Once upon a time in Sichuan province… —Colin’s adventures of summer 2019

In southwestern China, Sichuan province, runs the great range of the Daxue Mountains, with the tallest peak, Mount Gongga, reaching over 7,500 m a.s.l. (Fig. 1). In that mountain range, Colin and a team of scientists and students undertook a three-week long fieldwork this August. The field team consisted of Colin, Giulia Mengoli (Imperial College) and Sandy Harrison (University of Reading) from the UK side and Wang Han, Shengchao Qiao, Yuhui Wu and Yuxin Liu (Tsinghua University) and Li Meng (the team’s dedicated taxonomist from Nanjing Forestry University) from the Chinese side (Fig. 2).

Gongga sitesFigure 1.  Sampling locations in the Daxue Mountains, western Sichuan Province, Southwest China.

The fieldwork campaign was part of the project spearheaded by Wang Han with an overarching goal to assess relationships among some key plant functional traits and their responses to the environment. The working hypothesis is that there should be coordination between leaf photosynthetic traits and wood hydraulic traits. Although this question is a fundamental one, a comprehensive data set to answer it is still missing. The Gongga fieldwork aimed at filling this knowledge gap.

The project began last year with a field campaign on the eastern side of Mount Gongga (Fig. 1). This year, fieldwork continued on the western side of the mountain and revisited eastern sites to include some additional measurements. Western sites, although located at similar elevation to the eastern sites, are drier and, thus, create a precipitation contrast. The sampling locations were distributed on a long altitudinal gradient from 1,600 to 4,500 m a.s.l. with mean air temperature ranging from 5 to 22°C. These large environmental gradients allowed sampling of a broad variety of vegetation types from mixed deciduous-evergreen forests at lower elevations to boreal and shrub vegetation with high Rhododendron component at higher elevations (Fig. 2).

Figure 2. Fieldwork along the latitudinal gradient in the Daxue Mountains, August 2019. The vegetation changes from mixed deciduous-evergreen forest to “boreal” forest and eventually shrub tundra vegetation.

Measurements of several plant functional traits were made:

  • Photosynthetic traits: Vcmax (rate of carboxylation), Jmax (maximum rate of electron transport, by the two-point method),
  • Hydraulics: leaf area to sapwood area ratio, leaf turgor loss point, stem specific conductivity,
  • Leaf chemical composition: C, N, P, δ13C, δ15N,
  • Basic wood and leaf traits: wood density, leaf mass per area, leaf dry mass content,
  • Morphological traits including leaf phenology, size, shape, margin, hairs, spines, thorns and stem characteristics.

The campaign was an ambitious endeavour as it entailed measurements of a large number of species (>150) with some traits being time- and labour-intensive. Hydraulic traits were measured off-site by another team, not shown on the above photos, working in a field-lab at a research station in Moxi, a tourist town on the eastern side. The team consisted of Huiying Xu—Wang Han’s PhD student, as well as several undergraduate students from Tsinghua and Hehai Universities and Southern University of Science and Technology, and a postdoc from Nanjing Forestry University. The field campaign would not have been remotely possible without a platoon of keen and hard-working researchers and students!

The steep altitudinal and temperature gradients posed challenging work conditions. The team’s attire varied from T-shirts to thick jumpers and jackets (Fig. 2). These efforts were, however, rewarded by the beautiful scenery (Fig. 3), the experience of Tibetan culture (more prevalent on the western than on the eastern side of Mount Gongga), local bread, many yaks and large, exciting datasets!

Figure 3. Beautiful scenery… when it didn’t rain.

 


Before the Gongga field trip, Colin attended two international meetings: the 44th New Phytologist Symposium in Accra, Ghana, and the Congress of the International Union for Quaternary Research (INQUA 2019) in Dublin, Ireland.

44 NP symposium

The New Phytologist Symposium was titled “Determinants of tropical vegetation structure and function” and was organized by Prof. Jon Lloyd (Imperial College), Prof. William A. Hoffmann (North Carolina State Unviersity), and Dr Vincent Logah (Kwame Nkrumah University of Science and Technology). Abstracts of all oral and poster presentations can be found here. Apart from attending talks and poster presentations, Colin led one of the focus groups discussing how climate influences tropical vegetation structure and function.

The topic that sparked particularly impassioned discussion during the meeting revolved around the question: which is the primary driver of tropical vegetation structure: fire or climate/soil? At one end of the spectrum, it is argued that forest and savanna are Alternative Steady States (ASS), such that both could exist under the same climate and soil conditions, with fire history in a given area ultimately determining which vegetation type occurs. At the other end of the spectrum, it is argued that climate and soil play chief roles in shaping vegetation structure, with fire having an additional, less crucial effect. These are not new questions. The debate started several years ago in the pages of Biogeosciences (Lloyd et al. 2015, Veeneendaal et al. 2015, Staal and Flores 2015 – all three papers published in Biogeosciences, Lloyd and Veeneendaal 2016 in Biogeosciences Discussions, and more recently Veenendaal et al. 2018 in New Phytologist). The symposium discussion did not result in an agreement between the opposing camps. However, the researches have committed to working together to resolve this controversy.

 


In July, Colin attended the 20th Congress of the International Union for Quaternary Research (INQUA) in Dublin, Ireland. He was a co-author of one oral presentation “Climate changes in semi-arid Spain from the last interglacial to the late Holocene” by Dongyang Wei and a poster “Changes in speleothem δ13C through the deglaciation: a model-based study” by Sandy Harrison. INQUA meetings are large gatherings of geo- and climate scientists, which take place every four years.

Inqua-Banner-1

The Quaternary is the current geological period, which started ~2.6 million years ago. Many prominent processes taking place during this period have directly shaped the world as we know it today: “climate change, sea level rise, ice-ages, human evolution, the migration of peoples, cultures, plants and animals, and the formation of landscape and habitats of today” (link).

A highlight of the meeting was a plenary talk by Eric Wolff, Royal Society Research Professor in the Department of Earth Sciences at Cambridge University. Prof. Wolff has for several decades been an international leader in the study of polar ice cores, which are a key source of information on past climate and its evolution over recent glacial cycles. Information on 800,000 years in Antarctica and 128,000 years in Greenland are available. Ice cores are chronological libraries, where information about past climate accumulates year by year (similar to growth rings in trees but on a much longer time-scale). Past temperature is inferred from isotopic content of water molecules making up the ice, while past atmospheric composition is inferred from analysis of air bubbles trapped in the ice (link). During the talk, Prof Wolff discussed the current state of knowledge and future possibilities and new directions in ice core research. Through the European project “Beyond EPICA – Oldest Ice” he and colleagues in Europe are on a quest to find the oldest ice, and plan to drill an ice core encompassing 1.5 million years.

 

Written by Kasia Ziemińska, 18 Nov 2019

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