SPATIAL ELEMENTS OF MORTALITY RISK IN OLD-GROWTH FORESTS
Open Access
- 1 June 2008
- Vol. 89 (6), 1744-1756
- https://doi.org/10.1890/07-0524.1
Abstract
For many species of long‐lived organisms, such as trees, survival appears to be the most critical vital rate affecting population persistence. However, methods commonly used to quantify tree death, such as relating tree mortality risk solely to diameter growth, almost certainly do not account for important spatial processes. Our goal in this study was to detect and, if present, to quantify the relevance of such processes. For this purpose, we examined purely spatial aspects of mortality for four species, Abies concolor, Abies magnifica, Calocedrus decurrens, and Pinus lambertiana, in an old‐growth conifer forest in the Sierra Nevada of California, USA. The analysis was performed using data from nine fully mapped long‐term monitoring plots. In three cases, the results unequivocally supported the inclusion of spatial information in models used to predict mortality. For Abies concolor, our results suggested that growth rate may not always adequately capture increased mortality risk due to competition. We also found evidence of a facilitative effect for this species, with mortality risk decreasing with proximity to conspecific neighbors. For Pinus lambertiana, mortality risk increased with density of conspecific neighbors, in keeping with a mechanism of increased pathogen or insect pressure (i.e., a Janzen‐Connell type effect). Finally, we found that models estimating risk of being crushed were strongly improved by the inclusion of a simple index of spatial proximity. Not only did spatial indices improve models, those improvements were relevant for mortality prediction. For P. lambertiana, spatial factors were important for estimation of mortality risk regardless of growth rate. For A. concolor, although most of the population fell within spatial conditions in which mortality risk was well described by growth, trees that died occurred outside those conditions in a disproportionate fashion. Furthermore, as stands of A. concolor become increasingly dense, such spatial factors are likely to become increasingly important. In general, models that fail to account for spatial pattern are at risk of failure as conditions change.Keywords
This publication has 47 references indexed in Scilit:
- The relationship between tree growth patterns and likelihood of mortality: a study of two tree species in the Sierra NevadaCanadian Journal of Forest Research, 2007
- Competition-induced mortality for Mediterranean Pinus pinaster Ait. and P. sylvestris L.Forest Ecology and Management, 2006
- Growth patterns as indicators of impending tree death in silver firForest Ecology and Management, 2004
- Assessing the performance of theoretical and empirical tree mortality models using tree-ring series of Norway spruceEcological Modelling, 2004
- Spatial Dynamics in Model Plant Communities: What Do We Really Know?The American Naturalist, 2003
- Growth-dependent tree mortality models based on tree ringsCanadian Journal of Forest Research, 2003
- A Review of Forest Gap ModelsClimatic Change, 2001
- Forest Composition, Structure, and Change in an Old-Growth Mixed Conifer Forest in the Northern Sierra NevadaThe Journal of the Torrey Botanical Society, 1998
- DEMOGRAPHY OF A SHADE-TOLERANT TREE (FAGUS GRANDIFOLIA) IN A HURRICANE-DISTURBED FORESTEcology, 1998
- Demographics of Common Snapping Turtles (Chelydra serpentina): Implications for Conservation and Management of Long-lived OrganismsAmerican Zoologist, 1994