Return to Cayman – On the Mastic Trail (1)

Often neglected in the Caribbean is the land vegetation.  The coral and the deep seas get so much attention, as do the endemic birdlife, reptiles and amphibians.  But the curious mix of land habitats are worthy of mention.  Cayman is a fairly flat island, no volcanoes here, and the pitted limestone makes it a difficult environment for any vegetation to get a grip.  Most of the natural vegetation appears to be a tangle of spiny , half dead shrubs.  The glamorous stuff is to be found in gardens where the imported bougainvilleas and the crotons colour up any backyard.

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Conservationists are horrified at the amount of invasive species which have colonised the OTs.  Some, like the Casuarina trees, could not be eradicated, and many have been adopted by the islanders as loved local favourites.  Given the remote location of many islands, the native vegetation is often not as large or showy as those brought in for gardens and erosion control but there are many species out there in the scrub.  If only the scrub were not treated as wasteland; most developers have it in mind to “beautify” the island with their hotels, estates and shopping malls where they plant up the same plants out of pots that might line a highway in Miami.   This tangle of scrub to them is at best an eyesore, at worst, in need of simplifying down to grass verges and manicured monocultures.

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The dry scub of many Caribbean Islands  – this one in the British Virgin Islands

Cayman’s attempt to educate the island about the true value and the need to conserve its areas of natural vegetation is centred on the Mastic Reserve.  It is one of the only true wildernesses left on Grand Cayman, distant from the heat of development in Georgetown and away from the coast too.  Bordered by mangroves to the west and the coast road round the rest of the island, the poor terrain of old coral stone, plus the lack of access to the sea, meant it was relatively untouched by humans, and fortunate for itself, largely impenetrable.  We were driven in a minibus round to the north side of the island and down a little side track where we were dropped off and waited in the still sun drenched air for our guides.  Members of the National Trust came in another vehicle and were delayed en route, so we tried to find some shade.  It was difficult – the trees are not all that tall round here and they had an open structure which at best gave a dappled shade.

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Ready to start the Mastic Trail

Eventually our hosts turned up – but then spent ten minutes talking about the trail.  It was a good job we did because as soon as we started out on the footpath, it was clear that the group was going to split.  Many of the animal conservationists, the managers, the media types and GISsy people like myself were keen to have a good walk, enjoy the countryside and the key sights.  The botanists though went into field study mode.  They wanted to absorb every plant species they could find.  That meant not just the trees, but the shrubs, the herbaceous layers, the grasses, the epiphytes and parasites.  And it was not just a case of plant spotting, they had to look at the leaf, the stem, the root, the flower and fruit, maybe dissect them, discuss amongst themselves and make copious notes in their little books.

Most of us had gone a half kilometre before we realised we had left them behind.  One of the Cayman guides went back – reporting later that they had hardly passed the board which marked the start of the trail.

Walking the Beaches – the curse of the filao trees

Our second Pressure Zone was the stretch of the east coast usually referred to as Palmar or Bellemare.  Whilst not where the earliest set of hotels had been developed on Mauritius, it was certainly now packed with resorts and golf courses, but also had some of the longest stretches of Public Beach on the island.  A great favourite particularly with people from the urbanized centre of the island, at weekends almost every inch of the parkland under the filao trees were covered in large family groups, spread out over several blankets, perched on what seemed to be dining rooms chairs as well as deckchairs, or just sitting in cars or eating out the back of a minivan.  This last set of practices had been a cause of great stress for the Beach Authority who managed these Public Beaches.  The parkland was usually open to the road and people drove straight across to the point they wanted to picnic at, often close to the edge of the sea, and stopped.  A network of hard soil tracks had grown up, damaging the vegetation and causing occasional quagmires after heavy rain.  The Beach authority were actively trying to make better car parks at key points along the beach and put up logs, bollards or piles of dirt to stop people getting into the park.  Until the Beach Authority  could complete their ring of steel, people still snuck through any gap they could find.

