Rachmat Mulia

Users’ perspectives on validity of a simulation model for natural resource management

Managers of agro-ecosystems trade off food production and livelihood strategies against environmental services. They need tools to prospect a wide range of external conditions. Integrated simulation models allow stakeholders to discuss the plausible behaviour of agro-ecosystems and to evaluate dynamic trade-offs, as a basis for planning and policy making in agriculture and natural resource management. However, simulation models need to gain stakeholders’ acceptance before they will be utilized. Gaining stakeholders’ acceptance likely requires salience, credibility and legitimacy. We surveyed the perceptions and expectations of 122 potential model users in four countries, prioritizing these model attributes. A possible shift in user perception was assessed during a participatory model evaluation of a resource management model (FALLOW) for post-tsunami development in West Aceh (Indonesia). Potential model users, comprising natural resource managers, policy makers, lecturers and scientists, ranked salience as the most important characteristic for an integrated simulation model, followed by credibility and legitimacy. Model users’ occupation, prior exposure and interest in using a simulation model did not have a statistically significant influence on users’ perceptions of model attributes.

Reconciling root plasticity and architectural ground rules in tree root growth models with voxel automata.

Dynamic models of tree root growth and function have to reconcile the architectural rules for coarse root topology with the dynamics of fine root growth (and decay) in order to predict the strategic plus opportunistic behaviour of a tree root system in a heterogeneous soil. We present an algorithm for a 3D model based on both local (soil voxel level) and global (tree level) controls of root growth, with development of structural roots as a consequence of fine root function, rather than as driver. The suggested allocation rules of carbon to fine root growth in each rooted voxel depend on the success in water uptake in this voxel during the previous day, relative to overall supply and demand at plant level. The allocated C in each voxel is then split into proliferation (within voxel growth) and extension into neighbouring voxels (colonisation), with scale-dependent thresholds and transfer coefficients. The fine root colonisation process defines a dynamic and spatially explicit demand for transport functions. C allocation to development of a coarse root infrastructure linking all rooted voxels depends on the apparent need for adjustment of root diameter to meet the topologically defined sap flow through this voxel during the previous day. The allometric properties of the coarse root system are maintained to be in line with fractal branching theory. The model can predict the dynamics of the shape and structure (fine root density, coarse root topology and biomass) of the root system either independently of soil conditions (purely genetically-driven) or including both the genetic and environmental effects of roots interacting with soil water supply and its external replenishment, linking in with existing water balance models. Sensitivity of the initial model to voxel dimensions was addressed through explicit scaling rules resulting in scale-independent parameters. The model was parameterised for two tree species: hybrid walnut (Juglans nigra × regia) and wild cherry (Prunus avium L.) using results of a pot experiment. The model satisfactorily predicted the root growth behaviour of the two species. The model is sparse in parameters and yet applicable to heterogeneous soils, and could easily be upgraded to include additional local influences on root growth (and decay) such as local success in nutrient uptake or dynamic soil physical properties.

Evaluating a non-destructive method for calibrating tree biomass equations derived from tree branching architecture

Key messageFunctional branch analysis (FBA) is a promising non-destructive method that can produce accurate tree biomass equations when applied to trees which exhibit fractal branching architecture.AbstractFunctional branch analysis (FBA) is a promising non-destructive alternative to the standard destructive method of tree biomass equation development. In FBA, a theoretical model of tree branching architecture is calibrated with measurements of tree stems and branches to estimate the coefficients of the biomass equation. In this study, species-specific and mixed-species tree biomass equations were derived from destructive sampling of trees in Western Kenya and compared to tree biomass equations derived non-destructively from FBA. The results indicated that the non-destructive FBA method can produce biomass equations that are similar to, but less accurate than, those derived from standard methods. FBA biomass prediction bias was attributed to the fact that real trees diverged from fractal branching architecture due to highly variable length–diameter relationships of stems and branches and inaccurate scaling relationships for the lengths of tree crowns and trunks assumed under the FBA model.

Agroforestry solutions for buffering climate variability and adapting to change.

Th is chapter will focus on increasing the adaptive capacity of agricultural systems in tropical and subtropical regions through agroforestry. Agroforestry as a concept resists and tries to counteract the way agriculture has been segregated from forests and forestry. Understanding, using and improving agroforestry implies a focus on the interactions between trees, annual crops and domestic stock, given the local abiotic factors of climate, soils, water and nutrient balances, as well as the biotic context (pests, diseases, antagonists, predators, pollinators and dispersal agents), and the use of land, external inputs, labour and knowledge. We pose and review the hypothesis that the presence of trees increases the degree of buff ering of climate variability from the perspective of an annual food crop, and that retention and the increase of trees in agricultural landscapes can be a relevant part of climate change adaptation strategies.