We have quantified the current and potential carbon storage on conservation land. Conservation la... more We have quantified the current and potential carbon storage on conservation land. Conservation land was estimated to currently contain a total of 2578 Mt C (9461 Mt CO 2 e) in vegetation and soil. We estimate that conservation land could store up to 698 Mt CO 2 e more than at present, through reforestation (large gains per hectare), advance of existing shrubland successions (moderate gains per hectare) and recovery of existing forests from disturbances, including animal browsing, (small gains over large areas). Wild animal control plays a role in all three types of gain, but here we demonstrate that, for existing forests, it will be very challenging to quantify sequestration in existing forests that (a) can be attributed to wild animal control and (b) is additional to the sink that already exists. It is our view that the presence of a forest sink in existing forests is a strong endorsement of business-as-usual management of conservation land in forest and that this management should be maintained for the benefit of all New Zealanders. We recommend that any future effort to increase carbon sequestration through targeted wild animal control should focus on successional communities-removing wild animals from broadleaved-hardwood successions where the palatable canopy species of the future need to become established, and supporting other management actions to establish novel woody successions to indigenous forests within degraded grasslands. These actions should be evaluated alongside the carbon costs of undertaking these management activities. We note that on conservation land where natural succession does not readily occur, additional, and likely intensive, management will be required such as planting for shelter and provision of seed, with associated weeding requirements. The fastest, and most cost-effective, action to increase carbon sequestration on conservation land is to choose sites close to existing indigenous forest seed sources that are relatively warm (mean annual temperature > 9°C) and receive reasonable rainfall (> 1000 mm per annum) and retire these from grazing and to prevent fire and domestic or wild animal incursion as far as possible and allow natural regeneration to proceed unhindered. Further thought needs to be given to the carbon consequences of novel ecosystems-especially whether exotic woody species are able to play a desirable role in natural regeneration of indigenous forests.
Science for Conservation is a scientific monograph series presenting research funded by New Zeala... more Science for Conservation is a scientific monograph series presenting research funded by New Zealand Department of Conservation (DOC). Manuscripts are internally and externally peer-reviewed; resulting publications are considered part of the formal international scientific literature. Individual copies are printed, and are also available from the departmental website in pdf form. Titles are listed in our catalogue on the website, refer www.doc.govt.nz under Publications, then Science & technical.
Uncertainty about the mechanisms driving biomass change at broad spatial scales limits our abilit... more Uncertainty about the mechanisms driving biomass change at broad spatial scales limits our ability to predict the response of forest biomass storage to global change. Here we use a spatially representative network of 874 forest plots in New Zealand to examine whether commonly hypothesised drivers of forest biomass and biomass change (diversity, disturbance, nutrients and climate) differ between old-growth and secondary forests at a national scale. We calculate biomass stocks and net biomass change for live above-ground biomass, belowground biomass, deadwood and litter pools. We combine these data with plot-level information on forest type, tree diversity, plant functional traits,
We created small‐scale artificial canopy gaps to accelerate the growth of mature indigenous fores... more We created small‐scale artificial canopy gaps to accelerate the growth of mature indigenous forest canopy species for restoration of an 18‐year‐old exotic Pinus radiata plantation forest, in the Marlborough Sounds, New Zealand. Small and large circular gaps were formed by felling. Seedlings of two indigenous forest canopy species, Podocarpus totara (Podocarpaceae) and Beilschmiedia tawa (Lauraceae), were planted within artificial gaps and undisturbed plantation canopy. Seedling height growth, mortality, and occurrence of animal browse were monitored at approximately 6‐month intervals over 17 months. Both P. totara and B. tawa differed significantly in height growth and in animal browse occurrence among artificial gap treatments. Growth of the light‐demanding P. totara was better under large canopy gaps, whereas growth of the shade‐tolerant B. tawa increased under gaps of any size but was most consistent under small gaps. For P. totara, any significant restoration benefit of gap formation on height growth was lost when browsed seedlings were taken into account. Animal browse significantly limited B. tawa height growth in large but not in small gaps. Small‐scale canopy gap creation is an effective method of modifying light transmission to the plantation understorey and accelerating seedling growth rates. Canopy gap size can be used to optimize understorey illumination according to species‐specific light requirements. The increased occurrence of animal browse in gaps requires consideration. Artificial canopy gaps within planted monocultures create structural heterogeneity that would otherwise take an extended period of time to develop. These results further support the role of plantations as indigenous forest restoration sites.
