Branches of Dendrochronology
1 .Dendroarchaeology
Dendrochronology has gained recognition in archaeology as an accurate tool
for chronological control. Dendrochronologists have used tree rings to
date the construction of archaeological structures (Douglass 1929, Haury
1962, Dean 1978, Dean et al. 1985, Billamboz 1992, Cufar 2007), scars
from Native American use of the inner bark of pine trees (Kaye and
Swetnam 1999), and to verify the dating of historical works of art (Lavier
and Lambert 1996, Jansma et al. 2004, Cufar 2007) such as the panels in
paintings (Bauch and Eckstein 1970, Eckstein et al. 1986) or the wood in
violins (Grissino-Mayer et al. 2002).
Tree rings can also be used to dendro-provenance archaeological or historical
wood (Eckstein and Wrobel 2007). This is a fast growing sub-field of
dendrochronology that uses wood anatomy and correlation to regional
master chronologies to determine the origin of and trade routes for wood
that has been incorporated into artifacts.
The first contribution of dendrochronology to archaeology
was made by A.E. Douglass, who determined the exact
occupation dates of approximately 45 archaeological
sites in the southwestern United States (Douglass 1929,
Haury 1962, Nash 1999). This work started in 1914 when
Clark Wissler Curator of Anthropology with the American
Museum of Natural History suggested that Douglass use
tree rings to date the Native American structures in the
American Southwest. Douglass began to examine
samples that were submitted from archaeological sites in
New Mexico. In 1921, Neil Judd of the United States
National Museum approached Douglass about continuing
his dating efforts in the southwest and suggested
applying for funds from the National Geographic Society
(NGS), which provided funds for Douglass’ research from
1923-1930.
Archaeological methods
Many of the methods used in Dendroarchaeology are similar to those employed in
basic dendrochronology, such as crossdating, sample preparation, and
standardization. Other methods, such as site selection, cannot be employed,
because the site is determined by the location of the archaeological dwelling,
and the original locations of the trees are chosen by the residents of the
dwelling. Dendroarchaeology also has some unique field methods of its own.
Samples are often taken from structural beams in houses or wood that is in place
and has been in position and drying for hundreds of years. To reduce the
damage to the original structure and to be able to get a sample from dry wood, a
special archaeological borer is used. A drill guide can be used to hold the drill bit
steady as the researcher begins to core the beam. This drill guide is a metal plate
with a hole in the center of it, just larger than the diameter of the drill bit. It is
affixed to the beam with two short nails and is removed once the core is started.
The archaeological borer is driven by an electric drill and uses a specially made
extra long hole-saw to cut the wood away from around a 10-12mm diameter
core. The core is then removed from the hole with a bent wire which is inserted
down the side of the hole and twisted to break the core off at the center of the
beam.
Archaeologists must collect the outer surface of a beam
to be able to get the cutting date of a tree. That is the
most important date for a dendroarchaeologist. This
outer surface can be identified by bark, a smooth
outer surface that may gain a patina with age, or by
bark beetle galleries on the outer surface of the stem.
The bark beetle will feed in the cambium layer while
the tree is still alive and leave a small indentation in
the xylem of the tree. Other wood boring insects,
however, leave galleries in the xylem which should not
be mistaken for an indication of the outer wood
surface.
Studies in dendroarchaeology
• Dendrogeomorphology in Archaeology.
• Mast (massive fruit production in trees; specifically
acorns in this example) reconstructions from tree rings
(Speer 2001)
• Dating Artifacts
• Climate Reconstructions
• Ecological Reconstructions and Anthropogenic Ecology
• Fire in the southwestern United States
• Fire in the eastern United States
• Culturally Modified Trees
• Insect Outbreaks
2. Dendroclimatology
One of the first and most publicly debated applications in dendrochronology has been the
ability to reconstruct climate from tree rings. Because trees respond to their
surroundings, they are subject to climatic stresses such as variations in temperature,
rainfall, soil moisture, cloudiness days (number of days with clouds which reduces
photosynthesis), and wind stress. In fact, climate seems to be one of the main controlling
factors of most tree-ring growth across all spatial and temporal scales. The basic steps in a
climate reconstruction are relatively simple and are often normal procedures that are
done even before ecological reconstructions. But the statistical analyses of tree-ring
chronologies for dendroclimatic reconstructions have become increasingly sophisticated.
Dendroclimatologists are interested in past climate so that the variation and trend of modern
climate can be put into perspective. The natural range of variation of the climate system
can be reconstructed from examination of the past through tree rings (Morgan et al.
