Brennan Panzarella Victoria University of Wellington ERES 525
The new Labour government has set a goal for the people of New Zealand to plant one billion trees over the next 10 years (MPI, 2018). Although they are now including the 500 million trees already planned by the private sector, they are sticking to their goal (Shane Jones, 2018). There are indications that a large portion of the increase in plantings will be Radiata pine, a tree that already dominates NZ forestry land. Herein lies an opportunity for the government to encourage a middle ground between the needs of productive plantation forestry and the needs of our indigenous biodiversity. Through incentivising strategic incorporation of native hardwoods, New Zealand could grow its market for specialty timbers meanwhile increasing provision of habitat for indigenous species.
BIODIVERSITY AMONG FOREST PLANTATIONS
As seen in the chart below, Radiata pine is by far the most common species in plantation forests in New Zealand at 90% of total (MPI, 2018).
Plantation Forest Species Distribution as of 1 April 2017
Source: Ministry for Primary Industries. National Exotic Forest Description.
Though there is a pervasive idea that monoculture stands of exotics are species deserts, there are records of native species utilising plantation pine areas. Radiata plantations offer a number of ecosystem services that include subsistence for wildlife. In many older exotic tree plantations, the sub-canopy plant and soil layers can be similar in comparison to indigenous forests. Pine plantations are likely among the ‘lesser evil’ of the agroindustrial land uses most common in New Zealand and can often harbour a much greater biodiversity than dairy farms and other pastoral operations (Ogden, 1997).
New Zealand Falcon in front of Radiata plantings
Photo by Debbie Stewart/Source: NZ Geographic
Biodiversity among pine plantations is not well studied so it is inconclusive if these plantations provide permanent habitat or if the presence of native species is dependent on immigration from nearby bush. From the little we know, proximity to indigenous forest is one of the main factors in increased indigenous biodiversity on forest plantations (Ogden, 1997). Even incorporating native plant communities in small sections of exotic planted stands can help preserve biodiversity after clear cutting (Woodley, 1997). Incorporating indigenous trees amongst exotic plantations could be a fruitful experiment to further observe how indigenous species react.
On the other hand, plantations using native species have shown to be better at increasing species richness than plantations using exotic species. In one study, areas of primary forest transitioned to exotic plantation forest showed a 45% decrease in species richness. The same study showed native plantation forests significantly outperforming exotics when compared to control variables of paired secondary forests (Bremer, 2010). Again we are reaching the limits of peer-reviewed science publications on the topic but there is enough evidence to warrant government incentives and to incorporate more native trees during the billion trees program.
Percent Change in Species Richness (Transitions to Plantations of Exotic vs. Native)
Source: (Bremer, 2010)
One of the main tools in reaching out to private landowners and encouraging them to plant trees is the Ministry of Primary Industries’ Afforestation Grant Scheme (MPI, 2018). This gives $1,300 for each hectare of new plantings which also happens to be the average cost of planting up one hectare of Radiata pine (Shane Jones, 2018). The methods of implementation could be improved through encouraging the planting of a diversity of trees. By giving more grant money to planting schemes with multiple species plantings, habitats with a greater diversity of trees will support greater biodiversity. Also incentivising the planting of longer to mature species would benefit the steady maintenance of habitat for a species living in plantations as biodiversity is increased when there are stands of trees at different ages (Gjerde, 1997).
Source: Tane’s Tree Trust
A lot of old-timers will tell you, “they don’t make ‘em as good as the used to”. Regarding timber quality this is especially true. Radiata pine would be what the business world calls a “minimum viable product”. Genetically selected for as fast of growth as possible, the Radiata pine grown in New Zealand has a number of quality issues. It is the cheapest to grow and it is the fasting growing. But the quality of the timber makes it inferior for a number of building applications. And this is reflected in the price in that Radiata pine on average is by far the cheapest timber you can purchase in New Zealand.
Radiata pine needs to be treated with heavy metals and/or arsenic to achieve rot resistance. Offcuts from treated pine create unnatural concentrations of heavy metals in waste streams and for people working with the wood. On the other hand, native hardwoods like Totara, Puriri and Kauri are resistant to decay in their natural states. The major problem is that they take longer to grow; but with a bit more patience, a bit more grant money from the government and the stamp of approval from ecologists, we could be saving two birds with one stone.
