To Plant, or Not to Plant? - A Reforestation and Afforestation Dilemma?

There's a great post covering deforestation over at Harmonising Humans & Nature, so I won't bore you with the facts. There's no way we can deny that deforestation is unsustainable and having a vastly negative impact upon the Earth's ecosystems; 70% of the worlds land organisms live in forests, yet deforestation destroys the habitats of these plants and animals (National Geographic). With all this said, it seems that right thing to do would be to stop cutting down the trees and re-plant them; either where they once stood, or elsewhere.

Sadly, things are never as straight forward. Planting trees or letting natural succession take place until areas once wooded long ago are reforested may, in some areas, impact negatively on biodiversity. Planting forests where there were once no forests (afforestation), to replace those lost elsewhere, can also have detrimental effects - often more so than reforestation.

We humans have been shaping and leaving our footprints upon this planet for tens of thousands of years, and animals have partly evolved to coexist with us. Landscapes have been anthropogenically modified in Western Europe, through deforestation and agriculture, for at least 4000 years; in Asia this modification is likely to have been going on for even longer (Anson Mackay, 2013). This causes a dilemma, as though many argue for returning habitats to their 'pre-human' state, the animals now living in these 'new' habitats may have adapted to them, or may not be the original organisms that previously lived in the area.

 Rannoch Moor, Scotland; A natural peat-land, though many bogs are present due to human modification and management of the landscape in the northern hemisphere  - image by Martin Sojka on Flickr.

Reforestation and afforestation are generally beneficial; both can increase biodiversity, have economic benefits (such as providing timber), can reduce soil erosion and run-off, and reforestation can help restore natural habitats (Reino et al, 2010). However, both may also have negative impacts on plant and animal species that have adapted to a woodland-free environment. 

After the abandonment of traditional mountain agriculture in many regions, natural reforestation can lead to a loss of open spaces which has been linked to a decline in grassland plant species that are vulnerable to landscape fragmentation (Sitzia et al, 2010). Though reforestation is beneficial for alpine birds whose species often experience population increases, Sitzia et al, (2010) noted that landscape fragmentation can act negatively upon species unable to live in small, patchy habitats.

Two studies into the effects of anthropogenic afforestation of Mediterranean farmland in the Iberian Steppes of Spain show the negative effects that afforestation may have in certain regions, including the direct loss of habitat for species of conservation concern, and increase in the abundance of predators (Reino et al, 2009)(Reino et al, 2010).

Whilst the planting of forests may lead to an overall increase in bird abundance and diversity in farmlands adjacent to forest patches, the overall increase is at the expense of grassland specialists (Reino et al, 2009). Steppe birds show strong negative edge effects, with the abundances of Calandra Larks and Short-toed Larks in particular depleted in grasslands directly adjacent to forest plantations. The abundances of these species increased further away from the edges of the plantations, and the highest species abundance and richness were observed in large arable patches. Though both species were listed as 'Least Concern' in the latest IUCN Red List report, their populations are in decline (BirdLife, 2013 - Calandra Lark)(BirdLife, 2013 - Lesser Short-toed Lark); habitat loss due to afforestation, which has already been accredited to regional declines of Lesser Short-toed Larks, may lead to greater pressure upon both species.

As the number of forested patches increased, Reino et al (2010) also documented an increase in the abundances of generalist predators, such as foxes and corvids (crows, ravens, magpies...); the increases of which have been associated elsewhere to population declines of ground-nesting birds (Fletcher et al, 2010).

Increased nest predation by predators such as foxes may lead to significant population declines of ground nesting birds, such as Eurasian Curlews in Scotland and Northern England (Douglas et al, 2013) - image by Jans Canon on Flickr.

