Plant4Tawau: hornbill conservation by the replanting of Ficus in forest tracts of Tawau, South East Sabah
Our project
This is our latest conservation project in Sabah and it needs a bit of explanation. There is a growing attention now being given to the role of fig trees in the maintenance of biodiversity in the rainforests of Borneo; this will be better understood by referring to Quentin Philipps’ planned new publication on the Figs of Borneo (publication date to be confirmed).
It is a visionary, long term project that aims to reconnect fragmented areas of rainforest in Sabah; some of these are identified in Figure 1, which represents their locations in the district of Tawau in S.E. Sabah. For example, reconnections are planned between Tawau Hills Park, an area of 29,000 hectares, with the much smaller areas of Bukit Gemok, Tanjong Forest and Segama Reserves. It is intended to begin with Bukit Gemok, a reserve known to contain important populations of hornbills and primates. The resulting forest regeneration will re-establish a haven of diversity of native fauna and flora. Hornbills have been chosen as key indicator bird species for the monitoring of the impact of our project on rainforest biodiversity. In particular, this project is dedicated to the conservation of the Hornbills of Borneo.
These reforestation sites will be replanted with selected Ficus (fig) species. We intend that the project lifespan will be a minimum of 20 years and will follow these phases:
Cultivation of fig seedlings
identifying the ‘planting transepts’
fig planting using a number of different methods, including line planting, random planting, seed sowing and planting on host trees
camera trapping before, during and after fig planting
engagement with local communities
development of wildlife tourism
Figure 1: Forest fragments in Tawau identified for Ficus re-plantation; Park HQ refers to Tawau Hills Park headquarters
Map courtesy of Quentin Phillipps.
This sequence has been developed to enable the replanting and protection of the figs and the subsequent monitoring of their impact on biodiversity after they have begun to fruit. The project has the broader objectives of creating jobs for local communities and the development of tourism through safaris to view hornbills and other species attracted to these forested areas. Through our previously established Plant4BorneoElephants initiative (Can Elephants and Plantations co exist to a mutual benefit — 1StopBorneo Wildlife), we have demonstrated that this new project can also benefit from ‘tourist engagement’ by encouraging visitors to participate in fig planting during their safari.
Some background on figs
Figure 2: Fruit of Ficus carica
(Image is from an advertisement on eBay for Ficus carica seeds)
One fruit has been cut open to reveal the fleshy compound fruit containing many seeds.
For many European people, however, the fig remains a single species cultivated for its distinctive edible fruit: how little they know!
This fig is Ficus carica (F. carica), the ‘common fig’ tree, and it is thought to have originated in West Asia; it is likely to have been first associated with early human settlements around the Mediterranean from where it has been introduced to many regions of the world, including northern Europe and parts of the USA. Commercial cultivation today is dominated by Turkey that together with other countries such as Algeria, Egypt and Morocco contributes about two thirds of the world trade in these ‘figs’. There is little here to link F. carica to tropical rainforests. The fruit displayed in Figure 2 is highly valued for its flavour and has also been in remedies, such as for constipation, for example in the form of traditional ‘syrup of figs’.
However, the genus Ficus is far bigger, containing well over 800 species, many of which are tropical; as described by Phillipps (2020), there are over 500 species recorded in Asia and Australasia with 132 of these found in Papua New Guinea and a higher number, at least, 150, in Borneo. Species may differ from the typical small tree of F. carica: they may be large trees, shrubs, vines and even epiphytes. A feature that many species share is the production of a fruit that is an important food source for a wide range of animals; this is certainly true in the rainforests of Borneo and is the basis of our project.
Humans have also used products of some species for medicinal purposes; for example, F. maxima, widely distributed in Central and South America, has been used by indigenous people for treatments ranging from an antidote for snake bites (it’s leaves) to treatment for gastrointestinal parasites (it’s sap from branches or the trunk). This suggests that Ficus species are likely to be part of the huge reservoir of plants and their compounds that still await discovery in the world’s forests; yet another argument for urgent rainforest protection. Many homes in the UK have a ‘rubber plant’ as a decorative, indoor plant. This is F. elastica, a native of South and South-East Asia, where in the wild it grows to sizes way beyond the requirement of a household plant! It has nothing to do with commercial rubber production which is based upon a tree in a quite separate genus. In Asia, F. elastica may not be a very popular houseplant but the ‘Chinese Banyan’ (F. microcarpa) is widely cultivated both as an indoor bonsai plant and also grown in parks as a large tree for shade. F. religiosa, known as the sacred fig, is widely distributed around the tropics, where it has been often introduced for religious purposes. It is seen as a holy symbol and has been planted in temples by both Buddhists and Hindus.