Many studies have quantified uncertainty in forest carbon (C) storage estimation, but there is li... more Many studies have quantified uncertainty in forest carbon (C) storage estimation, but there is little work examining the degree of uncertainty in shrubland C storage estimates. We used field data to simulate uncertainty in carbon storage estimates from three error sources: (1) allometric biomass equations; (2) measurement errors of shrubs harvested for the allometry; and (3) measurement errors of shrubs in survey plots. We also assessed uncertainty for all possible combinations of these error sources. Allometric uncertainty had the greatest independent effect on C storage estimates for individual plots. The largest error arose when all three error sources were included in simulations (where the 95% confidence interval spanned a range equivalent to 40% of mean C storage). Mean C sequestration (1.73 Mg C ha-1 year-1) exceeded the margin of error produced by the simulated sources of uncertainty. This demonstrates that, even when the major sources of uncertainty were accounted for, we were able to detect relatively modest gains in shrubland C storage.
This paper is part of a series of studies that investigate the utility of nonharvest Pinus planta... more This paper is part of a series of studies that investigate the utility of nonharvest Pinus plantations as indigenous forest restoration sites in New Zealand.
ABSTRACT Increased afforestation of non-productive land could deliver win-win solutions for green... more ABSTRACT Increased afforestation of non-productive land could deliver win-win solutions for greenhouse gas mitigation through carbon sequestration and biodiversity gains, referred to here as increased ‘ecological integrity’. We examined the potential trade-offs when selecting non-forested lands in New Zealand for natural forest regeneration to maximise gains in either, or both, carbon and biodiversity. We also examine the effect on potential gains and trade-offs of excluding non-conservation lands from spatial planning for conservation. The most significant per-hectare gains, for both carbon and biodiversity, were those occurring on non-conservation lands because conservation lands are mainly restricted to low-productivity environments where indigenous vegetation is already well represented. By contrast, productive environments, such as alluvial plains, where almost no indigenous vegetation remains, are primarily on non-conservation lands. These lands will need to be included in any reforestation strategy or else the most degraded ecosystems will not be restored. We found that biodiversity suffers a greater trade-off when carbon gain is prioritised than carbon does when biodiversity is prioritised. Trade-offs between carbon and biodiversity were higher on non-conservation lands but decreased with increasing area regenerated. Our study shows that natural regeneration will provide substantial increases in carbon and biodiversity on non-conservation lands compared with conservation lands. This emphasised the need for improved incentives to private land owners if carbon and biodiversity gain from afforestation is to be maximised.
This thesis investigates the influence of carbon dioxide concentration on carbon assimilation in ... more This thesis investigates the influence of carbon dioxide concentration on carbon assimilation in tropical tree species. To investigate the response of tropical tree species to elevated CO2 concentration, seedlings of Cedrela odorata L. (Meliaceae) were grown in open-top chambers and exposed to atmospheric CO 2 at either ambient or twiceambient concentrations. Nutrient supply rate was also altered to investigate its interaction with elevated CO 2 concentration. This experiment was repeated on different seedlings over two years, 1995 and 1996. The seedlings of C. odorata grown in 1996 showed an acclimation response to elevated CO2 concentration, but those grown in 1995 did not. Plants grown in elevated CO2 concentration were only larger than those grown in ambient CO2 concentration in 1995 with a high rate of nutrient supply. It is hypothesised that high vapour pressure deficits restricted stomatal conductance and consequent photosynthesis in both years, but that this effect was particularly pronounced in 1996, when combined with a nutrient regime of excessively high concentration for the rate of growth. These effects are hypothesised to have triggered acclimation, or a reduction in CO2 fixation capacity, as indicated by changes in derived values for the enzyme kinetic parameters of the carboxylation enzyme, ribulose 1, 5 bisphosphate carboxylase-oxygenase (Rubisco). 'U ACKNOWLEDGEMENTS I thank John Grace for his guidance and good humour throughout this project. I am particularly grateful for his careful reading of this thesis in its final stages. I also thank Paul Jarvis for the insight, time and patience that I received throughout my work, again, during writing in particular. I thank Andy Gray for sharpening my selfesteem, Diarmuid O'Neill for help with harvests, Craig Barton for generous technical assistance, Alex Harrower and Dave McKenzie for helping me to build things, and Bill-and Bob for helping me to grow things. I also thank Tam and Joe, Mike
There are strong financial incentives for accurately estimating potential Kyoto-compliant carbon ... more There are strong financial incentives for accurately estimating potential Kyoto-compliant carbon sequestration on conservation land. However, estimation of potential carbon stocks is complicated, as it is unclear how the accuracy of estimates should be validated. One way of addressing this is to use several independent methods to estimate potential carbon stocks; the results can then be compared to indicate where uncertainty lies in predicting Kyoto-compliant carbon gain. In this study, the LUCAS vegetation survey plots were used in spatial predictive modelling to estimate current carbon stocks on conservation land in New Zealand. Three independent methods were then used to estimate potential carbon stocks, based on either regression models of potential forest cover using present-day forest survey data; spatial models of disturbance-adjusted carbon stock values for LUCAS plots; or a forest dynamics model that explicitly models changes in carbon. Kyoto-compliant lands were identified using the New Zealand Vegetation Cover Map. Conservation land was estimated to currently contain a total of 2578 Mt of C (9461 Mt CO 2 e) in vegetation and soil. The three different methods provided estimates of Kyoto-compliant carbon gain ranging from 63 to 186 Mt of C (231-682 Mt CO 2 e) as a result of land use change from nonforest to forest land. This equates to 3-8 years of New Zealand's total greenhouse gas emissions, based on estimated levels for 2005, and would take at least several centuries to be realised. Reasons for the variation in estimates, implications of results and limitations of the methods used are discussed. We acknowledge that uncertainties exist, primarily in the assumptions used to estimate total Kyoto-compliant forest areas and, to a lesser extent, extrapolation between plot-scale carbon measurements.
