Lead Investigators:

Bill Kaiser, Phil Rundel, Eric Graham

Overview

Two major terrestrial NIMS RD deployments occurred in 2006, apart from the continuing terrestrial program of NIMS RD over the AMARSS transect at the James Reserve (see that corresponding section for details).  The first deployment was a return to the White Mountains biological station to work with an updated NIMS RD system and set of equipment for thermal mapping of an alpine fellfield.  The second was a week-long deployment at the La Selva biological station in Costa Rica to quantify microclimate dynamics across forest edges.

Small-scale patterns in soil topography, substrate structure, plant cover, and soil moisture content have strong impacts on soil surface temperatures in arctic and alpine habitats.  High resolution models of soil surface temperatures are critical for modeling many ecosystem processes over a range of spatial and temporal scales.   A NIMS RD system was used as a thermal mapper to collect 24-hour patterns of surface temperatures at spatial scales of centimeters and temporal scales of minutes.   We use these to data to demonstrate the potential significance of microscale patterns of soil and plant surface temperatures in modeling ecological and ecosystem processes.

Sharp transitions from primary forest to open areas to provide a means of understanding the ecological effects of forest fragmentation.  Additionally, quantifying dynamic understory light environments with temporally and spatially dense understory measurements help explain complex forest patterns of growth and biodiversity.  The NIMS RD system was used to quantify the micrometeorological edge effects for a primary forest boundary at the La Selva Biological Station in Costa Rica.

Approach

For the White Mountains deployment, sensors were divided into “base station” and shuttle (mobile) components.  Three base stations consisted of an array of belowground and aboveground sensors including soil heat flux plates, soil temperature at two depths, aboveground air temperature, relative humidity, and photosynthetic active radiation.  The NIMS shuttle carried an infrared thermometer which could be positioned with great accuracy and repeatability over plants and bare soil along the transect to monitor the diurnal variation in surface temperatures associated with different substrates.

For the La Selva deployment, sensors were similarly arranged, however sensors specific to microclimate were used and the component net radiometer was carried on the shuttle.  Three transects into the forest of about 35 meters each were established as replicates for the edge.  The shuttle stopped at 1 m intervals along each transect for 30 seconds to allow sensors to equilibrate and a measurement was taken. Each pass on a transect required 30 minutes and each transect was allowed to run over 24 hours.

Systems/Experiments

Sensors and Measurements for the White Mountains. 

The first grouping is the set of sensors at each of the three NIMS base stations, the second is the collection carried on the NIMS shuttle (see figures 1 & 2):

• One Q7.1 net radiometer was placed 1 meter above the ground in a representative area that was characteristic of each site. One Kipp and Zonen all-wave net radiometer was used at the site mobile site for total and component net radiation.
• Two fine-gauge thermocouples to measure air temperature were installed at 0.5 m and at 2 m to measure air temperature gradients.
• One cup anemometer was located at 2 m above the ground.
• Two heat flux plates were buried at 8 cm depth, one under bare soil and one under a cushion plant to measure soil heat flux and the temporary energy stored in the surface layers.
• Two thermocouples were buried at 1 mm under the soil surface and at the soil surface under a plant for heat storage calculation
• Two thermocouples were buried at 4 cm under the soil and a plant and two at 8 cm under the soil and plant.  One thermocouple was buried at 20 cm in an open area for heat storage calculations.
• One infrared gas analyzer for CO2 measurements at two heights above the soil surface.

• Sony video camera for ground cover classification.
• Everest infrared temperature sensor for surface temperature measurements.
• Pan-tilt device for accurate placement of IR sensor.

Sensors and Measurements for La Selva. 

The first grouping is a collection of sensors set in a fixed location (NIMS base station), the second is the collection carried on the NIMS shuttle:

• Air temperature
• Relative humidity
• Cup anemometer for wind speed.
• Silicon Pyranometer for solar radiation.

• One all-wave net radiometer for total and component net radiation.
• Silicon pyranometer for solar radiation.
• PAR sensor for photosynthetically active radiation.
• Aspirated air temperature and relative humidity sensors

Accomplishments

The previous year’s White Mountains data is being prepared as a manuscript for submission to Arctic and Alpine Research within the month.  New analyses of the data have revealed some interesting trends.  For example, the below figure is the average (dark line) and the variations of temperature (lighter lines) during all the thermal scans within one hour around 1 pm at the granite site.  Note that the spread from the average is smaller around 4000 (the rock) and larger around other places, such as 4250 (plants).

     

This separation can be incorporated into a matrix of how similar a location is to other locations.  The next figure is that separation of surface temperature classes using linear discriminant analysis.  Classes 1, 2, and 3 are boulder, rock, and sand, respectively, and classes 4, 5, 6 are Eriogonum, Penstemon, and Poa, respectively.

These data will be used to demonstrate the potential significance of microscale patterns of soil and plant surface temperatures in modeling ecological and ecosystem processes.

The La Selva data is also currently being analyzed and prepared as a manuscript for submission to a scientific journal.  The main focus of analysis is the detection of the influence of the edge at a distance into the forest through statistical methods (piecewise polynomial regression) and the response of understory plants to the changing light environment across the edge.  Some micrometeorological results are presented below.  The three-panel line figure below is of photosynthetically active radiation (PAR) for each of the three transects for the corresponding five days of the deployment.  Note the spikes in the data corresponding to the periodic emergence of the shuttle from the forest into the clearing and the higher PAR there.  Data are on a log scale because of the extreme diurnal variations of PAR.

 

The second figure is of the third transect as an example of a mesh plot.  Data values are color coded, the x-axis is time of day, the y-axis is of position in the transect.  The clearing was from zero to 4 m.  Data are for PAR (top two panels, left is log-scale absolute, right is relative to the base station), air temperature (bottom left panel, absolute) and relative humidity (bottom right panel, absolute).  Notice the relatively “spotty” data for PAR values and the more consistent data for the air temperature and relative humidity into the forest

 

Using piecewise polynomial regressions, we can expose the transition point for each measured variable between the interior and the forest edge.  Rather than computing across a grid, a numerical solver can be used to minimize the drop in residual sum of squares.  As an example, to the left is a plot of the fit obtained by placing a “knot” at the point 10.61 meters for the variable of effective surface temperature.  The next figure is of a middle-day run of data for this variable and the piecewise polynomial fit, demonstrating that these “break points” can be determined mathematically and optimally.

Future Directions

A smaller-crewed and longer-duration deployment at the White Mountains biological station would allow us to avoid weather-specific limitations and for collection of a more complete data set.  We have learned from the La Selva deployment that a small group of people can easily handle a distant NIMS RD deployment and so further thermal mapper data collection with a smaller team is desirable.