## 6 Conclusions  
Forest inventories seek to measure the quantity and quality of a forest ecosystem, and form the foundation of forest planning and forest policy. The focus of the traditional forest inventory was on obtaining information on structural attributes, such as basal area, tree height, and number of trees. Recently, modern forest inventories have emphasized gaining information, not only on structural attributes, but also by addressing forest-functional attributes in order to understand the functioning mechanisms of forest ecosystems [112]. In addition, making full use of new technologies is one of the challenges that modern forest inventories face today. We aimed to evaluate the capability of two new technologies, ALS and IS, in characterizing a heterogeneous forest ecosystem.  
We conclude that estimates of TD in heterogeneous alpine landscapes challenge current technology and analytical approaches. Tree and canopy structure are the primary determinants of the success of TD estimates, which are, in addition, dependent on species and canopy species composition. For deciduous trees, for example, the applied local maximum approach has strong limitations, as a detection of the treetop is not completely unambiguous (cf. [PERSON] et al., 2006 [PERSON] et al., 2006 [PERSON] et al. (2006)). In terms of the structure, the occurrence of multi-stem trees sharing a common canopy needs to be considered. Further, ALS-based approaches show a sensitivity limit, in particular, when identifying small trees. Specific sampling schemes, e.g., multi-temporal ALS data acquisition with high point density, will partly allow an increase in the sensitivity and accuracy of TD estimation. Further, simple empirical approaches provide sufficient accuracy to reveal first insights into interrelationships between FP and topography effects. More sophisticated and mechanistic approaches are, however, required to yield in-depth knowledge. We conclude that airborne laser scanning and imaging spectroscopy and their combination provide crucial technology for assessing TD and FP for less heterogeneous stands, e.g., north-facing forested areas, at relevant ecological scales.  
We can confirm the existing theory that heterogeneous alpine forests are characterized by positive relationships between FP and TD, mainly due to a significant co-variance of both variables with elevation-dependent gradients of growth-limiting factors. We suggest extending this analysis by considering a wider range of forest types, landscape heterogeneity, topography, resource gradients and assessing the role of other forest structural attributes, e.g., canopy height and canopy cover, on FP. This ultimately allows the gaining of a deeper understanding of TD and FP variability and interrelationships across landscapes.  
This work was funded by the University of Kurdistan. We sincerely appreciate the logistic support during the fieldwork and the permission to use ALS data provided by the Swiss National Park. We are grateful to [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] for their support at the Forestry Department, University of Kurdistan. We would like to thank [PERSON] and [PERSON] for their help with the field data collection. The contribution of [PERSON] was supported by a grant of the Swiss University Conference and ETH-Board in frame of the Swiss Earth Observatory Network (SEON) project, the contribution of M.E.S. is supported by the University of Zurich Research Priority Program on \"Global Change and Biodiversity\". The authors would also like to thank the academic editors and three anonymous reviewers for their detailed reviews, which have improved the content of this paper.  
[PERSON], [PERSON], [PERSON], and [PERSON] designed the study and developed the methodology. [PERSON] collected the data. [PERSON], [PERSON], [PERSON], and [PERSON] performed the analysis. [PERSON] wrote the manuscript and all co-authors thoroughly reviewed and edited the manuscript.  
The authors declare no conflict of interest.