Ecoshare Ecological Departure

Biodiversity assessment can be organized as the structure, function, and composition of ecosystems over multiple scales of space and time. Approaches emphasizing landscapes and their function are referred to as coarse scale strategies. Those focusing on species at local scale in particular habitats, such as rare plants tied to unique ecosystems, are fine scale approaches. Although inevitably these approaches involve estimates, approximations, and leave out information, they are useful and effective in assessment and planning.

In setting objectives for land management, and to foster the function and resilience of landscapes, we need quantitative tools to describe our landscapes. On this section of the TEUI portal, we focus on an important coarse scale tool, known as a departure analysis. Analytical methods have been developed to compare the current seral stage composition of ecological types (potential natural vegetation types) within a functioning range. It is assumed that western North America before European settlement was functioning within a natural range of variation (NRV). Using the historical record (through tree-ring analyses), as well as modeling tools, we can estimate how far, or departed, a given current landscape is from this natural range. Moreover, in recent years these methods have been refined to estimate the acres in need of treatment (or succession to grow into a later stage) for each seral stage by potential vegetation type.

Landscapes functioning within NRV are assumed to be more resilient to disturbances and sustainable over time than those outside NRV. More specifically, the Ecological Departure and Restoration Needs analysis for the USDA Forest Service Pacific Northwest Region assesses vegetation departure from historical conditions (presumed to be the Natural Range of Variability). This analysis compares the contemporary abundance of different forest structural/successional classes (S-Classes) on a landscape to estimates of historical forest conditions to estimate what S-classes are in excess or deficit on the current landscape. It then assesses if disturbances (i.e., fire or thinning) or succession (growth) are needed to move the landscape towards the natural range of variability (NRV) for each of these S-Classes. These two types of restoration represent important components of landscape restoration but do not necessarily cover all restoration needs. The five S-Classes modeled in this analysis are: Early-seral, Mid-seral closed canopy, Mid-seral open canopy, Late-seral open canopy, and Late-seral closed canopy.

Broad potential natural vegetation (PNV) types, such as mixed conifer or ponderosa pine, are used to frame fire regimes. In other words, a PNV type will represent a distinct pattern of fire frequency and severity, as well as characteristic abundances for each of the seral stages associated with it. The analysis is performed at different spatial scales depending on the vegetation group being modeled and typically summarized to HUC5 watersheds. It can also be summarized to other spatial units using the pixel-level data that describes the proportion of similar pixels (with the same vegetation type, S-Class, and landscape analysis unit) in need of disturbance or succession to bring the vegetation type back within the NRV. It is critical to note these results need to be interpreted with caution at smaller spatial scales, because HRV is a landscape-scale process and the balance of vegetation structures needs to be considered in a landscape-scale context.

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Map of Succession Restoration Need by Watershed in 2022 (left) and Map of Disturbance Restoration Need by Watershed in 2022 (right). Image by Skye Greenler. Data from DeMeo, et al., 2018.

This model was run using 2017 Gradient Nearest Neighbor (GNN) Vegetation maps that were updated to include wildfires and treatments recorded in FACTS through the end of FY2023. This model only assesses forested vegetation, and results are only reported fort HUC5s that have greater than 10,000 acres of forested land. Disturbance and succession needs represent the minimum number of available acres needed to move conditions towards the calculated NRV range accounting for the balance between the "donating" and "receiving" S-class. This analysis was run in January 2024 by the Brian Harvey Lab at the University of Washington. A description of this analysis can be found in the following peer reviewed publications: Haugo, et al., 2015; DeMeo, et al., 2018; and Laughlin, et al., 2023.

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• DeMeo and Greenler, 2023. Ecological Departure Metrics in R6: A Short History.

• DeMeo, et al., 2018. Expanding Our Understanding of Forest Structural Restoration Needs in the Pacific Northwest.
• Haugo, et al., 2015. A new approach to evaluate forest structure restoration needs across Oregon and Washington, USA.
• Laughlin, et al., 2023. Trends in forest structure restoration need over three decades with increasing wildfire activity in the interior Pacific Northwest US.