Biomass: increasing or decreasing?

In a previous post, I raised the question how best to measure ‘Nature’, arguing the benefits of an overall Index including biodiversity, habitat diversity, human usage value and sheer volume of living organisms, biomass. Here a look is taken at whether biomass has been increasing or decreasing in recent decades.

The appeal of biomass as a measure of Nature is that it abstracts from anything innately human. Hence, if you asked an alien who has no innate affinity to any particular species to define the state of Earth’s ‘Nature’ then I can well imagine that alien defining it by biomass, which is the total mass of all life on earth. The trees, the plankton, the humans, the fungi, the fish, etc. Biologists talk of dry biomass, wet biomass, biomass with or without bacteria (who are hard to count), etc. One can argue that the more of all that there is, the more of ‘Nature’ there is. Biomass is then one measure of how much total ‘Nature’ the earth produces.

Now, the key thing of interest is the change in biomass: how much new life gets produced per period as the climate changes. The closest measured equivalent of this notion of Nature is ‘net primary production’ of biomass, which is the rate of new biomass produced. The question of how to divide biomass production into the bits benefitting this or that species is then a matter of inter-species politics that our imaginary alien might well just not be interested in. A living cell is a living cell, no matter what it is used for, the alien might well muse. So what if the humans use most of it for their benefit? To the victor the spoils the alien would argue.

By the way, humans constitute no more than 0.1 billion tonnes of dry biomass, making up only about 1 in ten-thousand of each kilogram of biomass on the planet. Our mass according to some estimates is half that of cattle or Antarctic krill, and only a third to one-thirtieth that of all ants. Clearly, we are not yet really on top of the inter-species biomass league!

So, what do we know about net primary production (NPP) over time? Well, probably the best study before 2000 (after which we have more comparable satellite data) is the 2003 Science study by Nemani et al. They essentially tried to count as much as they could what was happening to forests, wetlands, tundras, etc.

As their beautiful picture above indicates, most of the earth has seen a net increase in the 1982-1999 period (in green) and only a few areas saw a decrease (in brown). As one can see, the 1982-1999 period was good for Australian biomass production, as well as that of nearly all highly inhabited areas in the world. If you care about things that depend on our biomass production, such the potential for food production, then this is a very encouraging picture. If this was all you knew, you would want this trend to continue.

What about after 2000? Again the best evidence I could find comes via the Science magazine, albeit this time in response to an estimate. Zhao and Running in 2010 published an article talking about how drought in the Southern Hemisphere probably lead to a reduction in NPP there, counter-balancing the increases in the Northern hemisphere.

The problem with their study was that it was not actually based on data but on computer simulations. This opened the door to accusations of rigging and the reply posted a year later by a team of 6 scientists headed by Arindam Samanta said of this study that “the small trends, regional patterns, and interannual variations that they describe are artifacts of their NPP model. Satellite observations of vegetation activity show no statistically significant changes in more than 85% of the vegetated lands south of 70°N during the same 2000 to 2009 period.”

So where does this controversy, which still rages on and on, leave us in terms of best-guess NPP trends? Well, the picture below is the one produced for the 2000-2009 period by the 6 scientists basing themselves on as much data as they could find, mainly from satellites. It shows winners and losers, with central Australia this time a loser, but on a global level it is pretty much ‘no trend’. If anything, the consensus appears to be of an increase in NNP up till 2003 at least.

So, our imaginary alien would have to conclude that the climate change observed in this period had been good news for ‘Nature’ until the 2000s, after which there have been some Northern hemisphere winners and losers in Argentina and Australia, but no clear global trend on the surface.

As to the oceans, there are recent signs of greater net production in the Arctic (see http://www.agu.org/pubs/crossref/2011/2011JC007151.shtml) but also signs that ocean productivity as a whole is slightly reducing though it appears to be notoriously difficult to guess trends in the productivity of the oceans given how deep they are and how large areas are covered by ice. Generally speaking, cold water is able to hold more CO2 and is thus generally more life-abundant which would lead to less NPP as the oceans warm, but the major issue with oceans is the availability of nutrients in the water, not temperature, which is why warm coral reefs are full of life and the cold deep ocean is not. The amount of nutrients in turns is a complicated thing depending on currents and river systems and a whole host of other stuff, so we are awaiting better global data to tell us where the trend in ocean NPP is.

In conclusion, biomass production at the moment seems to be holding up for the world as a whole, at least to the extent that it is measurable. For an imaginary alien who cares nothing for species esthetically pleasing to humans and who would be solely interested in current ‘production’, this would mean Nature is not doing so badly.

Unlike the imaginary alien, I do think diversity of species and habitats is something worthwhile and even that some diversity is better than other diversity (diversity in higher order mammals is surely of greater aesthetic value to us than diversity in something like see-dwelling bacteria). So in a more composite index of Nature it would surely not be doing so well.

As to future trends in biomass, we will have to see if we are currently at the top of the mountain or merely at the top of the foothills in terms of world biomass production.

