This study therefore used bird population density as a proxy for
biodiversity. The population size of birds must be at least equal to a
minimum viable population. Shaffer (1981, p. 132) defined that “a
minimum viable population (MVP) for any given species in any
given habitat is the smallest isolated population having a 99% chance
of remaining extant for 1000 years despite the foreseeable effects of
demographic, environmental, and genetic stochasticity, and natural
catastrophes”. Shaffer suggested that the critical level for survival
probabilities might be set at any level, and the planning horizon can
be lengthened to 10,000 or shortened to 100 years. Franklin (1980)
and Bulte and van Kooten (2001) recommended that the MVP in the
short or medium term is about 50–100 individuals. Since the setting
of this research was in Vietnam with a time horizon of 50 years, the
MVP of 50 individuals (that is a desired population density if biodiversity
conservation to be considered) was employed. This population
sizewas also close to the bird density ha−1 in natural forests in Vietnam
identified by Hill et al. (2001) and in plantation forests in New Zealand
by Seaton et al. (2010).
2.2. The optimization model
This study therefore used bird population density as a proxy forbiodiversity. The population size of birds must be at least equal to aminimum viable population. Shaffer (1981, p. 132) defined that “aminimum viable population (MVP) for any given species in anygiven habitat is the smallest isolated population having a 99% chanceof remaining extant for 1000 years despite the foreseeable effects ofdemographic, environmental, and genetic stochasticity, and naturalcatastrophes”. Shaffer suggested that the critical level for survivalprobabilities might be set at any level, and the planning horizon canbe lengthened to 10,000 or shortened to 100 years. Franklin (1980)and Bulte and van Kooten (2001) recommended that the MVP in theshort or medium term is about 50–100 individuals. Since the settingof this research was in Vietnam with a time horizon of 50 years, theMVP of 50 individuals (that is a desired population density if biodiversityconservation to be considered) was employed. This populationsizewas also close to the bird density ha−1 in natural forests in Vietnamidentified by Hill et al. (2001) and in plantation forests in New Zealandby Seaton et al. (2010).2.2. The optimization model
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