THE ECOLOGICAL, ENVIRONMENTAL AND ECONOMIC BENEFITS OF EXOTIC CONIFERS
Conservation will only ever be second fiddle to the other priorities of the Government of the day. Consequently, the status quo, comprising the neglect of 80% of the conservation estate, will continue with large numbers of taxa nudging ever closer to extinction.
The benefits of all forests, native, exotic and mixed are listed in terms of order of importance as follows;
Production of oxygen
· Sequestration of sunlight energy
· Sequestration of carbon dioxide
· Creation and protection of soils from water, frost and wind erosion
· Creation and increase of soil fertility
· Minimisation of nutrient loss from soils
· Attenuation of water flows and water temperature fluctuation
· Harbour for biodiversity within forest and on forest margins
· Shelter and the creation of microclimates
· Replenishable supply of environmentally friendly building products.
Wilding forests could hold the key to an unprecedented restoration of native flora and fauna in the Department of Conservation (DoC) estate and beyond.
However it comes with the requirement for major shift in thinking by the both Government and DoC.
Firstly, the Government needs to ring fence revenue earned from the conservation estate to the maintenance and improvement of the estate rather than all monies going to the consolidated fund as does now. This is important in it that dis-incentivises DoC staff to be innovative with respect to problem of funding conservation matters.
Secondly, DoC will need to change the deeply ingrained ideology that it has in respect of the place of forests containing non-indigenous species. This ideology is prevents DoC staff from a course that will produce huge gains for the management of the conservation estate.
DoC has been running a programme against exotic conifers for many decades at huge cost to the exchequer, which by any measure, has been an abject failure. The reasons for this programme are intellectually weak.
The arguments against exotic conifers from the DoC website are shown in the appendix, but they centre around the following headings
· Uncontrolled expansion of exotic forests
· competition with native flora
· wild fires
· loss of biological diversity
· impact of grazing land
· impacts on soil
· impact on water yield
· in stream values
DoC concede that forests “may” protect soil against erosion and “may” result in the sequestration of CO2.
I want to put the case for forestry, which in this case I mean, plantation forestry, naturally generating forests of exotic trees and forest mixtures comprising native and exotic trees.
1. WHY NATURALLY GENERATING EXOTIC FORESTS DEVELOP ON DEGRADED RANGELAND
Originally, most of NZ was covered by forest. The native forest species of NZ are highly evolved to thrive and succeed, in the ecological sense of the word, within native forests ecosystems.
The critical agents that conspire against native forest succession and retention are; grazing animals, the animals that destroy the birds that disperse forest species, and exotic grasses.
Exotic grasses are particularly antagonistic to native forest species for two reasons. They support grazing animals and the mycorrhizae (root fungi) associations of grasses appear to be highly effective at preventing native forest species to grow, in a process that is easy to observe but is not well studied or understood.
In summary, we have imposed an exotic grass-grazing ecosystem over most of NZ that prevents the re-colonisation of native forest ecosystems, limiting native biodiversity throughout the country.
Under a healthy native forest ecosystem, if exotic conifers are present, they have great difficulty continuing with succession. This is because they are not specifically adapted to the NZ environment. When they do persist then there is invariably some ecological agent involved for example high pig populations that till up the soil and allow these exotics to re-seed.
Extensive areas of the both the North Island and South Island have been subject to a long history of burning and overgrazing, especially in upland areas. This has depleted the fertility of these soils to the point where exotic grasses can no longer thrive and only the hardiest exotic pioneer species that can survive with in a grazing ecosystem do so. Examples of these species are hieracium, thyme, sweet briar, broom, gorse and of course exotic conifers.
Many exotic conifers that are in NZ evolved to exploit the opportunity created by the retreat of the North American ice sheets, before soils had formed and in the presence of grazing animals. These species have adaptions that enable them to live in these poor soils where there is also grazing pressure.
In NZ, these exotic conifers have found a situation that closely resembles the environment they evolved in. A situation created by a century and a half of gross land mismanagement.
These conifers then set about to undo this damage by firstly increasing soil carbon or organic matter in the soil. Soil carbon is the main component of soil that influences the Cation Exchange Capacity (CEC) of the soil. The CEC is ability of the soil to hold fertility, the greater the CEC the more fertile a soil can become. The trees then mine nutrients (cations such as sodium, calcium magnesium, potassium etc.) from deep in the soil horizon and return these to the top soil layer where these nutrients are held by the organic matter in the soil. The build-up of soil carbon is quite rapid under conifers as can be shown with the sequestration tables developed for the purposes of the Emissions Trading Scheme (ETS).
