Post-Fire Forest Succession, Group-Gap Dynamics, and Implications for Fire Resilience in an Old-Growth Pinus ponderosa Forest
Open Access
- Author:
- Pawlikowski, Natalie Carmen
- Graduate Program:
- Geography
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 19, 2018
- Committee Members:
- Alan H Taylor, Thesis Advisor/Co-Advisor
Erica A H Smithwick, Committee Member
Robert P Brooks, Committee Member - Keywords:
- Forest structure
Group-Gap
Forest Development
Wildfire Resilience
Pinus ponderosa
Quercus kelloggii - Abstract:
- This research quantifies forest structure and examines how post-fire succession alters pine-oak composition, group-gap spatial structure, and wildfire resilience in an old-growth ponderosa pine (Pinus ponderosa) forest that was resilient to recent wildfires and exhibits a heterogeneous forest structure thought to be similar to forests before fire exclusion. To quantify forest structure and spatial patterns, trees were aged, mapped, and measured in the year 2000 – six-years after a wildfire – and in 2016 – 22-years post-fire – in six, 1-hectare, stem map plots in the Beaver Creek Pinery, located in the Ishi Wilderness, Southern Cascades, California. Regeneration – seedlings and saplings – were tallied in 10x10m cells. Rates of tree recruitment, mortality, and growth for the site’s two co-dominant species – ponderosa pine and California black oak (Quercus kelloggii) were estimated using demographic models. Local patterns in group structure was quantified using spatial clump algorithms and gap area was quantified using the empty space function. Potential fire behavior and effects were modeled for a range of fuel and weather conditions. Stand density and basal area in both 2000 and 2016 were within the historical range of variability for pre-fire exclusion ponderosa pine forests. Initially, wildfire promoted California black oak; however, oak abundance and regeneration has declined while pine abundance and regeneration has increased in the subsequent 22 years without fire. In 2000, ~15% of trees were classified as individuals and tree group sizes ranged from 2 to 75 trees. Small tree groups (2-4 trees) consist of similar-aged trees while larger groups are multi-aged. In 2016, the percent of trees classified as individuals decreased by ~30%, and the scale and intensity of clustering increased. The greatest change in spatial patterns occurred in plots with the highest rates of post-fire recruitment. The size and frequency of canopy gaps was similar in 2000 and 2016; however, higher densities of seedlings and saplings were associated with canopy gaps in 2016 which suggests, without future fire, canopy gaps will be infilled. Fire behavior models indicate the Beaver Creek Pinery is still resilient to high severity wildfire. Overall, this research broadens our understanding on the persistent effects of fire on spatial heterogeneity and demonstrates that wildfires can be used to restore resiliency to forests where wildfires have been suppressed for nearly a century.