Science for Conservation is a scientific monograph series presenting research funded by New Zeala... more Science for Conservation is a scientific monograph series presenting research funded by New Zealand Department of Conservation (DOC). Manuscripts are internally and externally peer-reviewed; resulting publications are considered part of the formal international scientific literature. Individual copies are printed, and are also available from the departmental website in pdf form. Titles are listed in our catalogue on the website, refer www.doc.govt.nz under Publications, then Science & technical.
Abstract:" New Zealand's responses in the face of climate change range from the central... more Abstract:" New Zealand's responses in the face of climate change range from the central government's Emissions Trading Scheme (ETS), to infrastructure adaptations in settlements, to reframing of how social research engages with the phenomenon of climate change. ...
Carbon assimilation by Cedrela odorata L. (Meliaceae) seedlings was investigated in ambient and e... more Carbon assimilation by Cedrela odorata L. (Meliaceae) seedlings was investigated in ambient and elevated CO 2 concentrations ([CO 2 ]) for 119 days, using small fumigation chambers. A solution containing macro-and micronutrients was supplied at two rates. The 5% rate (high rate) was designed to avoid nutrient limitation and allow a maximum rate of growth. The 1% rate (low rate) allowed examination of the effect of the nutrient limitation-elevated CO 2 interaction on carbon assimilation. Root growth was stimulated by 23% in elevated [CO 2 ] at a high rate of nutrient supply, but this did not lead to a change in the root:shoot ratio. Total biomass did not change at either rate of nutrient supply, despite an increase in relative growth rate at the low nutrient supply rate. Net assimilation rates and relative growth rates were stimulated by the high rate of nutrient addition, irrespective of [CO 2 ]. We used a biochemical model of photosynthesis to investigate assimilation at the leaf level. Maximum rate of electron transport (J max) and maximum velocity of carboxylation (V cmax) did not differ significantly with CO 2 treatment, but showed a substantial reduction at the low rate of nutrient supply. Across both CO 2 treatments, mean J max for seedlings grown at a high rate of nutrient supply was 75 µmol m-2 s-1 and mean V cmax was 27 µmol m-2 s-1. The corresponding mean values for seedlings grown at a low rate of nutrient supply were 36 µmol m-2 s-1 and 15 µmol m-2 s-1 , respectively. Concentrations of leaf nitrogen, on a mass basis, were significantly decreased by the low nutrient supply rate, in proportion to the observed decrease in photosynthetic parameters. Chlorophyll and carbohydrate concentrations of leaves were unaffected by growth [CO 2 ]. Because there was no net increase in growth in response to elevated [CO 2 ], despite increased assimilation of carbon at the leaf level, we hypothesize that the rate of respiration of non-photosynthetic organs was increased.
