Evaluation of yield regulation options for primary forest in Tapajós National Forest, Brazil
Introduction
The Amazonian rain forest is the world's largest contiguous area of tropical forest (Dubois, 1991, Asner et al., 2004), being recognised for its high biodiversity and importance to global climate (Malhi et al., 2002). Selective logging is one of the main land uses in the Amazon, being very important for the regional economy. From 1996 to 2003, logging occurred at a rate of 10–20 thousand km2 year−1, being responsible for an estimated annual round-wood production of 27–50 million m3, employing 350 thousand people and generating gross annual revenue of US$ 2.5 billion (Nepstad et al., 1999, Lentini et al., 2003, Asner et al., 2005).
Currently, with very few exceptions, logging activity is part of agricultural frontier expansion and follows the world-wide pattern of the boom-bust cycle (Vincent, 1992, Schneider et al., 2000). In order to avoid the loss of forest cover and its benefits (e.g. watershed, soil and nutrient conservation, and the preservation of biodiversity), sustainable forest management has been proposed as a solution (Schmidt, 1991, Whitmore, 1991, Pearce et al., 2003).
Definitions of SFM vary widely (Vanclay, 1996, Rice et al., 1998) generally agreeing that today's use of natural forest resources should not compromise its future use in line with the original definition of sustainable development produced by the United Nations Commission on Environment and Development (“The Brundtland Report”, UN Commission on Environment and Development, 1987). Most countries impose regulations to forested lands to ensure this (Vanclay, 1996).
Yield is regulated in Brazil during the approval process of the Sustainable Forest Management Plan and Annual Operating Plans. These documents must present the minimum logging diameter, maximum mean extracted volume and cutting cycle to be used. The minimum DBH of 45 cm is generally applied with a cutting cycle of 25–30 years (Barreto et al., 1998, Grogan et al., 2004). The rule of thumb for maximum mean extracted volume has been more flexible with plans commonly approving 60 m3 ha−1, however in recent years there has been more adherence to values of 40 and 30 m3 ha−1 so 35 is used for this study. Within a species, up to 90% of the trees above the minimum diameter limit may be harvested.
Growth and yield models are essential tools to evaluate forest characteristics over one or more cutting cycles. The precision of these estimates may, however, be constrained by data used to calibrate the model and assumptions used to develop the model (Vanclay, 1992, Soares et al., 1995). While many models have already been developed to simulate forest growth and ecology, only few models have been developed and applied to support forest policies (van Gardingen et al., 2002).
In the Amazon region, MYRLIN (Nicol et al., 2002) and GEMFORM (Alder, 2000, Marshall and Bird, 2002) were used in Guyana to estimate future yield. In French Guyana, an individual tree spatially explicit model was developed, called SELVA (Gourlet-Fleury and Houllier, 2000) and it was compared to a matrix model called StoMat, concluding that both modelling approaches generate similar predictions and that the current felling regime does not guarantee sustained yields (Gourlet-Fleury et al., 2005). In Bolivia, a simulation model based on diameter distribution, increment and natural mean mortality of commercial species was developed, revealing that complete volume recovery will not be possible under currently prescribed cutting cycles and minimum felling diameter (Dauber et al., 2005). The SYMFOR model originally designed for use in Indonesia (Phillips et al., 2003) was adapted for use in Guyana (Phillips et al., 2002a) and then the Brazilian Amazon (Phillips et al., 2004). This model for Brazil was further adapted for use in this study with the incorporation of new management options and translation into Portuguese to become the model SIMFLORA.
In the Brazilian Amazon, attempts to provide a technical basis for yield regulation were based on mean diameter increment and mortality of commercial species (Barreto and Uhl, 1993, Silva et al., 1995, Vidal, 2004). The initiatives related to forest dynamics modelling in the Brazilian Amazon known by the authors are (in chronological sequence):
- (a)
Standpro—stand class projections (Silva, 1989).
