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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. [ABSTRACT FROM AUTHOR]

Highlights • Field-based and remotely-sensed methods are complementary and should be used together. • Remote-sensing data for predicting tree species diversity and stand structure at large scale. • Field-inventories for information at local scales and validation of remotely-sensed data. • High resolution satellite imagery presents good tradeoff between cost and data quality. Abstract With forest fragmentation continuing in many parts of the tropics, it is likely that fragmented forests will become the rule for most remaining global tropical forests in the next decades. In this context, there is a need for practical tools to assess and monitor fragmented forests if we are to conserve tree species diversity as much as possible. Several methods, either using (1) field-based or (2) remote-sensing approaches could be used to achieve this goal. This paper aims at providing a state-of-the-art review of both approaches in order to make recommendations for rapid and cost-effective assessments of tree species diversity and forest structure, with specific applications in studies of fragmented tropical forests. Overall both methods have pros and cons, depending on the type of data needed to address the research objectives and the quantity of resources available. We suggest combining the use of both field-based and remotely-sensed methods as they can be complementary. Remote-sensing data should be used to predict and map the tree species diversity and stand structure at regional scales, while field-inventories provide accurate information at local scales and allow validation of remotely-sensed data. For field-inventories, we recommend the use of small (e.g. 20 × 50 m) plots with a 10 cm DBH minimum measurement. In terms of remotely-sensed techniques, if funding is sufficient, airborne imagery seems the best regarding the quality of information (i.e. hyperspectral and hyperspatial imagery, LiDAR). If funding is limited, a cost-effective alternative providing reasonably accurate estimates would be the use of high-resolution satellite imagery such as Worldview. Ultimately, for studies where data accessible for free is the only possible option, we recommend the use of Sentinel-2, although it is relatively coarser in terms of quality. However, further research needs to be done to validate these approaches in fragmented tropical forests. [ABSTRACT FROM AUTHOR]

To establish the methodological basis for developing optimal irrigation strategies for increasing the productivity of triploid Populus tomentosa plantations using modelling methods, the accuracy of HYDRUS models for simulating one-dimensional (HYDRUS-1D) soil water dynamics under rainfed natural conditions (NC), and two-dimensional soil water dynamics (HYDRUS (2D/3D)) under subsurface drip irrigated (SDI) conditions was evaluated using field data. The relationship between tree growth and soil water availability ( r θ ) at different depths, which has not been thoroughly investigated in poplar plantations, was also examined. In general, the average soil water content ( θ ) in different soil layers predicted by both HYDRUS models and the θ within the two-dimensional domain around drippers predicted by HYDRUS (2D/3D) agreed well with the observed values. Under both treatments, the r θ increased with depth and was most variable in the surface 30 cm soil. The amount of variation in basal area at breast height (ABH) growth explained by r θ in various soil layers ranged widely, suggesting that soil water at different soil depths made different contributions to the variation in growth. The proportion of variation in ABH growth explained by average r θ was highest ( R 2 = 0.709) in the 0–30 cm layer, and decreased with increasing integrated depth of the root-zone. Tree growth was unconstrained when the r θ of the 0–30 cm layer was above 0.7. Based on these results, it can be concluded that HYDRUS-1D and HYDRUS (2D/3D) can be used as tools to accurately simulate long-term soil water dynamics in P. tomentosa plantations, at least in sites with similar characteristics to ours. HYDRUS modeling can be used to assess the impacts of r θ on productivity of mature P. tomentosa plantations. This study also shows that monitoring soil moisture of the surface soil provides a robust means for predicting tree growth of P. tomentosa plantations at sites with similar soil to ours. [ABSTRACT FROM AUTHOR]

• Precise information on within-site soil chemical properties are rare yet invaluable. • High resolution topographic variables can provide useful information. • Soil chemical properties were meaningfully correlated with topographic variables. • The proposed approach can be useful to model within-site soil chemical properties. • The models also provided an advance understanding on the process. Precise spatial information on soil properties in plantation forests is needed to improve soil nutrient management and to sustain productivity. Soil nitrogen, phosphorus, potassium, organic matter, carbon and boron are important determinants and indicators of soil fertility and quality. Particularly in forests, these soil properties are highly variable in space and time. In this study, soils were sampled from three plantation forest sites in a dry sub-humid region near Blenheim, New Zealand. Thirty sampling points were selected, and samples were collected from the three sites across a range of slope and aspect strata. Soil samples were analysed for total carbon (totC), total nitrogen (totN), total phosphorus (totP), extractable potassium (exK) and hot-water extractable boron (exB). All examined soil properties varied significantly (p < 0.05) within sites. A set of fine-scale (5 m resolution) topographic surfaces, that might explain this variability, were then interpolated or derived in geographic information system software. Topographic surfaces included elevation, aspect, slope, profile and plan curvature, topographic position index (TPI), topographic wetness index (TWI), wind exposition index (WEI), and morphometric protection index (MPI). A generalised linear mixed-effect model was applied to develop predictive models. The study found all soil properties were positively correlated with MPI and negatively correlated with the WEI. This indicated that soil properties were correlated with shelter from surrounding relief and wind. Interestingly, within-site boron levels were correlated with both profile curvature (PrCurv) and topographic wetness index, indicating boron movement through the surface with the movement of soil moisture. The modelling approach in this study has potential for application to sustainable management of plantation forests using spatially-precise estimates of soil fertility. [ABSTRACT FROM AUTHOR]