A recent paper by Douglas et al (2013) on upland land use and declining waders populations highlights another case where afforestation and the fragmentation of moorland has been linked to increased predation rates, this time leading to a decline in breeding populations of the Eurasian Curlew (Numenius arquata), a bird listed as 'Near Threatened' in the latest IUCN Red List due to a 20-30% global population decline in the last 15 years (BirdLife - Eurasian Curlew, 2013). Both Douglas et al (2013) and Fletcher et al, (2010) also noted that predator control can help prevent population declines in species of conservation concern; for Lapwings, Curlews, Red Grouse and Golden Plovers, predator control lead to an observed population increase of ≥14% per annum, whilst a lack of predator control saw populations decrease by ≥17% per annum (Fletcher et al, 2010). 

The Eurasian Curlew, Numenius arquata - image by Davis Kwan on Flickr.

Though in the study by Reino et al (2010) it was concluded that nest predation rates (on artificial nests) showed no relation to predator abundances in the Iberian Steppes, they suggest that landscape composition and configuration may instead have a stronger impact due to edge density effects.With this, they recommend that afforestation in the Mediterranean -and other areas inhabited by ground-nesting birds of conservation concern- be avoided where possible. Where afforestation is unavoidable, they insist that populations be monitored closely for signs of declining numbers due to predation. They also suggest aiming to reduce habitat fragmentation and edge effects by afforesting a smaller number of large patches, rather than planting many relatively small patches (Reino et al, 2009).

References:

• Biodiversity and Landscape Change (Lecture) - Anson Mackay, 2013

Agricultural Expansion and Habitat Loss

Since 1700, there has been a six-fold increase in the global extent of agricultural land (Birdlife - Agriculture, 2008). In 1700, only 6% of global land area was being used for agriculture yet in 2011, this figure sat at 37.6% (WorldBank, 2013). The area of land used for agriculture is predicted to rise further as global population increases and with it the demand for commodities such as coffee, soy bean, palm oil and sugar-cane (BirdLife - Crop Expansion, 2013). The expansion of agriculture most often involves the transformation of natural habitats and a loss of biodiversity. In 2008, agriculture contributed to the declines of 87% of threatened bird species on the IUCN Red List.

The pressures of agricultural expansion are felt globally, but let us look at Brazil in more detail. Brazil is home to not only a large portion of the Amazon rainforest, but it is also home to the "forgotten" Cerrado; the worlds most wildlife rich savannah, which covers 21% of the country (WWF - Cerrado). The Cerrado once covered 2 million km², but has since been reduced to 43% of its former size and is being lost at a rate of 1% per year (Birdlife - Cerrado, 2008); if the rate of destruction continues, then the Cerrado is projected to be lost completely by 2030 (Mongabay, 2010).

The Cerrado; the  Brazilian savannah in the height of the summer dry season, which lasts approximately from May to September - image by Christoph Diewald on Flickr.

The Cerrado is extremely important for wildlife (WWF - Cerrado), and is home to over 10,000 species of plant and more than 1600 species of animal; including 935 species of bird. Amongst these animals is the incredibly gorgeous and fluffy Maned Wolf (Chrysocyon brachyurus - Near Threatened), Kaempfer's Woodpecker (Celeus obrieni - Endangered) and the Cone-billed Tanager (Conothraupis mesoleuca - Critically Endangered). New species are still being discovered, with one bird species among the 13 new species found in 2008 (Mongabay, 2010).

The majority of the loss of the Cerrado is due to highly mechanised soya farms (most of much is used for animal feed), but land is also cleared for cattle ranches and other farms. Models have shown that in areas converted into planted pastures, precipitation may be reduced by up to 10% and surface air temperature may increase by 0.5*C (Klink & Machado, 2005). Were all endemic bird species in the Cerrado to go extinct, then Batalha et. al. (2010) predict functional diversity (Tilman, 2001) to decrease by 27%.

Only 7.5% of remaining Cerrado is currently under protection, yet an estimated 20% of threatened animal and plant species live outside of the protected areas (Klink & Machado, 2005). That said, the future of the Cerrado need not be grim. State governments are focusing on creating new protected areas, extending existing protected areas and establishing ecological corridors. There are also NGOs promoting alternative economic activities to support the livelihoods of local communities, such as ecotourism, the sustainable use of fauna and flora products, and the use of plants for medicinal purposes (Klink & Machado, 2005). Sustainable farming may also help to slow down, and possibly eventually reverse, the decline in biodiversity in Brazil.

