Functional trait representation differs between restoration plantings and mature tropical rainforest
Introduction
Deforestation has resulted in substantial loss and fragmentation of the world’s tropical forests (Hansen et al., 2013; Taubert et al., 2018), reducing their ability to support biodiversity (Allnutt et al., 2008) and provide ecosystem services (Portela and Rademacher, 2001, Chazdon, 2008). Loss and fragmentation of tropical forests reduce population sizes (Brook et al., 2003, Ewers and Didham, 2006), gene flow (Hamilton, 1999, Ewers and Didham, 2006), and dispersal potential of both flora and fauna (Laurance et al., 2004, Hadley and Betts, 2009, Cole et al., 2011), exacerbating their vulnerability under changing climatic conditions and limiting migration to more suitable regions. Additionally, deforestation substantially impacts many ecosystem services provided by tropical forests including carbon cycling (Baccini et al., 2017), water cycling (Webb et al., 2005, Mahmood et al., 2013, Schlesinger and Jasechko, 2014), temperature regulation (Mahmood et al., 2013), and soil maintenance (Hartanto et al., 2003). In this context, ecological restoration is a useful tool for expanding and connecting habitat patches in fragmented landscapes to retain biodiversity value and provision of ecosystem services (DeFries et al., 2010; Hansen et al., 2013; Taubert et al., 2018).
Numerous global initiatives, such as the Bonn Challenge, recognize the importance of tropical forest restoration and are establishing pledges to restore 350 million hectares by 2030 (Chazdon et al., 2017, Dave et al., 2019). The sheer scale of plant material required to meet these initiatives is daunting. For example restoration projects in India and Ethiopia in 2019, planted 220 million trees and 350 million trees, respectively. However, it is not only the quantity of plant production that is important, but what species are selected and the implications this may have on plant survival, site succession, and the future ecological function of these restored forests. For example, Brancalion et al. (2018) compared the functional traits of planted and mature Atlantic forests in Brazil, and found that species with small animal-dispersed or wind-dispersed seeds were far more abundant in planted forests than in mature rainforest. Although species with these characteristics are common in naturally recovering forests (Goosem et al., 2016), planting millions of trees with similar traits could have important implications for successional trajectories because it may “inadvertently homogenize” plant communities across the landscape (Palma & Laurance, 2015).
Despite the potential for functional trait representation to influence recovery trajectories and biodiversity in tropical forest restoration, studies examining this are rare. After almost three decades of restoration activity in the Australian Wet Tropics, no studies have yet explored the ecological implications of planting composition. The aim of this study was to assess the relative abundance of species used in restoration plantings for both individual plantings, and the pool of all restoration plantings. Additionally, we aimed to compare species abundance relative to functional traits with direct influences on ecological function of restoration plantings, and the relative representation of these functional traits between restoration plantings and mature rainforest. The functional traits of seed type (size and dispersal mode), maximum height, wood density, and germination time were selected for comparison and binned into discreet functional groups based on previous ecological literature and available data. Two key questions were formulated: (1) How does seedling abundance at the level of individual plantings, and the pool of restoration plantings, differ between species and functional groups? (2) Does the relative representation of functional groups differ between restoration plantings and mature forest? We expected that species from functional groups associated with increased seed and seedling production (small seeds, shorter germination times, low wood density) would have higher abundance in restoration plantings, and that this reduction in the relative abundance of large-seeded, slow-growing species would result in a lower abundance of large tree species.
