Predicting Growth Carbon Sequestration and Salinity Impacts of Forestry Plantations

Nico Marcar, Tivi Theiveyanathan, Debbie Crawford, Charlie Hawkins, Tom Jovanovic, Philip Polglase, Anders Siggins, Jacqui England, Auro Almeida, Keryn Paul, and Brendan Christy

Abstract Farm forestry is an increasingly important form of diversifying farm income and helping to deal with environmental issues including dryland salinity, global warming and climate variability. Here we briefly describe the development, use and spatial application of improved versions of the plantation growth model, 3-PG, to provide estimates of productivity and carbon sequestration as well as salinity impacts. Several forestry scenarios using eucalypt species and Pinus radiata were tested with application to the Corangamite Catchment in south western Victoria, Australia.

Keywords Corangamite catchment ■ Carbon sequestration ■ Salinity stress ■ Forests

Contents

1 Introduction 144

2 Materials and Methods 145

3 Results and Discussion 146

4 Conclusions 148

References 148

N. Marcar, T. Theiveyanathan, D. Crawford, T. Jovanovic, P. Polglase, K. Paul (B) CSIRO Sustainable Ecosystems, GPO Box 284, Canberra, ACT 2601, Australia e-mail: [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]

CSIRO Sustainable Ecosystems, Private Bag 10, Clayton South, Victoria 3169, Australia e-mail: [email protected]; [email protected]; [email protected]

CSIRO Sustainable Ecosystems, Private Bag 12, Hobart, Tasmania 7001, Australia e-mail: [email protected]

Department of Primary Industry Victoria, 1145 Chiltern Valley Road, Rutherglen, Victoria 3685, Australia e-mail: [email protected]

M. Ashraf et al. (eds.), Plant Adaptation and Phytoremediation, 143

DOI 10.1007/978-90-481-9370-7_7, © Springer Science+Business Media B.V. 2010

1 Introduction

Amongst important issues in Australia at present are dryland salinity, climate variability and the need for water conservation. Rainfall is predicted to decrease in many parts of southern Australia over the next few decades. In south-eastern Australia, occurrence of dryland salinity is typically scattered and patchy, with stream salinity often a greater concern than land salinisation. Growing trees on farms for commercial or semi-commercial benefit (farm forestry) is an increasingly important and recognised form of diversifying farm income and providing environmental services in Australia. Tree planting may help reduce in-stream and end-of-catchment salinity, provide habitat to enhance biodiversity, produce timber and sequester carbon to offset greenhouse gas emissions and address global warming and climate variability.

The Corangamite catchment (13,350 km2) located in south-western Victoria, Australia (Fig. 7.1) provided a test region for applying predictive modeling as part of the Commercial Environmental Forestry (CEF) project (Polglase et al. 2006). Dryland salinity is estimated to affect 17,250 ha of land in this catchment (Nicholson et al. 2006) with stream salinisation an important issue in the northern part of the catchment. Land use is predominantly agriculture, including dairy in the higher rainfall areas to the south, broad-acre cropping in the north and mixed cropping and grazing throughout the extensive volcanic plains in the centre. There are more than 45,000 ha of plantation forestry in the catchment, mostly Pinus radiata (radi-ata pine) and Eucalyptus globulus (blue gum) mainly in higher rainfall (>700 mm) areas, with smaller farm forestry plantings (including E. cladocalyx - sugar gum) where rainfall is lower (450-700 mm).

The plantation growth model, 3-PG (Physiological Principles in Predicting Growth), originally developed by Landsberg and Waring (1997) and variously modified since then (e.g., Sands and Landsberg 2002), is a process-based forest growth model widely tested and applied (Sands and Landsberg 2002, Almeida et al. 2004,

Fig. 7.1 Location of the Corangamite catchment in south-western Victoria, Australia

Fig. 7.1 Location of the Corangamite catchment in south-western Victoria, Australia

Dye et al. 2004, Stape et al. 2004). In its simplest form, the model requires monthly climate inputs (total short wave incoming radiation, mean temperature and vapour pressure deficit, and total rainfall), knowledge of soil texture, soil water holding capacity, an indication of soil fertility, initial number of trees per hectare, and initial values for stem (including bark and branches), foliage and root mass per hectare to initialise the model at a selected age. The model incorporates simplifications of some well-known relationships, with the aim of describing complex physiological processes so that they can be applied to plantations or even-aged, relatively homogeneous forests. Many of the parameters used in 3-PG need to be calibrated for individual species or different genotypes within a species, however there are parameter sets for several species available in the literature (e.g., Almeida et al. 2004, Paul et al. 2007, Morris 2003).

