Christina L. Staudhammer

Testing a silvicultural recommendation: Brazil nut responses 10 years after liana cutting

Summary 1. Lianas or woody vines can be detrimental to the trees that support them. Research on liana cutting for tropical timber management has demonstrated positive yet costly benefits, but liana cutting to enhance commercial outputs of nontimber forest products has not been examined. We implemented a controlled experiment to quantify the effects of cutting lianas on Brazil nut Bertholletia excelsa Bonpl. fecundity. 2. We conducted our 10-year experiment in a Brazilian extractive reserve where local harvesters collect fruits from this Amazonian canopy-emergent species as part of their forest-based livelihood system. We cut 454 lianas with a total basal area of 241 m 2 from 78 of 138 host trees ≥50 cm diameter at breast height. 3. Treated trees were significantly better producers 3 ½ years after liana cutting, and these differences increased dramatically in subsequent years, with consistent proportionally higher production in treated versus untreated individuals. 4. The number of lianas rooted within 5 m of the host tree significantly explained production levels, suggesting both above- and below-ground liana–host tree competition. Once host crowns were liana-free, branch regrowth was highly visible, particularly in heavily infested trees, and crown reassessments suggested that liana cutting improved crown form. Additionally, liana cutting may induce some nonproducing trees to become producers and may circumvent mortality of trees heavily infested with lianas (> 75% crown covered). 5. Liana removal can be implemented easily when harvesting Brazil nut fruits. Only lianas associated with B. excelsa trees should be cut to conserve liana ecosystem functions. 6. Synthesis and applications. We quantified effects of liana cutting on Brazil nut host tree fecundity and provided estimates of increased commercial yields. Our long-term (10-year) study permits understanding of biological variation and informs related management decisions. Findings suggest that liana cutting reduces above- and below-ground competition with individual trees, ultimately allowing mature host crowns to recover such that 9–10 years after liana cutting, treated trees produced on average three times more fruits than untreated trees. Application of liana cutting to other tropical species would likely boost fruit and seed production, increase host tree fecundity and potentially enhance future recruitment.

Effects of Simulated Drought on the Carbon Balance of Everglades Short-Hydroperiod Marsh

Hydrology drives the carbon balance of wetlands by controlling the uptake and release of CO2 and CH4 . Longer dry periods in between heavier precipitation events predicted for the Everglades region, may alter the stability of large carbon pools in this wetlands ecosystems. To determine the effects of drought on CO2 fluxes and CH4 emissions, we simulated changes in hydroperiod with three scenarios that differed in the onset rate of drought (gradual, intermediate, and rapid transition into drought) on 18 freshwater wetland monoliths collected from an Everglades short-hydroperiod marsh. Simulated drought, regardless of the onset rate, resulted in higher net CO2 losses net ecosystem exchange (NEE) over the 22-week manipulation. Drought caused extensive vegetation dieback, increased ecosystem respiration (Reco ), and reduced carbon uptake gross ecosystem exchange (GEE). Photosynthetic potential measured by reflective indices (photochemical reflectance index, water index, normalized phaeophytinization index, and the normalized difference vegetation index) indicated that water stress limited GEE and inhibited Reco . As a result of drought-induced dieback, NEE did not offset methane production during periods of inundation. The average ratio of net CH4 to NEE over the study period was 0.06, surpassing the 100-year greenhouse warming compensation point for CH4 (0.04). Drought-induced diebacks of sawgrass (C3 ) led to the establishment of the invasive species torpedograss (C4 ) when water was resupplied. These changes in the structure and function indicate that freshwater marsh ecosystems can become a net source of CO2 and CH4 to the atmosphere, even following an extended drought. Future changes in precipitation patterns and drought occurrence/duration can change the carbon storage capacity of freshwater marshes from sinks to sources of carbon to the atmosphere. Therefore, climate change will impact the carbon storage capacity of freshwater marshes by influencing water availability and the potential for positive feedbacks on radiative forcing.

The importance of multimodel projections to assess uncertainty in projections from simulation models

Simulation models are increasingly used to gain insights regarding the long-term effect of both direct and indirect anthropogenic impacts on natural resources and to devise and evaluate policies that aim to minimize these effects. If the uncertainty from simulation model projections is not adequately quantified and reported, modeling results might be misleading, with potentially serious implications. A method is described, based on a nested simulation design associated with multimodel projections, that allows the partitioning of the overall uncertainty in model projections into a number of different sources of uncertainty: model stochasticity, starting conditions, parameter uncertainty, and uncertainty that originates from the use of key model assumptions. These sources of uncertainty are likely to be present in most simulation models. Using the forest dynamics model SYMFOR as a case study, it is shown that the uncertainty originated from the use of alternate modeling assumptions, a source of uncertainty seldom reported, can be the greatest source of uncertainty, accounting for 66-97% of the overall variance of the mean after 100 years of stand dynamics simulation. This implicitly reveals the great importance of these multimodel projections even when multiple models from independent research groups are not available. Finally, it is suggested that a weighted multimodel average (in which the weights are estimated from the data) might be substantially more precise than a simple multimodel average (equivalent to equal weights for all models) as models that strongly conflict with the data are given greatly reduced or even zero weights. The method of partitioning modeling uncertainty is likely to be useful for other simulation models, allowing for a better estimate of the uncertainty of model projections and allowing researchers to identify which data need to be collected to reduce this uncertainty.

