Remote Sensing‐Based Forest Modeling Reveals Positive Effects of Functional Diversity on Productivity at Local Spatial Scale.

Forest biodiversity is critical for many ecosystem functions and services. Yet, it remains uncertain how plant functional diversity influences ecosystem functioning across environmental gradients and contiguous larger areas. We integrated remote sensing and terrestrial biosphere modeling to explore functional diversity–productivity relationships at multiple spatial scales for a heterogeneous forest ecosystem in Switzerland. We initialized forest structure and composition in the ecosystem demography model (ED2) through a combination of ground‐based surveys, airborne laser scanning and imaging spectroscopy for forest patches at 10 × 10‐m spatial grain. We derived morphological and physiological forest traits and productivity from model simulations at patch‐level to relate morphological and physiological aspects of functional diversity to the average productivity from 2006 to 2015 at 20 × 20 to 100 × 100‐m spatial extent. We did this for model simulations under observed and experimental conditions (mono‐soils, mono‐cultures and mono‐structures). Functional diversity increased productivity significantly (p < 0.001) across all simulations at 20 × 20 to 30 × 30 m scale, but at 100 × 100‐m scale positive relationships disappeared under homogeneous soil conditions potentially due to the low beta diversity of this forest and the saturation of functional richness represented in the model. Although local functional diversity was an important driver of productivity, environmental context underpinned the variation of productivity (and functional diversity) at larger spatial scales. In this study, we could show that the integration of remotely sensed information on forest composition and structure into terrestrial biosphere models is important to fill knowledge gaps about how plant biodiversity affects carbon cycling and biosphere feedbacks onto climate over large contiguous areas. Plain Language Summary: We explored relationships between forest biodiversity and productivity at multiple spatial scales to better understand how plant traits and their diversity influence the functioning of forest ecosystems. To do this across large contiguous areas, we simulated a temperate mixed forest by combining process‐based terrestrial biosphere modeling with remotely sensed information about forest structure and composition. We found that higher functional diversity was associated with higher productivity at local spatial scale (tens of meters), while soil depth and texture were the main drivers of productivity at the hectare scale. At this larger scale, functional diversity tended to be saturated due to the low turnover of species and functional traits of the temperate mixed forest and the limited representation of physiological diversity in the model. Key Points: We explored forest functional diversity—productivity relationships using a terrestrial biosphere model initialized with remote sensingHigher functional diversity at 20 × 20 to 30 × 30 m scale was associated with higher productivity (p < 0.001) across all simulationsSoil depth and texture were the main drivers of productivity at the hectare scale, while functional diversity saturated at coarser scales [ABSTRACT FROM AUTHOR]