Submitter: Professor Euan G. Mason
Profile: Dr Euan
Mason is a Professor at the New Zealand School of Forestry, University of
Canterbury, where he teaches silviculture, statistics, modelling, and research
methodology. His research interests
include forest growth and yield modelling, tree physiology, and
silviculture. He has published numerous
peer-reviewed articles and a chapter in a textbook relating to climate change
and forestry, and has been employed by government ministries and political
parties to advise them on climate change issues from time to time. He is a New Zealand citizen, born in
Invercargill. He was educated at
universities in New Zealand and the United States of America.
Synopsis of submission
I provide a summary of our current state and the role of
forestry in helping New Zealand respond appropriately to climate change.
Many proposed changes to the emissions trading scheme (ETS),
particularly the idea of splitting credits into sequestered carbon versus
avoided emissions with only the latter of any market value, are irrational,
will create confusion, will lower confidence in carbon forestry, and will cause
us to fail to meet our targets. This will cost the nation potentially billions
of dollars in purchases foreign carbon credits of dubious quality, and in lost
markets as other countries begin to sanction our lack of action.
Continued expansion of forests, particularly exotic ones, is
vital for us to reach our national targets.
Unharvested exotic carbon forests could be assured of
ultimate conversion to native by:
a.
Carefully selecting sites on which these forests
are established,
b.
Requiring owners of such forests to place a
portion of their carbon credit revenues in an escrow account to pay for any
management required for their conversion.
More accurate assessments of sequestration on small woodlots
would encourage farmers to establish carbon forests on small portions of their
farms and reduce the likelihood of whole-farm conversions to forest that are
currently causing such anguish in the agricultural sector.
Our emissions trading scheme ignores those responsible for
more than half of our gross GHG emissions.
The “emissions leakage” argument used to exempt most
greenhouse gas (GHG) emitters from the ETS does not work, because it requires
us to assume that:
a.
We are the most greenhouse gas (GHG)-efficient
producers of primary products
b.
Other countries will not seek lower their GHG
emissions;
c.
People will continue to purchase goods with a
high greenhouse gas footprint as the climate crisis worsens.
Moreover, actual studies of emissions leakage show that it
is a negligible problem. Therefore the NZ agricultural sector and other
trade-exposed industries, responsible for 57.5% of our gross GHG emissions, should
not use the “leakage argument” as a justification for their exemption from
purchasing NZUs.
The discussion document suggesting changes to the ETS fails
to make the case that forest-based carbon credits threaten reductions in gross
GHG emissions by overwhelming the carbon market with cheap credits. This case
relies on the assumption that the supply of credits will increase while the
demand for credits will remain small. However, making trade-exposed industries
and agriculture responsible for their emissions would greatly increase the
demand for credits, invalidating the argument that forest-based credits
necessarily threaten reductions in gross emissions.
The pathway to lowering gross emissions is to:
a.
Require everyone, including farmers and trade-exposed
industries to submit credits for the full amount of their greenhouse gas
emissions;
b.
Allow the price of carbon credits to rise to the
point where it is more cost-effective to lower emissions that to purchase
offsets;
c.
Stop auctioning carbon credits;
d.
Stop giving away credits.
The threat of carbon forestry to our high country farming
culture can be mitigated by making carbon lookup tables accurate and/or
allowing owners of carbon forests < 100 ha in extent to measure actual
carbon sequestration in their woodlots. This would encourage farmers to
establish their own small woodlots, reducing the incentive to convert whole
farms to forest and greatly increasing the profitability of hill country farms.
Background
Aotearoa has so far failed to make substantial progress in
its response to climate change, and proposed changes to rules for permanent
forest carbon sinks will further undermine progress in meeting our net GHG
emission commitments for 2030 and 2050. That our nation is one of the worst
greenhouse gas polluters is beyond doubt. Climate Action Tracker provides an
assessment of our performance and rates it as highly insufficient (Figure 1).
According to our Ministry for the Environment, Aotearoa
emits about 78 million tonnes of CO2-e annually . These are known as
“gross emissions”. In 2018 we emitted 16.9 tonnes of CO2-e per
capita. This level of emissions placed us 16th worst among all
countries,
and is far above both the Organisation for Economic Cooperation and Development
average of 10.83 and the global average of 6.45 tonnes of CO2-e per
capita.
Aotearoa has agreed to two international commitments.
Firstly, we have agreed to a “Nationally Determined Contribution (NDC) to keep
our net GHG emissions at 50% of gross 2005 emission levels
between 2021 and 2030. Secondly, and more importantly, we have pledged to get
our net emissions down to zero by 2050, with perhaps some exceptions for
methane emissions from agriculture.
Recent progress has been made by setting up a Climate Change
Commission, providing incentives to purchase electric vehicles, and attempting
to negotiate with farming lobbyists. In addition an emissions trading scheme
has been set up so that for a bit less than half the country’s emitters there
is a price on greenhouse gas emissions. The price recently rose to as high as
$85/tonne of CO2, leading to some investment in carbon (C) forestry,
among other things, and some concern from hill country farmers about whole-farm
conversions to C forestry. Conversion of
whole, mostly hill country farms, has become a political issue, prompting some
lobby groups to push for legal constraints on conversions. Typically these
concerns are about impacts of whole-farm C forests on hill country farming as a
way of life. The farming lobby has been joined by an anti-exotic species lobby
that questions what might happen to exotic C forests that remain unharvested
and would much prefer to see indigenous species in C forests.
Figure 1 – An assessment of our national performance at
climate change mitigation, available on-line at https://climateactiontracker.org/countries/new-zealand/
(Accessed on 14/4/22)
The role of forestry
Creating new forests is the most efficient way we
currently know of to extract CO2 from the atmosphere. Trees absorb solar
energy and create sugar from CO2 and water. Some of the created
sugar is used to provide energy for living functions, and some is stored for
longer periods in biomass. Typically half the dry-weight biomass in wood is
elemental C, and amounts of CO2 extracted from the atmosphere (“sequestered”)
by trees can be calculated by multiplying the mass of stored elemental C by
44/12.
New forests are called “sinks” for CO2 because
they extract far more CO2 from the atmosphere than they emit through
respiration, but forests do not remain sinks forever. The name “permanent
forest sink” can therefore be misleading for those who are unfamiliar with
forestry. Eventually forest sinks become simple carbon reservoirs. Those that
are repeatedly harvested and re-established typically retain about 60-70% of
their maximum C content at harvest in long-term average storage, while
unharvested forests eventually reach the point where they are emitting as much
CO2 through respiration and decay of dead biomass as they absorb. Their
long-term storage may be punctuated by small- and large-scale disturbances such
as wildfires or windthrow that reduce their average long-term storage just as
periodic harvesting can reduce average long-term storage.
Establishing new forest sinks to absorb GHGs we emit can
only, therefore, be a temporary solution, with additional new forest
sinks providing a cheap way to extract our GHG emissions from the atmosphere, achieving
net GHG neutrality while we develop ways to reduce our gross GHG emissions to
zero. If we wished to rely on forest sinks to achieve GHG neutrality on a
permanent basis then we would need an unlimited supply of unforested land on
which to establish new forests each year. This fact was clearly recognised by
authors of the “Globe” study, a multi-partisan, parliamentary-initiated study
designed to explore how Aotearoa could reach GHG net neutrality by 2050 (Vivid_Economics, 2017).