Fig diversity, resilience and adaptability
As we have seen, figs have been exploited by humans in a number of ways, showing them to be highly adaptable and resilient. Strangler figs are among the most adaptable members of the Ficus genus, having the ability to grow in almost any terrestrial habitat, including in those without direct access to soil for their roots. Typically, they begin life as a sapling that germinates from a seed dropped in the faeces of an animal disperser; these seeds preferably germinate on host trees as epiphytes but can also grow on other substrates like rocks and building walls. As they mature, their roots grow long and thick, slowly covering the substrate on which they grow. Once the roots reach the ground, the fig will quickly spread as it gains more nutrients, and eventually strangles its host tree (Figure 3).
Figure 3: Strangler fig tree in a palm oil plantation
(Courtesy of Wong Chun Xing)
The fig’s roots are clearly seen growing around the host tree trunk and will eventually strangle it.
The strangler fig plant will slowly outgrow their host and fully envelop it with its roots, hence effectively “strangling” it. In some cases, after the host tree has long died, the fig tree remains standing and becomes a separate tree, with a hollow interior left behind by the decayed host.
Strangler figs that thrive in urban areas may grow on roadsides and buildings (Figure 4), which can cause damage to pavements and walls.
Figure 4: A small Strangler Fig tree colonising a wall
(courtesy of Wong Chun Xing)
This is a young tree with roots that have yet to reach the ground.
In some abandoned buildings, trees may grow out of control and envelop the entire building; some strangler figs have been known to increase the appeal of old buildings and become tourist attractions; Ta Prohm Temple in Cambodia is well known for its beauty which has in part been created by the excessive fig growth covering the temple with roots.
Perhaps the most dramatic strangler fig species have been described in the Indian subcontinent, where F. benghalensis became known as the banyan tree, as illustrated in Figure 5.
Figure 5 Ficus benghalensis tree
(Image is from eBay where seeds of F. benghalensis were being advertised).
This is an ancient tree with an extensive root system; the original host tree is completely enveloped by the strangler fig’s root system.
The name derives from Baniyas, Hindi for a community of traders, that colonising Europeans often observed trading in the shade of these dramatic trees. One individual tree in India, which has an incredible circumference of 486 m and covers an area of 1.89 hectares, originated from a single tree that has died; amazingly the tree structure remains standing since it is supported by the roots of a ‘clonal colony’ which have grown from the surviving branches and roots of the original parent tree. These striking trees may be thought of as part of the natural architecture of towns and cities where they occur in Asia; however, compared with forest figs, they are of considerably less importance in their contribution to biodiversity.
Oil palm plantations, which are tree monocultures, are often described as being low in biodiversity and disastrous for the ecosystem. This is partly true, but such plantations do have some ‘fig diversity’ since some Ficus may thrive in plantations where they can exploit the limited space available that inhibits the growth of less adaptable plants. Many epiphytic figs have made palm oil trees their host, providing compelling evidence that our reforestation can work in existing plantations, even without cutting down existing palm trees. We can directly plant fig saplings onto palm trees, which can then become beneficial to reforestation projects. It is worth remembering that oil palm trees already support a limited range of wildlife even without ‘fig planting’. The palm oil trees that will be used as hosts for our figs will be selected from older trees in a plantation, aged 25 years or more; by selecting these, which will be past their years of maximum palm nut yield, and so not being regularly harvested, we will ensure that plantation palm oil yields are unaffected.
Reforestation using other Ficus species can also useful on cleared land, especially after it has been logged or burned, since they are known to be important pioneer species, rapidly colonising empty, barren land. In fact, in contrast to strangler figs, these fig species grow best on cleared land where there is plenty of space for rapid growth. Consequently, there may be more large fig trees found in mature secondary forests than primary rainforest. In preliminary work, we have recorded a sapling of Ficus nota, a noted pioneer species of open land, as growing to 5m in height in only 2 years after planting.
The rapid, regenerative properties of Ficus species contribute to their resilience: roots can grow from wounds on a tree and separated parts of a tree can even form a new, independent tree; even a small, severed stem may survive and slowly develop into a new tree. This property of figs can be exploited for conservation since it enables the propagation of large numbers of saplings from cuttings and marcottings.
Ficus pollination
Ficus species do not produce ‘external flowers’ that are positioned to readily attract pollinators or be wind pollinated; instead, they possess a specialised structure called the synconium, within which multiple, small flowers (florets) develop, each one requiring pollination for seed production. The mature synconium, which is the familiar ‘fig fruit’ as shown in Figure 2, is, in fact, a compound structure that may be made up of many small fruits, the exact number depending on the Ficus species.
