Article

Rainfall partitioning and cloud water interception in native forest an invaded forest in Hawai'I Volcanoes National Park

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Abstract

In many Hawaiian forests, including cloud forests, native plant communities are being displaced by invasive tree species, possibly affecting rainfall partitioning and direct harvesting of cloud droplets by vegetation. In this study, the hydrological impacts of invasive species are examined, using measurements of rainfall (RF), throughfall (TF) and stemflow (SF), and estimation of wet-canopy evaporation and cloud water interception (CWI) by the canopy water balance approach in both native Metrosideros polymorpha-dominated and invaded, Psidium cattleianum-dominated forests within Hawai'i Volcanoes National Park (HAVO). Canopy water storage capacity was found to be more than twice as great at the native site (1·86 mm) compared to the invaded site (0·85 mm). Annual RF, CWI, TF and SF were 3233, 1188, 3700 and 261 mm, respectively, for the native site; and 3735, 734, 3033 and 1091 mm, respectively, for the invaded site. Net RF (TF + SF) was 123 and 110% of RF, respectively, at the two sites. Annual evaporation of water from the wet canopy was also greater at the native site (464 mm) than at the invaded site (347 mm). Low canopy water storage capacity and the exceptionally high SF total at the invaded site are related to morphological characteristics and high stem density of the invasive P. cattleianum tree, which favour efficient transport of intercepted water to the ground via the stems. Despite its more peripheral location near the edge of the orographic cloud, CWI at the native site was higher. The characteristics of the native M. polymorpha tree may facilitate more effective harvesting of cloud water droplets, enhancing CWI at the site. Species invasion results in a lower proportion of RF reaching the forest floor (110 vs 123%) and becoming available for groundwater recharge, suggesting that invasion by P. cattleianum may have significant negative effects on Hawai'i's aquatic ecosystems and water resources. Copyright © 2010 John Wiley & Sons, Ltd.

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... In other areas, invasions of fast-growing canopy species can lead to a transition to alien dominated forests, as is the case in most low elevation areas in Hawai'i Hughes and Uowolo, 2006). Although research remains limited, available studies have found that typical invasive trees and stands can have higher transpiration rates (Cavaleri et al., 2005;Cavaleri and Sack, 2010;Kagawa et al., 2009;Giambelluca et al., 2008), and lower fog interception rates (Takahashi et al., 2011), than typical native forest trees and stands. There is clear need for further research on the effects of invasions on hydrologic processes at multiple scales; while islands are particularly vulnerable, invasions increasingly represent important threats to forests worldwide and are a critical driver of global environmental change Holmes et al., 2009;Vitousek et al., 1996). ...
... Changes in forest land cover type can affect the water balance in multiple ways, including through changes in: actual evapotranspiration (Giambelluca et al., 2014;Kagawa et al., 2009); fog interception (Takahashi et al., 2011); and potentially the amount of water that infiltrates soils and recharges groundwater aquifers versus runs off as streamflow (Wright et al., 2018). Unfortunately, there are insufficient data available to model changes in fog interception and infiltration spatially with forest cover change. ...
... For native forest, the representative species was 'ōhi'a lehua (Metrosideros polymorpha) and for nonnative forest, strawberry guava (Psidium cattleyanum) (Giambelluca et al., 2014). Second, other processes, including cloud-water interception (Ponette-González et al., 2014;Takahashi et al., 2011) and infiltration (Wright et al., 2018;Perkins et al., 2018) can be affected by land cover type and characteristics, but we did not have information to include these parameters for different forest types. We thus consider our estimates conservative given that field crews and local experts perceive that native forest captures more fog and infiltrates more water than monotypic non-native forest with a less diverse understory, and Note: sp. ...
... In other areas, invasions of fast-growing canopy species can lead to a transition to alien dominated forests, as is the case in most low elevation areas in Hawai'i Hughes and Uowolo, 2006). Although research remains limited, available studies have found that typical invasive trees and stands can have higher transpiration rates (Cavaleri et al., 2005;Cavaleri and Sack, 2010;Kagawa et al., 2009;Giambelluca et al., 2008), and lower fog interception rates (Takahashi et al., 2011), than typical native forest trees and stands. There is clear need for further research on the effects of invasions on hydrologic processes at multiple scales; while islands are particularly vulnerable, invasions increasingly represent important threats to forests worldwide and are a critical driver of global environmental change Holmes et al., 2009;Vitousek et al., 1996). ...
... Changes in forest land cover type can affect the water balance in multiple ways, including through changes in: actual evapotranspiration (Giambelluca et al., 2014;Kagawa et al., 2009); fog interception (Takahashi et al., 2011); and potentially the amount of water that infiltrates soils and recharges groundwater aquifers versus runs off as streamflow (Wright et al., 2018). Unfortunately, there are insufficient data available to model changes in fog interception and infiltration spatially with forest cover change. ...
... For native forest, the representative species was 'ōhi'a lehua (Metrosideros polymorpha) and for nonnative forest, strawberry guava (Psidium cattleyanum) (Giambelluca et al., 2014). Second, other processes, including cloud-water interception (Ponette-González et al., 2014;Takahashi et al., 2011) and infiltration (Wright et al., 2018;Perkins et al., 2018) can be affected by land cover type and characteristics, but we did not have information to include these parameters for different forest types. We thus consider our estimates conservative given that field crews and local experts perceive that native forest captures more fog and infiltrates more water than monotypic non-native forest with a less diverse understory, and Note: sp. ...
Article
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Tropical forests provide a suite of benefits including biodiversity, cultural value, and a range of ecosystem services. Globally, there is increasing interest in incentivizing native forest protection as a multi-benefit natural infrastructure strategy to secure clean and ample water supplies. In addition to conversion to agriculture and other non-forest land uses, non-native species invasion represents a major threat to these systems, particularly on islands. Whereas several recent efforts have quantified the benefits of reforestation or avoided agricultural expansion in tropical forest areas, the hydrologic and associated economic benefits of avoided invasion have received less attention. To address this gap, we quantified the benefits of protecting native forest from conversion to non-native forest in East Maui, Hawai'i in terms of groundwater recharge, a highly valued hydrologic ecosystem service that water utilities increasingly seek to co-finance. Compared with two counterfactual invasion scenarios, the groundwater recharge benefits of planned conservation activities reached 40.9 to 146.3 million cubic meters over 100 years depending on invasion rate assumptions. This translated to 2.70 to 137.6 million dollars of cost savings to the water utility in present value terms (achieved through reducing reliance on more expensive water alternatives) under a range of discount rates and water scarcity assumptions. Our results suggest that investing in native forest conservation provides an important hydrologic ecosystem service benefit that complements the range of benefits provided by these ecosystems. These findings demonstrate that co-financing native forest conservation represents an important supply side option in water resources planning.
... Two studies from the upslope Alakahi region of windward Kohala reported significant levels of CWI over multi-year spans, and found that CWI inputs almost equaled rainfall levels during a dry period at one of the sites (Juvik & Nullet, 1995;DeLay, 2005). Another study from near the peak of Kīlauea found that CWI contributed 18.7% of total precipitation (Takahashi et al., 2011). While these studies indicate that CWI could contribute significantly to the crest and high leeward areas of Kohala, no CWI experiments have been conducted in leeward TMCFs like those present at high elevations in Kohala. ...
... In order to estimate CWI at each of our study sites, a simple canopy water balance model is employed (Takahashi et al., 2011): ...
... Many TF studies achieve high spatial coverage by funneling water through large systems of troughs into centralized tippingbucket gauges (e.g. McJannet et al., 2007a;Takahashi et al. 2011); however, due to budgetary constraints, this study was limited to 15 plastic buckets per ʻōhiʻa site. Two buckets at each site were allocated to RF measurements in nearby clearings, bogs, and pastures. ...
Thesis
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Cloud water interception (CWI) is a significant source of water for many tropical montane cloud forests (TMCFs) in Hawai‘i and elsewhere. As vast regions of the Hawaiian Islands have undergone extensive deforestation over the past several centuries, many have suggested that the loss of CWI and other ecohydrological characteristics of tropical forests may have resulted in lower rates of groundwater recharge and subsequent streamflow. Leeward Kohala is one such region where many hectares of closed-canopy TMCF and wet-mesic woodland were lost to the cattle industry, which planted exotic pasture grasses in their stead. Because leeward Kohala’s perched groundwater system is geologically-isolated from the intact forests of windward Kohala, the resulting loss of CWI could have significantly lowered recharge rates and water table levels throughout the leeward slope. But despite reports of reduced flow and increased flashiness in leeward streams, CWI in Kohala’s remaining leeward forests has not yet been quantified.Rainfall (RF) and throughfall (TF) were measured along an elevation gradient spanning the natural transition from mesic koai‘a woodland to closed-canopy ‘ōhi‘a forest atop leeward Kohala, Hawai‘i. By applying a simplified canopy water balance model, combined rates of CWI minus canopy interception losses (Ei) were determined at seven sites for twenty distinct measurement periods. These rates ultimately reflect the additional amount of (or loss of) precipitation contacting the land surface due to the presence of forest vegetation rather than flat pastureland. Near Kohala’s leeward crest, RF totaled 1,104.5±13.7 mm over 133 days while forest cover provided an additional 568.0±15.4 mm of water to the land surface. CWI contributions were progressively lower farther down Kohala’s leeward slope, with Ei appearing to outweigh CWI by 41.3±14.3 mm at the current man-made transition from ‘ōhi‘a forest to pasture. Two lower-elevation sites in remnant koai‘a woodlands exhibited a CWI-elevation trend distinct from that of the ‘ōhi‘a sites, with site D recording 50.9±16.8 mm of additional water input at the forest site compared to 457.2±14.0 mm of nearby pasture RF over the study period. At site E, the driest site, Ei exceeded CWI in almost all measurement periods (73.9±16.6 mm net water loss in the site E forest over the study period). Mean TF/RF across sites was 1.07, indicating CWI generally outweighed canopy Ei and added significant amounts of water to leeward Kohala.Spatial variations in CWI were driven by forest structure in addition to elevation: despite receiving the same amount of RF over the study period, different rates of TF and CWI were recorded between the three forested plots at site B. In general, denser forest tended to exhibit lower TF at both the site scale and gauge scale, although this relationship weakens in wetter periods due to higher canopy saturation. Wet periods with strong trade winds featured the highest overall CWI rates across the elevation transect, and CWI rates at all sites generally decreased when conditions become drier and less windy. While CWI, TF and RF are positively related to elevation, periods with weaker trade winds present flatter versions of these trends due to the waning influence of the orographic moisture responsible for both RF and CWI. Broadly speaking, wetness and elevation appear more explanatory than trade wind strength or forest structure for CWI rates in leeward Kohala.
... However, some studies have shown that in humid tropical forests, trees with DBH < 10 cm as well as understory woody plants can contribute importantly to overall Sf at the plot level (Germer et al., 2010;Jordan, 1978;Manfroi et al., 2004). Small trees and understory plants contribute importantly to overall Sf due to their much higher density in comparison to that of large overstory trees (Jordan, 1978;Takahashi et al., 2011). Additionally, some characteristic traits of understory vegetation enhance water channeling towards their stems (Siles, Vaast, Dreyer, & Harmand, 2010), including smooth-textured bark, monopodial stems, and vertical branch growth (cf. ...
... This is because the various methods that exist may yield rather different results (Aboal, Morales, Hernández, & Jiménez, 1999). The most frequently used methods are as follows: (a) the development of allometric equations between Sf and DBH or basal area (BA; e.g., Dietz, Hölscher, Leuschner, & Hendrayanto, 2006;Takahashi et al., 2011); (b) the use of equations to relate Sf to rainfall (Hanchi & Rapp, 1997); and (c) the extrapolation of mean stemflow yield (Sf y ) using data on tree density (Levia & Germer, 2015) or BA (Oliveira et al., 2015). To date, there is no consensus about which of these scaling methods is the most appropriate. ...
... However, in forests as diverse as ours that would imply the derivation of multiple relationships per vegetation group, requiring a sampling effort much beyond that currently performed (n = 41 trees). The literature shows mixed results regarding the relationship between Sf y and DBH or BA, with some studies finding acceptable relationships (Hanchi & Rapp, 1997;Manfroi et al., 2004) and others reporting poor (or complete lack of) correlation (Krämer & Hölscher, 2009;Levia & Frost, 2003;Takahashi et al., 2011;Zimmermann, Uber, Zimmermann, & Levia, 2015). ...
Article
Stemflow (Sf) measurements in tropical rain and montane forests dominated by large trees rarely include the understory and small trees. In this study, contributions of lower (1-2 m height) and upper (>2 m height and < 5 cm DBH) woody understory, small trees (5 < DBH < 10 cm) and canopy trees (>10 cm DBH) to Sf per unit ground area (Sfa) of a Mexican lower montane cloud forest were quantified for 32 days with rainfall (P) during the 2014 wet season. Rainfall, stemflow yield (Sfy), as well as vegetation height, density and basal area were measured. Subsequently, stemflow funneling ratios (SFR) were calculated, and three common methods to scale up Sfy from individual trees to the stand level (tree-Sfy correlation, P-Sfy correlation, mean Sfy extrapolation) were used to calculate Sfa. Understory woody plants, small trees and upper canopy trees represented 96, 2 and 2 %, respectively, of the total density. Upper canopy trees had the lowest SFRs (1.6 ± 0.5 SE on average), while the lower understory had the highest (36.1 ± 6.4). Small trees and upper understory presented similar SFRs (22.9 ± 5.4 and 20.2 ± 3.9, respectively). Different Sf scaling methods generally yielded similar results. Overall Sfa during the study period was 22.7 mm (4.5 % of rainfall), to which the understory contributed 70.1 % (15.9 mm), small trees 10.6 % (2.4 mm) and upper canopy trees 19.3 % (4.4 mm). Our results strongly suggest that for humid tropical forests with dense understory of woody plants and small trees, Sf of these groups should be measured to avoid an underestimation of overall Sf at the stand level.