1994). From various types of climate reconstructions (based on ice cores, marine and lake
sediments, and dendrochronology) we have learned about the glacial/interglacial cycle
(100,000 years), the shorter-term Holocene climate variation (past 10,000 years), and
documented recent warming in the modern era. Mann et al. (1998) reconstructed climate
variation from multiple proxies including tree rings for the past six centuries showing an
abrupt increase in temperature associated with the industrial revolution. This
reconstruction has been questioned from many quarters with the most constructive
criticism stating that it does not take low frequency climate variability into consideration
as shown by lack of evidence for the Medieval Warm Period and the Little Ice Age
(Moberg et al. 2005).
Climate phenomena, such as hurricanes, can be
reconstructed from tree rings because of the specific
signal recorded in ring width and in the isotopic
chemistry of the rings. Climatic reconstruction,
therefore, can be used to examine the proximal cause of
ring width, such as changes in temperature or rainfall, or
it can be used to examine broader scale patterns and
phenomena that are recorded along with changes in
temperature and rainfall. In the case of hurricanes, an
isotopic signature can be identified in the fluctuations of
wood chemistry through time (Mora et al. 2006).
Another powerful tool is use of tree-ring networks to
examine climate variability on a broad spatial scale such
that inferences can be drawn about long-term changes
in synoptic climatology (the flow in the climate system
including pressure differences) (Hirschboeck et al.
1996).
Methods of dendroclimatology
• Climate reconstruction starts with a site-level analysis of a tree species’ climate
response. Standard dendrochronological methods are used such as site selection,
coring at breast height, crossdating, and measuring the samples.
• Trees are chosen from climate sensitive sites, such as steep rocky slopes or northern
treeline. A variety of tree ages can be used in climate reconstructions because trees
may change in their climatic response with age. The oldest trees are chosen to obtain
the longest chronologies, but older trees may have a weakened climate signal due to
senescence. Trees with obvious injuries or sub-dominant canopy position are avoided
because of possible complication of the climate signal with other micro-environmental
factors. The climate signal in growth of very young trees may similarly be distorted by
such factors.
• Sample depth is always an important issue in dendrochronology, but of paramount
importance in climate reconstruction. Sample depth is simply the number of samples
that represent a phenomenon back through time. The ring-width measurements are
corrected for an age-related growth trend and the resultant index values are averaged
together to create a chronology with a stand-level signal that is analyzed for its climate
response. The goal is to create a robust climate reconstruction that maintains a
consistent climate signal whether sample depth is increased or the ring width series are
standardized in a different fashion.
Future perspectives of Dendroclimatology
• Growth-climate interpretation
• Climate Indices (El Niño Southern Oscillation (ENSO), Southern
Oscillation Index (SOI), Pacific Decadal Oscillation (PDO), North
Atlantic Oscillation (NAO), Multidecadal Oscillation (AMO) etc.
• Climatic Gradient Studies
• Dendrohydrology: Water Table Height and Flood Events
• Treeline Studies
• Climate phenomena at latitudinal gradient
• Archaeological Uses of Climate Reconstructions
• Climate reconstruction & future prediction
3. Dendroecology
Dendroecology uses dated tree rings to study ecological events such as fire
and insect outbreaks. Dendroecology was developed as a field of study
by Theodor Hartig and Robert Hartig in the late 1800s in Germany, with
Bruno Huber continuing the tradition from 1940-1960 (Schweingruber
1996).
In the United States, dendroecology did not develop until the 1970s with
early work proposed by Hal Fritts (Fritts 1971). Since the 1970s,
dendroecology has greatly expanded to include the study of fire history
(Dieterich and Swetnam 1984), insect outbreaks (Swetnam et al. 1985),
masting (synchronous fruiting in trees; Speer 2001), stand-age structure
(Lorimer and Frelich 1989), pathogen outbreaks (Welsh 2007), and
endogenous disturbance history (Abrams and Nowacki 1992).
All three of these subfields of dendrochronology have a sufficient amount
of research, refined methods, and techniques to be addressed
independently. For this work, I define dendroecology as analysis of
ecological issues such as fire, insect outbreaks, and stand-age structure
with tree rings.
Forest ecology questions
No apparent change?
Change in the growth rate
Change in regeneration
Change in disturbance
Change in distribution
Change in composition
Change in ……
Die off?
