integration note An Extension Note of the Foothills Model Forest
September 2006
Finding Common Ground: Some Definitions s the science of natural patterns evolves into practical applications, we
times as much area as would a more conservative definition. This is a critical
NATURAL DISTURBANCE PROGRAM INTEGRATION NOTE SERIES, ISSUE #1
communication gap that will inevitably lead to disputes among industrial,
By: David Andison
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need to develop an associated common natural pattern language. For example, an inclusive definition of an “island� may identify three to four
regulatory, environmental, public consultation, and certification agencies. At the very least, without a common set of definitions there is no defendable way of evaluating the degree to which plans may meet intended or required natural pattern objectives. This first instalment of the Foothills Model Forest Natural Disturbance Program Integration Note Series introduces a series of spatial definitions that have already been tried and tested in research and management applications or both natural and cultural disturbance data over several years. These definitions will continue to be used consistently throughout the Foothills Model Forest Natural Disturbance program presentations, workshops, research reports and Quicknotes.
Disturbances on Landscapes “disturbance” is an abrupt event that kills vegetation, and historically
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they affect virtually every part of all forested landscapes over time. Disturbance is thus – first and foremost – a landscape process. But the
pattern of disturbance is evident from the dead vegetation. Disturbance event patterns are thus nothing more than mortality maps – the patterns of which are detectable for many years. Figure 1 shows a recent disturbance event on a forest landscape. Note that only rarely do disturbances kill all vegetation within their boundaries. The different types of residuals are the basis for the hierarchical spatial classification system discussed in this note, and summarized below. Note that the primary distinction between the three different types of remnants in the figure below is the spatial scale at which they occur.
FIGURE 1
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Disturbance Events disturbance event is the general area affected by a single
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episode of disturbance where at least 20% of the vegetation is killed. The “event” represents a new
intermediate or meso scale of disturbance pattern. The concept of a disturbance event is intuitively straightforward. However, it is far more challenging to define an event in universal, concise, spatial terms. The Foothills Model Forest Natural Disturbance Program has adopted the following protocol:
STEPS 1) Draw boundary lines on the outermost edges of all areas that are disturbed. Ignore all internal (isolated) structure and include all partially disturbed areas. No part of the disturbance should exist outside these boundaries. If this results in multiple harvesting, wildfire, or other type of polygons, do not join them together. Frame A in Figure 2 shows a detailed map of three disturbed polygons from an actual wildfire. 2) Apply a 250 metre exterior buffer to all patches (the lighter area in Frame B in Figure 2 adjacent). This connects adjacent patches closer than 500 metres to each other. Any interior holes or “donuts” that remain from this buffering must be eliminated. 3) Apply a 250 metre interior buffer to the polygon formed from Step 2. Note that the final event polygon (shown in Frame C in Figure 2) more or less follows the outer boundaries of the disturbance area – much like the line that might be drawn around a single wildfire from an altitude of 4,000-6,000
FIGURE 2
metres. There are two ways that these rules may create more than one event from a spatial dataset. First, disturbed areas may be too far apart in space (>500 metres). Second, disturbed areas may be too far apart in time. Most natural disturbance events occur over a very short period of time (days to months), but cultural disturbance activities such as harvesting can occur over many years or decades over a small area. The biological justification of including an extended range of time for event membership should be carefully considered and agreed upon beforehand.
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Within Events isturbance events are composed of two primary
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spatial elements; Disturbed Patches and Matrix Remnants.
Disturbed Patches are individual, contiguous disturbance polygons. Note that they are the building blocks of disturbance events discussed in Step 1 on page 3. The boundary of a Disturbed Patch represents the continuous line between completely live vegetation and at least partially dead vegetation. Everything outside a Disturbed Patch is – always – undisturbed. Inside a Disturbed Patch vegetation can be completely disturbed, partially disturbed, or entirely undisturbed. One disturbance event may have several Disturbed Patches. The event shown in Figure 4 on page 5 has five Disturbed Patches.
