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Wildlife, Animals, and Plants |
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FIRE EFFECTS
IMMEDIATE FIRE EFFECT ON PLANT:Fire generally top-kills soaptree yucca, but it can be fire tolerant depending on the intensity and frequency of fire [40,43]. Two studies, both low-severity spring fires, one in the Sierrita Mountains near Tucson, Arizona, and one in the Whetstone Mountains of southeastern Arizona, found 25% and 27% mortality of soaptree yucca after several months, respectively [20,43]. In both cases, damage to the apical meristem was a frequent cause of mortality. Leaves remaining on the stem, whether dead or living, insulate conductive tissue and reduce fire damage to the stem and vascular tissue [42]. Meristem protection also increases fire tolerance of soaptree yucca: apical meristems are protected by the dense terminal rosette and belowground meristems along rhizomes are protected by soil [38,42,43].
DISCUSSION AND QUALIFICATION OF FIRE EFFECT:No entry
PLANT RESPONSE TO FIRE:Soaptree yucca sprouts from rhizomes, the root crown, and undamaged stems after fire [43]. Frequent production of belowground sprouts makes soaptree yucca unique among leaf succulents [38,42]. In the Whetstone Mountains of Arizona, 51% of soaptree yucca survived fire only by producing sprouts from belowground meristems [43], 33% of surviving soaptree yucca regrew from the apical meristem [43], 7% regenerated from the apical meristem and produced belowground sprouts, and 2% grew from seed. Few (7%) soaptree yucca were unburned, showing that the species is a fire tolerator rather than evader [43]. The authors concluded that in most cases, regeneration of soaptree yucca occurs via vegetative reproduction rather than from seed trees surviving on unburned patches [43]. Seedling establishment following fire is not thought to be a reliable means of recovery for soaptree yucca in most years, but it may be important during wet years following fire [42,43]. The estimated time for yucca species to recover to prefire density is 2-5 years [42].
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:No entry
FIRE MANAGEMENT CONSIDERATIONS:It is reasonable to expect 25% mortality of soaptree yucca following fire [20,43]. This may be problematic where fire frequently occurs [43]: young regrowth would likely be less fire tolerant because a larger proportion of stems would be shorter and exposed to lethal temperatures. Though long-term studies of different fire regimes' effects on soaptree yucca populations have not been conducted, it has been suggested that soaptree yucca would survive in the historic 3-10 year fire return interval of semidesert grasslands; however, in many areas its density would be lower than at present [43]. Managers often seek to eliminate undesirable shrubs by burning in high fuel years (after wet growing seasons or 1-2 years without grazing) to achieve maximum crown burning. This practice may result in high mortality of succulents including soaptree yucca. Damage to succulents is reduced by low-severity fires that kill shrub seedlings and scorch some crowns Although reduction of shrub canopy cover and seed production is not as great as that achieved with crown fires, greater coverage of soaptree yucca and other succulents is retained [38].
Related categories for SPECIES: Yucca elata | Soaptree Yucca |
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