WOODY PLANT

A woody plant is a plant that produces wood as its structural tissue. Woody plants are usually either trees, shrubs, or lianas. These are usually perennial plants whose stems and larger roots are reinforced with wood produced from secondary xylem. The main stem, larger branches, and roots of these plants are usually covered by a layer of bark. Wood is a structural cellular adaptation that allows woody plants to grow from above ground stems year after year, thus making some woody plants the largest and tallest terrestrial plants.

A section of rosemary stem, an example of a woody plant, showing a typical wood structure.

Wood is primarily composed of xylem cells with cell walls made of cellulose and lignin. Xylem is a vascular tissue which moves water and nutrients from the roots to the leaves. Most woody plants form new layers of woody tissue each year, and so increase their stem diameter from year to year, with new wood deposited on the inner side of a vascular cambium layer located immediately beneath the bark. However, in some monocotyledons such as palms and dracaenas, the wood is formed in bundles scattered through the interior of the trunk.

Woody herbs are herbaceous plants that develop hard woody stems. They include such plants as Uraria picta and certain species in family Polygonaceae. These herbs are not truly woody but have hard densely packed stem tissue. Other herbaceous plants have woody stems called a caudex which is a thickened stem base often found in plants that grow in alpine or dry environments.

Under specific conditions, woody plants may decay or may in time become petrified wood.

The symbol for a woody plant, based on Species Plantarum by Linnaeus is , which is also the astronomical symbol for the planet Saturn.

References

1. ^ Chase, Mark W. (2004). "Monocot relationships: an overview". Am. J. Bot. 91 (10): 1645–1655. doi:10.3732/ajb.91.10.1645. PMID 21652314.
2. ^ Stearn, William T. (1992) [1966]. Botanical Latin (Fourth ed.). Portland: Timber Press. ISBN 0881923214.

- Wikipedia 

DENDROLOGY

Dendrology (Ancient Greek: δένδρον, dendron, "tree"; and Ancient Greek: -λογία, -logia, science of or study of) or xylology (Ancient Greek: ξύλον, ksulon, "wood") is the science and study of wooded plants (trees, shrubs, and lianas), specifically, their taxonomic classifications. There is no sharp boundary between plant taxonomy and dendrology; however, woody plants not only belong to many different plant families, but these families may be made up of both woody and non-woody members. Some families include only a few woody species. Dendrology, as a discipline of industrial forestry, tends to focus on identification of economically useful woody plants and their taxonomic interrelationships. As an academic course of study, Dendrology will include all woody plants, native and non-native, that occur in a region. A related discipline is the study of Sylvics, which focuses on the autecology of genera and species.

Leaf shape is a common method used to identify trees.

Relationships with Botany

Dendrology is often confused with botany. However, botany is the study of all types of general plants, while dendrology studies only woody plants. Dendrology may be considered a subcategory of botany that specializes in the characterization and identification of woody plants.



Noted Dendrologists

• Mike Baillie, Queen's University of Belfast.
• Ludwig Beissner
• Francis A. Bartlett, founder of Bartlett Arboretum and Gardens and the Bartlett Tree Research Laboratory.
• William Douglas Cook, founder of Eastwoodhill Arboretum and Pukeiti (New Zealand).
• Michael Dirr
• Alan Mitchell
• Maciej Giertych
• Humphry Marshall.

External Links

• Iowa State - Dendrology
• Forest Biology and Dendrology Educational Sites at Virginia Tech
• Dendrology information and other tree identification resources

- Wikipedia 

DENDROCLIMATOLOGY

Dendroclimatology is the science of determining past climates from trees (primarily properties of the annual tree rings). Tree rings are wider when conditions favor growth, narrower when times are difficult. Other properties of the annual rings, such as maximum latewood density (MXD) have been shown to be better proxies than simple ring width. Using tree rings, scientists have estimated many local climates for hundreds to thousands of years previous. By combining multiple tree-ring studies (sometimes with other climate proxy records), scientists have estimated past regional and global climates (see Temperature record of the past 1000 years).

Variation of tree ring width translated into summer temperature anomalies for the past 7000 years, based on samples from holocene deposits on Yamal Peninsula and Siberian now living conifers.

Advantages

Tree rings are especially useful as climate proxies in that they can be well-dated (via matching of the rings from sample to sample, i.e. dendrochronology). This allows extension backwards in time using deceased tree samples, even using samples from buildings or from archeological digs. Another advantage of tree rings is that they are clearly demarked in annual increments, as opposed to other proxy methods such as boreholes. Furthermore, tree rings respond to multiple climatic effects (temperature, moisture, cloudiness), so that various aspects of climate (not just temperature) can be studied. However, this can be a double-edged sword as discussed in Climate factors.

