HANPP and Landscape Diversity

A recent empirical analysis focused on a study area of2,864 km2 around St. Pölten, the capital of lower Austria. This study was conducted at the scale of 1 X 1 km plots and asked to what extent a variety of landscape ecological indicators depended on HANPP (Wrbka et al. 2004).

The study showed that HANPP was clearly, monotonously, and highly significantly correlated with two indicators of landscape naturalness: hemeroby and urbanity (Figure 17.1). The urbanity index analyzes the domination of landscapes by strongly human-altered systems (O'Neill et al. 1988). It is defined as log10 of (U + A)/(F + W+ B) where U denotes urban, A agricultural, F forest, Wwater and wetland area, and B natural or seminatural biotopes. Hemeroby was introduced to describe gradients of human influence on landscape and flora (Jalas 1955) and is defined on an ordinal scale ranging from 1 (without actual human impact) to 7 (artificial landscape elements completely human dominated).

The study revealed that the relationship between HANPP and landscape diversity and landscape richness followed a hump-shaped curve (Figure 17.1). Landscape richness was defined as the number of different land cover classes present in each 1 X 1 km2

Figure 17.1. Findings of a case study on the relationship between HANPP and various landscape ecological indicators in lower Austria: (a, b) the scatter plot and response function of the correlation between HANPP and hemeroby (r2 = .84), (c, d) the correlation between HANPP and urbanity (r2 = .87), and (e, f) the correlation between HANPP and landscape richness (r2 = .35). The pattern for landscape diversity (not shown) was almost identical. In the regression, polynomials (restricted cubic splines) were fitted to the data using ordinary least-square techniques. All correlations were significant at p = .001. r2 are "corrected r2" values obtained in a bootstrap model validation with < 100 runs. For details see Wrbka et al. (2004). Reprinted from Land Use Policy, Vol. 21, "Linking pattern and process in cultural landscapes" pp. 289—306, with permission from Elsevier.

Figure 17.1. Findings of a case study on the relationship between HANPP and various landscape ecological indicators in lower Austria: (a, b) the scatter plot and response function of the correlation between HANPP and hemeroby (r2 = .84), (c, d) the correlation between HANPP and urbanity (r2 = .87), and (e, f) the correlation between HANPP and landscape richness (r2 = .35). The pattern for landscape diversity (not shown) was almost identical. In the regression, polynomials (restricted cubic splines) were fitted to the data using ordinary least-square techniques. All correlations were significant at p = .001. r2 are "corrected r2" values obtained in a bootstrap model validation with < 100 runs. For details see Wrbka et al. (2004). Reprinted from Land Use Policy, Vol. 21, "Linking pattern and process in cultural landscapes" pp. 289—306, with permission from Elsevier.

cell and landscape diversity was defined as the Simpson diversity index of the number of land cover classes. The relationship between HANPP and landscape diversity was almost the same as that of landscape richness.

We interpret these findings as follows: HANPP is almost linearly correlated with two indicators of the naturalness of landscapes. Conceptually this is nontrivial because HANPP is an indicator for human activities, whereas both naturalness indicators evaluate the state of landscapes. HANPP is much higher in urban areas and on agricultural land than in forests or natural areas, so for urbanity the result is not surprising. This is less so for hemeroby because hemeroby is defined with reference to changes in plant species composition. Because there is evidence of a strong negative relationship between hemeroby and bryophyte species richness (Zechmeister and Moser 2001) this is an indication for the potential value of HANPP as a pressure indicator for species loss.

Intuitively, the relationship between HANPP and landscape diversity or richness is also plausible: HANPP is low in forests (which tend to be large) and high in large-scale croplands, both having low landscape heterogeneity. Intermediate HANPP can be found in landscapes dominated either by grasslands or by a mix of different land cover classes, including forests, cropland, grassland, and urban areas. It is quite obvious, both empirically (as shown in our example) and theoretically, that land use can increase or decrease landscape heterogeneity and that there may be regular patterns along a gradient of intensification of land use, although the pattern may depend on geomorpholog-ical and socioeconomic conditions.

This may also have implications for species richness: A positive relationship between landscape heterogeneity and species richness is plausible and has been empirically demonstrated (Moser et al. 2002). Therefore, species diversity could be highest at intermediate HANPP values on a landscape scale, even if the relationship between species richness and energy flow (NPPt) were linear at small scales: The introduction of land cover types such as grassland or even cropland in large-scale forests is likely to increase habitat diversity (a diversity). This may result in a more heterogeneous landscape with higher species richness than in the initial state because b diversity may increase if g diversity rises, even if a diversity may decrease in some habitats. Edge effects and the introduction of ecotones may also play a role.

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