Of particular importance to the study of large-scale phenomena in physical geography is the modifi able areal unit problem (MAUP). While often viewed as only a problem in human geography (particularly demographic studies), the MAUP is an issue for all quantitative studies in geography of spatial phenomena (Openshaw and Taylor, 1979). Increasingly, remote sensing and Geographic Information Systems (GIS) are being used to assess the distribution of phenomena from a large scale. These phenomena are modelled using areal units that can take any shape or size resulting in complications with statistical analysis related to both the scale and method used to create the areal units. In this paper, we defi ne the modifi able areal unit problem, present examples of when it is a problem in physical geography studies, and review some potential solutions to the problem. Our aim is to increase awareness of this complicated issue and to promote further discussion and interest in this topic.

The spatial distribution of invasive alien plants has been poorly documented in California. However, with the increased availability of GIS software and spatially explicit data, the distribution of invasive alien plants can be explored. Using bioregions as defined in Hickman (1993), I compared the distribution of invasive alien plants (n = 78) and noninvasive alien plants (n = 1097). The distribution of both categories of alien plants was similar with the exception of a higher concentration of invasive alien plants in the North Coast bioregion. Spatial autocorrelation analysis using Moran's I indicated significant spatial dependence for both invasive and noninvasive alien plant species. I used both ordinary least squares (OLS) and spatial autoregressive (SAR) models to assess the relationship between alien plant species distribution and native plant species richness, road density, population density, elevation, area of sample unit, and precipitation. The OLS model for invasive alien plants included two significant effects; native plant species richness and elevation. The SAR model for invasive alien plants included three significant effects; elevation, road density, and native plant species richness. The SAR model for noninvasive alien plants resulted in the same significant effects as invasive alien plants. Both invasive and noninvasive alien plants are found in regions with low elevation, high road density, and high native‐plant species richness. This is in congruity with previous spatial pattern studies of alien plant species. However, the similarity in effects for both categories of alien plants alludes to the importance of autecological attributes, such as pollination system, dispersal system and differing responses to disturbance in the distribution of invasive plant species. In addition, this study emphasizes the critical importance of testing for spatial autocorrelation in spatial pattern studies and using SAR models when appropriate.

Vast resources are devoted annually to watershed management and wetland restoration. Historical wetland losses are often cited as a motivation for prioritizing ambitious wetland restoration efforts. However, analysis of historical conditions is often underutilized in the planning process. In this paper we demonstrate historical ecological analysis of the San Gabriel River watershed in southern California. We integrate multiple disparate data sources collected at different spatial and temporal scales to describe historical wetland extent and distribution. We compare historic wetlands to contemporary conditions to calculate wetland losses. From the results of this analysis, we conclude that the widely held view of southern California as naturally dry and desert-like with mainly ephemeral and intermittent streams may be an over generalization. Historically, the San Gabriel watershed has supported complex expanses of channels, ponds, sloughs, seeps, marshes, and seasonal wetlands that alternated between wet and dry conditions on multi-year to decadal cycles. We estimate that >86% of historical wetlands have been lost since ca. 1870, with the greatest losses occurring to palustrine alkali meadows in the lower floodplain. Despite the extensive losses, the analysis reveals areas of the watershed conducive to wetland re-establishment and provides insight into the most appropriate wetland types to prioritize for specific watershed settings.

We estimated the range expansion of Barred Owls (Strix varia) in California and the potential negative effects this species may have on Spotted Owls (Strix occidentalis). Barred Owl range expansion has been rapid over the past two decades. A total of 61 Barred Owls has been detected in 12 different California counties. Barred Owls were first sighted in California in 1981 in Del Norte and Trinity counties. They now have been detected as far south as Sonoma County in western California and Yuba County in the Sierra Nevada. The ratio of new Barred Owl sites found per new Spotted Owl territory has increased from one per 50 Spotted Owl territories in the 1980s to one per 10 to 20 new Spotted Owl territories in the mid 1990s. This suggests that the Barred Owl population in California is increasing. In addition, seven Barred Owl X Spotted Owl hybrids have been reported in California. Because of the potential for hybridization, competition for food and habitat, and predation, it appears that the Barred Owl could influence Spotted Owl populations negatively.

Despite the importance of documenting wetlands for legislative and conservation purposes, little work has been done to provide a regional inventory of wetlands in southern California. In this paper, we begin the process of documenting the diversity and distribution of wetlands in southern California and provide an analysis of the spatial distribution of wetlands relative to potential human impact. Using photointerpretation and classification techniques from the National Wetlands Inventory, we determined that in our Ventura County study area there were a total of 166 unique wetland classifications and 8,805 wetland polygons inventoried. The Palustrine wetland classification represented the greatest amount of wetlands, followed by Riverine and Lacustrine systems. Nineteen percent of the wetland areas inventoried were given special modifiers indicating they were either modified or human-made. A total 19,916 acres of wetland area were found to be in places facing significant human impact and therefore determined to be a conservation priority. Although 90 percent of original wetland area in California has been lost, Ventura County continues to display a wealth of diversity in wetland type. Contrary to common belief, as evidenced by this Ventura County project, southern California is characterized by significant wetland diversity.