The observation of acclimation in leaf photosynthetic capacity to differences in growth irradianc... more The observation of acclimation in leaf photosynthetic capacity to differences in growth irradiance has been widely used as support for a hypothesis that enables a simplification of some soil-vegetation-atmosphere transfer (SVAT) photosynthesis models. The acclimation hypothesis requires that relative leaf nitrogen concentration declines with relative irradiance from the top of a canopy to the bottom, in 1 : 1 proportion. In combination with a light transmission model it enables a simple estimate of the vertical profile in leaf nitrogen concentration (which is assumed to determine maximum carboxylation capacity), and in combination with estimates of the fraction of absorbed radiation it also leads to simple 'big-leaf' analytical solutions for canopy photosynthesis. We tested how forests deviate from this condition in five tree canopies, including four broadleaf stands, and one needle-leaf stand: a mixed-species tropical rain forest, oak (Quercus petraea (Matt.) Liebl), birch (Betula pendula Roth), beech (Fagus sylvatica L.) and Sitka spruce (Picea sitchensis (Bong.) Carr). Each canopy was studied when fully developed (mid-to-late summer for temperate stands). Irradiance (Q , µ µ µ µ mol m − − − − 2 s − − − − 1) was measured for 20 d using quantum sensors placed throughout the vertical canopy profile. Measurements were made to obtain parameters from leaves adjacent to the radiation sensors: maximum carboxylation and electron transfer capacity (V a , J a , µ µ µ µ mol m − − − − 2 s − − − − 1), day respiration (R da , µ µ µ µ mol m − − − − 2 s − − − − 1), leaf nitrogen concentration (N m , mg g − − − − 1) and leaf mass per unit area (L a , g m − − − − 2). Relative to upper-canopy values, V a declined linearly in 1 : 1 proportion with N a. Relative V a also declined linearly with relative Q , but with a significant intercept at zero irradiance (P < 0•01). This intercept was strongly related to L a of the lowest leaves in each canopy (P < 0•01, r 2 = 0•98, n = 5). For each canopy, daily ln Q was also linearly related with ln V a (P < 0•05), and the intercept was correlated with the value for photosynthetic capacity per unit nitrogen (PUN: V a / N a , µ µ µ µ mol g − − − − 1 s − − − − 1) of the lowest leaves in each canopy (P < 0•05). V a was linearly related with L a and N a (P < 0•01), but the slope of the V a : N a relationship varied widely among sites. Hence, whilst there was a unique V a : N a ratio in each stand, acclimation in V a to Q varied predictably with L a of the lowest leaves in each canopy. The specific leaf area, L m (cm 2 g − − − − 1), of the canopy-bottom foliage was also found to predict carboxylation capacity (expressed on a mass basis; V m , µ µ µ µ mol g − − − − 1 s − − − − 1) at all sites (P < 0•01). These results invalidate the hypothesis of full acclimation to irradiance, but suggest that L a and L m of the most light-limited leaves in a canopy are widely applicable indicators of the distribution of photosynthetic capacity with height in forests.
Natural regeneration of new forests has significant potential to mitigate greenhouse gas emission... more Natural regeneration of new forests has significant potential to mitigate greenhouse gas emissions, but how strong is the potential biodiversity co-benefit? We quantified carbon accumulation and biodiversity gain during secondary succession of two New Zealand lowland forests. The rate of carbon sequestration was the same for the kanuka-red beech succession as for the coastal broadleaved succession (c. 2.3 Mg C ha-1 year-1) over the first 50 years of succession. Mean above-ground carbon stocks were 148 ± 13 Mg C ha-1 for kanuka-red beech forests and 145 ± 19 Mg C ha-1 for tall coastal broadleaved forests after at least 50 years of succession. Biodiversity gain was investigated through the quantification of 'ecological integrity', which comprises dominance by indigenous species, occupancy of indigenous species or a group of species fulfilling a particular ecological role, and gain in representation of lowland forests within each ecological region. All components of ecological integrity increased with carbon accumulation for both successions. In addition, aboveground carbon stocks were correlated with the Shannon and Simpson diversity indices and species richness for both successions, suggesting that conventional metrics of diversity also show biodiversity gain with aboveground carbon during succession of recently non-forested lands to secondary forest.
Regional governance to address climate change is being constituted in New Zealand through domesti... more Regional governance to address climate change is being constituted in New Zealand through domestic policy measures and international discourses. We examine climate change responses in two regions: Marlborough and Waikato. Informants expressed a desire for more transparent government policy; that planning for climate change makes good business sense for farmers and other businesses; that technology is sought to increase productivity and decrease environmental impact; and research networks build capacity for local action, linking sectors and organisations. Often conflicting, these responses to climate change were informed by a mix of discourses shaping New Zealand, including participatory democracy, the knowledge economy and sustainable development.