Methods for Dendroecology
General methods of dendroecology usually involve the standard field and laboratory analyses,
with particular emphasis on establishment dates for succession studies, scar ring from
fires, or suppression and release events to document insect outbreaks or episodes of
logging. Some methods are specific to dendroecology; for example, in order to determine
exact establishment dates, cores are often taken at ground level and special care is
directed towards obtaining pith.
Practices in Dendroecology
Stand age structure
Ring width analysis
Tree scars
Basal Area Increment (BAI)
Gap Phase Analysis
Forest Productivity & Succession
Old Forest Performance
Growth Performance of Forest Trees
Dendropyrochronology
Distributional Limits of Species
Treeline and Subarctic Studies
Interactions of Multiple Disturbances
Treeline ecotone
Future Perspective
Dendroecology has been and is becoming more useful
for exploring a wide range of research topics that can
provide important information to wildlife, fisheries,
and forest resource managers. Combining the study of
tree rings and ecology can help us understand the
dynamics of natural processes such as disturbance and
the interactions between multiple natural
phenomena. Trees can provide long-term records on
many different phenomena at different spatial scales,
enabling dendroecologists to contribute to important
discussions on scaling laws that could aid
management in a changing environment.
4 .Dendrogeomorphology
Geomorphology is the study of landforms and the earth
surface processes that form and modify them (Gärtner
2007a). Dendrogeomorphology uses tree rings to date
geological processes that affect tree growth such as
landslides, river deposits, or glacial activity.. I consider
dendrogeomorphology to include the subfields of
ofdendroglaciology (the study of the movement or mass
balance of glaciers),dendrovolcanology (the study of past
volcanic eruptions),dendrohydrology (the study of stream
dynamics), and dendrosiesmology (the study of past
earthquake events and fault movements through the use
of tree rings) (Table 10.1).
Sources of information for geomorphology
(object from F.H. Schweingruber)
Larix decidua: exposed root
• Reaction wood
• Death dates
• Establishment dates
• Wound events
• Coarse Woody Debris (CWD)
• Roots
Subfields of Dendrogeomorphology
Tree cross‐section
exhibiting
“eccentric” growth
• Dendrovolcanology
• Dendroglaciology Up
hillside
• Isostatic adjustment
• Mass Movement
• Dendroseismology:
(Plate Boundaries,
Faults, and Earthquakes)
Down hill side
Future perspective
Dendrogeomorphology has greatly expanded in the last 20
years with a wealth of applications and studies documenting
past geologic events. The researcher has to think creatively
about how a past event may have been recorded by the
trees in the area. The variety of sampling techniques and
sources of data used in this subfield of dendrochronology
are probably more diverse than in any of the other
applications. As with all of dendrochronology, these studies
rely on the accuracy provided by crossdating. Without it,
researchers would not be able to definitely determine the
timing of events or to assign a specific event to a growth
response. In the next chapter, I will describe the use of
chemical and isotopic analysis of tree rings which is one of
the newest forms of data being drawn from tree rings.
Dendroglaciology
Early work in dendroglaciology set the precedent for the variety of information that
can be obtained from tree-ring studies as they apply to glacial research (Tarr and
Martin 1914, Lawrence 1950, Sigafoos and Hendricks 1961, Sigafoos and Hendricks
1972).
Glacial advance can be documented by dating mortality events of sheared trees that
are deposited in outwash till and glacial retreat can be documented by the
establishment of trees on newly exposed glacial till (Wiles et al. 1999). Between
these two techniques, mortality events from glacial advance is more precise
because the death of the trees can happen in a year or less, while it may take
decades for trees to establish on newly exposed rock and till after glacial retreat
(McCarthy and Luckman 1993). Through connections with climatic forcing factors,
glacial mass balance (periods of growth and ablation) can also be reconstructed
from tree rings (Mathews 1977, Laroque and Smith 2005).
Trees that grow at the trimline where the ice is directly next to the trees, can record
fine scale glacial fluctuation in time (Lawrence 1950, Wiles et al. 1996). Hard work
over the past few decades has produced evidence for many alpine and continental
glacial changes over the past 2,000 years that have been combined into broad scale
interpretation of glacial dynamics (Wiles et al. 2008). Such dendroglacial
reconstructions as these extend many centuries into the past and clarify the
mechanisms that drive glacial activity.
