Sunday 13 March 2022

Urban redwoods

Been getting a bit obsessed with UK redwoods of late. Now I've started seeing them, I can't stop! There are a lot of them around NE London, Essex, Kent and beyond. How they came to be here is an interesting story, tied up with wealth, empire and the cut-throat world of 19th C horticulture (no really). This site is a really excellent resource for UK redwoods, with an ever-expanding list of locations.

Most of the mature ones are all a very similar size. Which isn't surprising given they mostly arrived in 1853, brought by William Lobb, a savvy nursery collector. Some seeds had been brought earlier, but this was the first large-scale introduction. The lure of owning some of these incredible trees was clearly not lost on the monied classes of Victorian Britain; seedlings were planted in grounds and gardens, as well as in churchyards. 19th C parish vicars obviously weren't averse to a bit of triumphalism either. I mean who could resist, when they had already made such an impression.

Image: UC Berkely, Bancroft Library

Amazingly, many of the surviving mature trees seem to have been left after the original buildings have long gone, which is probably a testament to their grandeur. 

Here's a selection of some of the recent ones I've found. L to R: Epping; Chigwell churchyard; Dunmow fire station car park; Dunmow care home. These are all Sequoiadendron giganteum (or Giant redwood). 

This magnificent grove is in Havering Country Park, just NE of London. 

And when I started looking, turns out there's a whole lot of these in Hackney. Many of these have been planted in the last 10-15 years or so. Here's one in Springfield Park, with a couple of Dawn redwoods, Metasequoia glyptrostroboides, which has its own fascinating history.

Someone in Hackney Council is clearly a fan of the redwoods, as there are quite a few around. The first two of these are on Hackney Marshes, the third is North Millfields Park and I've seen others in London Fields and Victoria Park. I've also found a slightly random coastal redwood right by the railway line in Allens Gardens, N16.

And Hackney Council are obviously going all in on this. In Feb 2022, they've planted a whole selection on the East side of Hackney Marshes, a selection of 51 coastal, giant and dawn redwoods. It's an ambitious approach and it'll be fascinating to see the growth and survival rate of these.

So we're going to start measuring some of these UK redwoods with the TLS, to see where they sit on the mass spectrum compared to similar height / age individuals growing in California. Are UK redwoods following the same size-mass trajectory, or has the climate and often artificial location shifted them? Let's find out.

Thursday 11 February 2021

Hot off the 'presses' (or whatever the online equiv is - Icelandic server farm?)

Having been back in the field again at Wytham late last year (those were the days eh?), despite the odd covid-related hiccup (we're all getting sick of those, right :-/) it's always good to see work coming out in various papers. This is particularly true at the moment when it's easy to lose sight of the sunny uplands ahead. 

So I'm really thankful (& lucky!) to have some great colleagues & collaborators who are taking our work forward. We had a paper in Nov 2020 in Scientific Reports describing our redwood work, with Laura Duncanson, John Armston, Andy, Phil and myself. We show that the allometric models seem to underestimate redwood biomass significantly, while the TLS agrees really closely with the amazing crown mapping work of Steve Sillett. That paper got quite a bit of press, not least for Phil's beautiful image of the redwood 'usual suspects' lineup.

From Disney et al. (2020)

One of the best things about this, was the Laura's picture appeared in the Times, and our work was immortalised in comic form by the amazing Naomi Volain. That's a win! It was also covered in the Jan 2021 issue of Scientific American, a piece by Katherine Kornei.

Our long-term collaboration with Kim Calders and the Ghent CAVElab team resulted in Kim's horizon scan view of TLS in ecology, which was a great outcome of the meeting in Ghent in 2018, and summarises a whole range of work from TLS groups worldwide. It also includes another one of Phil's cool images, this time of our local Hardy Tree in Old Pancras churchyard.

Fig. 3
From Calders et al. (2020) RSE.

A really important piece of work that just came out was Andy's paper on the harvesting work we did at Caxuianã in Brazilian Amazon. This paper shows three important things: i) TLS biomass agrees really well with harvest measurements, even for large tropical trees with leaves on; ii) there is unexpectedly large mass in the crowns, which may explain differences with allometry; and iii) wood density varies a *lot* - not that that's news, but still! Again, this was a great collaboration with Matheus (as part of his PhD), Patrick Meir and Ingrid Coughlin at ANU Canberra, Lucy Rowland in Exeter, and Lola da Costa at Universidade Federal do Pará Belem. This is a really important bit of work in showing how TLS should be used in cal/val and for testing allometry.
Figure 3.
From Burt et al. (2021) Royal Soc. Open Science.

