Termites help rainforest survive drought
According to the conservation organisation Global Forest Watch, we lose a football-field sized patch of rainforest every second. The land is used for logging, cropping and housing and is also threatened by the effects of climate change. So scientists are working hard to understand how best to conserve the rainforests that we do have. And they discovered recently that we’d previously overlooked an unlikely hero that helps the ecosystem to defend itself in the face of droughts. Izzie Clarke spoke to researcher Hannah Griffiths from the University of Liverpool, to find out what it is...
Hannah - Principally we're interested in quantifying exactly what role termites have in maintaining ecosystem functions in the rainforest, but it just so happened that our large experiments happened to coincide with the big El Nino drought of 2015 and 2016. So we saw this as a really exciting opportunity to not only look at how termites influence ecosystem processes. We can actually look at how these ecosystem processes changed in response to drought and how termites might be responsible for maintaining some of these processes.
Izzie - So what were these termites doing during that massive drought?
Hannah - Yes, one of the really exciting and sort of surprising results was that their abundance our anchor and counter rates of termites almost doubled during the drought and this had a big impact on some of the processes we were measuring. So, firstly soil moisture: we had these experimental plots where we experimentally suppressed the numbers of termites, so we had areas of the forest where there were fewer termites and we had control areas where we haven't affected the communities. We found where termites were present during the drought soil moisture was higher, leaf litter decomposition was also higher, the heterogeneity (the variability of nutrients in the soil) was also higher. And this led to an increase in seedling survival rates. So where termites represent all of these things increased and where they were absent we saw a decrease in these activities, but only during the drought. These differences between the control and the suppression plots were only evident during the drought.
Izzie - So during a normal time it's sort of quite a balanced level, but during these droughts you'd almost expect the opposite to happen; that during a drought everything gets a bit drier and more arid.
Hannah - Exactly. That's exactly what we're expecting to see, so I mean of course during the drought everything did dry up. The forest is quite stark. You used to walk in through the forest and the leaf litter is wet and squishy, there's water dripping off the leaves. But during the drought everything just gets crispy and dry, and the trees start losing their leaves because everything's very, very stressed. So we expected all of these processes, this decomposition, the soil moisture, that too to decrease. We actually found that where termites were present they maintained these processes which was really exciting and really surprising.
Izzie - I see! So they're like these little engineers that help almost extract all of these nutrients which then help the rainforest keep taking over.
Hannah - Yeah that's exactly what we found.
Izzie - Do we know why this happens?
Hannah - We don't know exactly why. We can hypothesize as to why termites might be increasing in abundance during droughts. Termites move around the forest in tunnels largely underneath the soil surface, and it could be that under normal conditions where it's very very wet, it's actually quite difficult for them to move around them, and where the soil is dried out a little bit it could just be that they can simply move around more easily; their tunnels are less waterlogged. It could also be because, perhaps, they'd be released a little bit from predation from things like ants that perhaps don't do so well in the drought. So we don't know exactly why they increase in abundance during droughts but we've got some inklings that need to be tested further.
Izzie - And why is this so important?
Hannah - With climate change we know that drought is going to increase in frequency and severity. That's been predicted. We know that these rainforests are going to be increasingly stressed. We also know that where you disturb rainforest systems; where you selectively log or deforest, termite communities are affected - they're negatively affected. Diversity in the abundance of termites decrease and we know that termites are really important for keeping things going during the drought.
This means that we've got this massive area of sort of human modified forests where termites are reduced. This means that these forests are less resilient to drought, essentially, because of the reduction in the termite communities. And the other thing is, I think, this is sort of on a broader scale not just thinking about termites: I think it's demonstrating yet again the need to conserve intact biological communities because until we've looked at termites during the drought and outside of the drought, we wouldn't have known they were this important until the system was stressed. And that means there could be many other ecosystem processes and many other organisms that carry out these processes we haven't yet measured. But we're continuing to erode biodiversity which means we don't not know what protection we're losing until it's already gone.