Effects of blackberry ( Rubus discolor) invasion on oak population dynamics in a California savanna

We conducted studies to assess the effects of Rubus discolor encroachment on native oak recruitment on a cattle ranch in northern California. R. discolor (Himalayan blackberry) is an invasive exotic plant species, especially in more mesic areas of California rangelands. Our results demonstrated that...

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Bibliographic Details
Published in:	Forest ecology and management Vol. 228; no. 1; pp. 187 - 196
Main Authors:	Williams, Kimberlyn, Westrick, Lawrence J., Williams, B.J.
Format:	Journal Article
Language:	English
Published:	Amsterdam Elsevier B.V 15-06-2006 Elsevier
Subjects:	Advance regeneration Animal and plant ecology Animal, plant and microbial ecology Biological and medical sciences Browsing ecological invasion forest trees Fundamental and applied biological sciences. Psychology height invasive species natural regeneration Oak savanna plant establishment Quercus douglasii Quercus lobata Rubus Rubus discolor Rubus fruticosus Rubus procerus savannas seedling growth seedlings Shrub invasion shrubs Synecology Terrestrial ecosystems tree growth understory California United States North America America Rubus fruticosus Advance regeneration Quercus lobata Rubus procerus Browsing Oak savanna Shrub invasion Quercus douglasii Rubus discolor Grassland Growth Plant juvenile growth stage Rosaceae Rubus Plant Dicotyledones Angiospermae Damage Ungulata Bovine Savannah Fagaceae Experimental study Plant emergence Long term Invasion Vertebrata Mammalia Rangeland Spermatophyta Population dynamics Artiodactyla
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Summary:	We conducted studies to assess the effects of Rubus discolor encroachment on native oak recruitment on a cattle ranch in northern California. R. discolor (Himalayan blackberry) is an invasive exotic plant species, especially in more mesic areas of California rangelands. Our results demonstrated that saplings of both Quercus douglasii (blue oak) and Quercus lobata (valley oak) were preferentially associated with thickets of R. discolor. Analysis of browsing damage, growth forms, and reconstructed histories of height growth of small oaks suggested that berry thickets promoted oak seedling recruitment into the sapling size class by protecting them from browsing. Experimental plantings of acorns across the grassland/thicket interface, however, revealed that the interiors of the berry thickets were very poor locations for oak seedling establishment. The overall effect of blackberry encroachment appeared to be a transient effect, producing a pulse of recruitment into the sapling size class from a smaller size class. Long-term effects on oak recruitment will be negative, due to the elimination of oak seedling establishment inside berry thickets. Even if berry thickets had not suppressed seedling establishment, however, a simple model suggested that even temporary occupancy of a site by berry thickets would reduce recruitment of oaks into the sapling size class for many decades. In the model, the pulse of sapling recruitment, caused by protection from browsing, depleted the pool of short, suppressed oaks that gave rise to the saplings, thereby reducing rates of further sapling recruitment. Recognition of the importance of a pool of small, browsed oaks and its impact on population dynamics in savanna systems has wide-ranging implications for interpretations of current and historical oak population structures and for predicting long-term impacts of management practices in oak savanna.
Bibliography:	http://dx.doi.org/10.1016/j.foreco.2006.03.002 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0378-1127 1872-7042
DOI:	10.1016/j.foreco.2006.03.002