Abstract

This paper analyzes the effectiveness of a public agency’s managerial decision intended to promote biodiversity on the lands that it owns. The agency is the East Bay Municipal Utility District (EBMUD) that provides water to most of the eastern San Francisco Bay Area. In the 1940s, it planted non-native Monterey Pines on a 366 acre parcel by the San Pablo Reservoir referred to as the horse-logging area. Late in that century, it decided that the nonnative Monterey Pines were not consistent with its goal of promoting biodiversity on the lands that it stewards, and that these lands should be allowed to return gradually and naturally to their native oak woodland. By the turn of the century, many of the Monterey Pines were weak and dying. Starting in 2002, EBMUD allowed these lands to be regularly surveyed to assess the breeding bird population in them. This paper analyzes the survey data from 2002-2018 to consider how the bird population has changed and if the change is one that promotes biodiversity. The paper finds that biodiversity has increased significantly by multiple measures. The paper rejects two alternative hypotheses to explain the biodiversity increase: (1) that it could be part of a broader regional trend of avian biodiversity increase, and (2) that it could be an artifact of the survey methodology. EBMUD’s decision to allow these lands to return gradually to their native vegetation was effective; it has resulted in a significant increase in avian biodiversity. This increase includes the presence in 2010-2018 of important species that were not present in 2002-2009, including migratory species like the Olive-sided Flycatcher, Ash-throated Flycatcher, and Black-headed Grosbeak. More generally, the evidence in this study supports the idea that native vegetation promotes biodiversity.

Download File

EBMUD Management for Biodiversity: the Horse-logging Areas (11MB)