• Appropriate ANOVAs for augmented factorial experimental design were conducted. • Dirichlet regression model approach was used for the analysis of biomass allocation. • High-level irrigation significantly enhanced early stand growth. • Additional N fertigation did not affect early stand growth but affected biomass allocation. A field experiment was conducted in 2017–2018 to investigate the effects of drip irrigation and N fertigation (DIF) on stand growth and biomass allocation in a triploid Populus tomentosa plantation in the North China Plain. The experiment, which included a 3 × 4 factorial structure (four levels of additional N fertigation in each of three levels of irrigation) and an untreated control, was laid out as a complete randomized block design with 5 replicates. Based on the proper model for the augmented factorial design, the results of ANOVA for stand basal area increment and stand total biomass in 2017 and 2018 showed that high irrigation (irrigation when soil water potential at soil 20 cm depth reached −20 kPa) significantly enhanced early stand growth, but additional N fertigation did not further improve early stand growth. The Dirichlet regression model was directly fitted biomass proportion data from destructively sampled trees to differentiate between developmental and treatment effects on biomass allocation. After correction for the tree-size effect, the high irrigation or the high-fertigation associated DIF regimes altered biomass allocation to some extent. Additional N fertigation did not affect early stand growth but affected biomass allocation, suggesting the monitoring of longer-term responses is necessary. [ABSTRACT FROM AUTHOR]

Seed germination has been modelled extensively using hydrothermal time (HTT) models, that predict time to germination as a function of the extent to which seedbed temperature, T, and water potential, Ψ, exceed the base temperature, T b, and base water potential, Ψ b, of each seed percentile, g. Within a seed population the variation in time to germination arises from variation in Ψ b(g) modelled by a normal distribution. We tested the assumption of normality in the distribution of Ψ b(g) by germinating seed of two unrelated species with non-dormant seed (Buddleja davidii (Franch.) and Pinus radiata D. Don) across a range of constant Ψ at sub-optimal T. When incorporated into a HTT model the Weibull distribution more accurately described both the right skewed distribution of Ψ b(g) and germination time course over sub-optimal T than the HTT based on the normal distribution, for both species. Given the flexibility of the Weibull distribution this model not only provides a useful method for predicting germination but also a means of determining the distribution of Ψ b(g). [Copyright &y& Elsevier]

Abstract: The form and water uptake characteristics of the fine root system in a 5-year-old triploid Populus tomentosa plantation were investigated to make recommendations related to irrigation water management for P. tomentosa plantation. Fine roots for analysis were collected from 2106 soil cores taken around eight trees. Soil moisture, trunk sap flow and evaporation were measured concurrently for four months in two experimental plots using time-domain reflectometry, thermal dissipation sensors and micro-lysimeters, respectively. Nearly half (44%) of fine roots corresponded to 0.2–0.5mm diameter. Generally, lateral root distribution was even, however, the vertical root profile showed an unusual pattern (nearly an ‘S’ shape). Dense fine roots occurred in surface soil and nearly one third (28%) of total fine roots occurred below 100cm depth, indicating the plantation had developed a dimorphic root system. With increasing distance from the tree, root distribution tended to be shallower. Mean fine root diameter was significantly larger (P <0.05) below 120cm, probably due to soil texture change or/and anoxia. Root water uptake in the 0–20cm layer contributed 58% of that within the 0–90cm soil layer, suggesting surface roots played the major water uptake role in shallow soil (<90cm). On average, P. tomentosa extracted 57% of transpired water from deep soil (>90cm), implying deep roots can contribute significantly to the water relations of mature P. tomentosa plantations. This functional significance of deep roots might be determined by their high length density and relatively large diameter. Based on these results, three irrigation management strategies were recommended: (1) irrigation schedules should be devised based on periodic measurement of the depth to water table; (2) water should be mainly provided to and maintained in the surface 40cm soil; and (3) water should be applied to the zone within 1m from the tree. [Copyright &y& Elsevier]

• High conservation value of the studied forest remnants in terms of tree diversity. • Impacts of past logging activities outlined by forest structure and pioneer abundance. • Studied communities likely to experience time-delayed shifts in species composition. • Using 10 × 50 m plots provides estimates consistent with those from larger plots. As forest fragmentation continues in many parts of the tropics, the conservation value of forest remnants remains controversial. Our study aimed to assess the structure and tree species diversity of mixed dipterocarp forest remnants from the Planted Forest Zone (PFZ) located in the Bintulu Division, Sarawak, compared with a forest considered relatively undisturbed (i.e. that has experienced no recent logging activities). We also compared three plot methods (50 × 50 m, 20 × 50 m and 10 × 50 m plots) in order to evaluate which could be used for time- and cost-effective inventories of structure and tree species diversity in fragmented forests. No significant differences were found between the fragmented forests and the relatively undisturbed forest for stem density, species richness and diversity indices (Shannon and Simpson). Dissimilarities in species, genus and family composition were observed between fragmented and relatively undisturbed forest, as well as between forest remnants themselves. These dissimilarities were likely to be related to intrinsic variation in these highly diverse tropical forests. However, an unusually high abundance of pioneer species (i.e. Macaranga) was found in plots from forest remnants. The forest remnants also had significantly lower basal areas due to a lack of trees in large diameter classes, which is likely a result of impacts from past logging activities. Otherwise, our results highlight the current high conservation value of the forest remnants—although the studied communities are likely to experience time-delayed shifts in species composition and/or extinctions in the future, with the effect of fragmentation on biodiversity being currently underestimated. Finally, for further studies of fragmented forests we recommend the use of 10 × 50 m plots which are faster and easier to implement in the field while providing estimates of structure and tree species diversity that are consistent with those from larger plots. [ABSTRACT FROM AUTHOR]