We have quantified the current and potential carbon storage on conservation land. Conservation la... more We have quantified the current and potential carbon storage on conservation land. Conservation land was estimated to currently contain a total of 2578 Mt C (9461 Mt CO 2 e) in vegetation and soil. We estimate that conservation land could store up to 698 Mt CO 2 e more than at present, through reforestation (large gains per hectare), advance of existing shrubland successions (moderate gains per hectare) and recovery of existing forests from disturbances, including animal browsing, (small gains over large areas). Wild animal control plays a role in all three types of gain, but here we demonstrate that, for existing forests, it will be very challenging to quantify sequestration in existing forests that (a) can be attributed to wild animal control and (b) is additional to the sink that already exists. It is our view that the presence of a forest sink in existing forests is a strong endorsement of business-as-usual management of conservation land in forest and that this management should be maintained for the benefit of all New Zealanders. We recommend that any future effort to increase carbon sequestration through targeted wild animal control should focus on successional communities-removing wild animals from broadleaved-hardwood successions where the palatable canopy species of the future need to become established, and supporting other management actions to establish novel woody successions to indigenous forests within degraded grasslands. These actions should be evaluated alongside the carbon costs of undertaking these management activities. We note that on conservation land where natural succession does not readily occur, additional, and likely intensive, management will be required such as planting for shelter and provision of seed, with associated weeding requirements. The fastest, and most cost-effective, action to increase carbon sequestration on conservation land is to choose sites close to existing indigenous forest seed sources that are relatively warm (mean annual temperature > 9°C) and receive reasonable rainfall (> 1000 mm per annum) and retire these from grazing and to prevent fire and domestic or wild animal incursion as far as possible and allow natural regeneration to proceed unhindered. Further thought needs to be given to the carbon consequences of novel ecosystems-especially whether exotic woody species are able to play a desirable role in natural regeneration of indigenous forests.
Science for Conservation is a scientific monograph series presenting research funded by New Zeala... more Science for Conservation is a scientific monograph series presenting research funded by New Zealand Department of Conservation (DOC). Manuscripts are internally and externally peer-reviewed; resulting publications are considered part of the formal international scientific literature. Individual copies are printed, and are also available from the departmental website in pdf form. Titles are listed in our catalogue on the website, refer www.doc.govt.nz under Publications, then Science & technical.
Uncertainty about the mechanisms driving biomass change at broad spatial scales limits our abilit... more Uncertainty about the mechanisms driving biomass change at broad spatial scales limits our ability to predict the response of forest biomass storage to global change. Here we use a spatially representative network of 874 forest plots in New Zealand to examine whether commonly hypothesised drivers of forest biomass and biomass change (diversity, disturbance, nutrients and climate) differ between old-growth and secondary forests at a national scale. We calculate biomass stocks and net biomass change for live above-ground biomass, belowground biomass, deadwood and litter pools. We combine these data with plot-level information on forest type, tree diversity, plant functional traits,
We created small‐scale artificial canopy gaps to accelerate the growth of mature indigenous fores... more We created small‐scale artificial canopy gaps to accelerate the growth of mature indigenous forest canopy species for restoration of an 18‐year‐old exotic Pinus radiata plantation forest, in the Marlborough Sounds, New Zealand. Small and large circular gaps were formed by felling. Seedlings of two indigenous forest canopy species, Podocarpus totara (Podocarpaceae) and Beilschmiedia tawa (Lauraceae), were planted within artificial gaps and undisturbed plantation canopy. Seedling height growth, mortality, and occurrence of animal browse were monitored at approximately 6‐month intervals over 17 months. Both P. totara and B. tawa differed significantly in height growth and in animal browse occurrence among artificial gap treatments. Growth of the light‐demanding P. totara was better under large canopy gaps, whereas growth of the shade‐tolerant B. tawa increased under gaps of any size but was most consistent under small gaps. For P. totara, any significant restoration benefit of gap formation on height growth was lost when browsed seedlings were taken into account. Animal browse significantly limited B. tawa height growth in large but not in small gaps. Small‐scale canopy gap creation is an effective method of modifying light transmission to the plantation understorey and accelerating seedling growth rates. Canopy gap size can be used to optimize understorey illumination according to species‐specific light requirements. The increased occurrence of animal browse in gaps requires consideration. Artificial canopy gaps within planted monocultures create structural heterogeneity that would otherwise take an extended period of time to develop. These results further support the role of plantations as indigenous forest restoration sites.
Many studies have quantified uncertainty in forest carbon (C) storage estimation, but there is li... more Many studies have quantified uncertainty in forest carbon (C) storage estimation, but there is little work examining the degree of uncertainty in shrubland C storage estimates. We used field data to simulate uncertainty in carbon storage estimates from three error sources: (1) allometric biomass equations; (2) measurement errors of shrubs harvested for the allometry; and (3) measurement errors of shrubs in survey plots. We also assessed uncertainty for all possible combinations of these error sources. Allometric uncertainty had the greatest independent effect on C storage estimates for individual plots. The largest error arose when all three error sources were included in simulations (where the 95% confidence interval spanned a range equivalent to 40% of mean C storage). Mean C sequestration (1.73 Mg C ha-1 year-1) exceeded the margin of error produced by the simulated sources of uncertainty. This demonstrates that, even when the major sources of uncertainty were accounted for, we were able to detect relatively modest gains in shrubland C storage.
