Limey Uplands (Wupatki)
States [Due to a history of volcanism and long-term human occupation, appropriate reference vegetative communities in Wupatki should be defined with care. Here we emphasize what is likely possible under management scenarios today. Paleoecological studies have described reference communities from a variety of time periods. Some are not possible under current conditions. States are divided into pre-historic and historic-modern (manageable) to make this distinction]:
Pre-historic States (not possible under current management scenarios):
P1: Pre-eruption.An original vegetation state under approximately modern climate regimes is difficult to reconstruct, and sketchy at best. Based upon packrat midden and palynological analysis, it is likely that grasslands were common (Cinnamon 1988). Plant macrofossils demonstrate that Juniperus monosperma was present (Cinnamon 1988; but not confirmed by Ironside 2006) and also seems to suggest a greater prevalence of Stipa hymenoides, and the grass Enneapogon desvauxii, and the shrub Artemisia bigelovii. Other common species, also present today, include Hillaria jamesii, Chrysothamnus nauseosum, and Opuntia erinaceae. Notably Bouteloua spp-a current co-dominant- were only sparsely represented. Because biological crusts have very low potential on basaltic soils on the Colorado Plateau, they were likely a very minor ecosystem component (Bowker and Belnap 2007). Frequent ground fires (15-20 yr return interval) likely maintained grasslands and limited tree and shrub establishment (Cinnamon 1988, Hassler 2006).
P2: Post-eruption, post occupation. State P1 experienced two drastic changes which almost certainly led to rapid transitions. First the Sunset Carter eruption deposited up to several centimeters of volcanic ash and cinder possibly killing vegetation. Cinder deposition is thought to have improved water infiltration dynamics, and likely strongly altered hydrology (Sullivan and Downum 1991). Within a few decades an approximately century-long occupation of dry-farming societies ensued. These are though to have been abandoned due to declining soil nutrient stores (Sullivan and Downum 1991). Midden and palynological data indicates shifts in relative abundance of some taxa (Cinnamon 1988) including a decrease in Enneapogon, Artemisia bigelovii, and Stipa hymenoides, an apparent arrival of Stipa comata, and no major change in Hillaria jamesii. Frequent ground fires (15-20 yr return interval) likely maintained grasslands and limited tree and shrub establishment (Cinnamon 1988, Hassler 2006).
Current and recent states:
S1: Current potential Grassland
S1Phase1: Rested Grassland. Prior to the inititiation of grazing the area had over 500 years to recover from agricultural disturbance. We know little about this period, except that midden analysis suggests that relative abundance of plant macrofossils does not appear to have changed much over this time. Presumably cover increased. A range assessment of the region from the early 1970’s provides some seemingly overoptimistic estimates of “climax” cover at 60-90%. The assessment also suggests that a greater prevalence of Stipa species, and a lesser prevalence of Hillaria jamesii, Bouteloa gracilis (Doughty 1971). These assertions were based upon general knowledge of the range assessor rather than specific knowledge of the ecosystem. The greater importance of Heterostipa comata in the past is confirmed by midden evidence, but middens suggest that Hillaria is not a product of increasing dynamics under grazing. Rather it has been a major community component for centuries. The supposedly frequent ground fire interval (Cinnamon 1988, Hassler 2006) would tend to favor the rhizomatous species such as Hillaria and Bouteloua (Jameson 1962, Ford 1999).
Given this somewhat conflicting body of evidence, we can say that, if we accept the hypothesis that frequent ground fires were common, then rhizomatous grasses dominated. At least in some years cover and connectivity of grass and litter patches would have had to have been sufficient to carry a burn. Jameson (1962) estimated that a 1956 wildfire had 13% cover pre-burn, although these estimates could be biased because they were taken post-burn in nearby unburned areas. We can take this as a reasonable first approximation of a minimum cover to sustain fire. Finally, there may have been a greater prevalence of Heterostipa comata, though this tussock grass is not likely to have dominated.
S1Phase2: Grazed ecosystem.
