Margarida Tomé

Evaluating a growth model for forest management using continuous forest inventory data

Abstract Model evaluation should include qualitative as well as quantitative examinations of the model. The qualitative parts should comprise a critical appraisal of model logic as well as theoretical and biological realism of the model. The quantitative parts should comprise statistical tests and comparisons of predictions with observations independent of those used to fit the model. Comprehensive model evaluation requires several alternative approaches and criteria. Model evaluation is not one simple procedure, but consists of a number of interrelated steps that should not be separated from each other or from model construction. It is stressed that models can only be evaluated in relative terms, and their predictive value is always open to question. Thus, model evaluation is an ongoing process. A case study with the PBRAVO growth model for maritime pine (Pinus pinaster Ait.) in the Leiria forest, Portugal, illustrates the utility of selected criteria and graphical techniques. Based on theoretical examinations and tests with data from continuous forest inventories, we conclude that the Leiria version of the PBRAVO model does not adequately represent reality and that forecasts lack sufficient accuracy for forest management purposes.

The effect of organic-matter management on the productivity of Eucalyptus globulus stands in Spain and Portugal: tree growth and harvest residue decomposition in relation to site and treatment

Sustainable management of forest resources, including nutrient retention and protection of the soil structure, is required to ensure long-term soil fertility and productivity of later rotations. Potential depletion of soil nutrients is particularly likely in production systems based on fast-growing trees, such as eucalypts. We have studied production of second rotation Eucalyptus globulus stands at two sites in northern Spain and two in central Portugal, after replanting or coppicing, under four treatments, in which plant residues from the first crop were utilised. The residues were either removed from the sites (Treatment R), spread over the soil surface (Treatments S, uniform spreading, and W, in which the woody debris was confined to rows between the trees) or incorporated into the soil by harrowing to 15-cm depth (Treatment I). We measured tree height and girth at intervals over three growing seasons, and root biomass at the Portuguese sites. Decomposition of three residue components: leaves-plus-bark, twigs and branches, was measured in litter bags placed in the position corresponding to the placement of the organic residues. By the end of the experiment, tree height was significantly greater in Treatment I than in Treatment R at both Spanish sites, if planted as seedlings, with intermediate growth in S and W. In Portugal, tree height was smaller in R, though not significantly. DBH showed similar trends, although treatment differences were not significant. Coppiced trees grew faster than seedling trees, but a significant treatment effect on the growth was only observed at the inland Portuguese site, where it was better in Treatment I by the end of the experiment. The residues decomposed significantly faster in I than S or W at the Portuguese sites, but not in Spain. Leaves-plus-bark decomposed faster than twigs, and twigs faster than branches. The results are discussed in relation to recommended management options. # 1999 Elsevier Science B.V. All rights reserved.

Climate Change: Believing and Seeing Implies Adapting

Knowledge of factors that trigger human response to climate change is crucial for effective climate change policy communication. Climate change has been claimed to have low salience as a risk issue because it cannot be directly experienced. Still, personal factors such as strength of belief in local effects of climate change have been shown to correlate strongly with responses to climate change and there is a growing literature on the hypothesis that personal experience of climate change (and/or its effects) explains responses to climate change. Here we provide, using survey data from 845 private forest owners operating in a wide range of bio-climatic as well as economic-social-political structures in a latitudinal gradient across Europe, the first evidence that the personal strength of belief and perception of local effects of climate change, highly significantly explain human responses to climate change. A logistic regression model was fitted to the two variables, estimating expected probabilities ranging from 0.07 (SD ±0.01) to 0.81 (SD ±0.03) for self-reported adaptive measures taken. Adding socio-demographic variables improved the fit, estimating expected probabilities ranging from 0.022 (SD ±0.008) to 0.91 (SD ±0.02). We conclude that to explain and predict adaptation to climate change, the combination of personal experience and belief must be considered.

