Of Mice and Men in Gabon
by Ian Markham -- June 30th, 2014
In the moonlit forest of Ivindo National Park, the ‘thwack’ of a tiny metallic door snapping shut rang out in the night. Did the sound startle the elephant who left her colossal print beside the device that produced it? Did a passing cricket’s little heart leap thinking he’d stumbled into some big mean chirper’s territory? Did the riot of cicadas even miss a beat? Probably not. But one thing can be certain. There can be no philosophical debate of whether it made a sound or not. Somebody heard it for sure. That someone would be the hungry little mouse who, with that clink, found himself trapped like a rat (but smaller) with that delicious smelling mix of oats, peanut butter, and plantain that first caught his attention. And with that fateful clink, I’d like to think, began my Master’s project in earnest.
So at long last we get to it. Why am I here? What am I doing? Is there any purpose to all this toiling? Let’s skip the existential crisis and get to the brass tax. My work here will be looking at how the small mammal community changes with human impact on the forest, and begin to get at how those changes might affect the forest in turn. Basically I will be asking two questions: Do rats and mice get more common where humans log and hunt? and Do more seeds get eaten by rats and mice in places where people hunt and log? To answer the first question I brought with me a couple suitcases full of rodent traps for catching the little guys alive and kicking. To answer the second I brought another filled with wire and garden staples. Now that one’s less obvious though so lets come back to it later.
Now you are probably asking, for one, why on earth would somebody go halfway across the world to catch rats and mice? And for two, why Gabon of all places that nobody’s heard of? Well bear with me here because I’m going to encourage you to think like a mix between an ecologist and a wizard and eventually all will become at least clear-ish. The ecologist comes in because we need to remember that all parts of an ecosystem are interconnected. The wizard comes in remembering the wisdom of Middle Earth: Gandalf knew better than anyone that even the smallest among us can make all the difference.
Its something I don’t think many think or talk about but keep in mind that the forests of central Africa are the largest stretch of continuous rainforest in the world after the Amazon basin. They are not only a resource upon which many millions of Africans rely but are the very lungs of our planet. What’s more, if my advisor’s work estimating the carbon stocks of Gabon is correct they can hold two to three times more carbon than the forests of Amazonia per unit area, and thus represent massive stores for the carbon dioxide that’s warming our planet.
Now remember in the last post how I talked about logging in Central Africa being a bit different from what we are used to in the West? Throughout this region timber harvest means snaking roads through the huge tracts of forests to pull out just a handful of trees from each spot. Well more technically its an average of 3-5 trees per hectare and that ‘handful’ will be spread across two or three semi-trucks depending on the size of these colossal trees. Nevertheless, especially in Gabon the number of trees they are pulling from such a large area has the potential to be continued long into the future or perhaps even ‘sustainably.’ However, the sustainability of this selective logging hinges upon the trees that we pull out coming back on their own without being planted, i.e. natural regeneration. Well if you could magically push each tree down, and ‘poof!’ make it disappear, there’d probably be no problem.
That process occurs all the time. Old trees weary and worn out by long lives, full of fungi and laden with lianas eventually just have enough and one more droplet of rain, one more gust of wind, or one termite nibble too many sends them crashing to the ground. When a big tree, strapped into the forest with a harness of vines and woody lianas comes down, it often pulls another few down with it. The gap they open up then allows light otherwise blocked by the canopy to come rushing down to the hitherto dark forest floor. Sure enough waiting gratefully at the foot of the mighty fallen tree are often its offspring as well as other species of trees in seeds and saplings, waiting for a shot at crowning glory. And so the race begins to beat the others to fill the gap and literally overshadow the competition. Meanwhile the fungi and bacteria turn the old tree into fuel for the decade-long sprint.
Well that’s all very nice, sounds like as long as we don’t take too many or too quickly that nature will take care of itself. Well, yes, that is what we hope for and if the ‘poof!’-disappearing-tree act were possible it almost certainly would. The issue is that when humans enter a forest under the pretense of knocking down a few trees, they typically do a lot more than just that.
Some of it is the current necessity of logging. Much of it is not. During my spring break field course here I had the privilege (but not the pleasure) of visiting a Chinese-owned logging concession, and got insights into and photos of logging that I would like to get into in another post. But for now lump the impacts of logging into your head as one. For now we must sort of accept these as a necessity. The country needs to develop, livelihoods need to improve and timber is a valuable commodity. The part of logging that is not a necessity is the whole other suite of impacts associated with opening forests for hunting.
When large thoroughfares are cut into otherwise untouched forest, and populations of hungry workers are transplanted into those far flung spots, there is going to be an increase in bushmeat hunting. The biggest threat to conservation of central African mammals is doubtlessly not logging but hunting. And it may just turn out that hunting may also be a threat to the long-term prospects of selective logging. That is in large part what John’s PhD student and I are interested in with our projects here.