Limitations

Along with the advantages of dendroclimatology are some limitations: confounding factors, geographic coverage, annular resolution, and collection difficulties. The field has developed various methods to partially adjust for these challenges.

Confounding Factors

There are multiple climate and non-climate factors as well as nonlinear effects that impact tree ring width. Methods to isolate single factors (of interest) include botanical studies to calibrate growth influences and sampling of "limiting stands" (those expected to respond mostly to the variable of interest).

Climate Factors

Climate factors that affect trees include temperature, precipitation, sunlight, and wind. To differentiate among these factors, scientists collect information from "limiting stands." An example of a limiting stand is the upper elevation treeline: here, trees are expected to be more affected by temperature variation (which is "limited") than precipitation variation (which is in excess). Conversely, lower elevation treelines are expected to be more affected by precipitation changes than temperature variation. This is not a perfect work-around as multiple factors still impact trees even at the "limiting stand," but it helps. In theory, collection of samples from nearby limiting stands of different types (e.g. upper and lower treelines on the same mountain) should allow mathematical solution for multiple climate factors. However, this method is rarely used.

Non-Climate Factors

Non-climate factors include soil, tree age, fire, tree-to-tree competition, genetic differences, logging or other human disturbance, herbivore impact (particularly sheep grazing), pest outbreaks, disease, and CO₂ concentration. For factors which vary randomly over space (tree to tree or stand to stand), the best solution is to collect sufficient data (more samples) to compensate for confounding noise. Tree age is corrected for with various statistical methods: either fitting spline curves to the overall tree record or using similar aged trees for comparison over different periods (regional curve standardization). Careful examination and site selection helps to limit some confounding effects, for example picking sites undisturbed by modern man.

Non-Linear Effect

In general, climatologists assume a linear dependence of ring width on the variable of interest (e.g. moisture). However, if the variable changes enough, response may level off or even turn opposite. The home gardener knows that one can underwater or overwater a house plant. In addition, it is possible that interaction effects may occur (for example "temperature times precipitation" may affect growth as well as temperature and precipitation on their own. Here, also, the "limiting stand" helps somewhat to isolate the variable of interest. For instance, at the upper treeline, where the tree is "cold limited", it's unlikely that nonlinear effects of high temperature ("inverted quadratic") will have numerically significant impact on ring width over the course of a growing season.

Botanical Inferences to Correct for Compounding Factors

Botanical studies can help to estimate the impact of confounding variables and in some cases guide corrections for them. These experiments may be either ones where growth variables are all controlled (e.g. in a greenhouse), partially controlled (e.g. FACE [Free Airborne Concentration Enhancement] experiments—add ref), or where conditions in nature are monitored. In any case, the important thing is that multiple growth factors are carefully recorded to determine what impacts growth. (Insert Fennoscandanavia paper reference). With this information, ring width response can be more accurately understood and inferences from historic (unmonitored) tree rings become more certain. In concept, this is like the limiting stand principle, but it is more quantitative—like a calibration.

Divergence Problem

The divergence problem is the disagreement between the temperatures measured by the thermometers (instrumental temperatures) on one side, and the temperatures reconstructed from the latewood density or width of tree rings on the other side, at many treeline sites in northern forests.

While the thermometer records indicate a substantial warming trend, tree rings from these particular sites do not display a corresponding change in their maximum latewood density or, in some cases, their width. This does not apply to all such studies. Where this applies, a temperature trend extracted from tree rings alone would not show any substantial warming. The temperature graphs calculated from instrumental temperatures and from these tree ring proxies thus "diverge" from one another since the 1950s, which is the origin of the term. This divergence raises obvious questions of whether other, unrecognized divergences have occurred in the past, prior to the era of thermometers. There is evidence suggesting that the divergence is caused by human activities, and so confined to the recent past, but use of affected proxies can lead to overestimation of past temperatures, understating the current warming trend. There is continuing research into explanations and ways to avoid this problem with tree ring proxies.

Geographic Coverage

Trees do not cover the Earth. Polar and marine climates cannot be estimated from tree rings. In perhumid tropical regions, Australia and southern Africa, trees generally grow all year round and don't show clear annual rings. In some forest areas, the tree growth is too much influenced by multiple factors (no "limiting stand") to allow clear climate reconstruction. The coverage difficulty is dealt with by acknowledging it and by using other proxies (e.g. ice cores, corals) in difficult areas. In some cases it can be shown that the parameter of interest (temperature, precipitation, etc.) varies similarly from area to area, for example by looking at patterns in the instrumental record. Then one is justified in extending the dendroclimatology inferences to areas where no suitable tree ring samples are obtainable.

