Developing spatially explicit and stochastic measures of ecological departure

Background: Ecological departure is a metric applied to mapped ecological systems measuring dissimilarity between the distributions of observed and expected proportions of non-stochastic reference vegetation classes within an area.

Aims: We created spatially explicit measures of ecological departure incorporating stochasticity for each ecological system and all ecological systems from a central Nevada USA landscape.

Methods: Spatially explicit ecological departures were estimated from a radius from each pixel governed by a distance-decay function within a moving window. Variability was introduced by simulating replicate climate time series for each spatial reference condition and calculating departure per replicate.

Key results: Single system spatial ecological departure was highly and extensively departed, except for one area of low-elevation groundwater-dependent systems. Variance of spatial ecological departure was extensively low, except in areas of lower ecological departure, despite vegetation differences among replicates. The multiple-system ecological departure exhibited lower ecological departure.

Conclusions: Spatial ecological departure was warranted for efficient land management as results were concordant between non-spatial and spatial metrics; however, rapid coding languages will be required.

Methods
The goals of the study were to develop a new spatially explicit and stochastic metric of ecological departure from replicated reference conditions applied to single and all ecological systems within a search radius of each map pixel. Remote-sensed vegetation rasters of ecological systems and their vegetation classes originally created by The Nature Conservancy in Nevada for private industry were repurposed from a 2014 project.

The methodology involved four steps: (a) estimating the distance-adjusted proportions of observed vegetation classes per ecological system within a radius of each raster pixel, (b) simulating replicates of the vegetation reference condition for 700 years and estimating the distance-adjusted proportion of expected vegetation classes per ecological system within the same radius of each raster pixel and per replicate on year 700, (c) estimate the mean and variance of ED by applying Eq. 1 to each map pixel of the observed and expected rasters per replicate; and (d) recalculating the observed and expected distance-adjusted proportions among all ecological systems per map pixel and per replicate and application of Eq. 1.