These assets are accounted for under the cost model, which requires the assets to be carried at cost less accumulated depreciation  and any accumulated impairment losses. The following table presents the changes to the carrying value of the company’s  property, plant and equipment assets included in these operations: The following table presents the changes to the accumulated impairment losses of the company’s property, plant and equipment  within these operations: The following table presents the changes to the accumulated depreciation of the company’s other property, plant and equipment  within these operations: The company held 1,437 million acres of consumable freehold timberlands at December 31, 2013 (2012 – 2,512 million), of  which 203 million acres (2012 – 850 million) were classified as mature and available for harvest. Additionally, the company  provides management services to approximately 1.3 million acres (2012 – 1.3 million) of licensed timberlands. The following table presents the change in the balance of timberlands and other agricultural assets: YEARS ENDED DECEMBER 31  (MILLIONS) 2013 2012 Balance at beginning of year  $ 3,516 $ 3,381 Disposals of operations, net of additions  (2,991) 18 Fair value adjustments  205 374 Decrease due to harvest  (186) (239) Foreign currency changes  (42) (18) Balance at end of year  $ 502 $ 3,516 12.  SUSTAINABLE RESOURCES (MILLIONS) Dec. 31, 2013 Dec. 31, 2012 Timberlands  $ 449 $ 3,473 Other agricultural assets  53 43 Total  $ 502 $ 3,516 YEARS ENDED DECEMBER 31  (MILLIONS) 2013 2012 Balance at beginning of year  $ (813) $ (533) Depreciation expense  (217) (283) Disposals  110 — Foreign currency translation  (6) 3 Balance at end of year  $ (926) $ (813) YEARS ENDED DECEMBER 31  (MILLIONS) 2013 2012 Balance at beginning of year  $ (162) $ (104) Impairment charges  (94) (58) Balance at end of year  $ (256) $ (162) YEARS ENDED DECEMBER 31  (MILLIONS) 2013 2012 Balance at beginning of year  $  3,887 $  3,433 Additions, net of disposals  124 405 Acquisitions through business combinations  86 — Foreign currency translation  (113) 49 Balance at end of year  $ 3,984 $ 3,887 124 BROOKFIELD ASSET MANAGEMENT 