Use of a forest sapwood area index to explain long‐term variability in mean annual evapotranspiration and streamflow in moist eucalypt forests

Benyon, Richard G.; Lane, Patrick; Jaskierniak, Dominik; Kuczera, George; Haydon, Shane R.

doi:10.1002/2015wr017321

Cited by 25 publications

(25 citation statements)

References 51 publications

(129 reference statements)

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“…Benyon et al . [] provided supporting evidence that in a forested catchment, spatiotemporal T is dependent on the vegetation structure, density and composition, and hence vegetation changes due to disturbance or successional regeneration will impact annual streamflow yields. To the author's knowledge, we present the first modeling framework that applies readily available forest inventory data in forest growth models in order to estimate spatiotemporal changes in SA and L .…”

Section: Discussionmentioning

confidence: 99%

“…[] show that changes in catchment SA correlate with long‐term changes in annual streamflow. Across 15 catchments ranging between 4 and 122 ha in size, catchment SA was estimated using mean stem basal area BA μ at 1.3 m height (m 2 ) and overstorey N , which was derived from forest inventory measurements representing approximately 10% of each catchment's area:

S A = \frac{S T}{100} N π \sqrt{\frac{4 B A_{μ}}{π}} = \frac{S T}{100} \sqrt{4 π N \times B A} true({normalR}^{2} = 0.962 true)

where ST is overstorey mean sapwood thickness [cm], estimated using:

{S T = α}_{1} \times N^{α_{2}} true(R^{2} 0.72 true)

where

α_{1}

and

α_{2}

are respectively 7.56 and −0.23 using data from 15 plots with measured ST [ Benyon et al ., ]. We estimated spatiotemporal SA across our three catchments by applying PGP and LiDAR derived forest attributes in equations and , and then estimating each grid cell's L using the following equation [ Benyon et al ., ]:

L = 96.51 \times normalS normalA + 453.48 true(R^{2} 0.66 true)

…”

Section: Methodsmentioning

confidence: 99%

“…At each cell SA is estimated from LiDAR-based estimates of N and BA and relationships derived from PGP data. Using the Benyon et al [2015] relationship, the loss L is estimated and then L is subtracted from P in order to estimate the expected annual streamflow at each grid cell Q 100 (mm yr 21 ). The Q 100 are summed across the catchment to estimate the expected annual catchment streamflow Q.…”

Section: Methodsmentioning

confidence: 99%

“…In ash forests, Benyon et al [2015] show that changes in catchment SA correlate with long-term changes in annual streamflow. Across 15 catchments ranging between 4 and 122 ha in size, catchment SA was estimated using mean stem basal area BA l at 1.3 m height (m 2 ) and overstorey N, which was derived from forest inventory measurements representing approximately 10% of each catchment's area:…”

Section: Modeling Catchment Streamflow 241 Calculating Generated Smentioning

confidence: 99%

“…Benyon et al . [] suggest that a spatial representation of these forest attributes provides the main data requirement for predicting the spatial variation in potential streamflow generation across E. regnans forest.…”

Section: Introductionmentioning

confidence: 99%

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Predicting long‐term streamflow variability in moist eucalypt forests using forest growth models and a sapwood area index

Jaskierniak

Kuczera

Benyon

2016

Water Resources Research

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A major challenge in surface hydrology involves predicting streamflow in ungauged catchments with heterogeneous vegetation and spatiotemporally varying evapotranspiration (ET) rates. We present a top-down approach for quantifying the influence of broad-scale changes in forest structure on ET and hence streamflow. Across three catchments between 18 and 100 km 2 in size and with regenerating Eucalyptus regnans and E. delegatensis forest, we demonstrate how variation in ET can be mapped in space and over time using LiDAR data and commonly available forest inventory data. The model scales plot-level sapwood area (SA) to the catchment-level using basal area (BA) and tree stocking density (N) estimates in forest growth models. The SA estimates over a 69 year regeneration period are used in a relationship between SA and vegetation induced streamflow loss (L) to predict annual streamflow (Q) with annual rainfall (P) estimates. Without calibrating P, BA, N, SA, and L to Q data, we predict annual Q with R 2 between 0.68 and 0.75 and Nash Sutcliffe efficiency (NSE) between 0.44 and 0.48. To remove bias, the model was extended to allow for runoff carry-over into the following year as well as minor correction to rainfall bias, which produced R 2 values between 0.72 and 0.79, and NSE between 0.70 and 0.79. The model under-predicts streamflow during drought periods as it lacks representation of ecohydrological processes that reduce L with either reduced growth rates or rainfall interception during drought. Refining the relationship between sapwood thickness and forest inventory variables is likely to further improve results.