There is already a market in New Zealand for imported hardwoods like White Oak and Kwila (TimSpec 2018). Quality wood is difficult to source and expensive in New Zealand and this is largely because of the domination of Radiata pine. With a little push in the right direction now, New Zealand could drastically reduce needs for imported hardwoods and reduce its carbon footprint by sourcing hardwoods locally.
Rewarewa Timber (source nativetimber.co.nz)
Totara is one of the most common indigenous trees to regenerate from farmed land, especially in Northland (Bergin, 2000). This indicates that it would be a good starter species for North Island foresters wanting to plant natives for timber. Rewarewa, although difficult to season, is a strong and unique looking timber and could become a hot commodity. There is also a growing market for Rewarewa honey and Rewarewa plantations could provide resilience to a specialty honey market threatened by Myrtle Rust. A study of 60-year-old Kauri timber showed that it could match many of the attractive characteristics seen in timber of old growth indigenous forests. Kauri logs nearly 40 cm in diameter were found to be achievable within 50 years (Bergin, 2005). Although most of us will be retired and out of the rat race in 50 years, the next generations would likely be grateful.
Table top made with Black Maire (source: bushmansfriend.co.nz)
It would likely take more work and more patience but we can create forestry habitats that incorporate a range of tree species. This should be emphasised in MPI’s communication with the public. With a special focus on high value, slower-growing specialty hardwoods, forestry stakeholders will be achieving the majority of MPI’s goals in the implementing of the billion trees plan, allowing for greater economic and ecological resilience.
|MPI Stated Benefits of Forestry in Regard to the Billion Trees Program (MPI, 2018)||Monoculture Radiata||Polyculture Native Hardwood|
|Diversify income||Already the industrial norm, increase in quality depends on intensive wood treatments (NZ Herald, 2014)||Could lead to growth in market for specialty timbers and reduce need for timber imports|
|Invest in future||Low value per log (TimSpec, 2018), lower upfront costs||High value per log, higher upfront costs, less need for heavy metal treatments|
|Improve land productivity||Higher biomass accumulation (Ogden, 1997), lower maintenance (Shane Jones, 2018)||Closer plantings, more stems per hectare|
|Mitigate erosion||Faster growth but higher turnover and more frequent soil denudation||Slower to establish but more habitat permanence. Higher value timber would make selective logging more economical|
|Mitigate climate change||Faster C02 absorption per tree||Slower CO2 sequestration per tree but more stems per area land (Shane Jones, 2018)|
|Improve water quality||Probably better than traditional pastoral||More diverse forest absorbs and utilises more water (Aerts, 2011)|
|Moderate river flows||Not ideal to harvest riparian trees||Ideal for riparian improvement and indigenous species habitat|
|Provide important habitats for a range of native species||Better than pastoral and dairy, evidence of high native diversity of sub-canopy plants, insects, insect eaters and NZ falcon (Ogden, 1997)||Plethora of diversity and habitat|
|Create jobs||Faster turnover creates more planting, harvesting, processing jobs||More labour required for planting and maintenance|
Aerts, R. & Honnay, O. (2011) Forest restoration, biodiversity and ecosystem functioning. BMC Ecol 11: 29
Bergin, D. O. (2000). Current knowledge relevant to management of podocarpus totara for timber. New Zealand Journal of Botany, 38(3), 343.
Bergin, D. O., & Gea, L. (2005). Native trees: Planting and early management for wood production. Rotorua, N.Z.: Forest Research Institute.
Bremer, L. L., & Farley, K. A. (2010). Does plantation forestry restore biodiversity or create green deserts? A synthesis of the effects of land-use transitions on plant species richness. Biodiversity and Conservation, 19(14), 3893-3915.
Gjerde, I., & Saetersdal, M. (1997). Effects on avian diversity of introducing spruce Picea spp. plantations in the native pine Pinus sylvestris forests of western Norway. Biological Conservation,79(2-3), 241-250.
