Plan and methods

The research plan for the PINEA project is based on its objectives and is expected to be implemented through nine planned Tasks. The main objectives of the Project are:
(i) the calibration and validation of a process-based model for Pinus pinea in Portugal. This model will allow estimation of the productivity of existing stone pine plantations in the context of climate change, considering different climate scenarios,  and will provide a tool to support decision-making in relation to new plantings;
(ii) to evaluate the effects of water and nutrient availability on Pinus pinea growth and cone yields;
(iii) to improve existing empirical modeling equations describing growth and cone yield of Pinus pinea.

The PINEA Project also has the following subsidiary objectives:
(a) to analyze several fertilization alternatives in the establishment and early growth of Pinus pinea stands;
(b) to assess the success of grafting in response to several fertilization treatments;
(b) to analyze shifts in allocation of root, leaf and stem biomass in response to water and nutrients availability;
(c) to develop a methodology to include the fraction of cone biomass within the carbon allocation routines of a process based model.

The PINEA Project will be based on existing Pinus pinea data, including permanent sample plots and previous biomass trials, and will use an established fertilization trial. New data will be collected from an irrigation and fertilization trial that will be established. New data will also be collected in the existing permanent sample plots and fertilization trial. All these existing and new data will be validated and organized in databases. Following the database development the data will be analyzed by different methods, bearing in mind that one of the major objectives is to develop a process-based model calibrated for Pinus pinea. The methodology which will be used is detailed under the respective tasks.

One of the main challenges in calibrating and validating a process-based model for Pinus pinea is that a major concern is cone yield. An innovative approach will be required to include in a process-based model such as 3-PG an routine dealing with allocation to cone/fruit biomass. Fruiting bodies tend to be the highest priority sinks for carbohydrates from foliage. In extreme cases i.e. if there is a very heavy fruit (cone) load, the fruiting bodies will take virtually all available resources so that the leaves, particularly those in the immediate vicinity of the cones, may die back towards the end of the cone/nut growing season. PINEA Project intends to insert another sink for carbohydrates into the 3-PG code and, in any growth interval (month) make the allocation to nuts as the first priority, with the residual allocated to roots, stems and leaves on the same basis as in forest trees.

So we have:

dWc/dt + dWr/dt + dWs/dt + dWf/dt = dW/dt

where Wc,Wr,  Ws, Wf  = mass of cones, roots, stems and foliage, and W is total mass of the tree. If there are no cones then dWc/dt = 0 and partitioning is as in 3-PG. In finite difference form, with dt standard (say Δt is a month) the equation is:

Δ Wc + Δ Wr + Δ Ws + Δ Wf = ΔW, the change in mass over Δt.

The PINEA Project will be aimed at obtaining the data needed to test this hypothesis and parameterize the equations. The establishment of an irrigation and fertilization trial for stone pine will be an important step in this direction.

Tree growth measurements provide the basis for the carbon allocation analysis within a 3-PG type model. A hypothesis underlying the PINEA Project is that tree and branch growth will be affected by the number of cones the tree/branch is carrying. So if 2 trees start out the same size, but one has (a significant number of) cones (+) and the other zero cones(0), the + cones tree will grow more slowly – reflected in different diameter growth rates. Similarly, branches with and without cones will have different branch growth rates; we will attempt to identify this effect through measurements of foliage area/branch. We will plot cone mass (or some other measurement of cone size and growth) against foliage area per branch, and analyse the normalized plot (weight of cones/unit foliage area) for the information it may provide about carbohydrate production and allocation. We will also evaluate this on a whole tree basis. We assume cone growth is influenced by fertilizer and nutrition: since these result in increased foliage growth we would expect cone (nut) growth to be increased. The question that arises is: do these (sinks) take all the extra carbohydrate available?

The fertilization and irrigation trial will provide understanding about how water and nutrient availability influences cone yield, root biomass, leaf biomass and stem biomass. This experiment will impose a range of conditions wider than the range likely to occur naturally, which allows the researchers to assess the responses of the trees to conditions that might not normally be encountered. This is called ‘filling the variable space’. It allows the factors that limit growth to be assessed without the, sometimes confounding, interactions that may result from water shortages. Irrigation to eliminate water stress in some treatments also allows the response functions of various processes to be determined (are they linear or non-linear?) and provides information essential for the parameterization and testing of process-based models, which is one of the objectives of this project. It will be important to impose irrigation treatments on this experiment whether or not widespread commercial irrigation of stone pine is likely in Portugal. The resulting model should allow evaluation of the potential growth and productivity of the pines in any area and it will be able to make predictions under different climate change scenarios.