Characterization of the structure, dynamics, and productivity of mixed-species stands: review and perspectives

The growth and yield of mixed-species stands has become an important topic of research since there are certain advantages of this type of forest as regards functions and services. However, the concepts and methods used to characterize mixed stands need to be understood, as well as harmonized and standardized. In this review we have compiled a set of measures, indices, and methods at stand level to characterize the structure, dynamics, and productivity of mixed stands, and we discuss the pros and cons of their application in growth and yield studies. Parameters for the characterization of mixed stand structure such as stand density, species composition, horizontal (intermingling) and vertical tree distribution pattern, tree size distribution, and age composition are described, detailing the potential as well as the constraints of these parameters for understanding resource capture, use, and efficiency in mixed stands. Furthermore, a set of stand-level parameters was evaluated to characterize the dynamics of mixed stands, e.g. height growth and space partitioning, self- and alien-thinning, and growth partitioning among trees. The deviations and changes in the behaviour of the analysed parameters in comparison with pure stand conditions due to inter-specific interactions are of particular interest. As regards stand productivity, we reviewed site productivity indices, the growth–density relationship in mixed stands as well as methods to compare productivity in mixed versus monospecific stands. Finally, we discuss the main problems associated with the methodology such as up-scaling from tree to stand level as well as the relevance of standardized measures and methods for improving forest growth and yield research in mixed stands. The main challenges are also outlined, especially the need for qualitatively sound data.

Total aboveground biomass and net dry matter accumulation by plant component in young Eucalyptus globulus in response to irrigation

A system of equations describing total aboveground biomass, the proportion of total aboveground biomass accumulated by different plant components, and instantaneous net dry matter accumulation fraction is developed as a function of tree diameter, height, and the growth rates of diameter and height. This system is utilized in the analysis of a Eucalyptus globulus fertilization/irrigation experiment in central Portugal. The data were from the period prior to competition-induced mortality in the stands, but previous analyses had reported apparent changes in tree growth rates due to intraspecific competition in the experimental stands. The irrigation treatments affected the relationship between tree dimensions and total aboveground biomass as well as the accumulation of biomass by different aboveground plant components (p≤0.05). There were no differences in these relationships due to fertilization (p=0.05), in spite of previously reported increases in biomass production in response to fertilization. Even though irrigation affects dimensional biomass relationships in E. globulus, analyses demonstrate that previously reported differences in biomass production and accumulation by the various aboveground plant components are, to a much greater extent, due to changes in the growth rates of diameter and height among the treatments rather than to the changes in structural relationships due to the experimental treatments.

Sustainable forest management.

Foreword. Ecosystem perspectives. Ecological and landscape considerations in forest management - the end of forestry? R. Schlaepfer, C. Elliott. Sustainability in Forestry: Theory and a historical case study M. Hauhs, H. Lange. Sustained water yield in afforested catchments the South African experience P.J. Dye, J.M. Bosch. Social and political perspectives. A workers view on sustainable forestry J. Bowling. Making Rio work - The vision of sustainable development and its implementation through forest certification D. Burger. Perceived images of various actors engaged in sustainability discussions G. Hutte. Timber supply and forest management. Regulation of timber yield for sustainable management of industrial forest plantations - theory and practice J.P. Roise, et al. Theory and Practice of Yield Regulation Systems for Sustainable Management of Tropical and Subtropical Moist Natural Forests A.H.W. Seydack. Scenario Planning for Sustainable Forest Management K. von Gadow, J. Puumalainen.

Intraspecific competition in irrigated and fertilized eucalypt plantations

Abstract A field experiment to study the biomass production of Eucalyptus globulus under different irrigation and fertilization regimes was established in March 1986 in central-west Portugal. In this paper the start of competition under different availability of water and nutrients was analyzed through its consequences both at the individual and stand level. Individual-tree size frequency distribution and size variability, the relationship between mean annual relative growth rate and social status of the tree and percentage of survival were examined in each treatment. It was found that the start of asymmetric competition was strongly influenced by irrigation and fertilization as it occurred by the time of canopy closure, about 2.8 years and 4.8 years of age, respectively, in the irrigated and fertilized plots and in the control plots. Although at that time none of the plots had begun to suffer density-dependent mortality, severe suppression of smaller trees by the dominants (therefore asymmetric competition) was observed in all plots. Asymmetric competition was also detected by an increase in size variability occurring also at the time of canopy closure.