Annual Resolution

Tree rings show the impact on growth over an entire growing season. Climate changes deep in the dormant season (winter) will not be recorded. In addition, different times of the growing season may be more important than others (i.e. May versus September) for ring width. However, in general the ring width is used to infer the overall climate change during the corresponding year (an approximation). Another problem is "memory" or autocorrelation. A stressed tree may take a year or two to recover from a hard season. This problem can be dealt with by more complex modeling (a "lag" term in the regression) or by reducing the skill estimates of chronologies.
Collection Difficulties

Tree rings must be obtained from nature, frequently from remote regions. This means that special efforts are needed to map sites properly. In addition, samples must be collected in difficult (often sloping terrain) conditions. Generally, tree rings are collected using a hand-held borer device, that requires skill to get a good sample. The best samples come from felling a tree and sectioning it. However, this requires more danger and does damage to the forest. It may not be allowed in certain areas, particularly with the oldest trees in undisturbed sites (which are the most interesting scientifically). As with all experimentalists, dendroclimatologists must, at times, decide to make the best of imperfect data, rather than resample. This tradeoff is made more difficult, because sample collection (in the field) and analysis (in the lab) may be separated significantly in time and space. These collection challenges mean that data gathering is not as simple or cheap as conventional laboratory science. However, they also give the field's practitioners much enjoyment, working out of doors, with hands on trees and tools.

Other Measurements

Initial work focused on measuring the tree ring width—this is simple to measure and can be related to climate parameters. But the annual growth of the tree leaves other traces. In particular maximum latewood density (MXD) is another metric used for estimating environmental variables. It is, however, harder to measure. Other properties (e.g. isotope or chemical trace analysis) have also been tried most notably by L. M. Libby in her 1974 paper "Temperature Dependence of Isotope Ratios in Tree Rings". In theory, multiple measurements on the same ring will allow differentiation of confounding factors (e.g. precipitation and temperature). However, most studies are still based on ring widths at limiting stands.

Measuring radiocarbon concentrations in tree rings has proven to be useful in recreating past sunspot activity, with data now extending back over 11,000 years.

Notes

1. ^ IPAE RAS Dendrochronology group research results summary.
2. ^ ^a b D'Arrigo, Rosanne; Wilson, Rob; Liepert, Beate; Cherubini, Paolo (2008). "On the ‘Divergence Problem’ in Northern Forests: A review of the tree-ring evidence and possible causes" (PDF). Global and Planetary Change 60: 289–305. Bibcode:2008GPC....60..289D. doi:10.1016/j.gloplacha.2007.03.004. 
3. ^ Surface temperature reconstructions for the last 2,000 years.  Washington, D.C: National Academies Press. 2006. ISBN 0-309-10225-1.
4. ^ Luckman, Brian H. "Tree Rings as Temperature Proxies". (PDF). 2008 Gussow-Nuna Geoscience Conference. cspg.org.
5. ^ Libby & Pandolfi 1974.
6. ^ Solanki, S.K.; Usoskin, I.G.; Kromer, B.; Schüssler, M.; Beer, J. (2004). "Unusual activity of the Sun during recent decades compared to the previous 11,000 years".  Nature 431(7012): 1084–1087. Bibcode: 2004Natur.431.1084S. doi:10.1038/nature02995. PMID 15510145.

References

• Libby, L.M.; Pandolfi, L.J. (1974). "Temperature Dependence of Isotope Ratios in Tree Rings" (PDF). Proc. Natl. Acad. Sci. U.S.A. 71 (6): 2482–6. Bibcode: 1974PNAS...71.2482L. doi:10.1073/pnas.71.6.2482.  PMC 388483. PMID 16592163.
• Briffa, K.; Cook, E. (1990). "Sect. 5.6: Methods of response function analysis". In Cook, Edward; Kairiūkštis, Leonardas. Methods of Dendrochronology: Applications in the Environmental Sciences. Springer. ISBN 978-0-7923-0586-6.
• Fritts, Harold C. (1976). Tree rings and climate. Academic Press. ISBN 978-0-12-268450-0.
• Hughes, Malcolm K.; Swetman, Thomas W.; Diaz, Henry, eds. (2010). Dendroclimatology: Progress and Prospects. Springer. ISBN 978-1-4020-4010-8.
• Luckman, B.H. (2007). "Dendroclimatology". In Elias, Scott A. Encyclopedia of Quaternary Science 1. Elsevier. pp. 465–475. ISBN 978-0-444-51919-1.
• Schweingruber, Fritz Hans; Eidgenössische Forschungsanstalt für Wald, Schnee und Landschaft (1996). "Ch. 19". Tree Rings and Environment Dendroecology. Berne: Paul Haupt. ISBN 978-3-258-05458-2.

