climate change

Making sense of canopies

Béatrice Wedeux and David Coomes published a paper in Biogeosciences analysing how environmental factors and selective logging interact to shape the canopies of tropical forests. Using airborne laser scanning technology across a 750 km2peat swamp forest landscape in Borneo, the study reveals strong shifts in canopy height and gap patterns along environmental gradients linked to changing peat depth. In areas where logging roads were detected on historical satellite imagery, the canopy is lowered and has larger gaps, especially so on deep peat where tree growth is thought to be limited by low nutrient availability and waterlogging. The study identifies a close link between the height and the gap structure of tropical peat swamp forests at the landscape scale and reinforces the vulnerability of this ecosystem to human disturbance. The degradation of tropical peat swamps has been at the heart of climate negotiations in Paris, as emissions from fires in Indonesian peatlands over the last couple of months – exacerbated by a dry El Niño spell – approach the total annual emissions of Brazil (1.62 billion metric tons;www.wri.org).

image

Airborne laser scanning allows the detection of openings at different height cross-sections of the canopies of old-growth and selectively logged forests.

Read online: Wedeux, BMM and Coomes DA (2015) Landscape-scale changes in forest canopy structure across a partially logged tropical peat swamp, BIOGEOSCIENCES 12(22):6707–6719, DOI: 10.5194/bg-12-6707-2015.

Explaining the origins of species diversity

The July 2015 issue of New Phytologist has come out and its a doozy!  The entire issue features work on evolutionary plant radiations, drawing together a range of papers that summarize the current state of knowledge about “where, when, why, and how” plant radiations happened.  An editorial by Colin Hughes, Reto Nyffeler Peter Linder outlines the content of what will surely be a landmark issue for years to come!

Many, if not all, of these papers were presented at a symposium organized in Zurich that we attended with our New Zealand collaborators Professors Bill and Daphne Lee in June 2014:

We're somewhere in the crowd

We’re somewhere in the crowd …

For me, this was possibly one of the most intellectually stimulating meetings that I’ve ever attended.  Talks drew major figures in plant ecology, evolution, and systematics and really pushed the boundaries out on ‘diversification’ research.  The field itself is still arguably quite new, with many of the key questions synthesized in a 2008 paper by Peter Linder.  In fact, we have a PhD studentship available to follow-up some of these questions and build on what we talked about at the meeting.

You might have noticed that we even have a contribution in the New Phytologist Special Issue.  Our paper tests the mechanisms by which plant evolutionary radiations emerge and influence ecological dynamics.  We apply more of our expertise in structural equation modelling to focus on 16 species-rich genera in the alpine zone of New Zealand.

Diversity in New Zealand’s alpine.  Celmisia, Chionochloa, Dracophyllum, and Veronica all appear in this photo.

One of the most exciting aspects of our paper is that we’ve tried to reconstruct the niche space that each genus has occupied over the last 20 million years.  This is fairly ambitious and has involved tasks like reconstructing sea surface temperatures through the Cenozoic from isotopic measurements of foraminifera deposited in marine sediment cores, and then using these to estimate past land temperatures.  We’ve also had to consider that the alpine zone has grown immensely over time with uplift of the Southern Alps.  To do so, we collated radiometric dates of rocks and tried to infer their rate of uplift since the Miocene.

Overall, our results suggest that genera that colonized New Zealand earlier encountered more ‘vacant’ environmental space, which promoted species diversification and further occupancy of the environment.  Genera that occupied more environmental space were subsequently more dominant in present-day vegetation plots.  The key message is that time not only explains why diversity arises, but how this diversity influences ecological dynamics.  The Special Issue has many other fabulous papers, so do check it out!

What have we been learning about the Cerrado?

Cerrado landscape invaded by sugarcane fields.

Cerrado landscape invaded by sugarcane fields

In the beginning of 2014, my adventure in the Brazilian Cerrado had just started! It’s now been a year I took the airplane to Brasília, in the heart of Brazil. We decided to study the effects of agriculture, specifically of sugarcane crops, on the gases emissions from soils of this region. Nothing would have been possible without the collaboration with the EMBRAPA Cerrados. But why there??

