Human activity is reducing plant biodiversity around the world, according to a global study that took an unusual approach to reach that conclusion — accounting for the species that could be in a particular area but aren't.
"The problem is that over time, as we lose species due to human impact, we don't see the number of species that are lost because we only see what we can perceive," says Viktoria Wagner, a plant ecologist in the University of Alberta's Faculty of Science and co-author of the study published last month in Nature.
As Wagner explains, the typical process when ecologists study plant diversity involves marking off a particular area (for example, a 10 by 10 metre square) and then recording all the species present within that area. The trouble is, this approach doesn't give any information about the species that have disappeared entirely.
The emerging new approach provides a more accurate snapshot of the biodiversity in any given region by also looking at "dark diversity" — what's missing, rather than what's there.
"There's a silent loss of biodiversity happening that might have gone unnoticed using the traditional tools," says Wagner. "The concept of dark diversity is a way for us to understand what species could have been there but are currently lacking."
The study, led by the DarkDivNet Consortium, included data from 119 regions around the world. Wagner and fellow U of A ecologist James Cahill, along with graduate students Charlotte Brown, Raytha Murillo and Karina Salimbayeva, who led the field work, took samples from the Mattheis and Roy Berg Kinsella research ranches to represent two distinct ecosystems in Alberta. The researchers involved also categorized each sampled area according to the Human Footprint Index (HFI), which measures human impact on a particular ecological area on a scale from 0 (no impact) to 100 (maximum impact).
The researchers examined to what extent all species in the area that could inhabit a community (known as the species pool) are actually present (community completeness) or absent (dark diversity). This allowed them to get the most accurate view possible of biodiversity in the region.
In sites with lower HFI scores, about a third of the species that could have been in an area were present. In sites with higher AFI scores, only a fifth of potential species were present.
"This paper showed that the loss of diversity is global, it happens across the board, and it's important to invest in biodiversity protection," says Wagner.
Information on these biodiversity losses allows conservationists, ecologists, policy-makers and researchers to create more targeted strategies to increase biodiversity in their respective regions, Wagner notes.
"Through the use of dark diversity, we can identify species that are lacking in a site and actively try to reintroduce them."
Wagner adds that the paper showed human impact often has a wider reach than we think, so conservation efforts need to target a broad range of areas.
"We can't just focus our efforts on protecting specific areas like national and provincial parks. It's important to protect biodiversity outside these designated areas as well."