External Links

• Briffa, Keith. "Trees as Indicators of Past Climate". University of East Anglia.
• Tree Rings: A Study of Climate Change. Athena study guide for K-12.
• International Tree-Ring Data Bank, maintained by NOAA Paleoclimatology Program and World Data Center for Paleoclimatology.
• Grissino-Mayer, Henri D. " Ultimate Tree-Ring Web Pages. University of Tennessee at Knoxville.
• Lorrey, Drew. "Running rings around climate change". National Institute of Water & Atmospheric Research.

- Wikipedia 

DENDROCHRONOLOGY

Dendrochronology is a term used for the study of vegetation remains, old buildings, artifacts, furniture, art and musical instruments using the techniques of dendrochronology (tree-ring dating). It refers to dendrochronological research of wood from the past regardless of its current physical context (in or above the soil). This form of dating is the most accurate and precise absolute dating method available to archaeologists, as the last ring that grew is the first year the tree could have been incorporated into an archaeological structure.

Tree-ring dating is useful in that it can contribute to "chronometric", "environmental", and "behavioral" archaeological research.

The utility of tree-ring dating in an environmental sense is the most applicable of the three in today's world. Tree rings can be used to "reconstruct numerous environmental variables" such as "temperature", "precipitation", "stream flow", "drought society", "fire frequency and intensity", "insect infestation", "atmospheric circulation patterns", among others.

History

Tree ring laboratory scientists from Columbia University were some of the first to apply tree-ring dating to the colonial period, specifically architectural timbers in the eastern United States. For agencies like the National Park Service and other historical societies, Dr. Jacoby and Cook began dating historic structures in the lower Hudson River Valley, New Jersey and Eastern Pennsylvania. This was difficult at the time due to a lack of sufficiently long master dating chronology and access to suitable structures. Not until 1998 was a Boston area master dating chronology developed. Today, the effectiveness of tree ring laboratory archaeological dating chronologies covers most of the area that was settled by the first European colonists. The numbers of these are in the hundreds and include historically significant structures such as Independence Hall and the Tuckahoe estate.

Methodology

There are two types of dates that can be assigned to tree specimens: cutting dates, and noncutting dates. Which date is assigned to a specimen is dependent on whether or not there is evidence that the last ring present on the specimen was the last ring the tree grew before it died.

Cutting dates can be used for crossdated tree specimens that "possess evidence that the last ring present on the specimen was the last ring grown by the tree before it died." 

Noncutting dates are used for crossdated tree specimens "if there is no evidence indicating that the last ring present on the specimen is the last one grown before the tree died." Patterns of tree growth will be similar between trees of the same species, growing in the same climate. These matching patterns align growth rings in different trees formed in the same year. Once aligned, knowing the precise calendar year of any individual tree-ring is the same as knowing the calendar year of all the rings. The goal of a dendroarchaeologist is to determine the year when the last ring was formed. Crossdating, the skill of finding matching ring-width patterns between tree-ring samples, is used to assign the precise calendar year to every ring. This is affected by the climate that the timber was in. It is also important to have enough rings to actually confirm a date. Once the rings are dates, the chronology is measured. The last step is to compare the rings with that of ring-width patterns in sampled timbers and a master dating chronology.

For trees to be useful in archaeological analysis, they must "produce annual growth rings that are uniform around the tree stem", they must "live for decades and, preferably, centuries" and they "must have been used extensively by humans either for habitation or fuel."  One of the problems with this evaluation is that it is possible under certain conditions for a tree to miss a growth-ring or produce two growth rings in a season. During extreme drought there can be insufficient growth of xylem to form a noticeable ring. Alternatively, if a defoliating agent (e.g. drought, late frost, or insect damage) can arrest the growth of a tree early in a year, after which there is a secondary growth period of new foliage causing two rings to form. Another difficulty in the use of tree-ring dating as applied to archaeology is the variety and condition of wood used in construction of archaeological sites. Many such samples are encountered wet. Heartwood can normally retain much of its substance and can be dried out and polished for analysis. On the other hand, ancient wet sapwood samples seldom survive drying out. As a result the sapwood should either be measured wet and then allowed to dry, or it should be frozen or kept wet.

