Multidimensional forest health initiatives-those designed to restore and protect forest integrity in the large sense-require, among other things, a better understanding of the relationship between the structure of forests and (1) their susceptibility to wildfires outside the range of natural variability and (2) the level of treatment (if any) required to lower susceptibility into an acceptable range. Within the ponderosa pine zone (Pinus ponderosa Dougl. ex Laws.) on the eastern slopes of Oregon's Cascade Range, an average of 86% of trees >5 cm in diameter at breast height (dbh) were less than 101 years old, the density of young trees correlating negatively with the density of old trees (>150 yrs). Species composition differed significantly between age classes: 72% of trees older than 150 years were ponderosa pine, whereas 83% of trees younger than 101 years were either grand fir (Abies grandis [Dougl.] Lindl.) or lodgepole pine (Pinus contorta Dougl. ex). Loud Crown bulk density calculated to reflect the multiple canopy layer structure of these stands (CBDm) averaged 0.049 kg/m 3 , compared to 0.093 kg/m 3 using the standard approach ( p < 0.001), indicating that the latter significantly overestimates risk of active crown fire in stands with complex canopy structure. Nevertheless, modeling with CBDm predicts that under severe but plausible weather conditions (late summer fuel moisture and 48-kph winds) crown kill would exceed 70% on 5 of 14 plots and 50% on an additional 5 plots. Models also predict that thinning trees of <20 cm dbh, coupled with controlled burning to reduce logging slash, would prevent torching ( fire moving from the ground into crowns) on all plots, even under extreme fire conditions (low fuel moisture and 80-kph winds). The amount of thinning required to prevent spread from crown to crown (active crown fire) varied widely among plots and depended on the degree of risk deemed acceptable. The relationship between stand basal area and the critical wind speed required to maintain active crown fire followed a negative power law (r 2 = 0.92), implying that over certain ranges small changes in basal area result in relatively large changes in susceptibility (assuming that changes in basal area are due to addition or removal of smaller trees). Landsat thematic mapper correlates reasonably well with CBDm ( r 2 = 0.80) and may provide a tool for rapid risk assessment.Estructura del Bosque y Susceptibilidad al Fuego en Paisajes Volcánicos de Cascadas Altas del Este, Oregon.Resumen: Las iniciativas multidimensionales de salud de bosques (es decir, diseñadas para restaurar y proteger la integridad del bosque en sentido amplio) requieren, entre otras cosas, un mejor entendimiento de la relación entre la estructura de bosques y (1) su susceptibilidad a incendios más allá de su variabilidad natural y (2) el nivel de tratamiento (si fuera necesario) requerido para reducir la susceptibilidad a niveles aceptables. En la zona de pino ponderosa (Pinus ponderosa Dougl. ex Laws.) en las laderas orientales de la Sier...
Although Eucalyptus is widely planted in South China, whose effects on native biodiversity are unclear. The objective of this study was to quantify the richness and composition of understory plants in two contrasting Eucalyptus chronosequences in South China. One was in Zhangzhou City with plantation age of 2, 4, and 6 years after clear-cutting Chinese fir forests, while the other was in Heshan City with plantation age of 2, 3, and 24 years that reforested on barren lands. Results showed that the richness of understory plants and functional groups was not significantly altered in the Zhangzhou chronosequence, while increased in the 24-year-old plantations, with a significantly larger proportion of woody plants than the younger plantations for the Heshan chronosequence. Moreover, a higher richness of woody plants accompanied by a lower richness of herbaceous species was detected in the Zhangzhou chronosequence compared with the Heshan one. To balance the need for pulp production and plant diversity conservation, we suggest that intercropping approaches between exotic Eucalyptus plantations and native forests should be considered in the fast rotation Eucalyptus plantations. However, Eucalyptus plantations may be used as pioneer species to sustain ecosystem functioning for the degraded lands.
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There are limitations in conventional earthquake loss procedures if attempts are made to apply these to assess the social and economic impacts of recent disastrous earthquakes. This paper addresses the need to develop an applicable model for estimating the significant increases of earthquake loss in mainland China. The casualties of earthquakes were studied first. The casualties of earthquakes are strongly related to earthquake strength, occurrence time (day or night) and the distribution of population in the affected area. Using data on earthquake casualties in mainland China from 1980 to 2000, we suggest a relationship between average losses of life and the magnitude of earthquakes. Combined with information on population density and earthquake occurrence times, we use these data to give a further relationship between the loss of life and factors like population density, intensity and occurrence time of the earthquake. Earthquakes that occurred from 2001 to 2003 were tested for the given relationships. This paper also explores the possibility of using a macroeconomic indicator, here GDP (Gross Domestic Product), to roughly estimate earthquake exposure in situations where no detailed insurance or similar inventories exist, thus bypassing some problems of the conventional method.
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