In arid and semi-arid deserts, soils are commonly covered with biological soil crusts. The
study of arid biocrusts and their ecological function has become increasingly common in
the literature over the last several decades. Interestingly, no mention is made of
biological soil crusts in forested ecosystems, raising the question as to whether they exist
in these areas and if they do, why they have yet to be recognized as such? Through the
use a parallel logic, this study finds that biocrusts do indeed exist in forests, a novel
relationship in forest ecology and seeks to determine if there exist ecophysical
explanations for the abundance and distribution throughout the forest landscape.
This study examined the effects of climate variables and substrate types on the
abundance, distribution and overall cover of forest soil biocrust at fifty-two sites in
southern Oregon, U.S.A. Sites were randomly selected within established buffer zones in
the Siuslaw, Rogue-Sisikyou, Umpqua, and Fremont-Winema National Forests. The
methods of Belnap et al 2001 were tested and then modified for application in forested
ecosystems. Data were collected on the relative abundance and distribution of biocrust
morphological groups across available substrates, community biocrust morphology,
aspect, elevation and soil texture, pH and organic matter content. Site-specific data on
average annual precipitation and minimum/maximum temperatures was collected using
the PRISM Climate Model.
This study found substrate colonization by specific morphological groups mixed across
the study; though dominant communities were observed for each substrate present,
substrate availability appears to be confounded by a number of variables (climate, stand
age and structure and litter layer) not controlled for in this study. Biocrust community
morphologies varied across sites, primarily influenced by the surface texture of the
substrate and morphology of the individual. Relatively smooth surfaces (rock, bare soil)
often resulted in smooth biocrust morphologies, whereas rough surfaces (dead wood, bare
soil) tended to result in a rolling morphology. Litter layer directly influenced the relative
proportion of substrates colonized, notably affecting dead wood and mineral soil
biocrusts. Total biocrust cover increased as precipitation increased as did biocrust
preference for dead wood substrates while mineral soil remained unchanged and rock
surfaces were negatively represented. Aspect generally followed the anticipated
distribution of total biocrust cover with the highest cover on N and NW aspects and
lowest on the W aspect. Increases in elevation were negatively related to overall biocrust
cover. Soil texture was not found to be directly related to overall biocrust cover,
attributed in part to the highly adaptive nature of the biocrust community. Soil organic
matter (SOM) influenced total biocrust cover with positive correlations between total
cover and increasing SOM content. Soil pH increased as expected across the
precipitation range (17 to 159 in/yr) of the transect. Total biocrust cover was found to
trend with soil pH, but is believed to be attributed to the parallel relationship between
precipitation and pH, rather than pH alone given the relative moderate pH range (4.39 to
6.54) of the study. The distribution and abundance of forest soil biocrusts is strongly
influenced by precipitation. The confounding influence of precipitation to litter layer
depth and organic matter content (through gradients of vegetative productivity) and soil
pH further are concluded to influence substrate preference by morphological groups.
Across the variables examined, similarities between the two communities (arid and
forest) in response to climate and soil chemistry show parallel relations, justifying the
formal establishment of biological soil crust community in forested regions. The
differences between communities related to the presence of trees validate the
establishment of forest soil biocrusts as distinct community in both form and ecological
function with the forests. / Graduation date: 2013
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36077 |
| Date | 14 December 2012 |
| Creators | Olarra, Jennifer A. |
| Contributors | Noller, Jay S. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Relation | Oregon Explorer |
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