Principles of Dendrochronology

1.Uniformitarianism Principle James Hutton, British geologist (published 1785–1788) “The present is the key to the past.” Corollary to this principle: “The past is the key to the future.” Illustrates the “trajectory of science,” past, present, and future: James Hutton, British geologist (published 1785–1788) “The present is the key to the past.” Corollary to this principle: “The past is the key to the future.” Illustrates the “trajectory of science,” past, present, and future: A.Study processes as they occur at present B.Improved understanding comes from the past C.Extrapolate/predict the future = applied! A.Study processes as they occur at present B.Improved understanding comes from the past C.Extrapolate/predict the future = applied!

Examples: A. Reconstructions of past climate = Dendroclimatology Assumes that climatic processes operating today were operating similarly in the past. Present Past Future? 1.Uniformitarianism Principle

Examples: B. Reconstructions of past fire = Dendropyrochronology Assumes that wildfires operate today as an ecosystem process just as they did in the past. Present Past Future? 1.Uniformitarianism Principle

2. Principle of Limiting Factors Basic principle in biology Adaptation to dendrochronology: “Tree growth can proceed only as fast as allowed by the primary environmental and physiological mechanisms that restrict growth.” Sometimes, more than one mechanism operates to restrict growth. We MUST have variable tree growth! Basic principle in biology Adaptation to dendrochronology: “Tree growth can proceed only as fast as allowed by the primary environmental and physiological mechanisms that restrict growth.” Sometimes, more than one mechanism operates to restrict growth. We MUST have variable tree growth!

Narrow ring, thin latewood Wide ring, thick latewood

2. Principle of Limiting Factors

The “low precip – high temp” model:

The “high precip – low temp” model:

3. Ecological Amplitude A tree species will be more responsive and sensitive to changes in environmental conditions in the outer limits of its range. N N S S E E W W Optimal growth conditions, reduced sensitivity Stressful locations, increased sensitivit y Latitudinally and longitudinally

3. Ecological Amplitude Range map of sugar maple. 3. Ecological Amplitude Range map of sugar maple.

3. Ecological Amplitude A tree species will be more responsive and sensitive to changes in environmental conditions in the outer limits of its range. Also, elevationally! Good Not so good

4. Principle of Site Selection Within any given area chosen for study, specific site characteristics should be sought that will enhance a tree’s responsiveness to environmental factors. Notice how this is related to the principle of limiting factors. We should select sites where factors are more limiting. Notice also that recognizing the growth forms of trees will provide clues where such sensitive sites exist. Within any given area chosen for study, specific site characteristics should be sought that will enhance a tree’s responsiveness to environmental factors. Notice how this is related to the principle of limiting factors. We should select sites where factors are more limiting. Notice also that recognizing the growth forms of trees will provide clues where such sensitive sites exist.

Valley bottom: not good Slope: better Notice vastly different ring patterns Notice vastly different growth forms of these trees Thick soil: not good Thin soil with rocky substrate: better 4. Principle of Site Selection

Alta Peak, Sierra Nevada, CA

5. Aggregate Tree Growth Tree growth can be “decomposed” into five basic parts: R = ring width, t = the current year, and delta = presence (1) or absence (0) indicator  A = age-related trend  C = climate  D1 = exogenous (external) disturbance processes (examples?)  D2 = endogenous (internal) disturbance processes (examples?)  E = random error R = ring width, t = the current year, and delta = presence (1) or absence (0) indicator  A = age-related trend  C = climate  D1 = exogenous (external) disturbance processes (examples?)  D2 = endogenous (internal) disturbance processes (examples?)  E = random error

Only ONE can be the desired signal. All OTHERS constitute noise. We wish to maximize the signal to noise (S/N) ratio (concept borrowed from engineering). For example, if climate is our desired signal, we must (1) mathematically remove the effects of other parts, and (2) sample to ensure no other noise affects tree growth in our study area. Only ONE can be the desired signal. All OTHERS constitute noise. We wish to maximize the signal to noise (S/N) ratio (concept borrowed from engineering). For example, if climate is our desired signal, we must (1) mathematically remove the effects of other parts, and (2) sample to ensure no other noise affects tree growth in our study area. 5. Aggregate Tree Growth Tree growth can be “decomposed” into five basic parts:

6. Principle of Replication The environmental signal being investigated can be maximized (and the amount of noise minimized) by sampling more than one stem radius per tree and more than one tree per site. Obtaining more than one increment core per tree reduces the amount of "intra-tree variability" = the amount of undesirable environmental signal peculiar to only that tree. Obtaining numerous trees from one site (and perhaps several sites in a region) ensures that the amount of "noise" is minimized. The environmental signal being investigated can be maximized (and the amount of noise minimized) by sampling more than one stem radius per tree and more than one tree per site. Obtaining more than one increment core per tree reduces the amount of "intra-tree variability" = the amount of undesirable environmental signal peculiar to only that tree. Obtaining numerous trees from one site (and perhaps several sites in a region) ensures that the amount of "noise" is minimized.

Follows the basic statistical rule: INCREASE YOUR SAMPLE DEPTH !!! MORE IS BETTER !!! 6. Principle of Replication

7. Principle of Crossdating Matching patterns in ring widths or other ring characteristics (such as ring density patterns) among several tree-ring series allows the identification of the exact year in which each tree ring was formed. Both a principle and a technique. Without either, dendrochronology is unscientific ring-counting. The Principle of Crossdating concerns why trees have the same ring patterns. The Technique of Crossdating concerns how we can use this property to (1) ensure we have precisely assigned the correct calendar year to each tree ring, and (2) at the same time, account for those problem rings, such as false or locally absent rings. Matching patterns in ring widths or other ring characteristics (such as ring density patterns) among several tree-ring series allows the identification of the exact year in which each tree ring was formed. Both a principle and a technique. Without either, dendrochronology is unscientific ring-counting. The Principle of Crossdating concerns why trees have the same ring patterns. The Technique of Crossdating concerns how we can use this property to (1) ensure we have precisely assigned the correct calendar year to each tree ring, and (2) at the same time, account for those problem rings, such as false or locally absent rings.

Why does crossdating work? Because trees within a region will be responding similarly to the overall climate regime in which they grow. Different rates of growth may occur due to local micro- environmental effects, but this does not matter! Why does crossdating work? Because trees within a region will be responding similarly to the overall climate regime in which they grow. Different rates of growth may occur due to local micro- environmental effects, but this does not matter! -