An official website of the United States government
Abstract As drought variability increases in forests around the globe, it is critical to evaluate and understand ecosystem attributes that ameliorate drought impacts. Trees in arid and semi‐arid ecosystems can sustain tree growth and transpiration during drought by accessing shallow groundwater, yet the extent to which groundwater influences forest growth and transpiration in humid environments has largely been unexplored. We quantified groundwater's influence on tree growth and transpiration in northern humid forests with sandy soils. We hypothesized that even in wet regions, soil droughts occur relatively frequently in forests with sandy soils and result in water stress and reduced tree growth. Further, we hypothesized these reductions in productivity are ameliorated if the forest can access shallow groundwater during dry conditions. We evaluated tree growth responses using tree cores inPinus resinosatrees and estimated forest groundwater use from diel water table fluctuations across sites covering a 1‐ to 9‐m depth‐to‐groundwater (DTG) gradient. In areas of shallow groundwater (DTG < 2.5 m), we observed twice as much tree growth and high, frequent groundwater use (up to 81% of non‐rainy summer days). Groundwater's influence on tree growth and transpiration declined as groundwater deepened along the DTG gradient in the range 1–5 m below land surface. These findings suggest that water provided by a shallow water table subsidizes evapotranspiration in humid forests and results in enhanced tree growth. Our research provides a basis for understanding the role of groundwater in conferring drought resistance in humid forests to help guide sustainable water and forest management decisions.
more »
« less
This content will become publicly available on May 1, 2026
Evaluating Hysteresis Patterns in Sap Flow of a Red Pine Forest Subjected to Different Variable Retention Harvesting Treatments
Abstract Forests significantly influence regional and global water cycles through transpiration, which is affected by meteorological variables, soil water availability, and stand and site characteristics. Variable retention harvesting (VRH) is a forest management practice in which varying densities of trees, such as 55% and 33%, are retained after thinning or harvesting. These trees can be grouped together or evenly distributed. VRH aims to enhance forest growth, improve biodiversity, preserve ecosystem functions, and generate economic revenue from harvested timber. Application of VRH treatment in forest ecosystems can potentially impact the response of forest transpiration to environmental controls. This study analyzed the impacts of four different VRH treatments on sap flow velocity (SV) in an 83‐year‐old red pine (Pinus resinosa Ait.) plantation forest in the Great Lakes region in Canada. These VRH treatments included 55% aggregated (55A), 55% dispersed (55D), 33% aggregated (33A), and 33% dispersed (33D) basal area retention, and an unharvested control (CN) plot, 1 ha each. Analysis of counterclockwise hysteresis loops between SV and meteorological variables showed larger hysteresis areas between SV and photosynthetically active radiation (PAR) than vapor pressure deficit (VPD) and air temperature (Tair), particularly in clear sky and warm temperatures in the summer. It demonstrated that PAR was the primary control on SV across VRH treatments, followed by VPD andTair. Larger hysteresis loop areas and higher SV values were observed in the CN and 55D treatments, with lower values found in the 55A, 33D, and 33A plots. This suggests that maintaining dispersed retention of 55% basal area (55D) is the optimal forest management practice that can be utilized to enhance transpiration and forest growth. These findings will assist forest managers and other stakeholders to adopt sustainable forest management practices, thereby enhancing forest growth, water use efficiency, and resilience to climate change. Additionally, these practices will contribute to nature‐based climate solutions.
more »
« less
- Award ID(s):
- 2330317
- PAR ID:
- 10648157
- Publisher / Repository:
- AGU Advancing Earth and Space Sciences
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 130
- Issue:
- 5
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Trees regulate canopy temperature (Tc) via transpiration to maintain an optimal temperature range. In diverse forests such as those of the eastern United States, the sensitivity ofTcto changing environmental conditions may differ across species, reflecting wide variability in hydraulic traits. However, these links are not well understood in mature forests, whereTcdata have historically been difficult to obtain. Recent advancement of thermal imaging cameras (TICs) enablesTcmeasurement of previously inaccessible tall trees. By leveraging TIC and sap flux measurements, we investigated how co‐occurring trees (Quercus alba,Q. falcata, andPinus virginiana) change theirTcand vapor pressure deficit near the canopy surface (VPDc) in response to changing air temperature (Ta) and atmospheric VPD (VPDa). We found a weaker cooling effect for the species that most strongly regulates stomatal function during dry conditions (isohydric;P. virginiana). Specifically, the pine had higherTc(up to 1.3°C) and VPDc(up to 0.3 kPa) in the afternoon and smaller sensitivity of both∆T(=Tc − Ta) and∆VPD (=VPDc − VPDa) to changing conditions. Furthermore, significant differences inTcand VPDcbetween sunlit and shaded portions of a canopy implied a non‐evaporative effect onTcregulation. Specifically,Tcwas more homogeneous within the pine canopy, reflecting differences in leaf morphology that allow higher canopy transmittance of solar radiation. The variability ofTcamong species (up to 1.3°C) was comparable to the previously reported differences in surface temperature across land cover types (1°C to 2°C), implying the potential for significant impact of species composition change on local/regional surface temperature.more » « less
-