A male Bobolink (Dolichonyx oryzivorus) by Kelly Colgan Azar on Flickr.

To finish, I will leave you with an example of successful sustainable farming; the story of "bird friendly" Bob-o-Link Coffee. The brand is named after a migratory American blackbird, the Bobolink (Dolichonyx oryzivorus), whose species had experienced a 75% decline (Science for Brazil, 2013) in the last decade due to habitat lost to make way for sugar-cane plantations in the Cerrado. 

One of the reforested Bobolink Coffee plantations;
growing the coffee beans in the shade is said to improve
their taste and quality. 

Bob-o-Link Coffee have restored much of the forest on their 700 acre organic farm, through the planting of trees so that they can grow their coffee beans in the shade. Alongside producing higher quality coffee, this reforestation has restored habitats for the Bobolink and several other animal species (Science for Brazil, 2013). 

Bob-o-link coffee also encourages its farmers to keep beehives on their farms; this not only helps with pollination of the coffee plants, but if more farmers turned to bee-keeping then it might help slow the decline of bee populations in many countries (Bob-o-Link Coffee). 

Critically Endangered - The Philippine Cockatoo

I stumbled across an interesting article by BusinessMirror (2013) on the Red-Vented Cockatoo (Cacatua haematuropygia)  (IUCN, 2012) during a coach-trip back from visiting friends. Sometimes called the Philippine Cockatoo or Katala, this clever bird is one of the few bird species capable of mimicking human speech. Sadly, the population of these beautiful birds has plummeted rapidly (a decline of 60-90%) (Katala Foundation, 2013) in the last two decades due to anthropogenic activities.

The Red-vented cockatoo is listed as critically endangered on the IUCN Redlist with an estimate of roughly 1000 remaining in the wild, and with the remaining populations fragmented and dispersed across the Philippine islands  (IUCN, 2012). 

The Red-vented Cockatoo, by Edmond Sham on Flickr

Destruction of their natural coastal habitat poses one threat; deforestation and destruction of mangroves has been particularly extensive throughout their range, leaving the remaining populations vulnerable to typhoons (IUCN, 2012). The cockatoos are also persecuted for being agricultural pests, and are sometimes hunted for food (Birdlife, 2013).

Illegal trade of the birds for sale as pets, however, has probably been the largest impact that humans have had upon the species. The Red-vented Cockatoo is highly demanded as a cage-bird, as reflected in the price these birds can reach on the market (US$300 in Manilla, in 2006) (IUCN, 2012), and as such illegal trappers will remove any chicks from nests they come across  (Katala Foundation, 2013). 

Thankfully, things are being done to try and stop the decline of this species through the Philippine Cockatoo Conservation Program (PCCP). The PCCP has proposed protecting nests from poaching, restoring destroyed habitats, education and involvement in the community and conservation breeding for re-release as some of their conservation methods. 

Bird Extinction: The Pre-Industrial Picture

Extinction as a result of anthropogenic activities is not something that can be confined to the last century or two; as humans have expanded their reach across the globe, they have been contributing to a loss of biodiversity on Earth for at least 50,000 years (Braje & Erlandson, 2013). Human induced animal extinction rates are believe to be up to a thousand times higher than the natural background rate, and are associated with the loss of around 8500 species of bird since 1600 AD alone (Braje & Erlandson, 2013).

Whilst a loss of species diversity can be seen across the globe, some of the most prominent examples are on the many islands of the South Pacific, where Polynesian expansion across the pacific led to the extinction of many animal species (Pimm et al, 2006). Island populations are especially vulnerable to extinction, as their populations are often small, and may be confined to a minimal area of land. Their isolation also often results in the loss of adaptability to pathogens, predators and competitors that may be introduced, and to the rapid environment change often brought about by humans (Grayson, 2001).

