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Aim The assembly of a forest flora on sites abandoned from agriculture is potentially limited by the physical and chemical suitability of soils. This paper describes the post-agricultural development of soil in deciduous forest sites to gauge its importance in limiting a second-growth forest flora. Location Northern Delaware and south-eastern Pennsylvania, USA. Methods A chronosequence of 99 second-growth forest sites was assembled in the Piedmont region. Stand age ranged from 0–20 to > 100 years since canopy closure, as determined from historical aerial photographs. Seventy-four sites are likely to have experienced cultivation before regeneration of forest. The presence of large rocks or pit-and-mound microtopography suggests that the remaining 25 sites were not cultivated, although they were probably used as pasture and/or woodlot. Soil organic content, moisture, pH, and concentrations of extractable potassium, phosphorous, calcium, magnesium and sulphur were measured in samples from each site. Coarse woody debris, size of the largest tree, canopy openness and several microtopographic features were also recorded. Results Most soil variables fell into two separate but internally correlated groups: the first group including organic matter, moisture and sulphur; the second including pH, calcium, potassium and magnesium. In formerly cultivated sites, organic matter, moisture and sulphur increased gradually through the chronosequence, approaching values recorded in uncultivated sites at 81–100 years. Calcium, potassium, magnesium and pH declined sharply between the 21–40- and 41–60-year classes – probably an indirect effect related to geographic location and selective abandonment. Phosphorous also declined with time, but the decline was not as clearly defined. Main conclusions The progress of soil recovery observed here is faster than rates implied in other studies, possibly because these sites experienced a period as pasture before reversion to forest. Sites appear to have returned to undisturbed-forest levels as fast as or faster than the predicted accumulation of a forest flora, suggesting that assembly of second-growth forest communities is not limited by the rate of soil development in this region. [ABSTRACT FROM AUTHOR]

The debate over genetically modified foods has become one of the defining environmental and social issues of the past decade. As the public naturalize biotechnology within existing cultural systems, this produces what I term ‘cultures of GM’. This paper examines how these ‘cultures’ are legitimized and sustained through an appraisal of divergent North American and European conceptions of risk and their translation into food labelling policies. It is argued that the dialectical relationship between risk perception and its cultural context offers an instructive vantage point for critical reflection by geographers. [ABSTRACT FROM AUTHOR]

1 Areas burned annually in the United States between 1700 and 1990 were derived from published estimates of pre-European burning rates and from wildfire statistics of the US Forest Service. Changes in live and dead vegetation following fire and fire exclusion were determined for 18 types of biomes and added to a bookkeeping model to calculate the long-term effect of fire and fire management on carbon storage. 2 Over the 290-year period, burning declined by an estimated 98%, first, because wildlands were converted to agricultural lands, essentially eliminating fire from 236 x 10[sup 6] ha and, secondly, because wildfires were excluded and suppressed in the remaining forests and non-forests. 3 Adding fire and fire management to an analysis of land-use change (companion paper) reduced the emissions of carbon over the period 1700-1990 by 25% (8 PgC). Less carbon was released because fire reduced the average biomass of forests cleared and burned, and because fire exclusion led to an increase in carbon storage in forests. 4 The wildfire statistics of the USDA were insufficient for addressing two kinds of change: fire exclusion before 1926 and changes in the burning of non-forest ecosystems. We estimate here that as much as 4 and 12 PgC, respectively, may have accumulated in vegetation as a result of these changes, but the estimates are uncertain and likely to be upper limits. 5 The maximum rate of carbon accumulation attributable to all changes in land use, including fire management, was 300-400 TgC/year and occurred around 1980. Less than half of this uptake was in forests. Uptake by forests was constrained by the fact that most forests were already accumulating carbon in response to earlier harvests. Fire exclusion added little to this uptake. [ABSTRACT FROM AUTHOR]

1 Changes in the areas of croplands and pastures, and rates of wood harvest in seven regions of the United States, including Alaska, were derived from historical statistics for the period 1700-1990. These rates of land-use change were used in a cohort model, together with equations defining the changes in live vegetation, slash, wood products and soil that follow a change in land use, to calculate the annual flux of carbon to the atmosphere from changes in land use. 2 The calculated flux increased from less than 10 TgC/yr in 1700 to a maximum of about 400 TgC/yr around 1880 and then decreased to approximately zero by 1950. The total flux for the 290-year period was a release of 32.6 PgC. The area of forests and woodlands declined by 42% (160 x 10[sup 6] ha), releasing 29 PgC, or 90% of the total flux. Cultivation of soils accounted for about 25% of the carbon loss. Between 1950 and 1990 the annual flux of carbon was approximately zero, although eastern forests were accumulating carbon. 3 When the effects of fire and fire exclusion (reported in a companion paper) were added to this analysis of land-use change, the uptake of carbon calculated for forests was similar in magnitude to the uptake measured in forest inventories, suggesting that past harvests account for a significant fraction of the observed carbon sink in forests. 4 Changes in the management of croplands between 1965 and 1990 may have led to an additional accumulation of carbon, not included in the 32.6 PgC release, but even with this additional non-forest sink, the calculated accumulation of carbon in the United States was an order of magnitude smaller than the North American carbon sink inferred recently from atmospheric data and models. [ABSTRACT FROM AUTHOR]

People transform land by building, logging, and farming. The less land humans use, the more remains in its natural state. The authors search the past century for principles and trends influencing land use in the United States and contemplate the future when Americans might number an additional 100 million. Examples from American cities, counties, and states suggest that land covered by the built environment increases less than in proportion to population. For example, despite the rising use of paper relative to gross national product, the declining use of lumber combined with improved forestry kept the area of forest land fairly steady as population rose. Similarly, rising yields and changing tastes have countered the impact of rising population and wealth on cropland area. All told, a lightening tread of Americans on the land in the next century could spare for nature over 90 million hectares, an area equal to 100 times the size of Yellowstone National Park. [ABSTRACT FROM AUTHOR]