harvest+strategies

Once the mouse selection function is set up, we can set up the different types of harvest options. There are basically three different types of harvest systems we want to employ; clearcut, diameter limit cut, and a partial selection cut using a q-ratio.

=Clearcut=

The most straightforward of the harvest options, clearcutting removes all timber on the tile. This approach is typically used to promote even-aged management of early-successional species, but our application isn't that fine grained.

=Diameter limit cut=

A diameter limit cut is one that selects a given diameter class, and harvests everything either above or below that threshold. If everything //below// the specified limit is cut, it is generally analogous to a **thinning** or **intermediate treatment**. The intention here is to remove the smaller slow growing individuals to remove some of the competition from the larger, faster growing individuals. Cutting everything above the limit is a more traditional diameter limit cut, with the intention of removing only larger trees, and allowing smaller trees to grow into their place. Ideally this would allow more frequent harvests from the tile compared to a clearcutting strategy. In practice this approach is commonly associated problems with tree quality, but this is not accounted for in our system.

=BDq=

The most complex approach we will implement is the 'BDq' or 'Arbogast' method of calculating the allowable harvest. This involves determining three parameters; the target residual basal area left after the cut (B), the maximum diameter size class left after the cut (D), and the q-ratio (q), or the ratio of the number of trees within a size class to the subsequent size class. This information is used to create a target distribution of the number of trees in each size class, This method is a bit tricky to implement, as it begins with a basal area requirement, and then determines the number of trees in each size class that provide that amount of basal area, while being restricted to the specified q-ratio. In practice, foresters can reference example data (as seen here) to provide a starting point near their desired basal area and q-ratio restrictions, and then tweak number of individuals in each size class to meet their specific basal area demands while retaining the proper ratio. Your job is to implement this type of harvest in the netLogo vilas county model. Make sure that the user can specify the target basal area (anywhere from 60 - 140 square feet) and the q-ratio (1.1 - 2.0) using sliders or some other input device. The underlying algorithm should then calculate the desired number in each size class, and harvest any excess individuals in any size class. If the current number of trees in any size class is less than the target number, no action is performed on that size class. Our maximum size limit is fixed at the 24 inch size class, so that's one less variable you'll have to worry about.

In practice, lower values of q result in fewer total trees, but a higher proportion in the larger size classes. High q values generally produce more small trees, given the same basal area target. More information on this harvesting approach can be found here.


 * If you're having trouble with this one and are ready to wave the white flag in defeat, you can cheat.