Isostatic adjustment (the rise of land) after the retreat of
glaciers has been documented using the downslope
establishment of trees towards present day sea level to
document the rate of this uplift (Begin et al. 1993). During
the last glacial maximum at 21,000 calendar years ago
there were approximately six kilometers of ice above the
Canadian Shield. Once the weight of ice from a major
glacier is removed from the terrain, the land begins to
adjust to that lack of weight and to rise, sitting higher on the
mantle. New land surfaces are exposed upon which trees
can establish. In a research project located on the margins
of Hudson Bay in Québec, Begin et al. (1993) dated tree
establishment along transects to current sea level parallel to
the slope, documenting the progressive advancement of
this lower treeline. A similary pattern was identified from
land adjustment after Little Ice Age glacial retreat in Glacier
Bay Alaska where Motyka (2003) documented 3.2 m of
uplift since the late 18th century.
Mass movement
Tree rings can also be used to examine any mass movement such as
rockslides (Figure 10.4), landslides (Corominas and Moya 1999), rock
glaciers (Giardino et al. 1984), debris flow (Hupp 1984, Hupp et al.
1987), or volcanic mudflow (also known as a lahar; Yamaguchi and
Hoblitt 1995). Just as with flooding, trees can be scarred by mass
movements of earth, they can be killed, or fresh earth surfaces can be
deposited or exposed on which trees can establish (Hupp 1984, Hupp et
al. 1987, Corominas and Moya 1999, Fantucci and Sorriso-Valvo 1999).
Soil creep can cause curvature of stems, although it can be hard to
differentiate from curvature due to wintertime snow pressure (Shroder
1980). Soil erosion can expose roots causing root mortality (LaMarche
1968, Danzer 1996) or producing cells with different cell wall
thicknesses depending upon their depth in the soil.
Dendroseismology: Plate boundaries, fault, earthquakes
Any earthquake could cause damage to a tree by breaking fine and even large
roots for the locally affected trees. Jacoby (1997) provides a complete
review of paleoseismology from tree-ring analysis, noting that trees can
be damaged directly from shaking, elevation changes, and liquefaction, or
indirectly through earthquakes that induce landslides and tsunamis.
A massive earthquake that triggered a tsunami and landslide killed thousands
of trees sometime between A.D. 894 and A.D. 897, and was documented
by studying submerged logs from Lake Washington near Seattle,
Washington (Jacoby et al. 1992). This work combined dendrochronology
with 14C dating to determine a window of dates for a floating chronology
(a chronology not anchored in time) composed of trees that had been
killed in the same season of the same year by a tsunami triggered by this
earthquake. Atwater and Yamaguchi (1991) also found evidence for a
major coastal event that submerged trees in the Seattle area in A.D. 1700.
Suppression of ring width over several years may be another indicator of
seismological events in addition to tree mortality and damage. For
example, an 1887 earthquake in Kazakhstan resulted in ring-width
reduction for four to 15 years in most sampled trees (Yadov and Kulieshius
1992).
Considerable research has been conducted to study specific types
of plate movement associated with plate tectonics and fault
types such as transform plate boundaries (Page 1970, LaMarche
and Wallace 1972, Wallace and LaMarche 1979, Meisling and
Sieh 1980, Jacoby et al. 1988, Sheppard and Jacoby 1989, Lin and
Lin 1998, Vittoz et al. 2001, Wells et al. 1998), convergent plate
boundaries (Jacoby and Ulan 1983, Sheppard and Jacoby 1989,
Atwater and Yamaguchi 1991, Veblen et al. 1992, Yadav and
Kulieshius 1992, Kitzberger et al. 1995, Jacoby et al. 1997), strike-
slip faults (Stahle et al. 1992, Van Arsdale et al. 1998), reverse
faults (Ruzhich et al. 1982, Stahle et al. 1992, Van Arsdale et al.
1998), and normal faults (Sheppard and White 1995, Bekker
2004).
Because earthquakes are the results of plate tectonics, the study of
geological faults with dendrochronology uses the same
techniques as earthquake reconstructions. It is important that
the researcher take into account damage to trees and the spatial
distribution of sampling when determining whether or not
suppression of tree rings is directly related to the seismic events
under study (Jacoby 1997, Bekker 2004).
Dendrohydrology: Water table height & flood events
Dendrohydrology is the subfield of dendrochronology that uses tree rings to
reconstruct hydrological phenomena (Schweingruber 1996). Water table
changes, land subsidence, flood height and energy, and streamflow can all
be reconstructed using tree-ring data. Dendrohydrological records can be
reconstructed through suppression or release events in trees associated
with water table changes and land subsidence, scars and growth changes
associated with flood events, establishment of trees on newly deposited
surfaces, and changes in growth as a response to climatic phenomena that
drive river discharge.