Onwards and upwards, and here's to more trees in 2021.

Tuesday 21 July 2020

Back in the field: ash scanning in Wytham Woods

It's been a while, but y'know there's been stuff going on .... which is why it's been so nice to get back out into the field finally, collect some data, do something that feels a little bit 'normal', whatever that means now. Following a trip into the dept for the first time since March to pick up the kit, and getting our covid-19 risk assessment approved, Phil and I went out to Wytham Woods last week. We were collecting baseline TLS data from 15 plots as part of a NERC-funded project exploring the ecological impact of ash dieback. This is a large 4 year programme led by Yadvinder Malhi, with various colleagues from Oxford and elsewhere. It is fundamentally a manipulation experiment, assessing the response of high, medium and control (no ash) ash cover plots to the death of ash, which will be artificially facilitated by ring-barking in each plot. ADB is already widespread in Wytham and so this is just speeding up the process. The project is looking at the resulting impact on insects, small mammals, birds, bats, understory, soil composition and overstory including changes in light environment. We're using the TLS in a different way here - aiming to quantify the vertical structure and understory cover, rather than looking at tree structure.

To get at the vertical profiles and potentially very dense ground cover (some of the plots are just bramble apocalypse!) we rented a pump up 6m tower (see below). This enables us to get the TLS up into the canopy, and looking down on, and hopefully through the understory.

Looking up the pump-up tower into the ash canopy.
The pump-up tower worked really well, with the downside that carrying it through the plots was a pain - heavy and bulky, awkward to carry, sharp edges - gah! This meant longer days than planned, but hey after 4 months of lockdown and staying local, this felt like a bit of an adventure. After the dry weather there seemed to be a lot of mosquitoes and ticks - Phil seemed to be a particular delicacy for them, picking several off each day. It pays to be vigilant though as Lyme has been seen in Wytham although not this year, so far.
Daily tick check - put them in the tube, label them and put in the fridge. Someone's studying the ticks because of course they are - this is Wytham, someone's studying everything!
We stayed in the chalet in the woods - which has been refurbished into a really rather splendid, if slightly eccentric, field station. We didn't get as much done as we'd hoped - slowed down by the tripod, a single battery, and the terrain. And then the lidar had a disk read fail on the last day - nothing too serious we think, but we might lose a day's data which is always a pain. So we'll be back in September to finish off the leaf-on data, and then in January for the baseline leaf-off scans. But wow, it was good to be back doing some normal work again - long may it continue. Many thanks to the Oxford team, particularly Yadvinder for the lovely dinner, and Cecilia for showing us the plot locations - although you could've chosen ones with fewer brambles! :-) 

The only genuine Swiss chalet in Oxfordshire?

Sunday 3 November 2019

Return to Sonoma

Earlier this year I was part of a bid led by Lisa Bentley, from Sonoma State University, to explore new methods to estimate fuel loads and fire impacts in forest plots in Northern California. Lisa's bid for CALFire funding was successful (yay!) and as part of it, we are helping Lisa's team deploy TLS in these plots to see how well it can be used to estimate standing fuel, deadwood, brash etc. by looking at plots that were affected in the fires of 2016. The aim is to see how new tech (lidar, drones, mobile phones etc) might augment or improve existing fire risk assessments. 

The urgency of this was brought home very starkly by the huge fires that broke out right in the area we were working, and much more widely, and are still burning as I write this at the start of November 2019. The Kincade Fire in particular has burned right through the Pepperwood Preserve, as well as causing mass evacuation, rolling power blackouts etc. It's hard to imagine how life must feel for people living in close proximity, knowing that a period of dry weather followed by Santa Ana winds, and a spark can lead to this. Lisa and her kids were evacuated late October - all safely back now thankfully. But the conditions leading to these kinds of fires are seemingly only going to get worse i.e. prolonged drought periods followed by high winds.

Phil and I flew out in late September, and met up with Lisa and her team at Pepperwood. Pepperwood itself is an amazing 3200 acre site, in the Mayacamas Mountains between Sonoma and Napa counties, and is home to the non-profit Dwight Centre for Conservation Science, which carries out all kinds of public outreach activities as well as facilitating cutting-edge science.

The field team in one of the plots affected by the 2016 fires - all these trees (pines) are dead from the previous fires and so at some point will fall, becoming fuel for future fires.
The pine plot shown above, but looking up to the crown. These are large trees (probably > 40m) and so you can get an idea of how severe the fires were in 2016.
The TLS scans were being collected in about 25 plots spread across Pepperwood, each 50 x 50 m i.e. 0.25 ha. The sites were a mix of deciduous (oak and other), evergreen (pine), and more savanna-like plots in the rolling hills. 