S2 variant b: Denuded state. If heavy grazing continues unabated, a transition to a severly denuded state is possible. This state is characterized by greater cover of bare ground, an overall decrease in vegetation to very low levels, and an increase in the relative prevalence of unpalatable species (Chryosthanmus, Opuntia, Guiterrizia) and possibly invaders (Salsola). Although the cinder-covered surface and generally flat slopes of this ecosite lend it low erosion potential, such a reduction in vegetation cover could conceivably initiate erosion since water-stable aggregate structure is very poor (Generally <2>
S2 variant j: Denuded state, juniper overstory. If junipers were allowed to establish and grow to adulthood (see S3), and heavy grazing reinsitituted, we would expect a degradation of the soil surface similar to C4b, with an overstory of high-lined juniper trees. Similar states can be observed outside of park boundaries to the north closer to Cameron.
century climates regimes indicate that limey uplands have a high probability of invasion (Ironside 2006). If grazing keeps fines fuels low, fire cannot cull colonizing junipers making savannization likely. It is not known if this can proceed to a woodland state like some nearby areas on different soils, but this possibility is not favored by future climate projections thus is not considered here (Ironside 2006).
Photos (Jameson 1962) demonstrate both a denuded phase in 1906, and savannization in 1960 in the general area of Antelope Prairie.
Transitions:
T1: Cinder and deposition due to volcanism beginning in 1064 likely initially destroys much vegetation, but enhances infiltration and water retention dynamics of soils. From ~ 1200 - 1300 Shortly afterward, agricultural societies practiced dryfarming, exploiting the properties of the cinder soils.
T2. Long term rest (centuries) allowed succession to proceed to a fire-maintained grassland.
T3. (Syndromes B2, B5) Introduction of grazing reduces palatable herbage in favor of unpalatable vegetation, reduction of fine fuels eliminates frequent fire.
T4. (Reversal of syndromes B2, B5) Adequate rests allows reestablishment of fine fuels and fire.
T5. (Syndromes B6, A1, A4) High intensity grazing reduces plant cover to the point that these systems are susceptible to water erosion.
T6. (Reversal of B6, A1, A4) Some fairly well-denuded systems eventually recovered on a time scale of decades, exhibiting an unusual resiliency. T5 and T6 likely obey a threshold dynamic.
T7. (Syndromes B4) Elimination of fire also eliminates the major force preserving the grass life-form dominance. Trees and shrubs are able to colonize.
T8. (Syndrome B5) Global change-type drought leads to death of woody plants and reversion to a grass-dominated ecosystem. This transition has not yet been observed in Wupatki, but has been nearby outside of Sunset Crater (Bowker et al. 2010, Gitlin et al. 2006).
T9. Identical to T5 except that grazing occurs after Juniper establishment.
Useful indicators and rationale (bold italics indicates most important under current management scenarios):
I1. Fuel load, inclusive of grasses, dead herbaceous and woody material, and litter T3, T4. Fuel load could be estimated based on measured cover and height of plants, with a one-time calibration versus biomass. These indicators will help inform whether fire is possible.
I2. Connectivity of fine fuels could be measured in multiple ways. The mean length of bare areas would be one useful easy measure. Also, mean length of fine fuel islands (prep figure) could be key. T3, T4. Visual ordinal indices (Leonard 2009) and bare ground and rock cover (Knapp and Keeley 2006), though such indices leave much room for improvement. These indicators will help inform whether fire is possible.
I3. Woody plant density, e.g. number of individuals per area. Frequency may be an acceptable proxy. T3, T4, T7, T8. Because woody plants are long-lived and slow growing, the number of individuals may be more informative than cover in determining risk of savannization or other woody plant dominance
I4. Cover of bare ground. T6. Of the controls on erosion in this ecosite, only vegetation cover and its converse bare ground are likely to be dynamic. These will determine susceptibiltiy to erosion, because vegetation cover modulates erositivity.
I5. Proportion of live to dead junipers may come to be relevant during global change type droughts, but is not currently useful to monitor frequently.