Stream behavior can be documented by a variety of effects on tree growth
that include flood scarring, tree leaning from undercutting, and
establishment of trees on new sediment surfaces (Gottesfeld and
Gottesfeld 1990). For example, a flood history of the Potomac River in
Washington D.C. was determined using tree rings to date flood scars
(Sigafoos 1964). The height of the scars can also be used to document the
height of flood waters in the past. Begin (2000) recorded ice scarring on
the trees surrounding lakes in Quebec, Canada to record lake flood events.
Yanosky and Jarrett (2001) found distinct variations in the wood anatomy
of oak trees; they identified white rings that were formed from open
fibers when a tree’s root were submerged in water and earlywood vessels
when a tree was submerged and stripped of leaves at the end of the
growing season. These distinct anatomical changes are an excellent
indicator of past flood damage.
Information about long-term patterns of streamflow, flooding, and water level in
reservoirs is relevant to anyone who makes decisions about water allocation
(Meko and Woodhouse in press). Streamflow reconstructions, for example, can
help municipal water managers plan for the natural variability in water resources
(Woodhouse 2001). Correlations of ring width to streamflow data from the
Colorado Front Range was used to reconstruct streamflow along the South Platte
River and Middle Boulder Creek back to A.D. 1703 (Woodhouse 2001).
Stockton and Jacoby (1976) reconstructed stream flow for 12 stream gauge stations
in the Upper Colorado River Basin and found that flow was at record high levels in
the early 1900s based on their 450-year reconstruction. This meant that the
water allocation for the Colorado River based on the early 1900s levels could not
be met during a normal year of stream flow. This was actually known at the time
of the allocation decision based on research done by Douglass and Schulman.
The commission reduced the amounts that were allocated because of this higher
growth shown in the tree-ring chronologies, but they did not adjust it enough (see
Schulman 1938 for published reconstructions). Cook and Jacoby (1977) used
standard climate reconstruction techniques to document drought frequency in
the past as it relates to water supplies in the Hudson River Valley of New York.
Other work has demonstrated the direct connection between frequency of
drought events and the reliability of water reserves in various reservoirs (Stockton
and Jacoby 1976, Jain et al. 2002, Woodhouse et al. 2006).
Dendropyrochronology
Reconstruction of fire histories is one of the major applications of dendrochronology for use in
management of forests and the reestablishment of fire as a disturbance agent. Any prescribed fire
policy in the United States must be supported with scientific evidence for that tract of land. These
federal and state laws have motivated fire reconstructions on many parcels of land which, in turn
have generated a comprehensive view of the role that fire plays in these fire-prone landscapes. The
goal of the dendrochronologist is to determine the natural range of variability for fire on a particular
site (Landres et al. 1999). The natural range of variability describes the past occurrence of fire, how
frequently it affects a site, and the area that it has covered in the past. From this information, forest
managers can determine how fire has behaved on their land in the past and how fire regimes have
changed in the 20th century (Heyerdahl and Card 2000).
Three main fire types occur around the world. A surface fire is one that burns over the ground surface,
consuming duff and fine fuels. These fires usually move through an area fairly quickly and burn at a
low to moderate severity. Many forest types, such as ponderosa pine, red pine, and giant sequoia
(Figure 9.2) depend on these frequent low-severity surface fires to remove competition and to burn
off the duff layer, allowing seedlings access to mineral soil. Oak woodlands also seem to be
dependent upon frequent fire to maintain this forest type. Stand-replacing fires occur less
frequently when fuels have built up to a critical level and often cause high tree mortality. These
fires will often burn through the canopy of the trees and, therefore, are also calledcrown fires (Figure
9.3). Some pine forests, such as lodgepole pine, are adapted to this type of fire. Stand-replacing
fires burn through a forest and kill the mature trees. Many of the trees that are adapted to a stand-
replacing fire regime have serotinous cones which only open to spread their seed when they are
heated, as a coating of resin or woody layer is burned off.
Stand-replacing fires occur frequently in the boreal forest where
dry summers in a continental climate combined with little
topographic relief, warm winds, and convective storms result
in fire that can burn a large area of the landscape. The third
ground fire that actually burns under ground in the organic-
rich soils of histosols. These fires are common in Alaska
where they can burn for more than 30 years as they smolder
through the thick organic layers of plant material on the
ground.
