NetMap's Technical Help Guide

GIS Data and the Resource Manager

GIS Data and the Resource Manager
The obvious advantage of GIS for land use managers is its ability to provide spatial information at watershed and landscape scales and thus to provide the ‘big picture’ of where certain watershed attributes are located and how they relate (spatially) to other attributes (see for numerous examples; Benda et al. 2007). For instance, where are the unstable hillslopes located and are they in close proximity to the best aquatic habitats? Where is the most fire prone vegetation located with respect to the most erosion prone soils, and where do these areas overlap with sensitive fish habitats? Which segments of roads are located on unstable ground, and if a failure occurs, could it enter a fish bearing stream? Thus, first and foremost, land managers use GIS information, analysis, and associated model predictions for screening (e.g., to get the big picture) and for watershed scale planning. For instance, when planning stream or road restoration, GIS maps of potential impacts of roads on aquatic habitats can be used to prioritize field surveys.
One key recommendation is that as management plans built with GIS support are implemented, site-specific information (at the scale of an individual timber harvest plan or an individual stream reach restoration project) should be collected to fine tune management activities (or the projection of effects) in specific areas, and thus plans should be adjusted as necessary. For example, GIS information and analysis tools could be used to forecast forest growth and the effects of thinning on future forest stand structure, which affects shade from solar radiation and the amount and size distribution of wood in streams. To offset the predicted reduction of wood in streams due to thinning in riparian areas, other models are used to forecast how trees directionally felled into streams will increase wood storage and hence improve fish habitats across entire watersheds. This type of GIS analysis can support the development of forest plans and their evaluation across entire watersheds. When specific components of the management plan are implemented (for example, thinning along a certain stretch of stream), then a field reconnaissance or more detailed field measurements should be obtained to determine the exact structure of the forest stand to make more detailed site specific harvest (and tree felling) prescriptions at that site. In other words, after the planning stage that utilized GIS information (and associated model forecasts), the implementation phase will require some type of validation step, that might include collecting site-specific information (on existing forest structure and aquatic habitat condition) to make adjustments as necessary to the management activities.
The same recommendation also applies to the use of GIS information in other activities involving riparian management, slope stability, road restoration, and wildfire risk assessment. Consider slope failure potential and the use of GIS information. Increasingly, management planning is taking place at the watershed scale (or at the scale of an entire national forest). Thus, there is a need to consider slope stability conditions at that scale to help guide placement of harvest units for a 10-year forest plan.  First, we accept the premise that the application of one or more slope stability models utilizing 10-m DEMS provide acceptable results (Montgomery and Dietrich 1994, Miller and Burnett 2007). From a watershed scale perspective, a map of slope stability indicates where the unstable areas are located and their proximity to roads, stream channels, or high quality fish habitat. This information can be used to plan placement of new forest roads (or conversely locations where to abandon roads) and to plan forest harvest or forest restoration activities. In other words, watershed-scale maps are important guides to watershed-scale forest management planning.
How does GIS information, or associated modeling results about slope stability, get used in project specific planning? If geologists were asked to review or help design the placement of a forest road on a particular hillslope, the watershed-scale GIS maps would be very useful as a guide or screening tool, allowing them to see the big picture (e.g., the physical characteristics of a single hillslope compared to all the other surrounding hillslopes in the vicinity). At the project level, more site-specific information is needed.  Is the hillslope sufficiently steep to be of concern (e.g., is the GIS information on slope gradient accurate)? Are there other instability features such as slope convergence, evidence of previous failures or ground cracking? What is the likelihood of a failure, and would the associated sediment would impact important resources, including sensitive fish habitats? It is likely that the remotely sensed data and model predictions would match, approximately, what is found in the field. However, attributes such as evidence of previous failures would not be included in model predictions, but they can help with a final determination.

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