Fragmentation of tropical forests a forgotten process in the global carbon cycle?

Transcription

1 Fragmentation of tropical forests a forgotten process in the global carbon cycle? A. Huth 1,2, K. Brinck 1,3, R. Fischer 1, J. Groeneveld 1, S. Puetz 1 1 Helmholtz Centre for Environmental Research, Leipzig, Germany 2 University of Osnabrück, Germany 3 University of California, Berkeley

2 Overview 1. Global forests what do we know? 2. Fragmentation in the tropics 3. Analysis of fragmentation

3 Forests of the world forests cover 30 % of the terrestrial surface (0.5 ha forest per person) tropical forests (50 %), boreal (30 %) and temperate (20 %) around tree species (Fine & Ree 2006, Am Nat)

4 Forests in the global carbon cycle yr ppm 1.1 ± 0.8 2/27/ ± ± 0.7 pools in Gt C, flows in Gt C/yr current increase of carbon in the atmosphere: 4 Gt C per year different estimates for vegetation biomass e.g Gt carbon (atmosphere: 830 Gt C) Carbon is mainly stored in forests (tropical forests 50% / temperate 25 %). emissions by deforestation around 1.1 Gt per years (e.g. Houghton 2012, Biogeosciences) Harris et al. 2012, Science; Pan et al. 2011, Science; Peters 2011, Nature Climate Change; Le Quéré et al Nature Geos.; IPCC 2007; Figure Grace 2004, J. Ecol. modified

5 Deforestation of tropical forests Amazonas rain forest

6 Fragmentation of tropical forests core area of the forest cleared area edge area of the forest

7 Fragmentation of tropical forests Fragmentation changes dynamics of forests in the edge area: altered microclimate (e.g wind, temperature) Laurance 2000, TREE higher tree mortality, less biomass Laurance et al. 1997, Science, 2000, Nature altered species composition Laurance et al. 2006, PNAS depth d of edge area: between m Fragmentation experiments: Amazon Laurance 2008, Conserv Biol Borneo Ewers 2011, Phil Trans R So. B Kansas Robinson, Holt, Science 1992 Tollefson 2013, Nature fragmentation experiment Amazon, Laurance 2011 Biol Cons (photo: Smithsonian Tropical Research Institute)

8 Edge effects in tropical forests edge area edge depth d Laurence 2008, 2002 Biol Cons

9 Fragmentation of tropical forests biomass losses over time can be quantified by forest models (Groeneveld 2009, Ecol Model, Puetz 2010 Ecol Model) carbon losses of small fragments are higher due to large fraction of edge area increase of losses if additional disturbances occur (e.g. logging) (Puetz/ Huth 2014 in prep) Biomass [t ODM / ha] biomass losses Forest fragments Non-fragmented forest Fragment size [ha] N-f Puetz/Huth 2010 Ecol Model

10 Analysis of vegetation cover by remote sensing Satellites with optical sensors: Envisat MERIS Launched: by European Space Agency (ESA) spectral range: 0,2 μm 1,040 μm every 3 days spatial resolution: 300 m Map of vegetation types: GlobCover2009 (Bontemps, Defourny, Van Bogaert, Arino, Kalogirou, Perez 2011) similar measurements by MODIS (Nasa, e.g. Zhao & Running 2010, Science)

11 Analysis of fragmentation of tropical forests tropical forest no tropical forest GlobCover 2009 land cover map, ESA

12 Forest fragment counting in total: > 2,000,000 tropical forest fragments mean fragment size: 550 ha many small fragments and a few large ones three largest fragments (63% of forested area) (Amazon River Basin Congo rainforest Borneo Island)

13 Edge and core area of forest fragments total tropical forested area Assuming edge depth = 100 m: Total edge area: 111 million ha 10% of the total forested area Anthropogenic edge area: 93 billion ha 8% of the total forested area (84% of the total edge area) Page 13

14 Carbon losses from forest fragments edge area total carbon stock in tropical forested area: 183 Gt C (estimate based on forest area, Globcover 2009 Envisat, correspond to estimate from Pan 2011, Science, and Wright 2010, Am N Y Acad Sci) carbon stock in anthropogenic edge area (d = 100m): 15 Gt C based on field studies losses can be ε = (e.g. Laraunce 1997 Science, 1998 For Ecol Man, Dantas 2011 Trop Cons Sci) estimated total carbon losses in the forest edge area (ε =0.5): 7.7 Gt C (18.3 for d=300 m) edge depth d d = edge depth [m] ε = fraction of lost carbon [] d = 100m ε = 0.5 Page 14

15 Carbon losses from forest fragments estimated carbon losses from tropical forest fragmentation [t/ha] Asia & Australia Asia & Australia

16 Carbon losses from fragmentation ε = 0.5 d = 100 estimated carbon losses from tropical forest fragmentation [t/ha]

17 Conclusion Analysis of the tropical forest fragmentation using the GlobCover 2009 map of ESA (Envisat; 300 m resolution) 10 % of tropical forested area lies within 100 m of forest edges fragment size distribution follows a power law at all continents higher mortality of trees in the edge area causes additional carbon emission in the order 0.25 Gt C / yr fragmentation of tropical forest substantially contributes to carbon losses, until now this process is not included in the global carbon balance SEITE 17