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The beauty of filao trees

The tourist brochures may be full of palm trees and many resorts planted thousands to keep the idyll sacrosanct but the dominant tree along the Mauritian coastline is undoubtedly the filao.  It has become a pest of so many tropical coastlines and goes by the name of ironwood, Australian pine, beach oak, she oak and agoho.  Its scientific name is Casuarina, but most people in Mauritius refer to them as filao.  They grow tall and slender, the trunk clad in tough grey bark that branches down to small green twiglets with tiny leaves on.  The roots are shallow but extend widely across the sandy soils they grow on to gain the tree’s stability.  A single tree looks elegant enough but a wood of them produces a perfect picnic ground.  The root systems preclude other vegetation getting a strong foothold so only a grassy covering is possible, and since they grow relatively close to each other, there is enough shade across the woodland.  The light filaments of the twigs and the flexible branches are teased by winds and respond with a slightly haunting whooshing resonance even in a light breeze.   They mark out the territory of the majority of the Public Beaches and are ingrained in Mauritian culture, and some still say they provide a useful purpose as a halt against coastal erosion as the roots bind the top layer of sand together in all but the worst tempests.

Filao trees have as many enemies as friends.  They were introduced to the island for the erosion purpose, but have spread prolifically and at the expense of other species, including natives.  Some claim their erosion control role is overplayed and that when a filao tree uproots the erosion is worse as there is nothing else growing at the time to bind the sand and large blast holes are revealed.  Far-reaching  programmes to eradicate the filao have been put forward – but fortunately not implemented. To destroy so much mature vegetation in one go both would hurt the environment more than save it as re-establishing natives would take so much time.  Also, the aesthetics of the filao woodlands are one of the most charming aspects of the Mauritian coastline, for tourist and Mauritian alike.

Capturing the Diversity – Mapping the Vegetation

Kew had their own GIS section (whose members were also keen to travel to these amazing islands) so I never got a huge amount of work from these visits, but given I had helped Stedson over the years with his logging of plants, I was asked to come back to Ascension  on my own purely to look at the plant issues.   Phil had been pulled in to help Andrew with the detailed surveys.  They carved up both St Helena and Ascension Island into square blocks, and then did a comprehensive species list, not just looking for endemics but also natives and invasives, every type of high plant.  They also had to judge the abundance of each species.  I travelled out just for a week to help out on all the plant issues, and Andrew and Phil were beavering away with their surveys while I was there.  They absolutely loved it although the field work was exhausting.  They would spend several hours a day out surveying a square, not so bad if it were close to a road, but involving a long trek if it was not.  Up on Green Mountain where the vegetation was much thicker, they had subdivided the squares, and exploring each study area was made much more difficult by the steepness of slopes, wet slimy ground, and thick undergrowth to get through.  But they were out in the fresh air, doing what they loved.  And they had taken residence up at one of the cottages on Green Mountain, and they cherished the seclusion and at-oneness with nature that they got from there.

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Mountain top cottage

I joined them once for one of their easier days.  They had not completed much of the north east of the island.  I had never visited this quadrant before.  Much of it is covered by a firing range still used to this day by the military and you have to check in with them to make sure it is safe to enter, and just be careful not to tread on any stray ordinance which has been left behind.  We accessed the range by driving down the road at the back of Two Boats towards NE Bay.

Close to the flagpoles which would carry the warning flags if firing was scheduled, we gathered our kit up from the back of the Land Rover and started to tromp in.  The grid square was pretty much on the road and in its centre was a low lying area surrounded by conical hills of various sizes.  The western side was connected to an area which has seen the most recent volcanic activity, less than 700 years back.  These cones, in geological terms, are fresh, and full of loosely consolidated pieces of ash and small nuggets of lava. Their conical shape is so uniform as the material sorts itself to the maximum angle that the gravel can stay together, any steeper and pieces naturally roll down till equilibrium is re-established.  One of the craters, though, has been subjected to other factors and one side of the slope has collapsed.  It has been given the name Broken Tooth given the sharp jagged edges where the collapse took place.  In between the cones are the a series of lava flows, but they are not as black and angular (or difficult to traverse) as the ones around the coast or on the large north western coastal plain.  Wash from Green Mountain behind has filled up some of the gaps with a yellowish sandy soil, which is  more easy to walk through, but there are still lots of loose stones and hard angular rocks to be careful of when you hike.