... Climate warming is predicted to reduce precipitation across the Hawaiian archipelago as a result of alterations in rainfall patterns and reduced cloud water interception (Oki 2004;Timm & Diaz 2009;Takahashi et al. 2011). Hawai`i is in the midst of a 40+ year drying period, which corresponds to progressive declines in baseflow conditions (Oki 2004;Bassiouni & Oki 2013). ...
... Annual precipitation is predicted to decrease further due to reduced wet season rainfall (Timm & Diaz 2009). Additionally, cloud water interception (i.e., water input received directly from clouds), which is a significant source of surface flow in Hawaiian streams, is expected to decline as a consequence of rising cloud elevations (Oki 2004;Timm & Diaz 2009;Takahashi et al. 2011). Rainfall is also expected to occur in fewer, stronger storm events (Timm & Diaz 2009) that may further reduce cloud water interception (Takahashi et al. 2011). ...
... Additionally, cloud water interception (i.e., water input received directly from clouds), which is a significant source of surface flow in Hawaiian streams, is expected to decline as a consequence of rising cloud elevations (Oki 2004;Timm & Diaz 2009;Takahashi et al. 2011). Rainfall is also expected to occur in fewer, stronger storm events (Timm & Diaz 2009) that may further reduce cloud water interception (Takahashi et al. 2011). ...
Article
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Climate change can promote disease emergence if shifting conditions favour infection of native fauna by introduced parasites and pathogens. In Hawai'i, climate warming is predicted to reduce net precipitation and surface flow in streams, which in turn could increase parasitism of native stream fishes by non-native parasites. In this study, we utilised a natural precipitation gradient across the Hamakua coast on the island of Hawai'i to assess the relationship between precipitation and infection of Awaous stamineus, a native amphidromous goby, by the introduced nematode Camallanus cotti. We found that the abundance, intensity and prevalence of C. cotti in A. stamineus increased with declining rainfall. Our results also show that parasitism tracks precipitation patterns across the archipelago and that parasitism increases even with moderate decreases in rainfall. As the Hamakua coast precipitation gradient represents a proxy for predicted climate-driven reductions in precipitation, these findings suggest that infection of native Hawaiian fishes by introduced parasites will increase if climate conditions change as expected. Our findings also suggest that parasitism may be exacerbated by other factors that reduce surface flow, including water extraction for agricultural and urban uses. If so, then adaptive management of minimum flow standards in Hawai'i and elsewhere could improve the well-being of at-risk native fishes by alleviating parasitism under current and future climate conditions.
... In the context of plant invasions, a few studies have assessed the rainfall partitioning by exotic species and its association with plant morphological characteristics (Sadeghi et al., 2017;Safeeq & Fares, 2014;Takahashi et al., 2011;Whitworth-Hulse et al., 2020). ...
... Hawaii tropical dry forests ecoregion; Takahashi et al., 2011). In the Central Persian desert basins ecoregion (Iran), Sadeghi et al. (2017) highlighted that stemflow generation could be a key process for explaining the invasion of the smooth-barked tree Ailanthus altissima Mill. ...
... Wilgen et al., 2008). In summary, less rainwater reaching the soil, together with high water consumption of invasive plants, might generate a reduction of water availability for recharging groundwater and also streamflow(Farley et al., 2005;Le Maitre et al., 2015;Takahashi et al., 2011). These results will become increasingly important for the maintenance or increase of human well-being, highlighting the need for further inquiries determining the ecohydrological impacts on water provision of woody invasive species at the catchment scale. ...
Article
Aim: Invasive species have the potential to alter hydrological processes by changing the local water balance. However, general patterns of how rainfall is partitioned into interception, throughfall and stemflow for invasive species worldwide have been seldom explored. We (a) describe the percentage of interception, throughfall and stemflow for invasive woody plant species; (b) analyse the influence of morphological attributes (i.e. life-form, bark roughness, leaf type, leaf phenology and leaf area index) of invasive species on rainfall partitioning; and (c) compare the rainfall partitioning fluxes for co-occurring invasive and native species, testing whether the variation in these fluxes depends on water availability of the study location. Location: Global. Time period: Present. Major taxa studied: Plants. Methods: We compiled data of 100 studies that assessed rainfall partitioning by invasive species (n = 67) and registered their morphological attributes. By means of a meta-analysis we compared the rainfall partitioning by native and invasive species (n = 47 comparisons) and assessed how their fluxes were affected by water availability. Results: Interception, throughfall and stemflow ranged from 1.6–59.5, 39.1–92.7 and 0.1–31.6% of total rainfall, respectively. The bark roughness and leaf type were the most important attributes driving rainfall partitioning fluxes. While rough-barked species constrain rainfall inputs by promoting higher losses due to interception, smooth-barked species with broad leaves enhance the amount of rainwater reaching the soil by maximizing stemflow. For pairwise comparisons, invasive species have higher stemflow values than native species for both drylands and humid areas, and higher throughfall in drylands, but less in humid areas. Main conclusions: Our findings suggest that specific morphological attributes of invasive species determine higher localized water inputs, which may represent an ecohydrological advantage, particularly in water-limited ecosystems. These insights also suggest that the ecological role of stemflow, throughfall and interception should be considered in future plant invasions research.
... Though watershed partnerships and other conservation organizations protect and restore native forests for multiple benefits, including biodiversity, cultural value, and water quality for downstream coral reefs, water utilities are most interested in enhancing the quality and quantity of groundwater recharge within priority aquifers. While ecohydrology data are limited in Hawaiʻi, and across the tropics more broadly (Hamel et al., 2017;Wright et al., 2018), existing studies suggest that native-dominated forest stands capture more fog (Takahashi et al., 2011) and transpire less water (Cavaleri et al., 2014;Cavaleri and Sack, 2010;Giambelluca et al., 2008;Kagawa et al., 2009;Miyazawa et al., 2019) than invaded stands dominated by high water-use, non-native species. Feral pigs and other ungulate activity also pose a significant threat to remaining native forests, sometimes causing conversion to bare ground or non-native grass dominated systems (Nogueira-Filho et al., 2009), which leads to greater erosion and runoff (Strauch et al., 2016) and reduced fog interception (due to low stature vegetation) in high elevation areas (Engott, 2011). ...
... Changes in forest land cover type can affect the water balance in multiple ways, including through changes in: actual evapotranspiration (AET) (Giambelluca et al., 2014;Kagawa et al., 2009); fog interception (Takahashi et al., 2011); and potentially the amount of water that infiltrates soils and recharges groundwater aquifers versus runs off as streamflow (Wright et al., 2018). Unfortunately, there were insufficient data available to model changes in infiltration spatially with forest cover change. ...
... Cloud water interception or fog interception has been shown to be important in tropical forests in Hawaiʻi (Giambelluca et al, 2009Scholl et al., 2007;Takahashi et al., 2011). Thus, we also modeled changes in fog interception following USGS methods (Engott 2011) where fog interception is calculated as: ...
Article
Full-text available
Worldwide, water utilities and other water users increasingly seek to finance watershed protection and restoration in order to maintain or enhance water quality and quantity important for drinking water supply and other human use. Hydrologic studies which characterize the relative effectiveness of watershed management activities in terms of metrics important to water users are greatly needed to guide prioritization. To address this need, we worked with a local water utility in Hawaiʻi to develop a novel framework for prioritizing investments in native forest protection and restoration for groundwater recharge and applied it in the utility's priority aquifers and recharge areas. Specifically we combined land cover and water balance modeling to quantify the 50-year cumulative recharge benefits of: 1) protection of native forest from conversion to non-native forest, and 2) restoration of native forest in non-native grasslands. The highest priority areas (80th percentile of benefits) for native forest protection are projected to prevent the loss of over 48,600 m³ per hectare of recharge over 50 years. Incorporating land cover change modeling (versus assuming all areas are equally susceptible to invasion) shifts prioritization towards low to mid-elevation mesic forest areas at the highest risk of invasion by invasive canopy species as well as to high elevation, cloud forest areas at high risk of conversion to non-native grassland or bare ground. We also find that, in the highest priority areas with substantial fog interception, native forest restoration is projected to increase recharge by over 88,900 m³ per hectare over 50 years, but that decreases in recharge occur in areas with low fog interception. This study provides a framework for prioritizing investments in forest protection and restoration for groundwater recharge in a way that incorporates both the threat of conversion as well as changes in hydrologic fluxes. The framework and results can be utilized by current managers and updated as new ecohydrological data become available. The results also provide broad insights on the links between watershed management and groundwater recharge, particularly on islands and in other regions where species invasions threaten source watersheds and where groundwater is a primary water source.
... Mean annual precipitation varies between 250 to more than 11000 mm in Hawaii , and from 1000 to 12000 mm on La Réunion Island . The occurrence of fog, likely to increase effective precipitation height, is reported in many oceanic islands such as in Hawaii (US) [Brauman et al., 2010;Giambelluca et al., 2011;Takahashi et al., 2011], La Réunion Island (France) [Gabriel and Jauze, 2008], Madeira Island (Portugal) , Canary Islands (Spain) [García-Santos and Bruijnzeel , 2011], and Galapagos Islands [Pryet et al., 2012]. ...
... Giambelluca et al. [Rutter et al., 1972], running water budget interception model (e.g. Takahashi et al. [2011]). ...
... The occurrence of fog is reported in many oceanic islands and has been investigated by several recent studies such as in Hawaii (US) [Brauman et al., 2010;Giambelluca et al., 2011;Takahashi et al., 2011], La Réunion Island (France) [Gabriel and Jauze, 2008], Madeira Island (Portugal) , and Canary Islands (Spain) [García-Santos and Bruijnzeel , 2011]. ...
Thesis
Full-text available
With a growing population and limited freshwater resources, the hy- drogeology of the Galapagos Islands remains to a great extent un- known. Rainfall is relatively weak and unevenly distributed in space and time. The economical center of the archipelago, Santa Cruz Is- land, has only small intermittent streams, while several permanent streams are present on San Crist ́obal Island. In the frame of this study, an interdisciplinary approach is used to characterize the hy- drogeology of the archipelago. A new method has been developed to enhance the interpretation of airborne electromagnetics surveys. With geostatistical interpolation techniques, this method allows the construction of a 3D grid of re- sistivity. SkyTEM surveys completed in Galapagos were processed with this technique, and confronted to surface analysis with remote sensing and field work. The first hydrogeological conceptual model is proposed for San Cristo ́bal Island. Climatic conditions have been investigated with the installation of a monitoring network along the windward side of Santa Cruz Island. The occurrence of fog during six months of the year presents an addi- tional input in the water budget and increases groundwater recharge. This input has been quantified with a physically based canopy inter- ception model. The basal aquifer of Santa Cruz Island has been investigated from the analysis of tidal signal propagation, hydraulic tests, as well as fault and fracture mapping. Results show that young basalts, densely fractured by cooling joints, are highly permeable. Because they are poorly connected, faults have a limited impact over regional ground- water flow. Contrasting hydrogeological configurations in the Galapagos Islands are explained by an evolution pattern. In relatively young islands, such as Santa Cruz, basalts are fractured and permeable. Seawater intrusion is strong and freshwater rapidely flows to the ocean. On the opposite, conditions are more favorable for groundwater storage in older volcanic islands, where the regional permeability is smaller and valley incision leads to the existence of springs.
... Mean annual precipitation varies between 250 to more than 11000 mm in Hawaii , and from 1000 to 12000 mm on La Réunion Island . The occurrence of fog, likely to increase effective precipitation height, is reported in many oceanic islands such as in Hawaii (US) [Brauman et al., 2010;Giambelluca et al., 2011;Takahashi et al., 2011], La Réunion Island (France) [Gabriel and Jauze, 2008], Madeira Island (Portugal) , Canary Islands (Spain) [García-Santos and Bruijnzeel , 2011], and Galapagos Islands [Pryet et al., 2012]. ...
... Giambelluca et al. [Rutter et al., 1972], running water budget interception model (e.g. Takahashi et al. [2011]). ...
... The occurrence of fog is reported in many oceanic islands and has been investigated by several recent studies such as in Hawaii (US) [Brauman et al., 2010;Giambelluca et al., 2011;Takahashi et al., 2011], La Réunion Island (France) [Gabriel and Jauze, 2008], Madeira Island (Portugal) , and Canary Islands (Spain) [García-Santos and Bruijnzeel , 2011]. ...
Article
With a growing population and limited freshwater resources, the hydrogeology of the Galapagos Islands remains to a great extent unknown. Rainfall is relatively weak and unevenly distributed in space and time. The economical center of the archipelago, Santa Cruz Island, has only small intermittent streams, while several permanent streams are present on San Cristóbal Island. In the frame of this study, an interdisciplinary approach is used to characterize the hydrogeology of the archipelago. A new method has been developed to enhance the interpretation of airborne electromagnetics surveys. With geostatistical interpolation techniques, this method allows the construction of a 3D grid of resistivity. SkyTEM surveys completed in Galapagos were processed with this technique, and confronted to surface analysis with remote sensing and field work. The first hydrogeological conceptual model is proposed for San Cristóbal Island. Climatic conditions have been investigated with the installation of a monitoring network along the windward side of Santa Cruz Island. The occurrence of fog during six months of the year presents an additional input in the water budget and increases groundwater recharge. This input has been quantified with a physically based canopy interception model. The basal aquifer of Santa Cruz Island has been investigated from the analysis of tidal signal propagation, hydraulic tests, as well as fault and fracture mapping. Results show that young basalts, densely fractured by cooling joints, are highly permeable. Because they are poorly connected, faults have a limited impact over regional groundwater flow. Contrasting hydrogeological configurations in the Galapagos Islands are explained by an evolution pattern. In relatively young islands, such as Santa Cruz, basalts are fractured and permeable. Seawater intrusion is strong and freshwater rapidely flows to the ocean. On the opposite, conditions are more favorable for groundwater storage in older volcanic islands, where the regional permeability is smaller and valley incision leads to the existence of springs.