Panorama of an early morning walk to a lower stature oak-dominated plot, with mist lying over Santa Rosa in the distance.  The site is a working ranch so cattle grazing plays a strong role in the nature of the plots.

One of the plots reached from the walk above, showing the steep terrain in places down to creek beds as well as the noticeable impact of fire.

Working in the Dwight house, or accommodation for most of the time we were there. Great views from the balcony!
We were lucky to be able to stay for much of our trip in accommodation actually on the Preserve, in the Bechtel House, which adjoins the Dwight research station. The view from the lounge out over the hills was pretty spectacular, and the sunsets even more so!

Sunset / moonrise looking West from the porch of the Bechtel House, with Hairy Mountain in the foreground.
The weather was sunny but cool - having seen forecasts of 30+ degrees (C that is) Phil and I were maybe a little underprepared for overnight temperatures down in the low single figures and frost on the windows. Phil and I were reduced to sharing a hat.

Lisa's team very quickly picked up the challenge of using the TLS and the software, and were soon zipping through the plots, processing data and starting to think how to use them (them, Paris). A key part of this is likely to be how to provide baseline estimates of fuel loads that can be compared to used to update, the more rapid but more qualitative line transect estimates of fuel that form the basis of routine assessment currently. The challenge is to find ways to improve on those estimates, using approaches that are rapid and easy-to-deploy if possible. Lisa's team also used our ZEB-REVO to scan the ground layer - can those data be used to estimate ground fuel and even duff for example? Meanwhile, Matt Clark was collecting UAV spectral data over the same sites, in order to explore the possibilities for using eg SfM to estimate fuel loads over wider areas. 
Lisa, hard at work, controlling the Riegl with her cellphone (in left hand) - master of all she surveys.
Phil noticed this cool oak growing out of a large rock so we scanned it will Paris and Sean were climbing it. Phil then generated a nifty Sketchfab model of it!
Rock-grown oak.

We'll be back with Lisa's team next year, to carry out measurements at other sites, as well as potentially back to some of the existing plots if they've been affected by fire again in the current season. 

Tuesday 30 July 2019

Book alert!

The work of our group features in several chapters in a new book describing the new opportunities and challenges for measuring the biomass of forests from space. The book, "Forest properties and carbon cycle studies from Earth Observations", edited by Klaus Scipal, Anny Cazenave, Teodolina Lopez (ISSN: 0169-3298 (Print) 1573-0956 (Online)) is a Special Issue of Surveys in Geophysics (vol 40, issue 4) and is the outcome of a Workshop on “Space-Based Measurement of Forest Properties for Carbon Cycle Research” held at the International Space Science Institute (ISSI) in Bern, Switzerland, from 6 to 9 November 2017.

The ISSI workshop pulled together experts from various fields and space agencies to discuss key science questions, community needs and new technologies for estimating forest biomass from space. The book summarises the state-of-the-art in space-based observations of biomass including new space-based radar and lidar (laser) instruments being launched now and over the coming few years. In addition, there is an exploration of the various challenges to making best use of these new observations, both scientifically and in terms of policy aimed at reducing emissions due to deforestation and degradation.

I led a chapter on terrestrial laser scanning as a key tool for improved calibration and validation (cal/val) of satellite observations of biomass.
Figure from Disney et al. (2019): TLS of 3 contrasting forest types, with each individual tree coloured separately. Top to bottom: Wytham Woods, UK; Caxiuanã, Brazil; Lopé, Gabon.
I also contributed to a chapter by Laura Duncanson on new cal/val protocols for biomass, and to a chapter by Jerome Chave on the importance of more and better ground data to underpin these space missions.

Figure from Chave et al. (2019) illustrating the Super Site concept for ground-based data collection for cal/val of new EO missions providing biomass estimates.
The book is aimed at a general audience of those interested in carbon cycle science, but will be of particular interest to people at the interface of science and policy. The success of initiatives such as the UN REDD+ program to reduce deforestation and degradation will rely on the observations and methods described in the book.

Wednesday 17 April 2019

Tallest trees, new publications and Hardy Ash revisited ...

