Thread by @Nature_Based

1/n Controversial new paper alert!

WILD LARGE HERBIVORE DENSITIES AREN’T UNNATURALLY HIGH, & imo much higher numbers in the future could be a sign of successful nature recovery!

Thread – please hear me out :)
besjournals.onlinelibrary.wiley.com/doi/10.1111/13…
#restoration #rewilding @JAppliedEcology

@JAppliedEcology 2/n My career started in the Scottish Highlands @alladale1 , and restoring the Caledonian Pine Forest was the key restoration/rewilding goal. Standing in the way were red deer eating all the saplings. Solution: reduce deer numbers or fence them out, deer were the problem.

@JAppliedEcology @alladale1 3/n The red deer population at the time was about 13 per km2. So clearly 13 red deer per km2 is too many deer, and they were ‘overgrazing’, or in this case ‘overbrowsing’, as I had been taught and read.

@JAppliedEcology @alladale1 4/n There has been plenty written on how deer numbers in the UK are a threat to the environment and the countryside and how they need to be reduced, controlled and managed to avoid wreaking havoc! See headlines below.

@JAppliedEcology @alladale1 5/n But, are these numbers really that high? How do we know? In research led by @CamFlojgaard @AarhusUni we studied the relationship between total large >5kg herbivore biomass & net primary productivity in conservation areas across the world.

@JAppliedEcology @alladale1 @CamFlojgaard @AarhusUni 6/n I think the results are really interesting! First, looking at protected areas across Africa (yellow line) there is a positive relationship between net primary productivity & large herbivore biomass. The more productive the ecosystem is, the more large herbivores it supports.

@JAppliedEcology @alladale1 @CamFlojgaard @AarhusUni 7/n In contrast, on the other continents this relationship has been reduced and/or decoupled. In North America (dark blue) the large herbivore biomass is really low. While in Asia (light blue) and South America (red) there is no significant relationship.

@JAppliedEcology @alladale1 @CamFlojgaard @AarhusUni 8/n In Europe there is no relationship & herbivore biomass is either much lower compared to African sites of similar productivity, or on the higher side of African sites (but within natural variation). The former are protected nature areas, while the latter are #rewilding sites.

@JAppliedEcology @alladale1 @CamFlojgaard @AarhusUni 9/n From my experience in Scotland (data not included in the analysis), 13 per km2 is about 1700 kg/km2, with essentially no other large herbivores present, which is very low compared to what you’d expect to find in Africa with the same productivity (~4500 kg/km2)!

@JAppliedEcology @alladale1 @CamFlojgaard @AarhusUni 10/n So what is going on here? Is 13 red deer per km2 dangerously high and a threat to nature? If so, how are sites in Africa coping with far higher amounts of large herbivores. To be honest, the @alladale1 head stalker/ranger pointed the answer out to me back in the day …

@JAppliedEcology @alladale1 @CamFlojgaard @AarhusUni 11/n It WASN’T the deer that ate all the mature trees in the first place was it? These trees were cut down to provide timber for buildings and ships. The degradation of the ecosystem as a whole is the reason nature is struggling to bounce back now.

@JAppliedEcology @alladale1 @CamFlojgaard @AarhusUni 12/n Few old trees in the landscape today don’t spread much viable seed. Dense swaths of heather, bracken, and grass don’t offer space for trees to germinate. Only a few seedlings are getting established and so almost any number of deer will be too many.

@JAppliedEcology @alladale1 @CamFlojgaard @AarhusUni 13/n Is browsing by large herbivores reducing the number of trees regenerating? Yes. But should we be painting them as the villains of the piece? Imo No. This is a problem created by people and the solution needs to be focused on restoring nature as a system.

@JAppliedEcology @alladale1 @CamFlojgaard @AarhusUni 14/n Restoring nature as a system may well involve reducing large herbivore numbers now, but this should be seen as an opportunity for restoration to allow richer and more abundant nature across the board in the future, from plants to predators & incl herbivores. #rewilding

@JAppliedEcology @alladale1 @CamFlojgaard @AarhusUni 15/n While we perceive herbivore numbers to be really high in many parts of the world, compared to the more intact ecosystems in Africa (or from the past) herbivore communities are severely degraded in their diversity (number of species) and abundance. #shiftingbaseline

@JAppliedEcology @alladale1 @CamFlojgaard @AarhusUni 16/n The excellent @SerengetiRules highlighted how the recovery in abundance of Wildebeest in the Serengeti following rinderpest decimating their population was feared and resisted, but the recovery was spectacular and now seen as natural.

@JAppliedEcology @alladale1 @CamFlojgaard @AarhusUni @SerengetiRules 17/n Ecosystems outside of Africa are generally more degraded, likely to take longer to recover, may need recovery of the vegetation & carnivores first. But it may be possible to have our own spectacular recoveries of nature, incl large numbers of magnificent large herbivores.

@JAppliedEcology @alladale1 @CamFlojgaard @AarhusUni @SerengetiRules 18/n But space for more research in this area. Thanks to lead author @CamFlojgaard and fellow co-authors @JCSvenning Pil Pedersen and Rasmus Ejrnæs