Section snippets
Study area
The Wet Tropics biogeographic region of north-eastern Australia, henceforth referred to as the ‘Australian Wet Tropics’, encompasses an area of ~ 900,000 ha of tropical forest (Kanowski et al., 2003), that spans 450 km of north-eastern Australia (Fig. 1). The region represents an area of significant floral and faunal biodiversity with a high level of endemism (Williams et al., 2009), and is considered an area of Outstanding Universal Value (UNESCO, n.d.). To date, the Australian Wet Tropics has
Species diversity and abundance
Over a six year period, rainforest restoration in the Australian Wet Tropics incorporated a highly diverse selection of 515 tree species, making up 435,435 individual seedlings. The abundance of species produced in nurseries was extremely uneven (Fig. 2) with the 52 most abundant species comprising > 50% of all individual plants produced (the 20 most abundant species are reported in Table A1). Hence, the overwhelming majority of species had low abundances across the pool of seedling records,
Discussion
We found that seedling supply records for plantings in the Australian Wet Tropics to be some of the most speciose when compared to previous studies, in Australia and globally, at the level of both individual plantings (Palma & Laurance, 2015) and across the entire region (Brancalion et al., 2018). Relative abundance of tree species was highly variable, however, species possessing functional traits associated with greater seed supply and faster seedling production (such as smaller seeds, shorter
Conclusion
Species with functional traits promoting greater seedling production and faster growth (small seeds, shorter germination times, lower wood density) were substantially more abundant when analysing seedling supply records for restoration across the Australian Wet Tropics. This resulted in restoration plantings having a greater abundance of seedlings from small-seeded animal-dispersed species than was present in adult trees of mature rainforest within the same bioregion. However, this did not
CRediT authorship contribution statement
Jayden E. Engert: Conceptualization, Methodology, Formal analysis, Investigation, Data curation, Writing - original draft, Writing - review & editing, Visualization. Nara O. Vogado: Formal analysis, Writing - original draft. Kylie Freebody: Resources, Writing - review & editing. Basil Byrne: Resources, Writing - review & editing. Judy Murphy: Resources, Writing - review & editing. Gaylene Sheather: Resources, Writing - review & editing. Peter Snodgrass: Resources, Writing - review & editing.
Acknowledgements
We thank the wonderful staff of the six nurseries that supplied records and provided feedback for this research, from; Cairns Regional Council Stratford Nursery, Cassowary Coast Regional Council Tully Nursery, Douglas Shire Regional Council Mossman Nursery, Queensland Parks and Wildlife Service Lake Eacham Nursery, Rainforest Rescue Daintree Nursery, and Tablelands Regional Council Community Revegetation Nursery.
Declaration of Competing Interest
None.
References (79)
- et al.
Can active restoration of tropical rainforest rescue biodiversity? A case with bird community indicators
Biol. Conserv.
(2012) - et al.
Direct seeding of late-successional trees to restore tropical montane forest
For. Ecol. Manage.
(2011) - et al.
Restoration of seasonal semideciduous forests in Brazil: influence of age and restoration design on forest structure
For. Ecol. Manage.
(2004) - et al.
Factors affecting runoff and soil erosion: plot-level soil loss monitoring for assessing sustainability of forest management
For. Ecol. Manage.
(2003) - et al.
When and where to actively restore ecosystems
For. Ecol. Manage.
(2011) Effects of above- and below-ground competition of shrubs and grass on Calophyllum brasiliense (Camb.) seedling growth in abandoned tropical pasture
For. Ecol. Manage.
(1998)Economy and ecology of emerging markets and credits for bio-sequestered carbon on private land in tropical Australia
Ecol. Econ.
(2008)- et al.
Development of forest structure on cleared rainforest land in eastern Australia under different styles of reforestation
For. Ecol. Manage.
(2003) - et al.
Retention and restoration priorities for climate adaptation in a multi-use landscape
Global Ecol. Conserv.
(2019) - et al.
A dynamic model of patterns of deforestation and their effect on the ability of the Brazilian Amazonia to provide ecosystem services
Ecol. Model.
(2001)
Transpiration in the global water cycle
Agric. For. Meteorol.
How much carbon is sequestered during the restoration of tropical forests? Estimates from tree species in the Brazilian Atlantic forest
For. Ecol. Manage.
Abiotic and vertebrate seed dispersal in the Brazilian Atlantic forest: implications for forest regeneration
Biol. Conserv.
The role of animal seed dispersal in accelerating native forest regeneration on degraded tropical lands
For. Ecol. Manage.
A method for quantifying biodiversity loss and its application to a 50-year record of deforestation across Madagascar
Conserv. Lett.
Tropical forests are a net carbon source based on aboveground measurements of gain and loss
Science
Predation of cassowary dispersed seeds: is the cassowary an effective disperser?
Integrative Zool.
Long-term stem inventory data from tropical rain forest plots in Australia
Ecology
Maximizing biodiversity conservation and carbon stocking in restored tropical forests
Conserv. Lett.
What makes ecosystem restoration expensive? A systematic cost assessment of projects in Brazil
Biol. Conserv.
