TRENCH (Tree-Ring Environmental Network for Climate Change Monitoring): Entwicklung eines Jahrring-basierten Indikatorsystems für Auswirkungen von Umweltveränderungen auf Waldökosysteme in Südecuador

• Applicant: Professor Dr. Achim Bräuning
• Subject Area: Physical Geography ; Ecology and Biodiversity of Plants and Ecosystems
• Term: from 2013 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 227672301

• Final Report Year: 2019

Final Report Abstract

Within the project, most of the envisaged objectives have been accomplished. We established a tree growth monitoring network including different forest ecosystems and elevation belts. A comparison of stem diameter variations of different tree functional types to drought events revealed a specific response to climatic extreme events. As a result, sensitive climate indicator species for each forest ecosystem were identified. For the first time, tropical humid mountain rainforest species proved to be sensitive to short-term dry events, with an increasing sensitivity with increasing length of the drought event. Based on different recovery times after short-term droughts, we also identified tree species that might suffer from increased drought frequency or intensity and hence might be endangered under future climatic conditions. In the dry tropical forest of Laipuna, the hot lower elevation belt is more sensitive to climate warming by increasing vapor pressure deficit and shorter growing season than more humid higher elevation belts, if temperature will further increase. Initial stable oxygen and tree-ring width analyses of tropical dry forest tree species indicated a strong moisture control of the Pacific ENSO system on forest ecosystems in southeastern Ecuador (Tumbesian dry forests), although these analyses need further substantiation by additional measurements which are under way. Stable carbon analyses of fertilized rainforest trees indicated increasing water use efficiency, probably caused by and extended leaf area and modified wood anatomy. Stable oxygen isotope analyses revealed large-scale homogenous responses of tree-ring cellulose in mountain rainforest tree species with different proxy archives surrounding the Amazon basin, with a general sensitivity of δ18O variations to available moisture sources. Although some final analyses are still pending, the project results confirmed that a combination of selected word parameters from sensitive tree species of different ecological forest types in southern Ecuador can be meaningfully combined to establish an indicator network for climatic responses of forest ecosystems across elevation belts and climatic gradients.

Publications

• (2015): Wet season precipitation during the past 120 years reconstructed from tree rings of a tropical dry forest in Southern Ecuador. Global and Planetary Change. 133: 65–78
  Darwin Pucha Cofrep, Peters, T., Bräuning, A.
  
• (2016). Nutrient-induced modifications of wood anatomical traits of Alchornea lojaensis (Euphorbiaceae). Frontiers in Earth Science 4:50
  Spannl S, Homeier J and Bräuning A
  
• (2016): Climate seasonality limits carbon assimilation and storage in tropical forests. Biogeosciences, 13, 2537–2562
  Wagner, F.H. and 98 co-authors (... A. Bräuning, Hector Maza Chamba, Susanne Spannl, Franziska Volland)
  
• (2016): Climate variability, tree increment patterns and ENSO-related carbon sequestration reduction of the tropical dry forest species Loxopterygium huasango of Southern Ecuador. Trees - Structure and Function 30: 1245–1258
  Spannl, S., Volland, F., Pucha, D., Peters, T., Bräuning, A.
  
• (2016): Hydro-climatic variability in Southern Ecuador from tree-ring oxygen isotopes. Erdkunde 70: 69-82
  Volland, F., Pucha, D., Bräuning, A.
  
• (2016): Standard or modern techniques? Combination of common microscopic techniques and X-ray microtomography for wood anatomical analyses. TRACE 14: 149-153
  Spannl, S., Bräuning, A.
  
• (2016): Tree responses to moisture fluctuations in a neotropical tropical dry forest. Ecological Indicators
  Butz, P., Raffelsbauer, V., Graefe, S., Peters, T., Cueva, E., Hölscher, D., Bräuning, A.
  
• (2017): Stable oxygen isotope series in tropical trees – how much is enough to represent a robust signal? TRACE 15, 120-125
  Bräuning, A., Volland, F., Pucha, A.D.
  
• (2019): Tree circumference changes and species-specific growth recovery after extreme dry events in a montane rainforest in southern Ecuador. Frontiers in Plant Science 10, Article 342
  Raffelsbauer, V, Spannl, S., Peña, K, Pucha-Cofrep, D.A., Steppe, K. Bräuning, A.