Abstract
Much of the foothill and valley areas of coastal southern California are covered by stands of non-native grasses with occasional scattered patches of native bunch grasses. For decades, the dominant view held that these native bunchgrasses, particularly Stipa pulchra, once covered these lands and that grazing practices were a key cause of their decline. The so-called bunchgrass dominant paradigm (BDP) put forth by Clements influenced thinking on grassland ecology and biogeography for decades until it was discredited. Recent research suggests that grazing and related disturbances might have supported native bunchgrasses, but results are mixed and most studies cover only a short time frame. This research uses a long-term, repeat study design to analyze and compare data from three surveys of 15 permanent quadrats in La Jolla Valley, California, to determine changes in grassland cover over 34 years. A unique aspect of the study is that the site was selected by researchers precisely because it contained excellent ‘relic’ stands of Stipa pulchra (in accordance with the BDP) and the baseline study was conducted shortly after the area was released from grazing and placed under conservation management. We compared data on species frequency and percent cover collected using the same sampling routine for three periods: 1981, 1994, and 2015, to document the shifts in vegetation. We found that native grass cover decreased dramatically (especially on the valley floor), exotic grass cover fluctuated widely over time, while both native and exotic forb cover increased over time. The findings support the notion that prior grazing management practices may have supported the former stands of Stipa pulchra.
Highlights
Stands of non-native grasses cover much of the foothills and valleys of southern California (Minnich, 2008)
For decades the dominant view held that the original vegetation was composed of native bunchgrasses, the perennial Stipa pulchra, and Stipa lepida
2.1 Critical Physical Geography Critical physical geography (CPG) aims to scrutinize research findings, but importantly, the concepts and categories used in biophysical geographic research
Summary
Stands of non-native grasses cover much of the foothills and valleys of southern California (Minnich, 2008). As Sayre (2015) has argued, scientific ideas have histories; they should not be taken for granted as given, but understood as the result of actions taken by particular people in particular contexts This is especially critical in cases where repeated use over time cemented concepts into the literature and occluded the assumptions that attended them at the outset, as was clearly the case with the BDP. He came to California to study relic patches of vegetation in an effort to determine the lands’ original plant cover Based on his model, he inferred that the valleys in California were once dominated by perennial bunchgrasses that were converted to annuals by overgrazing. He inferred that the valleys in California were once dominated by perennial bunchgrasses that were converted to annuals by overgrazing These ideas held sway for decades (in spite of oftencontradictory research results) and they influenced thinking about native landscapes by many that followed (see below). Over time Clements’ theory was gradually challenged through careful examination of historical records by the likes of Holstein (2001), Schiffman (2005), and Minnich (2008), through paleoecological research by Evett and Bartolome (2013), as well as experimental studies (Bartolome and Gemmil, 1981) and a serious critique of Clements’ own theory and methods by Hamilton (1997)
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