Mapping Deforestation of the Brazilian state of Tocantins

(2001-2013)Ricardo Aguilar, Dr. Matthew Hansen, Dr. Peter Potapov, Dr. Alexandra Tyukavina

BSOS SRI 2015

IntroductionAccuracy assessments of maps generated using automated classification algorithms are important ways to ensure reliable information. The

assessment of the Brazilian state of Tocantins’ deforestation maps generated by the Brazilian National Institute for Space Research (Amazon

Deforestation Monitoring Project or PRODES map) and the University of Maryland Global Forest Watch (GFW map) is important to better

understand the current trends in forest cover dynamics, its underlying drivers, and implications for the ecosystem services, including climate

regulation, and to perform better socio-economic analyses of the area. Main sources of livelihood for the state include raising cattle and

growing crops such as corn and soy beans. In order to conduct an accuracy assessment for Tocantins, a total of 685 samples were selected

using simple random sampling. Each sample covered a total of 900 square meters. For each of the 685 samples, a set of annual Landsat cloud-

free mosaics were created. Each of the samples was visually interpreted for change and the findings were recorded and classified by loss cause,

year, and forest type.

Sources of DataAll the data used for this analysis was provided by the Department of

Geographical Sciences and Dr. Matthew Hansen’s lab. PRODES forest

change data was obtained through the official Brazilian forest loss

report.

Analysis

Once visual interpretation was completed and the samples belonging to Cerrado were excluded, the

changes in samples were categorized by year, cause of change, and forest type and results were compared

to PRODES and GFW change. The following steps were used to calculate area:

• Proportion (by class) of the total area was calculated using: 𝑃+𝑘 =𝑛+𝑘

𝑛(Stehman, 2013)

Where: 𝑃+𝑘 is the proportion of the total area (by class),

𝑛+𝑘 is the total number of samples per class (+𝑘), and

𝑛 is the total number of samples analyzed (219)

• The proportion was multiplied by the estimated studied area which was determined with the following

equation:

𝐴𝑟𝑒𝑎 = 𝑡𝑜𝑡𝑎𝑙 𝑠𝑎𝑚𝑝𝑙𝑒𝑑 𝑎𝑟𝑒𝑎𝑎𝑟𝑒𝑎 𝑤𝑖𝑡ℎ𝑖𝑛 𝑡ℎ𝑒 𝑇𝑟𝑜𝑝𝑖𝑐𝑎𝑛 𝑎𝑛𝑑 𝑆𝑢𝑏𝑡𝑟𝑜𝑝𝑖𝑐𝑎𝑙 𝑀𝑜𝑖𝑠𝑡 𝐵𝑟𝑜𝑎𝑑𝑙𝑒𝑎𝑓 𝐹𝑜𝑟𝑒𝑠𝑡

𝑇𝑜𝑡𝑎𝑙 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑇𝑜𝑐𝑎𝑛𝑡𝑖𝑛𝑠• Samples located on the boundary of forest and non-forest areas were counted as 0.5 when calculating

proportions.

MethodIn order to determine change, the samples were examined using

elements of visual interpretation. The samples were scrutinized to

determine if loss of forest was present by looking for changes in tone,

shape, pattern and texture. In order to help with interpretation, high

resolution imagery on Google Earth was used to better examine the

area. In some cases, pictures from Panoramio or Google Street View

imagery were used to determine what the samples were converted to.

• Following interpretation, an ArcMAP layer was created, containing

all the points, and all the information gathered during the visual

interpretation.

• Another mask which had biomes information was created using

data from the Olson et al. (2001) Terrestrial Ecoregions of the

World publication at the World Wide Fund for Nature (WWF).

• Using the Mask, all the samples belonging to the Cerrado

Woodlands and Savannas were eliminated, due to conflicts with

data presented on the PRODES map.

• In addition, a raster layer containing change information in the

GFW map within the Tropical and Subtropical Moist Broadleaf

Forest biome was created.

• All the data from the two newly created layers was exported into

Microsoft Excel to be further analyzed.

• The area of forest loss was calculated in km2 for the GFW map.

This is a raster layer; each pixel represented an area of 900 m2.

DiscussionWe found significant differences between the

analysis performed and the data from PRODES

and GFW maps. Some of the sources behind these

differences:

• Sampling (current study) vs. wall-to-wall

mapping (PRODES, GFW)

• PRODES only maps forest loss within primary

forests

• PRODES definition of what constitutes

primary forest is different from the current

analysis (Minimal Mapping Unit of Primary

forest in PRODES is 6.25 ha)

The results revealed that 82% of the forest

clearing was done to make space for pastures

which is not surprising given Tocantins’ heavy

reliance on cattle for its economy. A significant

amount of land was dedicated to agriculture (5%).

Land dedicated for dam construction accounted

for 11% of the clearing, however, this proportion

may be a statistical aberration due to the number

of samples used.

ReferencesHansen, M.C., Potapov, P.V., Moore, R., Hancher, M., Turubanova, S.A.,

Tyukavina, A., Thau, D., Stehman, S.V., Goetz, S.J, Loveland, T.R.,

Kommareddy, A., Egorov, A., Chini, L., Justice, C.O., Townhend, J.R.G. 2013.

High-Resolution Global Maps of 21st-Century Forest Cover Change. Science

850-853.

Olson, D. M., Dinerstein, E., Wikramanayake, E. D., Burgess, N. D., Powell, G.

V. N., Underwood, E. C., D'Amico, J. A., Itoua, I., Strand, H. E., Morrison, J. C.,

Loucks, C. J., Allnutt, T. F., Ricketts, T. H., Kura, Y., Lamoreux, J. F., Wettengel,

W. W., Hedao, P., Kassem, K. R. 2001. Terrestrial ecoregions of the world: a

new map of life on Earth. Bioscience 933-938.

Stehman, S. V. 2013 Estimating area from an accuracy assessment error matrix.

Remote Sensing of Environment 202-211.

Future of ResearchFrom this current study, we conclude that more

research using data with higher spatial and better

temporal resolution is needed to better understand

the difference between the current, sample-based

results and the maps (PRODES and GFW).

Improving spatial resolution would allow for more

accurate assessment of forest cover change and

change driver attribution. Better temporal

resolution would allow for a more accurate

attribution of the year of change.

0

500

1000

1500

2000

2500

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

Yearly Changes

Primary Total GFW PRODES 3 Yr. Average 3 Yr. Average (Primary)

82%

5%

11%2%

Chnages by Cause

Pasture Agricultural

Dam Construction Logging

The maps above show that 67% of Tocantins land lays on the

Cerrado Woodlands and Savannas which are part of the Tropical &

Subtropical Grasslands, Savannas & Shrublands biome, and the

other 33% belongs to the Tropical & Subtropical Moist Broadleaf

Forests biome.