Brett Wolfe

• PhD
• Professor (Assistant) at Louisiana State University

When municipal effluent is discharged into swamps, baldcypress trees ( Taxodium distichum ) generally respond with increased growth. This growth increase may be associated with increased transpiration (E), but if functional traits are also affected, they may modulate the response of E to environmental conditions such as atmospheric vapor pressure d...

Bark water vapor conductance (gbark) modulates forest transpiration during droughts, when leaf transpiration is highly reduced. If disturbances such as windstorms and floods impact gbark, they could affect tree performance during subsequent droughts. Bark traits, particularly lenticel traits, likely drive variation in gbark and may influence the ef...

Tree species in a temperate floodplain forest had leaf turgor loss point values similar to those of upland forest trees, suggesting physiological drought tolerance in this generally non-water-limited system. Leaf turgor loss point (TLP) is a key plant trait associated with drought tolerance. In the bottomland hardwood (BLH) forests that grow in flo...

This study aimed to understand how transpiration (J s) and crown conductance (G s) of tropical trees are impacted by environmental and physiological traits across a gradient from seasonally dry, intermediate, and ever-wet tropical forests (Fig. 1), and to quantify how leaf-to-air temperature decoupling impacts G s. Main hypotheses: H1: High vapor...

The representation of stomatal regulation of transpiration and CO2 assimilation is key to forecasting terrestrial ecosystem responses to global change. Given its importance in determining the relationship between forest productivity and climate, accurate and mechanistic model representation of the relationship between stomatal conductance (gs) and...

Within vascular plants, the partitioning of hydraulic resistance along the soil‐to‐leaf continuum affects transpiration and its response to environmental conditions. In trees, the fractional contribution of leaf hydraulic resistance (Rleaf) to total soil‐to‐leaf hydraulic resistance (Rtotal), or fRleaf (=Rleaf/Rtotal), is thought to be large, but t...

Considering the global intensification of aridity in tropical biomes due to climate change, we need to understand what shapes the distribution of drought sensitivity in tropical plants. We conducted a pantropical data synthesis representing 1117 species to test whether xylem‐specific hydraulic conductivity (KS), water potential at leaf turgor loss...

Tree water use is the dominant terrestrial hydrologic flux globally, and has a dominant regulatory influence over the carbon cycle. Sap flow through the tree is also a useful model diagnostic for FATES-Hydro. Our objective is to quantify variation in tree water use at three sites across a rainfall gradient in Panama. Our ultimate goals are to under...

Tropical leaf phenology—particularly its variability at the tree-crown scale—dominates the seasonality of carbon and water fluxes. However, given enormous species diversity, accurate means of monitoring leaf phenology in tropical forests is still lacking. Time series of the Green Chromatic Coordinate (GCC) metric derived from tower-based red–greenb...

Deep‐water access is arguably the most effective, but under‐studied, mechanism that plants employ to survive during drought. Vulnerability to embolism and hydraulic safety margins can predict mortality risk at given levels of dehydration, but deep‐water access may delay plant dehydration. Here, we tested the role of deep‐water access in enabling su...

Intensified droughts are affecting tropical forests across the globe. However, the underlying mechanisms of tree drought response and mortality are poorly understood. Hydraulic traits and especially hydraulic safety margins (HSMs), that is, the extent to which plants buffer themselves from thresholds of water stress, provide insights into species‐s...

Water deficit in the atmosphere and soil are two key interactive factors that constrain transpiration and vegetation productivity. It is not clear which of these two factors is more important for the water and carbon flux response to drought stress in ecosystems. In this study, field data and numerical modeling were used to isolate their impact on...

Leaf-level gas exchange data support the mechanistic understanding of plant fluxes of carbon and water. These fluxes inform our understanding of ecosystem function, are an important constraint on parameterization of terrestrial biosphere models, are necessary to understand the response of plants to global environmental change, and are integral to e...

Bark water vapour conductance (gbark) is a rarely considered functional trait. However, for the few tree species measured to date, it appears high enough to create stem water deficits associated with mortality during droughts, when access to water is limited. I tested whether gbark correlates with stem water deficit during drought conditions in two...

Transpiration in humid tropical forests modulates the global water cycle and is a key driver of climate regulation. Yet, our understanding of how tropical trees regulate sap flux in response to climate variability remain elusive. With a progressively warming climate, atmospheric evaporative demand (i.e., vapor pressure deficit, VPD) will be increas...

Leaf mass per area (LMA) is a key plant trait, reflecting tradeoffs between leaf photosynthetic function, longevity, and structural investment. Capturing spatial and temporal variability in LMA has been a long‐standing goal of ecological research and is an essential component for advancing Earth system models. Despite the substantial variation in L...

Stomata regulate CO2 uptake for photosynthesis and water loss through transpiration. The approaches used to represent stomatal conductance (gs) in models vary. In particular, current understanding of drivers of the variation in a key parameter in those models, the slope parameter (i.e. a measure of intrinsic plant water‐use‐efficiency), is still li...

Understanding the pronounced seasonal and spatial variation in leaf carboxylation capacity (Vc,max) is critical for determining terrestrial carbon cycling in tropical forests. However, an efficient and scalable approach for predicting Vc,max is still lacking. Here the ability of leaf spectroscopy for rapid estimation of Vc,max was tested. Vc,max wa...