Here we briefly describe the development, use and spatial application of two recent versions of the plantation growth model, 3-PG, for various forestry scenarios to provide predictions of growth, carbon sequestration, water use and salinity impacts at catchment and farm scales.

2 Materials and Methods

Two versions of 3-PG were developed and applied. 3-PG2 was improved to include the ability to model over- and under-storey, different planting configurations, responses to environmental factors such as soil water stress and salinity (termed 'growth modifiers'), and the water balance is now calculated in a more detailed way (Polglase et al. 2006; Almeida et al. 2004). 3-PG2 was used to spatially model (as 3-PG2 Spatial or 3-PG2S; 100 x 100 m grid resolution) growth, carbon sequestration and water use for the entire Corangamite catchment region. 3-PG+ (Morris 2003) was further modified to improve water balance prediction capability (using daily time-step climate inputs to better estimate run off and infiltration) to predict growth, carbon and water use, and it was also used within a hydrological modelling framework, the Catchment Analysis Tool (CAT, Beverly et al. 2006), as CAT_3-PG+ (20 x 20 m grid resolution), to predict impacts of stream salinity and flows, for salinity-prone, northern areas of the Corangamite catchment. CAT includes a suite of one dimensional farming system models linked to a distributed surface hydrology model and a groundwater model. Both 3-PG2S and 3-PG+_CAT used spatial input data layers including soil depth, soil texture, fertility index, road networks, hydrology and digital elevation.

3-PG2S was run for 21 forestry scenarios (combinations of species, silvicultural management and site fertility rating), and 3-PG+_CAT was run for five scenarios. The species of interest - Eucalyptus globulus, E. cladocalyx, Corymbia maculata (spotted gum) and P. radiata - were deemed to have suitable commercial prospects for regions of low to moderate annual rainfall (500-800 mm). The scenarios were developed in consultation with Department of Primary Industries Victoria and several private forestry companies as a compromise between reasonable practices for species being considered and constraints of modelling. Models were run for the entire plantable area (i.e., areas not occupied by roads, buildings, parks, existing native forest and plantations).

In order to calibrate both models for different species, trees at representative sites were destructively sampled into biomass components to compare with model predictions of biomass, which is later converted to stem diameter and volume in 3-PG. In order to test growth and carbon sequestration predictions using 3-PG, site, soil (texture, structure, depth) and tree growth (height, stem diameter at breast height, leaf area index, calculated stand stem volumes) data were collected for each species from existing plantations within the Corangamite and other catchments in Victoria. Soils data were subsequently used to check spatially-predicted soil depths and estimate soil water holding capacity and site fertility/quality for input into 3-PG. Analysed tree growth data were compared with predictions.

3 Results and Discussion

Initial testing of 3-PG+ and 3-PG2 suggested that these models capture the effect of major environmental gradients on growth for the four species considered. Based on regression and model efficiency analysis, there was generally good agreement between observed and predicted growth (the model explained between 61% and 84% of the observed growth) and carbon sequestration, and in the case of CAT_3-PG+, for stream flows and salt loading.

Fig. 7.2 Spatial output layer of the Corangamite catchment for mean annual increment in stem volume (MAI, m3 ha-1 y-1) of P. radiata (30 years, sawlog, medium fertility) from 3-PG2S

Fig. 7.3 Spatial output layer for the northern part of the Corangamite catchment from CAT_3-PG+ modelling for (a) mean annual increment in stem volume (MAI, m3 ha-1 y-1) and (b) change (positive number means an increase and negative number means a decrease) in stream salinity (^S cm-1 x 10-3) for P. radiata (30 year sawlog rotation, initial stocking of 1500 stems per ha, final stocking of 250 stems per ha)

Fig. 7.3 Spatial output layer for the northern part of the Corangamite catchment from CAT_3-PG+ modelling for (a) mean annual increment in stem volume (MAI, m3 ha-1 y-1) and (b) change (positive number means an increase and negative number means a decrease) in stream salinity (^S cm-1 x 10-3) for P. radiata (30 year sawlog rotation, initial stocking of 1500 stems per ha, final stocking of 250 stems per ha)

Effects of forestry scenarios on stream flow and salt load varied with species, scenario and sub-catchment. This means that there will be trade-offs between the reduction in stream flow and the salinity of these streams for different parts of the catchments depending on which species is planted and whether the system is a long (e.g., sawlog) or short (e.g., pulpwood) rotation. Generally, by planting trees in those parts of the catchment where water moves more freely and salts are more prevalent, there will be a tendency for greater reduction in movement of salts and water to streams. However, stream salinity will vary with the relative impact of stream flow and salt load. Modelling results would also be expected to differ if only certain parts of landscape within the catchment were targeted for forestry.

