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Open Access Publications from the University of California

Scholarly Works (21 results)

  • Article
  • Peer Reviewed
UC Santa Barbara Previously Published Works (2007)

Fog deposition is an important water source for endemic conifer species during the annual summer drought along the California coast ( and in other coastal and montane areas). We present a new design for a passive fog collector that is useful both for characterizing fog regimes ( timing and quantity of deposition) and for collecting fog water for subsequent isotopic analysis. The new collector both mimics vegetation collection efficiency and minimizes isotopic fractionation under a range of fog conditions. Low construction cost and collector durability allow widely distributed installation and greater insight into spatially heterogeneous fog patterns. We installed 21 fog collectors throughout a stand of Bishop pines ( Pinus muricata D. Don) on Santa Cruz Island. In general, there was greater fog deposition with increasing elevation and decreasing frequency farther inland. Within these broad patterns, there was large spatial and temporal variability in fog deposition. Monthly samples of fog and rain waters reveal differences in stable isotope composition ( delta O-18 and delta D) large enough to serve as tracers of different water sources moving through the ecosystem.

    Cover page: Evaluating patterns of fog water deposition and isotopic composition on the California Channel Islands
    • Article
    • Peer Reviewed
    UC Santa Barbara Previously Published Works (2004)

    We combined atmospheric CO2 measurements, satellite observations, and an atmospheric transport model in an inverse modeling framework to infer a key property of vegetation physiology, the light-use efficiency (LUE) of net primary production, for large geographic regions. We find the highest LUE in boreal regions and in the northern hemisphere tropics. Within boreal zones, Eurasian LUE is higher than North American LUE and has a distinctly different seasonal profile. This longitudinal asymmetry is consistent with ecological differences expected from the much greater cover of deciduous vegetation in boreal Eurasia caused by the vast Siberian forests of the deciduous conifer, Larch. Inferred LUE of the northern hemisphere tropics is also high and displays a seasonal profile consistent with variations of both cloud cover and C-4 vegetation activity.

      Cover page: Large-scale plant light-use efficiency inferred from the seasonal cycle of atmospheric CO2
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2010)
      Abstract In the early 1900s, tree-ring scientists began analyzing the relative widths of annual growth rings preserved in the cross sections of trees to infer past climate variations. Now, many ring-width index (RWI) chronologies, each representing a specific site and species, are archived online within the International Tree-Ring Data Bank (ITRDB). Comparing annual tree-ring-width data from 1097 sites in the continental United States to climate data, the authors quantitatively evaluated how trees at each site have historically responded to interannual climate variations. For each site, they developed a climate-driven statistical growth equation that uses regional climate variables to model RWI values. The authors applied these growth models to predict how tree growth will respond to twenty-first-century climate change, considering four climate projections. Although caution should be taken when extrapolating past relationships with climate into the future, the authors observed several clear and interesting patterns in the growth projections that seem likely if warming continues. Most notably, the models project that productivity of dominant tree species in the southwestern United States will decrease substantially during this century, especially in warmer and drier areas. In the northwest, nonlinear growth relationships with temperature may lead to warming-induced declines in growth for many trees that historically responded positively to warmer temperatures. This work takes advantage of the unmatched temporal length and spatial breath of annual growth data available within the ITRDB and exemplifies the potential of this ever-growing archive of tree-ring data to serve in meta-analyses of large-scale forest ecology.
        Cover page: Using Tree Rings to Predict the Response of Tree Growth to Climate Change in the Continental United States during the Twenty-First Century
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2009)
        Fog drip is a crucial water source for plants in many ecosystems, including a number of global biodiversity hotspots. In California, dozens of rare, drought-sensitive plant species are endemic to coastal areas where the dominant summer moisture source is fog. Low clouds that provide water to these semi-arid ecosystems through fog drip can also sharply reduce evaporative water losses by providing shade. We quantified the relative hydrological importance of cloud shading vs. fog drip. We then examined how both factors influence the range dynamics of an apparently fog-dependent plant species spanning a small-scale cloud gradient. The study area is on Santa Cruz Island off the coast of southern California. It is near the southern range limit of bishop pine (Pinus muricata D. Don), a tree endemic to the coasts of California and Baja, Mexico. We measured climate across a pine stand along a 7 km, coastal-inland elevation transect. Short-term (1-5 years) monitoring and remote sensing data revealed strong climatic gradients driven primarily by cloud cover. Long-term (102 years) effects of these gradients were estimated using a water balance model. We found that shade from persistent low clouds near the coast reduced annual drought stress by 22-40% compared with clearer conditions further inland. Fog drip at higher elevations provided sufficient extra water to reduce annual drought stress by 20-36%. Sites located at both high elevation and nearer the coast were subject to both effects. Together, these effects reduced average annual drought stress by 56% and dramatically reduced the frequency of severe drought over the last century. At lower elevation (without appreciable fog drip) and also near the inland edge of the stand (with less cloud shading) severe droughts episodically kill most pine recruits, thereby limiting the local range of this species. Persistent cloud shading can influence hydrology as much as fog drip in cloud-affected ecosystems. Understanding the patterns of both cloud shading and fog drip and their respective impacts on ecosystem water budgets is necessary to fully understand past species range shifts and to anticipate future climate change-induced range shifts in fog-dependent ecosystems.
          • Thesis
          • Peer Reviewed
          UC Santa Barbara Electronic Theses and Dissertations (2014)

          In my dissertation research, I investigated how coastal fog influences the water relations and distribution of Bishop pine (Pinus muricata D. Don), a drought sensitive species restricted to the fog belt of coastal California and offshore islands. I will discuss three related projects motivated by the following research questions: 1) Can the current spatial pattern of Bishop pine mortality on Santa Cruz Island be explained by important environmental and biological controls on plant available water? 2) How do summertime fog water inputs affect the water status of Bishop pines? Do adult and sapling trees respond to fog differently? and 3) What is the relative importance of fog-drip and fog immersion to the physiological function of Bishop pine saplings? I addressed these questions by using a variety of approaches ranging from remote sensing techniques to field-based plant physiology. The outcomes of these studies provide evidence that coastal fog is an essential element to augmenting plant available water during the dry season and that its occurrence supports the southern extent of its range on Santa Cruz Island. Moreover, this work advances our ability to make mechanistically-based predictions of how foggy coastal forests may respond to a warmer, drier climate.