In other words, the exotic conifers build a cradle for fertility and then fill that cradle with nutrients.
The following image extracted from the Ministry of Primary Industries (MPI) management strategy for Wilding Pines shows this process.
The text accompanying this photo in the Strategy states this represents an example of pines invading grazing land, but this land is no longer suitable for grazing because it is land largely occupied by scab weed (hieracium), the last species able to occupy the depleted soils before there is bare ground.
Some see these trees as the problem; I see the problem is the severely depleted rangeland largely occupied by hieracium that is now being restored to ecological health by Pinus contorta.
Walking through these areas, especially in spring, it is clear to see the halo of fertility that is developing around each tree with exotic grasses and clover growing. (Clover needs a soil pH of over 5.5 to thrive.)
Native birds, particularly fantails, are quick to occupy young exotic wilding forests, generally followed by bellbirds and robins. Once the populations of these birds reach high levels, NZ falcons start to turn up.
Native forest species then start to appear in the developing forests. The speed of this process depends of the location of seed sources and the populations of native birds.
Pinus contorta is not a particularly long live species and at the stage it becomes susceptible to wind and snow damage, this presents a management opportunity to seed these forest with beech and podocarp at relatively low cost.
Native Forest Species Regeneration in a 20 year old North Island Pine Forest formerly in Farmland
Wood has an energy component of around 15 GJ/m3. Assuming a wilding stand reaches a volume of 600 m3/ha at which point it starts to succumb to native forest regeneration, then the food energy available to the food chain amounts to 9x10^12 Joules or to give a sense of scale if a human being had the constitution of a termite that would be enough food from a hectare of forest to feed a person for 2700 years.
In stark contrast to exotic grassland, native forest species are successful colonisers in exotic conifer forests, presumably because exotic forests resemble the ecosystems that those species evolved in. In the fullness of time, exotic forest will succumb to native forest succession subject to two conditions; the control of grazing and the control of the pests that predate native birds-an important point for the future management of these forests.
In summary, with an exotic grass-grazing ecosystem, a native forest ecosystem, and an exotic conifer ecosystem, there is a circle like the scissors, paper, and rock game where exotic grasses beat native forest, exotic conifers beat exotic grass, and native forest beats exotic conifers.
DoC sees the propensity for pines to spread a problem, I see the propensity of these trees to spread as the symptom of the problem of severe land management malpractice that has gone for too long and for which no one has been held to account.
While these self-generating exotic forests are a symptom of a severe problem, they provide the solution in that they restore the life giving capacity of the land.
DoC see pines threatening tussock and low native shrub lands. It considers these lands to be “natural”. In fact those vegetation types have been generated by the clearance of native forest and held in that state by intentional and unintentional grazing. These ecological succession stages are unstable and will either degrade to hieracium based ecosystem or be subject to colonisation by woody plants of some ilk.
Exotic trees do not compete with native vegetation any more than any native forest species compete with each other in the process of ecological succession. Instead, these exotic trees provide a feasible succession pathway to climax native forest subject to some management input.
Grass is the real culprit when it comes to competing with native species and destroying native biodiversity.
2. DO WILDING EXOTIC FORESTS CHANGE EXISTING ECOSYSTEMS?
Compared to the near ecological desert that exists under degraded rangeland farming that has developed into a sea of hieracium, wildings create microclimates with large volumes of living space for all manner of native flora and fauna, much as a coral reef provides diverse opportunities for all manner of creatures to live.
A hectare of hieracium with a canopy of say 5 cm provides a living space volume of 500 m3 per hectare while a 30 metre conifer stand provides a living space volume of 300,000 m3/ha.
Native birds and bats need trees as a place to make defendable nests and the older the trees the better.
3. IMPACT ON GRAZING LAND?
Conifers are incapable of colonising healthy grass ecosystems. However in the situations where over grazing and burning has done so much damage to land that it can no longer support grazing, this then provides the opportunity for self-generating exotic trees to develop.
4. DO WILDINGS LIMIT FUTURE LAND USE OPTIONS
What are alternative land use options that could beat wilding forests? Wildings develop on land where other possibilities no longer exist. Wildings forests themselves create a fantastic option and economic opportunity, specifically under the Emissions Trading Scheme.
The average sequestration rate for Exotic Softwoods in the Schedule 6 tables of the Climate Change Response Act is 12.8 tonnes CO2 equivalent per ha per year over 50 years. However, there have been measurements under the Field Measurement Approach component of the Emissions Training Scheme that show wilding stands with sequestration rates more than 5 times that rate.
According to MPI about 1.1 million ha of land that is developing or could develop into wilding forest and using the Schedule 6 table average this represents a national sequestration rate of 14.1 million tonnes CO2= per year.
