Abstract
BackgroundRestoring erosion-prone land with indigenous species, whether by managed reforestation (planting) or by passive natural reversion, is reliant on knowing which species mix is likely to provide the quickest and most effective mitigation against shallow landslides. In turn, this requires knowledge of differences in growth metrics among plant species, particularly during their formative years. This study presents data on the root development and architecture of 12 of New Zealand’s commonest early colonising indigenous shrub and tree species. These data are crucial to the development of guidelines and policy for land use conversion and future land management options where unmitigated erosion is of increasing concern.MethodsIn a plot-based field trial, the growth performance of Coprosma robusta (karamū), Plagianthus regius (ribbonwood), Sophora tetraptera (kōwhai), Pittosporum eugenioides (lemonwood), Pittosporum tenuifolium (kōhūhū), Hoheria populnea (lacebark), Myrsine australis (māpou), Pseudopanax arboreus (fivefinger), Cordyline australis (cabbage tree), Knightia excelsa (rewarewa), Leptospermum scoparium (mānuka), and Coriaria arborea (tutu) was measured annually over five consecutive years.ResultsEleven species developed a heart-shaped root system and Cordyline australis, a tap-rooted system. By year 5, the root/shoot ratio ranged between 0.24 and 0.44, > 99.5% of the total root mass and root length of all species was confined to within 0.5 m of the ground surface and > 73% within 1 radial metre of the root bole. Regressions between root collar diameter (RCD over bark) and root length were highly significant (P < 0.001) (r2 values 0.55–0.92), as were regressions for root biomass (r2 values 0.31–0.97). RCD fitted best for below-ground biomass (r2 values 0.67–0.94).ConclusionsThe species with the greatest potential for mitigating shallow forms of erosion were Pittosporum eugenioides, Plagianthus regius, Coriaria arborea, Pittosporum tenuifolium, Hoheria populnea, Sophora tetraptera, and Cordyline australis. New data on differences in root metrics between species have improved our understanding of their strengths and limitations, alone or as mixed plantings, and of the time (years after planting) and density of plantings required to achieve a successful erosion control outcome. Modelling root-soil reinforcement and the role of root systems in mitigating the initiation of shallow slope failures should include roots > 1 mm in diameter.
Highlights
Restoring erosion-prone land with indigenous species, whether by managed reforestation or by passive natural reversion, is reliant on knowing which species mix is likely to provide the quickest and most effective mitigation against shallow landslides
The primary goals of this paper are to: (i) provide a first-ever description and classification of the root architecture of 12 of New Zealand’s more common early colonising species used predominantly in land use conversion and environmental restoration projects; (ii) present species-specific allometric equations with a focus on root biomass and length and the spatial distribution of roots with increasing distance from and below the root bole; and (iii) assess the potential effectiveness of different species mixes and planting strategies in mitigating shallow landslides and other forms of surficial erosion based on the growth performance of 5-year-old plantings
The only species to develop a tap-rooted system was Cordyline australis, which consisted of a central, tuberous root/rhizome with frequent lateral roots emerging at different depths in the soil profile (Additional file 1)
Summary
Restoring erosion-prone land with indigenous species, whether by managed reforestation (planting) or by passive natural reversion, is reliant on knowing which species mix is likely to provide the quickest and most effective mitigation against shallow landslides. A number of government-funded schemes (e.g. Afforestation Grant Schemes (Ministry for Primary Industries 2015a) and the Permanent Forest Sink Initiative (Ministry for Primary Industries 2015b) have been introduced to encourage the establishment of new areas of forest (exotic and indigenous) and to facilitate natural reversion of shrubland areas These schemes, together with a recently announced government goal to plant one billion trees over the 10 years, will likely target ~ 1.45 million ha of steep, erosion-prone pastoral hill country considered marginal for long-term agriculture and/or areas of short-rotation exotic forest where the erosion risk is high and the land better suited to transitioning to a permanent indigenous shrubland or forest (Trotter et al 2005). Thompson), account for ~ 70% of the total area of regenerating indigenous shrubland in New Zealand (Ministry for Primary Industries 2017)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
