Frame-based Landscape Model Help

Model Interface and Operation

The model is designed in the NetLogo environment to simulate a 10x10 km landscape centered on a restored wetland. The landscape land-use representation is obtained from a 30-m resolution National Land Cover Database (NLCD) land-use map which is resampled at 300-m resolution and reclassified to five classes. These five land-use classes are represented by different colors: light green = restored wetland, blue = water, yellow = active agriculture, dark green = natural forested wetlands (called woody wetlands in NLCD), and grey = other, (e.g., urban).

To begin a model run, select one of the four currently available “Sites” which loads the site and landscape variables specifically measured for that location. Next, select one of the three economic “Scenarios”, minimum (Min) or maximum (Max) “Connectivity” level, and turn the “Management” switch On or Off. An additional set of parameters are available for user to change in a text file. Then the user clicks “Setup” to initialize the model and “Run Simulation” to start the model run. The model runs with a one-year time step and the default model run is for 100 years.

The landscape map changes as active agriculture cells are converted to restored forested wetland which then convert to natural forested wetland as they age. Under certain economic scenarios, the restored cells are converted back to active agriculture. At the landscape scale, the spatial pattern is altered as the restored wetlands change their size, number and connectivity (due to economic factors that facilitate or limit the enrollment of new restored wetlands). For each of the five response variables, the model displays in graphical format the current value at landscape level (weighted average value for bird species richness or cumulative value for the other response variables – the green column), and the initial value (red column). The output at the end of the simulation is also presented in text format, including the departure from the initial value.

Process Descriptions

The bird species richness has a linear relationship to the number of tree stems on the restored forested wetland. The number of tree stems is increasing as the woody vegetation on existing and new cells grows older. This determines an increase in the bird species richness on restored forested wetland cells and changes the current landscape level value.

We assume that the initial age of the restored forested wetland cells is 5 years, initial age of natural forested wetlands is 55 years and that a restored forested wetland cell will convert to a natural forested wetland cell at 80 years. The increasing age for a restored forested wetland or natural forested wetlands cell changes the carbon stocks value for that cell according to the oak/hickory table from the COLE model (Carbon On Line Estimator) for Louisiana.

The nitrate retention value of a given cell is dependent on the measured potential denitrification values of the land-use type, the site flooding potential, and the number of agriculture cell neighbors that can provide a nitrate source. The “Connectivity” switch changes the number of agriculture cell neighbors from the maximum available to minimum (0).

The DED value for restored forested wetland is calculated at 59% of the DED value for natural forested wetlands, based on literature values. The “Management” switch refers to active management of the restored hydrology on a restored forested wetland and has the effect of doubling DED after 20 years of management following the restoration.

The frog occupancy rate is computed from field data estimating the proportion of sites occupied by a frog species (gray treefrog), categorized by the three land-use classes. For each cell, if a randomly drawn number is smaller than the occupancy rate (generated from a normal distribution for that land-use), then the cell is considered occupied. All occupied cells on the landscape are counted to determine the occupancy rate at landscape scale.

Three economic factors are used to control the land-use change (or frame switching): restored wetland conservation money is exceeded, restored wetland county cap is reached, agriculture income is larger than restored wetland payments. Three scenarios are defined based on the combination of factors being turned on or off:

Scenario 1: all economic factors are favorable to restored wetland area increase (agriculture -> restored wetland)
Scenario 2: the economic factors are unfavorable to restored wetland area increase (restored wetland -> agriculture or restored wetland is constant)
Scenario 3: intermediate scenario. All eight factor combinations and all three effects are possible depending on the factors being on or off. Scenarios 1 and 2 are extreme cases of scenario 3.

The “restored wetland conservation money exceeded” factor is switched on or off annually, based on a random number. The “Ag income > restored wetland payments” factor is switched on or off randomly every 5 years. The “restored wetland county cap reached” factor is turned on or off depending on the total area of restored wetland on the landscape (more or less than 25% of the landscape). The annual percentage of agriculture converting to restored wetland is considered 2%, based on historical WRP data. For restored wetland converting to agriculture, the annual percentage is arbitrarily selected to be 1%.

System Requirements

The applet requires Java 1.4.1 or higher. It will not run on Windows 95 or Mac OS 8 or 9. Mac users must have OS X 10.2.6 or higher and use a browser that supports Java 1.4. (Safari works, IE does not. Mac OS X comes with Safari. Open Safari and set it as your default web browser under Safari/Preferences/General.) On other operating systems, you may obtain the latest Java plugin from Sun's Java site.

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