Observations of “coarse” root development in young trees of nine exotic species from a New Zealand plot trial

Rowan²,

Lambie

2016

Self Cite

Background: Establishment of exotic forest on erosion-prone pastoral hill country in the East Coast region of New Zealand escalated following a major cyclonic storm in 1988. Pinus radiata D.Don is the predominant species used for erosion control. It has been suggested that planting densities could be reduced if faster growing P. radiata seedlings and cuttings from genetically improved seed lots were used.Methods: A field-based trial was established to measure and compare annual growth rates between P. radiata seed lots (GF 16 and GF 19 seedlings and cuttings grown from GF 23 seed) used during the period of early forest establishment (1960s onwards) in this region and genetically improved seed lots (GF 27 seedlings and GF 28 cuttings) developed at a later date. Over a 4-year period, the above-ground parameters (diameter at breast height, root collar diameter, tree height and canopy diameter) were measured before whole trees (canopy and root systems) were destructively sampled.Results: Root collar diameter (over bark) was most highly correlated with tree height, with r 2 ranging between 0.95 and 0.98 for all the seed lots, and all regressions were highly significant (P < 0.001). In any year of the trial, there were no differences among seed lots with respect to root collar diameter, total above-ground biomass or total below-ground biomass. By year 4, mean below-ground biomass comprised 17% of total biomass. There was no consistently significant difference among seed lots in the distribution of total below-ground biomass or root length with distance from the root bole, relative to depth, or in either their maximum lateral root spread or maximum root depth until year 4 when GF16S and GF27S had a greater (P = 0.05) maximum root spread than GF28C while the latter had developed a significantly greater (P = 0.05) proportion of its root biomass and root length within the top 0.5 m of the soil profile. The root cross-sectional area of vertical roots increased significantly with age but decreased with depth. Root orientation formed a 'bilateral fan-shaped' architecture. Conclusions: The absence of consistently significant differences among seed lots suggests that during the early 4 year post-establishment period, no one seed lot would provide earlier soil reinforcement or result in a superior level of slope stability than would any of the other seed lots trialled. Thus, irrespective of seed lot preferences, any reduction in the current recommended planting density for erosion-prone hill country would further increase the period of vulnerability and risk of young plantings to damage by storm-initiated landslides.

Section: Root Length and Root System Dimensions (Diameter)supporting

confidence: 57%

Section: Resultsmentioning

confidence: 99%

Root development and whole-tree allometry of juvenile trees of five seed lots of Pinus radiata D.Don: implications for forest establishment on erosion-prone terrain, East Coast region, North Island, New Zealand

Rowan²,

Lambie

2016

Self Cite

“…Differences in the root distribution within the same field site may be explained by the variability of the initial planting material and local variation of environmental factors. For instance, it is recognised that the size and volume of planting materials influence the initial growth rate of roots and shoots (Phillips et al 2014(Phillips et al , 2015Sulaiman 2006), due to the effect of rhizocauline (Schiechtl 1992) present in the cambium cells. The higher survival and growth rates of larger diameter poles may compensate for their extra start-up cost during field establishment (Sulaiman, 2006).…”

Section: Root Distribution and Reinforcementmentioning

confidence: 99%

Modelling of root reinforcement and erosion control by ‘Veronese’ poplar on pastoral hill country in New Zealand

Schwarz

Phillips

et al. 2016

Background: The control of erosion processes is an important issue worldwide. In New Zealand, previous studies have shown the benefits of reforestation or bioengineering measures to control erosion. The impetus for this work focuses on linking recent research to the needs of practitioners by formulating quantitative guidelines for planning and evaluation of ground bioengineering stabilisation measures. Methods: Two root distribution datasets of 'Veronese' poplar (Populus deltoides x nigra) were used to calibrate a root distribution model for application on single root systems and to interacting root systems at the hillslope scale. The root distribution model results were then used for slope stability calculations in order to quantitatively evaluate the mechanical stabilisation effects of spaced trees on pastoral hillslopes. Results: This study shows that root distribution data are important inputs for quantifying root reinforcement at the hillslope scale, and that root distribution strongly depends on local environmental conditions and on the tree planting density. The results also show that the combination of soil mechanical properties (soil angle of internal friction and cohesion) and topographic conditions (slope inclination) are the major parameters to define how much root reinforcement is needed to stabilise a specific slope, and thus the spacing of the trees to achieve this. Conclusions: For the worst scenarios, effective root reinforcement (>2 kPa) is reached for tree spacing ranging from 2500 stems per hectare (sph) for 0.1 m stem diameter at breast height (DBH) to 300 sph for 0.3 m stem DBH. In ideal growing conditions, tree spacing less than 100 sph is sufficient for stem DBH greater than 0.15 m. New quantitative information gained from this study can provide a basis for evaluating planting strategies using poplar trees for erosion control on pastoral hill country in New Zealand.

“…The trial site was established in 1999 on a low-lying, even-surfaced alluvial terrace located adjacent to the Taruheru River in Gisborne City ( Fig. 1) and was used subsequently to measure the plant growth performance of: (i) eight of New Zealand's more common indigenous conifer and broadleaved species (Marden et al 2018, in press); (ii) different clones of poplar and willow (Phillips et al 2014); and (iii) a range of exotic forest species (Phillips et al 2015). Temperatures over summer average 23°C and over winter 12°C.…”

Section: Study Sitementioning

confidence: 99%

Root system attributes of 12 juvenile indigenous early colonising shrub and tree species with potential for mitigating erosion in New Zealand

Lambie

Rowan³

2018

Background: 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. 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. Methods: In 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.Results: Eleven 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) (r 2 values 0.55-0.92), as were regressions for root biomass (r 2 values 0.31-0.97). RCD fitted best for below-ground biomass (r 2 values 0.67-0.94). Conclusions:The 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.