FREQUENCY-DEPENDENT CLIMATE SIGNAL IN UPPER AND
LOWER FOREST BORDER TREE RINGS IN THE MOUNTAINS
OF THE GREAT BASIN
MALCOLM K. HUGHES and GARY FUNKHOUSER
Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721, U.S.A.
Abstract. We examine the relationships, over the past millennium, between tree-ring chronologies
from long-lived pines at their upper and lower limits in four mountain ranges in and near to the semi-
arid Great Basin. We conﬁrm LaMarche’s (1974a) ﬁnding, based on a single mountain range in this
same region, and a much shorter period of comparison, that climate responses are frequency depen-
dent. In particular, upper and lower forest border chronologies in each mountain range are strongly
coherent at decadal periods and less, with particular strength in the 3–7 year band. This variability
is signiﬁcantly correlated with precipitation. Conversely, we ﬁnd no signiﬁcant correlation between
the low frequency ﬂuctuations (60 years and longer) of upper and lower forest border chronologies.
There are, however, signiﬁcant correlations between the low-frequency components of the upper
forest border chronologies in the different ranges, consistent with their containing a growing season
temperature signal on decadal time scales. The four upper forest border chronologies all show an
anomalous increase in growth since the late 19th century, and an apparent change in climate control
of ring growth.
LaMarche (1974a) explored the properties of bristlecone pine (Pinus longaeva)
tree-ring records along an ecological gradient, from lower- to upper- forest border
in the Snake Range of eastern Nevada. He showed that there were positive cor-
relations between high-frequency (one to several years) variations at all sites, but
that the longer term (multidecadal to multicentennial) trends and ﬂuctuations at the
upper forest border were negatively correlated with ﬂuctuations at the lower forest
border. Using both response function analysis and reasoning from the biology of
bristlecone pine, he concluded that the low-frequency variations were likely related
to warm-season temperature ﬂuctuations in the case of the records from the upper
forest border, whereas the positively correlated high-frequency variations were
related to precipitation. His response functions showed rather weak temperature
responses, but he argued that the longevity of needles in bristlecone pine, from one
to several decades, and the strong correlation between their length and summer
temperature would place a bidecadal and longer temperature signal in the upper
forest border ring series. This analysis was conducted using data for the period AD
1480 to 1965, from a single mountain range. These ﬁndings were subsequently
Climatic Change 59: 233–244, 2003.
© 2003 Kluwer Academic Publishers. Printed in the Netherlands.