Cerrado woodland vegetation

Cerrado woodland vegetation

Cerrado, the richest savannah in the world and the most extensive savannah complex in the Neotropics, has been historically affected by a number of human activities. By now, it has lost half of its 2 mi km2 of native vegetation. The expansion of the sugarcane fields, often used for bio-ethanol production, is one of the current threats to this biome.

We are currently measuring the emissions of greenhouse gases, specifically the nitrous oxide (N2O), in response to the management of fertilisers. Our preliminary results show a large increase in the emissions from the combined treatment using nitrogen and vinasse*, that is, 450 times more than the native areas on average! Our longer monitoring activities will be important to understand the variation on the emissions throughout the sugarcane cycle and to assess the sustainability of this crop in the region.

*Vinasse=a waste from the ethanol production that is re-used as fertiliser.  

Experimental sugarcane field in May/2014

Experimental sugarcane field in May/2014

Experimental sugarcane field in November/2014

Experimental sugarcane field in November/2014

Applying vinasse to the field

Applying vinasse to the field

                                              

Collecting gases in the Cerrado

Collecting gases in the Cerrado

Collecting gases from the sugarcane field

Collecting gases from the sugarcane field

Part of the staff in a rare relaxing time!!!

Part of the staff in a rare relaxing time!!!

Can plants get more carbon for less water?

This week’s group meeting featured a special joint production with Molecular Physiology to welcome Prof Graham Farquhar from the Australian National University.  Graham was in the UK to receive a Rank Prize Fund award for his contributions to food security by helping to guide the breeding of wheat varieties that use water more efficiently.

His talk, “Water user efficiency and water use effectiveness, a stomatal perspective using stable isotopes” was a far-reaching overview of his amazing research career, dating back to his time as a PhD student.  But he started his talk with a very provocative and timely consideration of global changes in rainfall and human population growth.

Rainfall is inherently random.  Sometimes there is too much, sometimes there is too little.  Australia is a country that experiences both these extremes.  For example, there are often heavy floods in the monsoon region while other areas, particularly where agriculture is concentrated in the southern part of the country, is drying up.  The desire to expand cultivated land inevitably means there is more pressure on more marginal rainfall.  An astounding statistic that Graham rolled off was that 1 ha of cultivated land was needed to feed 20 people.  20 people are added to the world’s population about every second!  Clearly, that’s a problem.

Graham’s talk then focused on how plants can use the least amount of water for a fixed amount of carbon.  He began by introducing his classic work on stomatal regulation of transpiration relative to carbon assimilation, which shows the two processes are fundamentally linked.  Changing evaporation will always change assimilation.  He then considered how plants could arrange the temporal expenditure of water to maximize assimilation of CO2.  Carbon isotopes are particularly useful here for discriminating among transpiration efficiencies associated with different genotypes and can help identify future crop varieties that use water more efficiently.  In dry conditions,  greater transpiration efficiency improves crop yield and selects for low C isotope discrimination in leaf dry mater.

As we ran out of time, we were left with questions about how the process of balancing carbon and water demands might be influenced by life history strategy (perennial versus annual) and competition for water in soil.

Standardizing radial growth

As I’ve been enjoying the tropical weather here in Sudbury over the past week

Everyone’s gone home for winter

I’ve been thinking about how ecologists report radial tree growth.  And I’m not sure we’re doing it right…

During my PhD, one of the papers I read often was:

Bee, J. N., Kunstler G. & Coomes, D.A. (2007) Resistance and resilience of New Zealand tree species to browsing. Journal of Ecology 95, 1014–1026.

Table 5 specifically is worth drawing attention to:

Picture1

It looks like trees in north temperate regions grow really fast – more so even than in the tropics (i.e. Panama).  But what happens in winter?  In Sudbury, temperatures have been awfully cold in December and they’re likely to hover around similar levels until March.

Sudbury minimum air temperatures (brrrrr)

Minimum air temperatures in Sudbury, ON — brrrrr……

Surely, there isn’t much growth in trees during this period.  So does it make any sense to report diameter growth from January to December?  Wouldn’t it be better to report growth relative to some standardized measure of growing season, such as the number of days when air temperatures are >6°C?