After extensively studying Aotearoa’s GHG-emitting and
forestry sectors, the authors of the Globe study stated that in their opinion
we could not reach net GHG neutrality by 2050 simply by reducing gross GHG
emissions to zero because new technologies had to be developed, and resistance
to rapid change would be strong. They recommended that new forest sinks be used
to fill the gap between what we wished to achieve by 2050 and what could realistically
be achieved by gross GHG emission reductions. This situation is clearly shown
in a graph that quantifies the gap in our accounts that we need to fill with sequestration
of CO2 by forest sinks while we reduce our gross emissions to zero (Evison & Mason, Forthcoming) (Figure 2).
Figure 2 – The Globe study’s “Innovative” scenario of gross
GHG emission reductions (red), the path Aotearoa has committed itself to for
net GHG emissions (green), and the gap in our national C accounts that needs to
be filled by forestry (blue dashed line) (Evison & Mason, Forthcoming). The graph and an accompanied
analysis of our options will soon be submitted to a peer-reviewed scientific
journal.
Reality is a bit more complicated than the situation
represented by Figure 2 because we have not consistently planted the same area
of new forests in Aotearoa each year. The last large-scale afforestation
programme occurred during the 1990s, and many of those forests will be
harvested in the 2020s, effectively reducing our carbon storage in forests, and
this needs to be taken into account if we wish to genuinely reach net GHG
neutrality by 2050. I’ll show that later, but for now let’s consider what
factors influence the rate of CO2 sequestration/hectare and the
maximum amounts of CO2-e storage in new forest sinks.
C sequestration by forests
Three factors overwhelmingly influence both rates on forest
sink sequestration and maximum storage in forest reservoirs. These three
factors are:
1.
The fertility, soils and climate on sites where
the forests are established;
2.
The species established on those sites; and
3.
The ways that forests are managed. We call this
management “silviculture”.
Impacts of site are easily illustrated, but are complicated
by the fact that, by definition, no forests are currently growing on candidate
sites for new sinks. We need to estimate potential productivity by examining
the impacts of soils and climate on tree physiology (Figure 3).
Such a map would be subtly different for each tree species,
because species differ in their responses to site conditions and pests.
If we ask which sites currently have no forest, and are not
prime farmland, i.e.: land use classes 5 and 6, we get a map like that shown in
Figure 4.
Rules for the national emissions trading scheme (ETS)
specify that forests planted on land that was unforested in 1990 can earn
carbon credits called New Zealand Units (NZU). One NZU is meant to represent 1
tonne of CO2 removed from the atmosphere as trees grow. Land areas
larger than 100 ha can be measured at various times and the tonnes of C stored
can be estimated. However, if a forest owner’s land area is less than 100 ha
then they are required to use default “lookup” table for sequestration. For
some species, such as radiata pine, the tables vary with region, but for others
there is simply one table. Tables tend to be conservative.
There is one lookup table for all native forests, which is a
simple Gompertz yield equation based on data from 52 sites that rises to an
asymptote of 445 t CO2-e/ha assuming no water deficit (Payton et al., 2010). Clearly this table has too low an asymptote for
many of the indigenous forests quoted in Table 1, and it was intended to be
used for young forests established after 1990. Almost all the 52 sites measured
contained manuka, kanuka and/or gorse with a few emergent native hardwoods.
Figure 3 – Megajoules/m2 of solar radiation (of
which ~50% is photosynthetically active) potentially useable by a species like
radiata pine over the 10 years between June 2008 and June 2018 across Aotearoa.
This geographical information system layer has approximately 3 million pixels,
each representing 9 ha. Green = more productive, and white = unsuitable. Scales
are NZTM eastings and northings.
Figure 4 – Areas in land use classes 5 and 6 that are
currently unforested, coloured by likely productivity as shown in Figure 3.
Estimates of forest CO2 sequestration rates and
storage per hectare vary widely (Table 1).
Table 1 – Example carbon dioxide sequestration rates and
storage by forests in Aotearoa. The first 10 entries were in natural stands,
while the other examples were in plantations. In some cases below-ground C was
considered while in others it was not.
Land cover
|
Sequestration
t CO2/ha/year
|
Storage
t CO2/ha
|
Below ground?
|
Reference
|
Native forest average
(from national vegetation survey)
|
|
525
|
No
|
(Hall,
2001)
|
Native woody scrub
|
|
128
|
No
|
(Tate
et al., 1997)
|
Manuka/kanuka shrub, ~25
years
|
10
|
238
|
No
|
(Scott
et al., 2000)
|
Manuka/kanuka shrub, ~35-55
years
|
|
554
|
No
|
(Scott
et al., 2000)
|
Manuka/kanuka shrub, 40
year span
|
7-9
|
|
Yes
|
(Trotter
et al., 2005)
|
Lowland native
podocarp-broadleaf forest
|
|
1238
|
No
|
(Tate
et al., 1997)
|
Mature beech-podocarp
forest
|
|
1287
|
No
|
(Beets,
1980)
|
Mature beech-podocarp
forest
|
|
1290
|
No
|
(Tate
et al., 1997)
|
Hard beech forest
|
|
1172
|
No
|
(Tate
et al., 1997)
|
Mountain beech forest
|
|
938
|
No
|
(Tate
et al., 1997)
|
Kauri, Northland, aged 67,
492 stems/ha
|
13.8
|
926
|
|
(Kimberley
et al., 2014)
|
Kauri, Fred Cowling
Reserve, aged 38, 1402 stems/ha
|
10.9
|
413
|
|
(Kimberley
et al., 2014)
|
Kauri, Fred Cowling
Reserve, aged 51, 11256 stems/ha
|
12
|
614
|
|
(Kimberley
et al., 2014)
|
Kauri, Fred Cowling
Reserve, aged 69, 1325 stems/ha
|
18.9
|
1306
|
|
(Kimberley
et al., 2014)
|
Kauri, Taranaki,
Brooklands Park, aged 50, 630 stems/ha
|
13.3
|
663
|
|
(Kimberley
et al., 2014)
|
Kauri, Taranaki, Brooklands
Park, aged 71, 630 stems/ha
|
14.5
|
1027
|
|
(Kimberley
et al., 2014)
|
Kauri, Taranaki,
Brooklands Park, aged 83, 630 stems/ha
|
13.4
|
1116
|
|
(Kimberley
et al., 2014)
|
Kauri, Hawkes Bay, aged 48,
1700 stems/ha
|
20.1
|
966
|
|
(Kimberley
et al., 2014)
|
Kauri, Northland, aged 36,
650 stems/ha
|
10.9
|
393
|
|
(Kimberley
et al., 2014)
|
Totara, Northland, aged
102, 1225 stems/ha
|
17.4
|
1770
|
|
(Kimberley
et al., 2014)
|
Totara, Northland, aged
102, 1825 stems/ha
|
13.3
|
1357
|
|
(Kimberley
et al., 2014)
|
Totara, Northland, aged 58,
816 stems/ha
|
6.5
|
376
|
|
(Kimberley
et al., 2014)
|
Totara, Hawkes Bay, aged
48, 1975 stems/ha
|
8
|
382
|
|
(Kimberley
et al., 2014)
|
Totara, Waikato, aged 30,
2831 stems/ha
|
6.1
|