Ministry for Primary Industries. (2018, April 10). Afforestation Grant Scheme. Retrieved from http://www.mpi.govt.nz/funding-and-programmes/forestry/afforestation-grant-scheme/
Ministry for Primary Industries. (2018, April 10). Planting one billion trees. Retrieved from https://www.mpi.govt.nz/funding-and-programmes/forestry/planting-one-billion-trees/
NZ Herald. (2014, March 5). New Zealand tech turns pine into hardwood. Retrieved April 29, 2018, from http://www.nzherald.co.nz/building-construction/news/article.cfm?c_id=24&objectid=11206599
Ogden, J., J. Braggins, K. Stretton, and S. Anderson. (1997). Plant species richness under Pinus radiata stands on the central North Island Volcanic Plateau, New Zealand. New Zealand Journal of Ecology 21: 17-29.
Pawson, S. M., Ecroyd, C. E., Seaton, R., Shaw, W. B., & Brockerhoff, E. G. (2010). New zealand’s exotic plantation forests as habitats for threatened indigenous species. New Zealand Journal of Ecology, 34(3), 342-355.
Shane Jones on the billion trees plan. (2018, February 27). Retrieved from https://www.radionz.co.nz/national/programmes/ninetonoon/audio/2018634023/shane-jones-on-the-billion-trees-plan
Woodley, S., Forbes, G. (1997). Forest management guidelines to protect native biodiversity in the Fundy Model Forest. Unpublished report by New Brunswick Coop. Fish and Wildlife Research Unit. University of New Brunswick, New Brunswick, 35 pp.
Author: Fetuao Nokise
Indigenous species in the Anthropocene face a wide range of challenges including habitat loss, invasive species1, over-exploitation2, and climate change3. With around 15-50% of global biodiversity estimated to be extinct by 2050, the planet will continuously be managed and shaped in innovative yet potentially controversial ways. The modification of genes is a particular inventive way in which humans could reduce extinction rates of species4, but where does this fit in ecological restoration? The modification of genes could potentially be done in three explicit ways; transferring genes from one species to another, transfer of alleles from better-adapted individuals to vulnerable populations and introducing individuals as vehicles for infusion of novel alleles known as “gene rescue”5. The individual suitability of each approach is based upon current and potential studies as well as social and cultural perceptions of modifying genes.
Species to species gene transfer is a contentious approach as the particular alleles of a species is fundamentally modified. Success has been seen in agricultural practices through drought and temperature resistant crops where tomatoes have become cold-resistant6 using specific rice and Arabidopsis genes. This enables endless potential crossover of genes which may facilitate adaptation. But the result of shifting genes between different species has increased difficulties. Consequently the major concern is that accidental and uncontrollable outcomes may carry too much uncertainty5.
The approach of directly transferring particular alleles from better-adjusted populations into individuals from vulnerable populations would enable selective increases in mean fitness. Dependency of such is the identification of the specific genes possessing the adaptive qualities5. The potential of this technique is reliant on the impact the particular trait. Researchers recently discovered alleles connected to heat tolerance in commercial rainbow trout, Oncorhynchus mykiss7. The insertion of these alleles into fish eggs and embryos of vulnerable populations could result in adaptation to increases in temperatures. Complex traits are often linked with several genes ensuing uncertainties and predictions in outcomes are often tricky8. Although this approach is viewed as the least risk and comprises the most integrity as it involves the exact same species5, there is a lack of current studies which use this technique due to clear intricacies in identification of exact genes for certain traits.
The modification of genes through “gene rescue” is currently the only option which has been implemented successfully8. It is the introduction of individuals as a medium for the infusion of novel alleles into c
ertain threatened populations. Population recovery and increased efficiency has been seen in the introduction of female Texas panthers (Puma concolor stanleyana) into Florida panther (Puma concolor coryi) populations creating hybrids9. Similarly population recovery has been seen by increased gene flow in Swedish adders10, bighorn sheep11, prairie chickens12 and very recently the Artic fox13.