Catastrophic extinctions follow deforestation in Singapore
Nature
Optimal Tree Canopy Cover during Ecological Restoration: A Case Study of Possible Ecological Thresholds in Changting
China. BioScience
Species wood density and the location of planted seedlings drive early-stage seedling survival during tropical forest restoration
J. Appl. Ecol.
Seedling growth responses to species-, neighborhood-, and landscape-scale effects during tropical forest restoration
Ecosphere
Towards a worldwide wood economics spectrum
Ecol. Lett.
A Policy-Driven Knowledge Agenda for Global Forest and Landscape Restoration
Conserv. Lett.
Beyond Deforestation: Restoring Forests and Ecosystem Services on Degraded Lands
Science
Survival, growth and seed mass in a mixed tree species planting for Atlantic Forest restoration
AIMS Environ. Sci.
Australian Rainforest Fruits
A global meta-analysis on the ecological drivers of forest restoration success
Nat. Commun.
Deforestation driven by urban population growth and agricultural trade in the twenty-first century
Nat. Geosci.
Growth performance and management of a mixed rainforest tree plantation
New Forest
Confounding factors in the detection of species responses to habitat fragmentation
Biol. Rev.
Height-diameter allometry of tropical forest trees
Biogeosciences
Species functional redundancy, random extinctions and the stability of ecosystems
J. Ecol.
Strategies for empowering the local people to participate in forest restoration
Agrofor. Syst.
Cited by (15)
Restoration opportunities beyond highly degraded tropical forests: Insights from India's Western Ghats
2024, Biological ConservationRestoration plantings in the Atlantic Forest use a small, biased, and homogeneous set of tree species
2024, Forest Ecology and ManagementReforestation success can be enhanced by improving tree planting methods
2023, Journal of Environmental ManagementGrowth form and functional traits influence the shoot flammability of tropical rainforest species
2022, Forest Ecology and ManagementCitation Excerpt :Pioneer (δ = 0.79) and understory shrubs (0.788) were above this expected value suggesting that as groups there was more variability among species than expected by chance. We qualitatively applied our species’ flammability rankings from Axis 1 rank ordination heat map (Fig. S1) to the plant species commonly used in rainforest restoration in the Wet Tropics region, Australia, from 2012 to 2017 (Engert et al., 2020). There were 75 of our species reported from the two studies that encompassed 151,227 seedlings planted out at 8300 sites over the five-year period between 2012 and 2017.
Response of leaf functional traits to precipitation change: A case study from tropical woody tree
2022, Global Ecology and ConservationCitation Excerpt :As a link between plant and environment, leaf traits are relatively sensitive to environment and climate change (Oktavia et al., 2020). Therefore, in those studies about individual, population, and ecosystem, leaf traits provide an essential basis for explaining changes in ecosystem processes, function, and stability (Heilmeier, 2019; Engert et al., 2020). In particular, leaves are regarded as the major organs for light energy absorption and carbohydrate assimilation, exhibit a stronger susceptibility to circumstance and rapidly alter their strategies for resource acquisition, utilization, and storage (Ivanova et al., 2018; Tor-ngern et al., 2021).
Do primary rainforest tree species recruit into passively and actively restored tropical rainforest?
2021, Forest Ecology and ManagementCitation Excerpt :Unfortunately, the number of species that can be practically included in these plantings is limited by seed availability, ease of seed germination, and the ability of germinated seedlings to survive in nursery conditions which may differ from the rainforest understorey in ways that are difficult for nurseries to recreate (Goosem and Tucker, 1995, 2013; Elliott et al., 2003, 2014; Brancalion et al., 2018; Engert et al., 2020). In practice, Maximum Diversity plantings contain only a subset of regional species diversity, and species with larger, vertebrate-dispersed propagules and species with high wood density are particularly under-represented (Brancalion et al., 2018; Engert et al., 2020). The traits of the species that are absent in Nurse Plantation and Framework Method plantings, and under-represented in Maximum Diversity plantings, are also the traits that typically describe the species most vulnerable to the effects of forest fragmentation and habitat loss and which are thus of greatest conservation concern (Tabarelli et al., 1999; Santos et al., 2008; Pütz et al., 2011; Osuri et al., 2017; Hooper and Ashton, 2020).