... Despite the fact that tipping bucket application dates back to 1928 (Nebol'sin, 1928), it has been used for surface/subsurface flows in small study area measurements, such as runoff (Calder and Kidd, 1978;Chow, 1976;Corona et al., 2013;Elder et al., 2014;Hollis & Ovenden, 1987;Khan & Ong, 1997;Klik et al., 2004;Kim et al., 2005;Johnston, 1942;Nehls et al., 2011;Peyrard et al., 2016;Perales-Momparler et al., 2017;Langhans et al., 2019;Wang et al., 2020;Whipkey, 1965), percolation (Lamb et al., 2019;Peyrard et al., 2016;Wang et al., 2020), throughfall (Takahashi et al., 2010;Zabret et al., 2018) and stemflow (Iida et al., 2012;Shimizu et al., 2018;Takahashi et al., 2010;Zabret et al., 2018). ...
... Despite the fact that tipping bucket application dates back to 1928 (Nebol'sin, 1928), it has been used for surface/subsurface flows in small study area measurements, such as runoff (Calder and Kidd, 1978;Chow, 1976;Corona et al., 2013;Elder et al., 2014;Hollis & Ovenden, 1987;Khan & Ong, 1997;Klik et al., 2004;Kim et al., 2005;Johnston, 1942;Nehls et al., 2011;Peyrard et al., 2016;Perales-Momparler et al., 2017;Langhans et al., 2019;Wang et al., 2020;Whipkey, 1965), percolation (Lamb et al., 2019;Peyrard et al., 2016;Wang et al., 2020), throughfall (Takahashi et al., 2010;Zabret et al., 2018) and stemflow (Iida et al., 2012;Shimizu et al., 2018;Takahashi et al., 2010;Zabret et al., 2018). ...
... Calder and Kidd (1978) identified a non-linearity of errors under increased flow, and thus proposed a new calibration curve by correlating the input flow and time interval between tilts. Based on the same central idea of describing the errors considering its non-linearity, other authors have also proposed calibration curves (Iida et al., 2012;Shimizu et al., 2018;Shiraki & Yamato, 2004;Takahashi et al., 2010). ...
Article
Inherent errors in tipping bucket flow meters may limit monitoring data reliability. In this work, we perform the static and dynamic calibration of four large tipping buckets, apply different regression curves and investigate the possible measurement error sources. The volumetric capacity (static calibration) of each piece of equipment was determined. They were tested (dynamic calibration) under ten flow intensities, ranging from low to high rainfall intensities (return period larger than 100 years). For each flow rate, the measurement was recorded during six time intervals (1, 2, 5, 10, 20 and 30 min) and four regression equations - linear, potential, T vs. 1/Q and quadratic - were tested. According to the static calibration, the equipment has a volumetric capacity of 11.63 mL (TB1), 64.16 mL (TB2), 139.86 mL (TB3) and 660.95 mL (TB4). When tested under different flow rates (dynamic calibration), underestimations were identified according to the size of the cavity: TB1 (3.31%), TB2 (5.75%), TB3 (9.33%) and TB4 (13.57%). Among the alternative curves, linear regression showed the best correlation (above 99%) with the monitored data. Using this method, the measurement errors were reduced to −1.35% (TB1), 0.04% (TB2), 3.18% (TB3) and 3.73% (TB4). We investigated how the different variables (tipping speed, cavity volumetric capacity and time interval of data collection) influenced the error. Errors follow a parabolic function of tipping velocity and a linear function of cavity volumetric capacity. The time interval of data collection interfered in the data sampled, however no statistical correlation was found. Among those variables, cavity size is the most important one. Given its low cost we aimed to minimize the inherent error in large tipping buckets flow meters and encourage its application, increasing in-situ collection of hydrological data.
... For example, management can influence spatial and temporal attributes of downstream water, nutrient, and sediment movement to coastal areas (Ensign and Doyle, 2006;Newcomer-Johnson et al., 2016) as well as overall hydrologic budgets (Strauch et al., 2017). These "ridge-to-reef" processes are especially sensitive on small islands in ocean environments, where watersheds are compact and for some islands systems, invaded by alien species (Takahashi et al., 2011;Santamarta et al., 2014). These factors can negatively impact hydrology budgets (Povak et al., 2017;Strauch et al., 2017) as well as the nearshore reef habitats that support both subsistence and tourism-oriented economies (Povak et al., 2020;Foo and Asner, 2021). ...
... The Hawaiian archipelago continues to be an important laboratory for developing and implementing DSSs in the context of climate change (Vorsino et al., 2014), water resources (Takahashi et al., 2011;Santamarta et al., 2014;Povak et al., 2017), and invasive species management (Giambelluca et al., 2009;Somers and Asner, 2013;Strauch et al., 2017Strauch et al., , 2018. Wall-to-wall remote sensing and other data greatly aids planning and implementation of spatial DSS Marvin et al., 2016;Niemiec et al., 2016). ...
Article
Invasive species alter hydrologic processes at watershed scales, with impacts to biodiversity and the supporting ecosystem services. This effect is aggravated by climate change. Here, we integrated modelled hydrologic data, remote sensing products, climate data, and linear mixed integer optimization (MIP) to identify stewardship actions across space and time that can reduce the impact of invasive species. The study area is the windward coast of Hawai'i Island (USA) across which non-native strawberry guava occurrence varies from extremely dense stands in lower watershed reaches, to low densities in upper watershed forests. We focused on the removal of strawberry guava, an invader that exerts significant impacts on watershed condition. MIP analyses spatially optimized the assignment of effective management actions to increase water yield, generate revenue from enhanced freshwater services, and income from removed biomass. The hydrological benefit of removing guava, often marginal when considered in isolation, was financially quantified, and single-and multiobjective MIP formulations were then developed over a 10-year planning horizon. Optimization resulted in $2.27 million USD benefit over the planning horizon using a payment-for-ecosystem-services scheme. That value jumped to $4.67 million when allowing work schedules with overnight camping to reduce costs. Pareto frontiers of weighted pairs of management goals showed the benefit of clustering treatments over space and time to improve financial efficiency. Values of improved land-water natural capital using payment-for-ecosystem-services schemes are provided for several combinations of spatial, temporal, economical, and ecosystem services flows.
... We examined whether the effects of P. cattleianum on soil properties and litter decomposition vary across sites with different rates of mean annual precipitation, though factors other than precipitation, such as temperature or parent materials may also affect decomposition (Scowcroft et al. 2000;Bothwell et al. 2014). Furthermore, because invasion by P. cattleianum can alter the hydrological cycle in Hawaiian forests (Mair and Fares 2010;Takahashi et al. 2011;Safeeq and Fares 2014), the soil moisture environment could be altered by the invasion. We also compared the effects of P. cattleianum among sites with vegetation that had developed under different precipitation regimes to examine whether direct effects of P. cattleianum could explain variation in the decomposition process independently of the soil environmental factors altered by the invasion. ...
... As a result, compared to the native stands, the soil moisture content in P. cattleianum stands tended to be lower in wetter sites, but higher in drier sites. Previous studies have shown P. cattleianum affects hydrological process in forest stands by decreasing throughfall via interception by the shoot (Mair and Fares 2010) and by increasing stemflow via smooth bark and steep branching architecture (Takahashi et al. 2011;Safeeq and Fares 2014). Although the reason for changes in soil water content are not clear in our study, the large mass of accumulated litter of P. cattleianum stands could increase soil water retention in drier sites; likewise, the high stem density of P. cattleianum stands also could increase soil water retention in drier sites. ...
Article
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To test the effects of invasion by strawberry guava trees (Psidium cattleianum) on the forest soil ecosystem, we compared soil properties between pairs of adjacent native and P. cattleianum stands. We set up six study sites that had developed under different mean annual precipitation levels in the Ko'olau Mountains on the island of O'ahu, Hawai'i. Accumulated litter mass and soil pH decreased with precipitation in the native stands. Invasion by P. cattleianum increased the amount of litter and reduced the differences in soil water content and pH among the sites. We compared the decomposition process using the Tea Bag Index, which is determined by the difference in dry mass of commercially available green and rooibos teas in nylon mesh bags before and after 90 days of burial. Psidium cattleianum increased the initial litter decomposition rate irrespective of precipitation and other soil properties. On the other hand, P. cattleianum increased the long-term litter stabilization factor of the Tea Bag Index in wetter sites. The accumulation of litter was likely caused by indirect effects of P. cattleianum through the alteration of soil moisture properties. In summary, this study shows that invasion by P. cattleianum could alter the soil properties in both wet and mesic sites, suggesting the possibility of change in composition and/or function of decomposers.
... Runoff and water would likely increase and replenishment of the islands' freshwater aquifer through cloud water interception would likely decrease. (Nanko, et al., 2013;Takahashi, et al., 2011). Because of its potential to outcompete native forest flora and its potential deleterious effects on watershed function, miconia has been prioritised for eradication on the Hawaiian Island of Oʽahu. ...
... Water recharge of the island's aquifers may also be at risk. A study on Hawaiʽi Island found that nativedominated 'ōhi'a forest intercepted 454 mm more cloud water than strawberry guava (Psidium cattleyanum -Myrtaceae) dominated forests due to the differences in bark structure and tree shape (Takahashi, et al., 2011). Miconia has smooth bark similar to strawberry guava and would likely have similar rates of cloud water interception. ...
Chapter
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The invasive tree Miconia calvescens (Melastomataceae) is a priority for control on the Hawaiian Island of Oʽahu due to its potential to replace native ʽōhiʽa (Metrosideros polymorpha, Myrtaceae) forests and degrade watershed function if allowed to establish. The Oʽahu Invasive Species Committee (OISC) is attempting to eradicate this species from the island of Oʽahu. OISC uses a buffer strategy based on estimated seed dispersal distance to determine the area under surveillance. This strategy has worked well enough to suppress the number of trees reaching reproductive age. The number of mature trees removed annually is now less than the number initially removed when the programme started in 2001. In 2016, just 12 mature trees were removed from 54.71 km2 surveyed compared to 2002, when 40 mature trees were removed from 8.26 km2 surveyed, a 96% drop in mature trees per square kilometre surveyed. However, miconia has a long-lived seed bank and can germinate after 20 years of dormancy in the soil. Funding shortages and gaps in surveys due to refusal of private property owners to allow access have resulted in some long-range extensions. OISC’s results suggest that seed bank longevity is an important factor when prioritizing invasive species risk and that allocating more resources at the beginning of a programme to eradicate a species with long-lived seed banks may be a better strategy than starting small and expanding.
... Similar to other invasive shade-tolerant woody species (Horvitz et al. 1998), strawberry guava is able to establish in intact forest where it dominates the understory and lower canopy. In Hawaiʻi, this invader changes rain forest structure (Asner et al. 2009), altering ecosystem processes (Takahashi et al. 2011) and reducing suitable habitat for native species (Paul Banko, personal communication). Also, large populations of insect pests of soft agriculturally important fruits such as papaya are supported by decaying strawberry guava fruit presenting a formidable challenge to agricultural production. ...
Article
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Understanding actual and potential selection on traits of invasive species requires an assessment of the sources of variation in demographic rates. While some of this variation is assignable to environmental, biotic or historical factors, unexplained demographic variation also may play an important role. Even when sites and populations are chosen as replicates, the residual variation in demographic rates can lead to unexplained divergence of asymptotic and transient population dynamics. This kind of divergence could be important for understanding long- and short- term differences among populations of invasive species, but little is known about it. We investigated the demography of a small invasive tree Psidium cattleianum Sabine in the rainforest of Hawaiʻi at four sites chosen for their ecological similarity. Specifically, we parameterized and analyzed integral projection models (IPM) to investigate projected variability among replicate populations in: (1) total population size and annual per capita population growth rate during the transient and asymptotic periods; (2) population structure initially and asymptotically; (3) three key parameters that characterize transient dynamics (the weighted distance of the structure at each time step from the asymptotic structure, the strength of the sub-dominant relative to the dominant dynamics, and inherent cyclicity in the subdominant); and (4) proportional sensitivity (elasticity) of population growth rates (both asymptotic and transient) to perturbations of various components of the life cycle. We found substantial variability among replicate populations in all these aspects of the dynamics. We discuss potential consequences of variability across ecologically similar sites for management and evolutionary ecology in the exotic range of invasive species.
... Early successional invasive plants often have higher stomatal conductance than native plants of the same growth form (Cavaleri & Sack, 2010), which-if leaf area also increases-could scale up to ecosystem-level differences in ET especially if leaf area also increases Huxman et al., 2005). In fog-affected forests of Hawaii, the invasive species Psidium cattleianum Sabine (Myrtaceae) develops a uniform canopy structure with a high density of small stems, smooth bark, and low epiphyte biomass; this trait contributes to lower cloud water interception and canopy storage (Takahashi et al., 2011). At a drier site, the same species generates higher stemflow than other invasive tree species (Safeeq & Fares, 2014), which may accelerate nutrient leaching. ...
