Design concepts adopted in long-term forest monitoring programs in Europe—problems for the future?

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Abstract

Long-term intensive monitoring in Europe is presently proceeding in more than 800 plots, where a number of investigations are carried out according to allegedly standardized protocols. While the potential of the program cannot be denied, certain aspects that are binding for data analysis may be a source of problems for future evaluation of program results. Here it is argued that: (i) current biological response indicators adopted by the program will not permit air pollution effects to be distinguished from effects due to other stressors and/or natural variation; (ii) the sampling strategy adopted to select monitoring sites does not enable European scale estimates of the status of attributes of interest or their changes; and that (iii) the sampling tactic suggested at plot level is ambiguous and cannot provide representative, unbiased estimates at plot scale. This latter point implies consequences when plot–level data are used in models, correlative studies and/or to infer cause–effect relationships.

Introduction

It is widely acknowledged that detection, assessment and monitoring of the effects of environmental changes on natural resources, (e.g. climatic changes, biodiversity loss and air pollution) require long-term integrated programs (Bricker and Ruggiero, 1998, Urquhart et al., 1998, Bull et al., submitted). Once the long-term and integrated features are met, the success of the program is often taken for granted. This belief seems to underlie some important and expensive monitoring programs, like Pan-European intensive monitoring of forest ecosystems (henceforth referred to as Level II program), (e.g. EC and UN/ECE, 2001), with relatively little attention paid to the development of robust design concepts. Unfortunately, long-term commitment to integrated monitoring is necessary but not sufficient to ensure the success of the program, as many other factors and design issues need to be considered, (e.g. Parr et al., 2002, Vos et al., 2000, Olsen et al., 1999).

This paper emphasizes the need for a formal statistical approach in order to provide reliable data to support policy decision making and resource management in a rigorous and defensible way (Urquhart et al., 1998). Although international long-term monitoring programs may always encounter difficulties in ensuring consistency and full harmonization of methods, in the case of Level II program we sustain that basic design issues were not satisfactorily addressed. We argue that this is in itself a likely source of problems for data analysis and may jeopardize future assessment of the program's result. To support our opinion, we concentrate on three major design issues as covered in the Level II program, (e.g. EC and UN/ECE, 2001 and the other reports of the same series): (i) choice of measurements, indicators and indices of ecosystem status and changes (relevance and priority); (ii) sampling strategy (selection of sites in which to perform measurements: preferential, model-based, design-based); and (iii) the sampling tactic (where to locate measurements within the site).

Section snippets

Measurements and indicators

Table 1 shows the measurements and indicator categories used in the Level II program. The indicators are classified according to Vos et al. (2000) in terms of explanatory (independent) and response (dependent) variables, with some variables (termed intermediate) playing both roles, (e.g. soil chemistry). For each indicator, an evaluation is given with respect to priority (based on the mandatory/optional criteria adopted by the EC regulations and on the coverage in terms of number of plots,

Sampling strategy

Although more than 800 Level II monitoring sites are installed and millions of euros are being spent for the program, it is important to recognize and admit that this huge expenditure of resources is incapable of providing quantitative estimates valid on national, subregional or regional (European) scales. In other words, although frequently reported, statements and data about ‘average bulk deposition fluxes as a function of geographic regions’ (EC and UN/ECE, 2000, p. 56, table 5.5) are not

Sampling tactic

The main potential of the Level II program is insights into forest condition, because research at plot level enables various multivariate studies. For such studies, plot-level statistical descriptors are used, and the validity of the results depends on having good estimates of the attributes of interest at plot level. These estimates need to be sufficiently precise and unbiased. While precision is approximately the function of the number of observations, bias is determined more by the way

Conclusions

Long-term integrated monitoring in Europe is an unprecedented chance for forest ecologists, researchers, resource managers and policy makers to collect and evaluate data for implementing sound environmental policy. However, despite the considerable effort that has gone into installing and implementing the program, certain problems have not been sufficiently considered. Many of these problems regard the design basis of the program, and include indicator development as well as sampling strategy

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