Abstract
This study develops an approach to automating the process of vegetation cover estimates using computer vision and pattern recognition algorithms. Visual cover estimation is a key tool for many ecological studies, yet quadrat‐based analyses are known to suffer from issues of consistency between people as well as across sites (spatially) and time (temporally). Previous efforts to estimate cover from photograps require considerable manual work. We demonstrate that an automated system can be used to estimate vegetation cover and the type of vegetation cover present using top–down photographs of 1 m by 1 m quadrats. Vegetation cover is estimated by modelling the distribution of color using a multivariate Gaussian. The type of vegetation cover is then classified, using illumination robust local binary pattern features, into two broad groups: graminoids (grasses) and forbs. This system is evaluated on two datasets from the globally distributed experiment, the Nutrient Network (NutNet). These NutNet sites were selected for analyses because repeat photographs were taken over time and these sites are representative of very different grassland ecosystems—a low stature subalpine grassland in an alpine region of Australia and a higher stature and more productive lowland grassland in the Pacific Northwest of the USA. We find that estimates of treatment effects on grass and forb cover did not differ between field and automated estimates for eight of nine experimental treatments. Conclusions about total vegetation cover did not correspond quite as strongly, particularly at the more productive site. A limitation with this automated system is that the total vegetation cover is given as a percentage of pixels considered to contain vegetation, but ecologists can distinguish species with overlapping coverage and thus can estimate total coverage to exceed 100%. Automated approaches such as this offer techniques for estimating vegetation cover that are repeatable, cheaper to use, and likely more reliable for quantifying changes in vegetation over the long‐term. These approaches would also enable ecologists to increase the spatial and temporal depth of their coverage estimates with methods that allow for vegetation sampling over large spatial scales quickly.
Highlights
Point quadrat analyses and visual cover estimation of vegetation are widely used, standard vegetation survey techniques that date back to the 1920s (Gleason, 1920)
In the case of the management of natural spaces on either private or public land, vegetation surveys and regular monitoring can be constrained by the availability of expert ecologists to be in the field with a reasonable assessment taking up to half a day per plot; survey time based on a plot size of 40 m2 (Vittoz & Guisan, 2007)
We find grass and forb cover estimates are correlated with estimates made in-situ by field ecologists
Summary
Point quadrat analyses and visual cover estimation of vegetation are widely used, standard vegetation survey techniques that date back to the 1920s (Gleason, 1920). These images are taken at the same time that the field ecologist estimates the amount and type of vegetation present.
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