forest ecology and conservation

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).

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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.

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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!!!

Climate change and the fate of New Zealand’s forests

By storing carbon in wood, forests currently play a key role in mitigating climate change. However, there is growing concern that as climate changes forests could shift from being a net carbon sink to a source. In our recent paper published in Global Change Biology we explore the consequences of climate change on wood production in New Zealand’s forests.

Using repeat census data from 1070 permanent forests plots, we looked at how wood production changes over temperature and rainfall gradient across New Zealand, and then use this information to predict how climate change will affect forest carbon dynamics in the near future. We find that climate influences wood production both directly, by driving physiological responses at the tree level, and indirectly, by determining the composition and structure of forests. If the composition and structure of New Zealand’s forests were to remain unchanged over the next 30 years, then wood production would increase by 6–23%, primarily as a result of physiological responses to warmer temperatures. However, if warmth-demanding trees were able to migrate into currently cooler areas and if denser canopies were able to form, then a different response is likely: forests growing in the cool mountain environments would show a 30% increase in wood production, while those in the lowland would hardly respond. We conclude that response of wood production to anthropogenic climate change is not only dependent on the physiological responses of individual trees, but is highly contingent on whether forests adjust in composition and structure.

Wood production in mixed species forests

Our latest paper aiming to untangle the mechanisms behind diversity-productivity relationships in forests has just been published in Journal of Ecology. Working in Mediterranean mixed forests in Spain, we find that complementary use of canopy space by oak and pine species means that mixtures of these two functional groups produce around 50% more wood each year compared to monocultures. However, the magnitude of the diversity effect on wood production fluctuates over time, decreasing noticeably in strength during drought years.

Tree cores of pine and oak species collected in the Alto Tajo Natural Park, Spain.

Tree cores of pine and oak species collected in the Alto Tajo Natural Park, Spain.

The study was conducted in the Alto Tajo Natural Park, in the Guadalajara province of central Spain, as part of the FunDivEUROPE project which aims to determine the functional significance of forest biodiversity. Using tree ring data from permanent forest plots we explored how mixing pine (Pinus sylvestris and Pinus nigra) and oak species (Quercus faginea and Quercus ilex) influences wood production in Iberian forests. We found that pine species receive more light, develop larger crowns and grow 138–155% faster when in mixture with oaks. However, this positive effect of species mixing on growth was severely reduced under drought conditions due to increased competition for water with neighbouring oaks. In contrast to pines, oak trees were less responsive to mixing, primarily as a result of their ability to tolerate shade and water shortage. Our results suggest that competition for light is key in driving positive diversity effects in forests, but also show that the strength of complementarity can change in response to climatic conditions.

A view of the Tajo river cutting through the valley below on its way to Lisbon.

A view of the Tajo river cutting through the valley below on its way to Lisbon.

More ways of living on a bush than on a bluebell

Some years ago, a fascinating article in the National Geographic described the exceptional diversity of bat species to be found in Barro Colorado Island, Panama – incidentally where Ed Tanner is currently with some of his PhD students. Research by the Smithsonian Tropical Research Institute and others had described 74 species, which managed to coexist by carving out distinct, often ingenious, niches. http://ngm.nationalgeographic.com/2007/06/panama-bats/panama-bats-text. Some bats are physically adapted to hunt in open spaces, others in gaps and along edges, still others in the fine interstitial spaces of lower understorey layers. It is a dramatic example of how habitat structural complexity is related to, and helps promote, species richness.

We explore this relationship between habitat structure and species richness, and its relevance, in an article recently published in Methods in Ecology and Evolution. Building on an earlier review (Tews et al 2004, J. Biogeog 31:79-92) through an analysis of 199 papers published 2004-2013, we find that a positive relationship between habitat complexity or heterogeneity and animal species richness or diversity is found in over 75% of investigated cases, across different taxonomic groups and ecosystem types. It seems that Lawton (1978) was right when he observed: “There are more ways of living on a bush than on a bluebell”. Given this common pattern, and building on Coomes Group’s developing experience of using airborne lidar to study forests, we argue that this powerful vertical-profiling tool could be used to deliver habitat structural indicators of species richness over large spatial extents. More spatially and temporally precise information on species richness and habitat quality is increasingly important in responding to the unceasing loss of biodiversity across the planet, so we hope the article might contribute to developing new tools to meet this challenge.