182
|
|
(Kimberley
et al., 2014)
|
Kahikatea, Waikato, aged
30, 2831 stems/ha
|
9.6
|
289
|
|
(Kimberley
et al., 2014)
|
Puriri, Bay of Plenty, aged
69, 588 stems/ha
|
15.2
|
1046
|
|
(Kimberley
et al., 2014)
|
Red Beech, Waikato, aged
16, 738 stems/ha
|
9.2
|
147
|
|
(Kimberley
et al., 2014)
|
Red Beech, Southland, aged
14, 1579 stems/ha
|
6.2
|
87
|
|
(Kimberley
et al., 2014)
|
Black beech, Southland,
aged 14, 1508 stems/ha
|
7
|
98
|
|
(Kimberley
et al., 2014)
|
Pasture without grazing
|
|
11
|
Yes
|
(Ford-Robertson
et al., 1999)
|
Pruned radiata pine on a
good site, 400 stems/ha (modelled), average over three 28 year rotations
|
|
814
|
Yes
|
(Ford-Robertson
et al., 1999)
|
Pruned radiata pine on a
poor site,
250 stems/ha (modelled),
average over three 28 year rotations
|
|
550
|
Yes
|
(Ford-Robertson
et al., 1999)
|
Pruned radiata pine, 250
stems/ha to age 28 Central North Island (modelled)
|
33
|
918
|
Yes
|
(Robertson
et al., 2004)
|
Untended radiata pine, aged
15, 2500 stems/ha, site index=23
|
38
|
571
|
Yes
|
(Yallop,
2021)
|
Untended radiata pine,
aged 15, 1250 stems/ha, site index=23
|
34
|
514
|
Yes
|
(Yallop,
2021)
|
Untended radiata pine, aged
15, 625 stems/ha, site index=23
|
27
|
401
|
Yes
|
(Yallop,
2021)
|
Paula Yarur Thys (2021)
measured C storage in planted native forest stands on Banks Peninsula, Canterbury
up to 59 years after planting, and compared their C storage to those estimated
by the lookup table assuming a water deficit (Figure 5). She found that data
were highly variable, that they more or less agreed with the lookup table for
young stands, but older stands had C storage exceeding that shown in the table.
Moreover, a nationwide survey by Beets et al. (2009)
demonstrated that many natural stands exceeded the asymptote in the lookup
table (Figure 6).
Figure 5 – Measured CO2-e storage (blue triangles) versus
age, and the Ministry for Primary Industry’s carbon sequestration lookup table
for native forests on dry sites in Canterbury (red line).
Figure 6 – C storage in Aotearoa’s native forests estimated
by Beets et al. (2009)
Kimberley et al. (2021)
reported some new observations of sequestration rates in plantations of native
species, including a number from Kimberley et al. (2014),
but some from 2014 appear to be missing from the 2021 graph and so I have added
them (Figure 7). Some of the implied sequestration rates they found are quite high
for native species, and so this is encouraging. However, as sequestration rates
vary also with site and stand management, I asked where their plots were in the
landscape and how the stands were managed. Mark Kimberley replied, “They are
scattered across the country, more in the North Island than South Island.” He
also assured me that full details will be provided when a paper is prepared for
peer review. If these plots were repeatedly measured then families of curves
might be fitted in order to represent sequestration rates and carbon storage on
a wide range of sites and stand management practices. It is difficult to judge how
the reported rates might apply across the range of sites available for carbon
forestry in the absence of detailed plot information, and repeated measures
would provide us with a more realistic appraisal of variation in sequestration
rates. For reference, on a roughly average site (site index=32 m in the central
North Island) radiata pine planted at 800 stems/ha and then thinned to 500
stems/ha can reach 1000 tonnes CO2-e/ha in about 25 years.
Figure 7 – Estimates of CO2-e storage in kauri and totara
plantations on a range of sites at a range of stems/ha Kimberley et al. (2021)
(triangles) and some extra points from Kimberley et al. (2014)
(circles). Lines are fitted to the 2021 data.
Radiata pine sequestration rates can be estimated by using
growth and yield models of stem dimensions combined with a carbon estimation
model called C_CHANGE (Beets et al., 1999) or by applying individual tree biomass models (Moore, 2010)
to stem measurements in tree lists from inventories. Thousands of permanent
sample plots are available for the construction of growth and yield models, and
thousands of inventory plots are established in Aotearoa’s plantations each
year. A small number of very large trees have been assessed for biomass,
however, which limits the applicability of C_CHANGE and Moore’s biomass models.
Growth and yield measurements of stems are more sparse for other species, and
comprehensive biomass data are rarely available.
Lookup tables for exotic species may greatly underestimate
actual sequestration and storage. A study undertaken in a 7.5 ha experiment at
Rolleston, Canterbury, across a range of stems/ha, combined with destructive
harvesting of 476 local trees for biomass estimation showed that the Canterbury
lookup table underestimated CO2 sequestration of radiata pine by up
to 63% (Yallop, 2021)
(Figure 8). For reference, this site has a very low site index of 23, and site
indices over 40 have been recorded in other parts of Aotearoa. A study at the
School of Forestry, University of Canterbury, examined how assessed
sequestration rates compared with lookup table rates on a wider range of sites
and with a wider range of stand management practices and found that lookup tables
frequently under-estimated our best estimates of actual sequestration (Nish, 2022).
Figure 8 – C sequestration and storage by radiata pine over
15 years at 2500, 1250, and 625 stems/ha and with two levels of weed
competition control: 2 years (N) versus 4 years (H) on a poor site in
Canterbury (Site index=23) compared to the Ministry for Primary Industry’s
default carbon sequestration lookup table for Canterbury (in purple) (Yallop, 2021).
In summary, forest sequestration rates and carbon storage
vary with site quality, species, and stand management. Sequestration rates in
highly stocked stands of some native species on highly productive sites might
approach 2/3 of those observed in radiata pine stands at lower stockings on
average sites, but in many cases sequestration rates and maximum storage of C
in native forests appears to be much lower than that achieved by our most rapidly-growing
exotics. Moreover, native plantations appear to take longer to reach their
highest rates of sequestration. Lookup tables for exotic species may be very
conservative, and those for native forests need to be more diverse, reflecting
the wide range of sequestration rates and storage values recorded in plots. The
lookup table for natives may be roughly right for some shrubs such as manuka
& kanuka or young stands of trees, but the level of maximum storage (the
asymptote) clearly underestimates what has been observed in some older, high
forest stands.
