Ecoshare Potential Natural Vegetation

This page contains information about PNV in Region 6 for which the data covers the entire extent of the states of Oregon and Washington. On this page you can discover which PNV is associated with different areas of this region and download information about each one. Follow the links on this page to download available PDFs or visit other pages on the Region 6 Hub Site.

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PNV represents land capability and occurs at multiple scales, from the stand to broad landscapes. Photo credit: McMahon

PNV is a classification system that uses indicator plant species to designate a biophysical environment (ecological potential) and infer a potential suite of ecosystem structures, compositions, and functions, through time. It integrates the climate, geology, geomorphology, soils, and vegetation in an area. PNV is a biological indicator of land capability for supplying the array of ecosystem services the landscape provides.

The Forest Service has defined PNV (from Winthers et al. 2005) is ...the vegetation that would become established if all successional sequences were completed without human interference under present climatic and edaphic conditions [adapted from Tüxen (1956) as translated by Mueller-Dombois and Ellenberg (1974)].

We define PNV with a more contemporary focus on describing the biophysical environment, incorporating the importance of ecological characteristics and processes (including disturbance), across landscapes. In this view, potential vegetation can be used to infer productivity, frame disturbance regimes and expected response to disturbance, describe wildlife habitat potential, and at broader scales, provide a coarse filter approach to assessing biodiversity and landscape pattern. PNV informs what management is both possible and recommended for desired conditions, the consequences of management actions, and what ecological goods and services can be generated, apart from the current existing vegetation.

There are two common approaches to defining PNV:

1. Setting-constrained (or climatically constrained) PNV, in which the set of vegetation seral stages (the sere) is viewed/perceived as having an endpoint in the absence of disturbance. This endpoint is used to designate the full productive potential as a function of environmental factors (climate, geology, geomorphology, and soils). The integration of these factors in the absence of disturbance results in late seral (or climax) vegetation dominating the site
2. Disturbance-constrained PNV reflects periodic disturbance and the maintenance of vegetation in a characteristic set of seral stages without advancing to climax, even though the land unit retains its basic potential for late succession in the absence of major disturbance (setting-constrained PNV).

Any given land unit reflects both setting-constrained and disturbance-constrained PNV, and the full set of structures, functions, and composition. For example, in Region 6, there are many landscapes where frequent fire historically maintained open ponderosa pine forest (disturbance-constrained PNV) even though Douglas-fir is the indicated climax tree component (setting-constrained PNV). Indeed, Douglas-fir dominates many of these stands as the result of a century of land use and fire suppression. In this case, knowledge of both setting- and disturbance-constrained PNV in a given area is critical for assessing ecosystem integrity, understanding possible future trajectories, and then for identifying possible management alternatives.

Implementing the PNV concept involves classification, mapping, and inventory, in accordance with Terrestrial Ecological Unit protocols.

Classification is organizing PNV units in a hierarchical taxonomy by scale, with vegetation data carefully analyzed to form taxonomic units, e.g., series, subseries, or plant association. It is important to note that classification involves non-spatial units.

Mapping is a spatial display of PNV. We use classification concepts in mapping, but mapping is not a simple display of units because taxonomic units are scattered across the landscape, and what is mapped at broader scale will be revealed to be made up of many smaller units at finer scale. PNV classification and mapping concepts used in the Pacific Northwest Region are displayed in Table 1.

Inventory is quantifying the area occupied by each mapping unit, usually expressed in acres or hectares.

PNV can be described at multiple scales, from the local forest stand level to broad ecoregions. At the local scale, plant associations are a powerful tool in developing silvicultural prescriptions, e.g., determining how a stand will respond to a disturbance, such as logging. At middle scales it is useful as a triage tool to address management issues, such as wildlife habitat. At the broadest scale it can help frame fire regimes. By knowing the broad scale PNV we can describe the natural range of fire frequency and severity, and in turn can then describe the departure from the natural range--a key metric in defining how sustainable and resilient our landscapes are.

PNV informs what management is both possible and recommended for desired conditions, the consequences of management actions, what ecological goods and services can be generated (apart from the current existing vegetation), and is also a key building block in describing terrestrial ecological units.

In practice using either approach, setting-constrained or disturbance-constrained, is correct. The important thing is to capture the land's ability to generate biodiversity and products, and support nutrient/water cycles and disturbance regimes. PNV reflects a substantial body of knowledge about the relationships between vegetation, land, and ecosystem processes, and provides a baseline from which to consider the effects ecological change and local management across the landscape.

