Data from: A 37-year experimental study of effects of structural alterations on a shrub community in the Mojave Desert, California

1. In 1977 an experiment was initiated in the Mojave Desert to investigate
how shrub interactions affect structure in a community dominated by
Ambrosia dumosa and Larrea tridentata. Here, as in much of the Mojave,
Larrea were regularly distributed, Ambrosia occurred in aggregations, and
the two were randomly distributed relative to each other. Pre-dawn xylem
pressure potentials (PDXPPs) of single Ambrosia or Larrea in centers of
100m2 circular plots were monitored to assess effects of intraspecific,
interspecific, and total removals of neighboring shrubs. Contrary to
theory, results over the next two years indicated interspecific
interference was more intense than intraspecific interference in both
species. 2. These plots were maintained through 2014. Measurements of
seedling recruitment from 1980 to 2014, and of PDXPP, aboveground biomass,
and canopy senescence from 2003 to 2014 were conducted. 3. Recruitment of
both species was substantial immediately after the removals, but declined
to very low levels after 1983. Ambrosia recruited into all Ambrosia and
Total-Removal plots, but Larrea recruited only into plots that contained
mature Ambrosia. 4. PDXPPs of monitored shrubs continued to be enhanced in
removal plots for at least 27 years, but this changed from most being due
to interspecific removals in both species to intraspecific removals
causing most enhancement in Ambrosia and inter- and intraspecific removals
causing nearly equal enhancements in Larrea. 5. Aboveground biomasses of
monitored shrubs of Ambrosia and Larrea were 2.1X and 2.8X larger in
Total-Removal plots, 1.6X and 1.7X larger in intraspecific removal plots,
respectively, and 1.1X larger in interspecific removal plots for both
species than those in Control plots, indicating the absence of
intraspecific interference had the dominant long-term effect. 6. Canopy
senescence differed between Ambrosia and Larrea in extent, timing and
effect of specific removal treatments; it was greatest for both species in
Controls, averaging 75% and 34%, respectively. 7. Synthesis. Shrub
interactions and their relations to community structure are
mechanistically and spatially complex. Differences between short-term and
long-term responses to removals reveal multi-tiered, temporally dynamic
feedback loops between shrub interactions and community structure driven
by demographics, species-specific root growth, resource competition,
communications, and territoriality.