The case for exotic tree species
Many imported species grow and
sequester CO2 much more rapidly than native species within the time
frames required to meet our 2050 target. Radiata pine has been chosen as an
example for the following reasons (although other species such as dryland
eucalypts or redwoods might do the job equally well or even better in some
cases):
1) It grows rapidly and sequesters C at a much
higher rate than native species. Between 2008 and 2012, our national carbon
accounts indicate that radiata pine planted after 1990 sequestered at an
average rate of 34 tonnes of CO2-e/ha/year, and rates might be even
higher with silvicultural regimes aimed at maximising value from sequestered
carbon credits. By contrast, estimated rates of sequestration for native
species are often below 10 tonnes of CO2-e/ha/year during the years
immediately following forest establishment (Scott et al., 2000; Trotter et al., 2005), and the slower development
of young native stands would mean that they would take longer to begin
effective sequestration. In older indigenous stand higher rates have been
reported on some sites, but not at the rates typical of radiata pine. To be fair,
studies of native forest sequestration are sparse, as outlined in the previous
section, but we can also get an idea of relative sequestration rates by
comparing the more numerous reports of growth rates of stems of various species
(Pardy et al., 1992; Silvester & McGowan, 1999), and native species often
take 3-4 times longer to reach equivalent stem volumes of radiata pine
plantations at harvest even at higher stockings.
2)
We are experts at producing seedlings for exotic
species and they are cheap.
3)
Radiata pine will grow on a wide range of sites
and we understand how to establish it on diverse sites, despite its sensitivity
to shade and frost.
4)
Radiata pine is not a high country wilding risk (Ledgard, 2008). It is
very intolerant of both shade and frost, and would only seed naturally on moist
lowland areas (Dickson et al., 2000) where adjacent land was not
intensively grazed (Beneke, 1967; Douglas, 1970; Ledgard, 1994)
(which is a relatively rare condition in New Zealand). Our wilding species are
commonly other, more hardy imports, such a P.
contorta, P. ponderosa, P. nigra and Douglas fir (Ledgard, 1994, 2001; Ledgard, 2008).
These wilding risk species should be avoided in carbon forests. Relative to these other species and areas of
plantation, radiata pine is only rarely a wilding, and this is on lowland, ungrazed
sites.
5)
On warm, moist sites (either medium or high
productivity categories), exotics can act as a nurse crop for native forest,
and the C reservoirs we establish would ultimately change to become native
forest so long as seed sources were available in the local vicinity (Figure 9).
Understoreys of native vegetation are common in plantations on such sites (Brockerhoff et al., 2003; Ogden et al., 1997). This issue has been much
studied by a PhD graduate from the School of forestry named Adam Forbes (Forbes et al., 2015a, 2015b, 2016).
In order for native forest to regenerate under pines local native seed sources
are essential.
6)
Studies suggest that radiata pine will continue
to sequester carbon for at least 100 years on some sites (Woollons & Manley, 2012). This means that exotic forests could remain
as sinks for some considerable time.
Afforestation with exotics and
conversion to native forest
I love our ngahere, and I would be
delighted to be able to recommend that all our carbon forests should comprise
native species, but unfortunately afforestation with native species is very
expensive, and the sequestration rates of native species are not only lower
than those of cheap exotics, but they take decades longer to reach appreciable rates
even on some of the best sites and at high stockings (Figure 7 and Table 1).
Figure 9 - Forest biomass dynamics
after introducing the exotic pine species Pinus
radiata to the native species pool. Dynamics are modeled for a site near
Christchurch, New Zealand. Species aboveground biomass is cumulative. "Kunzea and Leptospermum" include the early colonizing species K. ericoides and L. scoparium. "Others" include the species Griselinia lit- toralis, Pittosporum
eugenioides, Aristotelia serrata, Elaeocarpus hookerianus, Fuchsia ex-
corticata, Nothofagus fusca, and N.
solandri var. solandri Figure from Hall (2001).
Most of our imported, exotic
forest plantation species are pioneer species, intolerant of shade, and
although they can be regenerated under a canopy, the canopy needs to be
exceptionally sparse before any appreciable amount of regeneration to occur.
Figure 10 shows how sparse the canopy was after an attempt at continuous cover
forestry with radiata pine in the foothills of Canterbury.
It therefore makes sense to
consider the option of planting exotics in permanent C forests and then
converting them to native forests once the exotics have completed their task of
filling the gap in our national C accounts that is critical over the next few
decades.
Establishment of native species in
some areas of our exotic plantation forests occurs with no intervention as a
transition from mostly exotic weeds in young stands to increasingly native
species in old stands (Brockerhoff et al., 2003; Ogden et al., 1997), but as noted by Forbes &
Norton (2021),
this process is not guaranteed to occur in all stands. Proximity to seed
sources, extent of small scale disturbance, lack of a moisture deficit and
fertility may all promote an indigenous understorey (Figure 11).
Figure 10 – An attempt at
continuous cover forest regeneration using radiata pine at Woodside Forest,
Canterbury. Natural regeneration was achieved when the overstorey canopy had
been reduced enough through harvesting to allow a light-demanding species to
prosper.
Figure 11 – A radiata pine stand
in Maramarua Forest was a nurse crop for a vigorous native understorey on the
lower slopes where fertility was high (left), but lacked an understorey on a
less fertile hill top (right).
Figure 12 – Regeneration of native
understorey under a mixed species overstorey at Milnthorpe Park, Golden Bay.
Much of the regeneration is natural, but in some cases podocarps have been
deliberately planted.
Figure 13 – Natural regeneration
and planted natives under an exotic plantation (Credit: Dr Adam Forbes)
Figure 14 – A canopy gap in a
highly stocked radiata pine plantation created to initiate natural regeneration
(Credit: Dr Adam Forbes)
Figure 15 – Regeneration in a
created canopy gap (Credit: Dr Adam Forbes)
Figure 16 – A mixed stand of
exotics and a vigorous native understorey (Credit: Dr Adam Forbes)
Figure 17 – Native plants growing
under a radiata pine stand (Credit: Jeff Tombleson)
Figure 18 – Native plants growing
under a mature radiata pine overstorey at low elevation in the Bay of Plenty
There are several examples of
stands in transition from exotic species to native species (Forbes et al., 2015a, 2015b, 2016).
In some cases these stands required intervention, such as the creation of gaps,
or even direct planting of native species. Moreover, pest control and long-term
monitoring are vital.
For examples of where native
forest regeneration under exotics has been initiated, see Figures 12-15.
Figures 16-18 show examples where native vegetation has naturally regenerated
under exotic canopies. Figure 19, from Brockerhoff et al. (2001),
shows general trends in composition under repeatedly harvested pine canopies on
warm, wet sites.
Figure 19 – Trends in biodiversity
in repeatedly harvested radiata pine plantations on warm, wet sites (Brockerhoff et al., 2001)
Regeneration under gorse suggests
that in some instances species composition may not be the same as that in
stands that would have regenerated under native pioneer species such as manuka
and kanuka, according to Forbes & Norton (2021).
Forbes & Norton (2021)
recommend adaptive management in order to ensure that the transition takes
place, and also outline research that is required should we choose this path.
