OHM

Projets 2014


MUltiproxy investigation of human-climate Disturbance interaction in a high altitude catchment using CoUPled bio-geological archives (MUDCUP)

Porteurs du projet :

Structure de rattachement :

  • Coweeta LTER, University of Georgia, Athens, GA 30606-1619
  • Laboratoire GEODE, UMR 5602, Université de Toulouse 2 Le Mirail, France

Web :

Participants :

 

Résumé du projet MUDCUP :

The MUDCUP project proposes a multiproxy historical ecological investigation of human-climate-landscape interactions in a high altitude glacial basin (Lake Majeur, Haut-Vicdessos, Eastern Pyrenees) using disturbance proxies found in coupled bio-geological archives. Knowledge of historical disturbances that helped to shaped contemporary landscapes is paramount for designing adaptive conservation and management policy (Dearing et al. 2011). However, landscape trajectories in socio-ecological systems are ultimately determined by synergistic interactions between human land use, climate, and the biophysical template that are often not evident without long term perspectives. Thus, a principal question for sustainable management of socio-ecological systems concerns how human-driven (anthropogenic) disturbance such as landscape fire, interacts with climate and landscape over the long term. The key to answering this question will involve understanding the relationships between humans, climate, and landscape evolution.

In 2010 and 2011, 40 subfossil pine trunks (Pinus spp.) and 4 lacustrine sediment cores were collected from Lake Majeur as part of two separate Haut-Vicdessos, OHM Pyrenees initiatives. Along with an additional sediment core extracted from Lake Sigriou directly above the southern shore of Lake Majeur, lacustrine sediment cores revealed a variable sediment rate, with increasing sedimentation during the last 2,000 years. Lacustrine sediments also revealed a chronological series of sandy layers associated with the mid-holocene reactivation of clastic canyons during extreme hydrological conditions or events (e.g. extreme storms or avalanches) (Simonneau et al. 2013). Based on dendrochronological measurements and radiocarbon dates of 9 trees, the sandy layers appear to coincide with the occurrence of subfossil pines (figure 1).  This evidence suggests that these climate-driven hydrological disturbances have played a role in the death, transport, and deposition of the subfossil pines. Further, some of the subfossil pines are characterized by human modifications and tree-ring fire scars indicative of agro-sylvo-pastoral land use (e.g. resin tapping, timber extraction, and pastoral fire use). Thus far, radiocarbon dates of the subfossils suggest that these proxies of human-driven disturbance begin around 1800 cal. BP and increase in intensity between 1400 and 1100 cal BP (figure 1). This anthropogenic disturbance history is coincident with an increase in hydroclimate event frequency and a two fold increase in the sedimentation rate (Simonneau et al. 2013).


Figure 1. Mid- to late- Holocene disturbance coupling at Lake Majeur as inferred from subfossil pine and lacustrine sedimentary archives (dates calibrated BP).

 

Objectifs

The objectives of the proposed research are to develop a transdisciplinary approach, in order to :

  1. demonstrate the consequences of extreme hydrological events (inferred from the sandy layers identified in lacustrine archives) – that are climate-driven factors – on the life span of subfossil pines through the last 5000 years; and
  2. establish statistical associations between the fire history (inferred from subfossil pines and macro-charcoal from lacustrine archives) and soil erosion processes, quantified through the lacustrine sedimentary infill. To sum up, the MUDCUP project will be used to infer interactions between human disturbances, climate change, and landscape processes by:
    1. Cross-dating chronologically compatible subfossil samples for disturbance and climate signal sequences.
    2. Obtaining sedimentary macro-charcoal record from Lake Majeur sediment cores for inferring fire history.
    3. Conducting statistically analyses of event interactions.