Search for: All records

Some ecosystems require regular disturbances to maintain their biological and structural diversity. However, shifts in climate and changes in land management practices have altered global fire regimes, making it challenging to determine the most effective approach to maintain fire-dependent ecosystems. Measuring how ecosystems respond to disturbances can offer valuable insights into the effects of fire under contemporary conditions. In Everglades pinelands, we used satellite data to develop a machine learning model for the normalized difference vegetation index (NDVI), an effective proxy for primary productivity. Our findings showed that NDVI values ranged from 0.2 to 0.4 for Everglades pinelands, which were significantly influenced by fire history. Areas that experienced more frequent and more recent fires exhibited higher NDVI values compared to those that were less frequently burned. Conversely, pinelands that had not burned for an extended period (>15 years) showed signs of transitioning to less fire-dependent ecosystems. Following contemporary fires in Everglades pinelands, there was an initial reduction in NDVI of ∼6 %. However, on average, within 2 years, pinelands recovered to a higher post-fire NDVI (∼27 %) compared to their pre-fire levels. Our results suggest that more frequent fires enhance productivity and promote faster post-fire recovery in subtropical fire-dependent pinelands. 

Metal-ion-linked molecular multilayers on metal oxide surfaces are promising for applications ranging from solar energy conversion to sensing. Most of these applications rely on energy and electron transfer between layers/molecules which can be envisioned to occur via intra-assembly (IA; between metal-ion-linked molecules) and interlayer (IL; between separate layers of nonlinked molecules) processes. Here, we describe our effort to differentiate between IL and IA energy transfer using a bilayer composed of ZrO2, a phosphonated anthracene derivative (A), a zinc(II) linking ion, and a Pt(II)porphyrin (P). Both time-resolved emission and transient absorption measurements show no impact of diluting the anthracene layer with a spectroscopically inert spacer on the rate of 1A* to P and 3P* to A, singlet, and triplet energy transfer, respectively. These results indicate that energy transfer within the metal-ion-linked assembly (i.e., ZrO2-A–Zn-P) is more rapid than with an adjacent, nonlinked A molecule, even for a P derivative capable of laying down on the surface. These insights are an important step toward structural design principles maximizing the efficiency/rate of energy transfer in multilayer assemblies. 

Metal ion linked multilayers offer a means of controlling interfacial energy and electron transfer for a range of applications including solar energy conversion, catalysis, sensing, and more. Despite the importance of structure to these interlayer transfer processes, little is known about the distance and orientation between the molecules/surface of these multilayer films. Here we gain structural insights into these assemblies using a combination of UV-Vis polarized visible attenuated total reflectance (p-ATR) and Förster Resonance Energy Transfer (FRET) measurements. The bilayer of interest is composed of a metal oxide surface, phosphonated anthracene molecule, Zn(II) linking ion, and a platinum porphyrin with one (P1), two (P2), or three (P3) phenylene spacers between the chromophoric core and the metal ion binding carboxylate group. As observed by both time-resolved emission and transient absorption, the FRET rate and efficiency decreases with an increasing number of phenylene spacers (P1 > P2 > P3). However, from p-ATR measurements we observe a change in orientation of porphyrins in the bilayer, which inhibits a uniform determination of the orientation factor (κ2) across the series. Instead, we narrow the scope of viable structures by determining the best agreement between experimental and calculated FRET efficiencies. Additionally, we provide evidence that suggests, for the first time, that the bilayer structure is similar on both planar and mesoporous substrates.