Work package 1 – Experimental facilities

The research will be based on experimental manipulation of climatic factors in the field or in controlled environments. The experimental tools will be:

• New facility for experimental manipulation at the field scale
• Controlled environments
• Existing field scale facilities

New facility for experimental manipulation
at the field scale

WP1 is organizing a new Danish field manipulation site. The manipulation will be conducted in a semi-natural ecosystem with relatively low vegetation. Three factors affecting the terrestrial vegetation significantly will be altered in relation to current climate change prediction models. The factors are atmospheric CO₂ concentration, temperature and precipitation.

Climate change scenarios

The atmospheric CO₂ concentration will increase in the future, but the concentrations are tightly related to emission scenarios. The concentration will increase all over the globe and only small regional variations primarily related to seasonality are expected. In 2070 the IPCC models predict concentrations between 380 and 640 ppm. In relation to these predictions the manipulations with elevated CO₂ within CLIMAITE will employ concentrations of CO₂ at around 510 ppm. This correspond to an annual increment of 2 ppm, which is a continuation of the current yearly increase and is within the concentration increment range behind the DMI scenario. Based on the scenarios for greenhouse gas emissions the Danish Meteorological Institute (DMI) has developed a climate change scenario for Denmark for 2070-2100 with respect to air temperature and precipitation based on “business as usual”. Predictions are, that the average temperature will increase 2-4 °C and the precipitation pattern will change. The temperature increase will be higher in the spring, summer and autumn compared to the winter and the minimum temperature will increase more than the maximum temperature meaning that the night temperatures will increase more that the daytime temperatures as has already been seen (IPCC 2001). The annual precipitation patterns will change and in particularly increase the precipitation by 10-20% during the winter and correspondingly reduce the precipitation during the summer, which is likely to increase the frequency of drought periods (Christensen and Christensen, 2002; J.H. Christensen, personal communication).

Site

The experimental facility will be established at a suitable semi natural scrubland/grassland ecosystem at Zealand representative for this ecosystem type in Denmark and with a low vegetation of young scrubland vegetation and various grasses, herbs and mosses. The low vegetation is a requirement for the manipulations planned. The ecosystem will be subject to low management activities.

Manipulations

The three factors CO₂, temperature and precipitation will be manipulated in the field in a full factorial design. Each study plot will be 4 m2 and all treatments will be replicated 6 times (48 experimental plots in total) and established randomly at the site. The experimental treatments will be started in year 2 of the project leaving a full growing season for pre-treatment measurements, installation and testing of experimental techniques. The treatments are:

• Reference (R) - Untreated reference plots for assessment of treatment effects. The reference plots will be established similar to all treatment plots including “dummies” of heaters, CO₂ dozers etc. in order to make sheltering and shadow effects similar.
• CO₂-enrichment (C) - Free Air CO₂ Enrichment (FACE) experiment. The study plots will be exposed to elevated CO₂ concentrations in the air through fumigation. The target CO₂ concentration will be 510 ppm. The CO₂ will be added to the plots via a mini/mid FACE (Free-Air CO₂ Enrichment) system (e.g. Miglietta 1996 and Miglietta 1997) Concentrated CO₂ will be released from tubes surrounding the plots. The release will be controlled via a data-logger/CO₂ monitor feedback system. The target CO₂ concentration of 510 ppm shall be kept in the centre of the plot. To minimize the CO₂ consumption only tubes situated in the up-wind direction will release CO₂. Fumigations will only be done during daytime and fumigation will be reduced or interrupted during episodes with high wind speeds.
• Temperature increase (T) – The study plots will be heated from above by IR lamps (e.g. Shaw et al. 2002) or a passive nighttime warming system (IR reflective curtains e.g. Beier et al 2000) to increase the nighttime temperature in the air and topsoil layer by c. 2 °C. The IR lamps or reflective curtains will be chosen as they imply only minimal artifacts on light, water and wind conditions compared to most other systems (e.g. Beier et al., 2000). However, IR lamps may alter the energy balance and accelerate the evapotranspiration. Specific design of the heating system will be tested in the field and assessed in terms of heating efficiency, optimal lamp size and potential artifacts.
• Precipitation (W) - Study plots are exposed to changes in precipitation patterns. 10-20% of the precipitation will be removed during the summer (July-September) by automatically/manually operated plastic covers allowing prolonged summer droughts to occur. A similar amount of additional precipitation will be applied manually during the winter in 15 mm rain events (Dec-Feb). Precipitation for reapplication will be collected at the site shortly before application.
• CO₂-enrichment and Temperature increase (CT) – combination of the above C and T treatments
• CO₂-enrichment and Precipitation (CW) – combination of the above C and W treatments
• Temperature increase and Precipitation (TW)– combination of the above T and W treatments
• CO₂-enrichment, Temperature increase and Precipitation (CWT)– combination of the above C, T and W treatments.