As mentioned, potential vegetation is generally described in two ways: 1) as proceeding to the latest seral stage, constrained by climate, regardless of disturbance; and 2) as proceeding until there is a major disturbance. For instance, consider a subalpine fir ecosystem which will develop at higher elevation if there is no fire. This system, however, experiences wildfire at approximately 150 year intervals, and is dominated by lodgepole pine. Using the climatically constrained view, the PNV would be described as subalpine fir. With the disturbance constrained view, it is lodgepole pine.

Although ecologists have spent many hours arguing about these two classification methods, in practice it is easy to use either approach and develop crosswalks where needed. The important thing is to capture the land's ability to generate biodiversity and products, and support nutrient/water cycles and disturbance regimes.

PNV reflects a substantial body of knowledge about the relationships between vegetation, land, and ecosystem processes, and provides a baseline from which to consider the effects of global ecological change and local management (Somodi et al. 2012).

PNV has applications for everything from stand level silvicultural prescriptions to landscape assessments. For example, PNV was used for the assessment of departure from the natural (presumed resilient and sustainable) range of variation to help frame the disturbance (fire) regimes and is currently being used for the Region 6 downed wood and snag information within the DecAID program.

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Multiple potential vegetation types and stages of disturbance and succession, viewed from Calf Ridge, Umpqua National Forest. Photo credit: Devin McMahon

• Better use of landscape scale consistent PNV maps, coupled with information on existing vegetation structure and successional pathways, make for a powerful wildlife habitat planning tool, and facilitates a more complete understanding of habitat.
• At broad scale, PNV may be used to further refine fire regimes because each PNV type has a characteristic topography, climate, and productivity, along with a list of common species found on sites through time.
• PNV can provide a critical framework for organizing the landscape for ecological departure assessment, an important measure of landscape resilience and resistance.
• PNV can provide critical information on targeting response to treatments, both for commodity production and restoration. Consistent PNV landscape scale classification and maps can help address questions such as where are the most productive forests? What native or invasive species might be present? What is the likelihood of success for planting trees given the lands' suitability?

We built the new PNV map on the foundation of the wall-to-wall, 30-meter maps of current forest attributes developed using the gradient nearest neighbor (GNN) imputation mapping approach (Bell et al. 2021). GNN integrates Landsat multispectral remote sensing data, forest inventory plot data, and environmental data to assign current compositional and structural attributes from field observations to all land area deemed to have the potential to support forest (Ohmann and Gregory 2002, Bell et al. 2021). GNN provides some desirable qualities for mapping potential natural vegetation due to its spatially comprehensive nature, its temporal depth (data available from 1986-2017), and its inherent incorporation of environmental drivers of spatial patterns of primary productivity and species composition.

We exploited species composition data from the inventory plots used for GNN to assign each plot to a potential vegzone and subzone. For vegzone assignments, we established a hierarchical ranking of those tree species used as indicator species in plant association guides for National Forests across the study area, taking into account shade tolerance and longevity of species, and adhering as much as possible to the logic in the various plant association guides. Shade-tolerant species with the narrowest environmental distribution (e.g., Sitka spruce, redwood, and mountain hemlock) are highest in the hierarchy, followed by shade-tolerant species of broader distribution (e.g., Pacific silver fir, western hemlock), followed by less shade-tolerant species that represent earlier-seral conditions in many environments (e.g., Douglas-fir, lodgepole pine).

To see more detailed methods used to develop the PNV map, as well as the process for the accuracy assessment, please see the Guide to Understanding and Using the Potential Natural Vegetation (PNV) Map Layer by clicking the PNV Broad Scale Map Documentation link below.

Visit the Region 6 Data Viewer Map to download raster data for PNV.

• Guide to Understanding and Using the Potential Natural Vegetation (PNV) Map Layer

• Alpine and Subalpine Vegetation of the Wallowa, Seven Devils, and Blue Mountains
• Common Plants of the Colville National Forest
• Common forest zone plants, WIL-MTH-SIU
• Riparian shrub/herb indicators, Central Oregon
• Indicator Shrubs/Herbs Eastern Oregon
• Indicator species NE Oregon/SE Washington
• Sensitive Plants and Noxious Weeds, Wenatchee NF
• Species_List_Trees_and_Shrubs.pdf

• TEUI_DRAFT_VEG_SUBZONE_Descriptions_20230417.pdf
  • Please note, that until a final version is available as part of the GTR, we recommend using the above, which is the most recently edited version of the Veg zone and Subzone descriptions.
• Accuracy assessment.pdf

• PNV_Crosswalk_VZ_SUBZ_BpS_Final_20220110
• Departure_BpS_ModelNames
• Ecoclass_codes_20200809
• SpeciesList_SciName_CommonNames
• PNV Subzones to Ecoregions_20240505_Regional Standard