Anthropogenic activities dominated tropical forest carbon balance in two contrary ways over the Greater Mekong Subregion in the 21st century.

The tropical forest carbon (C) balance threatened by extensive socio-economic development in the Greater Mekong Subregion (GMS) in Asia is a notable data gap and remains contentious. Here we generated a long-term spatially quantified assessment of changes in forests and C stocks from 1999 to 2019 at a spatial resolution of 30 m, based on multiple streams of state-of-the-art high-resolution satellite imagery and in situ observations. Our results show that (i) about 0.54 million square kilometers (21.0% of the region) experienced forest cover transitions with a net increase in forest cover by 4.3% (0.11 million square kilometers, equivalent to 0.31 petagram of C [Pg C] stocks); (ii) forest losses mainly in Cambodia, Thailand, and in the south of Vietnam, were also counteracted by forest gains in China due mainly to afforestation; and (iii) at the national level during the study period an increase in both C stocks and C sequestration (net C gain of 0.087 Pg C) in China from new plantation, offset anthropogenetic emissions (net C loss of 0.074 Pg C) mainly in Cambodia and Thailand from deforestation. Political, social, and economic factors significantly influenced forest cover change and C sequestration in the GMS, positively in China while negatively in other countries, especially in Cambodia and Thailand. These findings have implications on national strategies for climate change mitigation and adaptation in other hotspots of tropical forests.

Determination of tropical deforestation rates and related carbon losses from 1990 to 2010.

We estimate changes in forest cover (deforestation and forest regrowth) in the tropics for the two last decades (1990-2000 and 2000-2010) based on a sample of 4000 units of 10 ×10 km size. Forest cover is interpreted from satellite imagery at 30 × 30 m resolution. Forest cover changes are then combined with pan-tropical biomass maps to estimate carbon losses. We show that there was a gross loss of tropical forests of 8.0 million ha yr(-1) in the 1990s and 7.6 million ha yr(-1) in the 2000s (0.49% annual rate), with no statistically significant difference. Humid forests account for 64% of the total forest cover in 2010 and 54% of the net forest loss during second study decade. Losses of forest cover and Other Wooded Land (OWL) cover result in estimates of carbon losses which are similar for 1990s and 2000s at 887 MtC yr(-1) (range: 646-1238) and 880 MtC yr(-1) (range: 602-1237) respectively, with humid regions contributing two-thirds. The estimates of forest area changes have small statistical standard errors due to large sample size. We also reduce uncertainties of previous estimates of carbon losses and removals. Our estimates of forest area change are significantly lower as compared to national survey data. We reconcile recent low estimates of carbon emissions from tropical deforestation for early 2000s and show that carbon loss rates did not change between the two last decades. Carbon losses from deforestation represent circa 10% of Carbon emissions from fossil fuel combustion and cement production during the last decade (2000-2010). Our estimates of annual removals of carbon from forest regrowth at 115 MtC yr(-1) (range: 61-168) and 97 MtC yr(-1) (53-141) for the 1990s and 2000s respectively are five to fifteen times lower than earlier published estimates.

Modeling landslide activity and sediment connectivity after eruptions: Insights from the Blanco River (Chile).

Volcanic eruptions can disrupt entire river basins by affecting the hydro-geomorphic characteristics of channel networks and hillslopes. Reports suggest a pulsed and delayed increase in landslide activity following the eruptions, which, depending on the degree of linkage between hillslopes and channels, i.e. sediment connectivity, can represent a massive source of sediment input for the fluvial system. Therefore, predicting landslide occurrence and sediment connectivity is fundamental for management risk strategies, especially in such dynamic and complex environments. The aim of this work is to develop and offer a more reliable approach to map the areas susceptible to landslides and connected to the active channel in a catchment impacted by volcanic eruption. The analyses were carried out in the Blanco River catchment in southern Chile, affected by the Chaitén eruption (2008-09). A combined approach is presented, based on landslide susceptibility models, carried out multi-temporally (from 2010 to 2019), and a threshold-based sediment connectivity map. The results showed that the highest landslide occurrence was reported 4 years after the eruption, whereas the faster increase in the overall area affected was observed only after 7 years. Landslide susceptibility models showed high accuracy when applied in the same year, but were less accurate in predicting future occurrences. This result is ascribed to the dynamic conditions of the vegetation, regenerating quickly after the mass movements. Nevertheless, considering the potential sources of error, the combined landslide susceptibility-connectivity map for the year 2019 well-identified relevant areas for catchment management. The largest part of the catchment was found non-susceptible and disconnected, while areas classified as susceptible and connected represent only 3.1 %. The application of this novel approach allowed to unravel the geomorphic trajectory of the study area and, more importantly, can represent a benchmark for future applications in other catchments affected by large disturbances.