Spatial elements of mortality risk in old-growth forests

Area of Science:

• Ecology
• Forestry
• Population Dynamics

Background:

• Tree survival is crucial for long-lived organisms' population persistence.
• Current tree mortality models often overlook spatial processes, relying solely on factors like diameter growth.

Purpose of the Study:

• To detect and quantify the relevance of spatial processes in tree mortality.
• To assess if spatial information improves mortality prediction models for key conifer species.

Main Methods:

• Analysis of mortality data from nine mapped long-term monitoring plots in a Sierra Nevada old-growth conifer forest.
• Examination of spatial aspects of mortality for four species: Abies concolor, Abies magnifica, Calocedrus decurrens, and Pinus lambertiana.
• Inclusion of spatial indices in mortality prediction models to assess their impact.

Main Results:

• Spatial information significantly improved mortality prediction models for three of the four studied species.
• Abies concolor showed decreased mortality risk with proximity to neighbors (facilitation), while Pinus lambertiana exhibited increased risk with neighbor density (Janzen-Connell effect).
• Models predicting risk of being crushed were substantially enhanced by spatial proximity indices.

Conclusions:

• Spatial patterns are critical for understanding and predicting tree mortality, particularly in dense stands.
• Models that do not incorporate spatial dynamics may fail as environmental conditions change.
• Accurate population persistence assessments require integrating spatial processes into ecological models.