Folia Geobot (2012) 47:119–134 DOI 10.1007/s12224-011-9108-7...



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Category: Ecological Research

Title: Overstory-Understory Relationships along Forest Type and Environmental Gradients in the Spring Mountains of Southern Nevada, USA

Author: * Abella, S.R., Hurja, J.C., Merkler, D.J., * Denton, C.W., * Brewer, D.

Subject: Climate change, Fire behavior, Management, Soil, Species richness

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 landmanagement 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 pinyonjuniper (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 cover in forests with overstories dominated by the fire-tolerant Pinus ponderosa. Overstory:understory Sørensen similarity averaged 43%−77% among six forest types, and there was little support for the supposition that similarity was lowest in midelevation forests. Distributions of individual overstory and understory species more closely corresponded with environmental gradients than did overstory:understory similarity. Results suggest that there is high potential for change in at least two of the six dominant forest types of the Spring Mountains. The direction of change (species of moist, higher elevation sites establishing in understories of drier forests) is the opposite of what would be expected for forest adaptation to the warmer, drier, more fire-prone conditions projected for the next century in the southwestern USA.

Date: 2012

Type: Journal

Source: Folia Geobot

Identifier: 47:119-134

Publisher: Springer-Verlag

Format: PDF

Language: English