Projection of tree growth and timber volume following strip clear-cutting in the Peruvian Amazon

Abstract

As part of an assessment of sustainability for the strip clear-cutting system (or Palcazú Forest Management System), we determined whether commercial tree species regenerating in two strips (30 m × 150 m) clear-cut in the Peruvian Amazon in 1989 would reach commercial size (≥30 cm diameter at breast height (dbh)) 40 years after the initial cutting, the expected harvesting cycle. We projected the growth of six common commercial species ( Eschweilera bracteosa, Guarea cinnamomea, Micropholis guyanensis, Pouteria guianensis, Qualea paraensis, and Cedrelinga catenaeformis) and two pioneer species ( Alchornea triplinervia and Miconia phaeophylla) using bootstrapping techniques (the Lieberman model), based on 2-year diameter increments (2004–2006) and mortality rates obtained from 1630 trees growing in secondary forest sites including the regenerating strips. These demographic data were further used to project the growth of all trees ≥6.5 cm dbh of commercial (sawnwood value) species from each strip, and from a deferment-cut treatment applied to half of one of the strips. Three models were used for growth projections: (1) using all diameter increments to simulate average growing conditions, (2) using diameter increments of trees exposed to high light to simulate growing conditions under intensive forest management with low mortality rates and (3) using diameter increments of the fastest growing individuals. Roundwood volume was calculated using allometric equations for emergent, canopy, and subcanopy species. Projections of all three growth models indicate that only two of the six focal commercial species, Cedrelinga and Qualea, would reach commercial size in 40 years. In the clear-cut strips, growth models 1 and 2 predict that 1–3% of the commercial trees (≥6.5 cm dbh) modeled would reach commercial size at the time of a second harvest, producing 3–8 m 3/ha of roundwood, as opposed to 12–14% (54–65 m 3/ha) of the commercial trees in the deferment-cut portion of strip 2. Growth model 3 predicted the highest number of trees reaching commercial size and thus the highest roundwood production for both the clear-cut strips (>30 m 3/ha) and deferment-cut (>130 m 3/ha). However, growth model 3 is the least realistic model out of the three; not all commercial trees in the strips are likely to grow continuously with such high growth rates in the next years. Thus, realistic growth projections (models 1 and 2) suggest that the strip clear-cutting system will not be financially profitable in a potential second harvest.