Forests Can Protect Humans from Disease

Here’s one more benefit of National Forests which needs to be considered in forest planning: protection from infectious human diseases.

A group of scientists published a study earlier this month in the Nature journal, citing mounting evidence that biodiversity loss frequently increases infectious disease transmission.

One of the primary authors, Felicia Keesing from Bard College, explained the general pattern to Science Daily: “biodiversity loss tends to increase pathogen transmission across a wide range of infectious disease systems.”  Keesing has been following the ecology of Lyme disease in northeastern forests for several years, and she said that evidence is mounting about biodiversity and disease.  For instance, an opossum can serve as a biological buffer between the Lyme bacterium and humans by picking and killing off ticks.  Opossums are poor hosts for ticks, but mice are good hosts.  As biodiversity is lost, opossums move away and mice remain.

The authors also cite the relationship of the mosquito-transmitted West Nile disease and low bird diversity, as well as the relationship of hantavirus and lower diversity of small mammals.  There are three reasons the loss of biodiversity can affect the transmission of infectious diseases:

  • The more diverse the number of intermediate hosts, the less likely that a specific host will be present that are dangerous to humans.
  • In a more diverse community, it’s more likely that the disease will end up in an unsuitable intermediate host.
  • Genetically diverse hosts are generally in better condition and more resistent to disease.

The authors conclude: “despite remaining questions, connections between biodiversity and disease are now sufficiently clear to increase the urgency of local, regional, and global efforts to preserve natural ecosystems and the biodiversity they contain.”

At the very least, the relationship of biodiversity and epidemiology is a very direct example of a principle the Forest Service has been using during the development of a new forest planning rule: that people and the environment are inseparable and interdependent.  The idea that forests are actually a safety net is a compelling argument for the maintenance and restoration of functioning and diverse ecosystems.


  1. Their summary is:

    “Current unprecedented declines in biodiversity reduce the ability of ecological communities to provide many fundamental ecosystem services. Here we evaluate evidence that reduced biodiversity affects the transmission of infectious diseases of humans, other animals and plants. In principle, loss of biodiversity could either increase or decrease disease transmission. However, mounting evidence indicates that biodiversity loss frequently increases disease transmission. In contrast, areas of naturally high biodiversity may serve as a source pool for new pathogens. Overall, despite many remaining questions, current evidence indicates that preserving intact ecosystems and their endemic biodiversity should generally reduce the prevalence of infectious diseases.

    This kind of implies that diseases of humans, animals and plants are “bad.” But they are entirely part of the universe, just trying to make a living like the rest of us. If you are a plant, diseases, insects, herbivores are all part of life. Are we on the side of plants and against diseases? Perhaps that leads to tension between being “for” plants and “for” herbivores?

    Also, infectious diseases are perhaps best prevented, say in Colorado, by public health measures; perhaps not so much protecting “intact” (whatever that is) ecosystems elsewhere.. unless ours are already intact…

  2. Andy- the definition of biodiversity is fraught with problems, some neatly outlined in this discussion by the Stanford Encyclopedia of Philosophy here. I was using it in the sense of ““Biodiversity” is often defined as the variety of all forms of life, from genes to species, through to the broad scale of ecosystems (for a list of variants on this simple definition see Gaston 1996).”This definition is part of the Stanford discussion.

    Separating out species with beating hearts does not fit that definition but does fit others listed. As for me, it does not fit from two perspectives (insects have hearts; not sure if they beat) and I hope to reduce bedbug population size and potentially genetic diversity, should I ever be infested ;). From the other side, if we are for biodiversity being all of life, we shouldn’t have a bias for Bilateria. Check it out on the wonderful Tree of Life Website Project here, and the numbers and diversity of other kinds of beings.

  3. Since the above article was published in Nature, some might be interested in this post by Pielke about an article by Sarewitz; in the comments Andy and I discuss the objectivity (or not) of the journals Nature and Science.

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