The Plot Network

For these analyses, we define a plot as an area of forest where all trees above 10-cm diameter at breast height (d.b.h., measured at 1.3-m height or above any buttress or other deformity) are tracked individually over time. All trees are marked with a unique number, measured, mapped, and identified. Periodically (generally every 5 years), the plot is revisited, and all surviving trees are re-measured, dead trees are noted, and trees recruited to 10-cm d.b.h. are uniquely numbered, measured, mapped, and identified. This allows calculation of: (i) the cross-sectional area that tree trunks occupy (termed "basal area"), which can be used with allometric equations to estimate tree biomass (Baker et al., 2004a); (ii) tree growth (the sum of all basal-area increments for surviving and newly recruited stems over a census interval); (iii) the total number of stems present; (iv) stem recruitment (number of stems added to a plot over time); and (v) mortality (either the number or basal area of stems lost from a plot over time). We present results from 50 to 91 plots, depending upon selection criteria for different analyses (most critically, the number of census intervals from a plot and whether only stem-count data or the full tree-by-tree data set is available). The number of plots used for stem-density changes is more than that used in the biomass study because full tree-by-tree data are required to calculate biomass (using Baker et al's, 2004a methods), whereas stem-change data can often be obtained from published studies. The plots span the Amazonian forests of northern South America (Figure 12.1), including Bolivia, Brazil, Ecuador, French Guiana, Peru, and Venezuela. Most are 1 ha in size and comprise —600 trees of > 10-cm d.b.h. The smallest are 0.4 ha and the largest is 9 ha, all large enough to avoid undue influence by the behavior of an individual tree (Chave et al., 2003). Many plots have been monitored for more than a decade, although they range in age from 2 to 25 years. The earliest plot inventory was started in 1971, the latest in 2002. Details of the exact plot locations, inventory and monitoring methods, and issues relating to collating and analysing plot data are omitted from this chapter for reasons of space, but are discussed in detail

Figure 12.1. Plot locations used in this study. Symbols represent approximate locations of each plot; grey circle for plots monitored for 5-10 years, black for those with >10 years of monitoring. The approximate extent of seasonal and highly seasonal areas of tropical South America are indicated.

Figure 12.1. Plot locations used in this study. Symbols represent approximate locations of each plot; grey circle for plots monitored for 5-10 years, black for those with >10 years of monitoring. The approximate extent of seasonal and highly seasonal areas of tropical South America are indicated.

elsewhere (Phillips et al., 2002a, b, 2004; Baker et al., 2004a, b; Malhi et al., 2002,2004; Lewis et al., 2004b).

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