This paper is part of a series of studies that investigate the utility of nonharvest Pinus planta... more This paper is part of a series of studies that investigate the utility of nonharvest Pinus plantations as indigenous forest restoration sites in New Zealand.
ABSTRACT Increased afforestation of non-productive land could deliver win-win solutions for green... more ABSTRACT Increased afforestation of non-productive land could deliver win-win solutions for greenhouse gas mitigation through carbon sequestration and biodiversity gains, referred to here as increased ‘ecological integrity’. We examined the potential trade-offs when selecting non-forested lands in New Zealand for natural forest regeneration to maximise gains in either, or both, carbon and biodiversity. We also examine the effect on potential gains and trade-offs of excluding non-conservation lands from spatial planning for conservation. The most significant per-hectare gains, for both carbon and biodiversity, were those occurring on non-conservation lands because conservation lands are mainly restricted to low-productivity environments where indigenous vegetation is already well represented. By contrast, productive environments, such as alluvial plains, where almost no indigenous vegetation remains, are primarily on non-conservation lands. These lands will need to be included in any reforestation strategy or else the most degraded ecosystems will not be restored. We found that biodiversity suffers a greater trade-off when carbon gain is prioritised than carbon does when biodiversity is prioritised. Trade-offs between carbon and biodiversity were higher on non-conservation lands but decreased with increasing area regenerated. Our study shows that natural regeneration will provide substantial increases in carbon and biodiversity on non-conservation lands compared with conservation lands. This emphasised the need for improved incentives to private land owners if carbon and biodiversity gain from afforestation is to be maximised.
This thesis investigates the influence of carbon dioxide concentration on carbon assimilation in ... more This thesis investigates the influence of carbon dioxide concentration on carbon assimilation in tropical tree species. To investigate the response of tropical tree species to elevated CO2 concentration, seedlings of Cedrela odorata L. (Meliaceae) were grown in open-top chambers and exposed to atmospheric CO 2 at either ambient or twiceambient concentrations. Nutrient supply rate was also altered to investigate its interaction with elevated CO 2 concentration. This experiment was repeated on different seedlings over two years, 1995 and 1996. The seedlings of C. odorata grown in 1996 showed an acclimation response to elevated CO2 concentration, but those grown in 1995 did not. Plants grown in elevated CO2 concentration were only larger than those grown in ambient CO2 concentration in 1995 with a high rate of nutrient supply. It is hypothesised that high vapour pressure deficits restricted stomatal conductance and consequent photosynthesis in both years, but that this effect was particularly pronounced in 1996, when combined with a nutrient regime of excessively high concentration for the rate of growth. These effects are hypothesised to have triggered acclimation, or a reduction in CO2 fixation capacity, as indicated by changes in derived values for the enzyme kinetic parameters of the carboxylation enzyme, ribulose 1, 5 bisphosphate carboxylase-oxygenase (Rubisco). 'U ACKNOWLEDGEMENTS I thank John Grace for his guidance and good humour throughout this project. I am particularly grateful for his careful reading of this thesis in its final stages. I also thank Paul Jarvis for the insight, time and patience that I received throughout my work, again, during writing in particular. I thank Andy Gray for sharpening my selfesteem, Diarmuid O'Neill for help with harvests, Craig Barton for generous technical assistance, Alex Harrower and Dave McKenzie for helping me to build things, and Bill-and Bob for helping me to grow things. I also thank Tam and Joe, Mike
There are strong financial incentives for accurately estimating potential Kyoto-compliant carbon ... more There are strong financial incentives for accurately estimating potential Kyoto-compliant carbon sequestration on conservation land. However, estimation of potential carbon stocks is complicated, as it is unclear how the accuracy of estimates should be validated. One way of addressing this is to use several independent methods to estimate potential carbon stocks; the results can then be compared to indicate where uncertainty lies in predicting Kyoto-compliant carbon gain. In this study, the LUCAS vegetation survey plots were used in spatial predictive modelling to estimate current carbon stocks on conservation land in New Zealand. Three independent methods were then used to estimate potential carbon stocks, based on either regression models of potential forest cover using present-day forest survey data; spatial models of disturbance-adjusted carbon stock values for LUCAS plots; or a forest dynamics model that explicitly models changes in carbon. Kyoto-compliant lands were identified using the New Zealand Vegetation Cover Map. Conservation land was estimated to currently contain a total of 2578 Mt of C (9461 Mt CO 2 e) in vegetation and soil. The three different methods provided estimates of Kyoto-compliant carbon gain ranging from 63 to 186 Mt of C (231-682 Mt CO 2 e) as a result of land use change from nonforest to forest land. This equates to 3-8 years of New Zealand's total greenhouse gas emissions, based on estimated levels for 2005, and would take at least several centuries to be realised. Reasons for the variation in estimates, implications of results and limitations of the methods used are discussed. We acknowledge that uncertainties exist, primarily in the assumptions used to estimate total Kyoto-compliant forest areas and, to a lesser extent, extrapolation between plot-scale carbon measurements.
