Aug 02, 2018
Science Thursday: An Argument for Heterogeneity, in the Kitchen Sink and in the Fields
Type: Research Synthesis
I have a confession to make: I am obsessed with stinky sponges. You know the type — the sponge that, despite looking new and clean, leaves your hands reeking for hours. You can scrub your hands with copious amounts of soap, you can apply strong-smelling lotion, and yet you still find yourself gagging hours later when your hand passes by your nose.
My obsession began eight years ago, when I worked in an office with a stinky sponge. The sponge was replaced regularly, yet it always smelled bad. Then I started working in my current office, only about a mile from my previous office, and again — a stinky sponge. I thought it might be location, something in the water, but then I noticed it in other places. Even my most fastidious, neat-freak friends had stinky sponges. They would microwave their sponges, run them through the dishwasher, disinfect them, replace them, and yet they’d still smell. And then there was me — tidy but definitely not a germaphobe — replacing my sponges only when they were falling to pieces. And honestly, even at their worst, my sponges never had that smell. The scientist in me was intrigued.
In August of last year, an article in The New York Times caught my attention. It pointed to a recent study that showed that kitchen sponges have bacterial densities on par with human stool samples — literally higher than anything else on earth. But that was not the most interesting part of the story; the most intriguing finding was that efforts to disinfect the sponge — microwaving, dishwashing, etc. — actually killed off mild bacteria and made space for the most aggressive, stinky bacteria to thrive. And suddenly it clicked: the common denominator of the stinky sponges in my life was not a lack of hygiene or the time since replacement — it was antibacterial dish soap!
You are probably wondering how this could possibly relate to fire, but in my mind there’s a fairly clear connection. This is a story about heterogeneity and resilience, diversity and balance. And it’s something that keeps coming up in the fire science literature that I’ve been reading.
Lately, I’ve been drawn to research on the relationships between fire and grazing, or “pyric herbivory” (Fuhlendorf et al. 2008; PDF, 376KB). There is a ton of interesting research on the connections between patterns of fire and the grazing response of domestic livestock and wildlife, most of which is coming out of Dr. Sam Fuhlendorf’s lab at Oklahoma State University, or from various collaborators of his at other universities. And the central crux of most of this research is the concept that management strategies focused on heterogeneity — shifting mosaics with spatial, temporal and structural complexities — create the most biodiverse, productive and resilient systems. More homogeneous systems, in contrast, are the proverbial stinky sponge of the landscape.
Many of us consider the benefits of biodiversity and heterogeneity as no-brainers, but in some contexts, it’s less intuitive. For example, grazing management has often focused on distributing disturbance over large areas to minimize areas of localized and thus more damaging disturbance (e.g., overgrazing). Makes sense, right? However, early work by Fuhlendorf and Engle (2004) showed that this kind of “management to the middle” was not the most conducive approach for meeting multiple objectives, including biodiversity and agricultural productivity, in Great Plains grasslands. Rather, a shifting yet concentrated patchwork of fire and grazing activity best promoted the mutual goals of livestock production and habitat conservation , because producers could maintain the same herd densities as they did under their traditional management, while also providing a habitat-rich patchwork of plant communities at different stages of development.
From the livestock perspective, the influence of fire on grazing behaviors cannot be overstated. In their 2004 paper, Fuhlendorf and Engle found that grazing animals spent 75 percent of their time in the area that had been burned. A more recent paper by Allred et al. (2011; PDF, 629KB) similarly found that cattle and bison both preferred recently burned areas and actively avoided areas that hadn’t recently seen fire (see below). This pattern was also documented by Augustine and Derner in more arid rangelands of Colorado (2014; PDF, 1532KB); however, it was less pronounced there than in areas with more rainfall and more productive soils, where much of the existing research has taken place. There is a need for further research on fire-grazing interactions across a broader spectrum of rangelands and climate conditions, including in the Pacific West where I work.
It’s not surprising that grazing animals are attracted to burned areas, given the influence fire has on the quality of forage. Forage quality can be two to three times higher in burned versus unburned areas, and crude protein levels are also consistently higher (again, see Allred et al. 2011). Recently burned areas are like a candy shop for cattle, deer and other grazers, and an approach that includes frequent and well-distributed patches of burned rangelands will ensure that high-quality forage is always available, even when other conditions change. A recent study in the southern Great Plains showed that heterogeneity caused by fire and grazing buffered the effects of drought on livestock production. In more homogeneous areas, livestock productivity decreased with drought, whereas in areas managed for heterogeneity, livestock productivity was stable through time (Allred et al. 2014; PDF, 384KB).
The grazing benefits of pyric herbivory likely extend beyond domestic livestock to other wildlife that depend on grasslands, and have inspired Fuhlendorf and his collaborators to look at the interactions between bird populations and patch-burn grazing. In a 2006 paper, they showed that focal areas of patch burning and grazing over several years created a more heterogeneous pattern of vegetation, which then resulted in a more diverse bird population. This management approach was able to mimic historical patterns of disturbance, better representing the habitats within which those bird communities had evolved.
Now I won’t lie — I’ve been slyly looking for a venue where I could share my revelations about stinky sponges. But you have to admit that the sponge story has broader implications, not only aligning well with the hygiene hypothesis (which you should check out if you haven’t heard of it), but also with all of this awesome new research on pyric herbivory and the larger case for promoting and sustaining heterogeneity. Even with the limited example of pyric herbivory, we see strong connections between heterogeneity and the resilience of ecological and economic systems. The messiness of these landscapes, with their wide variety of successional stages, plant communities, and intensities of disturbance, is exactly what’s keeping them alive and well. It’s the more homogeneous systems — those that look clean and orderly and have uniform disturbance — that are more vulnerable in the long run. But the good news is that you can turn things around: throw out that antibacterial dish soap, and even the stinkiest sponge will smell fresh in a matter of days. Then, go set some of your fields on fire!
Author’s note: I wrote this post last week, the same day my husband got assigned to the Carr Fire, but before the fire had begun its exponential growth, burned down the house of one of my best childhood friends (and the homes of hundreds of other families), and taken lives. To post a light-hearted, fire-science blog after the week we’ve had in northern California feels strange, and certainly doesn’t do justice to the deep sadness that we at FAC Net, the Watershed Research and Training Center, and the University of California Cooperative Extension feel for the communities that are dealing with wildfires right now. I hope that this blog might at least let us laugh a little (maybe at my expense, for being such a dork!), and give us an interesting topic to bookmark for the future. Here’s to hoping that the coastal fog where I am can sneak farther inland, and that August brings some reprieve to my home county and all the others who are suffering right now.
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