Article
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Tropical ecosystems offer a unique setting for understanding ecohydrological processes, but to date such investigations have been limited. The purpose of this paper is to highlight the importance of studying these processes—specifically, how they are being affected by the transformative changes taking place in the tropics—and to offer an agenda for future research. At present, the ongoing loss of native ecosystems is largely due to agricultural expansion, but parallel processes of afforestation are also taking place, leading to shifts in ecohydrological fluxes. Similarly, shifts in water availability due to climate change will affect both water and carbon fluxes in tropical ecosystems. A number of methods exist that can help us better understand how changes in land use and climate affect ecohydrological processes; these include stable isotopes, remote sensing, and process-based models. Still, our knowledge of the underlying physical mechanisms, especially those that determine the effects of scale on ecosystem processes, remains incomplete. We assert that development of a knowledge base concerning the effects of transformative change on ecological, hydrological, and biogeochemical processes at different spatio-temporal scales is an urgent need for tropical regions, and should serve as a compass for emerging ecohydrologists. To reach this goal, we advocate a research agenda that expands the number and diversity of ecosystems targeted for ecohydrological investigations and connects researchers across the tropics. We believe that the use of big data and open source software—already an important integrative tool/skill for the young ecohydrologist—will be key in expanding research capabilities.
... Rainfall interception has been widely studied in humid tropical systems (see Safeeq and Fares 2014, Chu et al. 2014, Giambelluca and Gerold 2011, Holwerda et al. 2011, Takahashi et al. 2011. In most cases, deforestation scenarios have been associated with reduced interception, increased surface runoff (Maris 2015, Panday et al. 2015, and exacerbated streamflow peaks and low flows, as seen in Bruijnzeel and Scatena (2011), Ty, Sunada, and Ichikawa (2011), Laurance (2007, and Brookhuis and Hein (2016). ...
Thesis
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Despite the prevailing assumption that hydrological flow variation is amplified and runoff increased with deforestation, evidence behind these claims is limited for very moist tropical regions. Data derived from field observations are needed to productively manage forested watersheds, optimize global climate models, and inform policymaking. First, I used a case study from mature forest and crop fields in Costa Rica to improve understanding of hydrological effects of forest conversion in tropical forests. Furthermore, I conducted a systematic review of the impact of public policies on forest cover in Mesoamerica. Examining micrometeorological differences between mature forest and cropland, leaf wetness duration (LWD) was 5 times longer in the forest. Within crop species, papaya dried significantly slower than the shorter taro and sweet potato. Average daily evapotranspiration (ETcrop) as calculated by the FAO56 modified Penman-Monteith crop coefficient method was 2.75 mm for forest compared to crop values for papaya (1.83), taro (1.76), and sweet potato (1.43). These results suggest the possibility of higher runoff and alteration of rainfall recycling in the humid tropics following forest conversion to cropland. Canopy height and LWD seemed to be good indicators of differences in ETcrop. In order to successfully protect forests, the public policy type most likely to result in positive effects was market-based conservation, as zero cases were linked to increased deforestation or decreased forest cover. 81% of the community based management policy cases and 66% of the protected areas cases were positive. 83% of the agricultural policy cases resulted in more deforestation. In order to increase effectiveness of forest conservation strategies, scientific reporting, such as this study, contributes knowledge to help inform policy. It can be inferred that longer LWD is associated with higher evapotranspiration of intercepted rainfall and lower runoff ratios in tropical forests compared to croplands. Therefore future policy directed at hydrological services should consider estimates of runoff from agricultural conversion in their decision-making process and target watersheds with high flood hazard potentials associated with large-scale deforestation.
... In a Swiss forest vegetated with Norway spruce, soil CH 4 uptake rates were negatively correlated with soil moisture and decreased from 5.24 μmol m −2 h −1 to nearly zero as the soil moisture increased from 18.4% to 50.7% w/w (20.3% to 56.0% WFPS) (Hiltbrunner et al., 2012). Across our dataset, soil moisture in the native sites was, on average, 28.2% w/w (49.8% WFPS) and significantly decreased to 23.8% w/w (43.4% WFPS) in the invaded sites, probably because of higher evapotranspiration and interception of invasive plant species (Giambelluca et al., 2008;Takahashi et al., 2011). The reduction in soil moisture caused by plant invasion provides more aerobic conditions for CH 4 oxidation and facilitates the diffusion of CH 4 and O 2 from the atmosphere to soil, thereby stimulating terrestrial CH 4 uptakes. ...
Article
Approximately 17% of the land worldwide is considered highly vulnerable to non‐native plant invasion, which can dramatically alter nutrient cycles and influence greenhouse gas (GHG) emissions in terrestrial and wetland ecosystems. However, a systematic investigation of the impact of non‐native plant invasion on GHG dynamics at a global scale has not yet been conducted, making it impossible to predict the exact biological feedback of non‐native plant invasion to global climate change. Here, we compiled 273 paired observational cases from 94 peer‐reviewed articles to evaluate the effects of plant invasion on GHG emissions and to identify the associated key drivers. Non‐native plant invasion significantly increased methane (CH4) emissions from 129 kg CH4 ha–1 yr–1 in natural wetlands to 217 kg CH4 ha–1 yr–1 in invaded wetlands. Plant invasion showed a significant tendency to increase CH4 uptakes from 2.95 to 3.64 kg CH4 ha–1 yr–1 in terrestrial ecosystems. Invasive plant species also significantly increased nitrous oxide (N2O) emissions in grasslands from an average of 0.76 kg N2O ha–1 yr–1 in native sites to 1.35 kg N2O ha–1 yr–1 but did not affect N2O emissions in forests or wetlands. Soil organic carbon, mean annual air temperature (MAT), and nitrogenous deposition (N_DEP) were the key factors responsible for the changes in wetland CH4 emissions due to plant invasion. The responses of terrestrial CH4 uptake rates to plant invasion were mainly driven by MAT, soil NH4+, and soil moisture. Soil NO3–, mean annual precipitation, and N_DEP affected terrestrial N2O emissions in response to plant invasion. Our meta‐analysis not only sheds light on the stimulatory effects of plant invasion on GHG emissions from wetland and terrestrial ecosystems but also improves our current understanding of the mechanisms underlying the responses of GHG emissions to plant invasion.
... These areas have long cattleranching histories, where forests and dryland field systems were converted into large pasture lands early in the 1800s, and where ranching persists today. Given that Hawaiʻi's native forests may have large cloud water interception 36 , deforestation may have led to less water capture over time. The coupled climate and environmental changes likely altered the moisture regime to such a degree that the area's indigenous agroecosystems cannot exist there under current conditions. ...
Article
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The value of land-use strategies that increase food production while conserving biodiversity is widely recognized. Many indigenous agroecosystems are productive, adaptive and ecologically principled, but are largely overlooked by planning in terms of their potential to meet current and future food needs. We developed spatial distribution models of indigenous agroecosystems in Hawai‘i to identify their potential past distribution, productive and carrying capacities, and future potential under current land-use and mild-to-severe future climate scenarios. Our results suggest that Hawaiʻi’s traditional agroecosystems could have had production levels comparable to consumption today. Carrying capacity estimates support hypotheses of large pre-colonial Hawaiian populations (>800,000). Urban development has reduced (−13%) traditional agroecosystems but 71% remain agriculturally zoned. Projected effects of three future climate scenarios vary from no change in potential production to decreases of 19% in the driest and warmest end-of-century scenario. This study highlights the food-producing potential of indigenous agriculture even under land-use and climate changes, and the value of their restoration into the future. © 2019, The Author(s), under exclusive licence to Springer Nature Limited.
... Based on evapotranspiration maps of Hawaii, approximately one-quarter of total evapotranspiration is accounted for by canopy interception (Giambelluca et al., 2014), and Safeeq and Fares (2014) found Hawaiian forests dominated by invasive tree species to intercept between 23 and 45% of incoming precipitation. Takahashi et al. (2011) found that the invasion of a Metrosideros forest resulted in more rainfall interception and less water available for aquifer recharge in comparison to the uninvaded forest. With respect to effects on soil evaporation, removal of invasive grasses in Hawaiian dry forests has been found both to increase (Thaxton et al., 2012) and decrease soil moisture (D'Antonio et al., 1998), indicating that results are dependent on site-specific attributes and methods of removal. ...
Article
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While the supply of freshwater is expected to decline in many regions in the coming decades, invasive plant species, often ‘high water spenders’, are greatly expanding their ranges worldwide. In this study, we quantified the ecohydrological differences between native and invasive trees and also the effects of woody invasive removal on plot-level water use in a heavily invaded mono-dominant lowland wet tropical forest on the Island of Hawaii. We measured transpiration rates of co-occurring native and invasive tree species with and without woody invasive removal treatments. Twenty native Metrosideros polymorpha and 10 trees each of three invasive species, Cecropia obtusifolia, Macaranga mappa and Melastoma septemnervium, were instrumented with heat-dissipation sap-flux probes in four 100 m2 plots (two invaded, two removal) for 10 months. In the invaded plots, where both natives and invasives were present, Metrosideros had the lowest sap-flow rates per unit sapwood, but the highest sap-flow rates per whole tree, owing to its larger mean diameter than the invasive trees. Stand-level water use within the removal plots was half that of the invaded plots, even though the removal of invasives caused a small but significant increase in compensatory water use by the remaining native trees. By investigating the effects of invasive species on ecohydrology and comparing native vs. invasive physiological traits, we not only gain understanding about the functioning of invasive species, but we also highlight potential water-conservation strategies for heavily invaded mono-dominant tropical forests worldwide. Native-dominated forests free of invasive species can be conservative in overall water use, providing a strong rationale for the control of invasive species and preservation of native-dominated stands.
... They concluded that rainfall partitioning at the rainfall event level depended strongly on the amount of rainfall and differed significantly between the leafed and the leafless period of the year. Takahashi et al. (2011) reported that due to the difference of leaf traits, the proportion of gross rainfall reaching the forest floor were higher in native Metrosideros polymorpha-dominated forests than in invaded, Psidium cattleianum-dominated forests within Hawai'i Volcanoes National Park. Total interception loss was higher in a mature forest (17% of annual rainfall) than in a secondary forest (8% of annual rainfall) (Holwerda et al. 2010). ...
Article
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The dynamic properties of rainfall interception were investigated at three growth stages in Chinese fir plantations. The results showed annual interception ratio was significantly higher in mature stands than in young stands. For a storm event, interception rainfall amount increased with increasing rainfall, but interception ratio decreased. In contrast to dry season conditions, interception amount was high in the wet seasons, while interception ratio was low. The rates of changes in interception ratio were extremely rapid in small rainfall events. There was little stemflow in Chinese fir forests due to their pyramid-shaped crown and thick and rough bark of the trees. The power model was suitable to describe the interception process for an individual rainfall event of any aged stands. Our results indicated that the interception process varied with different aged stands of Chinese fir plantations due to contrasting canopy structures.
... Island-w future land cover scenarios, for both the wet and dry future climate strongly impacted groundwater recharge in localized areas. Th Futures 1 and 4 due to the substantial increases in estimated irriga i can also affect processes that influence groundwater recharge, including cloud-water interception, net precipitation, infiltration, direct runoff, and transpiration [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. ...
Article
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This project developed an integrated land cover/hydrological modeling framework using remote sensing and geographic information systems (GIS) data, stakeholder input, climate information and projections, and empirical data to estimate future groundwater recharge on the Island of Maui, Hawaiʻi, USA. End-of-century mean annual groundwater recharge was estimated under four future land cover scenarios: Future 1 (conservation-focused), Future 2 (status-quo), Future 3 (development-focused), and Future 4 (balanced conservation and development), and two downscaled climate projections: a coupled model intercomparison project (CMIP) phase 5 (CMIP5) representative concentration pathway (RCP) 8.5 “dry climate” future and a CMIP3 A1B “wet climate” future. Results were compared to recharge estimated using the 2017 baseline land cover to understand how changing land management and climate could influence groundwater recharge. Estimated recharge increased island-wide under all future land cover and climate combinations and was dominated by specific land cover transitions. For the dry future climate, recharge for land cover Futures 1 to 4 increased by 12%, 0.7%, 0.01%, and 11% relative to 2017 land cover conditions, respectively. Corresponding increases under the wet future climate were 10%, 0.9%, 0.6%, and 9.3%. Conversion from fallow/grassland to diversified agriculture increased irrigation, and therefore recharge. Above the cloud zone (610 m), conversion from grassland to native or alien forest led to increased fog interception, which increased recharge. The greatest changes to recharge occurred in Futures 1 and 4 in areas where irrigation increased, and where forest expanded within the cloud zone. Furthermore, new future urban expansion is currently slated for coastal areas that are already water-stressed and had low recharge projections. This study demonstrated that a spatially-explicit scenario planning process and modeling framework can communicate the possible consequences and tradeoffs of land cover change under a changing climate, and the outputs from this study serve as relevant tools for landscape-level management and interventions.
... It is reported that CPA increases as DBH increases (Park & Hattori, 2002). In addition, numerous studies have found that changes in DBH are positively correlated with SF volume (Germer et al., 2010;Park & Hattori, 2002;Takahashi et al., 2011). However, Schooling and Carlyle-Moses (2015) found a negative correlation between DBH and SF for 2 to <5 mm rainfall depth class and reported large DBH trees with larger boles and greater surface area likely afford greater water storage capacity. ...