Pollination must occur within the synconium and is achieved when tiny female wasps belonging to the family Agaonidae enter via a narrow opening in order to lay their eggs. If these females are also inadvertently carrying Ficus pollen from another plant, they will also pollinate florets of the synconium. Afterwards, the egg-laying and pollinating female wasps die; next, there is simultaneous maturation of fig seeds and completion of the wasp life cycle to produce the next generation of adult wasps. The newly emerging male wasps fertilise new females before boring their way out of the synconium before dying. The females are able to leave via the males’ exit route before flying to detect an immature ‘fig fruit’ in which to lay her eggs.
The wasp and the fig are entirely dependent on one another for production of their next generation in a relationship described as mutualism, which has developed through co-evolution of wasp and fig. This dependency means that the loss, for example, of the wasp from an area of forest would mean that the fig will not produce ripe fruit. But it might mean more than this, since the possible reduction in availability of fruit for hornbills and many other species may also impact their populations.
The above description of mutualism between wasp and fig is much simplified; there are many fig and wasp species. In some cases, for example, a species of fig may be entirely dependent on a single species of wasp, whilst in others, pollination can be by a number of wasp species. There are many more ways in which this mutualism is made more complex but, for our purposes, the message is clear: fig ecology, and therefore the interaction between hornbill species and the figs they feed on, may be dependent on a range of factors.
Ecosystems are complex and any conservation intervention must plan for this. There are numerous examples of how an understanding plant/insect interaction can be important both commercially and in conservation. The palm oil industry of Malaysia and Indonesia, for example, received an enormous boost in the 1980s when an insect pollinator, a weevil, Elaeidobius kamerunicus, was introduced from West Africa. This eliminated the need for the slow, ’hand pollination’ of palm oil trees that had previously been required in Malaysia. More recently, however, it seems that weevil pollination is declining, perhaps illustrating the danger of introducing ‘non native’ species into an ecosystem. Such dangers should not be ignored during conservation projects: upsetting an ecosystem may have unforeseen consequences.
Why are figs so important in the rainforest?
Phillipps, in his Field Guide to the Mammals of Borneo (2016 p77) characterises the genus Ficus as containing ‘keystone species’ in the tropical forests of Borneo. He is referring here to their importance as the major food for a range of mammals, from gibbons to fruit bats, but it is also true for many birds, including green pigeons, partridges, pheasants and hornbills. Their ‘keystone’ role in the forest is further enhanced because they bear fruit asynchronously, providing a ‘continuous background’ of fruit; other fruit-eating (frugivorous) animals, for example the orang utan and many squirrels, rats and tree shrews, rely more heavily on fig fruit as ‘fall back’ food to compensate when other plants, seeds and fruits are not available.
It is not surprising, therefore, that we have observed that whenever a fig tree fruits, it can create a ‘wildlife frenzy’: in the canopy, during the day, many birds and mammals may be seen actively feeding. At night, too, fruit bats as well as civets, such as the binturong and masked palm civet, may be eating the figs, and, below a fig tree, there may be oriental bay owls and other owl species patiently waiting for rats coming to eat the figs.
This is not all, since we have also recorded Sumatran and Borneo Keeled pit vipers waiting for frugivorous prey, and fallen figs may be eaten by Bulwer’s pheasants, crested firebacks, bearded pigs: and the list goes on. It has even been claimed that some turtle species may supplement their diet with fallen figs.
A programme of Ficus planting
It should be obvious by now that controlled planting of specifically chosen fig trees could contribute enormously to forest biodiversity.
In this project, up to 25 species of rainforest Ficus will be planted with a special focus on identified key species, including those listed in Table 1 below, which all also provides links for background information on these species. All these figs have been recorded within the forests of the Tawau district (Cheema et al. unpublished data). Many are also known to be important for hornbills: Phillipps, for example, offers compelling evidence of the importance of Ficus fruits in the diet of the endangered helmeted hornbill (https://borneoficus.info/2018/05/26/fig-ecology-helmeted-hornbill/).
Table 1: Ficus species identified for planting; the species list will be broadened to include other species.
Ficus subcordata
Favourite of Hornbills
Ficus cucurbitina
Favourite of Hornbills, Civets and Orang utans
Ficus racemosa
Favourite of Orang utans,Civets, Binturong and Hornbills
All information in Table 1 has been obtained from https://borneoficus.info accessed 10/12/20.This site is regularly updated and serves as an excellent source of information on some of Borneo’s important Ficus species.