In the case of global comparisons, such as in the Bee et al. table, this might be a moot point.  North American trees still win, just by more.  But standardization is likely to be a real issue for studies that use latitudinal  gradients as a space-for-time substitution to test the potential effects of climate warming.  A few examples are:

Silva LCR, Anand M, Leithead MD (2010) Recent widespread tree growth decline despite increasing atmospheric CO2. PLoS ONE 5(7): e11543.
Huang, J., J. C. Tardif, Y. Bergeron, B. Denneler, F. Berninger, and M. P. Girardin. (2010) Radial growth response of four dominant boreal tree species to climate along a latitudinal gradient in the eastern Canadian boreal forest. Global Change Biology 16:711–731.
Lloyd AH, Bunn AG and Berner L (2011) A latitudinal gradient in tree growth response to climate warming in the Siberian taiga Global Change Biology 17: 1935–45.

Focusing on Fig. 1 in Silva et al. 2010, red maple (Acer rubrum) at 47°N seems to be growing slower than at 52°N.  But temperature, and hence growing season, differs between these two sites.  I wonder whether trees would grow at similar rates if annual basal increments were reported relative to the length of the growing season?…  Ultimately, what ecologists are regularly reporting is an “absolute” outcome – the product of growth and length of the growing season – rather than the “true” rate of growth.

Leave a comment and let me know what you think!

AJT

Climate Change: the Buried Agenda

Currently, the developed world seems content to accept that financial stringency is a price worth paying for bankers’ excesses. Meanwhile, anyone advocating strategies to meet the cost of mitigation and adaptation climate change are close to being vilified as scaremongering extremists. Yet, it seems that multinational corporations by and large accept the prognoses of the Stern report (http://bit.ly/1cdiDDx), and are examining strategies to protect their resource inputs and supply chains for the future (http://bit.ly/18bOlFo).

Of course, the problem is one of timing: hang around for 100 million years, and the current shift in CO2 and GHG emissions will appear as a mere blip in the geological record; but hanging in for 5 years, over the standard political renewal period, fuels current expectations that living standards, economic growth, and availability of mass transportation will progressively increase.

Another problem is one of resource availability, and ease of access. Fossil fuel resources have powered the astonishing technological progression in the past two centuries, using buried plant reserves which have allowed us to trade on past sunlight. It had been initially simple to mine or pump these reserves, but then increasingly difficult to exploit resources in the North Sea, Arctic and Gulf of Mexico. Now we have the prospect, or perhaps spectre, that extraordinary rendition of shale gas threatens to turn excessive US energy consumption from net importer to exporter (Hughes JD 2013 Nature 494, 307–308 doi:10.1038/494307a).

Yet using current solar capture systems, we could meet the annual global demand for energy via sunlight, perhaps, from an area 1,000 x 1000 kilometers of the Sahara  (equivalent to x4 the area of the UK: David Mackay, 2009 Sustainable Energy, UIT Cambridge, or http://www.withouthotair.com). Where is the investment, the vision, the technology to exploit this “free” source of energy? Recent governments have been seemingly indifferent to development of industry technologies to exploit renewables and improve energy efficiency in our housing and business stock. The UK should take a lead and set an example of best practice and embrace the mixed energy generation strategies proposed by Mackay. Say no to nimbyism and do it in your own backyard!

Can we afford to be indifferent, risk the compelling IPCC evidence that man-made climate change is a 95% certainty, and still look our grandchildren in the eye? What will it take to break us from our complacent acceptance of the climatic status quo, the political oxymoron of “sustainable growth” and the short-termist mentality embodied by the “out for nowt and here’s me barrow”- cheap flights, cheap clothes, cheap food is taken for granted by all. And what will it take to convince the general public that we need to act, and quickly, to limit fossil fuel consumption and curb GHG emissions?  Will we need to wait for several more “100 year” extreme climatic events in short order, leading to more human suffering, death and destruction, only this time in an area where real estate is valued considerably more than a few square metres of tin shack and their unfortunate human occupants in the Philippines?

So rather than allowing this agenda to be buried, let us resuscitate, rejoin and reinvigorate the climate change debate.

Howard Griffiths, denizen of a ginkgo-enveloped room, honoured to provide the first post on the Plantsci Ecologists blog