An analysis of Greek wood and wood product imports: Evidence from the linear quadratic aids

The consumption of wood and wood products in Greece is based greatly on imports necessitating every year a great proportion of public expenditures. The study of wood and wood product imports consequently, is important to the national economy and can be a useful guide for the forest farms, wood industries and wood firms. In this paper the Greek aggregate import demand for Unprocessed wood (such as logs) Processed wood (such as sawn wood), Veneer Crafts (such as veneer sheets) and Wood Manufactures during the period 1969–2001 is empirically analysed using the linear approximation of quadratic AIDS (QUAIDS) model. Imports of Unprocessed wood, Veneer Crafts and Wood Manufactures are found to be price-elastic, in contrast to Processed wood imports. Processed wood, Veneer Crafts and Wood Manufacture imports are found to be expenditure-elastic while Unprocessed wood is found to be an inferior good. Substitution possibilities are found to be significant between Veneer Crafts and all the remaining wood imports and between Processed wood and Unprocessed wood.     

Population decline in the epiphytic orchid Aspasia principissa

The population dynamics of the epiphytic orchid Aspasia principissa, growing in the moist tropical forest of Barro Colorado Island, Panama, were studied from 1997 until 2004. Using growth analysis, projection matrix analysis, elasticity analysis, and different types of simulations, we identified the components of the life cycle with the strongest effect on population growth rate (λ), and related differences in vital rates to environmental variation, mainly in precipitation. Such information, which is almost completely lacking for tropical orchids, is essential for the efficient conservation of these frequently rare and endangered plants. Elasticity analysis indicated that the population growth rate (λ), which averaged 0.92, was primarily affected by survival, and much less affected by growth or by sexual reproduction. Simulations, which included different levels of pollinator limitation, showed that complete pollination would raise λ to such an extent as to allow long-term persistence of the population. Pollinator limitation per se, however, is presumably not responsible for the currently observed population decline. Instead, we discuss a possible link between low λ and (a) a long-term decline in precipitation and (b) recent increases in forest dynamics: variation in annual rainfall significantly affected both recruitment and growth rates of smaller orchid individuals, while the hypothesised increase in the rates of branch and tree falls would increase mortality rates in this epiphyte.     

Estimating the rate of quasi-extinction of the Australian grey nurse shark (Carcharias taurus) population using deterministic age- and stage-classified models

Grey nurse sharks off the east coast of Australia are listed nationally as “critically endangered” under Schedule 1 of the Environmental Protection and Biodiversity Conservation Act (1999) and may number no more than 300 in New South Wales and southern Queensland waters. They are an inshore, coastal dwelling species and were severely depleted by spearfishing in the 1960s. The population has continued to decline despite protection since 1984. Their life history (long-lived to 25+ years), late maturation (6-8 years), low fecundity (maximum 2 live young biennially), specific habitat requirements, limited inshore distribution, and small population size render them particularly vulnerable to extinction. We estimated the time to quasi-extinction (years elapsed for the population to consist of ?50 females) for the grey nurse shark population off the east coast of Australia based on current estimates of abundance and known anthropogenic rates of mortality. Estimated minimum population size was 300 as of 2002, and minimum anthropogenic mortality assessed from recovered carcasses was 12/year of which 75% were females. We modelled time to quasi-extinction using deterministic age- and stage-classified models for worst-, likely and best-case scenarios. Population size was estimated at 300 (worst), 1000 (likely) and 3000 (best). Anthropogenic mortality was added to the model assuming either all carcasses are being recovered (best), or conservatively, that only 50% are reported (realistic). Depending on model structure, if all carcasses are being reported, quasi-extinction times for worst-, likely and best-case scenarios range from 13 to 16 years, 84-98 years and 289-324 years, respectively. If under-reporting is occurring, time to quasi-extinction ranges from 6 to 8 years, 45-53 years and 173-200 years, respectively. In all scenarios modelled the grey nurse shark population will decline if no further steps are taken to remove anthropogenic sources of mortality. Because estimates of quasi-extinction rate depend on initial population size, and sensitivity analysis revealed that population rate of change was most sensitive to changes in the survival probability of the smallest length classes, obtaining precise estimates of abundance and annual survival of young females is critical.