AN ABSTRACT OF THE THESIS OF
Jess Holcomb for the degree of Baccalaureate of Science in Bioresource Research,
Environmental Chemistry Option, presented on May 30, 2008.
Title: Effects of land management on carbon and nitrogen in soils from New Zealand
Abstract approved:
________________________________________________________________________
Kate Lajtha, Primary Mentor
The ability of soils to store large quantities of carbon (C) makes them an
important factor in the global C cycle. Small changes within soil C can lead to large
changes in atmospheric C. Land management practices can influence the amount of C
that is stored within the soil and rates of C accumulation or loss. The Purukohukohu
Experimental Basin in New Zealand provides a great opportunity to analyze C and
nitrogen (N) differences in soils as it contains three catchments with different land use
practices; native forest, pasture, plantation pine with Pinus radiata. By using Sequential
Density Fractionation I could examine differences in pools of C and N in each land use
type. Sequential Density Fractionation allows the soil organic matter to be analyzed
based upon the stability of the C and N in each of the density fractions, with heavier
density fractions generally corresponding to more stable C and N. The results showed a
loss of C from converting native forest to pasture and a gain of C from converting pasture
to plantation pine. The amount of C in the plantation pine was also larger than was the C
in the native forest. There was an increase in N from the native forest to the pasture and
the plantation pine had the highest N levels. The losses and gains of C in the plots are
attributed to stable C inputs from the forested sites. More stable C inputs results in more
C stored. The N increases were due to the planting of white clover in the pasture site,
which resulted in high N in the plantation as it was planted on a pasture site.
© Copyright by Jess Holcomb
May 30, 2008
All Rights Reserved
Effects of land management on carbon and nitrogen in soils from New Zealand
by
Jess Holcomb
A THESIS
submitted to
Oregon State University
Bioresource Research
in partial fulfillment of
the requirements for the
degree of
Baccalaureate of Science in Bioresource Research,
Environmental Chemistry
Presented May 30, 2008
Commencement June 2008
Baccalaureate of Science in Bioresource Research, Environmental Chemistry
Thesis of Jess Holcomb
Presented on May 30, 2008
APPROVED:
Kate Lajtha, Mentor
Markus Kleber, Secondary Mentor
Cary Green, Committee Member
I understand that my project will become part of the permanent collection of Oregon
State University, Bioresource Research. My signature below authorizes release of my
project to any reader upon request.
Jess Holcomb, Author
ACKNOWLEDGEMENTS
We are grateful to Kim Townsend and Lea Wilson for assistance in conducting
laboratory research. The authors would also like to thank Dr. Phil Sollins and Dr.
Markus Kleber for the use of their laboratory space and helping analyze the data
collected. Further analysis of data and helping collect field samples by Dr. Troy Baisden
was greatly appreciated.
TABLE OF CONTENTS
Page
1. Introduction………………………………………………………………..
1
2. Methods……………………………………………………………………
2.1 Site Description of the Purukohukohu Experimental Basin…………. 2
2.2 Sequential Density Fractionation and C/N Analysis…………………. 2
3. Results……………………………………………………………………..
5
4. Discussion………………………………………………………………….
4.1 Density fractions dry mass……………………………………………
4.2 Density fraction and total C…………………………………………..
4.3 Density fraction and total N…………………………………………..
4.4 Density fraction C:N ratios…………………………………………...
4.5 2.4 g/ml density fraction difference…………………………………..
9
9
11
12
13
5. Conclusion………………………………………………………………...
14
6. References………………………………………………………………….
15
LIST OF FIGURES
Figure
Page
Density Fraction Dry Mass……………………………………………………
5
Density Fraction Carbon Mass………………………………………………... 6
Density Fraction Nitrogen Mass………………………………………………
7
Total Soil Carbon Mass……………………………………………………….. 8
Total Soil Nitrogen Mass……………………………………………………...
8
Density Fraction C:N………………………………………………………….
8
LIST OF TABLES
Table
Page
Density Fraction Carbon Mass………………………………………………..