Forest leaf area has enormous leverage on the carbon cycle because it mediates both forest productivity and resilience to climate extremes. Despite widespread evidence that trees are capable of adjusting to changes in environment across both space and time through modifying carbon allocation to leaves, many vegetation models use fixed carbon alloca...

Questions Tropical dry forests that experience severe disturbances (e.g., fires) often remain degraded for long time periods, during which non‐native grasses and trees dominate. One barrier to native tree regeneration in degraded areas may be seed dispersal limitation. To better understand how dispersal limitation influences recovery from degradati...

Nonstructural carbohydrates (NSCs) are essential for maintenance of plant metabolism and may be sensitive to short‐ and long‐term climatic variation. NSC variation in moist tropical forests has rarely been studied, so regulation of NSCs in these systems is poorly understood. We measured foliar and branch NSC content in 23 tree species at three site...

Stomatal response to environmental conditions forms the backbone of all ecosystem and carbon cycle models, but is largely based on empirical relationships. Evolutionary theories of stomatal behaviour are critical for guarding against prediction errors of empirical models under future climates. Longstanding theory holds that stomata maximise fitness...

Climate change is expected to lead to increases in drought frequency and severity, with deleterious effects on many ecosystems. Stomatal responses to changing environmental conditions form the backbone of all ecosystem models, but are based on empirical relationships and are not well-tested during drought conditions. Here, we use a dataset of 34 wo...

Supporting information document contains Table A and Figures A-D. (DOCX)

Metadata describe the ancillary information needed for data preservation and independent interpretation, comparison across heterogeneous datasets, and quality assessment and quality control (QA/QC). Environmental observations are vastly diverse in type and structure, can be taken across a wide range of spatiotemporal scales in a variety of measurem...

Trees generally maintain a small safety margin between the stem water potential (stem) reached during seasonal droughts and the stem associated with their mortality. This pattern may indicate that species face similar mortality risk during extreme droughts. However, if tree species vary in their ability to regulate stem, then safety margins would p...

During droughts, leaves are predicted to act as ‘hydraulic fuses’ by shedding when plants reach critically low water potential (Ψ plant ), thereby slowing water loss, stabilizing Ψ plant and protecting against cavitation‐induced loss of stem hydraulic conductivity ( K s ). We tested these predictions among trees in seasonally dry tropical forests,...

Ecosystem models have difficulty predicting plant drought responses, partially from uncertainty in the stomatal response to water deficits in soil and atmosphere. We evaluate a ‘supply–demand’ theory for water‐limited stomatal behavior that avoids the typical scaffold of empirical response functions. The premise is that canopy water demand is regul...

Tree species in seasonally dry tropical forests likely vary in their drought-survival mechanisms. Drought-deciduousness, which reduces water loss, and low wood density, which may permit dependence on stored water, are considered key traits. For saplings of six species at two distinct sites, we studied these and two associated traits: the seasonal a...

Plantations of Tectona grandis in Central America are widely perceived to suppress forest regeneration in their understories, yet few studies have tested this assumption. We surveyed the understory woody vegetation growing in 7-year-old stands of T. grandis and the native tree species Terminalia amazonia in a plantation in western Panama that was m...

Trees' resistance to fire-induced mortality increases with bark thickness, which varies widely among species and generally increases with stem diameter. Because dry forests are more fire-prone than wetter forests, bark may be thicker in these forests. However, where disturbances such as hurricanes suppress stem diameter, trees may not obtain fire-r...

Trees' resistance to fire-induced mortality increases with bark thickness, which varies widely among species and generally increases with stem diameter. Because dry forests are more fire-prone than wetter forests, bark may be thicker in these forests. However, where disturbances such as hurricanes suppress stem diameter, trees may not obtain fire-r...

Throughout the tropics, non-native grasses invade, dominate, and persist in areas where subtropical and tropical dry forests have been highly degraded. In Central America and the Caribbean Islands, forests that regenerate in grass-invaded areas are generally composed of one to a few tree species, usually of the Fabaceae family and often non-native....

Background/Question/Methods Ecologists have debated the potential for ecological communities to exhibit multiple alternative stable states. Degraded plant communities may exist as alternative community states stabilized by feedback mechanisms maintaining the degraded community. These degraded communities may exhibit other characteristics of alter...

Background/Question/Methods Dry forests were widespread in the tropics before being cleared for agricultural and urban use in pre-Columbian through present times. They are now considered to be one of the most endangered ecosystem types. Cleared and degraded tropical dry forests commonly form stable exotic-grassland communities that are maintained b...

The chapters of this book on seed dispersal are divided into four parts: (1) frugivores and frugivory (8 chapters); (2) seed and seedling shadows (7 chapters); (3) seed fate and establishment (eight chapters); and (4) management implications and conservation (six chapters). The book presents both recent advances and reviews of current knowledge.

We surveyed Lepidoptera found on 11 species of Inga (Fabaceae:Mimosoideae) co-existing on Barro Colorado Island, Panama, to evaluate factors influencing diet choice. Of the 47 species of caterpillars (747 individuals) recorded, each fed on a distinct set of Inga. In the field, 96% of the individuals were found on young leaves. Growth rates of cater...