In summary, transitioning from
rapidly-growing exotic C forests to slower-growing indigenous ones is feasible
on some, but not all, sites. Warm, wet, fertile sites close to native seed
sources are the best prospects, and research is required to more clearly
identify where such an approach may be successful. There should be no such
thing as “plant and leave” in any C forest, either exotic or native, and
monitoring combined with adaptive management and in some cases a commitment to
active intervention to meet long-term objectives should be mandatory. Pest
control is vital in all C forests, whether exotic or native.
Filling the gap in our national
C accounts
The proper role of forests in
mitigating climate change is to act as sinks while we change our emissions
behaviour, thus implementing a planting programme to sequester, on an annual
basis, the gap shown in the blue triangle of Figure 2. We have developed
software to perform a national estate-level simulation of sequestration
resulting from various planting programmes, assuming that the planting was
equally likely to be in any of the LUC classes 6 and 7 areas that were “Kyoto
compliant” as shown in Figure 4. In previous versions of this analysis we
assumed that the last period of rapid new forest establishment, during the
1990s, was more or less on a long-term average trajectory, with periods of
emission at times of harvests followed by periods of sequestration by
re-established crops. However, this assumption is a bit unrealistic because the
period of rapid expansion in our plantation forest estate lasted little more
than a decade, and it was followed by a long period with almost no new
afforestation. The effect of this planting programme, compared to required
sequestration is shown in Figure 20.
Figure 20 – The effect of new
plantation forest establishment on annual emissions (negative) or sequestration
(positive) are shown in red, while the triangle initially estimated as required
annual sequestration is shown in blue. Scenario 1 is where we wish to get to GHG
neutrality by 1990
The consequence of our planting
during the 1990s are that the actual requirement on an annual basis is somewhat
more complicated (Figure 21).
Figure 21 – The blue triangle
(Figure 2) of required annual sequestration to reach GHG neutrality by 2050 is
somewhat more complicated after taking into account impacts of new forest
establishment between 1990 and 2021
As harvest ages of radiata pine
plantations are often between 25 and 30 years after planting, a period of rapid
afforestation during the 1990s followed by little new forest planting since
creates a deep deficit in our accounts during the 2020s that is difficult to
fill with new planting. Even radiata pine takes 4-5 years to appreciably begin
to sequester CO2, and so the best we can do is devise a planting
programme that is reasonably realistic to sequester the amount required between
2022 and 2082, while allowing for some initial swapping of amounts between
adjacent decades (Figure 22). The structural regime that fills the gap in our
accounts would require about 2.16 million ha of new forest, with a planting programme
is shown in Figure 23.
Tentative analyses suggest that as
little as 1 million hectares of unharvested exotic forests might be required.
A similar analysis for unharvested
native C forests is difficult to perform in detail until we get a clearer idea
of impacts of species, site quality and stand management on sequestration
rates, but tentative analyses using current data suggest that the area required
would be at least double the area required for structural regimes of radiata
pine to do the job, and possibly much more. Moreover, native species take much
longer than rapidly-growing exotic species to begin to sequester large amounts
of CO2, and so we would need extremely large areas established
during the next decade in order to make any worthwhile impact on our 2050 GHG
neutrality target. This disadvantage is even more problematic for native
species that are regenerated naturally. We shall do an analysis in detail once
plot locations providing estimates of native forest C sequestration are
publicly revealed.
Figure 22 – Sequestration from a
proposed planting programme on “Kyoto compliant” LUC classes 6 and 7 land of a
structural regime for radiata pine (brown) versus the gap in our national
carbon accounts after accounting for 1990-2021 plantings (blue)
Figure 23 – New exotic forest planting
programme for to fill the gap in our national C accounts
Such a programme is feasible, but
not necessarily on all the land shown in Figure 4. Many areas are too remote,
too erosion-prone, or too small to make harvesting environmentally safe and
worthwhile. This is particularly true of Maori tribal lands and hill-country
farmland whose profitability could be greatly enhanced by carbon forestry.
Permanent carbon forests are a much better solution for those areas. Moreover,
the area of unharvested carbon forest required to fill the gap in our carbon
accounts would be much smaller, because exotic species typically continue to
sequester CO2 at a rapid rate for many decades after typical
rotation ages for wood harvests.
Costs of afforestation
Costs of new forest planting vary
with species, seedling type, sites, site management activities, and stems/ha
established.
The cheapest option is likely to
be radiata pine, as seedling costs are usually 50 cents per tree, 800 to 1000
stems/ha is typical, planting stock is usually bare-rooted, and trees grow
rapidly enough that management of weeds is not required for long. Eucalypts are
a bit more expensive, because although bare-root seedling technology has been
developed for eucalypts, they are most often delivered as containerised stock,
at up to $1/plant in bulk. Planting into pasture is inexpensive, with often as
little as a year of spot weed control often required for effective survival
after planting and rapid initial growth. Under such circumstances plantation
establishment can cost less than $1500/ha, but this can rise if control of high
densities of woody weeds, soil cultivation, or fertilisation are required.
Adam Forbes (2022)
conducted a survey of native forest restoration costs. Plants are generally
delivered as containerised stock and costs ranged from $0.6-10 per plant.
Overall costs per hectare varied widely, but averaged just over $7000/ha. Many
forestry consultants regards this average as a low estimate. Bare-root seedling
systems were developed for many native species by the Forest Service, but these
technologies are rarely used today. Technology for seed collection and storage
requires more development, and there appears to be scope to make establishment
of native plants much more efficient.
The flawed ”emissions leakage”
argument
The “emissions leakage” argument
states that if we reduce GHG emissions in New Zealand by lowering production of
GHG emitting industries then this will result in an increase in global
emissions because production will increase in other, less GHG-efficient
producers in other countries. Three critical assumptions of this argument are
questionable.
a. The assumption that we are the most
GHG-efficient producers is sometimes supported by New Zealand studies and
widely trumpeted in New Zealand media, but studies elsewhere do not necessarily
agree. For instance, Wirsinius et al. (2020)
identify Denmark, France, Germany, Netherlands, Spain, and Sweden as countries
that have lower CO2-e emissions per kilogram of milk than New
Zealand does.
b. The assumption that other countries will not
seek to reduce emissions and simply allow expansions of their GHG emitting
sectors if we reduce ours is also questionable. As the climate crisis deepens
people will become increasingly reluctant to purchase products that have a high
GHG emission footprints, and governments are likely to place restrictions on
those products, such as border carbon adjustments (Branger & Quirion, 2014).
c. The assumption that international trading
partners will ignore our GHG pollution is unlikely to be tenable as the climate
crisis worsens.
Some analysts suggest that leakage
may be absent or even negative with technology spillovers, and in a meta study
of carbon leakage ratio (the increase in GHG emissions elsewhere divided by the
reductions in a country with stringent GHG reduction policies) rates of leakage
were found to be relatively modest, from 5-25% (Branger & Quirion, 2014). This means that reductions
in GHG emissions from New Zealand’s agricultural sector would still be
beneficial for the environment.