Conclusions from Dendropyrochronology. Fire history has been
one of the main tools of dendroecologists, supplying much
information about disturbance ecology over the past 30
years. While working with this application, researchers have
perfected techniques for seasonal resolution of dating scars
preserved in the trees and have made advances in spatial as
well as temporal analysis.
Dendroentomology
The study of insect outbreaks has become a major subfield of study in
dendrochronology because forest managers are interested in the historical
effects of insects on their managed lands. Dendroentomology documents
past occurrence of insect outbreaks and gives an understanding of insect
population dynamics including duration of outbreaks, interval between
outbreaks, and the spread of insect outbreaks (Swetnam et al. 1985). As
with all dendrochronological applications, dendroentomology provides a
long-term perspective for ecological dynamics in a forest system.
The earliest study of insect outbreaks using tree rings was conducted by a
German botanist, Ratzeburg (1866), who dated outbreaks of a defoliating
caterpillar with annual resolution (Ratzeburger 1866, as cited in Wimmer
2001 and Studhalter 1955). In an introductory textbook on forestry,
Hough (1882) shows a graphic of the reduced growth of tree rings related
to the defoliation of insects in the eastern U.S. The presence of this
graphic and statement in a forestry textbook in the late 1800s
demonstrates the general knowledge of tree growth, the ability to date
ecological phenomena with tree rings, and the effect of insects on trees
and their growth. The field of insect outbreak reconstructions started in
earnest in the 1950s and 1960s when a series of publications made this
discipline more accessible to researchers (Blais 1954, 1957, 1958a, 1958b,
1961, 1962, 1965, Hildahl and Reeks 1960
Blais (1958a) documented a decrease in ring width of balsam fir and white
spruce due to the effects of eastern spruce budworm (Choristoneura
fumiferana). In 1960, Hildahl and Reeks published a study on the effect of
forest tent caterpillar (Malacosoma disstria) on trembling aspen in Manitoba
and Saskatchewan. Blais (1962) did much to establish the techniques for
studying insect outbreak dynamics in his study ofeastern spruce budworm in
Canada. Long-term reconstructions covering the past 200-300 years have
demonstrated that spruce budworm has increased in frequency, extent, and
severity caused by human changes in the forest ecosystems (Blais 1983).
Swetnam et al. (1985) published a manual on how to approach insect
outbreak studies that became a standard in the field. This publication helped
to codify an approach to insect outbreak reconstruction that was quickly
followed from the 1990s to the present with a flurry of dendrochronological
insect outbreak publications. Canada is one of the more active areas in
insect outbreak reconstruction with work by Krause and Morin (1999), Zhang
and Alfaro (2002), and Campbell et al. (2007).
Insect outbreak studies come in many different forms depending upon how the
insects affect the trees; insects may be defoliators, cambium feeders, or root
parasites. The defoliators focus on a type of tree and consume leaves or
needles from those tree species. Examples of these types of insects include
western spruce budworm (Choristoneura occidentalis) (Swetnam and Lynch
1993), Douglas-fir tussock moth (Orgyia pseudotsugata) (Swetnam et al.
1995, Mason et al. 1997), and pandora moth (Coloradia pandora) (Speer et
al. 2001) (see Table 9.1 for a more comprehensive list). Insects that feed on
the cambium, usually killing the tree, include bark beetle larvae
(Dendroctonous and Ips species) (Eisenhart and Veblen 2000).
Reduction in tree growth reflects the period when defoliation
significantly impacts tree health and does not usually begin
precisely with the onset of the insect population’s increased
growth (Swetnam and Lynch 1993). Stored food reserves
can delay defoliation-induced growth loss by one or more
growing seasons (O’Niell 1963, Kulman 1971, Brubaker and
Greene 1979). Since a tree requires time to replace lost
foliage following severe defoliation, its growth may be
inhibited for several years after the insect populations have
crashed (Duff and Nolan 1953, Mott et al. 1957, Wickman
1963, Brubaker and Greene 1979, Alfaro et al. 1985, Lynch
and Swetnam 1992).
The tools developed from dendroentomology are now
being used for other forest health agents such as
fungal pathogens (Welsh 2007) and to address
complex disturbance systems involving multiple
agents (e.g. Thompson 2005). These concepts take
advantage of the aggregate tree growth model,
limiting factors, site selection, and replication, just to
name a few of the main principles of
dendrochronology that are applied and honed
through insect outbreak studies. These techniques
continue to grow as researchers expand to new insect
systems such as periodical cicadas and mountain pine
beetle. The management concerns of foresters force
the research agendas of many scientists as we react
to public concern and governmental interest.
