Dendrogeomorphology is a sub-discipline of dendrochronology, a dating technique based on the study of variations in tree-ring widths caused by variations in climate and environment at the time of ring formation.
Juniper section from Purgatoire Canyon, USA, with dated bands of narrow ring widths suggesting periodic retreat of the Canyon wall.
Dendrogeomorphological research began to gather pace in the 1960s, but the development of dendro techniques appropriate for geomorphological application have, until recently, received scant attention. This is surprising as trees provide precise dates for landscape events and show trends over time and are thus ideal indicators for investigations of the spatial and temporal aspects of earth surface processes over annual to centennial time scales.
Climate warming and increasing human pressure have produced an urgent need for improvements in our understanding of the mechanisms and dynamics of landforming processes, rates of environmental change and the impact of humans on the world. However, there are still very few laboratories focusing on dendrogeomorphological studies.
Our belief is that dendrogeomorphology can make its greatest contribution by extending the scope of dendrochronological techniques and by expanding its use to cover the widest possible range of geomorphological applications.
To further this aim we are developing methods of analysis of root and stem growth using trees and smaller plants. The rationale behind the use of a variety of plant types is based on the idea that all plants have a story to tell about their habitat and microclimate; our task is to learn to interpret the information. The combination of multiple stories may then provide a 'time-line' showing changes in the environment over the life spans of its plants. Where chronologies of dead and sub-fossil wood can be constructed, the time scale may potentially be increased to cover the whole of the Holocene.
The development of dendrogeomorphology by Dr Vanessa Winchester at the School of Geography and the Environment began in 1991. Her use of the technique was initially limited to an increment borer and annular-ring counting to obtain approximate rates of glacier retreat around the North Patagonian Icefield in Southern Chile. Participation in numerous summer field weeks, run by Fritz Schweingruber and his team in Switzerland and elsewhere (Italy, Russia, Czech Republic and Argentina), stimulated her interest in the further possibilities of dendrochronology as a useful tool for geomorphologists.
In 1998 the School of Geography and the Environment bought tree-ring measuring equipment and analytical software developed by Frank Rinn Distribution, Heidelberg. Since then Dr Winchester has been developing dendrogeomorphology in the School of Geography and the Environment with the exploration of novel areas for dendrogeomorphological applications. More information on recent research projects is provided below.
- LINTAB III system dedicated to growth rate and tree-ring measurement of increment cores, stem disks and other wood samples supported by Time Series Analysis and Presentation (TSAP) computer program for tree-ring analysis and presentation.
- Reichert sledge microtome for making thin sections for microscopic examination
The dendrogeomorphology equipment is used for teaching and tree-ring research applications by undergraduates, postgraduates, and researchers in the School of Geography and the Environment. It is also available for use by members of other Oxford University Departments.
While dendrogeomorphological techniques are most obviously relevant to the analysis of various types of gravitational mass movements other subjects, listed below, also have an impact on earth surface processes and landforms. Climate, especially, has already received a great deal of attention from dendrochronologists and frequently plays a leading role in many of the other research areas.
Slope Movements (dendrogeomorphology)
- Rockfall and landslide events and frequencies.
- Debris and mud flow events, their frequencies and magnitude.
- Dynamics of creeping and sliding slopes.
- Gully formation.
- Aggregation and degradation due to slope wash and aeolian activity.
- Sand dune movements.
- Climatic trends, changes in tree line limits.
- Temperature and precipitation variations, frosts, droughts, storms.
- El Niño and other cyclical climatic events.
Glacier movements (dendroglaciology)
- Reconstruction of glacier positions.
- Avalanche intensity and frequency.
- Rates of snow creep, frost and permafrost activity.
Tectonic activity (dendroseismology)
- Volcanic events, lava flows and earthquake frequencies.
- Tsunamis (and associated mass movements).
- Isostatic uplift.
- Uplift and subsidence.
- Peak flood levels in lakes and rivers; channel and bank changes.
- River channel variations, river and shoreline terraces.
- Lake variations, bog histories and outburst floods.
- Forest inundation (river catchments).
- Ice dammed lakes and ice push events.
- Water table variations.
- Sea-level changes and salt water ingressions.
- Erosion and accumulation.
- Forest fire history, events and frequencies.
- Lightning strikes.
- Animal impacts on the environment. Damage caused by browsing and scarring.
- Environmental issues, forest management, forest clearance, tourist and other land-use impacts; air and groundwater
Oxford: Vanessa inspecting ~200-year old Quercus ilex growing in New College Cloister. It proved a difficult tree to core. The wood is iron-hard; the trunk is callused and its 'pillared' structure suggests that its ring formations are eccentric and 'lensed'. Thus 'missing rings' could be a major problem for accurate dating.
- Tree-ring dating showing the extent of glacier retreat, debris flows, and outburst flood frequencies around the North Patagonian Icefield.
Kazakhstan, Tien Shan Mountains:
- Analysis of tree rings in relation to debris flow events, with the most severe affecting the city of Almaty and surrounding region.