Science for Conservation is a scientific monograph series presenting research funded by New Zeala... more Science for Conservation is a scientific monograph series presenting research funded by New Zealand Department of Conservation (DOC). Manuscripts are internally and externally peer-reviewed; resulting publications are considered part of the formal international scientific literature. Individual copies are printed, and are also available from the departmental website in pdf form. Titles are listed in our catalogue on the website, refer www.doc.govt.nz under Publications, then Science & technical.
Abstract:" New Zealand's responses in the face of climate change range from the central... more Abstract:" New Zealand's responses in the face of climate change range from the central government's Emissions Trading Scheme (ETS), to infrastructure adaptations in settlements, to reframing of how social research engages with the phenomenon of climate change. ...
Carbon assimilation by Cedrela odorata L. (Meliaceae) seedlings was investigated in ambient and e... more Carbon assimilation by Cedrela odorata L. (Meliaceae) seedlings was investigated in ambient and elevated CO 2 concentrations ([CO 2 ]) for 119 days, using small fumigation chambers. A solution containing macro-and micronutrients was supplied at two rates. The 5% rate (high rate) was designed to avoid nutrient limitation and allow a maximum rate of growth. The 1% rate (low rate) allowed examination of the effect of the nutrient limitation-elevated CO 2 interaction on carbon assimilation. Root growth was stimulated by 23% in elevated [CO 2 ] at a high rate of nutrient supply, but this did not lead to a change in the root:shoot ratio. Total biomass did not change at either rate of nutrient supply, despite an increase in relative growth rate at the low nutrient supply rate. Net assimilation rates and relative growth rates were stimulated by the high rate of nutrient addition, irrespective of [CO 2 ]. We used a biochemical model of photosynthesis to investigate assimilation at the leaf level. Maximum rate of electron transport (J max) and maximum velocity of carboxylation (V cmax) did not differ significantly with CO 2 treatment, but showed a substantial reduction at the low rate of nutrient supply. Across both CO 2 treatments, mean J max for seedlings grown at a high rate of nutrient supply was 75 µmol m-2 s-1 and mean V cmax was 27 µmol m-2 s-1. The corresponding mean values for seedlings grown at a low rate of nutrient supply were 36 µmol m-2 s-1 and 15 µmol m-2 s-1 , respectively. Concentrations of leaf nitrogen, on a mass basis, were significantly decreased by the low nutrient supply rate, in proportion to the observed decrease in photosynthetic parameters. Chlorophyll and carbohydrate concentrations of leaves were unaffected by growth [CO 2 ]. Because there was no net increase in growth in response to elevated [CO 2 ], despite increased assimilation of carbon at the leaf level, we hypothesize that the rate of respiration of non-photosynthetic organs was increased.
The observation of acclimation in leaf photosynthetic capacity to differences in growth irradianc... more The observation of acclimation in leaf photosynthetic capacity to differences in growth irradiance has been widely used as support for a hypothesis that enables a simplification of some soil-vegetation-atmosphere transfer (SVAT) photosynthesis models. The acclimation hypothesis requires that relative leaf nitrogen concentration declines with relative irradiance from the top of a canopy to the bottom, in 1 : 1 proportion. In combination with a light transmission model it enables a simple estimate of the vertical profile in leaf nitrogen concentration (which is assumed to determine maximum carboxylation capacity), and in combination with estimates of the fraction of absorbed radiation it also leads to simple 'big-leaf' analytical solutions for canopy photosynthesis. We tested how forests deviate from this condition in five tree canopies, including four broadleaf stands, and one needle-leaf stand: a mixed-species tropical rain forest, oak (Quercus petraea (Matt.) Liebl), birch (Betula pendula Roth), beech (Fagus sylvatica L.) and Sitka spruce (Picea sitchensis (Bong.) Carr). Each canopy was studied when fully developed (mid-to-late summer for temperate stands). Irradiance (Q , µ µ µ µ mol m − − − − 2 s − − − − 1) was measured for 20 d using quantum sensors placed throughout the vertical canopy profile. Measurements were made to obtain parameters from leaves adjacent to the radiation sensors: maximum carboxylation and electron transfer capacity (V a , J a , µ µ µ µ mol m − − − − 2 s − − − − 1), day respiration (R da , µ µ µ µ mol m − − − − 2 s − − − − 1), leaf nitrogen concentration (N m , mg g − − − − 1) and leaf mass per unit area (L a , g m − − − − 2). Relative to upper-canopy values, V a declined linearly in 1 : 1 proportion with N a. Relative V a also declined linearly with relative Q , but with a significant intercept at zero irradiance (P < 0•01). This intercept was strongly related to L a of the lowest leaves in each canopy (P < 0•01, r 2 = 0•98, n = 5). For each canopy, daily ln Q was also linearly related with ln V a (P < 0•05), and the intercept was correlated with the value for photosynthetic capacity per unit nitrogen (PUN: V a / N a , µ µ µ µ mol g − − − − 1 s − − − − 1) of the lowest leaves in each canopy (P < 0•05). V a was linearly related with L a and N a (P < 0•01), but the slope of the V a : N a relationship varied widely among sites. Hence, whilst there was a unique V a : N a ratio in each stand, acclimation in V a to Q varied predictably with L a of the lowest leaves in each canopy. The specific leaf area, L m (cm 2 g − − − − 1), of the canopy-bottom foliage was also found to predict carboxylation capacity (expressed on a mass basis; V m , µ µ µ µ mol g − − − − 1 s − − − − 1) at all sites (P < 0•01). These results invalidate the hypothesis of full acclimation to irradiance, but suggest that L a and L m of the most light-limited leaves in a canopy are widely applicable indicators of the distribution of photosynthetic capacity with height in forests.
Natural regeneration of new forests has significant potential to mitigate greenhouse gas emission... more Natural regeneration of new forests has significant potential to mitigate greenhouse gas emissions, but how strong is the potential biodiversity co-benefit? We quantified carbon accumulation and biodiversity gain during secondary succession of two New Zealand lowland forests. The rate of carbon sequestration was the same for the kanuka-red beech succession as for the coastal broadleaved succession (c. 2.3 Mg C ha-1 year-1) over the first 50 years of succession. Mean above-ground carbon stocks were 148 ± 13 Mg C ha-1 for kanuka-red beech forests and 145 ± 19 Mg C ha-1 for tall coastal broadleaved forests after at least 50 years of succession. Biodiversity gain was investigated through the quantification of 'ecological integrity', which comprises dominance by indigenous species, occupancy of indigenous species or a group of species fulfilling a particular ecological role, and gain in representation of lowland forests within each ecological region. All components of ecological integrity increased with carbon accumulation for both successions. In addition, aboveground carbon stocks were correlated with the Shannon and Simpson diversity indices and species richness for both successions, suggesting that conventional metrics of diversity also show biodiversity gain with aboveground carbon during succession of recently non-forested lands to secondary forest.
Regional governance to address climate change is being constituted in New Zealand through domesti... more Regional governance to address climate change is being constituted in New Zealand through domestic policy measures and international discourses. We examine climate change responses in two regions: Marlborough and Waikato. Informants expressed a desire for more transparent government policy; that planning for climate change makes good business sense for farmers and other businesses; that technology is sought to increase productivity and decrease environmental impact; and research networks build capacity for local action, linking sectors and organisations. Often conflicting, these responses to climate change were informed by a mix of discourses shaping New Zealand, including participatory democracy, the knowledge economy and sustainable development.
Book chapter in: Dr JR Dymond ed, Ecosystem services in New Zealand.
This chapter reviews all stocks and fl uxes of carbon in New Zealand, and reviews biophysical reg... more This chapter reviews all stocks and fl uxes of carbon in New Zealand, and reviews biophysical regulation through surface albedo. The terrestrial environment provides a climate-regulation service by assimilating, transforming, and adjusting to emissions of greenhouse gases that could otherwise lead to undesirable changes in global climate. Quantifying this service requires accounting for both stocks and fl ows. While greenhouse gas emissions and removals are reported in the national inventory, this inventory accounts only for human-induced changes in greenhouse gases, and omits some natural processes and ecosystems; for example, indigenous forest and scrub are not included but represent the largest biomass carbon pool in New Zealand. Emissions are mainly attributed to the energy and agricultural sectors, while removals come from exotic forestry and natural shrubland regeneration. Erosion plays a role as a carbon sink through natural regeneration of soil carbon on slopes. Biophysical regulation occurs through absorption or refl ection of solar radiation (albedo). Forests tend to absorb more radiation than crops or pasture, thus contributing to a lesser extent to global warming. Government currently provides some mechanisms to incentivise sustainable land management in favour of increased forest area on lands unsuitable for agriculture. However, carbon stocks are also at risk of being lost through degradation of natural ecosystems, and this requires active management and mitigation strategies.
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