 

Spring ephemerals in ancient woods

We had the opportunity over the Easter weekend to visit Hayley Wood, an ancient woodland located outside of Cambridge that pre-dates medieval times.  Presently, the Wood is managed under traditional coppice by standards, with large oaks that are estimated to be ca. 300 years old.  Professor Oliver Rackham’s work on the British countryside has been heavily influenced by Hayley, and in turn, he has been instrumental in its conservation.

Hayley Wood is particularly important, however, for its sizeable population of oxslips (Primula elatior).  During spring, the oxslips burst to life along with much of the other ground flora to produce a spectacular display of colour.  Carpets of bluebells (Hyacinthoides non-scripta) line the various woodland rides and we even managed to count 20+ orchids interspersed throughout one section of the Wood.  These seemed to fit the description of the early purple orchid (Orchis mascula), especially the spotted foliage, but do comment if you know what it is!

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Having spent many years in the Carolinian forest, even doing research there on spring ephemerals such as the showy white trillium (Trillium grandiflorum), I don’t ever feel homesick in British woodlands.  There’s always something to see in the Spring, with among the most beautiful floral displays anywhere in the world.

Punting Goodbyes

Sometimes, us ecologists in our Gingko-covered building like to venture outdoors when the weather is reasonably nice here in Cambridge. **cue joke/pun/grumblings about how weather in Cambridge is rarely nice**

We had the chance to do just that during a recent punting trip on the River Cam — a sending-off party of sorts for one of our Research Associates Rafi Kent, who has since returned to Israel to assume a teaching position at Bar-Ilan University. Over river-chilled hand-crafted beers and delectable Portuguese nibbles, we enjoyed a lovely afternoon of blue skies, gorgeous Cambridge riverside scenery, and fantastic company. Pictures from the afternoon are posted below for your perusal.

Congratulations to Rafi; we all send you our very best from Cambridge!

Out of the wild

My year started off with a field trip to the peat swamp forests of Borneo. The aim was to wrap up data collection for my PhD project looking at drivers, both environmental and human-made, of structural patterns in these little-studied forests. Supported by a fantastic team of three local research assistants, I established a series of plots and collected leaf samples of most abundant species for trait analyses.

Tropical peat swamp forests grow, as the name suggests, on peat layers that can extend to more than 10 m depth forming so-called ‘peat domes’. During their formation over thousands of years peat domes become purely ombrotrophic (rain-fed) and develop convex water tables that remain close or above the surface. Gradients in fertility and possibly waterlogging along peat domes are thought to lead to the observed succession of different forest communities. Tropical peatlands are major global carbon stores and are bound to play a key role in climate change mitigation.

Extreme conditions for the trees are matched by extreme conditions and many challenges for researchers: deep water, soft grounds full of hollows, mosquitoes without an end. But it all brightens up when an orange forest fellow makes an appearance.

 

The value of p-value

In the latest issue of Nature there is a piece by Regina Nuzzo about how un-reliable p-values are in interpreting statistical tests. She describes how researchers use the p-value entirely differently than how Fisher intended it to be used when he first published it in the 1920s. His significance, censu Nuzzo, was a mere means to test whether a result is worth pursuing. It has become the gold standard in scientific work to test for the 0.05 significance level without providing information about the feasibility of the hypothesis being tested, or on the strength of the effect being reported. Without that information, the p-value is not very informative and in many cases might be misleading. This paper can be related to a long historic feud among statisticians regarding the pros and cons of frequentist statistics versus, for example, Bayesian inference techniques.

The take home message from Nuzzo’s and other papers on the subject, is that it’s not enough to use p-value, one should always look for additional ways to test the rigor of one’s results, and to describe them in a way that renders them highly reproducible.

Book on Forests and Global Change

David and Will’s [and David Burslem‘s] edited volume Forests and Global Change now has a launch date and new website.

Featuring 15 invited contributions from the leading figures in forest ecology, the chapters build on plenary talks given at a British Ecological Society symposium of the same name that was held in Cambridge in 2011.

The book consists of three overarching themes:

(I) forest dynamics and global change;
(II) species traits and responses to changing resource availability;
(III) detecting and modelling global change;

and is published by Cambridge University Press as part of the influential Ecological Reviews series.

Having missed the meeting due to being in the depths of New Zealand, I’m looking forward to reading the book.  A quick read of the introductory material (freely available on the Cambridge University Press website) suggests that it aims to nurture an appreciation of the multiple drivers of forest change and inspire action for conservation.   It does so by bringing together individuals working at the forefront of the field with “big” datasets in vegetation monitoring and bioinformatics, new ecophysiological approaches, and computational advances in modelling and remote sensing.