carbon and nitrogen dynamics associated with post-wildfire stand development of boreal mixed conifer ecosystems : application of data in model validation and refinement
abstract
study site : northwestern ontario to make accurate and meaningful predictions about boreal forest ecosystem
development, a strong understanding of the processes that drive change within the
ecosystem s in required. once this knowledge is gained, it can be incorporated into
process-based ecosystem models that can be valuable tools for both making management
decisions and also guiding further research. in northwestern ontario, various calibration
and testing exercises for the century soil organic matter model have been
performed. however, it was identified that a validation exercise was required in order to
properly evaluate the ability of the model to simulate c and n dynamics through stand
development. in response to this need, this project involved the set up of a 110 year old
upland mixed conifer chronosequence of fire origin from which c and n dynamics were
measured (i.e. c and n pool levels and fluxes). by dividing the chronosequence into
four stand development stages (regeneration, crown closure, self-thinning, and mature),
it was found that pool levels were often not significantly different between stand
development stages; however, n mineralization and soil respiration rates were linked to
soil temperature, and substrate quality seems to decrease with time since fire
disturbance.
the validation exercise employed eight different tests to evaluate the ability of
the century model to simulate thirteen c and n pools, fluxes, and soil temperature
calculations. the exercise was much less successful than expected. in most cases the
pool levels were different and in other cases, the over time trends were very different.
for example, simulated n mineralization rates increase gradually through stand
development whereas real-world measured rates decreased into immobilization. it was
found that growing season soil temperatures (may to september) calculated by the
model were too high and thought that lowering these temperatures would result in some
of the simulated pools and fluxes being m ore similar to the real-world data. validation
of the new low er soil temperatures was very successful; however, this success did not
translate into better validation results for the other parameters. further work with
century is required before it can be relied upon to accurately simulate c and n
dynamics through stand development; however, this type of work is valuable in itself
because it generates new information and furthers out understanding of these forest
ecosystems.
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- retrospective theses [1604]