Are forest disturbances amplifying or canceling out climate change-induced productivity changes in European forests?

Recent studies projecting future climate change impacts on forests mainly consider either the effects of climate change on productivity or on disturbances. However, productivity and disturbances are intrinsically linked because 1) disturbances directly affect forest productivity (e.g. via a reduction in leaf area, growing stock or resource-use efficiency), and 2) disturbance susceptibility is often coupled to a certain development phase of the forest with productivity determining the time a forest is in this specific phase of susceptibility. The objective of this paper is to provide an overview of forest productivity changes in different forest regions in Europe under climate change, and partition these changes into effects induced by climate change alone and by climate change and disturbances. We present projections of climate change impacts on forest productivity from state-of-the-art forest models that dynamically simulate forest productivity and the effects of the main European disturbance agents (fire, storm, insects), driven by the same climate scenario in seven forest case studies along a large climatic gradient throughout Europe. Our study shows that, in most cases, including disturbances in the simulations exaggerate ongoing productivity declines or cancel out productivity gains in response to climate change. In fewer cases, disturbances also increase productivity or buffer climate-change induced productivity losses, e.g. because low severity fires can alleviate resource competition and increase fertilization. Even though our results cannot simply be extrapolated to other types of forests and disturbances, we argue that it is necessary to interpret climate change-induced productivity and disturbance changes jointly to capture the full range of climate change impacts on forests and to plan adaptation measures.

Cork weight prediction at tree level

In spite of the importance of cork and cork oak stands in the Portuguese forest and economic scenarios, little research work has been done with this species over the years. The main objective of this study is to define a system of prediction equations to assess air-dried cork weight using dendrometric variables of the tree as predictors. These equations can be used at an intermediate age of the cork production cycle, which is usually of 9 years, or at the year of the stripping process, with 9 years old cork. Several alternative models were developed, from simpler models, using variables easy to gather in the field, to more complex ones that maximise the prediction ability. The development of the weight prediction equations was based on data gathered on three stands located in a region located in the centre/south Portugal, the Coruche county, with average aptitude regarding cork production.

Airborne Lidar Estimation of Aboveground Forest Biomass in the Absence of Field Inventory

The scientific community involved in the UN-REDD program is still reporting large uncertainties about the amount and spatial variability of CO2 stored in forests. The main limitation has been the lack of field samplings over space and time needed to calibrate and convert remote sensing measurements into aboveground biomass (AGB). As an alternative to costly field inventories, we examine the reliability of state-of-the-art lidar methods to provide direct retrieval of many forest metrics that are commonly collected through field sampling techniques (e.g., tree density, individual tree height, crown cover). AGB is estimated using existing allometric equations that are fed by lidar-derived metrics at either the individual tree- or forest layer-level (for the overstory or underneath layers, respectively). Results over 40 plots of a multilayered forest located in northwest Portugal show that the lidar method provides AGB estimates with a relatively small random error (RMSE = of 17.1%) and bias (of 4.6%). It provides local AGB baselines that meet the requirements in terms of accuracy to calibrate satellite remote sensing measurements (e.g., the upcoming lidar GEDI (Global Ecosystem Dynamics Investigation), and the Synthetic Aperture Radar (SAR) missions NISAR (National Aeronautics and Space Administration and Indian Space Research Organization SAR) and BIOMASS from the European Space Agency, ESA) for AGB mapping purposes. The development of similar techniques over a variety of forest types would be a significant improvement in quantifying CO2 stocks and changes to comply with the UN-REDD policies.