood-pulse. This species preferentially occurs at macrohabitats flooded up to 10 months per year forming monodominant stands. We aimed to analyze the growth and mortality patterns of this species under pristine conditions (Jau National Park-JNP) and in an impacted igapo (Uatuma Sustainable Development Reserve-USDR) where the downstream flood-pulse disturbance occasioned by the Balbina hydroelectric plant caused massive mortality of this species. Using a total of 91 trees (62 living and 29 dead) at the USDR and 52 (31 living and 21 dead) from JNP, we analyzed age-diameter relationships, mean passage time through 5-cm diameter classes, growth change patterns, growth ratios, clustering of mean diameter increment (MDI), and dated the year of death from each individual using radiocarbon (14C) analysis. Growth and mortality patterns were then related to climatic or anthropogenic disturbances. Our results show similar structural parameters for both studied populations regarding the estimated maximum ages of 466 years (JNP) and 498 years (USDR) and MDI, except for one single tree at the USDR with an estimated age of 820 yrs. Living trees from JNP showed distinctly altered growth after 1975, probably related to consecutive years of high annual minimum water levels. Tree mortality in the JNP occurred during different periods, probably induced by extreme hydroclimatic events. At the USDR changes in growth and mortality patterns occurred after 1983, when the Balbina dam construction started. Despite being one of the best flood-adapted tree species, E. tenuifolia seems to be sensitive to both, long-lasting dry and wet periods induced by climatic or anthropogenic disturbances or resulting synergies among both. Even more than 30 years after the start of disturbances at the USDR, the flood-pulse alteration continues affecting both mortality and growth of this species which can potentially cause regional extinction.