6
Density Fraction Nitrogen Mass………………………………………………
7
1
Effects of land management on carbon and nitrogen in soils from New Zealand
1. Introduction
Small changes in the amount of carbon (C) stored in soils can result in a large change in
global C cycling (Amundson, 2001). This is due to soils containing vast pools of C
compared to other places in the environment on a global scale. Globally the amount of C
stored in soils is nearly three times that of above ground biomass and approximately
twice as much C as that found in the atmosphere (Dixon et al., 1991; Eswaran, 1993).
The C in the soils can be lost but at the same time these soils have the ability to sequester
C within the soil profile. Loss of soil C would result in large amounts of C being
released into the atmosphere, while increases would result in sequestration of
atmospheric C. Soil C may be highly resistant to decomposition; measurements of C in
North American soils show C that had accumulated from before European colonization in
1500 A.D. (Stevenson and Cole, 1999). This ability to store C for a long period of time
makes soils a great place for C to be sequestered to keep it out of the atmosphere.
Conversion of forested areas to pasture lands and other agricultural areas are
major influences on the modern landscape. Changes in land-use can affect the amount of
C that can be stored in the soil as well as the amount of N (Neill et al., 1999). Upon
conversion many pasturelands and agricultural lands are treated with N fertilizers to
increase production (Parfitt et al., 2006). The addition of these fertilizers and their longterm effects on soil properties are not yet known (Sparling and Schipper, 2004). These
changes could have an effect on how C and N are being stored within the soil
2
The Purukohukohu Experimental Basin near Taupo, New Zealand is a location
that has several different land-use practices in the same watershed (Beets and Brownlie,
1987). Within the basin there are three different catchments that consist of a native
podocarp/hardwood forest, improved pasture, and plantation pine (Pinus radiata) (MAF,
1999). It has been shown that the conversion from native forest to pasture can result in
small losses of C in the soil after the conversion, but less is known how the long-term
effects of the conversion have had on the amount of C in the soil (Lambert et al., 2000;
Elmore and Asner, 2006). The conversion of pasture to Pinus radiata is a major sink for
C in New Zealand, offsetting about half of the annual CO2 emissions from energy and
industrial uses (MfE, 1997). These new plantation forests can store this C in vegetation,
including live and dead forest C pools (Beets et al., 1999). It is uncertain however, how
conversion to pine plantation has affected the soil C at these sites (Johnson, 1992).
Our objectives are to: (i) determine how the land management practices affect the
amount of C and N stored in the soil; (ii) determine in what density fraction the soils are
either gaining/losing C and N based on the management practices.
2. Methods
2.1 Site Description of the Purukohukohu Experimental Basin
The Purukohukohu Experimental Basin is located in the Paeroa Range in the Central
North Island of New Zealand. A description of the vegetation, soil, climate, and pine
stand management history is given in Beets and Brownlie (1987). The parent materials
originated from Taupo volcanic center (1860 +/- 100 BP) and older ash showers from
3
Taupo and Okataina volcanic centers, which are classified as Pumice soils in the New
Zealand Soil Classification System (Hewitt, 1998). Elevation ranges from 500 to 700
meters and topography ranges from gently rolling hills with slopes under 12 degrees to
moderately steep slopes of 23 degrees to steep slopes of 30 degrees. Soils belong to the
Oruanui series, which are highly permeable with loamy sand, silty sand and gravel.
Rainfall averages 1500 millimeters per year, and temperature average 10oC. The basin
includes three land-use catchments. Maps showing the boundaries between the main
land-use catchments and the Puruki pine subcatchments have been published in Beets and
Brownlie (1987). The three land-use treatments are: 1. Puruorakau (37.2 ha): Indigenous
mesophyll forest classified as mixed podocarp/tawa (McKelvey, 1963). The indigenous
forest catchment includes large podocarp trees including Dacrydium cupressium and
Prumnopitys ferruginea, which can be 500-800 years old. No logging has occurred
within the majority of this site. 2. Purutaka (22.5 ha): Originally cleared in the 1920s to
seral scrub, then developed into improved pasture in 1957 for sheep and cattle grazing.
