Transpiration in a small tropical forest patch (original) (raw)
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Higher tree transpiration due to road-associated edge effects in a tropical moist lowland forest
Agricultural and Forest Meteorology, 2015
We studied edge effects on microclimate and tree transpiration rates during wet and dry seasons 25 along a 250 m transect spanning the edge of an unpaved road into an old growth tropical lowland 26 forest in the Central Brazilian Amazon. Canopy openness decreased only minimal from the road 27 (3.68%) towards the forest interior (1.69%). Vapor pressure deficit (measured at 2.2 m height 28 above ground) was lower in the forest interior. The edge effect on microclimate penetrated 29 deeper into the forest (>100 m) during the dry season compared to the wet season (<100 m).
Ecohydrology, 2019
32 Potential land-climate feedbacks in subarctic regions, where rapid warming is driving 33 forest expansion into the tundra, may be mediated by differences in transpiration of 34 different plant functional types. Here we assess the environmental controls of overstorey 35 transpiration and its relevance for ecosystem evapotranspiration in subarctic deciduous 36 woodlands. We measured overstorey transpiration of mountain birch canopies and ecosystem evapotranspiration in two locations in northern Fennoscandia, having dense 38 (Abisko) and sparse (Kevo) overstories. For Kevo, we also upscale chamber-measured 39 understorey evapotranspiration from shrubs and lichen using a detailed land cover map. 40 Sub-daily evaporative fluxes were not affected by soil moisture, and showed similar 41 controls by vapour pressure deficit and radiation across sites. At the daily timescale, 42 increases in evaporative demand led to proportionally higher contributions of overstorey 43 transpiration to ecosystem evapotranspiration. For the entire growing season, the 44 overstorey transpired 33% of ecosystem evapotranspiration in Abisko and only 16% in 45 Kevo. At this latter site, the understorey had a higher leaf area index and contributed 46 more to ecosystem evapotranspiration compared to the overstorey birch canopy. In 47 Abisko, growing season evapotranspiration was 27% higher than precipitation, 48 consistent with a gradual soil moisture depletion over the summer. Our results show that 49 overstorey canopy transpiration in subarctic deciduous woodlands is not the dominant 50 evaporative flux. However, given the observed environmental sensitivity of 51 evapotranspiration components, the role of deciduous trees in driving ecosystem 52 evapotranspiration may increase with the predicted increases in tree cover and 53 evaporative demand across subarctic regions.
Long term trends of stand transpiration in a remnant forest during wet and dry years
Journal of Hydrology, 2008
Daily and annual rates of stand transpiration in a drought year and a nondrought year are compared in order to understand the adaptive responses of a remnant woodland to drought and predict the effect of land use change. Two methods were used to estimate stand transpiration. In the first, the ratio of sap velocity of a few trees measured for several hundred days to the mean sap velocity of many trees measured during brief sampling periods (generally 6-7 trees for 5 or 6 days), called the E sv method is used to scale temporally from the few intensive study periods. The second method used was the Penman-Monteith (P-M) equation (called the E PM method). Weather variables and soil moisture were used to predict canopy conductance, which in turn was used to predict daily and annual stand transpiration. Comparisons of daily transpiration estimated with the two methods showed larger values for the E PM method during a drought year and smaller values for the E PM when the rainfall was above average. Generally, though, annual estimates of stand transpiration were similar using the two methods. The E sv method produced an estimate of 318 mm (61% of rainfall) in the drought year and 443 mm (42%) in the year having above average rainfall. The E PM method estimated stand transpiration as 379 mm (73%) and 398 mm (37%), respectively, for the two years. Both estimates of annual stand transpiration demonstrated that the remnant forest showed resilience to an extreme and long-term drought. More importantly, the annual estimates showed that in dry years a larger proportion of rainfall was used as transpiration, and groundwater recharge was absent but in years with above average rainfall recharge was significantly increased. Changes in leaf area index were minimal between years and changes in stomatal conductance were the dominant mechanism for adapting 0022-1694/$ -see front matter ª a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j h y d r o l to the drought. The remnant forest rapidly responded to increased water availability after the drought through a new flush of leaves and increased stomatal conductance. ª
Agricultural and Forest Meteorology, 2003
The relative contributions of overstory and understory plant transpiration and soil evaporation to total evapotranspiration (ET) in a semiarid savanna woodland were determined from stable isotope measurements of atmospheric water vapor. The savanna overstory was dominated by the deeply rooted, woody legume Prosopis velutina ("mesquite"), and the understory was dominated by a perennial C 4 grass, Sporobolus wrightii. "Keeling plots" (turbulent mixing relationships) were generated from isotope ratios (␦D and ␦ 18 O) of atmospheric water vapor collected within the tree (3-14 m) and understory (0.1-1 m) canopies during peak (July) and post-monsoon (September) periods of 2001. The unique regression intercepts from upper and lower profiles were used to partition the ET flux from the understory layer separately from that of the whole ecosystem. Although ET partitioning was problematic during the first sampling period in July, our results in September provided support to the validity of this method for measuring and understanding the dynamic behavior of water balance components in this semiarid savanna woodland.