In North America, "millennial-length chronologies have been developed for two species of bristlecone pine (Pinus longaeva in the Great Basin and Pinus aristata in the Rocky Mountains), bald cypress (Taxodium distichum), coast redwood (Sequoia sempervirens), Douglas-fir (Pseudotsuga menziesii), eastern cedar (Juniperus virginiana), juniper (Juniperus sp.), Larch (Larix sp.), lodgepole pine (Pinus contorta), limber pine (Pinus flexilis), mountain hemlock (Tsuga mertensiana), ponderosa pine (Pinus ponderosa), and giant sequoia (Sequoiadendron giganteum) (Jacoby, 2000a).” 

“In the southern hemisphere, successful crossdating has been achieved on alerce (Fitroya cupressoides) and pehuen (Araucaria araucana), also known as 'Chilean pine' or the 'monkey puzzle tree,' specimens in South America, kauri (Agathis australis) specimens in New Zealand, clanwilliam cedar (Widdringtonia cedarbergensis) specimens in Australia and Tasmania, and huon pine (Lagarostrobus franklinii) in Tasmania (Jacoby, 2000al; Norton, 1990).”

Applications

The main application of tree research laboratory science or dendroarchaeology is to produce records of past climates that might be unavailable otherwise. Timber remains give insight into what little remains of our national forests prior to colonel settlement. This also benefits the sciences of paleoclimatology.

Dendrochronological dating is potentially applicable wherever trees were growing, except in tropical regions. For use in absolute dating of archaeological sites, it is partially limited by the availability of a master reference chronology for the region concerned. If there is a gap in the chronology (e.g. the inability to use a chronology constructed from pine samples in the British Isle prior to the 17th century due to the lack of use of pine in architecture then) then absolute dating can not be applied. Additionally, non-climactic influences can also affect the tree-ring pattern of timber samples. Even if a reference chronology is available, care must be taken to identify aberrations in the ring pattern to determine if the sample is usable for dating.

Dendroarchaeology has been used extensively in the dating of historical buildings. After cross-matching the chronology from the building with the chronology of living trees, it is immediately possible to figure out the dates at which the historic timbers used in construction were felled. Similarly, if an extended chronology is available, then dating of samples from buildings of known or unknown date is possible. However, a limiting aspect of this application becomes apparent when dating medieval buildings. In such buildings, many timber samples lack completeness out to the underbark surface which can make the task of determining the felling year much more difficult.

The application of dendroarchaeology in uncovering past trade patterns also becomes possible as chronology records for timber around the world become more complete and accessible. Patterns from individual samples will match much more closely with their native chronologies than with their regional chronology. For example, strong cross dating is found between Irish and English chronologies, but individual ring patterns tend to match better against their local chronologies. Hence, this strong geographical component of tree ring chronologies can be used to source timber samples at archaeological sites to uncover trade routes required for the site construction. 

Dendrochronology can also be used in concert with radiocarbon dating to allow for more accurate date measurements using radiocarbon dating on archaeological sites. It is known that the concentration of carbon-14 in the atmosphere is not constant. By performing radiocarbon dating on timber samples in a known chronology, radiocarbon dates can be plotted against real time generating a calibration curve that can be used for future radiocarbon samples.

While dendrochronology is often considered the as an absolute dating method, it can also be used as a powerful tool in the relative dating of an archaeological site. Timber samples may be able to be compared with others on the site to help construct a timeline of events for that particular site. Such samples can also be used to settle issues in constructing a chronological typology, for artifacts found on site. The important point is that such within-site analysis can be done whether or not a chronology is available to date the whole assemblage.

References

1. ^ Feder K. Linking to the Past: A Brief Introduction to Archaeology. 2nd Ed. Oxford University Press. 2008
2. ^ ^{a b c d e f g h} Nash S. E. Archaeological Tree-Ring Dating at the Millennium. Journal of Archaeological Research, Vol. 10, No. 3 (September 2002), pp. 243-275
3. ^ "Dendroarchaeology".Columbia University. 2012. Retrieved April 12, 2012.
4. ^ "Scientific Application". Columbia University. 2012. Retrieved April 12, 2012.
5. ^ ^{a b c d e} Baillie, M.G.L. (1982). Tree-Ring Dating and Archaeology. London: Croom Helm Ltd. ISBN 0-7099-0613-7.
6. ^ "Scientific Application. Columbia University. 2012. Retrieved April 12, 2012.
7. ^ Aitken, M.J. (1990). Science-based Dating in Archaeology. New York: Longman Inc. pp. 37–47. ISBN 0-582-05498-2.
8. ^ ^a b Gӧksu, H.Y. (1991). Scientific Dating Methods. Luxembourg: Kluwer Academic Publishers. pp. 199–200. ISBN 0-7923-1461-1.

- Wikipedia