AvailableCarswell eton-line al.: Carbon at: http://www.newzealandecology.org/nzje/ coincides with biodiversity gain 191 Carbon and plant diversity gain during 200 years of woody succession in lowland New Zealand Fiona E. Carswell1*, Lawrence E. Burrows1, Graeme M. J. Hall2, Norman W. H. Mason3 and Robert B. Allen1 1Landcare Research, PO Box 40, Lincoln 7640, New Zealand 2Forest Ecology consultant, 315 Madras Street, Christchurch 8013, New Zealand 3Landcare Research, Private Bag 3127, Hamilton 3240, New Zealand *Author for correspondence (Email: [email protected]) Published on-line: 3 May 2012 Abstract: 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, above- ground 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 above- ground carbon during succession of recently non-forested lands to secondary forest. Keywords: biodiversity; ecological integrity; secondary succession; sequestration Introduction sequestration or species that can store a lot of carbon over a long period of time (Hall 2001). Carbon is not expected Growing international interest in measurement and to accumulate linearly in successions (Peet 1981); across optimisation of the co-benefits of carbon sequestration projects biomes, sequestration rate is generally greatest before (e.g. Klooster & Masera 2000; Ferretti & de Britez 2006) has maximum biomass is achieved (Marín-Spiotta et al. 2007; been mirrored within New Zealand. This is especially true Peri et al. 2010). However, patterns of carbon sequestration in within the Department of Conservation (DOC) as the primary regenerating forests of New Zealand are largely unknown. One agency charged with restoring and maintaining biodiversity. group of authors has examined recovery of carbon stocks in Land managed for biodiversity can contribute significantly to an indigenous forest during single-species stand development mitigation of New Zealand’s greenhouse gas emissions through following natural disturbance (Davis et al. 2003). Additionally, afforestation/reforestation of ‘currently’ non-forested lands as the sequestration rate of seral mānuka (Leptospermum well as through management of existing forests to promote scoparium) has been recorded at up to 2.5 Mg C ha–1 year–1, higher standing stocks of carbon. Increasing the carbon storage (Trotter et al. 2005), yet the rate of accumulation during within existing forests is difficult because of complex feedbacks succession to other species has not been measured. To date, (Wardle et al. 2007; Peltzer et al. 2010; Holdaway et al. 2012), change in carbon stocks during succession has simply been compared with the large, rapid and measurable carbon gains estimated through the use of an ecosystem-process-based that can be made through afforestation/reforestation of currently model, LINKNZ (Hall 2001). LINKNZ was developed to non-forested lands (e.g. Knapp et al. 2008; Pinno & Wilson simulate forest development under New Zealand conditions and 2011). Afforestation could promote net gains of at least 100 is a generalisation of the LINKAGES model designed for the Mg of total carbon stock per hectare (Hall 2001), even with a mainly deciduous temperate eastern forests of North America one-off loss of carbon from the soils of grassland ecosystems (Post & Pastor 1996). In this study, we measure carbon stocks that can occur during the process of land use change leading and estimate sequestration rates during secondary succession of to forest (Guo & Gifford 2002). In a survey of restoration two lowland forests. These measurements are compared with practitioners we found indigenous afforestation/reforestation the carbon accumulation predicted by LINKNZ, which uses establishment costs to be $750 to >$50,000 per hectare, when a process-based stochastic approach to simulate ecosystem planting is used. Given that current gross annual returns for behaviour from individual species (Hall & Hollinger 2000). carbon sequestration in indigenous forests range from $40 to ‘Ecological integrity’ has now been embraced by DOC $325 per hectare, natural succession is the most economically as its primary biodiversity outcome (DOC 2011). Ecological viable establishment method for new indigenous forests. integrity has been defined as ‘the full potential of indigenous New forests could be promoted through natural successions biotic and abiotic factors, and natural processes, functioning that favour either species with high initial rates of carbon in sustainable communities, habitats, and landscapes’ by New Zealand Journal of Ecology (2012) 36(2): 191-202 © New Zealand Ecological Society. 192 New Zealand Journal of Ecology, Vol. 36, No. 2, 2012 Lee et al. (2005). These authors suggest ecological integrity 1982; Walls & Laffan 1986; Wilson 1994) and the sampled has components of long-term indigenous dominance (high stands contained well-established seedlings and saplings influence of indigenous species on ecosystem processes of later-successional species demonstrating their ability to compared with exotic species), occupancy by all appropriate regenerate under senescing individuals of species of the biota, and full representation of ecosystems. The presence previous stage. Environmental variables (aspect, soil structure, of groups of species fulfilling a particular ecosystem role is topography, altitude) were closely matched among the sites now thought more important for ecosystem functioning than representing the different successional stages. For all study the presence or absence of any single plant species (Diaz sites the regenerating forest is legally protected and both wild & Cabido 2001). Therefore ‘occupancy’ of all biota should and domestic animals have been exterminated or heavily include occurrence of key functional types as well as species’ controlled to aid rapid achievement of tall forest. Altitude occurrence. Functional plant types include groups of plant spanned 70–200 m above sea level. species ‘sharing similar roles in (or effects on) ecosystems and The kānuka–red beech succession was investigated at biomes’ (Cornelissen et al. 2003). In this study we investigate Hinewai Reserve, near Akaroa on Banks Peninsula (43°50΄ the relative abundance of plant species that provide resources S, 173°04΄ E). About 25% of the property is covered by for birds – a key role in New Zealand’s indigenous forests. We an extensive mosaic of kānuka stands at various stages of ask, is there evidence for an increase in ecological integrity regeneration (Wilson 1994). Grazing stock was progressively with above-ground carbon stocks? removed from 1987 and pest herbivores such as possums and This study examined relationships between carbon stocks, goats have been intensively controlled since. Older stands ecological integrity, and species richness during two lowland previously protected from grazing are also present and consist successions to tall forest species. The successions were: kānuka of tall forest dominated by red beech, and to a lesser extent (Kunzea ericoides, Myrtaceae) to red beech (Nothofagus fusca, Hall’s totara (Podocarpus hallii). Predicted successional Nothofagaceae) forest, and tauhinu (Ozothamnus leptophyllus, trajectories at Hinewai Reserve have been previously described Compositae) to coastal broadleaved forest. These successions as involving progression to a beech–podocarp mix as the tallest were selected because they sit near the upper end of the potential forest stage (Wilson 1994). rate of both carbon gain and attainment of tall forest stature. The coastal broadleaved succession was investigated on Kānuka–red beech is thought to be a relatively widespread two adjacent peninsulas in the outer Marlborough Sounds, in lowland successional pathway (Sullivan et al. 2007), with order to capture the full range of pre-described stages. The kānuka currently occupying at least 400 000 ha of New Zealand first was Queen Charlotte Wilderness Park on Cape Jackson (Wiser et al. 2011). The coastal broadleaved succession is much (41°02´ S, 174°16´ E) and the second was Cape Lambert more localised in its occurrence (we estimate only 25 000 ha of Scenic Reserve (41°0´ S, 174°12´ E) on Cape Lambert. A coastal broadleaved forest remain nationally) but is a vegetation detailed description of this succession has been published in type now chronically under-represented in national terms; any Mason et al. (2011). increase representing an improvement.