 

 

This entry was posted in Uncategorized. Bookmark the permalink.

23 Responses to Biomass: increasing or decreasing?

  1. Pappinbarra Fox says:

    A monoculture might have a massive biomass but would it be considered healthy in ecological terms? I suspect not because the key to a healthy ecosystem is the interaction and interdependency beween species and the balances that derive from those.

  2. cbp says:

    If we ask “Is Somalia suffering?” and then observe that the Somalian population has increased 4 fold over the last 50 years we could be led to answer, “no, Somalia is doing just fine”. Clearly we need a better index.

    • Paul frijters says:

      Ha! And human diversity in Somalia has also increased! Pirates, fanatics, 4 governments in stead of one…..
      So the state of Somalia is not something similar to the state of Nature. And your point is? Your preferred index is?

  3. Mel says:

    Don’t be fooled into thinking that increased biomass is necessarily a good thing. In numerous Australian ecosystems, increased biomass is a result of exotic weed invasion for instance buffel grass displacing native grasses and leading to a massive increase in biomass and therefore much more destructive fires.

    Moreover palatability and nutrient levels are at least as important as biomass for running livestock.

    Another thing to be aware of is that low fertility is often associated with great biodivsersity, for instance the highly infertile biodiversity hotspots in the SE of WA and the fynbos in South Africa. In contrast you have high fertility low diversity systems like mangrove swamps.

  4. Mel says:

    “… I raised the question how best to measure ‘Nature’, arguing the benefits of an overall Index including biodiversity, habitat diversity, human usage value and sheer volume of living organisms, biomass … ”

    Blog posts are places for throwing around ideas so I don’t want to be too critical but I must point out that you are trying to do the impossible here. You really do need to define what you mean by Nature before you attempt to operationalise it with indicators. One problem is that anthropocentric nature and ecocentric nature are two very different things and in part contradictory. As an example, in my patch in central Victoria, habitat diversity and biodiversity are correlated with low biomass, low fertility (which I assume might be a component of human usage value).

    Presumably you are aware that Australian ecologists are actively engaged in trying to lower soil fertility (and as a consequence biomass) in degraded habitats to increase biodiversity. For examples see here.

    Even with respect to anthropocentric nature it may be argued that more of your indicators is not always a good thing. Queensland and northern NSW woody weed areas have high biomass but this high biomass reduces production. The same goes for the sheep farm across the road from my acreage: the dense gorse and blackberry thickets have much higher biomass than the surrounding grasses, while the low palatability patches of yorkshire fog grass have greater biomass but much lower palatability than the low biomass wallaby grasses.

    Sorry, but your index tries to do too much and ends up meaning nothing. It is a little like the The Meaning of Life Index = 42.

  5. conrad says:

    I don’t see why you are worried about creating an anthropocentric-free measure. I’m happy with one that does really relate to human activity, so things like biomass in terms of crop yields and so on would be important (it’s not like we haven’t modified most of the land surface of the Earth for our own benefit and fished out most of the fish that live in certain places). Even things like diversity concerns could be addressed to some extent with such a measure if it was used at different time-scales, since retaining diversity is good for the long term of many ecosystems which does have some benefits for humans.

  6. john r walker says:

    1982 to 1999 is a very short time frame. Further to what mel is saying a lot of the degrading of OZ farm and other lands happened in our great grand fathers time. Around were I live there have been improvements in the past twenty years , but its coming off a low base.

    PS biodiversity is strongly linked to closeness to the equator , the mappings suggest a loss of biodiversity.

  7. wilful says:

    The appeal of biomass as a measure of Nature is that it abstracts from anything innately human. Hence, if you asked an alien who has no innate affinity to any particular species to define the state of Earth’s ‘Nature’ then I can well imagine that alien defining it by biomass, which is the total mass of all life on earth. The trees, the plankton, the humans, the fungi, the fish, etc. Biologists talk of dry biomass, wet biomass, biomass with or without bacteria (who are hard to count), etc. One can argue that the more of all that there is, the more of ‘Nature’ there is. Biomass is then one measure of how much total ‘Nature’ the earth produces.

    There wasn’t much point asking people what they thought if you were to just ignore them, was there? Biomass is a useless measure, as multiple people have pointed out on each of the three threads.

    When speaking about ecology, you appear to make a very fine economist. Economists are the third professional group, after lawyers and physicists, that believe that they have some kind of deeper understanding that means they can opine knowledgeably about any subject.

  8. john r walker says:

    I doubt that net biomass would be of any use in creating a measure of the planets ability to sustain humans, on the contrary it could be worse than useless.

  9. Paul Frijters says:

    Mel, wilful,

    I say I favour a composite index of nature including X and all you can do is pick on X and pretend its the only thing I care about. Either you are deliberately being silly or have simply not read the thread in which most of your points are already raised.