Management of the pasture involves regular application of superphosphate fertilizer and
the use of legumes (clover) to fix nitrogen ( Beets et al., 2002). 3 Puruki (35.4 ha):
Initially was part of the Purutaka plot but switched land-use from pasture to Pinus radiata
in 1973. The stand was initially stocked at a rate of 2200 trees per ha and fenced to
exclude animal grazing. Puruki is subdivided into three subcatchments: Tahi, Rua, and
Toru. Each different subcatchment has different thinning regimes applied. The
understory is dominated by tall pasture species for the first three years until the canopy
closed at six years. Bracken fern has been the dominant understory since the pine was
thinned.
4
Soil samples were taken from each of the catchments from the depth of 0-15
centimeters below the litter layer. Three samples from each catchment were taken and
mixed to create one homogeneous mixture.
2.2 Sequential Density Fractionation and C/N Analysis
Samples from each plot were air dried and passed through a 2 millimeter sieve. Five
grams of each soil were placed into tins and dried at 50oC and 100oC to determine
moisture content. Fifty grams of each soil sample were placed into a 225-ml
polycarbonate centrifuge tube with conical bottoms and 5-cm diameter mouths. These
tubes allowed for physical separation of sediment and floating material while their
transparency allowed easier aspiration of the supernatant without disturbing the sediment.
A Sodium Polytungstate (SPT) solution with a density of 1.65 g cm-3 was added to the
conical vial until there was 175 ml of solution in the vial. Samples were shaken for two
hours. The soil suspensions were then centrifuged at 3500 rpm in a swinging-bucket
rotor for ten minutes. After centrifugation, the floating material was aspirated and rinsed
with deionized water on a glass fiber filter, Whatman GF/F, (0.7 μm) (Sollins et al.,
2006). The density of the remaining SPT solution was increased by adding the next
density SPT solution to the centrifuge tubes. Target densities for this fractionation were
1.65, 1.85, 2.00, 2.40, and 2.65 g cm-3. The 1.85 - 2.65 g cm-3 fractions were shaken for
one hour. Fractions 2.00, 2.40, and 2.65 were “washed” in the centrifuge instead of being
filtered. Deionized water was added to fractions and tubes were centrifuged until the
5
Fraction Mass (g soil)
Native
Pasture
Plantation Pine
20
15
10
5
0
1.65
1.85
2
2.4
2.65
>2.65
Density Fraction (g/ml)
Figure 1. Density Fraction dry mass of each density fraction for each of the treatments
supernatant had a density of 1.00 g cm-3. Soil remaining after the 2.65 g cm-3 step was
considered the >2.65 g cm-3. Fractions were dried at 50oC.
All dried fractions were ground in a Spex mixer mill. Samples were sent to the
Central Analytical Lab at Oregon State University for analysis of C and using a Leco
CNS 2000.
For the use of this experiment, only one trial of the samples were taken, this
eliminates any statistics from being used in this paper.
3. Results
The dry masses of the fractions from each land-use type were quite similar (Figure 1).
There was some difference in mass at each fraction but it was usually under a gram. In
most cases two of the treatments were almost similar at each density fraction and only
6
Table 1. Carbon mass for each of the density fractions
Fraction (g/ml)
1.65
1.85
2
2.4
2.65
>2.65
Total (g)
Native
1.508 g
0.320 g
0.635 g
1.127 g
0.175 g
0.004 g
3.771 g
Pasture
0.825 g
0.166 g
0.978 g
1.090 g
0.206 g
0.016 g
3.284 g
Plantation Pine
1.172 g
0.241 g
0.874 g
2.502 g
0.138 g
0.022 g
4.952 g
Native
Pasture
Plantation Pine
3
2.5
Carbon (g)
2
1.5
1
0.5
0
1.65
1.85
2
2.4
2.65
>2.65
Density Fraction (g/ml)
Figure 2. Carbon mass of each density fraction for each of the treatments
one treatment showed a difference at that fraction. The greatest variation occurred at
densities of 1.65, 2.4, 2.65, and >2.65. Each of these densities only had one fraction that
was varied slightly from the others.