FIGURE 3
Matrix Remnants are completely undisturbed areas at least 0.02 hectares in size between Disturbance Patches and the disturbance event boundary. They are so named because they are undisturbed remnants that are physically connected to the undisturbed surrounding forest Matrix. Matrix Remnants are a new idea, representing meso-scale residuals. Matrix Remnants can take different forms. For example, Matrix Remnant A in Figure 3 forms a continuous, undisturbed corridor between two Disturbed Patches. Matrix Remnant B forms a bay of undisturbed material. However, the distinction between the two is not always clear. For example, note that Matrix Remnant A separates Disturbed Patch 2 from Disturbed Patch 3, but it also forms bays in each of the Disturbed Patches. For simplicity, the Foothills Model Forest Natural Disturbance Program assumes that any Matrix Remnant that separates two Disturbed Patches at least one hectare in size is a corridor Matrix Remnant. It is important to keep in mind that Matrix Remnants are spatial artifacts of the event-defining procedure. Changing any of the event-defining rules (outlined on the previous page) will change the number, size, and total area of the Matrix Remnants. Changing the rules also means the resulting patterns cannot be compared to the Footbills Model Forest Natural Disturbance research output.
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Within Disturbed Patches ithin a Disturbed Patch survival can range between 0-100%. Areas that
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are at least 0.02 hectare in size with survival levels between 6-100% are Island Remnants – representing fine-scale residuals (shown in the
figure below). Areas of survival between 0-5% are Disturbed Areas (shown in the figure below). Any live stems within disturbed areas are Individual Remnants. Two main types of islands are recognized based on their relative locations. Detached islands are true “insular� islands in that they are physically isolated residuals surrounded on all sides by disturbed area. Edge islands are attached to the edges of Disturbed Patches.
Note that detached islands can be either
partially disturbed or entirely undisturbed, while edge islands can only be partially disturbed. For example, if Edge Island A were entirely undisturbed, it would fall outside of the Disturbed Patch boundary and potentially become a Matrix Remnant. In rare circumstances, a third type of island is possible. Disturbed Patch Islands are partially Disturbed Patches (such as surface fires or thinning). It is also possible to sub-classify island remnant polygons based on survival levels. In the figure above, lighter shades of green represent island areas of higher mortality. For example, Edge Island B spans from the north side of the Disturbed Patch to the south side, but it is composed of island polygons of several different mortality levels. Note that if Edge Island B were entirely undisturbed vegetation, it would become a Matrix Remnant, separating two Disturbed Patches on either side.
FIGURE 4
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How is this Information Useful? ssuming that the goal is to integrate natural pattern knowledge into forest management and monitoring activities, there are several ways of using the information presented here:
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Ignore the specifics, but adopt the concept. The most important practical need is to develop and clearly communicate an unequivocal but complete set of universally relevant spatial definitions. The exact structure of a spatial classification system is less important than having any set of definitions that function with any spatial data that does not leave any logical gaps without being ambiguous. Use these definitions as the foundation to design and communicate an alternate classification system to suit specific needs. The details of the definitions presented here could be altered without affecting the integrity of the system. For example, the 250 metre buffer width rule for creating events could be increased to reflect unique spacing circumstances. Similarly, the minimum survival for the island remnant designation could be shifted to 25% to reflect the biological response of a specific species. Neither of these changes would result in a less robust classification system. However, such changes would result in patterns that could not be compared directly to Foothills Model Forest Natural Disturbance research results. Adopt the definitions verbatim. The definitions presented here have been developed and tested over several years on a wide range of both natural and cultural data. They accurately capture natural disturbance patterns without logic gaps or ambiguity. They err on the side of caution, but do not integrate fine-filter biological assumptions. In other words, these definitions are universal, objective, and do not recognize specific biological requirements. Finally, these definitions are also the ones assumed by all of the Foothills Model Forest Natural Disturbance Program research. Thus, adopting these definitions means that no translations of results, or re-analysis of data, would be necessary to use Foothills Model Forest Natural Disturbance findings as management guides. Adopt the definitions presented here until the management partners agree to alternatives. In the absence of anything better, the classification presented here is a good start, and any changes to this system will be proposed, tested, and agreed upon collectively.
Box 6330 Hinton, AB T7V 1X6 T: (780) 865-8330 F: (780) 865-8331 fmf@fmf.ab.ca www.fmf.ab.ca
In summary, our first priority is to be able to communicate with each other. The exact nature of the definitions and terms used are less important. However, keep in mind that the fundamental innovation of the language outlined here is the introduction of an intermediate scale of measurement between patches and a landscape. The event concept not only translates well into operational reality, but is also a naturally occurring phenomenon. And in the end, understanding, measuring, and using natural patterns is the ultimate goal. For further information contact David Andison at 1-604-225-5669 or email at andison@bandaloop.ca.
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