Article
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Stemflow (SF) has been recognized as an important process which can exert considerable effects on the hydrology, biogeochemistry, and ecology of wooded ecosystems. The aim of this study was to quantify the relationship between SF (yields and funneling ratios, FR) of beech (F. orientalis) trees and rainfall characteristics, to evaluate the effects of tree traits on SF yield and the magnitudes of FR in differing rainfall classes. Event‐based measurements were carried out from April 2016 to November 2017 during the leafed‐out periods in a natural uneven‐aged beech stand located in the Hyrcanian forest of Iran. Tree density in the studied plot was 188 tree ha‐1 with a basal area (BA) of 51 m2 ha‐1. SF volume was measured in three diameter classes (10‐40 cm, 40‐70 cm and > 70 cm; n=3 per class). During the 25 rainfall events SF, SF% and FR were 3.22 mm, 0.41% and 1.11 on average, respectively. The linear regression analysis revealed that gross rainfall (GR) had the strongest correlation with SF yield and FR (P value <0.01). The linear regression with the trees structural traits indicated that CPA (crown projected area), DBH (diameter at breast height) and MCP (mosses cover percentage), respectively, strongly influence SF yield for rainfall<15 to >50 mm. FR significantly decreased with increasing tree height (H), DBH and MCP (all p‐values<0.05). Smaller trees concentrated more SF than tall and large DBH trees. Pearson correlation analysis indicated H, CPA and MCP were positively and significantly correlated to DBH (P value <0.01; r≥0.87). Therefore, SF generation in the present study is more associated with DBH. Our findings could assist managers to optimize the management strategies of deciduous forest via promotion of some large DBH trees along with small DBH trees to optimize water inputs via SF in water‐limited forest ecosystems.
... Monotypic stands of non-native vegetation, such as strawberry guava, pose a different but also important threat to watershed hydrology (Calder andDye, 2001 Huenneke andVitousek, 1990). The spread of Psidium cattleianum, introduced to Hawai'i from Brazil in the 1800s, alters community composition by shading understory species and displacing epiphytic communities; increasing canopy evaporation and stem flow while reducing cloudwater interception and throughfall (Mair and Fares, 2010, Safeeq and Fares, 2012, Mudd and Giambelluca, 2006, Takahashi et al., 2011. Psidium cattleianum spreads clonally through rhizomes and produces large quantities of fruit that pigs consume and distribute (Huenneke and Vitousek, 1990). ...
... Other studies are purely quantitative, being based on empirically derived equations that model some aspects of invasion (e.g. population dynamics; interspecific interactions, alterations to nutrient cycling processes; Harrison et al. 2006;Gó mez-Aparicio and Canham 2008;Atwood et al. 2010;Takahashi et al. 2011). Modelling methods allow researchers to address research questions that would otherwise be difficult-if not impossible-due to logistical, economic or ethical constraints (Jackson et al. 2000). ...
Article
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Methods used to evaluate the ecological impacts of biological invasions vary widely from broad scale observational studies to removal experiments in invaded communities and experimental additions in common gardens and greenhouses. Different methods provide information at diverse spatial and temporal scales with varying levels of reliability. Thus, here we provide a synthetic and critical review of the methods used to evaluate the impacts of plant invasions and provide recommendations for future research. We review the types of methods available and report patterns in methods used, including the duration and spatial scale of studies and plant functional groups examined, from 410 peer-reviewed papers published between 1971 and 2011. We found that there has been a marked increase in papers published on plant invasion impacts since 2003 and that more than half of all studies employed observational methods while less than 5% included predictive modeling. Most studies were temporally and spatially restricted with 51% of studies lasting less than one year and almost half of all studies conducted in plots or mesocosms less than 1m(2). There was also a bias in life form studied: more than 60% of all studies evaluated impacts of invasive forbs and graminoids while less than 16% focused on invasive trees. To more effectively quantify invasion impacts, we argue that longer-term experimental research and more studies that use predictive modeling and evaluate impacts of invasions on ecosystem processes and fauna are needed. Combining broad-scale observational studies with experiments and predictive modeling may provide the most insight into invasion impacts for policy makers and land managers seeking to reduce the effects of plant invasions. Published by Oxford University Press on behalf of the Annals of Botany Company.
... Feral pigs (Sus scofa) in Hawai'i have been observed to negatively impact soil and groundcover, and consequently infiltration and runoff (Dunkell et al., 2011;Strauch et al., 2016). Because pigs and other invasive ungulates are also a major pathway for invasive plant seed dispersal, ungulate exclusion from pristine native forest areas upgradient of the aquifer impedes invasion by alien plant species, which tend to have higher evapotranspiration rates (Giambelluca et al., 2008;Kagawa et al., 2009;Cavaleri et al., 2014) and lower fog capture potential (Takahashi et al., 2011) than native canopy tree species. Thus, investment in ungulate-proof fencing, by limiting potential negative impacts of invasive species, supports the maintenance of recharge capture for the downstream groundwater resource (Fig. 1). ...
Article
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We develop and operationalize an integrated groundwater and watershed management model using data from the Kīholo aquifer on the west coast of Hawai'i Island. Results from a numerical simulation suggest that investment in fencing (passive management) is preferred to invasive species removal (active management) if we are limited to selecting a single conservation tool. However, using both instruments jointly increases net present value relative to using either instrument independently in most cases tested, and the additional benefit of invasive species removal increases as water becomes scarcer. The general results are largely insensitive to variations in the invasive species uptake rate and recharge benefits of fencing, and in all cases, use of both instruments reduces the loss resulting from the imposition of a safe minimum standard for groundwater-dependent ecosystems more effectively than either instrument alone.
... Many invasive plants have the capacity to replace native forests by generating monospecific and dense invaded patches (Crooks, 2002;Richardson and Rejmánek, 2011), which could also alter the net amount of rainfall reaching the soil (Imada et al., 2013;Mair and Fares, 2010;Takahashi et al., 2011). However, the hydrometeorological mechanisms behind rainfall partitioning by invasive species, as well as its ecohydrological implications on the invasion processes, remain largely unknown. ...
Article
Vegetation canopy plays a key role in the local water balance by partitioning rainfall into interception, throughfall and stemflow in dry forests. Many invasive plants have the capacity to replace native species and alter the net amount and spatial distribution of rainfall reaching the soil. In this paper, we aimed to compare the rainfall partitioning for the invader Ligustrum lucidum and the dominant native Lithraea molleoides, to evaluate the influence of morphological characteristics on stemflow generation in both species, and to explore spatio-temporal patterns of throughfall at stand scale. Stemflow percentage for L. lucidum was hugely higher than for L. molleoides (18 and 1%, respectively), which overcompensated its lower throughfall percentage (58.1 and 68.6%, respectively). Interception losses were lower for L. lucidum than for L. molleoides (23.2 and 30.6%, respectively). The minimum rainfall amount needed to generate throughfall and stemflow was 1.8 and 0.5 mm for L. lucidum, while 2.2 and 7.2 mm for L. molleoides. The differences in morphological characteristics between species mainly explained the stemflow generation. The increment on tree basal area, projected canopy area, and number of branches favored stemflow in L. lucidum, but not in L. molleoides. The throughfall spatial patterns showed that the dripping from different canopy densities was homogenous in L. lucidum stands, whereas throughfall increase towards more opened-canopies in L. molleoides stands. Lateral inflows were registered from small-scale crown sections at both forest stands, but less frequent in L. lucidum stands. The time stability of throughfall pattern differed between forest stands. Based on our results, relatively higher stemflow and lower interception losses for L. lucidum than for L. Molleoides may represent a competitive advantage in terms of plant invasion in water-limited ecosystems. These findings highlight the need for further inquiries determining the underlying role of rainfall partitioning in the invasion process of woody species.
... Protection of native vegetation is a priority because native forests in Hawaii are comprised of ecologically-and culturally-valuable plant species more likely to support endemic bird and insect populations. Native vegetation can also have lower evapotranspiration rates and can contribute to stream baseflow via fog drip at high elevations more effectively than nonnative vegetation (Takahashi et al., 2011). Native vegetation cover in this study is characterized by the Hawaii Habitat Quality Dataset, which delineates areas of native forests with limited nonnative vegetation (Price et al., 2012). ...
Article
Functional ecosystems depend on biotic and abiotic connections among different environmental realms, including terrestrial, freshwater, and marine habitats. Accounting for such connections is increasingly recognized as critical for conservation of ecosystems, especially given growing understanding of the way in which anthropogenic landscape disturbances can degrade both freshwater and marine habitats. This need may be paramount in conservation planning for tropical island ecosystems, as habitats across realms are often in close proximity, and because endemic organisms utilize multiple habitats to complete life histories. In this study, we used Marxan analysis to develop conservation planning scenarios across the five largest islands of Hawaii, in one instance accounting for and in another excluding habitat connectivity between inland and coastal habitats. Native vegetation, perennial streams, and areas of biological significance along the coast were used as conservation targets in analysis. Cost, or the amount of effort required for conservation, was estimated using an index that integrated degree and intensity of anthropogenic landscape disturbances. Our results showed that when connectivity is accounted for among terrestrial, freshwater, and marine habitats, areas identified as having high conservation value are substantially different compared to results when connectivity across realms is not considered. We also showed that the trade-off of planning conservation across realms was minimal and that cross-realm planning had the unexpected benefit of selecting areas with less habitat degradation, suggesting less effort for conservation. Our cross-realm planning approach considers biophysical interactions and complexity within and across ecosystems, as well as anthropogenic factors that may influence habitats outside of their physical boundaries, and we recommend implementing similar approaches to achieve integrated conservation efforts.
... With seeds readily dispersed by birds and pigs, it has become a dominant invader in wet forests of tropical islands (Lorence and Sussman 1986;Space 2013), for example, forming dense thickets and displacing native species across tens of thousands of hectares in Hawaii (Fig. 2.5). In addition to reducing habitat for many endangered species (State of Hawaii 2011), strawberry guava increases water loss from forested watersheds (Takahashi et al. 2011), impedes sustainable native hardwood forestry (Baker et al. 2009), and serves as the primary reservoir host for a major fruit fly pest of agriculture (Vargas et al. 1990). The USDA Forest Service developed a leaf-galling scale insect (Tectococcus ovatus) as a biological control agent, with the intention of substantially reducing vegetative growth and fruit production of strawberry guava (State of Hawaii 2011). ...
Chapter
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The introduction, establishment, and spread of invasive species in terrestrial and aquatic environments is widely recognized as one of the most serious threats to the health, sustainability, and productivity of native ecosystems (Holmes et al. 2009; Mack et al. 2000; Pyšek et al. 2012; USDA Forest Service 2013). In the United States, invasive species are the second leading cause of native species endangerment and extinction, and their costs to society have been estimated at $120 billion annually (Crowl et al. 2008; Pimentel et al. 2000, 2005). These costs include lost production and revenue from agricultural and forest products, compromised use of waterways and terrestrial habitats, harm to human and animal health, reduced property values and recreational opportunities, and diverse costs associated with managing (e.g., monitoring, preventing, controlling, and regulating) invasive species (Aukema et al. 2011; Pimentel et al. 2005). The national significance of these economic, ecological, and social impacts in the United States has prompted various actions by both legislative and executive branches of the Federal Government (e.g., the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990; the Noxious Weed Control and Eradication Act of 2002; Executive Order 13112 of 1999, amended in 2016).
... Humans have dramatically affected the hydrologic cycle through land-cover alteration (Abbott et al., 2019). In Pacific Islands, anthropogenic land-cover change has been linked to disruption of hydrologic processes, such as stream baseflow, cloud water interception, infiltration, soil moisture parameters, and surface water runoff (Loague et al., 1996;Ziegler and Giambelluca, 1998;Kagawa et al., 2009;Takahashi et al., 2011;Perkins et al., 2012;Izuka et al., 2018). Expansion of impervious surfaces associated with human development increases surface runoff, thereby decreasing groundwater recharge and other water budget components (e.g. ...
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Study region Oceania, South Pacific, Polynesia. Study Focus Changing climates have the potential to significantly impact global water resources availability. On many volcanic islands, groundwater is the primary drinking water source, thereby making it essential to manage this limited resource carefully. In this study, we developed high temporal and spatial resolution groundwater recharge estimates for the Island of Tutuila, American Samoa using the Soil Water-Balance-2 (SWB2) model. Additionally, we predicted future recharge by running the calibrated model with combinations of dynamically downscaled general circulation climate model (GCM) predictions, and future land-cover scenarios developed collectively with local stakeholder groups. New hydrological insights Present-day results indicate 57 % of Tutuila’s rainfall becomes groundwater recharge, 8 % evaporates from the canopy, 15 % evapotranspires, and 20 % discharges as stormflow-runoff. Future climate scenarios suggest recharge may increase by 8 % or 14 % depending on global emissions. Land-cover was a less significant driver of hydrologic change, although increases in impervious surfaces showed a negative impact on recharge. This work is maintained as an active open-source project on GitHub, the world’s leading software development platform, thereby enhancing transparency, reproducibility, and participation from stakeholders and managers in American Samoa. This study is the first of its kind from a location within the South Pacific Convergence Zone, and provides insights into how human activities on global and local levels affect the future sustainability of essential resources.
... Despite the hydrological and ecological importance of cloud forest ecosystems, very few studies have quantified the wet canopy evaporation, and of these, only a few have also measured sap flow and canopy wetness Takahashi et al., 2011). Therefore, our study objectives were the following: ...