The amount of carbon in each fraction were all similar among land-use types
(Table 1). At the 2.4 g/cm3 density fraction the plantation pine was much larger than was
that of the other two treatments (Figure 2). At the 2.4 g/cm3 density fraction the
7
T able 2. Nitrogen mass for each of the density fractions
Fraction N (g/ml)
1.65
1.85
Native
0.062 g
0.0152 g
Pasture
0.040 g
Plantation Pine
0.053 g
2.4
2.65
>2.65
0.031 g
0.055 g
0.008 g
0.001 g
0.174 g
0.009 g
0.063 g
0.069 g
0.015 g
0.001 g
0.199 g
0.011 g
0.051 g
0.185 g
0.009 g
0.002 g
0.313 g
Native
2
Pasture
Total (g)
Plantation Pine
Nitrogen (g)
0.2
0.15
0.1
0.05
0
1.65
1.85
2
2.4
2.65
>2.65
Density Fraction (g/ml)
Figure 3. Nitrogen mass of each density fraction for each of the treatments
difference between the plantation pine and the other treatments was larger than at the
other density fractions. This was the only fraction that showed a large difference
between the treatments.
The amount of nitrogen in the density fractions were all fairly similar amongst all
of the treatments (Table 2). There was a large increase in nitrogen in the 2.4 g/cm3
fraction for plantation pine (Figure 3).
The total C and N is calculated as the sum of all of the density fractions.
Plantation pine contained the most C, followed by the native forest, and the pasture
treatment having the least amount of total C (Figure 4). Plantation pine had the greatest
8
Pasture
Plantation Pine
Native
6
0.35
5
0.3
N mass (grams)
C mass (grams)
Native
4
3
2
1
Pasture
Plantation Pine
0.25
0.2
0.15
0.1
0.05
0
0
Total
Total
Figure 4. Total soil carbon at each of the
Figure 5. Total soil nitrogen at each of the
treatments. Totals are a sum of all of the density
treatments. Total is a sum of all of the density
fractions.
fractions.
Native
Pasture
Plantation Pine
C:N value (g C:g N)
30
25
20
15
10
5
0
1.65
1.85
2
2.4
2.65
>2.65
Fraction Density (g/ml)
Figure 6. C: N ratio for each of the density fractions for each treatment
mass of N, followed by the pasture, and the native forest had the lowest mass of N
(Figure 5).
The forest plot had the highest C: N ratio at all density fractions (Figure 6). The
plantation pine plot had the next highest C: N ratio at all densities fractions except for the
9
2.4 g/cm3 and the >2.65 g/cm3. At these density fractions the plantation pine had the
lowest C: N ratio. The pasture plot had the lowest C: N ratio at all of the density
fractions except the 2.4 g/cm3 and the >2.65 g/cm3 were the plantation pine had the
lowest C: N ratio.
4. Discussion
4.1 Density fractions dry mass
The masses of the dry density fractions were all similar for each treatment at each
corresponding density fraction (Figure 1). This result was expected as all of the
treatments came from the same watershed. The parent material of all of the soil as well
as the soil composition should be similar as all came from the same location. These soils
were all in the Oruanui series, which are highly permeable with loamy sand, silty sand,
and gravel (Beets et al., 2002). These fractions each have the same mass, but the amount
of C and N in the organic matter that is sorbed to each fraction is what will set them
apart. Each treatment will have different amounts of C and N in each of their fractions.
4.2 Density fraction and total C
The differences in the amount of C in each of the treatments can be linked directly to the
amount of C that is added through vegetation. The native forest had the second highest
mass of total C (Figure 4). This mass was due to the forest’s input of longer
decomposing forms of organic matter. This organic matter being woody materials with
high C:N that decompose at a slower rate than that of grasses. The vegetation on the
native site decreases decomposition time and allows C to build up in the soil due to its
10
long turn over time. The forested site is the only site in all of the treatments to have
retained pre-bomb C (Manning and Melhuish, 2001). This shows that the C in the native
forest has not been lost, showing a stable C form.
The pasture treatment had the lowest total C of all of the treatments analyzed.
This is due to the losses of the stable C that was on the site before the conversion to
pasture. The pasture did have C inputs into the system through its own organic matter but
it is not as recalcitrant as forest C. The pasture soils have the greatest rates of C
mineralization in all of the treatments, showing that the pasture soils have labile inputs of
C and not recalcitrant C pools (Parfitt et al., 2003). These labile pools of C lead to the
carbon being easily lost from the system, unlike the stable forms of carbon from the
native forest. The loss of C from the system is hard to account for as there seems to be
no dominant form of C loss. The lack of erosion at the site makes it unlikely that the C is
being lost through erosion (Schipper et al., 2007). The grazing intensity at these sites and
changes in the type of livestock grazing has been suggested as a possible form of the C
loss at this site but further work needs to be done to better prove this hypothesis (Elmore
&Asner, 2006).
