Click on the article title to read more.

The effect of microsite on juvenile forest plantation yield is rarely explored. This is because juvenile plantation growth is considered to be reasonably homogenous due to a lack of resource competition between trees prior to canopy closure. However, models of juvenile plantation height growth and survival that are sensitive to microsite variation could aid decisions relating to site preparation, plantation establishment and early silvicultural treatments. In this study, juvenile Eucalyptus bosistoana and E. globoidea height growth and survival proportion were modelled against topographic and environmental microsite characteristics as independent variables. The experiment included three different sites situated in a sub-humid region of New Zealand. A total of 540 plots were planted with 18,540 trees in regular rows and columns. Micro-topographical variables significantly influenced height growth and survival proportion of both E. bosistoana and E. globoidea, but species differed in their responses. More sheltered microsites yielded greater height growth and survival for both species. The height of both species was influenced by wind exposure, morphometric protection, and distance from the nearest ridge. E. bosistoana height was also influenced by topographic position and surface plan curvature. Survival was affected by surface profile curvature for both species, while E. globoidea survival was also impacted by surface plan curvature and distance from the top ridge. This study identified microsite factors influencing juvenile height and survival of two Eucalyptus species.

In New Zealand, a commonly sown pasture combination is perennial ryegrass with white clover. The hydrothermal time model (HTT) was used to quantify germination under different temperature ( T ) and water potential ( WP ) conditions for white clover ‘Nomad’ and perennial ryegrass ‘Stellar AR1’. Seeds were germinated in vitro under a range of T  × WP combinations, and HTT models were fitted to germination time course data. Rapid germination of white clover under optimum T and WP was reflected by a much lower value for its HTT constant compared with perennial ryegrass (10.8 vs 80.7 MPa°C d). However, the lower base water potential for perennial ryegrass (−1.29 vs −0.495 MPa) and a higher threshold temperature for thermoinhibition (21.8 vs 18.3°C), meant that predicted perennial ryegrass germination was more resilient in warm dry conditions. HTT models can be used to assist decisions about the timing of perennial ryegrass and white clover sowing.

In many active landscapes debris-flow hazards are largely unrecognised and, as a result, developments can be sited in locations where they are unknowingly exposed to debris-flow impact, with correspondingly unrecognised risks to lives. While modelling can represent debris-flow occurrence and behaviour, it is unsuited to the routine use at local office level that is required to identify potentially unacceptable debris-flow risks to existing and proposed developments. To address this urgent and widespread need, we develop an empirical procedure for estimating the maximum probability of debris-flow occurrence at a specified location, involving (i) calculation of catchment Melton ratio R from topographic data; (ii) a well-defined linear upper-bound envelope of field relationships between catchment R and the probability of evidence for debris-flow occurrence; and (iii) an upper bound from field data relating R to the annual probability of debris-flow occurrence. We test this procedure against a model-based risk-to-life analysis for Matatā, New Zealand and find satisfactory agreement. The procedure is intended to enable local officials to routinely identify locations where debris flow risk to life might exceed acceptable levels so that expert risk modelling and analysis can be utilised where required. Our data suggest that any development that can be impacted by debris flows is likely to require detailed risk assessment to ensure that risk-to-life is reduced to acceptable levels.

Many debris-flow catchments pose an underappreciated hazard, especially where there are dwellings on debris-flow fans and other depositional areas. There is a need to make communities and those involved in community governance aware of situations where there may be a credible risk to life from debris flows. This needs to be simple and cheap to do, since funding is often not available to study unrecognised natural hazards. Here, we use published models to (1) estimate the threshold annual recurrence interval (ARI) for debris flows in a catchment, below which there is an unacceptable annual risk to life for the occupants of any dwellings, and (2) identify the “window of non-recognition” where debris flows are sufficiently infrequent within a catchment that it is not recognised as susceptible yet frequent enough that the risk to life exceeds the acceptability threshold. Using four Aotearoa New Zealand (NZ) studies, we estimate a 95 % credible interval range for the ARIs of life-threatening debris flows of between 100 and 500 years. We show that given these credible intervals and precautionary but realistic assumptions about debris-flow behaviour and the vulnerability of dwellings and their occupants, catchments with no history of debris-flow activity can pose an unrecognised and unacceptable annual risk to life (P=0.256 that the annual risk-to-life threshold of 1 in 1000 is exceeded).