The success of gene rescue highlights the significance and relevance of genetic modification in the anthropocene era. Scientific barriers do exist such as outbreeding depression, fitness reductions due to mating between hereditarily opposite individuals14, new diseases, disturbance of social interactions and cross-breed swarms15. Precautious planning and monitoring around introductions will mitigate and minimize these barriers and risks in conjunction with guidelines which have already been proposed for certain species15.
The biggest barrier to gene rescue is in certain social and cultural values. The concern of genetic purity and integrity of the target species causes reluctance in accepting and pursuing genetic rescue. But this is a process without biological constrictions and can happen “naturally” in the wild between subspecies or closely related species. The diversity of species categorized into hierarchy of class, order, genus and species assume species are fixed and discounts the complexity of reality8. This leads to the ecological restoration of forms in comparison to ecological processes fundamental to biodiversity. But many evolutionary examples showcase “natural” occurrences through hybridization16 and horizontal gene transfer17. The reluctance to recognize the value of gene rescue could potentially result in even more species extinctions18, 19.
From a scientific view there are certain measures which can be taken in order to maintain the purity and integrity of populations. Gene rescue strategies could be developed in ways which allows the infusion of alleles into threatened populations which raise fitness without losing the general gene distinctions between species8. Although specific examples of such are yet to exist, the principle of such is seen in introgressed species examples. In the example of the Florida panther earlier, the introduced females were removed after frequent breeding so that the particular introduced allele could remain but were back crossed with the enduring Florida panther9.
The modification of genes does not solve the problems of continual decreases in global biodiversity. It is a multi-faceted tool box where each tool is appropriate to a particular situation and species. This enables the persistence of species in light of continuous challenges. In an ecological restoration context, the modification of genes to facilitate population recovery may not completely restore historic ecosystems but may offer an opportunity to restore their ecological functions.
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- Rebl, A., Verleih, M., Köbis, J. M., Kühn, C., Wimmers, K., Köllner, B., & Goldammer, T. (2013). Transcriptome Profiling of Gill Tissue in Regionally Bred and Globally Farmed Rainbow Trout Strains Reveals Different Strategies for Coping with Thermal Stress. Marine Biotechnology,15(4), 445-460. doi:10.1007/s10126-013-9501-8
- Love Stowell, S.M., Pinzone, C.A. & Martin, A.P. Overcoming barriers to active interventions for genetic diversity. Biodivers Conserv (2017) 26: 1753. https://doi.org/10.1007/s10531-017-1330-z
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- Bateson, Z.W., Dunn, P.O., Hull, S.D. et al (2014) Genetic restoration of a threatened population of greater prairie-chickens. Biol Conserv 174:12–19. doi:1016/j.biocon.2014.03.008
- Hasselgren, M., Angerbjörn, A., Eide, N.E. et al (2018) Genetic rescue in an inbred Arctic fox (Vulpes lagopus) population. Proc R Soc B Biol Sci 285:1875. doi: 10.1098/rspb.2017.2814
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- Hedrick, P.W., Fredrickson, R. (2010) Genetic rescue guidelines with examples from Mexican wolves and Florida panthers. Conserv Genet 11:615–626. doi:1007/s10592-009-9999-5
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- Baltrus, D.A. (2013) Exploring the costs of horizontal gene transfer. Trends Ecol Evol 28:489–495. doi:1016/j.tree.2013.04.002
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Alex Gault, Victoria University of Wellington
As humans continue to ravage the earth to feed their consumerist habits, global biodiversity is disappearing at an unprecedented rate. Overexploitation, invasive species and climate change are a few of the drivers of these losses and despite attempts every so often to ramp up conservation efforts, humans simply haven’t been able to take their foot off the accelerator towards a sixth mass extinction. But just as human inventions may have been part of the undoing of many species, technology repurposed for conservation may help relieve the pressure on the world’s ecosystems.
HUMANS – TECHNOLOGICAL PIONEERS
Throughout human history, problems have been solved by turning ideas into technologies. Focus on human environmental impact and expanding research has seen fragmented ecosystems reconnected with highway wildlife overpasses, remote camera technology revolutionising studying species behaviour and invasive pests being taken out with species-specific toxins.