CYCLIC OCCURRENCE OF FIRE AND ITS ROLE IN CARBON DYNAMICS ALONG AN EDAPHIC MOISTURE GRADIENT IN LONGLEAF PINE ECOSYSTEMS

Fire regulates the structure and function of savanna ecosystems, yet we lack understanding of how cyclic fire affects savanna carbon dynamics. Furthermore, it is largely unknown how predicted changes in climate may impact the interaction between fire and carbon cycling in these ecosystems. This study utilizes a novel combination of prescribed fire, eddy covariance (EC) and statistical techniques to investigate carbon dynamics in frequently burned longleaf pine savannas along a gradient of soil moisture availability (mesic, intermediate and xeric). This research approach allowed us to investigate the complex interactions between carbon exchange and cyclic fire along the ecological amplitude of longleaf pine. Over three years of EC measurement of net ecosystem exchange (NEE) show that the mesic site was a net carbon sink (NEE = −2.48 tonnes C ha−1), while intermediate and xeric sites were net carbon sources (NEE = 1.57 and 1.46 tonnes C ha−1, respectively), but when carbon losses due to fuel consumption were taken into account, all three sites were carbon sources (10.78, 7.95 and 9.69 tonnes C ha−1 at the mesic, intermediate and xeric sites, respectively). Nonetheless, rates of NEE returned to pre-fire levels 1–2 months following fire. Consumption of leaf area by prescribed fire was associated with reduction in NEE post-fire, and the system quickly recovered its carbon uptake capacity 30–60 days post fire. While losses due to fire affected carbon balances on short time scales (instantaneous to a few months), drought conditions over the final two years of the study were a more important driver of net carbon loss on yearly to multi-year time scales. However, longer-term observations over greater environmental variability and additional fire cycles would help to more precisely examine interactions between fire and climate and make future predictions about carbon dynamics in these systems.

Seasonal patterns in energy partitioning of two freshwater marsh ecosystems in the Florida Everglades

We analyzed energy partitioning in short- and long-hydroperiod freshwater marsh ecosystems in the Florida Everglades by examining energy balance components (eddy covariance derived latent energy (LE) and sensible heat (H) flux). The study period included several wet and dry seasons and variable water levels, allowing us to gain better mechanistic information about the control of and changes in marsh hydroperiods. The annual length of inundation is ~5 months at the short-hydroperiod site (25°26′16.5″N, 80°35′40.68″W), whereas the long-hydroperiod site (25°33′6.72″N, 80°46′57.36″W) is inundated for ~12 months annually due to differences in elevation and exposure to surface flow. In the Everglades, surface fluxes feed back to wet season precipitation and affect the magnitude of seasonal change in water levels through water loss as LE (evapotranspiration (ET)). At both sites, annual precipitation was higher than ET (1304 versus 1008 at the short-hydroperiod site and 1207 versus 1115 mm yr−1 at the long-hydroperiod site), though there were seasonal differences in the ratio of ET:precipitation. Results also show that energy balance closure was within the range found at other wetland sites (60 to 80%) and was lower when sites were inundated (60 to 70%). Patterns in energy partitioning covaried with hydroperiods and climate, suggesting that shifts in any of these components could disrupt current water and biogeochemical cycles throughout the Everglades region. These results suggest that the complex relationships between hydroperiods, energy exchange, and climate are important for creating conditions sufficient to maintain Everglades ecosystems.

Effects of seasonality, litter removal and dry-season irrigation on litterfall quantity and quality in eastern Amazonian forest regrowth, Brazil

Litterfall quantity and quality may respond to alterations in resource availability expected with ongoing land-use and climate changes. Here, we quantify the effects of altered resource availability on non-woody litterfall quantityandquality(nitrogenandphosphorusconcentrations)ineasternAmazonianforestregrowth(Brazil)through two multi-year experimental manipulations: (1) daily irrigation (5mm d −1 ) during the dry season; and (2) fortnightly litterremoval.Consistentwithothertropicalforestdatalitterfallexhibitedseasonalpatterns,increasingwiththeonset of the dry season and declining with the onset of the rainy season. Irrigation did not affect litterfall mass and had little impactonnitrogen(N)orphosphorus(P)concentrationsandreturn,exceptfordecreasinglitterPconcentrationatthe end of two irrigation periods. Litter removal did not alter litterfall mass or P concentration, but progressively reduced litterfall N during the course of the experiment. Overall, these results suggest significant resistance to altered resource availabilitywithintheboundsofourexperimentaltreatments;ourfindingsmayhelptoconstraincarbonandnutrient cycling predictions for tropical forests in response to land-use and climate changes.

