Spatial Results: Annual Forest Disturbance from 1600 to 1997
Forest disturbance, proportion of forestland harvested annually,
was estimated at the state level and then interpolated to the 0.5o
latitude by 0.5o longitude grid scale. Shown here are the population-adjusted
estimates of forest disturbance over time.
Modeling Land Use Shifts from 1600 to 1992
Land use changes were modeled as follows: annually, harvested
area was computed by multiplying the harvest proportion by the available
timberland (total forestland minus reserve forestland), area to
be harvested was taken from primary and older cohorts first. Land
was converted between forest and agriculture depending on the historical
data for agriculture (Ramankutty and Foley 1999).
Forestland area declines with conversion
to agricultural land use.
Model-estimated Forestland follows the
Temporal Dynamics of Inventory-estimated Forestland Area (data from
Cumulative Area Harvested
Cumulative area harvested under the linear interpolation suggests
that an equivalent area of the entire US forestland has nearly been
cutover twice (1.94) whereas the population adjusted estimates suggest
only recently has an equivalent US area been cut (0.88).
The two different harvest estimation procedures result in similar
age class distributions through time but differ from inventory estimates
in the young and very old age class.
Using the Two Different Disturbance Histories to Assess Cumulative
Changes in Ecosystem Carbon Pools through Time
The linear interpolation of forest disturbance results in more
carbon accumulation earlier than the population adjusted extrapolation,
with little difference later.
We have established a method to estimate harvested area over time
and link with land use change model. Modeled estimates of total
forestland area follow the temporal dynamics of the inventory forestland
estimates and are within 6-10%. The model produces a larger proportion
of young and very old age classes than suggested by inventory data,
although this comparison is confounded by uneven age stands in inventory
data and the lack of fire as a disturbance in the model.
For more information, contact: Linda Joyce, email@example.com