Response to questions in
chapter 2 of the discussion document
I agree that we ultimately need to
reduce gross GHG emissions to near zero. Forests can only be temporary carbon
sinks, allowing us time to make other changes that will reduce gross emissions.
However, as shown by the Globe study (Vivid_Economics, 2017), we cannot reduce our gross
emissions rapidly enough to meet our 2050 net GHG zero target, and exotic
carbon forests are vital tools for filling the gap in our accounts, as shown
above. Native forests are too expensive, take too long to establish, and also
sequester CO2 much more slowly than exotic forests, hence greatly
reducing their cost:effectiveness as a means to fill the gap in our national
carbon accounts.
I do not agree with the assessment
of the threat posed by exotic carbon forests to our gross emission reduction
objective. Writers of the discussion document assume that the supply of NZUs
will increase while the demand for them remains small, while overlooking the
requirement for us to greatly increase the demand for NZUs.
Using the flawed “leakage
argument” as an excuse, we exempt agriculture, which emits 49% of our national
gross GHG emissions (MfE, 2023),
as well as gifting 6.5 million NZUs (8.5% of our total gross emissions) to
trade exposed industries. If these polluting sectors were required to purchase
NZUs then the demand would greatly increase, and the impact of forest-based
credits on the NZU price would be much less. Moreover, changes to the
assessment of sequestration on small woodlots less than 100 ha would further
reduce the impact.
As outlined above, small woodlots
are required to use lookup tables for calculating C sequestration that in the
case of exotic species often greatly underestimate C actually sequestered in
woodlots. This motivates people to purchase whole farms in order to establish
larger C forests, driving up land values in the hill country and threatening
hill country communities based on pastoralism. Returns from pastoralism in our
hill country are small, and so large-scale conversions to forest do not
threaten our economy, but they do threaten hill-country culture. If farmers
could earn more from small C woodlots then whole-farm conversions would be less
frequent, farms with small woodlots would be more profitable, and the ETS would
become more popular in these communities.
So, we need much more new forest
than we currently have in order to get to our 2050 net zero target, and instead
of regarding forests as a threat we should welcome their contribution, we can
and should afforest differently, though, encouraging small woodlots on farms,
with ultimate conversion to native forest as a long-term objective. More
realistic estimates of sequestration rates in small woodlots and also entry
into the ETS of agriculture and trade-exposed industries would get us there.
Response to questions in
chapter 3 of the discussion document
The Globe study (Vivid_Economics, 2017) made it clear that we need
removals of CO2 with forest sinks in order to meet our 2050 target.
Response to questions in
chapter 5 of the discussion document
Both gross emission reductions and
GHG removals are important, because new forests are only temporary sinks, and
ultimately reducing emissions is the only sustainable option. However, we can’t
immediately get to zero gross emissions and our 2050 target must be partly met
by removals. Currently it is often cheaper to pay for removals than make
reductions, but that is with 57.5% of emitters not participating in the ETS and
small woodlots poorly rewarded for sequestration.
Response to chapter 6 of the
discussion document
The status quo is not working
well. Most of our emitters aren’t even in the ETS, auctioned credits are
essentially fraudulent, sector lobby groups have far too much political
influence, and the price of credits fluctuates to the point where most money is
made via speculation in the ETS rather than by actually helping to mitigate
climate change.
Option 1 is partly sound. The
government should not auction credits.
Option 2 is deeply flawed. The
last time we allowed emitters to purchase international credits our NZU price
dropped to $3, and people still hoarded them because international credits were
available for as little at 10 cents each. This policy created the credit
hoarding problem we now face. Moreover, in the unlikely event that purchased
international credits were not fraudulent, we would be paying other people to
make changes in emission behaviour that ultimately we will have to make
ourselves.
Option 3 would distort an already
deeply distorted ETS. We already pay polluters to pollute by giving them free
allocations or auctioning credits at low prices, when really the only people
awarded credits should be those sequestering C. Credits that do not represent
anyone cleaning up GHG emissions are the largest threat to our ETS market and
credit price (See appendix 2). Credits for reduction activities should not
exist. The reward for reducing pollution should be that the former polluter no
longer has to purchase credits.
Option 4 is fundamentally
irrational. The government proposes to allow people who purchased fraudulent
credits or who were simply gifted fraudulent credits due to an irrational fear
of leakage to sell their right to pollute while those actually removing
pollution from the atmosphere would face a hugely restricted market and lower
credit price. This is fundamentally unfair.
The government’s suggested changes
to policy are potentially damaging over-reactions that are unsupported by what
we currently know about sequestration rates of native & exotic forests and
the potential to convert exotic C forests to native forests after they have
served their purpose as rapid carbon sinks. They have already sent shivers
through the forestry sector and undermined attempts to create forests to fill a
well-known gap in our national C accounts, meaning that we may face billions of
dollars in foreign credit purchases in future without changing our behaviour
substantially.
Response to chapter 7 of the
discussion document
7.1 Should co-benefits be
recognised in the value or quantity of carbon credits awarded for
afforestation?
Making a change such as this would
further distort the ETS, and the idea of “greenhouse gas neutrality”, so vital
to the credit market, would become even less tenable. By all means put more
money into increasing indigenous biodiversity, but don’t pretend that it
sequesters more C than it actually does.
7.3 Should a wider range of
removals be recognised?
All verifiable C sinks should be
included in the ETS.
Comments on C forestry
Whole-farm conversions
It has been suggested that
whole-farm conversions to carbon forests are a threat to vital export
industries, but this is not so. This would be true if conversions were of dairy
farms, but almost all carbon forests are established on hill country farms,
usually land use capability classes 5 or 6, and on such land farming makes very
small returns on investments even in good years. We need to recognise that such
conversions are not threatening our economy, but instead they are perceived as
a threat to a way of life. They are a social problem, not an economic one.
We should therefore seek to enable
farmers to establish carbon forests on small portions of their farms.
Under-estimates of sequestration
rates in MPI’s lookup tables provide an incentive for whole-farm conversions
because areas of C forest greater than 100 ha allow land owners to avoid using
low lookup table rates. It is therefore vital that lookup tables for all
species be made more accurate across a range of species, sites, and stand
management activities. An alternative would be to develop cheap assessment
strategies, such as LiDAR, to rapidly assess biomass in small woodlots so that
farmers might gain the full value of the carbon they sequester. This change
would make small C forest woodlots on small portions of farms more financially
viable.
Given weaknesses of the underlying
assumptions and results from empirical studies, use of the leakage argument in
New Zealand as a justification for doing nothing in some sectors cannot be
justified.
Exotic versus native species
As outlined above, exotic species
generally sequester at much more rapid rates than native forests on the same
sites, given similar management, and exotics are currently far cheaper to plant
than native forests. Natural regeneration of native forests is feasible but
usually takes far too long to be of use during the critical stage when we
require forests sinks to fill the gap in our carbon accounts.
If we proposed to fill the gap in
our national C accounts with unharvested exotics we would probably need as
little as 1 million ha of new forest.