The hornbills of Sabah
Sabah is blessed with 8 of the world’s species of hornbill, conspicuous birds with large bills, loud calls and sometimes audible wing beats. Often hornbills possess an extension from the upper part of the bill known as a casque; our Rhinoceros hornbill gains its name because its bill and casque are large and brightly coloured. The biggest of them, the Helmeted hornbill, is sadly critically endangered after extensive hunting for its ivory casque.
All the hornbills are important seed dispersers for a variety of rainforest trees since they feed mainly on wild fruits that contain these seeds. Often, all of a fruit is ingested but only its flesh is digested, leaving the seeds to pass out undamaged in a bird’s faeces. It is, of course, why fruit trees such as figs have evolved edible fruits: to attract animals such as hornbills to disperse their seeds across the forest after flying from the ‘feeding tree’. For this reason, hornbills have been called ‘farmers of the forest’, reflecting their importance in primary and ‘old growth’ secondary forest where they are most likely to be found. Some birds, for example Rhinoceros and Bushy-crested hornbills, may travel several kilometres after feeding, so that they may actually spread seeds not only within a rainforest but also between isolated forested areas. The larger species, such as the Helmeted, Wreathed and Rhinoceros, need large territories and forest destruction often has a serious impact on their numbers. Smaller species, for example the Oriental Pied and Black hornbills, may tolerate humans better and so may even be seen breeding and feeding in plantations. Hornbills sometimes feed on a variety of smaller animals, including insects, snakes, small birds and bats. However, their main food source is fruit, especially the numerous figs of Borneo.
The helmeted hornbill, Rhinoplax vigil, is mentioned here because it so critically endangered; the importance of the figs it feeds on to its survival is extensively logged at https://borneoficus.info/2018/05/26/fig-ecology-helmeted-hornbill/. It is clear the balance between strangler figs and their seed dispersers such as the helmeted hornbill is delicate: a decline in one population can result in a linked decline of the other. It is the intention of this project to demonstrate that the opposite can occur: an increase in fig numbers can lead to a resulting increase in seed disperser numbers. The crisis threatening helmeted hornbill populations is well documented. Initiatives like the one outlined by Birdlife (The Helmeted Hornbill crisis and BirdLife’s conservation efforts | Birdlife accessed 1.12.20) clearly show this.
However, it is important to realise that different hornbill species may feed on fruits of different Ficus species or may prefer fruiting trees of different heights or in different locations within a forest. In Borneo, the eight hornbill species may coexist by displaying niche segregation, that is different species avoid competition for food by selecting to feed in different parts of the forest and on different fruits. Clearly, our project will be influenced by this, in particular by which Ficus species are selected for cultivation and subsequently where saplings are planted. For example, it has been reported that Helmeted and Wreathed hornbills prefer to forage in the upper canopy whereas Bushy-crested and Rhinoceros species tend to feed in the middle canopy below. This, of course provides some explanation for why the latter two species are easier to spot within the rainforest.
Selection of different fruit types has also been described: Helmeted and Rhinoceros hornbills feeding preferentially on fruits, including figs, with higher sugar content compared with smaller hornbills, such as the Bushy-crested, that show a preference for a higher fat content. Cheema et al. (2021) The Ecology of Hornbills.
provide a more detailed review of the ecology of hornbill species of Borneo.
Since we aim through this project to contribute to the conservation of hornbill species, such understanding of hornbill ecology should prove vital in our approach to fig cultivation. Observations on hornbill feeding and seed dispersal are by no means complete, however, and this is unsurprising given the distance hornbills may fly and the inaccessibility of many areas of a rainforest. There are other aspects of hornbill-fig ecology, for example the indirect impact of hornbill feeding where fruits drop onto the forest floor providing food for a variety of ground-dwelling animals, which illustrate how hornbill feeding is part of a much more complex food cycle in the forest.
It is, therefore, an important aim in itself to protect these fascinating and attractive birds; however, by choosing them as indicator species for our forest fig replanting project, we are illustrating how vital they can be, not just as tourist attractions, but more importantly as models for the monitoring of rainforest conservation. Fig-hornbill conservation should contribute to reforestation and wildlife corridor creation but is just one of many actions needed in order to minimise the impact of human activities on rainforest ecosystems.
References
Phillipps, Q. (2016) Phillipps’ Field Guide to the Mammals of Borneo John Beaufoy Publishing Ltd. First Edition.
Cheema et al. Can Elephants and Plantations co exist to a mutual benefit — 1StopBorneo Wildlife(accessed 11/2/20)
Phillipps, Q. (2020) https://borneoficus.info (accessed 10/12/20)
BirdLife (2020) The Helmeted Hornbill crisis and BirdLife’s conservation efforts | BirdLife (accessed 1/12/20)
Cheema et al. (2021) The Ecology of Hornbills.