Abstract
Smoke-cued seed germination and emergence is common in some frequent-fire ecosystems, but this process is little studied in frequent-fire conifer forests of the southwestern United States. To assess whether aqueous smoke promotes plant emergence in frequent-fire ponderosa pine (Pinus ponderosa) forests in northern Arizona, I conducted three experiments at different scales (seed, seed bank, and plant community) in both greenhouse and field settings. In the first greenhouse experiment, aqueous smoke significantly increased (P < 0.05) emergence of seeds of 13 % of 61 assayed species. Five of eight (63 %) Penstemon species exhibited significant increases ranging from two- to ten-fold. In the second greenhouse experiment, aqueous smoke increased emergent density by 67 % and species richness by 60 % in soil seed bank samples collected from nine sites that had undergone tree thinning. Contrary to these greenhouse experiments, spraying aqueous smoke on 0.05 ha field plots at nine sites in the third experiment had no effect on plant species cover, richness, or composition relative to control plots 15 mo after treatment. Many factors, such as time since fire or interactions with other cues, could have contributed to this lack of response. While aqueous smoke appears promising for some applications such as enhancing seed germination for plant production, its potential for promoting emergence in field settings is currently uncertain.
Highlights
Seed germination and emergence are key components of terrestrial ecosystems, partly regulating plant regeneration and many ecosystem processes affected by seed-based plants
Smoke has been assessed as a germination or emergence cue in both laboratory and field settings, and at three different scales: individual seeds, soil seed bank samples, and in field plots
Seeds have been screened for responses to smoke in a variety of species from South African fynbos communities (Brown 1993), Australian eucalyptus and other communities (Dixon et al 1995, Thomas et al 2007), chaparral in California, USA (Keeley and Fotheringham 1998), and arable weed communities (Adkins et al 2003, Daws et al 2007)
Summary
Smoke-cued emergence in plant SpecieS of ponderoSa pine foreStS: contraSting greenhouSe and field reSultS. To assess whether aqueous smoke promotes plant emergence in frequentfire ponderosa pine (Pinus ponderosa) forests in northern Arizona, I conducted three experiments at different scales (seed, seed bank, and plant community) in both greenhouse and field settings. In the second greenhouse experiment, aqueous smoke increased emergent density by 67 % and species richness by 60 % in soil seed bank samples collected from nine sites that had undergone tree thinning. The purpose of this study was to determine the effects of aqueous smoke on (1) seeds of a variety of species native to ponderosa pine forests, (2) soil seed bank samples collected at nine northern Arizona ponderosa pine sites, and (3) field plots at those same sites. I tested the hypothesis that aqueous smoke increases emergence at all three of these scales, and with or without exposure to grazing by large herbivores in the field experiment
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