I was surprised just how much vegetation was in the grid square.  Again, probably because of Green Mountain behind, seeds have been carried down in the sediment and given the landscape a much richer flora than similar geological areas further away from the mountain.  There were plenty of Mexican Thorn here but it was not dominant.  Casuarina trees were prevalent and seemed adept at gaining a foothold on the scoria cones.  Trees were one thing, but the whole area was carpeted in herbaceous and annual plants, so many little flowers and seeds, once gaining a foothold in the rubble, forever more established.  Andrew and Phil recorded each species and where necessary, guessed the abundance.  There were still not that many species; maybe twenty frequently occurring and a few other specials.  They both rolled their eyes when they remembered the long lists they had to compile up in the mountain tops.

It was a real pleasure to explore this part of the island with them, but unbeknownst to me , things were going wrong underfoot.  I had been wearing my heavy duty boots, with steel caps and base plates.  They were great clunking things but surprisingly comfortable from the inside.  The terrain in Ascension is unforgiving though, and although Broken Tooth was mild in comparison with the big lava flows, I managed to rip the sole from the upper.  The front became completely detached, and I gingerly flopped back to the Land Rover.  I asked around if anyone had any strong glue.  Some of the Conservation staff sucked through their teeth, but Stedson came up trumps with Araldite.  I pasted the gloopy mix and put it in a vice in his workshop.  Ten minutes later I had a single shoe again, and continue to wear it to this day.

Capturing the Diversity – Invasion of the Mexican Thorn Trees

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The Thorn trees dominatiing

Of all the species that have spread themselves over the island, the most invasive is the Mexican Thorn Tree.  Much has been done to try and stop this plant spreading , especially by the Royal Botanic Gardens at Kew in London.  But watch out!  There is suggestion that Kew Gardens gave some advice to the BBC in the 1950’s to plant Mexican Thorn as an ornamental bush in the BBC’s own village at Two Boats, to stabilise slopes and pretty up the harsh environment.  It spread, and spread and spread.  Some estimates originally gave it as covering over 2/3 of the island, and people who travelled round would say it was “everywhere”.  My own exploration of Ascension showed it to be by no means everywhere, it was not up Green Mountain, it was not round the south eastern side of the island.  For Edsel’s and my project I had obtained a couple of satellite images of Ascension, and given the size that these spiky bushes could grow to, I could clearly see many of them on the images.  I made a decision at home one night to put the argument to rest.  Scouring over the images square by square, I started to digitize the crowns of the trees.  Instead of drawing every little nook and cranny I used circles to represent the largest extent of the canopy; after all, unimpeded they tended to grow evenly out from a central trunk.  Of course I could not capture every single plant, some were too small to be identified on a satellite image, even one of high resolution.  Other places plants were growing too close together to be identified individually, but eventually I made over 31,500 circles on my map.  What a job!  But I love digitising when it is nice and easy  – like some people can do knitting for hours.  I tried to work out where the densest patches were, and then started looking at the factors that might be affecting the presence.  It appeared they favoured the looser lava flows, gravels of scoria cones and the like, over the more consolidated rocks of the south east of the island, where anyway there was much more competition from existing vegetation.  There also seemed to be a trend that they were gradually spreading down water catchments.  Now that is a very difficult thing to discern on Ascension Island.  Being essentially a big load of volcanoes, the geology is so loose and open that water usually get soaked up inside the rock very quickly.  Only in a few places to watercourses form, and they only rarely get filled.  But I suppose there have been several serious rainfall events, causing temporary flash flooding.  This could have flushed seeds and even small plants down the water courses.  Certainly those valleys which come out from Two Boats where the first trees were planted appear to have the highest concentrations of these trees.  Some people have blamed the donkeys for spreading them, but I think water is a much more likely solution.

