Source: Whitney Crawford

November 6

Dendroecology

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

Source: William Ciesla

Western spruce budworm Choristoneura occidentalis Freeman

Wind-thrown red pine Quetico Provincial Park, Canada

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

Why does Ecologyneed dendroecology?

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

“ ”Tom Swetnam and Peter Brown

Dendroclimatology, 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.

“ ”Tom Swetnam and Peter Brown

Dendroclimatology, 2010

Forest demography

Growth dynamics

Disturbance ecology

DENDROECOLOGY

Rt = At + Ct + δD1t + δD2t + Et

THE PRINCIPLE OF AGGREGATE TREE GROWTH

Forest demography

Source: Kurt KipfmuellerSource: Dawn Hopkins

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

“ ”Tom Swetnam and Peter Brown

Dendroclimatology, 2010

Source: Kurt Kipfmueller

200019001800170016001500

200019001800170016001500

Tree recruitment dates (by 50-year periods)

200019001800170016001500

Tree mortality dates (by 50-year periods)

Pinyon Demography at Sevilleta LTER, Central New Mexico

Source: Betancourt et al. (2004)

Sampling dead trees in the pinon-juniper woodlands Tom Swetnam

COMPLICATING FACTORS

Photograph: John Krumm

The condition of dead trees a!ects the continuity of their record.

Snags may have lost an unknown number of outer rings.

TREERECRUITMENT

DATE OFGERMINATION

DOESNOT

EQUAL

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

It’s more di#cult 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.

Source: 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.

The 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.

THE ‘FADING RECORD’

PROBLEM

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.

“ ”Tom Swetnam and Peter Brown

Dendroclimatology, 2010

Source: Kurt KipfmuellerSource: Dawn Hopkins

Germination pulses of ponderosa pine have coincided with warm, wet summers.

Source: Swetnam and Brown (2010)

Growth dynamics

Source: Kyle Pierce

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

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

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

Growth release caused by 1966 timber harvest.

Source: Fri"s and Swetnam, 1989

Growth suppressions are caused commonly by defoliating insects.

Source: Eli Sagor

Suppression, possibly caused by A.D. 1064 eruption at Sunset Crater in Arizona.

Source: Fri"s and Swetnam, 1989

Release events can be used to identify past insect outbreaks.

Source: Berg et al. (2006)

You really need to study the frequency of releases across MANY stands.

Source: Berg et al. (2006)

Disturbance ecology

Source: Miguel Vieira

Rt = At + Ct + δD1t + δD2t + Et

THE PRINCIPLE OF AGGREGATE TREE GROWTH

Western spruce budworm Choristoneura occidentalis Freeman

White fir Abies concolor

Source: brewbooks

Douglas-fir Pseudotsuga menziesii

Source: William Ciesla

Source: 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.

“ ”David Fellin and Jerald Dewey

Western Spruce Budworm, 1982

Source: Dave Powell

NON-hOSTHOST

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.

“ ”Tom Swetnam and Peter Brown

Dendroclimatology, 2010

Western spruce budworm Choristoneura occidentalis Freeman

Source: Brewbooks

NON-hOSTHOSTWhite fir

Douglas-fir Ponderosa Pine

Growth suppression in white fir defoliated by spruce budworm

Source: Tom Swetnam

Rt = At + Ct + δD1t + δD2t + Et

THE PRINCIPLE OF AGGREGATE TREE GROWTH

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

potential outbreak

Source: Ryerson et al. (2003)

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

Source: Ryerson et al. (2003)

Comparisons between hosts and non-hosts can help 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)

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

“ ”Tom Swetnam and Peter Brown

Dendroclimatology, 2010

Do drought conditions inhibit spruce budworm outbreaks?

Source: Ryerson et al. (2003)

Source: Whitney Crawford

November 6

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

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 di#cult to interpret.

Limitations of dendroecology

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