Article
Evapotranspiration (ET) and canopy wetness were measured over a 2-year intensive field campaign at the Chi-Lan Mountain cloud forest site in Taiwan. Eddy covariance and sap flow methods were applied to measure ET and tree sap flow of the endemic yellow cypress (Chamaecyparis obtusa var. formosana). ET was 553 mm yr−1 over the study period with an annual rainfall and fog deposition of 4893 and 288 mm yr–1, respectively. The duration of canopy wetness exceeded actual fog or rain events (mostly in the afternoon), and the intercepted water was evaporated later in the following dry morning. The cumulative wet duration accounted for 52% of time over the study period, which was longer than the duration of rainfall and fog altogether (41%). As it adapted to the extremely moist environment, the yellow cypress behaved in a wet-enhanced/dry-reduced water use strategy and was sensitive to short periods of dry atmosphere with high evaporation potential. During dry days, the sap flow rate rose quickly after dawn and led to conservative water use through midday and the afternoon. During periodically wet days, the canopy was mostly wetted in the morning, and the interception evaporation contributed largely to the morning ET. The initiation of morning sap flow was postponed 1–3 h, and the sap flow rate tended to peak later at midday. The midday canopy conductance was higher in the periodically wet days (10.6 mm s–1) as compared with 7.6 mm s−1 in the dry days. Consequently, the dry-reduced water use strategy led to much lower annual ET with respect to the available energy (~46%) and high precipitation input (~11%). The moist-adapted ecohydrology we report reveals the vulnerability of montane cloud forests to prolonged fog-free periods. More research is urgently needed to better understand the resilience of these ecosystems and formulate adaptive management plans. Copyright © 2012 John Wiley & Sons, Ltd.
... Ongoing climate change may introduce yet further regime shifts in Hawaiian forests owing to differences between native and non-native trees in their ecohydrology. Differences in canopy structure and epiphyte abundance between native and non-native species cause differences in cloud water interception (Juvik and Nullet, 1995;Takahashi et al., 2011), further exacerbating drought effects. Several studies have shown lower water-use efficiency of non-native plants (see Section 5), with higher transpiration rates reducing local soil moisture (Michaud et al., 2015) and downstream watershed yields (Strauch et al., 2017). ...
Article
As the most remote archipelago in the world, the Hawaiian Islands are home to a highly endemic and disharmonic biota that has fascinated biologists for centuries. Forests are the dominant terrestrial biome in Hawai‘i, spanning complex, heterogeneous climates across substrates that vary tremendously in age, soil structure, and nutrient availability. Species richness is low in Hawaiian forests compared to other tropical forests, as a consequence of dispersal limitation from continents and adaptive radiations in only some lineages, and forests are dominated by the widespread Metrosideros species complex. Low species richness provides a relatively tractable model system for studies of community assembly, local adaptation, and species interactions. Moreover, Hawaiian forests provide insights into predicted patterns of evolution on islands, revealing that while some evidence supports “island syndromes,” there are exceptions to them all. For example, Hawaiian plants are not as a whole less defended against herbivores, less dispersible, more conservative in resource use, or more slow-growing than their continental relatives. Clearly, more work is needed to understand the drivers, sources, and constraints on phenotypic variation among Hawaiian species, including both widespread and rare species, and to understand the role of this variation for ecological and evolutionary processes, which will further contribute to conservation of this unique biota. Today, Hawaiian forests are among the most threatened globally. Resource management failures – the proliferation of non-native species in particular – have led to devastating declines in native taxa and resulted in dominance by novel species assemblages. Conservation and restoration of Hawaiian forests now rely on managing threats including climate change, ongoing species introductions, novel pathogens, lost mutualists, and altered ecosystem dynamics through the use of diverse tools and strategies grounded in basic ecological, evolutionary, and biocultural principles. The future of Hawaiian forests thus depends on the synthesis of ecological and evolutionary research, which will continue to inform future conservation and restoration practices.
... Stemflow volume and its nutrient contents generally depend on the meteorological factors: such as gross rainfall amount (Levia, 2004;Andre et al., 2008;Gonzalez-Ollauri et al., 2020), rainfall direction and intensity (Muzylo et al., 2012;Owens et al., 2006), fog (McJannet et al., 2007), and drivenwind direction (Dunkerley, 2014;Van Stan et al., 2011), among others. Moreover, stemflow is also influenced by canopy structure which depends on many interrelated factors such as plant species (lida et al., 2005(lida et al., , Cayuela et al., 2018, plant growth stage (Siles et al., 2010), plant density (Schroth et al., 2001), plant morphology (Takahashi et al., 2011), plant age (Buttle & Farnsworth, 2012;Murakami, 2009), succession phase (lida et al., 2005), epiphyte, fungi and bacteria presence (Ceccherini et al., 2008;Hölscher et al., 2004), and branch or bark characteristics (Cayuela et al., 2018;Gonzalez-Ollauri et al., 2020;Van Stan & Levia, 2010). In addition, the seasonality of the rainfall regime can add complexity to rainfall-stemflow relationship. ...
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Rainfall is generally partitioned into throughfall, stemflow, and interception in ecosystems. Stemflow variability can affect the hydrology, ecology, and soil chemistry patterns. However, the influence of canopy structure and rainfall characteristics on stemflow production in sugarcane plantations which are important for renewable energy production remain poorly understood. By using funnels attached to the sugarcane stems, the present study determined the stemflow amount during the period of sugarcane growth and its relationship with plant development. Approximately, 14% of gross rainfall reached the soil as stemflow, and the funneling ratios was 60. In general, it was observed a positive relationship between stemflow rates with both leaf area index and plant height. This was attributed to an increasing number of acute branching angles of the sugarcane leaves as well as high stem tillering and density. However, at the end of growth cycle, stemflow rate was lower than in previous periods which can be attributed to changes in sugarcane canopy such as stems inclination and lodging, reducing the effectiveness of water conveyance along the stem. Our study showed the need to include stemflow to better understand the hydrology of sugarcane plantations.
... A reduction in the availability of freshwater from this source could lead to the use of other, more expensive methods of freshwater production to meet public demand (Burnett et al. 2020). High elevation 'ōhi'a forests protect watersheds across the state, and, because of their lower water usage compared to fast-growing non-native species, allow for greater recharge of groundwater (Kagawa et al. 2009;Takahashi et al. 2011;Cavaleri et al. 2014). Additionally, a study by Burnett et al. (2017) found that the cost of protecting freshwater by conserving native Hawaiian forests is less than half the cost of freshwater production via large-scale reverse-osmosis of seawater per thousand liters. ...
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Metrosideros polymorpha Gaud. (‘ōhi‘a) is the most abundant native forest tree in Hawai‘i and a keystone species of cultural, ecological, and economic importance. ‘Ōhi‘a forests, particularly on Hawaiʻi Island, are being severely impacted by Rapid ‘Ōhi‘a Death (ROD), which is caused by the fungal pathogens Ceratocystis lukuohia and C. huliohia. ROD is characterized by branch dieback, crown wilting, and mortality. Initial disease resistance screening of four varieties of M. polymorpha with C. lukuohia demonstrated that varieties may differ in susceptibility. Several survivors of field or screening-based infections still exist, providing strong impetus for the establishment of the ‘Ōhiʻa Disease Resistance Program (ʻŌDRP). Here, we outline a framework for guiding the ʻŌDRP throughout the process of identifying and developing ROD resistance in M. polymorpha and, possibly, all Hawaiian Metrosideros species. Core ʻŌDRP projects include: (1) evaluating and operationalizing methods for greenhouse-based production and screening of test plants; (2) greenhouse screening of seedlings and rooted cuttings sampled from native Metrosideros throughout Hawaiʻi; (3) establishing field trials to validate results from greenhouse assays; (4) understanding environmental and genetic drivers of resistance to characterize the durability of resistance to ROD; (5) developing remote sensing and molecular methods to rapidly detect ROD-resistant individuals; and (6) conducting breeding trials to improve the degree and durability of ROD resistance. Ultimately, the ʻŌDRP seeks to produce ROD-resistant material for the perpetuation of M. polymorpha across Hawai‘i, with the goal of preserving the ecology, culture, and communities that are dependent on this tree species.
... Calibrated canopy parameters p and S are comparable with values found in the literature (Aston, 1979;Holwerda et al., 2012;Lloyd, Gash, Shuttleworth, & de O. Marques, 1988;Takahashi et al., 2011;Wallace & McJannet, 2008). Although the value of p is comparable with the one found by Pryet et al. (2012) and slow drainage capacity (Köhler, Tobón, Frumau, & Bruijnzeel, 2007;Richardson, Richardson, Scatena, & Mcdowell, 2000;Villegas et al., 2008). ...
Article
With changes in climate looming, quantifying often-overlooked components of the canopy water budget, such as cloud water interception (CWI), is increasingly important. Commonly, CWI quantification requires detailed continuous measurements, which is extremely challenging, especially when throughfall is included. In this study, we propose a simplified approach to estimate CWI using the Rutter-type interception model, where CWI inputs in the canopy vegetation are proportional to fog interception measured by an artificial fog gauge. The model requires the continuous acquisition of meteorological variables as input and calibration datasets. Throughfall measurements below the forest are used only for calibration and validation of the model, thus, CWI estimates can be provided even after the cessation of throughfall monitoring. This approach provides an indirect and undemanding way to quantify CWI by vegetation and allows the identification of its controlling factors, which could be useful to the comparison o
Chapter
Ceratocystis lukuohia and Ceratocystis huliohia are two newly recognized fungi that have arrived in Hawai‘i and are causing a serious vascular wilt and canker disease, respectively, of ‘ōhi‘a trees (Metrosideros polymorpha), the most common and important tree species in Hawai‘i. Management of these diseases has presented challenges due to unique etiological aspects and the exceptionally pathogenic nature of one of these fungi (C. lukuohia) once it gains access to the tree’s vascular tissue. Careful study of the spread of the pathogens has resulted in an understanding of the role of ambrosia beetles and the frass they produce that carries the pathogen, as well as the wounding of trees by many different agents by which the pathogen can access and infect the vascular tissue. A variety control measures are being used. These include a state-of-the-art monitoring program to detect diseased and recently killed trees and molecular biology approaches that can confirm if a given tree was infected by Ceratocystis. Based on monitoring more than one million trees have been estimated as killed by the diseases to date. A major part of the program includes the deployment of a field crew that seeks out and fells large infected ‘ōhi‘a trees as these trees are the main source of most of the infective Ceratocystis-laden frass. Long-term control measures also include fencing of some forests to reduce the amount of wounding to ‘ōhi‘a trees by feral cattle and pigs that allows entry of the fungi and quarantine restrictions to ensure there will be no inter-island movement of the pathogens in ‘ōhi‘a products. Finally, methods are also being developed to restore ‘ōhi‘a forests affected by these diseases by determining effective regeneration practices and developing genetically resistant ‘ōhi‘a stock. Hawai‘i has an active extension program dedicated to providing information on how residents and visitors can contribute to protecting ‘ōhi‘a trees from these diseases. More than 500,000 people have participated in this program. Hawai‘i residents have a very deep appreciation for this tree species and do what they can to help prevent these diseases from destroying more of their most treasured tree species.
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Many geoscientists now recognize stemflow as an important phenomenon which can exert considerable effects on the hydrology, biogeochemistry, and ecology of wooded ecosystems and shrublands. Despite the explosive growth of stemflow research, until this review there has been no comprehensive attempt to summarize and synthesize this literature since 2003. Topical areas of substantive new knowledge in stemflow research include: (1) the interrelationships among stemflow and meteorological conditions, especially within individual rain events; (2) the dynamic interplay between stemflow and canopy structure; (3) stemflow and the cycling of solutes and transport of particulate matter; (4) stemflow and its interactions with canopy fungi and corticolous lichens; and (5) stemflow-soil interactions. Each of these five topical areas of substantive new stemflow research are summarized and synthesized, with areas of future research opportunities discussed. In addition, we have reviewed the parameters which can be used to describe stemflow and critically evaluate their utility for different purposes. This review makes a call for scientists studying stemflow to utilize common metrics in an effort to increase the cross-site comparability of stemflow studies. Capitalizing on the insights of prior research, exciting research opportunities await hydrologists, biogeoscientists, and forest ecologists who will conduct studies to deepen our knowledge of stemflow which will enable a better and more accurate framing of stemflow in the larger context of watershed hydrology and biogeochemistry.
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Background/Question/Methods In tropical island systems, freshwater is a vital resource for agriculture, development, consumption, and native biota. While freshwater resources are threatened by climate change and invasive species, few studies have examined how these stressors or their potential interactions affect stream flow in tropical watersheds. We used the Distributed Hydrology-Soil-Vegetation Model (DHSVM) to assess the effect of climate warming, altered precipitation and expanding invasive species cover on stream flow in 87 watersheds located along the Hilo-Hamakua Coast on Hawaii Island. Watersheds were located along a highly constrained precipitation gradient spanning 3,500 mm in mean annual precipitation (MAP), while all other variables (landcover, geomorphology, topography) were held constant, thus providing a space-for-time substitution examining the impacts of changing MAP. Using the DHSVM calibrated for a six-year period (water years 2006 to 2011), we assessed how 1) mean annual temperature change; 2) MAP change; and 3) change in Psidium cattleianum (strawberry guava) cover will influence daily, monthly, and annual water flow as well as flow variability. Results/Conclusions Changes in MAP were the principle driver of stream flow while increased spread of P. cattleianum cover also reduced downstream flow. We also found a negative relationship between modeled flow variability (Q10:Q90) and MAP, and a positive relationship between modeled flow variability and watershed size across the precipitation gradient. Furthermore, watersheds with higher MAP experienced a greater loss of mean monthly stream flow compared to similarly-sized watersheds with lower MAP, whereas the percent of total flow lost was greater in lower MAP streams. Watersheds with lower MAP had much more variable stream flow compared to similarly-sized watersheds with higher MAP. We conclude that predicted climate and vegetation changes in tropical environments will decrease stream flow and increase flow variability, with anticipated impacts on human and biological systems, especially downstream water users and in-stream freshwater biota. Restoration of degraded and/or invaded forest will reduce the impact of climate change variables on stream flow.
