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Summary: Overstory-Understory Relationships along Forest Type
and Environmental Gradients in the Spring Mountains
of Southern Nevada, USA
Scott R. Abella & James C. Hurja &
Douglas J. Merkler & Charles W. Denton &
David G. Brewer
# Institute of Botany, Academy of Sciences of the Czech Republic 2011
Abstract Isolated forested mountains in deserts have numerous ecological and societal
values, but land-management practices (e.g., fire-regime alteration) and climate change
can affect forest composition. We analyzed tree overstory-understory relationships on
123 sites in the Spring Mountains within the Mojave Desert near Las Vegas, Nevada,
USA to assess three hypotheses. We hypothesized that: the tree species comprising
understories are less tolerant of fire than species in overstories, reflecting land-
management practices of fire exclusion; mid-elevation forests have the lowest overstory:
understory similarity because this zone could have maximum species mixing; and
overstory:understory similarity is correlated with environmental gradients (consisting of
14 topographic and soil variables). We found that Pinus monophylla comprised greater
relative canopy cover in understories of juniper (32% relative cover) and pinyon-
juniper (78%) forests than it did in overstories of these forests (0% and 53%).
Similarly, fire-intolerant Abies concolor had 6-fold greater understory than overstory
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