Leaf area index determination in pure Norway spruce stands

Ing. Jakub Černý, Ph.D.

Disertační práce

Abstract:

Leaf area index (LAI) is a key canopy variable that quantifies the photosynthetic assimilatory surface and governs energy and mass exchange between forest vegetation and the atmosphere. In pure Norway spruce stands, estimating LAI indirectly using optical methods is challenging because complex canopy architecture, hierarchical foliage clumping, and non-photosynthetic woody components conflict with the random foliage distribution assumed by gap-fraction techniques. Measurement accuracy is further influenced by the sensor field of view (FOV) configuration, post‑processing artefacts such as blooming in digital hemispherical photography (DHP), and sampling variability across developmental stages. This dissertation aims to improve the accuracy, comparability, and interpretability of ground‑based indirect LAI estimates across Norway spruce stands at different developmental stages. It also demonstrates the ecological importance of these estimates for understanding ecosystem responses to silvicultural practices. The approach integrates data from early-stage plantations, pole-stage stands, and mature forests, using the LaiPen LP 110, LAI‑2200 PCA, DHP and PAR-transmittance-based measurements. Technical optimisation includes a two-step clumping-correction framework that produces a clumping-corrected, optically derived LAI benchmark (LAIbench). Monte Carlo simulations are used to determine spatially balanced sampling layouts that account for directional autocorrelation. To assess functional significance, the study links seasonal LAI dynamics, measured with photosynthetically active radiation sensors and calculated using the modified Beer‑Lambert law, to stand production efficiency and soil-water dynamics. The findings show that the LaiPen LP 110 is an effective alternative to established instruments, reducing field data collection time by approximately one-third. However, within its calibration range for structurally comparable mature stands, accurate measurements require a substantial empirical correction (LAIbench = 2.85 × LAIe,LP) due to multi-scale clumping. Comparisons indicate that optical methods are not directly interchangeable because of FOV-dependent sensitivities. In contrast, spatially balanced block-row-column layouts outperform traditional sampling in capturing within-plot variability. Functionally, heavy pre-commercial thinning (PCT) improves production efficiency per unit leaf area, increasing leaf area efficiency (LAE) and the canopy production index (CPI). Although thinning-induced LAI reduction modified soil-water dynamics, rapid canopy recovery in mildly thinned stands caused the soil-water signal to converge with that of unthinned controls within two growing seasons. Overall, this dissertation provides a robust operational basis for standardised canopy monitoring, offering essential reference data to validate satellite-derived LAI products and support adaptive silvicultural strategies under changing climatic conditions.

Keywords

Picea abies, LaiPen LP 110, LAI-2200 PCA, digital hemispherical photography, canopy transmittance, gap fraction, foliage clumping, sampling design, forest monitoring

Jazyk práce: angličtina

Datum vytvoření / odevzdání či podání práce: 20. 7. 2026

Obhajoba závěrečné práce

• Vedoucí: doc. Ing. Ivana Tomášková, Ph.D.

Česká zemědělská univerzita v Praze

Fakulta lesnická a dřevařská

Doktorský studijní program:
Global Change Forestry