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The thorn trees take over

The trees could be said to have prettified much of the landscape of the western part of the island, and indeed when the fresh green growth comes out they stand aesthetically pleasing against the red rocks.  But they are so prevalent now and continue to grow.  In the few years of trips I have been on, they have crept up the side of the Two Sisters Hills, which looked beautiful when they were pure red screes of rock.

They have grown over old relics of the past like the storage tanks between Two Boats and Georgetown.  They are reaching out on to the beaches where the turtles lay their eggs, their extensive roots frustrating females from digging deep down.  And no one knows where they will stop. They also have provided food and cover for some of the more invasive animal species, especially the rat.

Nobody has the resources to eradicate this tree; it is an alien that has to be lived with, but some control in key sites to stop it harming other species is being carried out.  There is a moth whose caterpillars can devour thorn trees, but consideration needs to be given to work out if its introduction  could damage other species more than the control of the thorn.

Capturing the Diversity – The Green Oasis

High in the clouds above the rest of Ascension island is a lush oasis of vegetation.  From the west, Green Mountain looks like a sharply pointed peak, but in fact it is a heavily eroded ridge orientated west to east, with several fatter spurs coming out especially on its southern side.  It is battered by every type of weather, but that plays to its inhabitants advantage.  For Green Mountain’s topography  produces so many different elevations, aspects and niches that everything can thrive up there in its proper place.   There was one problem with this, and that was to get plant seeds and spores there in the first place for them to experiment, evolve and thrive.  Being so far from any other land made it so difficult for plants to colonise.

It is difficult to imagine what Green Mountain looked like 500 years ago.  Only a small number of higher plant species are known to have existed there. Most of these are the ferns, whose spores could have travelled hundreds of miles on the wind.  The spurge too might have reached by wind perchance, or more likely from being stuck in the gullet or foot of a migratory bird.  But not much else.  The only other plants which seemed to find their niches were the lower ones, called bryophytes.  Algae and moss, liverworts as well, had set up their stalls on rock faces and in crevasses and maybe in amongst the rocks themselves. Maybe those people searching for life on Mars could learn a few hiding places by searching the lava flows of Ascension Island.

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The natural vegetation types

So why is Green Mountain and the surrounding area coated in grasses, shrubs and trees?  Quite simply, it was a huge experiment.  Various settlers and scientists, the most famous being Joseph Dalton Hooker of Kew Gardens,  used the slopes to see how you might be able to colonise a pristine environment with species from other places.  Seeds of all types, shapes, sizes and from a variety of climates were brought, and the mountainside was literally planted up.  Some were a complete failure, others you have to search hard for examples, like coffee beans or tea plants, but some relished the lack of competition and went rampant.

It was part experiment, but also was a way of trying to humanize the island.  As one of the first visitors to the island, the explorer Dampier, discovered, if you wanted to live on the island long term, you needed to get food, water and shelter.  The lack of vegetation made a lot of that very difficult – and so planting up timber forests not only supplied you with building materials, but help capture moisture, stabilise slopes and temper the climate.

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Lush Green Mountain Vegetation

So in came pine trees, eucalyptus, the casuarina tree.  Also came fruiting shrubs like raspberries, guava, bananas.  The guava in particular loved the climate and has spread far and wide over the south eastern portion of the island.  In theory they could be sizeable shrubs, but the winds of the south eastern corner of the island often stunt their growth down to barely a few inches off the surface of the rocks.   Look closely though, and you might find specimens that are several metres long, but their trunks and branches are flattened against the ground.

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Horizontal Tree

Flax, bamboo and other grasses have gone unbridled on some slopes.  Ginger too has expanded, it knots itself in amongst other vegetation and is a devil to remove.

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Flax and other plants on the roof of the island