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A field and simulation study of the initiation phase in Douglas-fir plantations Boldor, Marius Ioan

Abstract

The stand initiation phase of stand dynamics has important implications for subsequent stand development, yet it is generally not addressed in growth and yield models. Planted trees may or may not grow as expected if there is significant recruitment of natural regeneration and/or herb and shrub competition and if the interactions between the planted trees and other vegetation is not managed. Two experiments initiated at Malcolm Knapp Research Forest (MKRF) in the early 1980's were re-measured to produce extended data sets that describe stand development in the face of invasion by non-crop trees and the competitive effects of shrubs. These data sets were then used to test the predictive ability of the ecosystem management model FORECAST (a stand level hybrid simulation model) to represent early stand development. The Blaney Lake experiment was established to examine the vegetation development in a chronosequence of young Douglas-fir plantations on four adjacent small clearcuts that incorporated a local topographic sequence of soil moisture regimes - xeric, mesic and hygric. The data showed that there is a relatively short temporal window (up to 10 years) for non-crop tree recruitment, that this varies from year to year, and that the outcomes pose a difficulty for predicting future stand development. The data also suggest that unmanaged recruitment may invalidate early stand development predictions of models that ignore non-crop recruitment and interactions with planted trees. FORECAST was capable to capture the effects of these complex interactions. The Vegetation Competition experiment was initiated to study the effect of different levels of non-crop vegetation on growth of two conifer species and the results were compared with output from FORECAST to assess its ability to represent the competitive interactions. Again, for most of the variables FORECAST made predictions that mimicked the field data. The results presented here provide evidence of the utility of the ecosystem model FORECAST in projecting the development and growth of young conifer plantations in the CWHdm biogeoclimatical subzone. This study increases confidence in the FORECAST model for application in young stands. However, it must be emphasized again that the accuracy of model performances will reflect the availability of appropriate calibration data sets.

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