Given NZ 1990 emissions base line is 62 million tonnes CO2= and its current emissions are around 78 million tonnes CO2= per year, there is a difference of 16 million tonnes CO2= over the 1990 base line.
Currently the difference is being covered by the existing Post 1989 forest estate, however this situation will go into reverse when harvesting of these forests commence, which will be soon. In other words, wilding forests provide the best hope for NZ to meet the Government’s currently stated goal of a net 5% reduction on 1990 emission levels by 2030.
Currently (Jan 2017) the NZ Carbon Unit (NZU) price is around $17.00. Meaning the carbon sequestration benefit could be around 14 million NZU x $17=$240 million per year.
DoCs current budget is around $340 million per year. At carbon price of around $25/NZU (being the maximum price currently allowed for under the ETS the value of wilding forest could be equal to the DoC budget. Internationally much wilder prices to the order of US$100/carbon unit have been speculated as being the levels necessary to bring green-house gas emission levels into decline.
NZ has one of the highest per capita emissions profiles in the world after the US, Canada and Australia (excluding the Arabian Gulf states which are in league of their own). Wildings provide perhaps the last chance for NZ salvage its “Clean Green” image which is now failing to pass the smell test.
On the other side of the ledger DoCs campaign against exotic trees and forests is resulting in significant contribution to national emissions and a consequential significant fiscal risk to the Crown as NZ international obligations for emissions reductions come to bear.
5. LANDSCAPE MATTERS
In their native state the wilding conifers grace some of the most beautiful landscapes on earth, the Rocky Mountains of North America. So the forests are not inherently ugly. Few tourist photos of Mt Cook are not framed by wilding forests.
The argument then goes that these forests are not natural to NZ. However, these forests only develop in areas where the existing native vegetation has largely been destroyed so those landscapes can hardly be described as being “natural”. As a forester with 35 years’ experience, I never seen an example of exotic conifers taking over a healthy native forest ecosystems.
What I believe is one of the most hideous sight in the country is vast areas of the McKenzie basin that are now being occupied by electric green grass, overlorded by huge, kilometre long, silver centipedes. The shortest book in NZ would be called the “Native Biodiversity on a Dairy Farm”.
6. FUTURE MANAGEMENT OF WILDING FORESTS
DoC is flying in the face of Mother Nature who is desperately trying to reclothe herself after century and half of abuse.
Ecological forces will not allow the current situation to remain static. So attempts to control wilding forest will result in a blow out of other perhaps much less desirable species such as sweet briar, gorse, broom etc. The expenditure of infinite treasure will not make the matter go away.
Rather than fight Mother Nature, the strategy should be to work with her by encourage wilding forest to develop and then promote the succession of native forest within these wilding forests.
This would take the form of grazing prevention, control of the animals that predate native birds and perhaps aerial seeding with natives when the time is right (this could be when these stands become snow damaged).
The wilding forest could fund these management operations through revenue from the ETS.
The use of wilding forests could lead to the greatest native forest regeneration project since the Taupo eruption and revenues from these forests could be used to fund protection of the rest of the native forest estate of which over 80% is wallowing in a disgraceful state of near total neglect.
From the Department of Conservation Website
Why are wilding pines a problem?
Pines seed very efficiently from pine cones. The wind-blown seeds are widely distributed and need no nurturing to take root.
Wilding pines are a nuisance in areas where native forest does not occur, such as above the bushline, in mineral belts and tussock grasslands. In areas such as these it creates a major intrusion and modification to natural ecosystems.
In areas where native forest regrowth is being encouraged pines are visually intrusive.
They compete for forest space with native trees and plants, but provide none of the advantages these offer, such as berries and nectar, to encourage bird life and insects. Pine needles form a carpet which discourages regeneration of native forest floor species.
3.1 The effect of wilding conifer spread on ecological values
The most obvious effect of wilding conifers is visual. However, wilding conifer spread affects more than just visual or landscape values. Introduced conifers can have a significant effect on native plant and animal communities, species, soils, and water yields. They can also affect land uses such as pastoral farming and recreation. These effects are discussed below.
Effects on plant communities
The most obvious ecological effect of wilding conifers is their ability to invade and suppress low-stature plant communities. The relatively fast growth rates of the introduced conifers, and the ability of some species to grow at harsher sites and at higher altitudes than native woody species, allows wilding conifers to out-compete and suppress native vegetation. This is the most significant effect of wildings throughout most of the South Island high country, where the most widespread plant communities are grassland and shrubland.
