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THE MOWING TRIAL

Map showing the configuation of the Mowing Trial
Figure 1. Experimental design of the Mowing Trial; Tranquillity Land Retirement Demonstration Site. Code to treatments: NN, Control (i.e., neither seeded nor mown); NM, Mown but not seeded; SN, Seeded but not mown; SM, Seeded and Mown.

Overview

The Mowing Trial was developed to test whether various mowing regimes could facilitate the establishment of native species by reducing weed competition. The trial was originally intended to be situated on the North Avenue Parcel, and we had advanced so far as to delineate the experimental plots. However, repeated incidences of trespass grazing on that property necessitated that the trial be relocated to Section 23.

Two treatment factors, seeding and mowing, were incorporated into the design (Figure 1). Restoration (imprinting, berming, and transplanting) had been attempted on Section 23 in 2000; however, the entire area had been trespass grazed in the summer following restoration, and few plants survived the grazing. Hence, unseeded plots were incorporated into the study design as it was hoped that mowing might help release any imprinted seed remaining in the seed bank..

Plots were ca. 0.2 ha (0.5 ac) in size; a complete randomized block design was applied, with treatments replicated four times. A mixture containing seed of five native species (Table 1) was imprinted. In order to subject the non-seeded plots to the same level of disturbance as the seeded plots, an empty imprinter was run over the non-seeded plots. The plots were imprinted on 13 November 2002. The "mowing" plots were mown a single time (March 28, 2003). As with the Section 10 Burn Trial, weed growth was not sufficient to warrant additional treatment applications. Vegetation monitoring was conducted on 1 May and 6 May, 2003. Data (percent cover and species composition) were collected from 12 quadrats (35 x 70 cm) per plot.





Table 1. Species planted in the Mowing Trial, including family, common name, life-form, and seeding rate. Seeding rates are expressed as pure live seeds per square foot (PLS/ft2).

TaxonFamilyCommon NameLife-formSeeding Rate
Grindelia camporum Asteraceae gumplant perennial herb 16.49
Heliotropium curassavicum Boraginaceae seaside heliotrope perennial herb 4.11
Hemizonia pungens Asteraceae common spikeweed annual herb 17.69
Phacelia ciliata Hydrophyllaceae Great Valley phacelia annual herb 17.09
Sesuvium verrucosum Aizoaceae western sea-purslane perennial herb 5.35

Page created: March 1, 2005; Last updated: March 13, 2006

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The Land Retirement Program is a Department of the Interior program
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