size-class (cm) trees/ha km 83: y = * x (0.124) ( ) R ² = RSE = 0.2 on 16 df km 67: y = * x (0.106) ( ) R ² = RSE = 0.16 on 12 df Overview Motivating questions: (1) What is the present status of Amazonia as a source or a sink for atmospheric carbon dioxide? (2) What are the ecological and climatic controls on the interannual carbon balance in the Amazon basin? (3) What is the effect of selective harvest on forest carbon cycling and atmospheric exchange? Approaches: (1) ground-based biometry (woody tree increment and litterfall), combined with (2) whole-system CO 2 fluxes (eddy covariance) at the local scale in an old-growth Amazonian rainforest (Tapajos National Forest, km 67, Santarem, PA, figure 1). Also: (3) measurement of continental-scale boundary-layer CO 2 gradients (from continental interior to margin). Preliminary Results (Biometry): Dendrometers were installed in December 1999 (figure 2) based on results of the initial tree survey in July 1999 (figure 3), which included about 260 species in 50 families. The initial survey indicates that the tree size structure is slightly biased towards large trees relative to the selective harvest site at km 83. The dendrometry sample was random-stratified to guarantee adequate representation of each taxonomic group and to capture the disproportionally high biomass contained in the largest trees. Three months of monitoring indicate that growth rates are relatively even across size classes, but are dominated by a few taxonomic families, and by the tallest trees (figure 4A). The projected mean annual DBH increment in live trees is 0.44 cm yr -1 (data not shown), or 4 Mg carbon ha -1 yr -1. However, during the study period tree damage/mortality reduced the stock of live tree carbon at an annual rate of 3.5 Mg carbon ha -1 (data not shown). The absolute frequency of tree damage/mortality is dominated by the smallest size class (figure 4B), but is distributed evenly across canopy status and taxa. Methods analysis on this preliminary data set is shown in figure 4C. Two standard allometries for tropical forests (one quadratic and one exponential) yield total annualized biomass increments differing by less than five percent. A comparison between two dendrometer designs suggests possible measurement artifacts in the first year after installation. Through continued monitoring, it is anticipated that more will be learned about the variability in the interannual and seasonal cycles of carbon sequestration in trees. Natal meters Biometry plots upwind of flux tower, with locations & sizes of all trees >35cm DBH Km 67 Rio Tapajós Km 83 Santarém Rio Amazonas Measuring carbon balances in the Amazon basin: I. Woody vegetation dynamics in an old-growth tropical rainforest S. R. Saleska 1†, L. Hutyra 1, E. Hammond-Pyle 1, E.G.T. Guimarães 2, S.C. Wofsy 1 1 Dept. of Earth & Planetary Sciences, Harvard University; 2 FFT † corresponding author: Figure 2. Dendrometry study. Spring-mounted dendrometer bands were installed on trees at breast height, allowing precise estimates of tree diameter growth rates. We banded 1000 trees (out of the ~2600 inventoried). Tree biomass increase is calculated from DBH increase using allometric relations (e.g. Brown et al. 1997). Buttressed trees (see right) were banded above the buttress using a ladder. Twenty percent of the banded trees have a second band installed (see above) for comparison between different dendrometer designs. Figure 1. Site location and biometry study design. The site is located ~70 km south of Santarém, Pará, Brazil, in the Tapajós National Forest (“km 67 site”), the location of the eddy-flux tower. Three transects (50 m x 1000 m) were laid out in the tower footprint, toward the predominant winds (east). A fourth transect runs perpendicular. Large trees (diameter at breast height, DBH > 35 cm) located within 25 m of either side of each transect line were identified, tagged, and measured. Smaller trees (between 10 and 35 cm DBH) were also identified, tagged, and measured in a narrower swath, 5 m of either side of each transect line. A total of ~950 large trees (indicated by circles above), and 1650 small trees (not shown) were identified. Figure 3. Site characteristics. Figure 4. Preliminary results of dendrometry (tree survey conducted July 1999; dendrometers installed December 1999; dendrometer measurements conducted February-May, 2000). A. 76-day DBH increments (cm) fraction of sample n=13n=2n=1 n=2 (ii). By taxonomic family: (iii). By canopy status: B. 10-month (7/99-5/00) damage/mortality rates (i). By size-class: C. Aboveground biomass changes during initial study period DBH (cm) tons (biomass)/ha Brown (1997) quadratic (total = 303 t/ha) Brown (1997) exponential (total = 317 t/ha) (i). Wood increment rates from dendrometry (76 days during Feb-May, 2000) (ii). Loss rates due to damage/mortality (300 days from July ‘99 - May, 2000) (i). By size-class: DBH increment(cm) Size class (cm) n=411n=153 n=82n=74n=50n=37n=22 n=37n=17n=15n=10 n=7 n=8n=1 Elacocarpaceae Sterculiaceae Hippocrateaceae Verbenaceae Simaroubaceae Celastraceae Caryocaraceae Monimiaceae Rubiaceae Connaraceae Tiliaceae Olacaceae Apocynaceae Myrtaceae Moraceae Boraginaceae Quiinaceae Leguminosae-Papi Lauraceae Burseraceae Lecythidaceae Melastomataceae Sapotaceae Annonaceae Humiriaceae Ebenaceae Flacourtiaceae Guttiferae Euphorbiaceae Bombacaceae Myristicaceae Nyctaginaceae Sapindaceae Malpighiaceae Combretaceae Flacourticeae Vochysiaceae Rosaceae Anacardiaceae Meliaceae Leguminosae-Caes Leguminosae-Mimo Cecropiaceae noniaceae Araliaceae Aquifoliaceae Chrysobalanaceae DBH increment (cm) EmergentCanopySub-CanopySuppressed DBH Increment(cm) n=238n=281n=172n=265 (iv). By dendrometer design: EmergentCanopySub-CanopySuppressed Fraction of Sample n=247n=295n=178n= DBH size class(cm) Trees/ ha DBH size class (cm) Biomass (t/ha) (i). Frequency of trees (N=2596) Bombacaceae Combretaceae Connaraceae Ebenaceae Euphorbiaceae Lecythidaceae Leguminosae-Caes Leguminosae-Mimo Leguminosae-Papi Rubiaceae Sapotaceae Simaroubaceae % Damage n=2n=1 n=2n=3n=2n=3n=1n=3n=1 (ii). By taxonomic family: (iii). By canopy status: Mean DBH Increment(cm) Days Chambers Harvard (ii). Distribution of biomass: (iv). Size class distribution, km 83 vs km 67: (iii). Allometric comparison (v). Dendrometry Measurement: