Tropical forest canopies and their relationships with climate and disturbance： results from a global dataset of consistent field-based measurements

Background： Canopy structure, defined by leaf area index （LAI）, fractional vegetation cover （FCover） and fraction of absorbed photosynthetically active radiation （fAPAR）, regulates a wide range of forest functions and ecosystem services. Spatially consistent field-measurements of canopy structure are however lacking, particularly for the tropics. Methods： Here, we introduce the Global LAI database： a global dataset of field-based canopy structure measurements spanning tropical forests in four continents （Africa, Asia, Australia and the Americas）. We use these measurements to test for climate dependencies within and across continents, and to test for the potential of anthropogenic disturbance and forest protection to modulate those dependences. Results： Using data collected from 887 tropical forest plots, we show that maximum water deficit, defined across the most arid months of the year, is an important predictor of canopy structure, with all three canopy attributes declining significantly with increasing water deficit. Canopy attributes also increase with minimum temperature, and with the protection of forests according to both active （within protected areas） and passive measures （through topography）. Once protection and continent effects are accounted for, other anthropogenic measures （e.g. human population） do not improve the model. Conclusions： We conclude that canopy structure in the tropics is primarily a consequence of forest adaptation to the maximum water deficits historically experienced within a given region. Climate change, and in particular changes in drought regimes may thus affect forest structure and function, but forest protection may offer some resilience against this effect.

A Mega-Tsunami in the Baltic Sea 1171 BC: Geological Records with Special Reference to the Lake Mälaren Area in Sweden

At about 3000 C14-year BP or 1200 cal. yrs BC, the Baltic Sea experienced a mega-tsunami with a wave-height of 10 m or more, and a run-up height of up to 16.5 m. This event had significant geological and archaeological effects. We explore the records from the Lake M?laren area in Sweden. The tsunami event is linked to seismic ground shaking and methane venting tectonics at several sites. The triggering factor is proposed to be the Kaali meteor impact in Estonia of the same age. The documentation of a mega-tsunami in the middle of the Bronze Age has wide implications both in geology and in archaeology. The archaeological key sites at Annelund and Apalle are reinterpreted in terms of tsunami wave actions remodelling stratigraphy. By extensive coring, we are able to trace the tsunami effects in both off-shore and on-shore environment. At the time of the event, sea level was at +15 m (due to isostatic uplift). The tsunami wave erosion is traced 13.5 m below sea level. The tsunami run-up over land is traced to +29.5 m to +31.5 m (occasionally even higher), implying a run-up of 14.5 - 16.5 m. In ?ngermanland, the tsunami event was absolutely dated at 1171 varve years BC. Archaeologically, the tsunami event coincides well with the transition between Periods II and III of the South Scandinavian Bronze Age. Period III has traditionally been difficult to identify in the cultural materials of the Lake M?laren region.