The extinction of endemic flightless birds alongside plants and mammals in Australia coincides with the arrival of humans (Braje & Erlandson, 2013), which may have been visiting the country as early as 22,000 years ago (Flannery & Roberts, 1999), as suggest by a rise in charcoal and a change in tree pollen in the sedimentary record. This has been contributed to anthropogenic deforestation through fire, and not down to climate change (Flannery & Roberts, 1999).

The same applies to New Zealand, which wasn't colonised until much later in the 13th Century (Irwin & Walrond, 2012). Prior to humans living in New Zealand, it was home to many species of endemic birds that are now extinct. 21 species of small landbird are no longer with us today, and alongside them were 11 species of Moas (Braje & Erlandson, 2013) (Grayson, 2001). The only birds known to be totally wingless, the enormous Moa were a family of herbivorous flightless birds. The two largest species, Dinornis robustus and Dinornis novaezelandiae weighed over 200kg, and could reach a height of 3.6m (12ft) if they stood with their neck outstretched (Wikipedia, 2013).

Published in 1879; a photograph of Richard Owen, the director of London's Natural History Museum, standing beside a reconstructed skeleton of Dinornis novaezelandiae - Image via Wikipedia Commons

The only natural predator of the Moa was the Haast's Eagle which was also driven to extinction when the Moa were wiped out completely in just over a century since the Maori populated the islands. Their extinction is believed to be a result of multiple factors, but all are attributed to human activities (BBC, 2009) (Grayson, 2001). Before the arrival of our species it is estimated that up to 90% of New Zealand was covered in forested, yet within a few hundred years almost all of the lowland forest had been destroyed, and with it vanished the habitats of the Moa and other animals (Grayson, 2001). Human predation, evidence of which has been gained from many archaeological sites, was another large factor in the Moas disappearance (Holdaway & Jacomb, 2000). Lastly, the unintentional introduction of Polynesian rats (Rattus exulans) is believed to have played a large role in the extinction of birds not only in New Zealand, but across the whole of the South Pacific (Pimm et al, 2006). Whilst it's doubted by many archaeologists that there was direct predation of Moa eggs by the rats, the rodents are likely to have caused competition for food and impacted the vegetation on which the Moa and other landbirds depended (Grayson, 2001).

Madagascar suffered similar losses following human colonisation roughly 2300 years ago; it too was home to two genera of large flightless bird (Mullerornis and Aepyornis) that are often referred to as Elephant Birds which went extinct between 1600 and 1700 AD (Braje & Erlandson, 2013). Aepyornis was the larger of two, and is believed to have reached weights of up 400kg and a height of 3m (10ft). The causes of extinction are less clear, but signs of butchery from archaeological sites suggest humans played a primary role (Burney & Flannery, 2005).

The birds of other remote islands didn't fare much better. Grayson (2001) suggests that, alongside anthropogenic predation, predation by invasive dogs, pigs and Polynesian rats brought to the islands by humans may have been largely responsible for the disappearance of endemic Hawaiian species. Of 17 species of landbird known from archaeological deposits, only four remain on Hawaii today (Braje & Erlandson, 2013). Rats are also believed to be partly responsible for the loss of 6 species of landbird and several seabird colonies, alongside much of the vegetation (through eating nuts and seeds and thus impairing the ability of the plants to reproduce) on Easter island, which in turn contributed to the breakdown of human society on the island (BBC, 2009)(Braje & Erlandson, 2013).

Grayson (2001) raises the possibility that anthropogenic activities may have, in some instances, created habitats for some subsets of bird species which would not be present were it not for such changes. Despite this, the general consensus is that the increased colonisation of Oceania by humans correlates with an increase in avian extinctions. The past extinction of island fauna paints a grim picture; it shows how easy it is for anthropogenic activities to lead to a loss of biodiversity. Unless we try to minimise our impacts and attempt to preserve and conserve the species that have so far survived, many more species of bird may join the mighty Moa. 

New Zealand by Steve Taylor, on Flickr

Cited:

• Extinctions in Near Time: Causes, Contexts and Consequences - Chapter 10: Late Quaternary Extinctions in Australia (T.F. Flannery & R.G. Roberts, 1999)