Instead of restricting species choice to slower, more expensive native carbon
sinks, the government could reduce the likelihood of unwanted outcomes by
requiring that all “permanent forest carbon sink” establishment proposals, for
both native and exotic forests, be accompanied by a comprehensive plan,
outlining:
1.
The long-term future envisioned for the forest
2.
A monitoring plan
3.
An adaptive management plan
4.
A plan for pest control
5.
A plan for financial support of stand management
and required research
The plan should be a binding
agreement between land owners and the crown. The requirement for approved
management plans for harvesting of native forests on private land is a
precedent for this kind of policy.
If we filled the gap with
periodically harvested exotics we would need about 1.75 million ha of new
forest, and the future of that forest would be to provide extra value to our
economy via increased exports of wood products. We should, however, be mindful
that not all sites are suitable for production forestry with exotics, and these
new forests should only be permitted in suitable land, where harvesting and
re-establishment will not pose a risk of erosion and slash movement during
cyclones.
Estimates of the area required to
fill the gap with native species, allowing for the types of land available, are
problematic because we cannot simply say native species might ultimately
sequester at half the rate of our fastest growing exotics, therefore we need
twice the area, because native trees take a long time to establish, and our
target year for greenhouse gas neutrality is only 27 years away. A very
conservative estimate suggests that we might need approximately 3 million ha of
planted, unharvested native forest on hill country land to fill the gap. This
option would be extremely expensive and the required area may be even greater
than our optimistic projections.
Some alternative proposals
It is clear that with appropriate
planning we can record our current trajectories and plan required pathways to
get to our 2050 target and beyond (for instance see Figure 21 above). At present we are doing far too little to
address climate change because:
1.
we give away or auction too many fraudulent
credits;
2.
more than half of our GHG emitters do not have
to pay for polluting;
3.
our lookup tables of sequestration rates for
species, sites and silvicultural management are extremely inaccurate for small
woodlots. We therefore incentivise mainly large blocks of C forest and deny
farmers the opportunity to profit fully from small blocks of trees while they
continue to farm;
4.
we use a highly questionable rationale to
continue polluting that we call “leakage” despite the fact that it is based on
faulty assumptions and that international evidence suggests it is not a serious
problem even for leakage to third world countries that have few, if any,
international climate change mitigation commitments;
5.
we make knee-jerk changes to the ETS that
further complicate it and often water down the effectiveness of the scheme,
resulting in wild fluctuations in credit prices.
The most obvious improvements in
the ETS, consistent with its original intent, would be to:
1.
stop creating fraudulent credits and auctioning
them;
2.
stop giving credits away for allowed pollution
under the highly questionable justification of “leakage”;
3.
bring all greenhouse gas emitters into the
scheme on an equal basis;
4.
enable realistic rewards for sequestration with
woodlots < 100 ha;
5.
require C foresters to lodge a plan for the
long-term future of their C forests, and if necessary, set aside funding to pay
for future management.
Such measures would greatly
restrict the supply of NZUs while increasing demand, providing an incentive for
people to reduce emissions rather than purchase credits.
Appendix 1: Research required
Several avenues for research can
improve our knowledge and allow us to make better policy decisions:
1.
We need to be able to predict with more
certainty where exotic species can act as effective nurse crops, and also to
understand where this might happen naturally, and where more costly
intervention is required to make it happen.
2.
We need much better estimates of how rates of C
sequestration are influenced by species choice, sites and silviculture for both
exotic and native species, and lookup tables need to be more realistic.
3.
We need to work to make growth of native
seedlings in nurseries more efficient, and to improve survival and growth after
planting them.
4.
We need to more clearly delineate sites where
debris flows after harvesting will be a problem, and implement technologies to
ensure that they do not occur.
Appendix 2: Why auctioned and
gifted credits are irrational
In a well-functioning emissions
trading scheme, polluters would have to submit credits in order to be allowed
to pollute, and they would purchase credits from those who cleaned up their
pollution. So if the cost of cleaning was higher than the cost of reducing
pollution in the first place then they'd choose to reduce emissions. Either way
the atmosphere would not receive any more GHGs and purchasers of carbon credits
could rightly call themselves "greenhouse gas neutral".
However, that's not what's happening. If a polluter reduces their
pollution then they can sell credits gifted to them for their “allowed”
pollution because of an irrational fear of “leakage”, or that they have
purchased in an auction where fraudulent credits are simply made from thin air
and don’t represent anyone cleaning up the atmosphere. They also assert that
purchasers of their credits can claim to be "greenhouse gas neutral".
They are wrong.
There are many ways to explain why they are wrong. You could use stories,
mathematics, graphs or even children's blocks. Let's use the latter.
Blocks below represent levels of greenhouse gas in the atmosphere and levels
planned to be emitted by two polluters.
Figure 1
Then polluter 2 opts to no longer pollute and has grandfathered carbon credits
for sale. Polluter 1 purchases those credits and is allowed to pollute. The
result is more greenhouse gas in the atmosphere, as shown below. Polluter
1 clearly cannot claim to be "greenhouse gas neutral".
Figure 2
So, what kinds of credits can confer greenhouse gas neutrality on a purchaser?
Let's reach for the blocks again. In this case, we have the atmosphere, a
potential polluter and someone who will take greenhouse gas from the atmosphere
(maybe using new trees, a scrubber, or perhaps by seeding the ocean with iron
to promote plankton); a sequesterer.
Figure 3
The sequesterer receives carbon credits for removing greenhouse gasses from the
atmosphere. They are purchased by the polluter, who then goes ahead and
pollutes, but the amount of pollution is exactly equal to the amount of
sequestration and so the result is shown below:
Figure 4
Clearly, the atmosphere gains no new greenhouse gas and the polluter can now
claim to be greenhouse gas neutral.
It is generally much cheaper to do nothing than to extract greenhouse gasses
from the atmosphere. If we allow people to sell carbon credits for simply
reducing outputs of greenhouse gas, we effectively pay them for nothing because
their reward for reducing emissions should be that they no longer have to
purchase credits.
Our current scheme is essentially irrational with respect to gifted and
auctioned credits.
References
Beets, P.,
Robertson, K. A., Ford-Robertson, J. B., Gordon, J., & Maclaren, J. P.
(1999). Description and validation of c_change: A model for simulating carbon
content in managed Pinus radiata
stands. New Zealand Journal of Forestry
Science, 29(3), 409-427.
Beets, P. N.
(1980). Amount and distribution of dry matter in a mature beech/podocarp community.
New Zealand Journal of Forestry Science,
10(2), 395-418.
Beets, P. N.,
Kimberley, M. O., Goulding, C. J., Garret, L. G., & Paul, T. S. H. (2009). Natural forest plot data analysis: carbon
stock analyses and remeasurement strategy. Ministry for the Environment.
Beneke, U. (1967).
The weed potential of lodgepole pine. New
Zealand Grasslands and Mountain Lands Review, 13(September), 37-44.
Branger, F., &
Quirion, P. (2014). Would border carbon adjustments prevent carbon leakage and
heavy industry competitiveness losses? Insights from a meta-analysis of recent
economic studies. Ecological Economics,
99, 29-39.
Brockerhoff, E.