Technology excites people. Its evolution has taken Homo sapiens from inventing a wheel to driving mechanised metal boxes to get around. Redirecting the enthusiasm to the environmental cause could have astounding outcomes. Smartphones, olfactory analysis devices and remote-sensing technologies are readily-available and relatively cheap technologies– a simple tweak here or there could produce a tailor-made conservation tool that is cheaper and less intrusive than current biosecurity, field research and pest control methods.
REPURPOSED PROBLEM SOLVERS
Preventing incursions of invasive species and curbing trade of rare species is a pressing issue for countries worldwide. Biosecurity could be transformed by electronic “noses”, utilising odour-detecting technology initially developed for commercial chemical analysis to detect illegally-traded wildlife and smuggled biohazardous materials[6-7]. Costs for biosecurity would be reduced, increasing the capacity of operations and reducing risk of error from sniffer-dogs and humans.
Even human overexploitation could have a hi-tech solution. 3D printing rhino (Rhinocerotidae) horns to leak into the black-market has been proposed as a novel answer to thwart poaching. However, concerns have been raised that synthetic horns won’t fool buyers as a stand-in for real rhino horn. A history of failed attempts to stop poaching make sceptics more tentative – the issue is more deeply ingrained than a synthetic replacement can solve on its own. Research into the matter shows that the state of market saturation will have a large influence on whether or not the scheme may work, as well as the price and likeness at which synthetic horn is set. The jury may be out on this one yet.
The future holds exciting new prospects. Humankind has now extended beyond mechanised tools and are now dipping toes into the unchartered waters of artificial intelligence (AI) and genetic modification (GM). The fear of being outsmarted by an AI robot or genetic mutants running rampant – a story gaining a regular spot in Hollywood – has alienated people from the potential of these technologies. However, to preserve a thriving biodiverse environment, AI and GM should be embraced. Without them the potential for further conservation successes will be limited to that which can be achieved by man-power alone. This is not to say that caution and restraint shouldn’t be practiced – it must be certain that AI and GM products won’t become uncontrollable when unleashed.
Nevertheless, artificial intelligence and genetic modification represent the next big technological revolution, and conservation science will definitely be getting amongst the action. Artificially-intelligent robots have already been employed to inject poison into destructive coral-eating crown-of-thorns starfish (Acanthaster planci) off the Great Barrier Reef (see video below). Early success in the project suggests that AI technology could be rolled out into other fields of invasive species management in a similar way. AI to analyse video footage and remote-sensing data would exponentially increase the capacity to collect valuable data, replacing the need for people to watch through thousands of hours of recordings, or for a risky voyage across the Southern Ocean to locate tiny colonies of seabirds on inaccessible islands. The conceivable scale of projects simply dwarfs those possible using bare hands.
Video: A “COTSbot” in action, locating and lethally injecting a crown-of-thorns starfish.
Genetic modifications shouldn’t be ruled out either – GM plants have fed a globe of rapidly reproducing humans where ‘wild’ strains have been unable. Giving species a push in the right direction to become better suited to fragmented, warmer habitats by facilitating inheritance of an advantageous gene could ensure species survival. The process, called a gene-drive, can be used both to prevent undesirable species proliferating or to fix advantageous genes in a struggling population.
Here in New Zealand, gene drives have been floated as a novel method to stamp out the plethora of invasive insects and mammals gorging on native biota. However, despite its promise, research warns that the technology is not yet ready to release into the wild. The method, while excellent in theory, is less likely to pan out faultlessly in practice. Genetic modification also has significant opposition in the public sphere, especially from people who are less scientifically-informed. Nevertheless, while gene drive technology is still in its early days, with a bit of public education to bolster support, the concept may not be far off becoming a remarkable conservation tool inspired by evolution itself.
Technology cannot solve all the world’s problems. Evidently, putting a definitive end to human’s destructive habits would be the ultimate solution to halt global biodiversity losses. But as with many problems in human society, that is easier said than done. In the meantime, merging technology with conservation would help to facilitate more conservation successes for the environment. Refashioning mainstream tech to be environmentally-focused could drastically change the way science and environmental management moves forward, providing more tools to solve problems previously thrown into the “too hard” basket.
