}pASCIIK}.pl0 ES&P 400 readings

CALIFORNIA STATE UNIVERSITY, LONG BEACH

ES&P 400 Readings
Environmental Science and Policy Capstone Project

==========

Hypotheses and Questions about CSS Recovery

(from midway in the Fall 2012 Geography 640 seminar
updates are in blue

==========

  1. CSS declines or won't recover in the presence of high soil nitrogen
    • Mentioned in Allen et al. 2000
    • Argued in Allen et al. 1998
    • Artemisia californica responds to N inputs at first but then adults die off
    • Native gardening experts strongly discourage use of fertilizer for native plant gardens
    • CSS becomes more open and lower and there's more die off in areas with high N deposition
    • Introduced exotic annual grasses/forbs and native shrubs can take up and exploit increased N
    • But shrubs grown with exotics do not produce as much biomass: Exotics better able to use N throughout their life cycles
    • Soil N should scale with proximity to roads, industrial areas, and ports (idling trucks) and with proximity to agricultural activities, which the Allen group has found in the Inland Empire
    • Thesis project?: Mapping soil nitrogen content (ammonium, nitrate, nitrite, and ???)
    • There should, therefore, be an association between soil nitrogen concentration (measured how? C:N? qualitative kits?) and the health of CSS (measured as biodiversity, native:exotic balance, ground cover, expansion/contraction of territory with respect to grassland)
      • GDEP found no significant difference in soil nitrogen content in CSS-covered and grass-covered sites (using Dr. Stevens' lab to measure C:N in soil and also in using garden soil test kits)
      • There was no significant difference between the soils of recovering and of stable CSS-grassland boundaries, either.
      • With so few samples, however, these studies are underpowered, so the nitrogen question remains unanswered.

  2. Does allelopathy maintain the dominance of exotic forbs?
    • Grassland, dominated by exotic annuals, is itself vulnerable to invasion by particularly invasive exotics, such as Brassica nigra (black mustard), Fœniculum vulgare (common fennel), Cirsium vulgare (bull thistle), Carduus pycnocephalus (Italian thistle), Bromus tectorum (cheatgrass), and B. diandrus (ripgut brome). Some of these can produce monospecific stands in grassland, and these can persist for decades. How do some of these maintain their dominance?
    • One hypothesis is that certain of them practice allelopathy: Brassica nigra (and other mustards) has been suspected for a long time (1973) of suppressing everything else around through some phytotoxin that leaches out of dead dry stalks. More recent work (2009) identifies glucosinolates-myrosinase as the culprit compounds.
    • GDEP tried to get at that through the infamous mustard mulch experiments.
      • 2009 tests compared mustard-mulched pots planted with the native California poppy (Eschscholzia californica) with pots having no mulch: Mulched pot seedlings were smaller and yellower than unmulched pots.
      • 2010 tests showed little to no differences among pots mulched with mustard and burnt mustard, redwood and burnt redwood, and sphagnum moss and burnt moss.
      • So, the rôle of mustard allelopathy is inconclusive.

  3. Soil attributes might have something to do with the persistence of CSS and grassland

  4. Are there soil attribute differences between recovering and stable CSS/grassland boundaries?
    • Dr. Laris and I decided that, even if we saw differences along a given transect running from grass into CSS, it could well reflect nothing more than long ago farmers' choices about what kind of soil to plow and where they did not dare venture for fear of damaging their equipment
    • Now, we are trying to get information on soil differences between recovering and stable boundaries between the two vegetation associations -- La Jolla Valley and Serrano Valley. Here are the data on the GDEP transects (which were 50 m long, not 20 m like we did in November -- a bit of overkill): https://home.csulb.edu/~rodrigue/geog640/data/FieldDataConsolidatedNewNames.xls
    • We need to add our data to this form (centering our 10 m on their 25 m, with two grass quadrats and two CSS quadrats, rather than five each)
    • Only half the GDEP 2010 transects have soil penetrometer data (we had one penetrometer and two groups working).
    • We didn't take Kelway data (don't remember why -- I think the assumption was we'd do it in the lab afterwards, but didn't).