            Cover page: Influences of coastal fog on the physiology and distribution of Bishop pine on Santa Cruz Island, California
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2008)
            The coast of California is home to numerous rare, endemic conifers and other plants that are limited in distribution by drought sensitivity and the summer-dry climate that prevails across most of the state. Ecologists have long assumed that some coastal plant populations survived the early Pleistocene transition to a warmer and drier environment because they benefit from frequent fog and stratus clouds that provide water and shade during the rainless summer. One such population is that of Torrey pine (Pinus torreyana ssp. Insularis) on Santa Rosa Island in Channel Islands National Park. Here we report that the tree-ring width record from this population indicates strong growth sensitivities to summer fog drip and cloud shading. We quantified the effects of summer cloud cover by comparing ring-width indices to coastal airport cloud-frequency records (1944-2004). For the first time observed, summertime cloud frequency correlated positively with ring-width indices, regardless of whether the effect of rainfall was first removed from the ring-width record. The effect of ground-level fog was strongest in July early mornings (03:00 PST, R(2) = 0.262, P < 0.0002). The effect of clouds high enough to provide shade but not fog water was also strongest in July, but climbed steadily throughout the day before becoming strongest in late afternoon (16:00-18:00 PST, R(2) = 0.148, P < 0.004). Correlations were substantially stronger in years with higher soil moisture, suggesting that growth response to summer clouds is strongly affected by pre-summer rainfall. A change in the height and/or timing of coastal cloud formation with climate change would likely affect this and other populations of California's coastal vegetation.
              Cover page: The influence of summertime fog and overcast clouds on the growth of a coastal Californian pine: a tree-ring study
              • Article
              • Peer Reviewed
              UC Santa Barbara Previously Published Works (2019)
                Cover page: Linking tree physiological constraints with predictions of carbon and water fluxes at an old‐growth coniferous forest
                • Article
                LBL Publications (2002)
                In this paper we describe measurements and modeling of 18O in CO2 and H2O pools and fluxes at a tallgrass prairie site in Oklahoma. We present measurements of the d18O value of leaf water, depth-resolved soil water, atmospheric water vapor, and Keeling plot d18O intercepts for net soil-surface CO2 and ecosystem CO2 and H2O fluxes during three periods of the 2000 growing season. Daytime discrimination against C18OO, as calculated from measured above-canopy CO2 and d18O gradients, is also presented. To interpret the isotope measurements we applied an integrated land-surface and isotope model (ISOLSM) that simulates ecosystem H218O and C18OO stocks and fluxes. ISOLSM accurately predicted the measured isotopic composition of ecosystem water pools and the d18O value of net ecosystem CO2 and H2O fluxes. Simulations indicate that incomplete equilibration between CO2 and H2O within C4 plant leaves can have a substantial impact on ecosystem discrimination. Diurnal variations in the delta18O val ue of above-canopy vapor had a small impact on the predicted delta18O value of ecosystem water pools, although sustained differences had a large impact. Diurnal variations in the delta18O value of above-canopy CO2 substantially a ffected predicted ecosystem discrimination. Leaves dominate the ecosystem 18O-isoflux in CO2 during the growing season, while the soil contribution is relatively small and less variable. However, interpreting daytime measurements of ecosystem C18OO fluxes requires accurate predictions of both soil and leaf 18O-isofluxes.
                  Cover page: {sup 18}O composition of CO{sub 2} and H{sub 2}O ecosystem pools and fluxes in a tallgrass prairie: Simulations and comparisons to measurements
                  • Article
                  • Peer Reviewed
                  UCLA Previously Published Works (2016)
                    • Article
                    • Peer Reviewed
                    UCLA Previously Published Works (2010)
                    In recent decades, intense droughts, insect outbreaks, and wildfires have led to decreasing tree growth and increasing mortality in many temperate forests. We compared annual tree-ring width data from 1,097 populations in the coterminous United States to climate data and evaluated site-specific tree responses to climate variations throughout the 20th century. For each population, we developed a climate-driven growth equation by using climate records to predict annual ring widths. Forests within the southwestern United States appear particularly sensitive to drought and warmth. We input 21st century climate projections to the equations to predict growth responses. Our results suggest that if temperature and aridity rise as they are projected to, southwestern trees will experience substantially reduced growth during this century. As tree growth declines, mortality rates may increase at many sites. Increases in wildfires and bark-beetle outbreaks in the most recent decade are likely related to extreme drought and high temperatures during this period. Using satellite imagery and aerial survey data, we conservatively calculate that ≈ 2.7% of southwestern forest and woodland area experienced substantial mortality due to wildfires from 1984 to 2006, and ≈ 7.6% experienced mortality associated with bark beetles from 1997 to 2008. We estimate that up to ≈ 18% of southwestern forest area (excluding woodlands) experienced mortality due to bark beetles or wildfire during this period. Expected climatic changes will alter future forest productivity, disturbance regimes, and species ranges throughout the Southwest. Emerging knowledge of these impending transitions informs efforts to adaptively manage southwestern forests.
                      Cover page: Forest responses to increasing aridity and warmth in the southwestern United States
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