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a. Fish Wildlife. 2017. Animals playing technology. Retrieved from https://www.youtube.com/watch?v=IbgiML8v334
b. The Straits Times. 2015. Take a walk along Eco-Link@BKE bridge especially reserved for animals. Retrieved from https://www.straitstimes.com/singapore/environment/take-a-walk-along-eco-linkbke-bridge-specially-reserved-for-animals
c. TechCrunch. Pembient Rhino Horn 3D Printing. Retrieved from https://www.youtube.com/watch?v=AjzVF9_-xuM
d. Hesman Saey, T. 2015. Gene drives aren’t ready for the wild, report concludes. Retrieved from https://www.sciencenews.org/blog/science-ticker/gene-drives-aren’t-ready-wild-report-concludes
Video: TheQUTube (2016). COTSbot injects a COTS. Retrieved from https://www.youtube.com/watch?v=Gij5i66UujU
By Amanda Healy
Ecological reservation is currently used as a primary technique for preserving species or ecosystems. By disallowing the exploitation of an ecosystem, it is assumed that the area will be protected, and will therefore be able to exist into perpetuity. However, due to the rapidly increasing temperatures caused by anthropogenic climate change, many different species are moving away from their previous ranges into more climatically suitable locations (Chen et al., 2011; Loarie et al., 2009). This essay will look at how that may affect ecological reserves, and what we may need to do to keep up with the ever-changing climate.
Climate-change induced range shifts are occurring in a vast number of species (Shoo et al.,2006). One study found that on average, species are moving to higher latitudes and altitudes at rates of 16km and 11m per decade, respectively (Chen et al., 2011). These rates obviously vary, depending on the intensity of climate change in any given area and the ranging ability of the species in question; migratory species are able to shift their ranges quickly, but sedentary species (such as trees) take much longer (Parmesan et al., 1999).
Because of the movement of species out of their original ranges, our current system of protected reserves may become redundant in the future. One estimate states that in 100 years, only 8% of our reserves will still have the same climate as they have today (Loarie et al., 2009). This means that many of the species that we are aiming to protect will no longer be able to live within these reserves. They will either move outside of the reserve’s borders, or even worse, barriers will inhibit their movement and they will go locally extinct.
The protection of these reserved species will likely require assisted colonisation in the future (Lunt et al., 2013). The barriers that inhibit the movement of species, such as habitat fragmentation or the fencing around reservations, mean that these species will need help to move to a habitat that is suitable in the changing climate. The same applies to species that are slow moving or sedentary, as they are unlikely to be able to keep pace with the rate of climate change (Parmesan et al., 1999). This concept goes against traditional ideas of conservation and reservation, as it would often mean introducing a species to a geographical area that they have never occupied previously (Hoegh-Gulberg et al., 2008). Most reservations work to preserve only species that are native to the area. However, in order to save many of these species, it will likely be the best option in the coming years.
For these reasons, it is likely that nature reserves, for the purpose of species or ecosystem preservation, have a limited lifespan. At some point, as temperatures continue to rise and climates continue to move, we will have to reconsider our concepts of reservation ecology. Alternative solutions will need to be considered in order to protect the organisms that these reserves are currently housing.
Chen, I. C., Hill, J. K., Ohlemüller, R., Roy, D. B., & Thomas, C. D. (2011). Rapid range shifts of species associated with high levels of climate warming. Science, 333(6045), 1024-1026.
Hoegh-Guldberg, O., Hughes, L., McIntyre, S., Lindenmayer, D. B., Parmesan, C., Possingham, H. P., & Thomas, C. D. (2008). Assisted colonization and rapid climate change. Science (Washington), 321(5887), 345-346.
Loarie, S. R., Duffy, P. B., Hamilton, H., Asner, G. P., Field, C. B., & Ackerly, D. D. (2009). The velocity of climate change. Nature, 462(7276), 1052-1055.
Lunt, I. D., Byrne, M., Hellmann, J. J., Mitchell, N. J., Garnett, S. T., Hayward, M. W., … & Zander, K. K. (2013). Using assisted colonisation to conserve biodiversity and restore ecosystem function under climate change.Biological conservation, 157, 172-177.
