Arthropod Monitoring for Fine-Scale Habitat Analysis: a Case Study of the El Segundo Sand Dunes
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DOI: 10.1007/s002679910035 ENVIRONMENTAL AUDITING Arthropod Monitoring for Fine-Scale Habitat Analysis: A Case Study of the El Segundo Sand Dunes RUDI MATTONI correspondence analysis, detrended correspondence TRAVIS LONGCORE* analysis, two-way indicator species analysis, and Ward’s UCLA Department of Geography method of agglomerative clustering. The results showed Box 951524 high repeatability among replicates within any sampling Los Angeles, California 90095-1524, USA arena that permits discrimination of (1) degraded and rela- VOJTECH NOVOTNY tively undisturbed habitat, (2) different dune habitat types, Institute of Entomology and (3) annual change. Canonical correspondence analysis Academy of Sciences of the Czech Republic showed a significant effect of disturbance history on com- Branisovska 31 munity composition that explained 5–20% of the variation. 370 05 Ceske Budejovice, Czech Republic Replicates of pitfall and yellow pan traps on single sites clus- tered together reliably when species abundance was con- ABSTRACT / Arthropod communities from several habitats sidered, whereas clusters using only species incidence did on and adjacent to the El Segundo dunes (Los Angeles not group replicates as consistently. The broad taxonomic County, CA) were sampled using pitfall and yellow pan traps approach seems appropriate for habitat evaluation and to evaluate their possible use as indicators of restoration monitoring of restoration projects as an alternative to assess- success. Communities were ordinated and clustered using ments geared to single species or even single families. Although researchers have documented the numeri- most species, arthropods serve as probes that quickly cal preponderance of arthropods within terrestrial com- respond to environmental change. They are also as- munities (Gaston 1991), their use in monitoring for sayed inexpensively and efficiently with a few simple purposes of conservation biology has been limited trapping methods. Our paper presents a 3-year study to (Kremen and others 1993) but is increasing (Parmenter assess arthropod assemblages on habitats having experi- and MacMahon 1990, Parmenter and others 1991, enced different degrees of disturbance on the El Seg- Niemela¨ and others 1993, Williams 1993, Garono and undo sand dunes in coastal Los Angeles County, Califor- Kooser 1994, Streever and others 1996, Andersen 1997, nia. Our intention is to develop a method to evaluate Andersen and Sparling 1997, Rykken and others 1997, revegetation attempts on the dunes. The results show Lawton and others 1998). Their role in ecosystem high repeatability among replicates within any sampling function is significant across all levels of food chains, arena that permits discrimination of (1) degraded and from herbivores to detritivores to parasitoids, prompt- relatively undisturbed habitat, (2) different habitat ing Wilson (1987) to refer to them by his oft-quoted types, and (3) annual change. remark as ‘‘the little things that run the world.’’ An The El Segundo sand dunes persist as a 115-ha especially important attribute of these animals lies in fragment of their former 1200-ha extent, bordered by their microgeographic distributions, which may reflect the Pacific Ocean to the west and historically sur- fine-scale heterogeneity in habitats to which most verte- rounded by the Los Angeles coastal prairie (Mattoni brates are insensitive. 1993, Mattoni and Longcore 1997). Dense urban devel- With the growing trend of attempting restoration of opment isolates the surviving habitat. Persistence of the degraded habitats, monitoring the dynamics of arthro- pod assemblages may provide the most convincing fragment depends on its location at the west end of the evidence for estimating success or failure of any given Los Angeles International airport (LAX). Prior to project. Because of high turnover and growth rates for construction of the present airport configuration, devel- opers had built 850 homes on part of the land, includ- ing some still under construction when a referendum KEY WORDS: Arthropods; Ecological monitoring; Revegetation; Res- permitted condemnation and removal of the residences toration; Correspondence analysis; Canonical corre- spondence analysis; Cluster analysis in the 1970s. The residential development and construc- tion of a major highway that now borders the east side of *Author to whom all correspondence should be addressed. the fragment reduced relatively undisturbed dune habi- Environmental Management Vol. 25, No. 4, pp. 445–452 2000 Springer-Verlag New York Inc. 446 R. Mattoni and others Figure 1. Map of site designations on the El Segundo dunes at the Los Angeles International Airport with a superimposed