Appropriate spatial scale for potential woody cover observation in Texas savanna

Context: Potential woody cover, the upper bound of woody plant cover in savanna ecosystems, represents the end-point of woody plant encroachment and is highly relevant to the dynamics of savanna ecosystems. Objectives: This study aims to identify the appropriate spatial scale for potential woody cover observation in the savanna of central Texas, USA. Methods: The upper bound of woody plant cover was modeled over the east–west precipitation gradient of Texas savanna, at four different spatial scales respectively (30 m, 100 m, 250 m, and 500 m). Results: The estimated upper bound of woody plant cover demonstrates a three-segment pattern across the precipitation gradient at all the four observation scales. The pattern begins with a low stable level and ends at a high stable level, with a linear transitional level in between. The magnitude of the upper bound under given precipitation conditions decreases with spatial scale, but stabilizes by 250 m scale. Conclusions: A spatial scale between 250 and 500 m is recommended for potential woody cover observation. Water availability plays a more important role in limiting woody plant cover at larger spatial scales in savanna ecosystems. In addition, the scale dependency of upper bound woody plant cover is more pronounced in the arid region.