Steven E. Greco

How to define a patch: a spatial model for hierarchically delineating organism-specific habitat patches

Landscape analysis and delineation of habitat patches should take into account organism-specific behavioral and perceptual responses to landscape structure because different organisms perceive and respond to landscape features over different ranges of spatial scales. The commonly used methods for delineating habitat based on rules of contiguity do not account for organism-specific responses to landscape patch structure and have undesirable properties, such as being dependent on the scale of base map used for analysis. This paper presents an improved patch delineation algorithm, “PatchMorph,” which can delineate patches across a range of spatial scales based on three organism-specific thresholds: (1) land cover density threshold, (2) habitat gap maximum thickness (gap threshold), and (3) habitat patch minimum thickness (spur threshold). This algorithm was tested on an “idealized” landscape with landscape gaps and spurs of known size, and delineated patches as expected. It was then applied to delineate patches from a neutral random fractal landscape, which showed that as the input gap and spur thickness thresholds were increased, the number of patches decreased from 59 (low thresholds) patches to 1 (high thresholds). The algorithm was then applied to model western yellow-billed cuckoo (Coccyzus americanus occidentalis) nesting habitat patches based on spur and gap thresholds specific to this organism. Both these analyses showed that fewer patches were delineated by PatchMorph than by rules of contiguity, and those patches were larger, had smoother edges, and had fewer gaps within the patches. This algorithm has many applications beyond those presented in this paper, including habitat suitability analysis, spatially explicit population modeling, and habitat connectivity analysis.

Spatial scale effects on conservation network design: trade-offs and omissions in regional versus local scale planning

Ecological patterns and processes operate at a variety of spatial scales. Those which are regional in nature may not be effectively captured through the combination of conservation plans derived at the local level, where land use planning frequently takes place. Conversely, regional conservation plans may not identify resources important for conservation of intraregional ecological variation. We compare modeled conservation networks derived at regional and local scales from the same area in order to analyze the impact of scale effects on conservation planning. Using the MARXAN reserve selection algorithm and least cost corridor analysis we identified a potential regional conservation network for the Central Valley ecoregion of California, USA, from which we extracted those portions found within five individual counties. We then conducted the same analysis for each of the five counties. An overlay of the results from the two scales shows a general pattern of large differences in the identified networks. Especially noteworthy are the trade-offs and omissions evident at both scales of analysis and the disparateness of the identified corridors that connect core reserves. The results suggest that planning efforts limited to one scale will neglect biodiversity patterns and ecological processes that are important at other scales. An intersection of results from the two scales can potentially be used to prioritize areas for conservation found to be important at several spatial scales.

Temporal mapping of riparian landscape change on the Sacramento river, miles 196–218, California, USA

The middle Sacramento River is a low-gradient meandering sector in which vegetation patches are continuously created and destroyed within a complex landscape mosaic. The erosion and subsequent deposition of sediment begins a process of vegetation succession which continues until the meandering action of the river returns its course to that location. The objectives were: (1) to develop a methodology for photo-interpretation of land cover and canopy height using recent aerial photographs; (2) to validate the results of this methodology through field verification; and (3) to apply the methodology to a time sequence of historical aerial photographs to develop land cover maps to measure cumulative (gross) decadal changes. This research was carried out on a 31-km reach (|similar|6700 ha) of the Sacramento River that exhibits dynamic channel meandering behaviour. The results of the study suggest that the riparian landscape mosaic can change structure dramatically over the course of decades. Thus, conservation planning aimed at recovering threatened and endangered species should take these habitat changes into explicit consideration.

Multi-scale predictive habitat suitability modeling based on hierarchically delineated patches: an example for yellow-billed cuckoos nesting in riparian forests, California, USA

The discipline of landscape ecology recognizes the importance of measuring habitat suitability variables at spatial scales relevant to specific organisms. This paper uses a novel multi-scale hierarchical patch delineation method, PatchMorph, to measure landscape patch characteristics at two distinct spatial scales and statistically relate them to the presence of state-listed endangered yellow-billed cuckoos (Coccyzus americanus occidentalis) nesting in forest patches along the Sacramento River, California, USA. The landscape patch characteristics calculated were: patch thickness, area of cottonwood forest, area of riparian scrub, area of other mixed riparian forest, and total patch area. A third, regional spatial variable, delineating the north and south portions of study area was also analyzed for the effect of regional processes. Using field surveys, the landscape characteristics were related to patch occupancy by yellow-billed cuckoos. The area of cottonwood forest measured at the finest spatial scale of patches was found to be the most important factor determining yellow-billed cuckoo presence in the forest patches, while no patch characteristics at the larger scale of habitat patches were important. The regional spatial variable was important in two of the three analysis techniques. Model validation using an independent data set of surveys (conducted 1987–1990) found 76–82% model accuracy for all the statistical techniques used. Our results show that the spatial scale at which habitat characteristics are measured influences the suitability of forest patches. This multi-scale patch and model selection approach to habitat suitability analysis can readily be generalized for use with other organisms and systems.

