Necromass in undisturbed and logged forests in the Brazilian Amazon

Necromass is an important stock of carbon in tropical forests. We estimated volume, density, and mass of fallen and standing necromass in undisturbed and selectively logged forests at Juruena, Mato Grosso, Brazil (10.48°S, 58.47°W). We also measured standing dead trees at the Tapajos National Forest, Para, Brazil (3.08°S, 54.94°W) complementing our earlier study there on fallen necromass. We compared forest that was selectively logged using reduced-impact logging methods and undisturbed forest. We estimated necromass density accounting for void volume for necromass greater than 10 cm diameter at Juruena for five decay classes that ranged from freshly fallen (class 1) to highly decayed material (class 5). Average necromass density adjusted for void space (±S.E.) was 0.71 (0.02), 0.69 (0.04), 0.60 (0.04), 0.59 (0.06), and 0.33 (0.05) Mg m^-3 for classes 1 through 5, respectively. Small (2-5 cm) and medium (5-10 cm) size classes had densities of 0.52 (0.02) and 0.50 (0.04) Mg m^-3, respectively. The average dry mass (±S.E.) of fallen necromass at Juruena was 44.9 (0.2) and 67.0 (10.1) Mg ha^-1 for duplicate undisturbed and reduced impact logging sites, respectively. Small and medium sized material together accounted for 12-21% of the total fallen necromass at Juruena. At Juruena, the average mass of standing dead was 5.3 (1.0) Mg ha^-1 for undisturbed forest and 8.8 (2.3) Mg ha^-1 for forest logged with reduced impact methods. At Tapajos, standing dead average mass was 7.7 (2.0) Mg ha^-1 for undisturbed forest and 12.9 (4.6) Mg ha^-1 for logged forest. The proportion of standing dead to total fallen necromass was 12-17%. Even with reduced impact harvest management, logged forests had approximately 50% more total necromass than undisturbed forests.