Closed Canopies Crowd Out Bats: Planning Artificial Gap Creation
Authors:   ,   Portland State University, Simmons Alana 
Published: October 2021

Managed even-aged forest stands often lack small to medium-sized canopy gaps that help to increase habitat diversity and, in turn, wildlife diversity. A large body of literature suggests that this habitat diversity is especially important for bat communities and that bat activity and diversity can be depressed in closed canopy, even-aged stands. Open- and edge-adapted bats have evolved specific wing morphologies and echolocation call structures that make them reliant upon forest gaps as energy efficient foraging grounds in otherwise structurally cluttered forests. Artificial gap creation projects that increase habitat diversity have been implemented to benefit ungulates, and a similar approach could also be applied to support foraging activity of bats in even-aged forests that lack dynamic natural disturbances. However, little consideration has been given to the use of gaps by bats and no comprehensive approach for artificial gap creation for the benefit of bats has been proposed. In response to this lack of guidance for forest managers in the Pacific Northwest region, this document provides a focused review of existing literature regarding bats and gaps. This information was used to create specific management recommendations regarding physical characteristics of gaps and their spatial context on the landscape. To identify ideal locations for gap creation on the ground according to these recommendations, a weighted overlay method is suggested. This document has been written for the use of forest managers throughout the entire Pacific Northwest region. However, the Siuslaw National Forest (NF), a Late-Successional Reserve on the coast of Oregon, was used as a specific case study to demonstrate how the proposed approach can be applied to a specific management unit. The document is broken into the four following chapters. Chapter 1 introduces the Siuslaw NF and briefly describes the forest’s bat community, major vegetation zones, forest succession, disturbance regime, and management. Using previous research from the region as a guide, Chapter 2 provides background information regarding bat biology and ecology and it details the importance of gaps, forest edges, and interior stands as habitat for forest-dwelling bats. Different types of forest gaps common to the Pacific Northwest are discussed including both artificially created and naturally occurring gaps. Chapter 3, again guided by review of existing literature, highlights important gap parameters including physical characteristics and spatial context to promote bat activity as well as provides specific gap management recommendations. Chapter 4 provides an example of how to input management recommendations into a Geographic Information System (GIS) to pinpoint ideal locations for gap creation within a management unit. A weighted overlay analysis, a common GIS tool, was conducted in the Siuslaw NF following the management guidelines, and resulting maps are discussed. The ultimate goal of this document is to provide forest managers in the Pacific Northwest region with the knowledge and planning tools necessary to promote foraging activity of specialized open- and edge-adapted species. While other management units may have different or additional managerial constraints than those of the Siuslaw NF, thIS proposed approach can be easily adapted to meet the varied needs of different forests. By following this approach, forest managers can provide the habitat diversity and complexity necessary to promote high levels of bat activity and diversity within even-aged, closed canopy forests.