MICHAEL G. BARBOUR
MOST SIGNIFICANT CONTRIBUTIONS (16)
PUBLICATIONS (156) 1969--2007
“Patterns of genetic similarity between Larrea diveracata of North and South America” (1969). I was able to show that each of the three warm deserts in North America contained a different chromosome race of creosote bush: as one moved to the drier and hotter west, the ploidy increased. In the same paper I was able to show that creosote bush in Argentina was ecologically different from creosote bush in North America: in appearance it was very leggy, with scattered foliage facing in all directions, and the plants were restricted to semi-riparian situations, where the precipitation was augmented by runoff.
“Is any angiosperm an obligate halophyte?” (1970) This was my first attempt at a review, and it continues to receive wide attention from botanists and ecolo-gists. I was the first to define an obligate halophyte as having a bell-shaped curve of growth in moderately saline conditions, but very low growth in both low-salt and high-salt environments, whereas facultative halophytes have good growth in both low and moderately high salt conditions, and then decline with higher salinities. This paper supported the USDA’s choosing of 0.5% salt as the dividing point between sweet and saline water, based on the fact that many non-halophytes performed well up to 0.5% salt, and then they rapidly declined. In the literature, only one species of pickleweed (Salicornia) appeared to be an obligate halophyte.
“Saga of the west coast sea-rockets, Cakile edentula ssp californica and C. maritima. (1971) This was a detective-like search through the literature and herbarium specimens. Where did we first see these two species, and when? I was able to demonstrate that both species were introduced, first C. edentula (from the east coast of North America) in the 1800s and then C. maritima in the 1930s. Furthermore, C. maritima appeared to have driven C. edentula extinct throughout California and most of Oregon, but C. edentula continued to co-occur with C. maritima north of Oregon. How could competition be a factor in such an open habitat as the strand? Much later (1993), working with a graduate student of mine (Dr. Robert Boyd), we were able to show that competition could and did occur in the strand because the seemingly open habitat had only a small number of “safe sites.” We documented the rate of spread of C. maritima as being approximately 50 mi/yr, much faster than the 8 mi/yr of more inland weeds, because the fruits were able to float in sea water and be dispersed by currents.
“Review of North American Pacific Coast beach vegetation.” (1974) This was my first plant geography research, and it showed that there were about four floristic regions along the coast, and we used a statistical approach to determine where the break points were between those regions. There was a very long temperate zone in the north, a much narrower Mediterranean zone, an arid zone, and a sub-tropical zone, each with its own characteristic cluster of taxa. The Mediterranean region was the richest in species and the highest in endemism. Our review was improved in 1975 with “Additions and corrections to a review of North American Pacific Coast beach vegetation.”
“Germination, establishment, and demography of coastal bush lupine (Lupinus arboreus) at Bodega Head.” (1977) This was my first paper that discussed animal behavior as an explanation for plant behavior. We showed from a series of air photos that clumps of lupine were very dynamic in the coastal grassland. On average, they lived for only 6 yr and then declined rapidly. We showed that the decline was caused by herbivory from three insect species. This paper was seminal many years later for a decade-long series of papers by others that examined this relationship to a much deeper degree.
“Salt spray as a microenvironmental factor in the distribution of beach plants at Point Reyes, California.” (1978) This remains, in my opinion, as the best paper to measure salt spray at the height above-ground where vegetation is concentrated and to correlate the distribution of species on the beach with the amount of salt spray received. This correlation was shown to be a cause-and-effect one by subsequent greenhouse and growth chamber experiments.
“Relationships between sunfleck dynamics and red fir seedling distribu-tion.” (1984) This was a study of microenvironmental monitoring as a tool to explain the patchy distribution of red fir seedlings. We showed that—up to the age of 10-20 yr—seedling survival was optimal where incidence of sunflecks was minimal. We showed that the light saturation point was much lower than the intensity of light in sunflecks, and that higher light intensities created high soil surface temperatures around the hypocotyl. This information later was used to explain why planted red firs in Sierran clearcuts were notoriously unsuccessful: it takes about 13 yr to create enough shade (from shrubs) for naturally-germinated red fir seedlings to survive. Our results also explained that older saplings react positively to sunflecks, but this is only after they have established a significant root system, after the age of 13 yr.
“The myth of chaparral convergence.” (1990) This was the result of a lengthy
search through the literature to find measurements of vegetation in five parts of the world in which the same methods of data callection were used. To this date there has been no other review that included all five areas. We concluded that there were more differences than similarities among the five chaparral regions; that the five regions were abiotically/environmentally different, not just floristically or vegetationally different.; and therefore that the search for evidence of convergent evolution could not be found with this system.
“Sixty years of change in California conifer forests of the San Bernardino Mountains.” (1995) This work involved revisits to plots that had initially been surveyed for vegetation in the 1930s. By repeating the same method of sampling we were able to quantify vegetation change during that time—change that we hypothesized was due to the suppression of wildfires. The density of trees younger than 100 yr had quadrupled, and the balance of species abundances had dramatically shifted from a 1:1 fir-to-pine ratio to a much higher ratio.
“Ecological fragmentation in the fifties,” (1995 and also published as “American ecology and culture in the 1950s: who led whom?”1996) This has been my only nature-and-culture contribution, and it was enormously rewarding to me. In my opinion, I was able to attribute a major shift in how ecologists viewed the vegetated landscape to synchronous changes in such other areas as genetics, literature, and politics. This was written while I was a member of a team of ecological historians, anthropologists, landscape designers, and ecologists/conservationists—a very rich sabbatical experience that taught me a new vocabulary and set of methods for research.