For all the scenarios that were run it was predicted that plantations reduced stream salinity but also stream flow, the extent dependent on which species and scenario was tested. Example spatial outputs are presented here for P. radiata (30 year rotation for sawlog production) for (i) estimated stem volume growth (using 3-PG2S) over the entire Corangamite sub-catchment (Fig. 7.2), and (ii) estimated growth and change in stream salinity1 (using CAT_3-PG+) for the northern part of the Corangamite catchment (Fig. 7.3a, b). Shortcomings in 3-PG+ include an inability to include more than one thinning as a management option (3-PG2 overcomes this), and effects of soil salinity and groundwater were not accounted for.

4 Conclusions

The plantation growth model, 3-PG, which was modified, calibrated and extensively verified, has been applied at catchment and farm scales to provide spatial estimates of productivity, carbon sequestration and salinity impacts of tree planting on farms. Within scenarios, stream salinity was predicted to decrease in some parts of the region and increase in others. Information obtained from modeling approaches coupled with further field studies provides land managers and government agencies with increased confidence and flexibility in making land use decisions, especially with respect to forestry.

Acknowledgments The CEF project was jointly funded by CSIRO (at that time through the entity 'Ensis') and Department of Agriculture, Forestry and Fisheries (DAFF) with support from the Corangamite Catchment Management Authority (CCMA), the Department of Primary Industries (DPI) Victoria and Central Victorian Farm Plantations.

References

Almeida AC, Landsberg JJ, Sands PJ (2004) Parameterisation of 3-PG model for fast-growing

Eucalyptus grandis plantations. Forest Ecol Manag 193:179-195 Beverly C, Christy B, Weeks A (2006) Application of the 2CSalt-model to the Bet Bet, Wild Duck,

Gardiner and sugarloaf catchments in victoria. Department of Primary Industries, Victoria Dye PJ, Jacobs S, Drew D (2004) Verification of 3-PG growth and water-use predictions in twelve

Eucalyptus plantation stands in Zululand, South Africa. Forest Ecol Manag 193:197-218 Landsberg JJ, Waring RH (1997) A generalised model of forest productivity using simplified concepts of radiation-use efficiency, carbon balance and partitioning. Forest Ecol Manag 95:209-228

1 'End-of-valley' stream salinity (EC in ^S cm 1) was calculated by dividing salt load by stream flow.

Morris JD (2003) Predicting the environmental interactions of Eucalyptus plantations using a process-based forest model. In: Turnbull J (ed) ACIAR Proceedings on Eucalyptus in Asia No. 111, pp 185-192

Nicholson C, Dahlhaus P, Anderson G, Kelliher C, Stephens M (2006) Corangamite Salinity Action Plan 2005 - 2008. Corangamite Catchment Management Authority, Colac, Victoria. http://www.ccma.vic.gov.au/publications/Uploaded/SalinityActionPlan.pdf Paul KI, Booth TH, Jovanovic T, Sands PJ, Morris JD (2007) Calibration of the forest growth model 3-PG to eucalypt plantations growing in low rainfall regions of Australia. Forest Ecol Manag 243:237-247

Polglase P, Booth T, England J, Falkiner R, Hawkins C, Jovanovic T, Marcar N, Paul K, Theiveyanathan T, van Dijk A, Freudenberger D, Cawsey M, Barrett G (2006) Commercial environmental forestry: targeting new forests for multiple benefits. In: Sustainable forestry -everybody benefits. Proceedings Australian forest growers international biennial conference. Launceston, Australia. 22-25 October 2006. pp 168-175 Sands PJ, Landsberg JJ (2002) Parameterisation of 3-PG for plantation grown Eucalyptus globulus.

Forest Ecol Manag 163:273-292 Stape JL, Ryan MG, Binkley D (2004) Testing the utility of the 3-PG model for growth of Eucalyptus grandis x urophylla with natural and manipulated supplies of water and nutrients. Forest Ecol Manag 193:219-234

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