  5. What about mycorrhizæ?
    • As we saw this semester (Vogelsang and Davis [1993]), mycorrhizæ may strongly mediate the competition among exotics and natives in a variety of vegetation associations around the world
    • We collected a few soil samples with more or less intact root balls from both CSS and grass
    • Small samples of these can be stained with India ink and vinegar (http://mycorrhizas.info) to evaluate whether there are differences in their prevalence and/or types/species
    • Ms. Mills took this on and it eventually became the topic of her master's thesis.
      • She has found mycorrhizæ in CSS species' rootballs in CSS-occupied sites
      • The number of infected roots drops in samples taken from the grasslands.
      • She is now comparing subsurface mycorrhizal biodiversity with aboveground mycorrhizal biodiversity along an elevational gradient in the Transverse Ranges of Southern California to see if they mirror one another and if aboveground biodiversity depends on subsurface biodiversity.

  6. What about geology?
    • Draping the Dibblee maps onto a common image on which Kyra's boundary maps are also projected might allow evaluation of boundary type associations with Topanga shales, Topanga sandstones, Conejo diabase volcanic outcrops, and Quaternary alluvium -- or with the faults on his maps?
    • There may be finer-grained geological maps available, too
      • Messrs. Nesbit and Winslow performed that analysis and were unable to find any associations among underlying geological units and vegetation patches or boundary types.
      • They did feel that the Dibblee maps are at too coarse a scale to pick out subtle geological substrate influences that may be important and encouraged others to do field geology to classify substrates, soils that develop over each substrate, and associations with the vegetation.

  7. Are there differences in the assemblages of species found in recovering and stable boundaries?
    • Which CSS species are found out ahead of the recovering boundaries, the ones that can establish in grassland, the vanguards?
    • Are there soil conditions unique to the grassland sites with CSS vanguard species?
    • Which CSS species are found in the CSS just behind the leading edge of a recovering boundary? Maybe these are the secondary stages in CSS type- conversion/succession
    • Which CSS species are found in the CSS just behind a long-stable boundary? In La Jolla and Serrano valleys, there are often sharp boundaries between CSS and grassland, demarcated by a strip of nearly bare ground, sometimes as little as half a meter wide to as much as 3 m wide. In other places in these valleys, the ecotones are more gradual. Is there an association between these transitions and the type of boundary?
    • Some of these were GPSed by Dr. Laris' group in Fall 2012. These could be plotted on Kyra Engelberg's maps of moving boundaries as one way of working out the association. That hasn't been done as far as I know.
    • Something we noticed qualitatively back in 2010 is that the bare transition zones, where they exist, do have small numbers of small plants in them, and Melica imperfecta and Stipa (Nasella) pulchra, native bunchgrasses, were commonly among these. We can go over the GDEP species censuses, using Chi-square, to see if those (or other) species are disproportionately found in such bare transitions. The GEOG 442 group surveyed similar bare versus ecotone-like borders in Charmlee Park in westernmost Malibu and found a different mix of low-slung species in the bare transitions there: Erodium botrys and Rumex crispus.
    • What might that mean ecologically?
    • What causes those strips of bare ground? Is it browsing herbivores walking along, snacking on CSS as they go? Dr. Laris and I are wondering if it's rabbits -- web-cam project?
    • Why aren't these bare strips found on Palos Verdes (lack of deer? are rabbits missing, too?)
    • Anyone up to a cheap web cam experiment back in La Jolla or Serrano valleys?
    • Data for identifying the vanguard, leading-edge pioneers, and the species in the bare transitions we already have from GDEP and our GEOG 640 field trip.
    • We can do species lists for each type of boundary and then we can do cross-tabs (eventually producing a diagram like the one in https://home.csulb.edu/~rodrigue/geog442/PVsppassociationsF11.png
    • If we can find vanguard and leading-edge pioneer species, a natural next step would be an experimental restoration on grassland that mimics the vanguard/leading-edge pioneer succession and see if it has better persistence/success than other methods of attempting restoration (Samantha Antcliffe's thesis, PVPLC projects at White Point).
    • We need a concerted effort to find other studies that may have noted the same species leading CSS self-restoration (maybe in pieces irritated with CSS incursions into grassland, such as those two "how to kill chaparral" pamphlets!). Anyone partial to a more library-focussed project?

