Marco Lentini

Big-leaf mahogany Swietenia macrophylla population dynamics and implications for sustainable management

Summary 1. The impacts of selective harvesting in tropical forests on population recovery and future timber yields by high-value species remain largely unknown for lack of demographic data spanning all phases of life history, from seed to senescence. In this study, we use an individual-based model parameterized using 15 years of annual census data to simulate population dynamics of big-leaf mahogany Swietenia macrophylla King in southeast Amazonia in response to multiple harvests and in the absence of harvesting. 2. The model is based on regression equations of stem diameter growth, mortality, and fruit production estimated as a function of stem diameter and prior growth; it includes functions for germinating seeds, growing trees from seedling to adult senescence, producing seeds, and creating disturbances at specified spatial scales and return intervals, including logging. We simulate six harvest scenarios by varying the minimum diameter cutting limit (60 cm, 80 cm) and the retention rate requirement (20%, 40% and 60% commercial population retained). 3. Without logging, simulated populations grew over 100 years by 182% from observed densities, indicating that one or more parameters in the model may overestimate long-term demographic rates on this landscape. However, 100-year densities did not far exceed values reported from forests across this region, and other modelled demographic parameters resembled observed behaviours. 4. Under current harvest regulations for mahogany in Brazil (60 cm minimum diameter cutting limit, 20% commercial-sized tree retention rate, minimum 5 commercial-sized trees 100 ha � 1 retained after harvest, 30-year cutting cycle), commercial densities at the study site would decline from 39� 7t o 11 � 3 trees 100 ha � 1 before the fourth harvest in year 90, yielding an estimated 16� 4% of the initial harvest volume during the fourth harvest. Increasing retention rates caused first-cut harvest volumes to decline but improved population recovery rates between harvests. Under both minimum diameter cutting limit scenarios, increasing retention rates led to more robust population recovery compared with the current 20% rate, and higher subsequent harvest yields relative to initial (first-cut) values. 5. Synthesis and applications. These results indicate that current harvest regulations in Brazil for mahogany and other high-value timber species with similar life histories will lead to commercial depletion after 2–3 cutting cycles. Increasing commercial-sized tree retention rates improved population recovery at the cost of reduced initial harvest volume yields. Sustainable harvests will require, in combination, a moderate increase in the retention rate, investment in

Following the Rules: Brazilian Logging Concessions under Imperfect Enforcement and Royalties

Debates about forest concessions in the Brazilian Amazon have focused on the government’s enforcement capacity. Using an optimization model largely parameterized with data from the Eastern Amazon, we investigate the effectiveness of renewability audits and performance bonds in inducing compliance with reduced-impact logging and harvest volume requirements. In weak enforcement environments, audits are unlikely to induce full compliance with harvest regulations, while performance bonds may be more effective. The use of royalty instruments such as the ad valorem and revenue-based royalties can generate revenues and, in the case of revenue-based instruments, modify harvest behavior, but only under limited circumstances. (JEL Q23, Q28)

A Decision Support System for Land Allocation under Multiple Objectives in Public Production Forests in the Brazilian Amazon

Logging in natural forests is a vital economic activity in the Brazilian Amazon. However, illegal and unplanned logging is exhausting forests rapidly. In 2006, a new forestry law in Brazil (Lei 11,284/2006) established the legal framework to develop state and national public forests for multiple uses. To support public forest planning efforts, we combine spatially explicit data on logging profits, biodiversity, and potential for community use for use within a forest planning optimization model. While generating optimal land use configurations, the model enables an assessment of the market and nonmarket tradeoffs associated with different land use priorities. We demonstrate the models use for Faro State Forest, a 636,000 ha forest embedded within a large mosaic of conservation units recently established in the state of Para. The datasets used span the entire Brazilian Amazon, implying that the analysis can be repeated for any public forest planning effort within the region.