“Through-growth of Douglas-fir: a model of rapid forest change without canopy gaps.” (2001). This work showed that there was another type of forest dynamics beyond “gap dynamics.” In gap dynamics, mature trees die and fall, leaving a gap in the overstory, within which light-demanding species can germ-inate and become established. The adjacent shaded areas cannot support such tree species, so a mosaic of patches of different age and species composition results. Given enough time and gaps, the forest changes. But forest dynamics in mixed evergreen forest are different: Douglas-fir has enough tolerance of shade to grow up beneath the shade of broad-leaf evergreens, and then to grow through their canopies and overtop them, creating shade that causes the broad-leaved trees to decline and die. We called this “through-growth dynamics” and through-growth dynamics can change the forest much faster over a larger area than can gap dynamics.
“Present and past old-growth forests of the Lake Tahoe Basin, Sierra Nevada.” (2002) This was a team approach to studying vegetation change over a 150-yr time period. From our own search for old-growth patches within the Tahoe Basin, and from my work in southern California and Baja California mountains, we were able to reconstruct the pre-contact mixed conifer forest of Alta California, quantifying density of young and old trees, the ratio of fir:pine, overall canopy cover, and tree basal area, among other attributes. These data have been used by others to frame restoration targets for the management of modern, forests that have experienced densification as a consequence of
“Vernal pool vegetation of northern California: within-pool vegetation.” (2003 and also 2004 and 2005) This paper completely changed the way my research team (and now other wetland ecologists in general) looked at vernal pool vegetation, how to sample it, and how to classify it. Vernal pool vegetation is no longer considered to be a single one-community-type entitiy, but rather each pool typically contains 2-3 different community types. Only when each type or zone is sampled can we create a classification, because classifications must be built up from local pieces of homogeneous vegetation and vernal pools are not homogeneous. We had a hard time getting the paper accepted for publication because we sampled each community type with a single large releve plot (10 square meters), instead of multiple small quadrats (typically 0.5 square meters and arranged in some array), and this was not the typical American method for sampling vegetation. Furthermore, we classified each community type by naming it after “diagnostic species” that were either endemic to that type or much more often found in that type than any other. This too contravened the American way of classifying based on dominant species. I’m very proud that we successfully got this paper published, because we began to follow the way the rest of the world samples and classifies vegetation. By doing so we ensured that the results of our work in California would be read and understood by ecologists in other parts of the world. I’m pleased that federal and state agencies have
adopted our classification work.
“Species richness and stand stability in conifer forests of the Sierra Nevada.” (2006 and 2005) This was a project designed with one of my brightest graduate students. It addressed an important hypothesis commonly accepted by ecologists: the richer in species a patch of vegetation is, the more stable and productive it is over year-to-year variations in the environment. We were able to show that the hypothesis could not be completely accepted because the species themselves mattered, not merely how many were present. The study’s import- ance is indicated by its publication in the top international ecology journals, Journal of Vegetation Science and Ecology.
“Resistance and resilience of vernal pool vegetation.” (2007) According to most ecologists, a vegetation type or a plant community type can be either resistant or resilient, but not both. Resistant types tolerate disturbance by changing as little as possible. Resilient types are significantly changed by the disturbance but they quickly recover back to the pre-disturbance state. These assumptions were tested and found to be false for vernal pool vegetation. For example, dry years affect the size and biomass of plants but not the presence of the species, and this is clearly resistance. Vernal pools can become decimated by disturbance but (as shown restoration/creation of pools). They are capable of recovering their pre-disturbance community types in half a dozen years, and this is clearly resilience.
“Age structure of young- and old-growth Quercus pyrenaica stands in Spain.” (2007) + “Species characteristics and stand
structure of Quercus garryana and Q. pyrenaica woodlands in the Mediterranean regions of California and Spain.” (2008)
These two papers are representative of my interest in comparing the vegetation of California and Spain. During the past 15 years I’ve found colleagues in Spain who have similar interests in vegetation convergence and we have collaborated
on comparative studies of broad-leaf forests, conifer forests, and serpentine scrubs and grasslands. The search for convergence in vegetation thousands of kilometers apart and floristically distant, yet sharing similar environments is of
ienormous importance. If significant convergence can be demonstrated, then
that conclusion suggests a given type of habitat can only support one “best” type of vegetation, meaning that evolution might be operating at the complex level of plant communities—far beyond our understanding of evolution at the level of one or two populations of one or two species. The work we did in oak woodlands suggests that convergence appears to act at the levels of community architecture (physiognomy) and stand dynamics, and similar conclusions are surfacing from our work on vernal pools in both regions.
Spanish academics and doctoral students who have worked with me include: J. Antonio-Molina, R.G. Gavilan, G. Garcia-Baquero, F. Llamas, J. Loidi, J. Rey-Benayas, S. Rivas-Martinez, P. Rodriguez-Rojo, and D. Sanchez-Mata. Spanish-speaking research collaborators outside of Spain include: S. Bagella (It), C. Caria (It), J. Delgadillo (Mex), I. Espejel (Mex), D. Espiritu-Santo (Pt), P. Moreno (Mex), and C. Pinto-Cruz (Pt).
MOST SIGNIFICANT CONTRIBUTIONS (16)