| This study was directed to improve our understanding of the ecology of Swiss needle cast (SNC) of Douglas-fir, a disease that produces extensive damage to forests and plantation in the coastal region of Oregon and Washington. A disease prediction model for the coastal area of Oregon was built by establishing the relationship between the distribution of disease severity and the environment. Currently available methods of determining the distribution of SNC were analyzed, and the possibility of mapping the disease using Landsat TM satellite images was explored.; Two types of regression approaches were used to study the relationship between disease severity and climate, topography, soil and forest stand characteristics. Although both types provided useful information and insight, the multiple regression approach was chosen over the regression tree analysis to build the model, due to its capacity to produce a continuous prediction response.; Fog occurrence, precipitation, temperature, elevation and slope aspect, were the variables that contributed to explain most of the disease severity variability. Findings agree with and formalize our previous understanding of the ecology of SNC: cool and wet conditions in summer appear to increase disease severity. When the model was applied to past climate conditions, retrospective predictions suggest that changes in climate in the last two decades could help to explain the observed recent regional increase in SNC disease severity.; The resulting model was used to construct a disease prediction map. This map showed an accuracy equivalent to the currently available SNC aerial survey. The prediction model, however, is able to produce a continuous prediction surface, more suitable for testing and appropriate for assisting in disease management and research.; A strong relationship between mature stand canopy defoliation and the Landsat TM indices greenness and brightness, indicates that it is possible to use satellite imagery to map SNC. In contrast, young stands showed high variability, most likely due to the relatively high proportion of exposed understory vegetation.; The possibility of mapping stand defoliation is of great importance because this symptom can be directly linked to tree growth and forest productivity. Satellite imagery can be used in future and in retrospective disease mapping. |
