1 / 21

Dawn M. Lawson U.S. Navy SSC Pacific

Patterns of recruitment and mortality in mixed coast live oak/ Engelmann oak woodlands in southern California over 24 years. Dawn M. Lawson U.S. Navy SSC Pacific. Paul H. Zedler University of Wisconsin-Madison. Leslie Seiger Mesa College. We would like to thank the

phil
Download Presentation

Dawn M. Lawson U.S. Navy SSC Pacific

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Patterns of recruitment and mortality in mixed coast live oak/ Engelmann oak woodlands in southern California over 24 years Dawn M. Lawson U.S. Navy SSC Pacific Paul H. Zedler University of Wisconsin-Madison Leslie Seiger Mesa College We would like to thank the UC Integrated Hardwood Range Management Program and Marine Corps Base, Camp Pendleton for funding and access for this work.

  2. Engelmann Oak Coast Live Oak Quercus engelmannii Quercus agrifolia

  3. Typical Oak Woodland

  4. Distribution of Mixed Oak Woodlands on Camp Pendleton

  5. Establishment and Recruitment Lawson 1993; Lawson, Zedler and Seiger 1997 • Seedling establishment is episodic and patchy. • The seedlings and saplings of the two species do not differ in growth rate. • Canopy location is the most important factor affecting both establishment and relative growth rate, but it does so in opposite ways.

  6. Seedling Bank

  7. Growth Rate in Gaps

  8. Establishment and Recruitment Lawson 1993; Lawson, Zedler and Seiger 1997 • Q. agrifolia establishes more seedlings and recruits more individuals into the sapling size class. • Q. engelmannii has a greater ability to establish in the gaps where mortality is lower and relative growth rate higher. • Seedlings and saplings may be maintained in smaller size classes in areas of high fire frequency. • Based on the number of stems, seedlings and saplings may be most severely effected by moderately frequent fires.

  9. Suppression and Burnout Model High fire frequency causes juvenile oaks to be maintained in the smaller size classes. Fire causes the continual attrition of larger trees through the “burnout” process. The canopy slowly declines at rates that may be difficult to discern in short term studies.

  10. Episodic Escape Model High fire frequency causes juvenile oaks to be maintained in the smaller size classes. Fire causes the continual attrition of larger trees through the “burnout” process. but occasional recruitment to the canopy offsets decline.

  11. Episodic Escape Model dead oak ring of recruits

  12. Canopy Change Analysis Oak Canopy 1928

  13. Canopy Change Analysis Oak Canopy 2000

  14. Canopy Change 1928 to 2000 • N = 9 • Mean +78% • Range 31% to 166% • stdev – 30% • The canopy in coast live/ Engelmann oak woodlands increased increased significantly between 1928 and 2000. • The largest increase occurred in the sparsest woodlands. • High fire frequency did not prevent this increase.

  15. Was this canopy increase a result of increasing size of individuals or recruitment of new individuals?Did the increase involve one or both species?

  16. Methods • Sampled oaks along belt transects • saplings and adults in 15m belt • seedlings (<50 cm ht) in 1m belt • Recorded • stem diameter at base, dbh, height and canopy location • Transects oriented along the • primary environmental gradient. • Initial sample 1987 • 15 stands • Resamples 1997 and 2011 • 5 stands

  17. Stand Characteristics • Density ranges from 50 to 171 trees (dbh>10cm) per ha. • The stands occur in two elevational bands from 100 to 200 m and from 600 to 800 m. • Rainfall varies from 35 cm at the lower elevations to 60 cm at the higher elevations. • Fire history ranges from 4 to 10 fires over the last 40 years. • Engelmann oak composition varies from 8% to 27%.

  18. Stand Structure Change 1987 to 2011(n=5)

  19. Stand Structure Change 1987 to 2011low elevation (n=3) & high elevation (n=2) mortality = 11.8% mortality=11.5% 1987 – 2011 1987 - 2011

  20. Conclusions • The canopy in coast live/ Engelmann oak woodlands has increased significantly in the last century. • The stand structures appear to reflect both fire history and by differences in precipitation between low elevation and high elevation sites • In the last 24 years a pulse of recruitment has moved through the stands. • Q. agrifolia has increased in numbers but not at the expense of Q. engelmannii. • High fire frequency did not prevent this increase. • The large seedling bank under canopies contains more than enough oaks to compensate for mortality.

  21. Conclusions cont. • Demographic differences between high and low elevation sites may be useful in anticipating the effects of climate change.

More Related