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Land cover change and carbon emissions over 100 years in an African biodiversity hotspot

Land cover change and carbon emissions over 100 years in an African biodiversity hotspot
Land cover change and carbon emissions over 100 years in an African biodiversity hotspot
Agricultural expansion has resulted in both land use and land cover change (LULCC) across the tropics. However, the spatial and temporal patterns of such change and their resulting impacts are poorly understood, particularly for the pre-satellite era. Here we quantify the LULCC history across the 33.9 million ha watershed of Tanzania's Eastern Arc Mountains, using geo-referenced and digitised historical land cover maps (dated 1908, 1923, 1949 and 2000). Our time series from this biodiversity hotspot shows that forest and savanna area both declined, by 74% (2.8 million ha) and 10% (2.9 million ha), respectively, between 1908 and 2000. This vegetation was replaced by a five-fold increase in cropland, from 1.2 million ha to 6.7 million ha. This LULCC implies a committed release of 0.9 Pg C (95% CI: 0.4-1.5) across the watershed for the same period, equivalent to 0.3 Mg C ha?1 yr?1. This is at least three-fold higher than previous estimates from global models for the same study area. We then used the LULCC data from before and after protected area creation, as well as from areas where no protection was established, to analyse the effectiveness of legal protection on land cover change despite the underlying spatial variation in protected areas. We found that, between 1949 and 2000, forest expanded within legally protected areas, resulting in carbon uptake of 4.8 (3.8-5.7) Mg C ha?1, compared to a committed loss of 11.9 (7.2-16.6) Mg C ha?1 within areas lacking such protection. Furthermore, for nine protected areas where LULCC data is available prior to and following establishment, we show that protection reduces deforestation rates by 150% relative to unprotected portions of the watershed. Our results highlight that considerable LULCC occurred prior to the satellite era, thus other data sources are required to better understand long-term land cover trends in the tropics.
afforestation, deforestation, land use change, protected area, reforestation, carbon, emission, ecosystem service
1354-1013
1-38
Willcock, Simon
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Phillips, Oliver L.
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Platts, Philip J.
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Swetnam, Ruth D.
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Balmford, Andrew
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Burgess, Neil D.
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Ahrends, Antje
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Bayliss, Julian
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Doggart, Nike
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Doody, Kathryn
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Fanning, Eibleis
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Green, Jonathan M.H.
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Hall, Jaclyn
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Howell, Kim L.
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Lovett, Jon C.
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Marchant, Rob
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Marshall, Andrew R.
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Mbilinyi, Boniface
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Munishi, Pantaleon K.T.
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Owen, Nisha
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Topp-Jorgensen, Elmer J.
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Lewis, Simon L.
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Willcock, Simon
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Phillips, Oliver L.
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Platts, Philip J.
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Swetnam, Ruth D.
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Balmford, Andrew
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Burgess, Neil D.
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Ahrends, Antje
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Bayliss, Julian
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Doggart, Nike
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Doody, Kathryn
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Fanning, Eibleis
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Green, Jonathan M.H.
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Hall, Jaclyn
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Howell, Kim L.
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Lovett, Jon C.
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Marchant, Rob
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Marshall, Andrew R.
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Mbilinyi, Boniface
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Munishi, Pantaleon K.T.
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Owen, Nisha
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Topp-Jorgensen, Elmer J.
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Lewis, Simon L.
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Willcock, Simon, Phillips, Oliver L., Platts, Philip J., Swetnam, Ruth D., Balmford, Andrew, Burgess, Neil D., Ahrends, Antje, Bayliss, Julian, Doggart, Nike, Doody, Kathryn, Fanning, Eibleis, Green, Jonathan M.H., Hall, Jaclyn, Howell, Kim L., Lovett, Jon C., Marchant, Rob, Marshall, Andrew R., Mbilinyi, Boniface, Munishi, Pantaleon K.T., Owen, Nisha, Topp-Jorgensen, Elmer J. and Lewis, Simon L. (2016) Land cover change and carbon emissions over 100 years in an African biodiversity hotspot. Global Change Biology, 1-38. (doi:10.1111/gcb.13218).

Record type: Article

Abstract

Agricultural expansion has resulted in both land use and land cover change (LULCC) across the tropics. However, the spatial and temporal patterns of such change and their resulting impacts are poorly understood, particularly for the pre-satellite era. Here we quantify the LULCC history across the 33.9 million ha watershed of Tanzania's Eastern Arc Mountains, using geo-referenced and digitised historical land cover maps (dated 1908, 1923, 1949 and 2000). Our time series from this biodiversity hotspot shows that forest and savanna area both declined, by 74% (2.8 million ha) and 10% (2.9 million ha), respectively, between 1908 and 2000. This vegetation was replaced by a five-fold increase in cropland, from 1.2 million ha to 6.7 million ha. This LULCC implies a committed release of 0.9 Pg C (95% CI: 0.4-1.5) across the watershed for the same period, equivalent to 0.3 Mg C ha?1 yr?1. This is at least three-fold higher than previous estimates from global models for the same study area. We then used the LULCC data from before and after protected area creation, as well as from areas where no protection was established, to analyse the effectiveness of legal protection on land cover change despite the underlying spatial variation in protected areas. We found that, between 1949 and 2000, forest expanded within legally protected areas, resulting in carbon uptake of 4.8 (3.8-5.7) Mg C ha?1, compared to a committed loss of 11.9 (7.2-16.6) Mg C ha?1 within areas lacking such protection. Furthermore, for nine protected areas where LULCC data is available prior to and following establishment, we show that protection reduces deforestation rates by 150% relative to unprotected portions of the watershed. Our results highlight that considerable LULCC occurred prior to the satellite era, thus other data sources are required to better understand long-term land cover trends in the tropics.

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Willcock_etal_2015_GCB_2_revised_final.docx - Accepted Manuscript
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Accepted/In Press date: 14 December 2015
e-pub ahead of print date: 8 January 2016
Keywords: afforestation, deforestation, land use change, protected area, reforestation, carbon, emission, ecosystem service
Organisations: Centre for Biological Sciences

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Local EPrints ID: 385817
URI: http://eprints.soton.ac.uk/id/eprint/385817
ISSN: 1354-1013
PURE UUID: 46579d6e-e187-454f-bddc-6c8b647e612d

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Date deposited: 25 Jan 2016 09:50
Last modified: 16 Dec 2019 20:09

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Contributors

Author: Simon Willcock
Author: Oliver L. Phillips
Author: Philip J. Platts
Author: Ruth D. Swetnam
Author: Andrew Balmford
Author: Neil D. Burgess
Author: Antje Ahrends
Author: Julian Bayliss
Author: Nike Doggart
Author: Kathryn Doody
Author: Eibleis Fanning
Author: Jonathan M.H. Green
Author: Jaclyn Hall
Author: Kim L. Howell
Author: Jon C. Lovett
Author: Rob Marchant
Author: Andrew R. Marshall
Author: Boniface Mbilinyi
Author: Pantaleon K.T. Munishi
Author: Nisha Owen
Author: Elmer J. Topp-Jorgensen
Author: Simon L. Lewis

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