So how is it that hunting could threaten logging? Well the ecologist in us would point out that baby trees don’t get where they grow by magic. They are dispersed one way or another from their parent tree. Now some trees are simply dispersed by gravity. Plop and roll. Others have little sails or cotton for the wind to help them voyage forth. Others still, recruit help from warm, furry friends. Well at least that’s the fuzzy disney way to think of it. In truth, animal-dispersed seeds have a bit of a tricky balance to strike. They often ‘want’ to use animals like a sort of taxi service. Although in this analogy they would be trading their bodies for that ride… Not in that way though! Sheesh. Dirty minds! In any case, they often either do so by putting tasty flesh around a hard or toxic seed which animals will gnaw on while having a meal on the go. Or they count on being swallowed whole and being ‘deposited’ at their destination with a nice heap of miracle grow. However, not all animals will play their game. Some animals won’t carry seeds. Many will simply destroy them. Or worse if there are no around animals at all the seeds may just fall under the parent and rot in heaps. It’s a delicate balance that relies on the right animals being around in the right numbers at the right time.
Therein lies the problem. It’s already one push away from balance when humans go and cut gaps in the forest through which wind dispersed species flow more freely. But then when those gaps also open the forest to an infantry invasion of bushmeat hunters things can get pushed really out of whack. My advisor’s work in Congo has begun to show how hunting in logged forest can lead to even more pronounced shifts in forests towards fast-growing wind-dispersed colonizing plant species, tangles of lianas and fewer animal-dispersed tree species. He calls this process “Ecological Erosion.” Among the consequences of this erosion is the decline of valued timber species, and a lowering of the amount of carbon stored in the forest for a given age. In a country like Gabon, these two factors are a big deal. And that’s what I am particularly interested in with my rodents.
You see when you hunt out the big guys that eat fruit and keep the understory open with their trampling you probably change the game for the little guys. The rodents would love a go at the fruits the big guys are taking so if there’s more of it around because there are no big guys to eat it, they have a feast. And when the understory starts filling with a carpet small seedlings, a demonstrated consequence of “defaunation” aka taking out big animals as well as logging, there are more places for rodents to hide from predators, not to mention probably even more food! Given that, I’m looking to see if areas with heavy human impact have larger numbers and biomass of rodents than areas with a similar environment but remain in protection. My undergraduate advisor Dr. Rodolfo Dirzo calls the subsequent explosion of rats and mice that he has found as a result of human impacts “rodentation” and recently published a study in PNAS that documented a massive spike in disease-ridden rodents as a consequence of simulated human impact in East African savannas. But more than just a disease threat the rodents also exert their own changes on the forest. They have their own preferences for seeds and fruit and these may change with whats available. Moreover, only the biggest of them (too big for me to catch at around big stonking rabbit-sized) commonly disperse seeds in a way that benefits the plant. Most will destroy seeds in feeding which makes them more seed predator than disperser and potentially has a distinct impact on forest regeneration.
So a big change in the rodent population can maybe lead to big changes in the rate at which seeds are destroyed. And that is the second part of my study. I have these nifty little cage things that I will set out over peanuts and palm nuts with the intention of looking at the relative rates at which seeds are taken impacted and protected sites. To me “cage” implies keeping things in, so the more sciencey word we use is “exclosure.” The total exclosure, essentially a closed cage, is meant to keep out all mammals, letting only insects attack the seeds if they can. The partial exclosure should allow rodents in but keep the larger stuff out, basically a low roof with open side. And the open treatment is essentially just seeds on the ground for anyone who wants ‘em. The idea then is to be able to compare across sites to see if seed predation due to rodents and seed predation in total changes significantly between impacted sites and protected sites. Sounds simple enough, but with rabbit-sized rats and unknown bandits willing to tunnel under wire and lawn staples, coming up with an effective cage design that I can cary eight of deep into the forest has been tricky enough!
So it may just turn out, that indeed there are way more rats and mice in the spots we are hunting. And if so they probably are eating a whole bunch more seeds off the forest floor. If that’s the case then we’ve laid the foundation for important insights to this whole process of ‘ecological erosion.’ Is it rodents stopping certain trees from coming back? Are they giving others a leg up on the competition? It may be. It may not be.It could even be that the rodents are what helps make the logged trees in Gabon come back given their favorite target Okumé is wind-dispersed. But we’ll never know if we don’t try to find out. That’s science. The fun is in the mystery! And the truth is if we don’t find out we may be shooting ourselves in the foot in the long run without even knowing it.
The great promise of working in Gabon, is in the fact that their government really does seem to care. About their natural resources in all senses: not just oil and timber but wildlife, carbon storage, and biodiversity. The will from the top for conservation to go hand in hand with development is strong. The nation is beginning a likely decade-long process of strategic land use planning. A better understanding of the impacts of bushmeat hunting particularly in logging concessions may just result in changes in policy. Moreover, if this process of ‘ecological erosion’ really does degrade the timber value or carbon sequestration, documenting it may be the incentive that logging concession managers or the government need to limit hunting in logged forests. Doing so would have tremendous positive effects for biodiversity conservation and in a country filled with gorillas, chimpanzees, mandrills, and elephants that is a big deal. And on a global scale if the link between intact animal communities and the sustainability of a forestry operation is more clearly demonstrated likely organizations like FSC (Forest Stewardship Council) may incorporate measure to decrease hunting in their certification schemes, which would impact far beyond the borders of Gabon.
But that is getting ahead of ourselves. Hopefully now though you can see why this might be interesting to more than just myself. This is just a piece of the foundation. The first round to a longer line of inquiry. Foundations however are essential. Also remember to think like a wizard. Even the smallest things can make a big difference and from little things, big things grow.
Now back to building mini-fort Knoxes that these infernal rodents can’t burrow their way in to! After I watch the light fading from the forested banks of the Ivindo river.