Data Availability: Sparse
Hassler (2006) likely conducted some sampling of Juniperus density, growth rate, and fire mortality on Limey uplands
DeCoster and Swan (2009) summarizes the first years of the I & M program and contains the most purposefully collected dataset for Limey Uplands. May capture unexploited recovery from fire gradients (1 plot in 1995 north fire, 3-4 plots in the 2002 Antelope fire). Contains good information on vegetation structure and ground cover but lacks indices of connectivity of fine fuels, or average bare ground length. Sites may all be in more or less the same state.
Bowker and Belnap (2007) sampled biological soil crust cover and soil stability on limey uplands assumed to be at potential condition.
Miller et al. (2007) sampled 7 plots on limey uplands.
Recommendations for I & M program:
Consider low intensity (perhaps one time only) sampling of key variables in plots outside of monument boundaries on Limey Uplands. This will help confirm that the state-and-transition model is reasonable, and may provide a data-based confirmation of estimated threshold points in key monitoring variables. Examples include savannized limey uplands south of the monument boundary on the Wukoki lava flow, and various stages of grazed systems, and denudation on Antelope Prairie north of the monument boundary.
Refine and implement monitoring data which relate to fuel load and connectivity, the manageable aspects of fire susceptibility. Consider pursuing a site-specific fire susceptibility model.
Utilize the different fire histories in analysis of the current monitoring plots. Opportunistically monitor plots in future fires.
Literature Cited
Cinnamon, S.K. 1988. The vegetation community of Cedar Canyon, Wupatki National Monument as influenced by prehistoric and historic environmental change. Master’s Thesis, NAU.
Doughty, J.W. 1971. Soil survey and range site and condition inventory. Wupatki National Monuments, Arizona. A special report. USDA SCS.
DeCoster, J. K., and M. C. Swan. 2009. Integrated upland vegetation and soils monitoring for WupatkiNational Monument: 2008 summary report. Natural Resource Data Series NPS/SCPN/NRDS—2009/022. National Park Service, Fort Collins, Colorado.
Knapp, E.E., and J.E. Keeley. 2006. heterogeneity in fire severity in early and late season prescribed burns in a mixed conifer forest. International Journal of Wildland Fire 15: 37-45.
Hassler, F. 2006. Dynamics of juniper invaded grasslands and old growth woodlands at Wupatki National monument, Northern Arizona, USA. Master’s Thesis, Northern Arizona University.
Leonard, S. 2009. Predicting sustained fire spread in Tasmanian Native grasslands. Environmental Management 44: 430-440.
Miller, ME, Witwicki, DL, Mann, RK, Tancreto, NJ. 2007. Field evaluation of smapling methods for long-term monitoring of upland ecosystems on the Colorado Plateau. USGS Open File Report 2007-1243.
Bowker, M.A. and Belnap, J. 2007. Spatial Modeling of Biological Soil Crusts to Support Land Management Decisions: Indicators of Range Health and Conservation–restoration Value Based Upon the Potential Distribution of Biological Soil Crusts in Montezuma Castle, Tuzigoot, Walnut Canyon, and Wupatki National Monuments, Arizona.
Bowker, MB, Munoz, AA, Martinez, T., Lau, MK. 2010. Rare drought-induced mortality of juniper: edaphic and climatic stressors promote hydraulic failure. unpublished manuscript.
Gitlin, AR, Sthultz, CM, Bowker, MA, Stumpf, S., Paxton, K.L., Kennedy, K., Munoz, A., Bailey, J.K., Whitham, TG. 2006. Mortality gradients within and among dominant plant populations as barometers of ecosystem change during extreme drought. Conservation Biology 20: 1477-1486.
Ford, PL. 1999. Response of buffalograss (Buchloe dactyloides) and blue grama (Bouteloua gracilis) to fire. Great Plains Research 9: 261-76.
Ironside, K. 2006. Climate change research in national parks; paeloecology, policy, and modeling the future. Master’s Thesis, Northern Arizona University.
Jameson, D.A. 1962. Effects of Burning on a Galleta-Black Grama Range Invaded by Juniper. Ecology 43: 760-763.
Sullivan, AP, Downum, CE. 1991. Aridity, activity, and volcanic ash agriculture: a study of short-term prehistoric cultural-ecological dynamics. World Archaeology 22: 271-287.
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