U.S.A, High Plains, Colorado:
- Investigations of landscape dynamics governing arroyo formation, based on tree rings and roots.
- West London: Evaluation of standard oak tree-growth in the green belt, Bedfordshire.
- Determination of hedge age to resolve a boundary dispute.
Undergraduate and MSc projects
- Isotopic analysis of heavy metals in stem growth beside a main road in southern England and a study of ground-water pollution in a Welsh quarry.
- Studies of root and shrub growth as indicators of slope movements near Lyme Regis and the Isle of Wight.
- The effects of M40 Motorway construction on tree-growth. The study showed that Picea abies growth within 1 km of the Motorway west of London was suppressed during the construction period but recovered shortly afterwards.
- Examination of ecological and geographical relationships in a fluvial landscape in the Cotswolds.
- Slope movements and cliff instability in hazard-prone areas in Southern England.
Recent research project work can be summarized as follows:
View of Lago Leones from summit of end moraine, with North Patagonian Icefield in the distance.
Debris flow of terrace sediments in the Rio Nef Valley, east side of North Patagonian Icefield. The surrounding trees could date the flow - if only the intervening river could be crossed.
Tree ring dates obtained from Nothofagus nitida around the rim of the North Patagonian Icefield suggest that warming following the 'Little Ice Age' began in the 1860s. Studies around the San Rafael Glacier on the western side of the Icefield show that, despite measured ice-flow rates averaging 17 m/day near the terminus, this calving glacier has receded over 3.5 km in the last 30 years with some intermediate oscillations. A similar pattern of retreat was found for the neighbouring land-based San Quintin and San Benito Glaciers. Since 1945 San Quintin has undergone rapid frontal collapse and the tongue of this, the largest of the ice field's glaciers, could shortly retreat within the mountain wall. The Arco, Colonia, Arenales, Nef and Leon Glaciers on the eastern side of the Icefield, all show similar retreat patterns, with the Arco Glacier prone to frequent outburst floods.
(left) Chile: Lago Arco east of the North Patagonian Icefield. Tree-ring dates on the vegetation trim line above the end moraine (on the right side of the view) suggest that lake water, accumulated behind a blocked outwash channel, was released in a great outburst flood in 1881 as the Arco Glacier began to retreat.
(right) Chile: Aerial view of North Patagonian Icefield looking towards the San Rafael Glacier. The surrounding 'rim' of bare rock shows the maximum thickness of the icefield around 140-years ago at the end of the 'Little Ice Age' as dated by the age of Nothofagus antarctica shrubs.
Ice front retreat of these eastern glaciers has been some 2-3 km since the 'Little Ice Age' maximum. Glacier retreat and icefield thinning since then suggest that warming over the last 140 years in this region has been synchronous with that in the Northern Hemisphere.
Kazakhstan: Boulder upended by a flood against a tree growing in the upper Almatinka Valley in 1878.
Kazakhstan Tien Shan Mountains
Tree-ring analysis of the species Picea schrenkiana subsp. tianshanica, was used in a study of mud and debris flow frequencies in the Tien Shan Mountains 1750-2000. Two major periods of landforming activity were deduced from tree establishment dates (early 17th and mid 18th centuries). Individual mudflow/flooding events in the 19th and 20th centuries were identified together with a 60% growth increase 1800-2000. Declining levels of flood damage to trees in the lower Almatinka valley since 1977 suggest a reduction in the geomorphic hazard status of the valley over the recent period.
View of Little Grand Canyon, Colorado High Plains, USA. An excellent place to study soil dynamics! As the Canyon walls retreat tree and plant roots become exposed while on the canyon floor roots are progressively engulfed.
U.S.A, High Plains, Colorado
A study is in progress of the dynamics and timing of gully and arroyo development in Colorado based on information provided by ring structures from roots and stems of the species Juniperus monosperma.
(left) USA: Purgatoire sample collecting.
(right) Juniperus monosperma. A tree on the brink of Purgatoire River Canyon, USA.
Thin section from Lawson's cypress hedge, UK. a) Cell structures collapsed due to drought following transplanting. b) Annual rings. c) False pruning rings.
- Evaluation of standard oak tree-growth in London's green belt in four woodlands to the west of London showed no significant growth response other than that attributable to annual weather conditions or insect attack between 1820s to 1970s. Some evidence for increasing ring widths in recent decades could be due to an improvement in air pollution levels since the 1970s and/or to climatic amelioration.
- A forensic study was undertaken in Bedfordshire to discover the age of a Lawson's cypress (Chamaecyparis lawsoniana) hedge for a client involved with his neighbour in a boundary dispute. The study showed that while the hedge was mostly planted 13 years ago, at least half its length was transplanted by the neighbour only 11 years previously. As 12 years is the minimum time required to establish land ownership the client's right to the land was confirmed.
More information on dendrogeomorphology in the School of Geography and the Environment can be obtained from:
Dr Vanessa Winchester
School of Geography and the Environment
Oxford University Centre for the Environment
University of Oxford
South Parks Road, Oxford, OX1 3QY, UK.