In extreme cases wilding conifer spread may lead to the local extinction of plant communities. Native grassland and naturally stunted native shrubland communities on ultramafic substrates in the Red Hills-Hackett area of Nelson/Marlborough are threatened in this way by wilding conifer spread. Remnant shrubland and grassland communities in the intermontane basins of the South Island high country are threatened with local extinction by wilding conifers.
Wilding conifers can also alter the structure of intact native forest communities. Douglas fir seedlings will readily establish within native mountain beech forest, and have been recorded within beech forest at densities of over 80,000 seedlings per hectare (ref 14). Most seedlings will not persist beneath a dense forest canopy, but light gaps are frequently created in mature beech forest and may allow the successful establishment of Douglas fir trees. The ability of Douglas fir to invade beech forest is well illustrated on the slopes of Ben Lomond, Queenstown, and at Bealey Spur near Arthur's Pass.
The structure of shrubland and regenerating forest can also be affected by wilding conifers. Openings within these communities, and the low stature of the surrounding vegetation, allow the light-demanding wilding conifers to establish and out-compete native woody species. Large areas of regenerating forest and shrubland in the Marlborough Sounds are affected in this way, mostly by radiata pine. Site conditions (and wilding conifer control) will determine whether wilding conifers or the regenerating native forest will become dominant in the long term.
A further, secondary, effect on plant communities is the increased susceptibility to damaging fires. The presence of wilding conifers in non-woody plant communities may, in the event of wild fire, mean that fires burn longer and hotter than otherwise due to the presence of both dead and live wood. Some species of introduced conifer are well adapted to regenerate after fire.
Effects on individual species
The effects of wilding conifers may not be limited to plant community structure. Individual species may be displaced or habitat may be created for other species. Where low-stature plant communities are completely overwhelmed by wilding conifer spread, local extinction of individual species may occur. Populations of species, such as Hebe armstrongii in the Waimakariri Basin, and Hebe cupressoides throughout the high country, are threatened with local extinction by wilding conifers.
Animal species may also be threatened by wilding conifer spread, notably native lizards and invertebrates in open communities, as the establishment of conifers can alter the habitat of existing species and create new forest habitat. Important examples are the Cromwell chafer beetle (Prodontria lewisi), threatened by wilding conifer spread at its only known location in the Clutha Valley, and the robust grasshopper (Brachaspis robustus), in the Mackenzie Basin (see following page). Freshwater fish populations may be affected by wilding conifer spread, through shading of streams or reduced water flows. Felling operations may cause a reduction of water quality.
Conversely, the establishment of introduced conifer forests can sometimes create useful habitat for native and introduced species. Several rare native orchid species are commonly found in conifer forests (ref 20), and mature Northland pine plantations can provide habitat for North Island brown kiwi (ref 21). However, in general, fewer native bird species are found in plantation forests than in native forests (ref 22). And, invariably, the establishment of forests of introduced conifers leads to the displacement of native species and a net loss in biological diversity.
Effects on soils and hydrology
Other, perhaps less obvious, effects of wilding conifer spread are the effects on soils, nutrients, and hydrology. Wilding conifers in tussocklands take up and hold a larger pool of nutrients than the snow tussocks they replace (ref 23), presumably through increased mineralisation of the soil organic matter or through nutrient transfer from deeper soil horizons (ref 24). It is possible that introduced conifers will accelerate acidification and eventual podzolisation of soils that formerly supported native forest, though there has been insufficient time to measure this possible effect in New Zealand (ref 25).
Forest cover - native or exotic - may protect soils from some forms of erosion more effectively than either pasture or crops. Analysis of East Coast (North Island) slopes after Cyclone Bola indicated that the extent of slope failure under mature exotic plantations or regenerating indigenous scrub and forest, was only 10% of that under pasture (ref 26). Afforestation may reduce greenhouse gas emissions by storing carbon from the air and soil in the tree, and by reducing methane emissions through a reduction in livestock numbers (ref 25). However, if these are favoured objectives for DOC-administered land, they should be achieved through the regeneration of native shrubland and forest communities, not by the uncontrolled spread of wilding pines.
Introduced conifers can also affect water yield. Exotic plantations yield lower mean water flows and lower low flows than either native forest or pasture (ref 27). Pine planting on pasture and gorse covered hills in the Moutere Catchment (Nelson) reduced annual run-off by 55% and ground water recharge by nearly 70% (ref 28). And, research in the Mackenzie Basin predicted that the conversion of tussock grasslands to pine plantations would result in a 25-30% reduction in water yield (ref 29). This effect has significant implications for populations of in-stream flora and fauna, as well as water supplies for domestic and pastoral use.