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Section: Discussionmentioning

confidence: 99%

S A = \frac{S T}{100} N π \sqrt{\frac{4 B A_{μ}}{π}} = \frac{S T}{100} \sqrt{4 π N \times B A} true({normalR}^{2} = 0.962 true)

where ST is overstorey mean sapwood thickness [cm], estimated using:

{S T = α}_{1} \times N^{α_{2}} true(R^{2} 0.72 true)

where

α_{1}

and

α_{2}

L = 96.51 \times normalS normalA + 453.48 true(R^{2} 0.66 true)

…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Modeling Catchment Streamflow 241 Calculating Generated Smentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Predicting long‐term streamflow variability in moist eucalypt forests using forest growth models and a sapwood area index

Jaskierniak

Kuczera

Benyon

2016

Water Resources Research

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Change in fire frequency drives a shift in species composition in native Eucalyptus regnans forests: Implications for overstorey forest structure and transpiration

et al. 2022

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The world's most iconic forests are under threat from climate change. Climate-firevegetation feedback mechanisms are altering the usual successional trajectories of forests. Many obligate seeder forests across the globe are experiencing regeneration failures and subsequent alterations to their recovery trajectories. For example, the persistence of Eucalyptus regnans F. Muell. forests in southeast Australia is highly vulnerable to the effects of climate-driven increases in wildfire frequency. Shortening of the wildfire return interval from >100 years to < 20 years would inhibit or entirely stop regeneration of E. regnans, leading to replacement with understorey species such as Acacia dealbata Link. In this study, it is hypothesised that following such replacement, forest overstorey structure and transpiration will diverge. An experiment was designed to test this hypothesis by measuring and comparing overstorey transpiration and structural properties, including sapwood area and leaf area, between E. regnans and A. dealbata over a chronosequence (10-, 20-, 35-and 75-/80-year-old forests). We found that overstorey structure significantly diverged between the two forest types throughout the life cycle of A. dealbata after age 20.The study revealed strikingly different temporal patterns of water use, indicating a highly significant eco-hydrologic change as a result of this species replacement.Overall, the results provide a strong indication that after age 20, overstorey transpiration in Acacia-dominated forests is substantially lower than in the E. regnans forests they replace. This difference may lead to divergence in water yield from forested catchments where this species replacement is widespread.

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Increasing fire frequency may trigger eco‐hydrologic divergence

Lakmali

Benyon

Sheridan

et al. 2023

Hydrological Processes

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Climate‐induced fire regimes may change species abundance and species composition in affected forest types, potentially altering pyro‐eco‐hydrologic feedbacks. In some fire‐prone forests across the globe, eco‐hydrologic thresholds (changing points, or tipping points, in ecohydrology when vegetation shifts from one steady vegetation to another) are being exceeded due to changes in relationships between climate, fire and vegetation. Following compound disturbances, forests may fail to maintain ecological resilience. Under multiple burn conditions, Eucalyptus regnans F. Muell. forests in south east Australia are highly vulnerable to ecological tipping points. In Victoria, over 189 000 ha of obligate seeder forests have been burned two or more times within 18 years. These short return‐interval fires allow Acacia dealbata to become the dominant overstorey species. Such a dramatic species replacement may result in a new evapotranspiration (ET) regime, leading to a new hydrologic state. Stand scale dynamic models were combined with field estimated ET in E. regnans and A. dealbata forests aged 10, 35 and 75/80 years. We found that long‐term forest structure, ET and water yield significantly diverge between E. regnans and A. dealbata forests with increasing age. These divergences imply a non‐equilibrium state after A. dealbata replaces E. regnans under high‐frequency fire conditions. In senescing A. dealbata, understorey transpiration contribution of 29.8% to system ET was similar to that of overstorey transpiration (31.2%), indicating the understorey and overstorey contribute equally to total ET at the final stage of Acacia forests. In contrast, in 75‐year‐old E. regnans forests, understorey contribution to the total system evapotranspiration is about 16%. This suggests that, after the Acacia life cycle finishes, the ET regime will transit into a new state that will be dominated by shrubby understorey species. Our findings suggest that this climate‐induced species replacement would decrease long‐term ET, inferring an increase in streamflow.

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Use of a forest sapwood area index to explain long‐term variability in mean annual evapotranspiration and streamflow in moist eucalypt forests

Cited by 25 publications

References 51 publications

Predicting long‐term streamflow variability in moist eucalypt forests using forest growth models and a sapwood area index

Predicting long‐term streamflow variability in moist eucalypt forests using forest growth models and a sapwood area index

Change in fire frequency drives a shift in species composition in native Eucalyptus regnans forests: Implications for overstorey forest structure and transpiration

Increasing fire frequency may trigger eco‐hydrologic divergence

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