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The control of dominant, non-native trees can alter the water balance of soils in forest ecosystems via hydrological processes, which results in changes in soil water environments. To test this idea, we evaluated the effects of the mortality of an invasive tree, Casuarina equisetifolia Forst., on the water content of surface soils on the Ogasawara Islands, subtropical islands in the northwestern Pacific Ocean, using a manipulative herbicide experiment. Temporal changes in volumetric water content of surface soils at 6cm depth at sites where all trees of C. equisetifolia were killed by herbicide were compared with those of adjacent control sites before and after their mortality with consideration of the amount of precipitation. In addition, the rate of decrease in the soil water content during dry periods and the rate of increase in the soil water content during rainfall periods were compared between herbicide and control sites. Soil water content at sites treated with herbicide was significantly higher after treatment than soil water content at control sites during the same period. Differences between initial and minimum values of soil water content at the herbicide sites during the drying events were significantly lower than the corresponding differences in the control quadrats. During rainfall periods, both initial and maximum values of soil water contents in the herbicided quadrats were higher, and differences between the maximum and initial values did not differ between the herbicided and control quadrats. Our results indicated that the mortality of non-native trees from forest ecosystems increased water content of surface soils, due primarily to a slower rate of decrease in soil water content during dry periods.
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Isotopes of water (²H/¹H and ¹⁸O/¹⁶O) are commonly used to trace hydrological processes such as moisture recycling, evaporation loss, and moisture source region and often vary temporally in a given region. This study provides a first‐ever characterization of temporally‐variable precipitation mechanisms San Cristóbal Island, Galápagos. We collected fog, rain and throughfall samples over three field seasons to understand the mechanisms driving seasonal and event‐based variability in the isotopic composition of precipitation in Galápagos. We establish that fog is a common phenomenon on San Cristóbal, especially during the dry season, and we found that fog is consistently enriched compared to co‐collected rainfall. We further suggest that the relative contribution of fog formed via different mechanisms (orographic, advective, radiation) varied seasonally. We found that the source region is the most dominant control of the isotopic composition of rainfall in the Galápagos at both the seasonal and event scales, but sub‐cloud evaporative processes (the non‐traditional manifestation of the amount effect) became a dominant control on the isotopic composition of rainfall during the dry season. Overall, our findings suggest that understanding seasonally‐variable water‐generating mechanisms is required for effective water resource management on San Cristóbal Island and other semi‐arid island ecosystems under current and future regimes of climate change.
Chapter
This chapter discusses strawberry guava in Hawaii, in which conflicting views of the targeted plant engendered substantial opposition to biological control. Invasion by strawberry guava has devastating consequences for Hawaiian ecosystems. Explorations for natural enemies in strawberry guava's native range were conducted. Tectococcus ovatus had never been recorded as a pest of any agricultural or ornamental plants, and never attacked common guava, which grows throughout its native range. A petition for release of the agent was submitted by the Forest Service to the Hawaii Department of Agriculture, the state agency charged with regulating biological control introductions. Once people recognized evidence of host specificity in everyday examples, most were readily convinced of the value and acceptability of managing invasive species with biological control. Improving the initial strawberry guava environmental assessment (EA) to meet Hawaii's regulatory laws better required substantial effort.
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Climate change is anticipated to affect freshwater resources, but baseline data on the functioning of tropical watersheds is lacking, limiting efforts that seek to predict how watershed processes, water supply, and streamflow respond to anticipated changes in climate and vegetation change, and to management. To address this data gap, we applied the distributed hydrology soil vegetation model (DHSVM) across 88 watersheds spanning a highly constrained, 4500 mm mean annual rainfall (MAR) gradient on Hawai?i Island to quantify stream flow at 3-h time-steps for eight years in response to the independent and interactive effects of (1) large observed decrease in MAR; (2) projected warming and altered precipitation; and (3) four scenarios of forest invasion by the high water-demanding non-native tree species Psidium cattleianum. The model captured 62% of variability in measured flow at daily time scales, 95% at monthly time scales, and 98% at annual time scales. We found that low DHSVM modeled flow (Q90) and storm flow (Q10) responses to observed declines in rainfall dwarfed those of projected temperature increase or invasion, with flow decline positively correlated with MAR. As a percentage of streamflow, temperature and invasion reductions were negatively correlated with MAR. By comparison, warming alone had little effect on Q90 or Q10, but both decreased with increasing P. cattleianum cover, and projected effects of declining MAR were accentuated when combined with P. cattleianum and warming. Restoration mitigated some effects of climate warming by increasing stream base flows, with the relative effects of restoration being larger in drier versus wetter watersheds. We conclude that potential changes in climate in tropical environments are likely to exert significant effects on streamflow, but managing vegetation can provide mitigating benefits.
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Non-native species invasions, growing human populations, and climate change are central ecological concerns in tropical island communities. The combination of these threats have led to losses of native biota, altered hydrological and ecosystem processes, and reduced ecosystem services. These threats pose complex problems to often underfunded management entities. We developed a watershed decision support tool (WDST) for the windward coast of Hawai‘i Island aimed at prioritizing catchments for invasive species removal and native forest protection from non-native species invasions. Using the Ecosystem Management Decision Support (EMDS) system, we integrated spatial data from four sources: (i) native and invasive species coverage; (ii) modeled water yield; (iii) treatment cost and efficacy; and (iv) native species conservation value. We used a distributed hydrology model (DHSVM) to estimate catchment-level (∼90 ha) water yield under six climate and non-native species invasion scenarios to identify where (1) invasive species removal and (2) protection from invasion would have the greatest benefit to increasing or maintaining native biodiversity and hydrologic functioning. The hydrology model predicted a 30% decline (386 Gl yr⁻¹) in total water yield under a drier future climate (20% reduction in rainfall), with an additional 2% reduction when catchments were fully invaded by non-native species. Increased temperatures had a small compensatory effect on water yield. The WDST identified 6.3% of the study area as high priority for invasive species removal, based on characteristics of large hydrological response to the removal treatment (concentrated in high rainfall areas), high quality road or trail access, and high conservation value. High protection priority from invasive species (5.9% by area) occurred in higher elevation catchments, near the upper range of strawberry guava (the main invasive species), where water yield was most sensitive to invasion. Climate change scenarios had little influence on the spatial distribution of priority scores despite large changes in overall water yield. In contrast, priority scores were sensitive to very high variation in treatment costs, which were influenced largely by travel times to catchments via road and trail networks. This last finding suggests that future management feasibility will hinge on improvements to road and trail networks, or development of alternative management strategies that reduce travel costs and time.
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Large tipping-bucket flow meters (TBFs, one tip > 200 ml) have been employed by hydrologists to quantify various water fluxes in a variety of contexts. The over-arching goal of this study is to develop a generalized correction equation for various TBFs. Based on our testing, we recommend the following to minimize TBF error: (1) periodic checking of the static calibration volume (c) since c is a gauge-specific value which has been found to vary after field deployment; and (2) for dynamic calibration, the use of our newly derived generalized correction equation when the tipping rate is less than 0.2 Hz. In equation form, the generalized correction equation for common TBFs with flat triangular buckets is: V = −0.75Q² + 0.72Q + 1 (R² = 0.843; p <0.0001), where V = v/c and v is the water volume for one tip under dynamic conditions, and Q = q/c [s⁻¹] and q is the water flow rate into the TBF. From our field test in a Japanese cedar forest stand, using stemflow (SF) as an example, we found that use of the generalized correction equation was successful in eliminating the 2–3% error in SF amounts. Moreover, we found that the generalized correction equation performed nearly as well as gauge-specific derived correction equations. Thus, our generalized correction equation is applicable to correct flow estimates of TBFs when one does not have time and/or laboratory set-up for the laborious task of testing individual TBFs themselves. Although our correction procedure may not completely eliminate all error, we recommend use of the generalized correction equation for TBFs to improve the accuracy of water flux calculations in hydrologic studies.
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In forested watersheds, interception loss (EI) and transpiration (ET) constitute the majority of evapotranspiration. Accordingly, their precise evaluations are necessary to understand and quantify fluxes within the hydrologic cycle. EI is commonly measured by tipping-bucket rain gauges and flow meters, while ET is often estimated by sap flow techniques. To obtain reliable estimations of EI and ET, we describe detailed procedures to calibrate tipping-bucket rain gauges and flow meters as well as sap flow techniques. For tipping-bucket rain gauges and flow meters, we measure the one tip static volume, and then changes in the one tip amount with different inflow rates for dynamic calibration. Without proper calibration, the significant evaluation error in EI can range from 40% underestimation to 20% overestimation. We calibrate three sap flow techniques—thermal dissipation (TD), heat field deformation (HFD), and heat ratio (HR) methods—for Japanese cedar (Cryptomeria japonica) from two sites. The clear radial and azimuthal trends in sap flux density (FD) are confirmed for the artificial sap flow generated by a vacuum pump. Among segments sampled at a site, TD and HFD methods do not have any tendencies to overestimate and underestimate FD. While at the other site, TD and HFD methods underestimate FD, and therefore ET, by at least 30%, the HR method shows a 30% overestimation. Thus, we highly recommend the calibration of tipping-bucket rain gauges, flow meters, and sap flow techniques to obtain valid estimates of EI and ET.
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The 1976-1981 distribution, elevation, and median annual rainfall of six alien plant species in upland habitats on the island of Hawaii are described based on data collected at 7,864 sampling points (stations) along 117 transects within a 1,930-mi 2 (5,000-km ) study area. Focal species were Malabar melastome (Melastoma candidum), banana poka (Passiflora mollissima), fountain grass (Pennisetum setaceum), strawberry guava (Psidium cattleianum), yellow Himalayan raspberry (Rubus ellipticus), and German ivy (Senecio mikanioides). Three species, strawberry guava, fountain grass, and banana poka, were widely distributed throughout the study area, while the remaining three species were found on less than 2% of the stations sampled. Relatively xeric habitats (median annual rainfall 49 in. or < 1,250 mm) and low-elevation areas (1,640-4,265 ft or 500-1,300 m) were found to be consistently invaded by three or more of the species. Forty-six (72%) of the 64 vegetation types sampled contained at least one of the six alien plant species. Portions of the two largest vegetation units, `ohia (Metrosideros polymorpha) rain forest, andohia-koa (Acacia koa) rain forest, were colonized by five of the six species analyzed. Elevation and median annual rainfall ranges were used to predict the potential geographical distribution of each species in the study area, assuming no restriction in plant invasion over time. Four of the six species (banana poka, German ivy, strawberry guava, and yellow Himalayan raspberry) showed great potential for expansion of their ranges if they continue to invade areas with environmental conditions similar to those where they were found during this survey.
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What is the most appropriate sampling scheme to estimate event-based average throughfall? A satisfactory answer to this seemingly simple question has yet to be found, a failure which we attribute to previous efforts' dependence on empirical studies. Here we try to answer this question by simulating stochastic throughfall fields based on parameters for statistical models of large monitoring data sets. We subsequently sampled these fields with different sampling designs and variable sample supports. We evaluated the performance of a particular sampling scheme with respect to the uncertainty of possible estimated means of throughfall volumes. Even for a relative error limit of 20%, an impractically large number of small, funnel-type collectors would be required to estimate mean throughfall, particularly for small events. While stratification of the target area is not superior to simple random sampling, cluster random sampling involves the risk of being less efficient. A larger sample support, e.g., the use of trough-type collectors, considerably reduces the necessary sample sizes and eliminates the sensitivity of the mean to outliers. Since the gain in time associated with the manual handling of troughs versus funnels depends on the local precipitation regime, the employment of automatically recording clusters of long troughs emerges as the most promising sampling scheme. Even so, a relative error of less than 5% appears out of reach for throughfall under heterogeneous canopies. We therefore suspect a considerable uncertainty of input parameters for interception models derived from measured throughfall, in particular, for those requiring data of small throughfall events.
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Nutrient fluxes in stemflow and throughfall were compared among three successional stages of an upper montane rain forest and related to structural characteristics of the stands (stem density, leaf area, epiphyte abundance). An old-growth forest stand, an early successional (10-y-old) forest stand and a mid-successional (40-y-old) forest stand were studied in the Cordillera Talamanca, Costa Rica. All three sites were dominated by Quercus copeyensis with a variable admixture of other tree species. There was no difference in the average stand leaf area index between the old-growth forest and the early successional forest. A significantly higher leaf area was found in the mid-successional forest. There were large differences in litterfall from non-vascular epiphytes (mosses, liverworts and lichens) which reflected differences in epiphyte abundance, with highest values in the old-growth forest. Total nutrient transfer via stemflow and throughfall from the canopy to the soil showed only minor differences among the stands. The stands differed widely in the ratio of nutrient transport via stemflow to the total nutrient flux by water below the canopy. The K flux with stemflow accounted for 5% of the total in the old-growth forest but it accounted for 17% (early successional forest) and 26% (mid-successional forest) in the secondary forests. It is concluded that differences in canopy structure and epiphyte abundance in old-growth and secondary forests resulted in large differences in the partitioning of nutrient transport into stemflow and throughfall components although total nutrient transfers via water reaching the soil were similar.
