UC Davis Department of Plant Sciences

Aspen Stands - restoring and managing

Project 4: Aspen Stand Condition Under Dynamics of Increasing Conifer Cover and Persistent Aspen at Lassen Volcanic National Park, California 

Participants – Sarah McCullough, Donna Dutra, Natalie Stoddard, NPS Klamath Network Inventory, Lassen Volcanic National Park, Dr. Daniel Sarr, Dr. Michael Whiting, Dr. A. Toby O'Geen

Any Comments or Questions?


We sampled 29 aspen stands in Lassen Volcanic National Park, where park managers are in the initial stages of management planning for aspen. Many stands are small in size, vegetative sprouts are heavily browsed by deer, and stands are experiencing competition from white fir (Abies concolor) and lodgepole pine (Pinus contorta ssp. murrayana). 

Our objective was to determine trends in a suite of forest structure, understory plant community, and soil surface variables to indicate stand condition along the local gradient of conifer cover in aspen stands.  We also estimated the amount and rate of change in conifer cover over the past 50 years by stand, and correlated cover changes with stand condition indicators

aspen stand condition         

We examined current aspen stand condition in 2007-08.

Examining relationships between current conifer cover and stand condition indicators revealed that for each 10% increase in conifer cover, aspen recruitment decreased by 6 sprouts/100 m2, and herbaceous species richness decreased by 1.6 species.  Conversely, litter depth increased by 0.5 cm. 

aspen and conifer aspen stands

click thumbnail for larger size

We conducted an interpretation of aerial photos from 1952 and 1998 to determine directional changes in percent conifer and aspen cover in each of the 29 stands.

A dynamic of increasing conifer occurred in half the sampled stands, with a mean rate of conifer increase of 1% a year.  The remaining stands demonstrated a persistent aspen dynamic, with no significant increase in percent conifer cover.

aspen and conifer stands graph

click thumbnail for larger size

Trends in conifer cover 1952-1998 by stand from photo interpretation.  The persistent aspen category is defined as cover change less than or equal to 10% and increasing conifer is defined as cover change greater than 10%.

 

In stands with a dynamic of increasing conifer, mean percent conifer cover increased from 22 to 66%, and mean percent total cover increased by 30% to 92%, nearly closing the canopy.  Percent conifer cover increased by an average of 1% a year, while percent aspen cover declined by 0.3% a year.  In stands with a dynamic of persistent aspen, mean percent aspen cover increased from 38 to 50%, and mean total cover increased from 62 to 80%.  Percent total cover increased in these stands as aspen trees filled in gaps in the canopy. 

Stand dynamic

 

Persistent aspen

Increasing conifer

Percentage of Stands

48

52

Mean Cover (% change/yr)

Conifer

0.00

0.96

Aspen

0.28

-0.32

Total

0.39

0.69

Stand condition indicators were more strongly associated with stand dynamic and current percent total canopy cover (1998) than initial percent conifer cover (1952) and rate of change in percent conifer cover.  Stand dynamic and percent total canopy cover interacted to determine species richness, diversity, recruitment, and the relative masses of woody and fine soil litter. 

For every 10% increase in percent total cover, the number of aspen sprouts increased by 16 sprouts/100m2 in stands with an increasing conifer dynamic, but decreased by 3 sprouts/100m2 in stands with persistent aspen (Figures a, b). 


Figures a, b persistent aspen, increasing conifer

 

For every 10% increase in percent total cover, species richness decreased by less than one species in stands with persistent aspen, but decreased by 5 species in stands with increasing conifer (Figures c, d). 

figures c and d
persistent aspen, increasing conifer

The Shannon Wiener diversity index increased by 0.01 for every 10% increase in percent total cover in stands with persistent aspen, but decreased by 0.05 in stands with increasing conifer (Figures e, f).

 
figures e and f
persistent aspen, increasing conifer

For every 10% increase in percent total cover in stands with increasing conifer, the ratio of woody to fine litter increased by 0.2 g woody cm3 / g fine cm3, but the ratio decreased by 0.02 g woody cm3 / g fine cm3 in stands with persistent aspen (Figures g, h). 


figures g and h

 

Management Implications
The ecosystem values associated with aspen stands are negatively associated with percent conifer canopy cover in Lassen Volcanic National Park. Although some stands appear to be persistent through time, the remaining stands will likely require management attention if their values are to be maintained for future generations.

© 2011-2012 UC Davis | California Rangeland Watershed Laboratory | One Shields Ave | Davis, CA 95616 | Last update: September 26, 2013