null (Ed.)Small-scale treefall gaps are among the most important forms of forest disturbance in tropical forests. These gaps expose surrounding trees to more light, promoting rapid growth of understory plants. However, the effects of such small-scale disturbances on the distribution of plant water use across tree canopy levels are less known. To address this, we explored plant transpiration response to the death of a large emergent tree, Mortoniodendron anisophyllum Standl. & Steyerm (DBH > 220 cm; height ~40 m). Three suppressed, four mid-story, and two subdominant trees were selected within a 50 × 44 m premontane tropical forest plot at the Texas A&M Soltis Center for Research and Education located in Costa Rica. We compared water use rates of the selected trees before (2015) and after (2019) the tree gap using thermal dissipation sap flow sensors. Hemispherical photography indicated a 40% increase in gap fraction as a result of changes in canopy structure after the treefall gap. Micrometeorological differences (e.g., air temperature, relative humidity, and vapor pressure deficit (VPD)) could not explain the observed trends. Rather, light penetration, as measured by sensors within the canopy, increased significantly in 2019. One year after the tree fell, the water usage of trees across all canopy levels increased modestly (15%). Moreover, average water usage by understory trees increased by 36%, possibly as a result of the treefall gap, exceeding even that of overstory trees. These observations suggest the possible reallocation of water use between overstory and understory trees in response to the emergent tree death. With increasing global temperatures and shifting rainfall patterns increasing the likelihood of tree mortality in tropical forests, there is a greater need to enhance our understanding of treefall disturbances that have the potential to redistribute resources within forests.more » « less
-
Abstract Trees in residential environments are affected by a unique combination of environmental and anthropogenic factors, including occasional insect outbreaks that are increasing in frequency and severity due to climate change. We studied loblolly pine trees infested by bark beetles in a residential backyard in a southeastern US city. We investigated the responses of tree and stand‐level transpiration to environmental factors (solar radiation, atmospheric vapor pressure deficit, and soil moisture), severe weather events (strong winds and heavy storms), bark beetle infestation, and human actions (insecticide treatments and tree removals). We used constant heat dissipation probes to make continuous sap flux measurements (J0) in tree boles. Over 22 months of the study,J0of trees with confirmed infestation decreased from ~90 to ~60 g cm−2 day−1andJ0of the rest of the trees increased from ~60 to ~80 g cm−2 day−1. One infested tree died, as itsJ0steadily declined from 110 g cm−2 day−1to zero over the course of 2 months, followed by a loss of foliage and visible signs of severe infestation 6 months later.J0was sensitive to variations in incoming solar radiation and atmospheric vapor pressure deficit. In most trees,J0linearly responded to soil water content during drought periods. Yet despite complex dynamics ofJ0variations, plot‐level transpiration at the end of the study was the same as at the beginning due to compensatory increases in tree transpiration rates. This study highlights the intrinsic interplay of environmental, biotic, and anthropogenic factors in residential environments where human actions may directly mediate ecosystem responses to climate.more » « less
-
Background The post-harvest recovery and sustained productivity of Nothofagus pumilio forests in Tierra del Fuego may be affected by the abundance and composition of ectomycorrhizal fungi (EMF). Timber harvesting alters EMF community structure in many managed forests, but the impacts of harvesting can vary with the management strategy. The implementation of variable retention (VR) management can maintain, increase, or decrease the diversity of many species, but the effects of VR on EMF in the forests of southern Patagonia have not been studied, nor has the role of EMF in the regeneration process of these forests. Methods We evaluated the effects of VR management on the EMF community associated with N. pumilio seedlings. We quantified the abundance, composition, and diversity of EMF across aggregate (AR) and dispersed (DR) retention sites within VR managed areas, and compared them to primary forest (PF) unmanaged stands. EMF assemblage and taxonomic identities were determined by ITS-rDNA sequencing of individual root tips sampled from 280 seedlings across three landscape replicates. To better understand seedling performance, we tested the relationships between EMF colonization, EMF taxonomic composition, seedling biomass, and VR treatment. Results The majority of EMF taxa were Basidiomycota belonging to the families Cortinariaceae ( n = 29), Inocybaceae ( n = 16), and Thelephoraceae ( n = 8), which was in agreement with other studies of EMF diversity in Nothofagus forests. EMF richness and colonization was reduced in DR compared to AR and PF. Furthermore, EMF community composition was similar between AR and PF, but differed from the composition in DR. EMF community composition was correlated with seedling biomass and soil moisture. The presence of Peziza depressa was associated with higher seedling biomass and greater soil moisture, while Inocybe fibrillosibrunnea and Cortinarius amoenus were associated with reduced seedling biomass and lower soil moisture. Seedling biomass was more strongly related to retention type than EMF colonization, richness, or composition. Discussion Our results demonstrate reduced EMF attributes and altered composition in VR treatments relative to PF stands, with stronger impacts in DR compared to AR. This suggests that VR has the potential to improve the conservation status of managed stands by supporting native EMF in AR. Our results also demonstrate the complex linkages between retention treatments, fungal community composition, and tree growth at individual and stand scales.more » « less
