Vegetation Structural Complexity across Tenerife’s Zonal Vegetation Types, captured by Terrestrial Laser Scanning

Samantha Suter , Rüdiger Otto, José María Fernández-Palacios, Lea de Nascimento Reyes, Felipe Rodriguez Arvelo, Natalia Sierra Cornejo, Nathaly Guerrero Ramirez, Martin Ehbrecht , Holger Kreft, Delphine Clara Zemp

Questions: Vegetation structural complexity, defined as the density and distribution of plants in three-dimensional (3D) space, is a key ecological property of plant communities, influencing biodiversity and ecosystem functioning. Yet, how vegetation structural complexity varies across contrasting vegetation types, and which factors drive this variation remain poorly understood. This knowledge gap is particularly relevant on oceanic islands, where diverse vegetation types occur across steep environmental gradients and are often highly vulnerable to disturbance. Specifically, we asked: (1) how does vegetation structural complexity vary among and within vegetation types, (2) by which structural dimensions do the vegetation types most differ, and (3) which climatic factors explain this variation? 

Location: Tenerife, Canary Islands. 

Methods: With 140 scans in 28 plots covering 6 major zonal vegetation types, we derived the Stand Structural Complexity Index (SSCI), which measures the 3D arrangement of vegetation, and other metrics related to vertical stratification, vegetation density, and canopy openness, captured by terrestrial laser scanning (TLS) 3D point clouds. For each metric, mean values and coefficient of variation (CV) per plot were analysed with a permutation Analysis of Variance (ANOVA) and a Principal Component Analysis (PCA). Relationship with long-term climatic plot data was analysed using robust linear models.  

Results: The SSCI differed significantly among zonal vegetation types (permutation ANOVA, p < 0.001). The SSCI ranged from a high mean value and low variability in laurel forests (mean = 7.00, CV = 10.1%) to the lowest mean value in the summit scrub (mean = 2.65, CV = 65.6%) but highest variability in the tabaibal coastal scrub (mean = 4.93, CV = 91.0%). PCA indicates that vegetation structural complexity in forests was characterised by high vertical stratification and closed canopy. In contrast, scrub types displayed greater canopy openness and a high variation in 3D vegetation density. Greater annual precipitation were associated with linear increased SSCI across zonal vegetation types, positively related to increased vertical stratification and canopy height and negatively related to canopy openness and 3D vegetation density. 

Conclusions: Our results suggest that TLS-derived metrics of vegetation structural complexity captures within and across vegetation type variation. The SSCI can provide meaningful information beyond forests when interpreted alongside other structural metrics. Our results suggest that differences across vegetation types are associated with climatic gradients. This study provides a basis for future studies and applications of TLS beyond forests, that can aid biodiversity monitoring and conservation of environmentally-distinct and disturbance-prone island vegetation.