Parmesan, C., Ryrholm, N., Stefanescu, C., Hill, J. K., Thomas, C. D., Descimon, H., … & Tennent, W. J. (1999). Poleward shifts in geographical ranges of butterfly species associated with regional warming. Nature,399(6736), 579-583.
Shoo, L. P., Williams, S. E., & Hero, J. (2006). Detecting climate change induced range shifts: Where and how should we be looking? Austral Ecology, 31(1), 22-29.
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By Andrea Gregor
Non-native species are known to be a strong driver of native species decline and habitat degradation (D’Antonio & Meyerson, 2002). All invasive species are non-native, yet not all non-native species are invasive (Clewell & Aronson, 2013). Non-native species have the ability to infect natives with disease, outcompete them and alter ecosystem functions (D’Antonio & Meyerson, 2002). Non-native species, however, have also been shown to enhance the process of ecological restoration by acting as an alternate food source, or increasing nutrients in soil and becoming an important part of ecosystems. I focus on non-native plant species, however non-native animal species follow similar trends, and equal research should be performed. If ecological restoration is the restoring of native landscapes, then is there any room for non-native species to be part of this process? How can we assure that non-natives used in ecological restoration will not become invasive?
The Potential Impact of Non-Native Species
An area of land that is to go through ecological restoration often has had disturbance caused by human action or environmental events (Keenleyside, Dudley, Cairns, Hall, & Stolton, 2012). According to Vilà and Weiner (2004), disturbance increases the chance of invasion by non-native species as species that have the potential to become invasive tend to be good colonisers after disturbances. As well as this, many create seed banks which allow them to endure for a long period, and make eradication difficult. With an increased risk of invasion, we get an increased risk of interspecific competition between native and non-native species. Studies conducted are unable to say that all non-native species always outcompete natives; however there is still a strong competitive effect on native species, which can cause a decline in the population of native species (Vilà & Weiner, 2004). Species compete for light, nutrients and space (Wilson & Tilman, 1993). Therefore including certain species of non-natives in restoration runs the risk that the introduction, be it accidental or not, could be detrimental to the persistence of that ecosystem through potential outcompeting and overcrowding.
If inadequate research is done, non-native species have the potential to become invasive in certain environments. Invasive species have been recognised as the second largest threat to global biodiversity after habitat fragmentation (Allendorf & Lundquist, 2003). Throughout the world, invasive species cost governments billions of dollars. Management of plants and animals listed under the Endangered Species Act cost $32-$42 million annually, in which 90% of those funds are allocated to mitigate the effects of invasive species (Wilcove & Chen 1998; D’Antonio & Meyerson 2002). In New Zealand invasive species cost $840 million each year to control, and produce a $1 billion loss in productivity (Giera & Bell, 2009). With such a large economic impact that invasive species have on New Zealand and the world, should we risk using species that have the potential to be invasive in ecological restoration?
Are All Non-Natives That Evil?
With adequate research, there is room to include non-natives in ecological restoration. Some non-native species, particularly plant species have been shown to increase the population of native species. Non-native species being used as an alternate food source for native species can lead to an increase in native population numbers due to the increased resources. For example, in the US, introduced honeysuckles are improving native bird populations (Figure 1). It is also found that seed dispersal of native plants is the highest where non-native honeysuckles are the most abundant due to dispersal by the now more populated native birds (Davis, et al., 2011). This positive effect of a non-native plant has enhanced the population of native bird species, as well as other native plants. Subsequently, removing non-native species can have negative effects to an ecosystem removal of these pine plantations will demolish the favourable , and successful eradication so far has been limited to small islands (Zavaleta, Hobbs, & Mooney, 2001). With declining native habitat, half of New Zealand’s threatened indigenous plants are found in historically rare ecosystems with localised distributions (Pawson, Ecroyd, Seaton, Shaw, & Brockerhoff, 2010). Encouraging natives to use non-native habitats as substitutes could help the continuation of species. The New Zealand large bird orchid (Chiloglottis valida) has been found within non-native Pinus nigra plantations. The microclimate under these pine trees which allow orchids to survive outside of their original habitat. Because of this reason, a small orchid reserve in this plantation has been created, while the rest of the plantation has been logged (Pawson, Ecroyd, Seaton, Shaw, & Brockerhoff, 2010). This example is one of many which show the necessity of keeping specific non-native species in order to retain native species.