Profile Charts for Monitoring Lumber Manufacturing Using Laser Range Sensor Data

Real-time technologies using noncontact laser range sensors (LRS) have recently been introduced to improve statistical process control (SPC) programs in automated lumber mills by greatly increasing the volume of data available for SPC. However, present SPC procedures based on sampling theory developed for manual data collection do not fully utilize data from these systems. A new system of control charts is introduced here that simultaneously monitors multiple lumber surfaces and specifically targets three common sawing defects (taper, snipe/flare, and snake). Nontraditional control charts are suggested based on the decomposition of LRS measurements into trend, waviness, and roughness. The proposed charts can be used to monitor the slope parameter of a multiple linear regression model and the peak-to-peak waviness of observations from each board. Applying these methods should lead to process improvements in sawmills by better detecting common sawing problems and identifying the causes.

El Niño Southern Oscillation (ENSO) Enhances CO2 Exchange Rates in Freshwater Marsh Ecosystems in the Florida Everglades

This research examines the relationships between El Niño Southern Oscillation (ENSO), water level, precipitation patterns and carbon dioxide (CO2) exchange rates in the freshwater wetland ecosystems of the Florida Everglades. Data was obtained over a 5-year study period (2009–2013) from two freshwater marsh sites located in Everglades National Park that differ in hydrology. At the short-hydroperiod site (Taylor Slough; TS) and the long-hydroperiod site (Shark River Slough; SRS) fluctuations in precipitation patterns occurred with changes in ENSO phase, suggesting that extreme ENSO phases alter Everglades hydrology which is known to have a substantial influence on ecosystem carbon dynamics. Variations in both ENSO phase and annual net CO2 exchange rates co-occurred with changes in wet and dry season length and intensity. Combined with site-specific seasonality in CO2 exchanges rates, El Niño and La Niña phases magnified season intensity and CO2 exchange rates at both sites. At TS, net CO2 uptake rates were higher in the dry season, whereas SRS had greater rates of carbon sequestration during the wet season. As La Niña phases were concurrent with drought years and extended dry seasons, TS became a greater sink for CO2 on an annual basis (−11 to −110 g CO2 m−2 yr−1) compared to El Niño and neutral years (−5 to −43.5 g CO2 m−2 yr−1). SRS was a small source for CO2 annually (1.81 to 80 g CO2 m−2 yr−1) except in one exceptionally wet year that was associated with an El Niño phase (−16 g CO2 m−2 yr−1). Considering that future climate predictions suggest a higher frequency and intensity in El Niño and La Niña phases, these results indicate that changes in extreme ENSO phases will significantly alter CO2 dynamics in the Florida Everglades.

Modeling Relationships among 217 Fires Using Remote Sensing of Burn Severity in Southern Pine Forests

Pine flatwoods forests in the southeastern US have experienced severe wildfires over the past few decades, often attributed to fuel load build-up. These forest communities are fire dependent and require regular burning for ecosystem maintenance and health. Although prescribed fire has been used to reduce wildfire risk and maintain ecosystem integrity, managers are still working to reintroduce fire to long unburned areas. Common perception holds that reintroduction of fire in long unburned forests will produce severe fire effects, resulting in a reluctance to prescribe fire without first using expensive mechanical fuels reduction techniques. To inform prioritization and timing of future fire use, we apply remote sensing analysis to examine the set of conditions most likely to result in high burn severity effects, in relation to vegetation, years since the previous fire, and historical fire frequency. We analyze Landsat imagery-based differenced Normalized Burn Ratios (dNBR) to model the relationships between previous and future burn severity to better predict areas of potential high severity. Our results show that remote sensing techniques are useful for modeling the relationship between elevated risk of high burn severity and the amount of time between fires, the type of fire (wildfire or prescribed burn), and the historical frequency of fires in pine flatwoods forests.

Effects of drought and prescribed fire on energy exchange in longleaf pine ecosystems

The structure and function of longleaf pine savanna ecosystems is regulated by cyclic fire, yet there is a lack of understanding about how the frequency of fire influences longleaf pine ecosystem energy dynamics. There are further uncertainties in how predicted changes in temperature and precipitation may affect the interaction between fire and energy exchange in these ecosystems. We investigated energy dynamics in three frequently burned longleaf pine ecosystems along a gradient of soil moisture availability using eddy covariance techniques. We analyzed sensible energy (H), latent energy (LE) and soil heat flux (G) over time since fire, using micrometeorological variables as covariates. Based on statistical tests of autocorrelation, data were analyzed as 30-day averages with general linear models. Over three years of measurement, we found that sensible energy, latent energy and soil heat flux recovered to pre-fire rates within one month following prescribed fire. Changes in water availability associated ...