Geog696M: Geography and DendrochronologyFall 2008

Dendrochronology and Forest Demography

• Variability in spatial patterns of tree demography due to climate and disturbance as documented with dendrochronology. • Shifts in treeline* at upper and lower forest borders • Changes in forest composition and density due to fire suppressing, grazing and other disturbances, • Patterns and process related to episodes of recruitment and mortality over past centuries to millennia.

When and where to meet? This time/place OK?

Focus of class: upper, lower treeline?

Idea of publication of literature review? If so, what aspects should the review cover and can we make an outline of the sections of the review, and select an order of readings?

Organization: generate outline that identifies topic areas of interest to be covered (for a review or not); students take one or more topics, identify relevant papers to read, and lead weekly discussions.

*by treeline, I mean the limit of tree growth of any form; treeline sometimes means the limit of upright trees, while timberline means the limit of tree growth

Large scale, region-wide treeline related to climate

At a smaller scale, more spatial variability obvious; tree forms, disturbance agents, topographic limits

Topographic and substrate constraints on treeline

Variability in species, tree growth form, changes over time?

Disturbance at treeline or a climate influence?

Changes at treeline; recent recruitment above current treeline

Changes in treeline: Evidence of a higher treeline in the past

Some General Treeline Topics (many of these overlap with each other):

Causes and controls of treeline, physiologic, topographic, climate (including large scale circulation)

Treeline ecotone dynamics, patterns, processes, feedbacks

Subarctic treeline, changes over recent times, role of climate

High elevation treeline, evidence for change, role of disturbance

Lower forest border treeline changes, esp. drought, changes in species, invasion into grasslands

Paleo treelines and climate, evidence of past treeline

Other topics to consider:

Treeline and the forms it takes

Upright trees

Krummholz

Tree islands

Lower treeline characteristics

Influences on treeline – constant vs variable

Topography (aspect, slope, top vs basin)

Substrate (soils, geology, frozen ground)

Climate (for both recruitment and mortality); precip, snowpack and deposition, temperature, wind….

Disturbance (fire, avalanche, drought, insects and disease, humans; inter-relationship between these)

Biological factors (seed crops, dispersal, recruitment and survival, competition)

Time scales and time characteristics of treeline change

Short term (decadal), long term (millennial)

Holocene; late, early, entire period, recent changes, human-influenced climate change impacts

Trends vs extreme events

Threshold responses vs gradual response

Spatial scales to consider: Micro-environments, Regional, U.S. west-wide,or broader, circumpolor

Possible to define and/or narrow focus: • Upper vs lower treeline?• “Upper” as in elevation or latitude?• Types of influence – all or narrow?• Time scales of change?• Locational focus?

Strategy for Structuring the Tree Demography/Treeline Seminar/Literature Review• 3 general background papers to get started

• Develop an outline of topics and/or a lit. review

• Students select topics of interest (several of your per topic area is fine) and come up with papers for discussion

• Each week, we’ll discuss 2 papers

• If we go the literature review route, these papers can be the basis for the review for this topic area, which will be written by discussion leaders .

* We have 14 weeks after today (I’ll be gone Oct. 20th)

Three paper to get us started:

Brubaker, L.B. 1986. Responses of tree populations to climate change. Vegetatio 67, 119-130.

Overview of biological mechanisms controlling tree-population response to climate; general (not specific to treeline) background on factors that influence populations and timing of changes, as well a focus on treeline (high elevations and high latitude)

Smith, W.K., M.J. Germino, T.E. Hancock, and D.M. Johnson, 2003. Another perspective on altitudinal limits of alpine treelines. Tree Physiology 23, 1101-1112.

Review of hypotheses for timberline causation from a physiological perspective, and a new hypothesis regarding the role of tree establishment based on microsite factors.

LaMarche, V.C., 1973. Holocene climatic variations inferred from treeline fluctuations in the White Mountains, CA. Quaternary Research 3, 632-660.

Classic paleoclimatic study of treeline changes over the Holocene, including a global literature review, and a discussion of the role of climate as a control on treeline. Long paper, but lots of detail on site, methods.

Today:• Time and place to meet each week

• 3 papers for next meeting on web site, password protected (geog696m)

• 3 volunteers to do brief overviews of these papers (20 minute max); everyone else come with questions

• Decide on literature review (yes/no?)

• Decide on focus for seminar (how can we limit it?)

• Outline/order for seminar topics – at least the first topic, and someone (or more than one person) to select a couple of papers for discussion