Implications on Soil Nutrients
Exotic plants can alter ecosystem processes through differences in nutrient cycles. They can cause an increase, or decrease to the soil nutrients created by native species (Ehrenfeld, 2003). Negative effects of the changes in the soil microbial community can lead to an increase in the invasiveness of an ecosystem from other species (Green, O’Dowd, Abbot, Jeffery, Retallick, & Mac Nally, 2011). This has the potential to create an invasion meltdown which would undo all restoration efforts thus far and render a project useless. Changes in soil structure, such as an increase in nitrogen can encourage growth from other invasive species which outcompete natives, and shroud out the light with denser canopies, reducing the growth of native species (Allison, Nielsen, & Hughes, 2006). In Hawai’i, nitrogen fixing invasive tree Falcataria moluccana (figure 2) alters the soil structure which limits the growth of native species. Along with this, F. moluccana facilitates the invasion of another non-native species, Psidium cattleianum (also known as the strawberry guava) which outcompete natives for resources (Allison, Nielsen & Hughes, 2006). If a species such as this was used in ecological restoration without research, it has the potential to become invasive and harm the ecosystem, rather than benefit it. Changes in soil structure can also have positive effects; non-native species are able to be used positively as substitutes for slower growing natives when restoring areas with poor productivity soils which have had disturbances such as overgrazing or mining (Wong, 2003). Fast growing nitrogen fixing trees from Asia were found to grow well in degraded pastures in Puerto Rico and accelerated regeneration of native forests (D’Antonio & Meyerson, 2002). Without exotic species in circumstances like this, ecological restoration would not be able to get under way, especially if natives we are wanting to maintain struggle to establish in degraded soils. Non-natives in this case are essential to effective recovery of native sites. The differences in the nutrient cycles of non-native species and native species we want to restore will determine the impact non-natives will have on the soil composition and therefore the native species. These impacts can differ from site to site and can cause ecological restoration to fail or succeed. Research is our greatest tool to ensure we only use species that succeed, and remove species that will cause our project to fail.
With continued human movement, non-natives are becoming more and more abundant, creating many novel ecosystems (Marris, 2011). In ecological restoration, you must pick your battles; it is not possible to remove all introduced species. If a non-native has no potential of becoming invasive, and is doing no harm to an ecosystem, then leaving that species and focusing money on other areas would seem like the way forward. In some cases, I feel we should learn to embrace novel ecosystems, especially in circumstances where we are unable to return ecosystems back to their original state. Non-natives may have changed the habitat of an area to make it unsuitable for future natives, whether the non-native is present or not through changes in soil or species composition, and abundance (Norton, 2009) . According to Norton (2009), it has passed the biotic threshold, and there is no way to return the ecosystem back to its original state. If this is to have happened, and a non-native has taken over the niche of a native without affecting other species, it may be in our best interests just to embrace the change leave it there as part of a functioning ecosystem.
Non-native species have a place in ecological restoration, however we must be wary of which species we choose to include in these projects. The fact that invasive non-native species are one of the largest threats to ecological restoration means that using non-natives in these practises can lead us to walk on a fine edge between enhancing native species, and causing an invasive meltdown. Introducing non-native species seems like we are encouraging the opposite of what we are trying to achieve, however it has been shown in many cases to work. We have little room for error, therefore we must use short lived, well researched species and we must monitor them closely to ensure ecological restoration is achieved successfully. We must also acknowledge that there is always a chance of failure; a species may interact with its surrounding different than we had planned. This is a risk that is shared in all conservation and restoration projects which can be minimised, but never removed. In this essay. We must also look at the possibility of leaving non-natives that have been determined low risk to ecosystems; we can never restore every area back to its original state, but if we pick our fights correctly, we are able to nurse many native species back with the help of non-natives.
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