The amount of C at this site since the conversion to pasture has been steadily
declining (Figure 4) and it is not known if this site has reached an equilibrium or if it will
continue to lose C in the future. Studies also show that there may be losses deeper in the
pasture soil profile past one meter in depth (Veldkamp et al., 2003; Lettens et al., 2005b).
Losses from deeper in the profile would only intensify the amount of total C lost at this
site and increase the amount of CO2 being contributed to the atmosphere.
11
The amount of the total C at the plantation pine treatment was the highest of all of
the treatments. These high C values can be attributed to the high levels of litter that does
not decompose readily. The plantation pine had the most mass of C at the 2.4 g/ml
density fraction (Figure 2). The 2.4 g/ml density fraction indicates more stable organic
matter as it is not being broken down and more tightly sorbed to the soil surface (Sposito,
1984). This increase in the 2.4 g/ml density fraction shows that this treatment has an
increase in the amount of stable C that has been introduced into the soil. This increase in
C can be attributed to the amount of new growth in the pine plantation. The younger pine
grow faster and are putting organic matter in the soil as a result of their growth compared
to the native forest which is growing at a slower rate. The use of this area for logging is
another source of the stable C entering the soil. During logging operations pine debris is
directly added to the soil because it is unwanted timber. This results in woody debris
being buried in the soil horizons (Oliver et al., 2004). The reintroduction of longer
decomposing woody debris is a stable form of C as it decomposes. The amount of these
lignified residues increase with the age of the stand (Paul et al., 2003b). This site is more
than likely not reached equilibrium on its C pool as it is continually being harvested and
replanted.
4.3 Density fraction and total nitrogen
The native forest had the lowest amount of N in the soils due to the lack of N being added
into the system. The N that was added to the native forest was mostly from wet and dry
deposition, with wet deposition being the largest contributor to the N at the native forest
with the addition of 3-6 kg N ha-1yr-1 (Dyck et al., 1987; Nichol et al., 1997). This is the
12
only source of N for the native forest which makes it have the lowest mass of N between
all of the treatments.
The increase of N in the pasture was due to legumes, white clover, planted at
these sites upon conversion to pasture. Legumes are able to fix N so this site had more N
added to the site compared to the native forest. The combination of P fertilizer and white
clover in the pasture has shown to add 140-170 kg N ha-1yr-1 (O’Connor et al., 1979).
The plantation pine had the highest mass of N out of all of the treatments because
of its ability to produce stable organic matter. The plantation site was planted on
previous pasture site that has had N fixation due to the white clover. The N in the soil
was able to be used by the pine in the plantation and converted into organic matter. Since
the pine has more stable organic matter the N is able to stay in the soil for a longer period
of time. By looking at Figure 3 it can be seen that the largest difference between the
treatments is at the 2.4 g/ml density fraction which is the stable organic fraction. The
increase of N in this fraction shows that the pine’s ability to incorporate the N into its
organic matter and then make them into a stable organic form is the reason that there is
more N in the plantation pine soil. The N in the stable fraction is harder to use by
microbial processes as it takes more energy to get at it so it stays in the soils. As a result
the plantation pine soil is able to expand its N pool in the soil.
4.4 Density fraction C: N ratios
The native forest had the highest C: N ratio at all density fractions. This is due to the
litter quality in the native forest. The native forest had a high mass of C and a low mass
of N due to the low N inputs at the site. This yielded vegetation that had a higher C: N
13
ratio. Forest sites also have higher C: N ratios as they are made up of woody material
that naturally has higher C: N ratios.
The pasture site had the lowest C: N ratio at all fractions except the 2.4 g/ml and
the >2.65 g/ml. The pasture was expected to have a low C: N ratio because the quality of
its organic material. Pasture grasses do not have a high C: N ratio so the organic matter
that they put into the soil will also have a low C: N ratio. The presence of N from the
legumes also increases the amount of N at the site allowing for more N to be in the
vegetation.