  8. Does CSS "only" restore downhill?
    • We have a lot of data from GDEP, GEOG 442, and 640, and possibly now ES&P 400 that might allow evaluation of this idea.
    • Transect data include information on slope, both from clinometers and GPS units
    • Boundaries on Kyra's maps (or Scott Eckardt's maps in Cheseboro Canyon area or Mike Ferris' maps for Palos Verdes) could be overlaid on a DEM

  9. Aspect might be important, too
    • There's been some work on chaparral and CSS recovery and the nature of the slopes they're on
    • Chaparral seems better able to recover down steep slopes that face northward CSS seems better able to recover down hot slopes
    • GDEP 2010 did some work on this in La Jolla Valley: https://cla.csulb.edu/departments/geography/gdep/2010/biogeography/posters/Chea.ppt
    • We have azimuth data from our own field day out there and from GDEP 2010, and Dr. Laris' class' fieldwork

  10. Fire frequency?
    • Keeley's associates have argued that too-frequent fire (especially return intervals in the 2-5 year range) induces type-conversion from chaparral to grass or CSS and from CSS to grass. The introduction of annual plants that leave behind fine fuels (kindling, basically) encourages frequent fires, to which they are well adapted, better adapted than shrubs (resprouters can have their subterranean energy reserves depleted after too many fires, and obligate germinators' soil seed banks eventually thin out and are swamped in the competition for living space by the profuse seed production of annual grasses and forbs
    • Fire perimeter maps can be used to construct fire frequency maps (e.g., https://cla.csulb.edu/departments/geography/gdep/graphics/woodsfirefreqLSAMP.jpg )
    • How reliable are these at the fine spatial scale of restoring and stable boundaries?
    • If they are not riddled with mismatched scale problems, overlaying maps of restoring and stable boundaries on fire maps could allow evaluation of this hypothesis
    • Jade Dean's team in GDEP 2009 worked with the fire perimeter data in Palos Verdes back when we were focussing on environmental correlates with current CSS and grassland

  11. Other types of disturbance history are important in CSS recovery
    • GDEP 2009 and 2010 and the Engelberg and Eckardt theses evaluated fire frequency, grazing history, and mechanical disturbance
      • CSS comes back after grazing ends (both in the Santa Monicas and Palos Verdes)
      • CSS is present in areas that burned four times in ten years! (Palos Verdes)
      • CSS does not recover after plowing/mechanical disturbance (mycorrhizal effects?)
    • "Word on the street" is that Serrano Valley was plowed/farmed but La Jolla Valley was not (being used for cattle and horse grazing), making the pair of adjacent valleys a nice test-bed for the effects of mechanical disturbance
    • Charmlee Park, too, was used as a cattle ranch
    • But, when we were out there trying to figure out why the "cow" (see remote sensed images of La Jolla Valley) and other grass covered areas were so persistent, we saw subtle signs of plowing in the form of faint ridge/trough lines running parallel to one another across field-sized parcels Those turned out later to be weed-whacker tracks as the Pt. Mugu State Park people tried to control Harding grass up there)
    • There was some mention in the history of Rancho Guadalasca that Richard Broome (who inherited it in the 1920s) was raising draft horses and cattle up there and that he let tenant farmers use part of it.
    • But his lands extended far past La Jolla Valley up into Camarillo and the Oxnard Plain (IIRC) and it isn't clear whether tenant farmers used more accessible pieces of his land or were actually in La Jolla Valley.
    • This might reward archival work for anyone with a social science bent and a fondness for local history. Also, talking to the State Parks people might shed light on those plow-like marks up there (as well as what's up with the obvious weed-whacking in places) It did: They were doing weed-whacking to nail the Harding grass)
==============================
ES&P 400 Home  | Dr. Rodrigue's Home  |   Dr. Lipo's Home  |   Mr. Langdon's Home  |   Ms. Mills' Home  |   ES&P Home   |  
==============================
This document is maintained by Dr. Rodrigue
First placed on web: 01/08/12
Last revised: 01/18/14
==============================

[ four photographs of California sage scrub, C.M. Rodrigue ]