292
G.A. Bradshaw et al.
of disturbances characteristic of the area direct the distribution of stands
of varying successional stages.
Temporal Heterogeneity
Disturbances such as wildfire, windthrow, flooding, and insect outbreaks
also play an important role in imposing pattern on the landscape by
redistributing resources (Morrison & Swanson, 1990; Spies & Franklin,
1991). Within-stand heterogeneity of resources (e.g., downed wood,
canopy gap structure) reflects the integration and coupling of disturbance
patterns (e.g., mortality due to wildfire, root pathogens) at several temporal and spatial scales. In a study comparing a set of old growth, mature,
and young Douglas-fir dominant stands in the western Cascades, Oregon,
hemlock seedling distribution showed a gradual increase with stand age
and percent woody debris cover (Bradshaw, 1991). More interestingly,
20
0.10
,...,
E
t)
"0
0
If)
10
-0.10
-0.20
Log (m)
Figure 14.9. Wavelet cross-covariance calculated between hemlock seedling and
downed log distributions. The x-axis refers to the lag at which correlation between
the two variables occurs; the y-axis refers to the scale at which correlation occurs
(meters) . Downed logs and hemlock seedling distribution are correlated on
average at approximately nine meters in this mature Douglas-fir stand.
G.A. Bradshaw et al.
of disturbances characteristic of the area direct the distribution of stands
of varying successional stages.
Temporal Heterogeneity
Disturbances such as wildfire, windthrow, flooding, and insect outbreaks
also play an important role in imposing pattern on the landscape by
redistributing resources (Morrison & Swanson, 1990; Spies & Franklin,
1991). Within-stand heterogeneity of resources (e.g., downed wood,
canopy gap structure) reflects the integration and coupling of disturbance
patterns (e.g., mortality due to wildfire, root pathogens) at several temporal and spatial scales. In a study comparing a set of old growth, mature,
and young Douglas-fir dominant stands in the western Cascades, Oregon,
hemlock seedling distribution showed a gradual increase with stand age
and percent woody debris cover (Bradshaw, 1991). More interestingly,
20
0.10
,...,
E
t)
"0
0
If)
10
-0.10
-0.20
Log (m)
Figure 14.9. Wavelet cross-covariance calculated between hemlock seedling and
downed log distributions. The x-axis refers to the lag at which correlation between
the two variables occurs; the y-axis refers to the scale at which correlation occurs
(meters) . Downed logs and hemlock seedling distribution are correlated on
average at approximately nine meters in this mature Douglas-fir stand.