The plantation pine had the second highest C: N ratio at all fractions except the
2.4 g/ml and > 2.65 g/ml where it had the lowest C: N ratio. The high C: N ratio at all
the other fractions is attributed to the woody organic matter that is being produced at this
site. Similarly to the forest, the pine plantation produces vegetation that naturally has a
high C: N ratio. The low C: N ratio at the 2.4 and >2.65 g/ml density fraction is
attributed to the amount of N at these fractions. As seen in Figure 2 the pine plantation
has the largest amount of N at the 2.4 g/ml density fraction. This N is in a stable form
and is more resistant to decomposition. This increase in N at this fraction leads to the
low C: N ratio. This low C: N ratio is not an indicator of the vegetation C: N ratio, rather
it shows the ability of the plantation pine to create stable forms of soil organic matter that
are able to sequester N with in the soil for long periods of time.
4.5 The 2.4 g/ml density fraction difference
Each of the density fraction graphs (Figures 1, 2, 3) show a similar pattern in their
appearance. Each one of the figures show a spike at the 2.4 g/ml density fraction for the
14
plantation pine. The dry fraction mass shows a difference of 2.2 grams between the
plantation pine and the native forest. The C fraction mass shows a difference of 1.2
grams between the plantation pine and the native forest. The C difference is about half of
the dry fraction difference. Organic matter is composed of about 50% C, so the increase
of organic matter dry mass at the 2.4 g/ml density fraction directly yielded the increase of
C at this same fraction density. Similarly the N difference between the plantation pine
and the native forest at the 2.4 g/ml density fraction was 0.11 grams which gives a C: N
ratio of 10. This C: N ratio is common in many forms of organic matter. This suggest
that the increase in both the C and N at this fraction is due to the increase of organic
matter at this fraction. This fraction is associated with stable organics, so the plantation
pine treatment can easily be seen to be increasing in the amount of stable organic matter
that is being put into the soil. As a result of this stable organic matter being re-introduced
into the soil, the C and N levels in the plantation pine are able to rise.
Another possibility for this spike in the plantation pine at the 2.4 g/ml density
fraction could be an error in our experiment. Unfortunately we did not run multiple trials
so we cannot be absolutely sure that this spike at the 2.4 g/ml density fraction at the
plantation pine is due to stable organic matter or if it is an error.
5. Conclusion
The conversion of native forest to pasture resulted in the loss of total soil C due to the
loss of a stable organic C being put into the system. The conversion of pasture to the
plantation pine resulted in an increase in total soil C due to the reintroduction of a stable
15
organic C source in the Puruki pine. The loss of C in the pasture and the gain of C in the
plantation is all a result of stable organic C being put into the system. This stable organic
C is the reason a soil is going to lose or gain C. The increase of N in both the pasture and
the plantation pine was a direct result of the planting of legumes in the pasture. This
addition gave these treatments N that was unavailable to the native forest. This resulted
in the pasture and the plantation pine to both have a larger total N mass than the native
forest.
6. References
Amundson R., 2001. The carbon budget in soils. Annual Review of Earth and Planetary
Sciences 29, 535-562.
Beets P.N., Brownlie R.K., 1987. Puruki experimental catchment: site, climate, forest
management, and research. New Zealand Journal of Forestry Science 17, 137160.
Beets P.N., Oliver G.R., Clinton P.W., 2002. Soil carbon protection in
podocarp/hardwood forest, and effects of conversion to pasture and exotic pine
forest. Environmental Pollution 116, S63-S73.
Beets P.N., 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, 409427.
16
Compton J.E, Boone R.D., 2000. Long-term impacts of agriculture on soil carbon and
nitrogen in New England forests. Ecology 81, 2314-2330.
Dixon R.K., Schroeder P.E., Winjum J.K., 1991. Assessment of promising forest
management practices and technologies for enhancing the conservation and
sequestration of atmospheric carbon and their costs at the site level. US
Environmental Protection Agency, USA.
Dyck W.J., Mees C.A., Hodgkiss P.D., 1987. Nitrogen availability and comparison to
uptake in two New Zealand Pinus radiata forest. New Zealand Journal of
Forestry Science 17, 338-352.