A qualitative spatial model of hardwood rangeland state- and-transition dynamics

We present a method for computerizing the transition rules of a state-and-transition model and then linking this model to a geographic information system. The resulting simulation characterizes rangeland vegetation dynamics in space and time. The method makes use of an expert system, a computer program that forms logical chains of transition rules. Simulation using state-and-transition rules, sometimes called qualitative simulation, has the disadvantage that it is less precise than traditional numerical simulation. However, it may have the advantage of being able to generate more robust simulation of complex vegetation communities. We demonstrate the application of the method by constructing a model of hardwood rangeland in the western foothills of the Sierra Nevada. The model is tested by comparison with historic black-and-white aerial photographs. The model is found to agree generally with the observed data but to differ substantially in some locations. Implications of this difference are discussed.

Boundaries Make a Difference: The Effects of Spatial and Temporal Parameters on Conservation Planning*

Conservation planning and resulting ecological target identification require selection of both a planning area boundary and temporal baseline or reference condition. We examined the effects that these selections can have on resulting amount and location of identified conservation targets. A gap analysis for California was conducted using five different sets of ecoregion boundaries to identify and compare existing conservation shortfalls in major land cover type representation in protected areas using a threshold of 30 percent per ecoregion per type as the minimum required for future ecological viability. Another gap analysis was run for a single ecoregion using two temporal baselines (current and pre-1900) for the land cover followed by a comparison of identified conservation needs. We found that the boundaries of different ecoregional schemes affected both the total area needed to meet the per ecoregion land cover conservation goals and the spatial location of underprotected land cover types. Choice of temporal baseline also had a significant effect on the establishment of conservation targets for the highly human-impacted Central Valley ecoregion. To meet the given conservation threshold using a historic rather than contemporary baseline, a substantial amount of restoration is required. The results can help identify areas of both conservation needs consensus and those that vary widely based on the chosen planning boundary, as well as aid in the selection of appropriate restoration targets in degraded ecosystems. Because all landscapes are continuous in nature and planning area boundaries are discrete, similar results are likely to be found in analyses conducted in other regions.

Relative Elevation Topographic Surface Modelling of a Large Alluvial River Floodplain and Applications for the Study and Management of Riparian Landscapes

Abstract This paper presents a novel and useful spatial modelling technique to create a topographic surface that estimates a floodplains elevation relative to the average low-flow water surface elevation of a river channel. This model was applied to a 121 km study area of the middle Sacramento River, California, USA, where it was tested as a surrogate for observed water table depth and an observed 3.3 year recurrence interval flood inundation surface using independent data sets. The modelled relative elevation topographic surface correlated significantly (p < 0.005) to observed well water depths suggesting that the modelled surface reflected a reasonable approximation of vertical distance to the water table. Results from a flood inundation pattern analysis indicated an overall accuracy of 79% for correctly predicting inundated and non-inundated zones. The model was then used to measure relative channel bank height and the distribution of riparian plant communities to examine landscape ecological relationships.

Quantifying process-based mitigation strategies in historical context: separating multiple cumulative effects on river meander migration

Environmental legislation in the US (i.e. NEPA) requires defining baseline conditions on current rather than historical ecosystem conditions. For ecosystems with long histories of multiple environmental impacts, this baseline method can subsequently lead to a significantly altered environment; this has been termed a ‘sliding baseline’. In river systems, cumulative effects caused by flow regulation, channel revetment and riparian vegetation removal significantly impact floodplain ecosystems by altering channel dynamics and precluding subsequent ecosystem processes, such as primary succession. To quantify these impacts on floodplain development processes, we used a model of river channel meander migration to illustrate the degree to which flow regulation and riprap impact migration rates, independently and synergistically, on the Sacramento River in California, USA. From pre-dam conditions, the cumulative effect of flow regulation alone on channel migration is a reduction by 38%, and 42–44% with four proposed water diversion project scenarios. In terms of depositional area, the proposed water project would reduce channel migration 51–71 ha in 130 years without current riprap in place, and 17–25 ha with riprap. Our results illustrate the utility of a modeling approach for quantifying cumulative impacts. Model-based quantification of environmental impacts allow scientists to separate cumulative and synergistic effects to analytically define mitigation measures. Additionally, by selecting an ecosystem process that is affected by multiple impacts, it is possible to consider process-based mitigation scenarios, such as the removal of riprap, to allow meander migration and create new floodplains and allow for riparian vegetation recruitment.