Recognizing culture, and diverse sources of knowledge, can improve assessments

We describe and reflect on seven recurring critiques of the concept of ecosystem services and respective counter‐arguments. First, the concept is criticized for being anthropocentric, whereas others argue that it goes beyond instrumental values. Second, some argue that the concept promotes an exploitative human–nature relationship, whereas others state that it reconnects society to ecosystems, emphasizing humanity's dependence on nature. Third, concerns exist that the concept may conflict with biodiversity conservation objectives, whereas others emphasize complementarity. Fourth, the concept is questioned because of its supposed focus on economic valuation, whereas others argue that ecosystem services science includes many values. Fifth, the concept is criticized for promoting commodification of nature, whereas others point out that most ecosystem services are not connected to market‐based instruments. Sixth, vagueness of definitions and classifications are stated to be a weakness, whereas others argue that vagueness enhances transdisciplinary collaboration. Seventh, some criticize the normative nature of the concept, implying that all outcomes of ecosystem processes are desirable. The normative nature is indeed typical for the concept, but should not be problematic when acknowledged. By disentangling and contrasting different arguments we hope to contribute to a more structured debate between opponents and proponents of the ecosystem services concept.

A statistical description of static granular material requires ergodic sampling of the phase space spanned by the different configurations of the particles. We periodically fluidize a column of glass beads and find that the sequence of volume fractions φ of post-fluidized states is history independent and Gaussian distributed about a stationary state. The standard deviation of φ exhibits, as a function of φ, a minimum corresponding to a maximum in the number of statistically independent regions. Measurements of the fluctuations enable us to determine the compactivity X, a temperature-like state variable introduced in the statistical theory of Edwards and Oakeshott [Physica A 157, 1080[Physica A 157, (1989].PACS numbers: 64.30.+t, 47.55.Kf Granular materials consist of a large number N (typically more than 10 6 ) dissipative particles that are massive enough so that their potential energy is orders of magnitude larger than their thermal energy. The large number suggests that a statistical description might be feasible. Edwards and coworkers [1] developed such a description with the volume V of the system, rather than the energy, as the key extensive quantity in a static granular system. The corresponding configuration space contains all possible mechanically stable arrangements of grains.Brownian motion is insufficient for a granular system to explore its configuration space, so energy must be supplied by external forcing such as tapping [2], shearing [3] or both [4]. The theory of Edwards requires that the forcing assures ergodicity: all mechanically stable configurations must be equally probable and accessible. A necessary condition for ergodicity is history independence: the physical properties of the system must not depend on the way a specific state was reached. History independence has previously been demonstrated only by Nowak et al.[2] for tapped glass beads at volume fractions φ > 0.625.In this paper we explore the configuration space using a periodic train of flow pulses in a fluidized bed. A stationary column of glass beads in water is expanded by an upward stream of water until it reaches a homogeneously fluidized state [5], and then the flow is switched off. The fluidized bed collapses [6] and forms a sediment of volume fraction φ, which we find depends in a reproducible way on the flow rate Q of the flow pulse. This forcing results in a history independent steady state where the volume exhibits Gaussian fluctuations around its average value.A central postulate of the Edwards theory is the existence of a temperature-like state variable called compactivity X = ∂V /∂S. The entropy S is defined in analogy to classical statistical mechanics as S(V, N ) = λ ln Ω, where Ω is the number of mechanically stable configurations of N particles in V , and λ is an unknown analog to the Boltzmann constant. The assumption that X is a relevant control parameter in granular systems has found support in simulations of segregation in binary mixtures [7], compaction under vertical tapping [8], and shearing [9]. How...

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Using sedimentation to obtain precisely controlled packings of noncohesive spheres, we find that the volume fraction RLP of the loosest mechanically stable packing is in an operational sense well defined by a limit process. This random loose packing volume fraction decreases with decreasing pressure p and increasing interparticle friction coefficient . Using x-ray tomography to correct for a container boundary effect that depends on particle size, we find for rough particles in the limit p ! 0 a new lower bound, RLP 0:550 0:001.