We've been involved in some exciting work measuring what is likely to be the tallest tree ever measured in the tropics, in the rainforests of Sabah, Malaysian Borneo. The tree, nicknamed “Menara” or Malay for “tower”, may also be the tallest angiosperm (flowering plant) in the world, a title currently held by "Centurion", a Eucalyptus regnansin Tasmania, Australia, measured at 99.67 m in 2016. Menara is a Shorea faguetiana (common name Yellow Meranti), of the Dipterocarpaceae family that dominates the humid lowland rainforests of SE Asia, and is 100.8 m from top to ground. It was originally identified in airborne lidar by a team from Nottingham University and partners including the South East Asia Rainforest Research Partnership) in 2014. The tree was then located on the ground by a Malaysian team and climbed and measured by Unding Jami. Phil then helped train local researchers to operate our laser scanner, in conjunction with a team from Oxford University led by Allie Shenkin. 
The view from the bottom of the tallest tropical tree in the world
'Menara', picture by Unding Jami. See
Allie also produced some amazing visualisations of the tree using the TLS and drone data. More pictures soon when the paper on this comes out.

We've been busy at the start of spring preparing for new campaigns in Peru, Gabon, the UK and in Germany. This means piecing together the jigsaw of travel plans and logistics, which Andy and Phil are leading. The German work will be in support of an ESA campaign in Kermeter, Germany later in the year, where airborne P-band radar and lidar data are being collected as part the lead up to the BIOMASS mission in 2021.

Matheus has defended his PhD, and passed with minor corrections - of course! Examined by Prof. Mark Danson from Salford, and Prof. Peter Muller from MSSL here at UCL, they were both impressed by his work. Matheus has already published 5 papers before submitting his PhD, including the most recent one in MEE summarising his leaf-wood separation work. This is a really excellent paper, providing a significant advance in what we're able to do with TLS data and opening up lots of new areas of exploring tree structure and function.

We've had a few other new papers out since the last post, perhaps most notably one of a collection by various authors on forest biomass, in an edited volume that is coming out in Surveys in Geophysics: Forest Biomass and Structure from Space. This book arises out of the ISSI-organised meeting in Bern in late 2017 and will be an excellent resource, as it will contain a really useful summary of the state-of-the-art in the field. Our first contribution is the chapter "Innovations in ground and airborne technologies as reference and for training and validation: Terrestrial Laser Scanning (TLS)".

Figure 1 from Disney et al. (2019) showing various examples of TLS point clouds.
Meanwhile I've been out and about doing various talks, including an invitation to speak as part of the lunch-time lecture series to staff at Kew Gardens (including a live feed to the Kew Millenium Seedbank at Wakehurst Place, Sussex). This was a real honour and slightly nerve-wracking as talking about trees to the Kew experts seems a little like teaching your grandmother to suck eggs as the expression goes. I also recently appeared via video link to speak as part of the Climate Conversations lecture series at Lawrence Berkeley National Laboratory, SF - another fun and interesting experience. Last but by no means least I was invited to my daughter's school in Hackney to talk about their current topics, trees and the Amazon - it's always fun to try out new material on a tough crowd - if it's not snappy they lose interest pretty quickly.

News from the GEDI mission - things are looking very good so far and the first release of data is pretty impressive. Glad to see they're continuing to rinse the Star Wars link for all it's worth :-) Can't wait to start seeing some of these data over our sites - this is going to be fascinating.

GEDI returns over US, from: 

Lastly, Phil went back to scan the Hardy Ash in Old Pancras Church yard following some remedial tree pruning work. See the details here, but also Phil's Sketchfab model below.

Monday 25 February 2019

Vegetable monsters

We've been keeping an eye out for unusual urban trees we can potentially scan. This is partly to build up a collection of the 3D tree structures in more extreme environments, extreme in this case being the level of pressure and management they are likely to have undergone. More generally, this is part of understanding the wider issue of urban tree cover, and how and why some trees survive and thrive. Mostly this is down to management and preservation but of course that reflects what has been planted in the first place and why.

Phil was alerted to these amazing redwoods on Canons Drive, Stanmore via twitter - the go-to research tool for urban forests, obvs! This private drive has an avenue of sequoias (or Wellingtonia - see below for some history of that name) planted by the Duke of Chandos. How we ended up with sequoias in the UK is an interesting bit of history as well; clearly the Duke of Chandos wanted to build an estate that was right on the cutting edge of the latest horticultural fad.

Phil, KC and I spent a morning admiring the trees and scanning up the drive. The tallest is around 33 m and you can see from the figure below the range of shapes. This is another great illustration of the variety of 3D structure we see from particular species in the same climate, but under different other external pressures.

Extracted point clouds of the Canons Drive sequoias (P. Wilkes)

Phil has also produced a rather nice flythrough down the drive based on these data.
Canon St Giant redwoods from Phil Wilkes on Vimeo.