The Sky Canopy Gap Irradiance (SCANGIR) Model: a technique for the estimation of ‘effective gap’ solar radiation regimes in closed-canopy forests

There is now widespread consensus among researchers that treefall gaps play a key role in the structure and function of closed-canopy forests, such as rain forests, with virtually all canopy tree species requiring growth in a gap to reach maturity. Until recently many believed that latitude and the size of treefall gaps were the main factors determining the availability of solar radiation in gaps and associated microclimates and vegetation dynamics. However, if solar radiation availability is the main limiting resource in such forests, then studies of gap dynamics need to take into account the other factors affecting the penetration and distribution of direct and diffuse irradiance within gaps. As a consequence, this is the first attempt to develop a universal model for the estimation of ‘effective gap’ solar radiation regimes that, along with latitude and gap size, incorporates factors such as slope angle, slope aspect, height of surrounding vegetation, sky conditions and daily and seasonal variation in the position of the sun. Results of three computer simulations are presented to demonstrate how latitude, topography and sky conditions affect solar radiation availability beneath circular canopy gaps of various configurations. Finally, the implications of these simulations for forest regeneration, reforestation and forest management are discussed.     

COPPER AND BARIUM AS DIETARY DISCRIMINANTS: THE EFFECTS OF DIAGENESIS

In skeletons excavated from Woodland sites, copper and barium levels are found to have been contaminated by influx from the soil environment. Electron microprobe scans for both elements show build-up along the outer surface of femur cross sections. Elemental levels for Cu and Ba are lower in the femur or fibula than in the more porous rib. The distribution of Cu in the immediately surrounding soil is highly anisotropic. These observations indicate that Cu and Ba should not be used for dietary inferences about ancient populations without independent evidence that diagenesis is not important.     

The direction of migration: a dynamic general equilibrium model

A two-sector dynamic general equilibrium model is developed "to investigate the direction of migration in response to differing demographic and consumption demand behavior, as well as variations in production conditions." The model, which involves a rural sector and an urban sector, incorporates "returns to scale and the natural rate of sectoral population growth as important determinants of the direction of migration, in addition to price and income elasticities, and the sectoral technical change rate with which...previous studies dealt."     

THE NEIGHBOURHOOD EFFECT IN A LOCAL ELECTION

One of the more popular ideas in electoral geography is that there is a positive correlation between residential proximity and voting behaviour. Often referred to as the neighbourhood effect, the idea is quite simply that individuals within a given local area tend to vote similarly. The process involves, it is suggested, social contacts between neighbours leading to political discussion and information flow which exerts an influence on the way people vote. Closely related to, but distinguishable from the neighbourhood effect is the friends-and-neighbours effect whereby neighbours of a particular candidate will tend to know him better, discuss him more, and support him more avidly than they will other candidates. Since the concepts of the neighbourhood effect and the friends-and-neighbours effect have been adopted into the literature of political geography, and have become central as explanatory models for certain spatial patterns of voting behaviour,¹ the rather inconclusive and contradictory findings of researchers using these concepts require examination, and the concepts and process require an empirical test.     

PROCEDURES FOR COMPARING AND COMBINING RADIOCARBON AGE DETERMINATIONS: A CRITIQUE

Archaeologists, along with other Quaternary researchers, seldom rely upon a single radiocarbon determination to provide an estimate of the age of the phenomenon which is the object of their study. There is an evident need for an explicitly formulated procedure for comparing sets of radiocarbon determinations from the same and from adjacent strata or sites, and for combining these where statistical and archaeological criteria indicate that this combination is warranted. The present contribution provides explicit modelling for a series of recommended procedures, a critique of previous methods, and paradigms for application of the recommended procedures.