geog3839.16, dendroecology

D E N D R O E C O L O G Y

Many ecosystem processes, especially those affected by climate changes, manifest themselves only over longer time periods and broader spatial scales than encompassed in typical ecological studies.

“”Swetnam and Brown, 2010

Understanding the dynamics of long-lived organisms and ecosystems — and the role of climate in controlling these dynamics — requires decadal to centennial and landscape- to regional-scale perspectives.

“”Swetnam and Brown, 2010

Dendroecology is the use of tree-ring dating and analyses to investigate events and processes involving the interactions of organisms with their environment.

Rt = At + Ct + δD1t + δD2t + Et

THE PRINCIPLE OF AGGREGATE TREE GROWTH

Rt = At + Ct + δD1t + δD2t + Et

THE PRINCIPLE OF AGGREGATE TREE GROWTH

A. Forest demography

B. Growth dynamics

C. Disturbance ecology

DENDROECOLOGY

A. Forest demography

Photograph: Kurt KipfmuellerPhotograph: Dawn Hopkins

Ecologists have long recognized that time series of tree births and deaths are of fundamental value for understanding forest and woodland dynamics.

“”

Swetnam and Brown, 2010

Photograph: Kurt Kipfmueller

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Tree recruitment dates (by 50-year periods)

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Tree mortality dates (by 50-year periods)

TREERECRUITMENT

DATE OFGERMINATION

DOESNOT

EQUAL

Pith

Hi"ing the pith is easy when you collect an entire cross-section

It’s more difficult when coring, especially if growth is asymmetric.

Coring height

Root collar

How many years separate the root collar from the stem at coring height?

Source: Gutsell and Johnston (2002)

The germination date can be much earlier than tree age at coring height.

Photograph: Kurt Kipfmueller

Germination doesn’t happen immediately a$er disturbance.

The ecesis interval is the amount of time between an initial disturbance and the successful establishment of the first trees.

Photograph: John Krumm

The condition of dead trees affects the continuity of their record

Snags may have lost an unknown number of outer rings.

How can we reduce the effects of these different sources of uncertainty?

In old, uneven-aged forests, sometimes hundreds of trees must be sampled to obtain adequate characterization of age structure distributions.

“”

Swetnam and Brown, 2010

Demographic surveys in the Mazama Mountains Tom Swetnam

5-ha plots

Sampling dead trees in the pinon-juniper woodlands Tom Swetnam

Pinyon Demography at Sevilleta LTER, Central New Mexico

Source: Betancourt et al. (2004)

Severe sustained drought in the Southwest during the 1950s

Source: Swetnam and Betancourt (1998)

less than 85% of average precipitationfor 10 or more years

Germination of ponderosa pine coincides with warm, wet summers

Source: Swetnam and Brown (2010)

THE ‘FADING RECORD’ PROBLEMThe preservation of dead trees becomes less common with time before present, and obtaining estimates of past mortality events depends both on persistence of woody material and the ability to adequately sample the material to obtain death dates.

B. Growth dynamics

Photograph: Kyle Pierce

A growth suppression is a rapid reduction of growth from one year to the next, usually lasting for several years.

Growth suppressions are caused commonly by defoliating insects.

Photograph: Eli Sagor

Suppression, possibly caused by 1064 eruption at Sunset Crater

Source: Fri!s and Swetnam, 1989

A growth release is the opposite of a suppression, with growth increasing rapidly for several years.

Growth releases may be caused by the death of ‘overstory’ trees.

Growth release caused by 1966 timber harvest.

Source: Fri!s and Swetnam, 1989

Using release events to identify insect outbreaks

Source: Berg et al. (2006)

Studying the frequency of growth releases across many stands.

Source: Berg et al. (2006)

C. Disturbance ecology

Photograph: Miguel Vieira

Rt = At + Ct + δD1t + δD2t + Et

THE PRINCIPLE OF AGGREGATE TREE GROWTH

Photograph: William Ciesla

Western spruce budworm Choristoneura occidentalis Freeman

White fir Abies concolor

Photograph: brewbooks

Douglas-fir Pseudotsuga menziesii

Photograph: William Ciesla

No typical pa"ern or trend in western spruce budworm epidemics has been apparent; most of the early epidemics lasted for a few years and then subsided naturally; others persisted longer, at times without spreading over large areas.

“”Fellin and Dewey, 1982

Photograph: Dave Powell

The tree-ring basis for developing outbreak chronologies is the observation of very sharply reduced ring growth in the host species during the defoliation episode, which typically lasts for a decade or longer.

“”

Swetnam and Brown, 2010

Growth suppression in white fir defoliated by spruce budworm

Photograph: Tom Swetnam

Rt = At + Ct + δD1t + δD2t + Et

THE PRINCIPLE OF AGGREGATE TREE GROWTH

?

NON-hOSTHOST

NON-hOSTHOSTWhite fir

Douglas-fir Ponderosa Pine

Photograph: Brewbooks

G(HOST) < G(NON-HOST) =

potential outbreak

Source: Ryerson et al. (2003)

GRAY = Host > Non-hostBLACK = Host < Non-host

Source: Ryerson et al. (2003)

Using host/non-host comparisons to identify budworm outbreaks

Percentage of trees recording an outbreak of western spruce budworm in the Rio Grande National Forest, Colorado

Source: Ryerson et al. (2003)

397 trees

Do drought conditions inhibit spruce budworm outbreaks?

Source: Ryerson et al. (2003)

Dendroecology is the use of tree-ring dating and analyses to investigate events and processes involving the interactions of organisms with their environment.

Strengths of dendroecology

1. Tree-ring records provide a much longer perspective than documentary records or modern surveys.

Strengths of dendroecology

1. Tree-ring records provide a much longer perspective than documentary records or modern surveys.

2. Tree-ring evidence has a high degree of temporal precision compared to other paleoecological tools.

Strengths of dendroecology

1. Tree-ring records provide a much longer perspective than documentary records or modern surveys.

2. Tree-ring evidence has a high degree of temporal precision compared to other paleoecological tools.

3. Chronological control allows multiple lines of evidence to be compared.

Strengths of dendroecology

Limitations of dendroecology

1. Tree-ring records are fragmentary and can be distributed irregularly in time and space.

Limitations of dendroecology

1. Tree-ring records are fragmentary and can be distributed irregularly in time and space.

2. Some species, events or processes cannot be reconstructed and therefore remain unknown.

Limitations of dendroecology

1. Tree-ring records are fragmentary and can be distributed irregularly in time and space.

2. Some species, events or processes cannot be reconstructed and therefore remain unknown.

3. Past ecological conditions may have no analog in the modern system, making their behavior difficult to interpret.

Limitations of dendroecology

ASSIGNED READINGTom Swetnam and Peter Brown (2010), Climatic inferences from dendroecological reconstructions. M.K. Hughes et al. (eds.), Dendroclimatology, Developments in Paleoenvironmental Research.

D. Fire history and fire climatology

Class visitor Dr. Kurt Kipfmueller

FOR NEXT CLASSRead sections 9.2.1 (Fire History and Fire

Climatology) and 9.3 (The Late Eighteenth-Century, Early Nineteenth-Century Fire Gap)