classification of habitat types based on historic land disturbance. tat to 16 ha. The authority of the Endangered Species lates with floral communities differing in amount of Act, invoked to protect the endangered El Segundo cover and species composition. The foredune, in contrast blue butterfly, Euphilotes bernardino allyni, in combina- with the backdune, is subject to almost continuous diurnal tion with political action engendered by active environ- westerly winds and drying afternoon sun. During the mental groups, led to 80 ha of the 120-ha parcel owned warmest summer months, the backdune usually escapes by the airport to be set aside as a preserve in 1991. The morning solar exposure because of fog. These factors, only surviving fragment of the coastal prairie is a totally combined with wind deflection, make the backdune on degraded 10 ha within the preserve area, a fraction of its average more humid with ameliorated temperatures. historic 95 km2 extent. Degradation of the site involved three activities: (1) We classify habitats across the preserve as ex- home construction with import of foreign soil to aid residential, sandmined, and undisturbed foredune, dis- landscaping, (2) road building with attendant grading, turbed and undisturbed backdune, and disturbed prai- and (3) sandmining for contouring the radar hill or rie and Oakley sand, as they existed prior to VOR (Figure 1). Removal of the residences in the 1970s commencement of the revegetation effort in 1989 was superficial, leaving some foundations, substantial (Figure 1). Edaphic characteristics define the two major rubble, foreign soil, roads, and other infrastructure. habitats, dunes and prairie. Free-flowing sand character- Vegetation regenerated without assistance, producing a izes the dunes, and the consolidated sand of a Pleis- cover of predominately iceplant (Carpobrotus edulis) and tocene dune formation underlies the prairie (Cooper acacia (Acacia cyclopis) with patches of a few highly 1967). A third edaphic area of Oakley sand occupies 10 dispersive dune shrub species. Contouring the back- ha at the NE corner of the airport land and is presently dune for road construction was more destructive. An outside the preserve limit (Nelson 1919). The Oakley airport contractor revegetated the contoured slopes in sand appears to be a result of intensive earlier farming 1975 with a ‘‘native’’ seed mix of coastal sage species, practice, which we classify as prairie substrate, that none of which was native to the dunes (including farmers repeatedly ploughed and fertilized. The dunes Eriogonum fasciculatum, E. giganteum, E. cinereum, Coreop- proper are sharply differentiated into foredune and sis gigantea, Atriplex canescens, Lupinus excubitus, and backdune, the foredune formed by the gradual upslope other non-native species). The landscaper also applied of sand from the strand, the backdune by the unstable the same mix to the entire prairie area. The only species slope of sand eroding from the dune crest (Cooper of this mix to persist was the California buckwheat (E. 1967). The topoclimatic effect of the two aspects corre- fasciculatum), the cover otherwise becoming again chiefly Arthropod Monitoring for Habitat Analysis 447 iceplant and acacia. This alien buckwheat was an impor- the rim and covered it with a 20-cm square thin plywood tant factor threatening the viability of the small popula- lid supported 2 cm above the rim by wooden legs. We tion of the El Segundo blue butterfly then present by filled the traps to a depth of 2 cm with ethylene glycol as bolstering populations of competing Lepidoptera (Pratt preservative and collected the contents at 2- to 3-week 1987). The sandmined area revegetated naturally. The intervals, depending on climatic conditions. We col- flora that reestablished there, although covered with lected all sample stations on the same day. high density of iceplant and acacia, carried a 50% Yellow pan traps were 1-pint plastic containers painted higher cover of dispersive native shrubs than the ex- lemon yellow. We filled them with 2 cm of ethylene residential area, probably a consequence of clean sand glycol and generally placed them adjacent to the pitfall being exposed without a human artifact load with all traps, but buried about 2 cm in the sand to minimize edges bordering undisturbed sites (Figure 1). Mattoni loss during heavy winds. Collection was always concor- directed efforts in 1986–1989 to remove the exotic dant with pitfall sampling. Within 1 day we sorted the buckwheat, iceplant, and acacia across undisturbed contents collected from both trapping methods, scored dune sites, followed by a revegetation project com- the readily determinable species using standard keys pleted in 1994. However, none of the areas used in this (Borror and White 1970, White 1983, Borror and others study were revegetated during