Special Sessions
Sponsored by the Geomorphology Specialty Group
Association of American Geographers 103rd Annual Meeting
San Francisco, California, April 17-21.

Scale Matters 1: The role of fine-scale phenomena in landscapes

Paper Session 1427
Tuesday, 4/17/07, from 2:00 PM - 3:40 PM

Sponsorship(s):

Biogeography Specialty Group
Geomorphology Specialty Group

Organizer(s):

Bronwyn Sigrid Owen - Truckee Meadows Community College
Jake E. Haugland

Chair(s):

Jake E. Haugland

Abstract(s):

• 2:00 PM Author(s):
  *Susan W. Beatty - University of Colorado
  

  Abstract Title: The Role of Fine-scale Heterogeneity in Maintaining Species Richness.

  
  

  North-eastern deciduous forest communities are characterized by the occurrence of treefall gap disturbances. Treefalls disturb the soil, leaving persistent mound-pit microtopography for hundreds of years after the treefall event. Landuse management that obliterates this microtopography, such as clearing and plowing, provides a less heterogeneous soil surface for recolonization during forest regeneration. Comparisons were made between similar aged forests, but with different landuse histories and different degrees of fine-scale soil heterogeneity. In addition, forested sites with microtopography were monitored for species composition in microsites (mounds and pits) for 25 years. Forested sites without microtopography had a lower species richness and greater degree of dominance by a few species. Sites with a very high degree of microtopographic variation also had a lower species richness, than did sites with an intermediate degree of spatial heterogeneity. Sites that had been previously plowed, with a very homogeneous soil surface relief, had a similar species richness to intermediate heterogeneity sites, but with a higher number and degree of dominance of exotic species. In the non-plowed forested sites with microtopography present, the native species were much more likely to be found only in one microsite (a mound or a pit), whereas 60% of the exotic species occurred on both mounds and pits. The presence of microtopography appears to be important for maintenance of native species with higher equitability, but is not an impediment to colonization by exotics.

  Keywords: deciduous forest, heterogeneity, treefall, richness, microtopography

  
  
• 2:20 PM Author(s):
  *Ryan Danby - University of Alberta
  David Hik - University of Alberta
  

  Abstract Title: Plant Physiology Influences Landscape Pattern at Subarctic Alpine Treeline.

  
  

  Despite an absence of large natural disturbances, the white spruce treeline in southwest Yukon exhibits substantial variability at the landscape scale. We examined the causes of this heterogeneity at two focal scales. At a coarse scale we analyzed patterns of spruce distribution and abundance. Potential direct solar radiation was identified as the topoclimatic factor most responsible for treeline heterogeneity. Treeline was nearly 100m higher on south-facing slopes but stem density was greater on north-facing slopes. At a fine scale we examined growth and physiology of seedlings on opposing aspects. Soil temperatures were significantly warmer on south aspects and the snow-free period was longer. These seedlings had higher rates of above-ground productivity, but had reduced Photosystem II efficiency and experienced higher needle mortality. Thus, lower densities of treeline spruce on south-facing slopes appear related to cold-induced photoinhibition and winter desiccation which increase seedling mortality. The depressed elevation of treeline on north-facing slopes appears due to growth inhibition resulting from lower soil temperatures. We conclude that a reciprocal "top-down/bottom-up" interaction exists in this system: terrain-induced gradients of solar radiation result in fundamental differences in plant-scale biological processes which, in turn, structure vegetation pattern at the landscape scale.

  Keywords: alpine, arctic, biogeography, scale, Yukon

  
  
• 2:40 PM Author(s):
  *Bronwyn Sigrid Owen - Truckee Meadows Community College
  Jake E Haugland
  

  Abstract Title: Successionary lag effects resulting from fine-scale frost disturbance in a recently deglaciated landscape.