    As to biomass being an economist’s wet dream, this is such a childish statement, so obviously wrong. Who do you think these authors are that have measured and estimated biomass over the last few decades? Who are the editors that give it space in their journals? And do you think these people are interested in biomass to please economists or because they themselves think it measures something of value and interest to us humans? Of course they are not economists and of course they think volume matters. The degree to which volume matters versus other aspects is open for debate but its plain dumb to pretend the volume of living things is not a desirable feature of a measure of Nature.

    Put it the other way: if biomass had been reducing rapidly, we would be hearing about it a lot more.

    • FDB says:

      If biodiversity had been reducing rapidly, we’d be oh wait.

      You wanna invoke the experts, and what they make big noises about? Then biodiversity is THE ONLY GAME IN TOWN.

      We aren’t hearing much about biomass because nothing much is happening with it. Kudos to the folks mapping it diligently, but it’s basically a zero sum game. Energy in … biomass out.

      You’ve answered your own question, but can’t see the trees for the wood.

      • conrad says:

        There was a great graph in the economist a couple of months ago looking at the density of fish now versus the density of fish in 1800 (sorry I can’t find it with a quick search). It showed massive declines due to over-fishing. Are you saying a biomass measure wouldn’t be useful for measuring this, especially if you were using bins for biomass of things of different sizes (i.e., big fish vs. plankton vs. single cell organisms)? It would basically be a convenient measure that is independent of fish type.

        I’d also be interested to see whether the acidification of our oceans is reducing life in general across certain large clusters of sizes. Biomass would be a good start for looking at that.

        • FDB says:

          Sure, you can break biomass down further and further, and it becomes more and more useful as a measure of the ecological health of the biosphere.

          At the species level, it really comes into its own!

  10. Mel says:

    Sigh. More biomass equals good is possibly reasonable in deforested and overgrazed landscapes in much of Africa and Asia. It is obviously and observably not OK in various other contexts, such as fire prone grasslands and woodlands. Type “fire biomass buffel grass australia” into google and educate yourself. Also think about fuel reduction burns in the drier parts of Victoria, WA and NSW.

    One size does not fit all. Period.

  11. Paul Frijters says:

    Mel,

    the notion that more biomass can lead to local problems for humans is a footnote in this kind of issue. By the same token, one can say that the box jellyfish is an unwanted piece of biodiversity that we would not want in various places. Indeed, anything toxic is unwelcome in various cases. Such trivialities do not mean though that one as a measure of Nature would not want biodiversity as a positive thing.

    One hence has to get into the spirit of the endeavour: much like we all want a higher GDP even though some aspects of a higher GDP might not in fact be all that desirable (like more arms exports!), the question becomes what roughly this ‘Nature’ is that we want to have more of. And yes, biodiversity and biomass should both feature in such a measure as a positive even though one might not always favour that locally.

    If you are looking for a perfect measure of Nature (or GDP or anything at the aggregate level for that matter), you will be waiting forever. The living have to make do with imperfect measures.

  12. murph the surf. says:

    So if we start hearing that an increase in biomass is due to factors considered negative to other parameters measuring “nature” such as the index of biodiversity then how can we compare different indices?
    This all sounds suspiciously organic too.
    Where are the inorganic included in our survey of the current majesty of the natural world? Wave action , wind ,water flows ,solutes in bodies of water, rock and mineral formation rates , soil qualities are all part and parcel of nature too.
    Can we believe that biomass is a suitably sensitive indicator of their situation currently?

  13. Mel says:

    Paul:

    “If you are looking for a perfect measure of Nature (or GDP or anything at the aggregate level for that matter), you will be waiting forever. The living have to make do with imperfect measures.”

    We need a range of different indicators for those things that you decided mean Nature and you’ve already identified many of them. My point is that adding them up gives you a meaningless big dumb number.

  14. Mel says:

    Plus we already have things like annual State of the Environment reports. Not perfect, but still one thousands times more meaningful than a big dumb number.

  15. Paul frijters says:

    Mel,
    We will have to agree to disagree on this one. Like GDP, I think a measure of Nature at the global or continental level would be very successful.
    I saw the environmental reports indices. Indices of various poorly measured things, of course. Their main use seems to be to tell countries about local issues. They don’t measure what you would think of as Nature.

  16. murph the surf. says:

    “They don’t measure what you would think of as Nature.”
    Could we have a definition of this Nature you write about?
    If indices are reflecting local problems I agree they have a limited use.
    Is there any consideration of the non sentient /inert in your deliberations?

  17. James says:

    Hi there,
    Large political and scientific bodies are in agreement that extinction levels are much higher than would be expected.
    Wouldn’t this lead us to believe that biomass is decreasing alongside it? How could we be losing species and expect biomass to remain the same?

    • paul frijters says:

      nope, as far as I have followed this, biomass is now believed to have been increasing rapidly the last few decades.

      Extinctions in higher order animals are almost irrelevant for biomass levels because the vast majority of biomass is things like trees, bacteria, fungi, etc. It is mainly via their function in nature that extinctions of big animals matters for overall levels of biomass.

Leave a Reply

Your email address will not be published. Required fields are marked *

Notify me of followup comments via e-mail. You can also subscribe without commenting.