Yield decline in Chinese-fir plantations: a simulation investigation with implications for model complexity

A variety of competing hypotheses have been described to explain yield decline in Chinese-fir ( Cunninghamia lanceolata (Lamb.) Hook.) plantations. The difficulty in implementing field experiments suggests ecosystem modeling as a viable option for examining alternative hypotheses. We present a conceptual model of Chinese-fir yield decline and explore its merits using the ecosystem-based FORECAST model. Model results suggest that yield decline is caused primarily by a decline in soil fertility, largely as a consequence of slash burning in conjunction with short rotations. However, as tree leaf area declines, there is a transition (over subsequent rotations) from seed rain based competition to bud bank based competition, increasing the competitive impact of minor vegetation on tree growth. Short rotations increase understory survival between rotations and may cause a gradual shift from tree dominance to shrub/herb dominance over subsequent rotations. These effects are most evident on nutrient-poor sites, but understory competition poses a significant yield decline risk on good sites as well. We conclude that sustainable production in Chinese-fir plantations requires the avoidance of activities that compromise soil fertility and increase understory competition. The risk and severity of yield decline would be reduced by increasing rotation lengths and avoiding plantations on infertile sites.

The Use of the Land Survey Record to Assess Changes in Vegetation Structure. A Case Study From the Darling Downs, Queensland, Australia.

Fifteen references to vegetation structure from the historical land survey record for the eastern Darling Downs were calibrated with historical photographs to determine the use of the surveyors' structural terminology (Open: 'open', 'light': Dense: 'heavy', 'thick', 'dense'). Sites with less than 40% canopy cover were only described by terms included within the Open category, and sites with greater than 50% canopy cover were only described by terms included within the Dense category. These results provide calibrations of the surveyors' structural terminology indicating terms were unambiguously applied outside the 40-50% canopy cover range. The use of corner tree distances as an absolute measure of vegetation density is warned against because corner trees had to meet certain criteria and were not necessarily the nearest tree to any corner. However, the distance from allotment corners to "corner trees" provided a measure of the relative use of the surveyor's structural epithets and is consistent with standard application among their fraternity. Survey records dating from 1864-1910 were compared with the structure of existing remnants (projective crown cover measured from recent 1:25,000 aerial photography) to assess changes in vegetation structure. The analysis suggests that 88% of the 34 sites included in the analysis have not changed from the broad structural category that was assigned by the surveyors. Using the assumptions developed by this study, two sites were assessed as having thickened substantially. These results suggest that only minor vegetation thickening has occurred in the Darling Downs since the early land surveys. This conclusion is supported by direct comparison of the historical photographs with existing remnants. indicating that only one site out of 17 has thickened substantially.

Growth characteristics of Phellinus (Poria) weirii in soil and on root and other surfaces

Growth of Phellinus (Poria) weirii (Murr.) Gilbertson from alder block inoculum into the surrounding soil to infect healthy roots was less than 10 cm. Tree-to-tree spread of this root rot fungus, beyond that which would occur as a result of root contact, may be facilitated by growth of the mycelium over roots of minor vegetation and over wood buried in soil. Ectotrophic mycelium is profuse on the bark of infected roots of Douglas fir (Pseudotsugamenziesii (Mirb.) Franco) and western hemlock (Tsugaheterophylla (Raf.) Sarg.), limited on infected roots of pine (Pinusmonticola Dougl., P. contorta Dougl, P. ponderosa Laws.), and nearly absent on infected roots of western red cedar (Thujaplicata Donn). Rate of spread of P. weirii root rot through stands with a high component of western red cedar or pine, or both, should be considerably slower than in pure stands of Douglas fir.

Relative Influence of Moisture–Aeration and Nutrients on Vegetation and Black Spruce Growth in Northern Ontario

Results from a principal component analysis suggest that nutrient regime is more important to vegetational variation than the moisture–aeration regime. Correlations between site index and habitat measures suggest that the moisture–aeration regime influences tree growth more than the nutrient regime. For particular components of vegetational variation and for segments of the total data, the proportional influence of the two gradients varies. Moisture–aeration and nutrient regimes explain a large proportion of the variation in minor vegetation and tree growth on black spruce peatlands.

Successes and Failures with Oil Spills in the Southeastern Inland Waters

ABSTRACT This paper presents a brief review of several spill cases that have occurred in the Southeast in the recent past. Each case describes a unique situation — either in terms of containment, retention or removal methodology. At Athens, Georgia, a pipeline break caused the closure of the Athens Water Supply System for twenty-four (24) hours. Poor initial retention allowed taste, odors, and some light sheens to pass through the filters at the water plant into the home, causing some sixty-four (64) complaints within a matter of hours. Several inexpensive changes in retention procedures and water treatment techniques returned the situation to normal in a matter of hours. A pipeline break near Shepherdsville, Kentucky, forced some 16,000 gallons of crude oil into a subsurface layer of gravel. Storage of the oil in this fashion constituted a leaching source for the nearby water course that could have persisted for a year or more. Interception trenches were used to tap the gravel layers and water was forced into the layer up the gradient in order to “flush” the system. Ninety percent recovery was achieved at moderate expense. A vandalized storage tank adjacent to the Congaree River was emptied of 10,000 gallons of Bunker “C” near Columbia, South Carolina. Elaborate containment and recovery procedures were employed downstream. The oil, however, disappeared — save for minor vegetation stain. Not even a sheen reached the recovery site. River velocity, wind speed, temperature of the water and turbidity are discussed as contributors to this phenomena. At Jackson, Mississippi, a broken sludge pond dyke at a drilling operation dumped 40,000 gallons of “oil slops” and brine into the Big Black River. Retention on the surface was impossible because of the eight to ten knot river velocity. Light disposable sorbing booms were used to recover an estimated eighty percent of the oil. At Memphis, Tennessee, a piston film “Herder” was used to aid in recovering a portion of a 100,000 gallon spill. Because of surface debris, wind and river velocity, the Herder forced the oil into difficult tree and brush infested areas. The oil literally “ringed” every obstacle floating – or fixed — in the area. Cleanup costs soared. Pictures and sketches will be utilized to emphasize technical aspects of each situation.