Study plots

The full factorial design of 8 treatments and 4-6 replicates means that 32-48 study plots will be established. The study plots will be laid out randomly at the site. The study plots will be sized to match the space requirements for both plant, soil and fauna investigations (c. 4 m2). Each plot will be split into areas assigned to specific types of measurements and sampling. In order to minimize shelter and shadow effects a 1-1.5 m high metal pole will be erected outside each plot to carry all technical equipment e.g. IR-lamps or IR reflective curtains, rain exclusion foils, irrigation system. A flexible and easy movable scaffolding/latter system will be developed to ensure secure and easy access to the plots during measurements without disturbing the plots (no trampling) and a fencing system will be developed to protect the plots from trampling and large herbivores. If necessary to prevent migration of meso- and microfauna and preventing uptake of nutrients and water from outside the treatment plots by the plant roots the fence will be installed down to 25 cm below ground.

Basic instrumentation and measurements

A cabin will be installed at the site for protection of measuring equipment. Electricity, a CO₂ supply system for the FACE and a water tank for the irrigation system will be installed. Telephone connections will be installed for surveillance and automatic data transfer. A series of basic measurements will be initiated and used for data evaluation and treatment documentation. All measurements will be stored as average, max. and min. values in data loggers at appropriate time intervals. Basic instrumentation and measurements include:

• Meteorological parameters – A 3m high meteorology mast will be erected at the site and equipped with the following sensors: Air temperature, wind direction, wind speed, relative humidity and PAR. The data will be used simultaneously in the FACE control system, but also stored as 10 min average with maximum and minimum values in a data logger.
• Nitrogen deposition – wet deposition (funnels for precipitation input of NO₃^- and NH₄⁺) and dry deposition (passive samplers for NO_x and NH₃) will be monitored on a monthly or biweekly basis.
• Air and soil temperature in treatment plots will be measured continuously. Detailed studies of the temperature distribution patterns will be done.
• CO₂ concentrations in treatment plots will be measured continuously to regulate fumigation and to document treatments. Specific studies on CO₂ distribution patterns will be done in campaigns.
• Soil moisture in various depths will be measured continuously by TDR to be used for data-evaluation of treatment effects, documentation of treatments and hydrological modeling.
• Water input to treatment plots will be sampled in each plot by funnels to control and document treatments
• Net radiation balance will be measured in a few selected plots.
• Surface temperature will be measured in a few selected plots.

Controlled environments

Field scale experiments have the advantage of being relatively realistic regarding the ecosystem and the interactions with the treatments. However, natural ecosystems are normally subject to large spatial and temporal variations, which may pose limitations for certain types of studies. Also, testing of interactions with additional impacts may be difficult or practically or economically impossible. In such cases studies will be conducted in the laboratory or in controlled growth chambers. For example meso-ecosystems / monoliths will be transplanted to growth chambers with controlled CO₂ and climate environments to investigate specific mineralization and immobilization processes. Furthermore, interactions between climate and other stress factors such as UVB-radiation, ozone or N deposition may be investigated in controlled environments. The participating institutions have excellent growth chamber and laboratory facilities, which will be employed wherever needed.

Existing field scale experiments

Existing sites with manipulation experiments are available at Mols (DK), Abisko (S) and Zackenberg (Greenland). These sites have involved manipulations with climatic factors alone or in combination with other factors (e.g. nutrient addition) for 8-20 years and are still in operation. None of these sites are in them selves suitable for the manipulations with multiple stress factors planned in this project (logistics, situation, accessibility etc.). However, they provide an excellent opportunity to supplement the studies at the new site for several reasons:

• Long-term studies – Even though the new site will be manipulated for 4 years, which in terms of research projects is relatively long time, this time span will still be relatively short in relation to the time span for ecosystem processes. This inherently causes a problem when using the results to predict future changes. Using the ongoing long-term studies provides an opportunity to assess the long-term sustainability of the observed changes.
• Generality and representation – results obtained at a single site may inherently cause problems when trying to upscale the results to larger areas, as it often remains uncertain to what extent the results represent general trends or are restricted to the site. The ongoing sites provide an opportunity to assess the generality of the results obtained at the new site by comparing results across sites.