- (b)
Inform—diameter class and nutrient cycling hybrid model (Biot et al., 1997).
- (c)
Cafogrom—cohort model (Oliveira, 2000, Alder and Silva, 2000, Alder and Silva, 2001, Keller et al., 2004).
- (d)
Transition matrix used to predict commercial species diameter structure (Cunha et al., 2002).
- (e)
SYMFOR—individual tree spatially explicit model (Phillips et al., 2004).
Simflora is a framework which includes forest ecology and management models. The ecological model is individual-based and spatially explicit. Further details on its calibration and validation in Brazil and its limitations and assumptions are described elsewhere (Phillips et al., 2004).
This study aimed to evaluate options of yield regulation for primary forest in Tapajós National Forest, Brazil. The approach adopted in this study differed from previous modelling studies using data from the Tapajós region (Silva, 1989, Alder and Silva, 2000, Phillips et al., 2004, Keller et al., 2004) in that the application of ecologically-based Simflora model permitted the analysis of a wider range of logging scenarios and criteria of sustainability, moving beyond the consideration of sustained timber yield, towards the objective of sustainable management of the timber resource.
Specific objectives of the current study were to:
- •
Evaluate the current Brazilian yield regulation system against objective criteria for Sustainable Forest Management.
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Compare the current system with a range of possible alternatives derived through modifications of the length of cutting cycle and maximum harvested volume limit.
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Analyse predicted changes in the ecological composition of forests under simulated management scenarios as a criterion of sustainability.
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Analyse the way that the volume increment responds to management options and provide an estimate of the expected maximum commercial volume increment to be used to set limits for sustainable forest management.
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To apply the yield and ecological analysis to define possible strategies to increase future sustainable yield from the Brazilian Amazon.
Section snippets
Data
The dataset comes from Tapajós National Forest, in Belterra municipality, Pará State (54°56′5″W and 3°18′46″S). The vegetation consists of typical terra-firme (dry-land) high forest, with basal area ranging from 30 to 35 m2 ha−1 (DBH ≥ 5 cm) and standing volume of 150–200 m3 ha−1 (DBH ≥ 45 cm). The regional climate is classified as Ami under Köppen system, with mean annual rainfall of 1900–2110 mm and temperature of 25 °C. Soils are classified as yellow latosols and topography is slightly rolling (Silva et
Timber yield
The predicted yield resulting from the current Brazilian yield regulation system with a maximum extraction of 35 m3 ha−1 and a cutting cycle of 30 years is shown as Fig. 1. This figure shows that whilst the desired harvest is achieved in primary forest (year 0), this is not sustained for any of the subsequent harvests. The observation that this system does not produce sustainable yield given the current commercial species list is supported by previous modelling studies in the Amazon region (Alder
Implications for forest management in the Amazon
Forest managers need to explore means to increase the productivity of the forests to meet their economic objectives, whilst also meeting demands from society to adapt to new social and environmental norms. In addition, the benefits associated with timber certification schemes provide incentives for change. Managers have a much wider range of options available than those explored in the current study. Previous work with the equivalent model for Indonesia (SYMFOR) (Phillips et al., 2003)
Conclusions
The simulation of growth and yield from the Tapajós region in this paper has suggested that the sustainable yield for current management practice may be as low as 0.33 m3 ha−1 year−1, or 10 m3 ha−1 over a 30-year cutting cycle. This is considerably lower than levels currently being discussed for legislation in Brazil. There is no doubt that such an approach to sustainable management will be unwelcome to some parts of the forest industry. The move towards forest certification provides an opportunity
Acknowledgements
We thank James Grogan, Mark Schulze and two anonymous reviewers for reviewing this article. The authors would like to acknowledge the staff of Embrapa Amazonia Oriental for the collection and provision of the data necessary for this work. The specific assistance of Dr. J.N.M. Silva is gratefully acknowledged for the provision of data and his helpful inputs into the design of the project and comments on this manuscript. This study was initially supported by the Dendrogene Project (a cooperation
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