How transpiration by forests and other vegetation determines alternate moisture regimes
2022
The terrestrial water cycle links the soil and atmosphere moisture reservoirs through four fluxes: precipitation, evaporation, runoff and atmospheric moisture convergence. Each of these fluxes is essential for human and ecosystem well-being. However, predicting how the water cycle responds to changes in vegetation cover, remains a challenge (Lawrence and Vandecar, 2015; Ellison et al., 2017; te Wierik et al., 2021). Recently, rainfall was shown to decrease disproportionally with reduced forest transpiration following deforestation (Baudena et al., 2021). Here, combining these findings with the law of matter conservation, we show that in a sufficiently wet atmosphere forest transpiration can control atmospheric moisture convergence such that increased transpiration enhances atmospheric moisture import. Conversely, in a drier atmosphere increased transpiration reduces atmospheric moisture convergence and runoff. This previously unrecognized dichotomy can explain the seemingly random observations of runoff and soil moisture sometimes increasing and sometimes reducing in response to re-greening (e.g., Zheng et al., 2021). Evaluating the transition between the two regimes is crucial both for characterizing the risk posed by deforestation as well as for motivating and guiding global ecosystem restoration. 1 Precipitation, column moisture and mass conservation Forests play an important role for atmospheric moisture generation and transport through transpiration and atmospheric moisture convergence. Deforestation and reforestation can therefore strongly alter the hydrological cycle depending on the prevailing climate regime in the region. Based on data for a tropical island, Holloway and Neelin (2010) showed that the rainfall probability rises sharply with increasing column water vapor W (see also Yano and Manzato, 2022). Using the radiosonde data for several meteostations in Brazil (Fig. 1a), Makarieva et al. (2014) concluded that, in the Amazon forest, a small relative in-1
Functional Ecology, 2010
1. Measuring transpiration simultaneously in time and space can establish a better understanding of how to mechanistically scale spatiotemporal values.2. This study tested the following predictions to falsify a tree hydraulic hypothesis of spatial variation in transpiration: (i) stands with larger trees will a have longer range and greater sill and nugget at a given vapour pressure deficit (D); (ii) the range, sill and nugget will decline faster with increasing D with larger trees; and (iii) soil moisture, texture and/or N levels will be correlated with transpiration.3. We used cyclic sampling to efficiently collect spatial sap flux data from 144 trees in two forested stands in northern Wisconsin: an Aspen-dominated stand with small trees and a Maple–Pine-dominated stand with larger trees.4. In the Maple stand, the range of spatial autocorrelation in half-hourly transpiration dropped from 80 to 20 m with increased D, whereas in the Aspen stand the range dropped from 55 to 35 m with a similar increase in D.5. Differences in the range of spatial autocorrelation at a given D were driven by sapwood area, which is a function of tree size.6. These results show that species and tree size as well as individual tree hydraulics drive spatial variability in transpiration with little additional variation explained by the measured edaphic conditions.7. Scaling from individual tree transpiration to the landscape in time and space should incorporate atmospheric drivers in time and investigate other potential drivers of tree size in space such as light competition.
1991
The regionalization problem in evaporation is a special case of the general problem of scale. A classification of scale is discussed which is based on the atmospheric stratification in Leaf Boundary, Internal Vegetation, and Surface Layers with successive decrease of decoupling from the Planetary Boundary Layer. The Penman-Monteith approach can be used to integrate lower level processes. For upscaling to the regional level we need to know more on the reaction of the Surface Layer to land surface discontinuities. This reaction is studied in the SHEAR project. First results indicate in a qualitative sense that due to the edge effects, many small forests may have somewhat higher evaporation loss than a single large forest.
2005
we used the eddy covariance and associated hydrometric methods to construct energy and water budgets along a chronosequence of loblolly pine (Pinus taeda) plantations that included a mid-rotation stand (LP) (i.e., 13-15 years old) and a recently established stand on a clearcut site (CC) (i.e., 4-6 years old) in Eastern North Carolina. Our central objective was to quantify the differences in both energy and water balances between the two contrasting stands and understand the underlining mechanisms of environmental controls. We found that the LP site received about 20% more net radiation (R n ) due to its lower averaged albedo (a) of 0.25, compared with that at the CC (a = 0.34). The mean monthly averaged Bowen ratios (b) at the LP site were 0.89 AE 0.7, significantly (p = 0.02) lower than at the CC site (1.45 AE 1.2). Higher net radiation resulted in a 28% higher (p = 0.02) latent heat flux (LE) for ecosystem evapotranspiration at the LP site, but there was no difference in sensible heat flux (H) between the two contrasting sites. The annual total evapotranspiration (ET) at the LP site and CC site was estimated as 1011-1226 and 755-855 mm year À1 , respectively. The differences in ET rates between the two contrasting sites occurred mostly during the non-growing seasons and/or dry periods, and they were small during peak growing seasons or wet periods. Higher net radiation and biomass in LP were believed to be responsible to the higher ET. The monthly ET/Grass Reference ET ratios differed significantly across site and season. The annual ET/P ratio for the LP and CC were estimated as 0.70-1.13 and 0.60-0.88, respectively, indicating higher runoff production from the CC site than the LP site. This study implied that reforestation practices reduced surface albedos and thus increased available energy, but they did not necessarily increase energy for warming the atmosphere in the coastal plain region where soil water was generally not limited. This study showed the highly variable response of energy and water balances to forest management due to climatic variability.