Elmore A.J., Asner G.P., 2006. Effects of grazing intensity on soil carbon stocks
following deforestation of a Hawaiian dry tropical forest. Global Change Biology
12, 1761-1772.
Eswaran H., Van Den Berg E., Reich P., 1993. Organic carbon in soils of the world. Soil
Science Society of America Journal 57, 192-194.
Hewitt A.E., 1998. New Zealand soil classification. Landcare Research Science Series
No. 1, 2nd Edition, Mannaki Whenua Press.
MAF 1999. A national exotic forest description as at April 1998. Ministry of
Agriculture and Forestry, Wellington, New Zealand, ISSN: 1170-5191.
Manning M.R., Melhuish W.H., 2001. Atmospheric 14C record for Wellington. Online
TRENDS. A compendium of data on global change. cdiac.esd.ornl.gov.
McKelvey P.J., 1963. The synecology of the West Taupo indigenous forest. New
Zealand Forest Service Bulletin No. 14.
17
MfE 1997. Climate change: the New Zealand response II. New Zealand’s second
communication under the framework convention for climate change. Ministry for
the Environment, Wellington, New Zealand 191 pp.
Neill C., Piccolo M.C., Melillo J.M., Steudler P.A., Cerri C.C., 1999. Nitrogen dynamics
in Amazon forest and pasture soil measured by 15N-pool dilution. Soil Biology
and Biochemistry 31, 567-572.
Nichol S.E., Harvey M.J, Boyd I.S., 1997. Ten years of rainfall chemistry in New
Zealand. Clean Air 31, 30-37.
O’Connor M.B., Prime P.N., Wilkinson R.C., 1979 Nitrogen fixation in pasture IV.
Central North Island pumice-land, Wairakei. New Zealand Journal of
Experimental Agriculture 7, 15-17.
Oliver G.R., Beets P.N., Garrett L.G., Pearce S.H., Kimberly M.O., Ford-Robertson J.B,
Robertson K.A., 2004. Variation in soil carbon in pine plantations and
implications for monitoring soil carbon stocks in relation to land-use change and
forest site management in New Zealand. Forest Ecology and Management 203,
283-295.
Parfitt R.L., Schipper L.A., Baisden W.T., Elliot A.H., 2006. Nitrogen inputs and outputs
for New Zealand in 2001 at national and regional scales. Biogeochemistry 80,
71-88.
Parfitt R.L., Scott N.A., Ross D.J., Salt G.J., Tate K.R., 2003. Land-use change effects
on soil C and N transformations in soils of high N status: comparisons under
indigenous forest, pasture and pine plantation. Biogeochemistry 66, 203-221.
18
Paul K.I., Polglase P.J., Richards G.P., 2003b. Predicted change in soil carbon following
afforestation or reforestation, and analysis of controlling factors by linking a C
accounting model (CAM-For) to models of forest growth (3PG), litter
decomposition (GENDEC) and soil C turnover (ROTHC). Forest Ecology
Management 177, 485-501.
Schipper L.A., Baisden W.T., Parfitt R.L., Ross C., Claydon F.F., Arnold G., 2007.
Large losses of soil C and N from soil profiles under pasture in New Zealand
during the past 20 years. Global Change Biology 13, 1138-1144.
Sollins P., Swanston C., Kleber M., Filley T., Kramer M., Crow S., Caldwell B.A., Lajtha
K., Bowden R., 2006. Organic C and N stabilization in a forest soil: Evidence
from sequential density fractionation. Soil Biology & Biochemistry 38, 33133324.
Sparling G.P., Schipper L.A., 2004. Soil quality monitoring in New Zealand: trends and
issues arising from a broad-scale survey 1995-2001. Agricultural Ecosystems and
Environment 104, 545-552.
Sposito G., 1984. The surface chemistry of soils. Oxford, New York, NY, 234p.
Strickland T.C., Sollins P., Rudd N., Schimel D.S., 1992. Rapid stabilization and
mobilization of 15N in forest and range soils. Soil Biology & Biochemistry 24,
949-955.
Swanston C.W., Torn M.S., Hanson P.J., Southon J.R., Garten C.T., Hanlon E.M., Ganio
L., 2005. Initial characterization of processes of soil carbon stabilization using
forest stand-level radiocarbon enrichment. Geoderma 128, 52-62.