| The demand for forest products has been increasing in Latin America due to population and economic growth during the last two decades. To satisfy this regional and worldwide demand, a new forest plantation area has been established using fast growth species like eucalypt and pine. To reach this goal, a larger planted area is not the only necessity. The forests also need to have high productivity to allow developers to concentrate forest plantations in a smaller area, thereby enhancing the company profitability. To increase forest productivity, it is necessary to understand what the main growth limiting factors are, and to estimate how large the gap is between current and attainable productivity in order to determine where silvicultural treatments should be applied economically. In Venezuela, industrial forest plantations have been established during the last 40 years, mainly with caribbean pine; as a result, there is a lack of information regarding the more productive clonal Eucalyptus forests. We used a large permanent inventory plot network to characterize Eucalyptus plantations' growth patterns in Venezuela's western llanos, based on the Sullivan Clutter growth and yield model. The inclusion of rainfall in the model increased its accuracy, highlighting the effect of water supply on Eucalyptus growth. A simulation was performed to assess the impact of annual rainfall variability on yield, indicating that the risk of drought can be incorporated into forest planning decisions. To estimate the gap between current and attainable productivity of clonal Eucalyptus forest in Venezuela, we established 53 pairs of inventory plots covering different site and forest conditions. In each pair, a control plot received the regular management applied by the company, and the paired plot (twin plot) received extra fertilization plus extra weed control. The intensive silviculture management response was estimated as 2.6 Mg ha-1 yr-1 after two years, representing 20% over the current productivity (12.4 Mg ha -1 yr-1). In 25% of the sites, where 75% of the surface was covered by weeds, a third plot (triplet) was established receiving only extra weed control besides the operational management applied traditionally. Stem biomass gain was 1.7 and 3.9 Mg ha-1 yr-1 (13% and 28% over the control) after 2 years for the extra weed control and extra weed control plus extra fertilization treatments respectively, showing that both fertilization and weed control are needed to increase yield. We estimated the intensive silviculture profitability, using the average response and the Venezuelan prices, which showed a Net Present Value (NPV) of 402 USD ha-1. A linear model was fitted to identify the profitable responsive stands through their soil and stand attributes. Biomass growth of the control plot and landscape position were identified as the main explanatory variables for this tool. The NPV considering the probability of misclassifying responsive and no responsive stands was estimated in 224 USD ha-1. Two strategies were tested to eliminate classification uncertainty: 1) long term strategy: reducing the model error by fitting a better predictive model, and 2) short term strategy: applying the treatment in the most responsive sites, shifting the median response to the right, but at the same time reducing the proportion of treated stands. The NPV turned to be 568 and 364 USD ha-1 respectively, which represents an increase of 344 and 140 USD ha-1 over the case where all the area was treated. These long term strategies' increased NPV represents be maximum amount of money that could be invested in research to reduce uncertainty by identifying where and when silvicultural treatments should be applied to obtain a higher profitability. |
