|
||
Water x Nutrients
The most important constraint to plantation productivity in Chile is water availability because of three or more months during the growing season with little or no rainfall, a characteristic of the Mediterranean climate. As a result, Chilean plantations can provide an excellent field resource to experimentally test techniques to actively manage water availability through genetic selection (species, families, clones), stand density management (initial planting density and thinning regimes), vegetation control, and irrigation. The two largest forest companies in Chile (Arauco and CMPC Forestal) have recently joined the Forest Nutrition Cooperative (co-directed by Dr. Allen). These companies have now established 11 field trials that could serve as a base for more fundamental research by graduate students on the relationships between forest production and water availability. Dr. Allen plans to pursue these research possibilities during his sabbatical in 2005.
Currently growth rates in pine plantations in the southeastern US average less than 10 m3/ha/year and are substantially lower than forest plantations in many other parts of the world, including Chile. From a resource availability perspective, water availability, whether too little or too much, has historically been considered the principal resource limiting pine productivity in the South. While this is true on most sites for young seedlings and for specific soil types (e.g. very wet or very dry soils) throughout the rotation, recent analyses suggest that chronically low levels of available soil nutrients, principally N and P, but also potassium (K) and boron (B) on loamy or sandy soils, are currently more limiting to growth in established stands than water limitations. Water availability is thought to have less effect on leaf area than nutrient availability because most leaf area production occurs in the spring when soil water availability is high and evapotranspiration demand is low. In contrast, water availability is thought to have a greater effect on growth efficiency because photosynthesis of existing leaf area can be reduced by drought during summer months when soil water availability may be low and evapotranspiration demand is high. However, with the predicted changes in climate in the Southeast US, water constraints to leaf area development and growth could become much more important in the near future.
|
||
|
