Climatic Inferences from Dendroecological Reconstructions - Dendroclimatology - page 281

0.4

Wetter

0.2

0.0

-0.2

-0.4

-0.6

Drier

1600 1650 1700 1750 1800 1850 1900 1950 2000

3.0

12

2.5

10

2.0

8

1.5

6

1.0

4

0.5

2

0.0 0

1600 1650 1700 1750 1800 1850 1900 1950

Year

Fig. 9.10 Composite age structure data from a network of 12 ponderosa pine stands and recon-
structed summer Palmer Drought Severity Index (PDSI) from corresponding grid points in the
southwestern United States (Cook et al. 1999 , 2004 )

other surface fuels. Hence, it seems quite likely that historically, the favorable germi-
nation and establishment periods of ponderosa pine in the Southwest corresponded
with wetter conditions for the reasons described above; i.e., more successful ger-
mination and survival during these periods, and relatively longer intervals between
fires during these wet periods (see also Fig. 9.8 ) . It is likely that climate affected
recruitment in many of these forests both through direct effects on demographic
processes (seed production, germination, and seedling growth) as well as by mod-
ifying fire frequency and timing (and perhaps other disturbances, such as insect
outbreaks; e.g., Fig. 9.6 ) . In a later section of this chapter, we will discuss timing
of longer fire-free intervals, and their relationships to both climate and patterns of
regional tree recruitment shown in Fig. 9.10 .
As in most dendrochronological studies involving networks of chronologies,
regional-scale emergent patterns of ecological synchrony may be reasonably inter-
preted to reflect, at least in part, the important role of climatic variability. This
is not to discount the important role of local factors in causing unique distur-
bances or demographic peculiarities at the tree or stand level. Interactions between