Browsing by Author "Schaafsma, Marije"

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Detecting and predicting forest degradation: a comparison of ground surveys and remote sensing in Tanzanian forests
(Plants, People, Planet (PPP), 2021-01-08) Ahrends, Antje; Bulling, Mark T.; Platts, Philip J.; Swetnam, Ruth; Ryan, Casey; Doggart, Nike; Hollingsworth, Peter M.; Marchant, Robert; Balmford, Andrew; Harris, David J.; Gross-Camp, Nicole; Sumbi, Peter; Munishi, Pantaleo; Madoffe, Seif; Mhoro, Boniface; Leonard, Charles; Bracebridge, Claire; Doody, Kathryn; Wilkins, Victoria; Owen, Nisha; Marshall, Andrew R.; Schaafsma, Marije; Pfliegner, Kerstin; Jones, Trevor; Robinson, James; Topp-Jørgensen, Elmer; Brink, Henry; Burgess, Neil D.
Tropical forest degradation is widely recognised as a driver of biodiversity loss and a major source of carbon emissions. However, in contrast to deforestation, more gradual changes from degradation are challenging to detect, quantify and monitor. Here, we present a field protocol for rapid, area-standardised quantifications of forest condition, which can also be implemented by non-specialists. Using the ex- ample of threatened high-biodiversity forests in Tanzania, we analyse and predict degradation based on this method. We also compare the field data to optical and radar remote-sensing datasets, thereby conducting a large-scale, independent test of the ability of these products to map degradation in East Africa from space. • Our field data consist of 551 ‘degradation’ transects collected between 1996 and 2010, covering >600 ha across 86 forests in the Eastern Arc Mountains and coastal forests. • Degradation was widespread, with over one-third of the study forests—mostly protected areas—having more than 10% of their trees cut. Commonly used opti- cal remote-sensing maps of complete tree cover loss only detected severe im- pacts (≥25% of trees cut), that is, a focus on remotely-sensed deforestation would have significantly underestimated carbon emissions and declines in forest quality. Radar-based maps detected even low impacts (<5% of trees cut) in ~90% of cases. The field data additionally differentiated types and drivers of harvesting, with spa- tial patterns suggesting that logging and charcoal production were mainly driven by demand from major cities. • Rapid degradation surveys and radar remote sensing can provide an early warning and guide appropriate conservation and policy responses. This is particularly im- portant in areas where forest degradation is more widespread than deforestation, such as in eastern and southern Africa.