  
  

  The role of fine-scale frost disturbance on patterns of vegetation succession was examined on recently deglaciated terrain in the Jotunheimen region of Norway. Our goal was to compare successionary trends on microsites of varying frost disturbance intensity with relatively 'stable' ground. A chronosequence along the foreland of the glacier Styggedahlsbreen supplied terrain with documented ages since deglaciation (0-150 years before present), where frost disturbance generally decreases with increasing terrain age. Vegetation was sampled along the chronosequence in three differently-aged units, and at three different disturbance intensities within each unit. Results show that fine-scale frost disturbance in patterned ground features produce a lag effect by delaying vegetation succession when compared to surrounding 'stable' terrain. In addition, individual species found early on 'stable' ground are found only older disturbed sites. These finescale disturbances are therefore important to overall landscape heterogeneity, although unlikely to be detected in landscape-level studies.

  Keywords: fine-scale, disturbance, succession, cryoturbation, Jotunheimen

  
  
• 3:00 PM Author(s):
  *Jennifer E. Miller - University of Texas
  

  Abstract Title: Scaling Urbanization: Consequences for Wildlife in Changing Watersheds.

  
  

  Increasing urbanization results in increased impervious surface cover. However, the spatial-temporal pattern of impervious surface cover degrades water quality and alters wildlife habitat in scale-dependent ways. Stream plethodontid salamanders are widespread, abundant, and are effective bioindicators of water quality. This study was designed to investigate the effects of impervious surface cover and forested riparian buffer width on the abundance of larval southern two-lined salamanders (Eurycea cirrigera). Fifty-meter reaches of forty-three low-order streams were sampled to represent the range of impervious surface cover and forested riparian buffer width combinations across Wake County, North Carolina, USA. Larval abundance decreased with increasing impervious surface cover at the watershed scale. Further variation in abundance was explained by site-scale measurements, including percent detritus cover, percent pebble substrate, and the interaction between intermittency and substrate interstice sedimentation. Larval abundance was not affected by forested riparian buffer width measured at the site scale, as typically measured for regulation. To minimize the effects of urbanization on stream salamanders, (1) forested riparian buffers should be managed at the watershed scale, requiring complete buffers without drainage bypasses, (2) sediment pollution should be minimized, especially as caused by new construction, and (3) further research should be conducted as to the role of impervious surface cover in reducing stream base flow.

  Keywords: Impervious Surface, Stream, Urbanization, Watershed, Wildlife

  
  
• 3:20 PM Author(s):
  Norman W. Clippinger - University of Colorado
  

  Abstract Title: Influence of fine-scale land use on the presence of meadow jumping mice (Zapus hudsonius preblei).

  
  

  Human land use may have a major influence on the presence or absence of various species of wildlife. Residential development, excessive grazing or agriculture in grasslands, gravel mining, and industrial activity may have a detrimental effect on riparian habitat in the Colorado piedmont. Riparian habitat is essential for populations of Preble's meadow jumping mouse (PMJM; Zapus hudsonius preblei), a subspecies listed as threatened by the U.S. Fish and Wildlife Service. In this study, I employed a land cover dataset in a GIS to model any possible differences in land use between PMJM capture sites and non-capture sites in riparian habitats of Colorado. I used ArcView to identify the land use classifications (using the NLCD database) of surface water, low-intensity residential development, grasslands, and forest- or shrub-lands at 960 PMJM trapping sites. In addition, a series of new land use category grids (at the same 30 m resolution as the original grid) were created by calculating the land use of the majority of cells within a radius at varying distances from capture sites: 60 m, 90 m, 120 m, 150 m, 180 m, and 210 m. Logistic regression was used to analyze the resulting dataset. There was a significant negative effect of low-intensity residential development on the presence of jumping mice, and significant positive relationship between shrub-land and presence of jumping mice. This pattern was repeated at all radial distances from capture sites, indicating that land use at varying scales surrounding these sites had similar effects on jumping mouse populations.

  Keywords: land use, meadow jumping mouse, Zapus, gis, scale