G., Ecroyd, C. E., & Langer, E. R. (2001). Biodiversity in New Zealand
plantation forests: policy trends, incentives, and the state of our knowledge. New Zealand Journal of Forestry, 46(1),
31-37.
Brockerhoff, E.
G., Ecroyd, C. E., Leckie, A. C., & Kimberley, M. O. (2003). Diversity and
succession of adventive and indigenous vascular understorey plants in Pinus
radiata plantation forests in New Zealand. Forest
Ecology and Management, 185(3), 307-326.
Dickson, R. L.,
Sweet, G. B., & Mitchell, N. D. (2000). Predicting Pinus radiata female
strobilus production for seed orchard site selection in New Zealand. Forest Ecology and Management, 133(3),
197-215.
Douglas, J. A.
(1970). The Cockayne plots of Central Otago. Proceedings of the New Zealand Agricultural Society, 17, 18-34.
Evison, D., &
Mason, E. G. (Forthcoming). What is the most appropriate role for new forests
in mitigating New Zealand’s greenhouse gas emissions?
Forbes, A. S.
(2022). Review of Actual Forest
Restoration Costs, 2021 (Contract report, Issue. Te Uru Rakau.
Forbes, A. S.,
& Norton, D. A. (2021). Transitioning
Exotic Plantations to Native Forest: A Report on the State of Knowledge
(Technical paper, Issue. New Zealand Ministry for Primary Industries.
Forbes, A. S.,
Norton, D. A., & Carswell, S. E. (2015a). Accelerating Regeneration in New Zealand’s Non-harvest Exotic Conifer
Plantations Sixth World Conference on Ecological Restoration, Manchester,
United Kingdom.
Forbes, A. S.,
Norton, D. A., & Carswell, S. E. (2015b). Artificial canopy gaps accelerate
restoration within an exotic Pinus radiata plantation. Restoration Ecology. https://doi.org/10.1111/rec.12313
Forbes, A. S.,
Norton, D. A., & Carswell, S. E. (2016). Tree fern competition reduces
indigenous forest tree seedling growth within exotic Pinus radiata plantations.
Forest Ecology and Management(359),
1-10.
Ford-Robertson, J.
B., Robertson, K. A., & Maclaren, J. P. (1999). Modelling the effect of
land-use practices on greenhouse gas emissions and sinks in New Zealand. Environmental Science and Policy 2,
135-144.
Hall, G. M. J.
(2001). Mitigating an organisation's future net carbon emissions by native
forest restoration. Ecological
Applications, 11(6), 1622-1633.
Kimberley, M.,
Bergin, D. O., & Beets, P. N. (2014). Carbon
sequestration by native trees and shrubs (Planting and managing native
trees, Issue. Tane's Tree Trust.
Kimberley, M.,
Bergin, D. O., & Silvester, W. (2021). Carbon
sequestration by native forest - setting the record straight. Tane's Tree
Trust.
Ledgard, N.
(1994). A form for assessing the risk of conifer spread in the high countrv. New Zealand Journal of Forestry, 39,
26-28.
Ledgard, N.
(2001). The spread of lodgepole pine (Pinus contorta, Dougl.) in New Zealand. Forest Ecology and Management, 141,
43-57.
Ledgard, N. J.
(2008). Assessing risk of the natural regeneration of introduced conifers, or
wilding spread [Conference paper]. New
Zealand Plant Protection, 61, 91-97.
MfE. (2023). Te Rārangi Haurehu Kati Mahana a Aotearoa:
He Whakarāpopoto New Zealand’s Greenhouse Gas Inventory: Snapshot 1990-2021.
New Zealand Ministry for the Environment.
Moore, J. R.
(2010). Allometric equations to predict the total above-ground biomass of
radiata pine trees. Annals of Forest
Science, 67. https://doi.org/10.1051/forest/2010042
Nish, F. (2022). Assessing interactions between silvicultural
treatment and site effects on carbon sequestration in Pinus radiata D.Don
Plantations [BForSc Hon Dissertation, University of Canterbury].
Ogden, J., Braggins, J., Stretton, K., & Anderson, S. (1997). Plant species richness under Pinus radiata stands on the Central
North Island volcanic plateau, New Zealand. New
Zealand Journal of Ecology, 21(1), 17-29.
Pardy, G. F.,
Bergin, D. O., & Kimberley, M. O. (1992). Survey of native tree plantations (FRI Bulletin, Issue.
Payton, I. J.,
Barringer, J., Lambie, S., Lynn, I., Forrester, G., & Pinkney, T. (2010). Carbon sequestration rates for
Post-1989-compliant indigenous forests (Landcare Research Contract Report
LC0809/107, Issue. Lancare Research.
Robertson, K.,
Loza-Balbuena, I., & Ford-Robertson, J. (2004). Monitoring and Economic
Factors affecting the economic viability of afforestation for carbon
sequestration projects. Environmental
Science and Policy, 7, 465-475.
Scott, N. A.,
White, J. D., Townsend, J. A., Whitehead, D., Leathwick, J. R., Hall, G. M. J.,
Marden, M., Rogers, G. N. D., Watson, A. J., & Whaley, P. T. (2000). Carbon
and nitrogen distribution and accumulation in a New Zealand Scrubland
Ecosystem. Canadian Journal of Forest
Research, 30, 1246-1522.
Silvester, W.,
& McGowan, R. (1999). Proceedings of
a Conference entitled "Native Treees for the Future".
Tate, K. R.,
Giltrap, D. J., Claydon, J. J., Newsome, P. F., Atkinson, A. E., Taylor, M. D.,
& Lee, R. (1997). Organic Carbon Stocks in New Zealand's Terrestrial
Ecosystems. Journal of the Royal Society
of New Zealand, 27(3).
Trotter, C., Tate,
K., Scott, N., Townsend, J., Wilde, H., Lambie, S., Marden, M., & Pinkney,
T. (2005). Afforestation/reforestation of New Zealand marginal pasture lands by
indigenous shrublands: the potential for kyoto forest sinks. Annals of Forest Science, 62, 865-871.
Vivid_Economics.
(2017). Net Zero in New Zealand: Scenarios
to achieve domesticemissions neutrality in thesecond half of the century.
Wirsinius, S.,
Searchinger, T., Zionts, J., Peng, L., Beringer, T., & Dumas, P. (2020). Comparing the life cycle greenhouse gas
emissions of dairy and port systems across countries using land-use carbon
opportunity costs (Working Paper, Issue. World Resources Institute. http://www.wri.org/publication/comparing-life-cycle-ghg-emissions
Woollons, R. C.,
& Manley, B. R. (2012). Examining growth dynamics of Pinus radiata
plantations at old ages in New Zealand Forestry,
85(1), 79-86.
Yallop, K. (2021).
Effect of silvicultural regimes on carbon
sequestration in Pinus radiata forest in Canterbury [BForSc Hon
Dissertation, University of Canterbury].
Yarur-Thys, P. D. (2021). Carbon
sequestration rates of native restoration plantings, Southern Port Hills and
Quail Island, Canterbury [MForSc Thesis, University of Canterbury].