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Tropical montane cloud forests (TMCF) typically experience conditions of frequent to persistent fog. On the basis of the altitudinal limits between which TMCF generally occur (800–3500 m.a.s.l. depending on mountain size and distance to coast) their current areal extent is estimated at ∼215 000 km2 or 6·6% of all montane tropical forests. Alternatively, on the basis of remotely sensed frequencies of cloud occurrence, fog-affected forest may occupy as much as 2·21 Mkm2. Four hydrologically distinct montane forest types may be distinguished, viz. lower montane rain forest below the cloud belt (LMRF), tall lower montane cloud forest (LMCF), upper montane cloud forest (UMCF) of intermediate stature and a group that combines stunted sub-alpine cloud forest (SACF) and ‘elfin’ cloud forest (ECF). Average throughfall to precipitation ratios increase from 0·72 ± 0·07 in LMRF (n = 15) to 0·81 ± 0·11 in LMCF (n = 23), to 1·0 ± 0·27 (n = 18) and 1·04 ± 0·25 (n = 8) in UMCF and SACF–ECF, respectively. Average stemflow fractions increase from LMRF to UMCF and ECF, whereas leaf area index (LAI) and annual evapotranspiration (ET) decrease along the same sequence. Although the data sets for UMCF (n = 3) and ECF (n = 2) are very limited, the ET from UMCF (783 ± 112 mm) and ECF (547 ± 25 mm) is distinctly lower than that from LMCF (1188 ± 239 mm, n = 9) and LMRF (1280 ± 72 mm; n = 7). Field-measured annual ‘cloud-water’ interception (CWI) totals determined with the wet-canopy water budget method (WCWB) vary widely between locations and range between 22 and 1990 mm (n = 15). Field measured values also tend to be much larger than modelled amounts of fog interception, particularly at exposed sites. This is thought to reflect a combination of potential model limitations, a mismatch between the scale at which the model was applied (1 × 1 km) and the scale of the measurements (small plots), as well as the inclusion of near-horizontal wind-driven precipitation in the WCWB-based estimate of CWI. Regional maps of modelled amounts of fog interception across the tropics are presented, showing major spatial variability. Modelled contributions by CWI make up less than 5% of total precipitation in wet areas to more than 75% in low-rainfall areas. Catchment water yields typically increase from LMRF to UMCF and SACF–ECF reflecting concurrent increases in incident precipitation and decreases in evaporative losses. The conversion of LMCF (or LMRF) to pasture likely results in substantial increases in water yield. Changes in water yield after UMCF conversion are probably modest due to trade-offs between concurrent changes in ET and CWI. General circulation model (GCM)-projected rates of climatic drying under SRES greenhouse gas scenarios to the year 2050 are considered to have a profound effect on TMCF hydrological functioning and ecology, although different GCMs produce different and sometimes opposing results. Whilst there have been substantial increases in our understanding of the hydrological processes operating in TMCF, additional research is needed to improve the quantification of occult precipitation inputs (CWI and wind-driven precipitation), and to better understand the hydrological impacts of climate- and land-use change. Copyright © 2010 John Wiley & Sons, Ltd.
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Photosynthesis was limited by low-intensity photosynthetically active radiation (PAR) and leaf wetness in a lower montane cloud forest (LMCF) of Cauca, Colombia. Mean PAR intensity remained below the saturation level for leaf-scale net photosynthesis (P n) throughout the solar day during the wet season and for most of the solar day during the dry season. PAR represented a smaller fraction of total solar radiation (K↓) in LMCF than in lowland rain forest (LRF). In LMCF trees and shrubs, mean PAR-saturated P n ranged from 4.3–10.6 µmol C m −2 s −1 at 1450 m, and from 3.5–10.2 µmol C m −2 s −1 at 2150 m. P n was reduced by abaxial wetness in leaves of some trees and shrubs, and eliminated in others. This study indicates that persistent cloudiness and interception of cloud water by leaves limit LMCF productivity.
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Island tropical montane cloud forests may be among the most sensitive of the world's ecosystems to global climate change. Measurements in and above a montane cloud forest on East Maui, Hawaii, document steep microclimatic gradients. Relatively small climate-driven shifts in patterns of atmospheric circulation are likely to trigger major local changes in rainfall, cloud cover, and humidity. Increased interannual variability in precipitation and hurricane incidence would provide additional stresses on island biota that are highly vulnerable to disturbance-related invasion of non-native species. Because of the exceptional sensitivity of these microclimates and forests to change, they may provide valuable listening posts for detecting the onset of human-induced global climate change.
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In this study, we designed and built an automated system of collection and measurement of throughfall and stemflow, developing a new sampling methodology. Throughfall was measured by trough-type system of collectors, each collector with sampling area of 5 cm × 6 m, connected every six troughs to a large tipping bucket raingauge. Our throughfall measurement system covered a larger surface area than do most commonly used randomly relocated gauges, reducing the spatial variability. Temporal resolution was high (5 min), allowing the study of the short-term dynamics of the interception process. Stemflow was collected from 65 trees and also measured by large tipping bucket raingauges. Water vapor exchange at the forest–atmosphere interface was derived from eddy covariance data from a flux tower in the same area as the interception study. During the study period (November 2002–October 2004) a mild El Niño year developed and total annual rainfall was considerably lower than the average for the region. The interception loss in the year with normal rainfall was 13.3%, compared to 22.6% of gross precipitation in the dry year. The interception difference is explained by the comparison of mean intensity and duration of events in the normal year (8.77 mm/h and 1.88 h) versus the driest year (5.36 mm/h and 2.32 h). Interception loss for the whole period represented 16.5% of the gross rainfall, with throughfall 82.9% and stemflow 0.6%. We used the analytical Gash model to estimate the interception loss. The model succeeded in capturing the variability associated to the variability in the characteristics of precipitation. This is the first study to show the variability of interception in relation to rainfall (seasonally and between years).
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The partitioning of gross rainfall into throughfall, stemflow and evaporation of intercepted rainfall was studied in four forest ecosystems in the Middle Caquetá, Colombian Amazonia. Data on climate was collected automatically on an hourly basis during a five-year period. Weekly measurements of rainfall, throughfall and stemflow were carried out during a period of two years, while daily measurements, on an event basis, were carried out during two subsequent years. Throughfall, stemflow and evaporation in each forest were checked for correlations with gross rainfall characteristics, canopy gap fraction, tree crown area and bark texture. Canopy gap fraction differed between forests, ranging from 9% on the flood plain to 17% on the Tertiary sedimentary plain. Rainfall was rather evenly distributed over the year, with one dry period from December to February. 92% of the rain fell in single showers of less than 30 mm and most of the storms (56%) fell in less than one hour, during the afternoon or early night. Throughfall ranged from 82 to 87% of gross rainfall in the forests studied and varied with gross rainfall in all forests. It depended on the amounts and characteristics of rainfall, but differences in throughfall among forests, when comparing similar rainfall events, clearly indicated that throughfall also depends on forest structure. Stemflow contributed little to net precipitation (on average 1.1% of gross rainfall in all forests) and showed a power relation with gross rainfall. Correlations between stemflow per tree, projected crown area and bark texture were very poor as indicated by the low coefficients of determination. Evaporation during rainfall events exhibited a linear relation with rainfall duration and the ratio of evaporation over gross rainfall increased with forest cover (1-gap fraction) in the forests studied. The structure of the forests seemed to vary considerably and given its influence on rainfall partitioning it may explain both differences and similarities between results from this study and those from most other studies within Amazonia.
Chapter
Within the topo-climatically complex tropical mountains of Hawai’i, there are four distinctive montane forest zones where the direct canopy interception of wind-driven cloud water (also referred to as “fog drip”) plays a significant role in forest ecology and hydrology. Not all of these four zones can be characterized as classic tropical montane cloud forest (TMCF), but to varying degrees each is influenced by ground-level, orographic cloud.
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Based on field measurements made at dry (Auwahi) and wet (Waikamoi) cloud forest sites on the island of Maui, a preliminary analysis of fog gage measurements and wet-canopy water balance estimates was made. Accounting for effects of wind-blown rainfall and varying wind direction, estimates of cloud water flux were derived based on fog gage observations. Throughfall (TF) measurements, incident rainfall estimates, and calculated amounts of wet-canopy evaporation were used to estimate event totals of cloud water interception (CWI) by the vegetation at each site. Measured TF was about 37% of incident rainfall at Auwahi, and 119% at Waikamoi. At both sites TF was dominated by rainfall, but was significantly influenced by fog at Waikamoi only. Fog contributed at an average frequency of once every two days at Auwahi and about twice in three days at Waikamoi. Derived CWI totals were equivalent to 151 mm year–1 at Auwahi and 1073 mm year–1 at Waikamoi. At Auwahi, however, the majority of intercepted water was re-evaporated from the wet vegetation, and never reached the ground. Total CWI was related to fog screen catch and cloud water flux at Waikamoi, but not at Auwahi.
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Research on fog climatology and cloud water interception (CWI) in the montane cloud forests of Hawai'i spans nearly 50 years, from the pioneering work of Wendell Mordy and Paul Ekern on Lâna'i in the 1950s, through the continuing efforts of James Juvik since 1972. This work has helped to improve understanding of the spatial patterns of fog occurrence and to quantify CWI in forests and other vegetation. Reported CWI or fog incidence estimates are as high as 4982 mm year-1 at particularly exposed locations, although most windward sites within the cloud zone are in the range between 280 and 1130 mm year-1, with leeward sites receiving between 100 and 500 mm year-1, and less than 250 mm year-1 in high-elevation areas above the trade-wind inversion. Most of the early work was based on mechanical fog gage measurements whose well-known limitations make accurate estimation of actual CWI by a forest canopy difficult. Advancing the current level of understanding will have to come from studies incorporating other methods, such as the wet-canopy water budget and stable isotope mass balance approaches, in addition to the continued use of recording fog and throughfall gages.
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This paper reviews current knowledge of the effect of forest type, ground cover and climate on rainfall partitioning into throughfall, stemflow and interception. It considers the variety and reliability of measurement techniques that have been used and interprets the results of interception studies in relation to methodological, vegetational and climatic factors. The review illustrates that it is difficult to draw general conclusions about interception losses by particular forest types because they almost always depend on the type of rainfall and other meteorological conditions during the study period. Characteristics of a forest that affect interception are not always easy to identify and quantify. Characteristics such as trees/ha, branch angle, the uniformity or lack of uniformity in crown height, the nature and thickness of the bark layer, leaf shape and inclination, and leaf area index will all influence interception. The major difficulty is reliable estimation of throughfall. It is not unusual for measured throughfall to exceed the rainfall value, causing interception to be negative. The difficulty in estimation of throughfall is discussed. while also addressing the need for accurate measurement of rainfall. In forests where stemflow volumes are large enough to significantly influence the interception values, the methodological approach is even more difficult. Measurement of interception on a periodic basis presents fewer problems than estimation on an individual event basis because the variables that affect the values of throughfall and stemflow can change over very short periods, for example the intensity and angle of rainfall, and wind speed and direction. However, carefully conducted event-based studies can quantify the influence of a number of the variables. Copyright (C) 2000 John Wiley & Sons, Ltd.
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Myrica faya, an introduced nitrogen-fixing tree, is rapidly invading volcanically disturbed forests in Hawaii Volcanoes National Park on the island of Hawai'i. We investigated the direct effects of Myrica on the establishment and growth of the native tree, Metrosideros polymorpha, in a forest that is recovering from burial under a 10-200 cm deep layer of volcanic cinder. The number of Metrosideros seedlings found under Metrosideros trees, in the open, and under Myrica trees was 0.12/m^2, and 0.01/m^2, and zero, respectively. Myrica litter inhibited Metrosideros germination in field experiments; germination occurred only when Myrica litter was removed. In open sites, the addition of nitrogen-rich Myrica soils increased dry mass accumulation of transplanted Metrosideros seedlings. Shade from Myrica canopies (or shade cloth) increased survivorship and height growth but not dry mass accumulation of Metrosideros seedlings. Isolated Metrosideros trees increased diameter growth in response to nitrogen fertilizer but not in response to the presence of adjacent Myrica trees, despite previous findings that Myrica trees elevate available nitrogen in the soil. Myrica basal diameter and height growth were consistently greater than that of Metrosideros in all size classes. Although Myrica does not readily invade closed, late-successional Metrosideros forests, on young, volcanically disturbed soils it is rapidly establishing dense, monospecific stands under which Metrosideros does not regenerate.
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The atmospheric deposition of N and base cations in fog, precipitation, and dry deposition was measured over 5-7 years at the Hawaii Volcanoes National Park, Hawaii. Precipitation deposition was measured for 1.5 years at the Kokee State Park/Na Pali Kona Forest Reserve, Kauai. Fog interception on Hawaii was 158 +61/-32, 148 +69/-36, 251 +85/-51, 251 +91/-51, 243 +96/-59, and 181 +56/-38 cm per year for the years 1995 to 2000 respectively. This represents an average of 46% of the total water input and 83% of precipitation. An analysis of the lowest uncertainty that could realistically be achieved using our water balance method yielded a minimum uncertainty of +16% and -14% for annual fog interception values and +54% and -53% for individual fog events. At the Thurston Lava Tube site, fog interception was by far the largest deposition pathway for K+, Mg2+, Ca2+, and N. Sea salt contributes the majority of cations, while local biomass burning on Hawaii and Asian dust are significant sources for some years. Fog N deposition at Thurston averaged 20 kg N ha-1 yr-1. Organic N was on average 16% and 12% of the N in rain and fog. Several methods were used to determine whether volcanically produced N significantly impacted the Thurston site. Back trajectory analysis showed that air can blow from the volcano to our sampling site when there is an interruption in the northeasterly trade winds. Collected fog during one such episode had measurable NO2-, indicating very high atmospheric concentration of atmospheric NO2. NH4+ concentrations were higher for fog events with back trajectories that indicated volcanic influence than for those without, indicating that the volcano is also a reduced N source. Enough fog events were sampled from 1998 to 2000 to statistically show higher concentrations of NO3- , NH4+, and organic N in events with volcanic influence versus those without. Lower deposition of NO3 - in precipitation on Kauai also argues that volcanic N is significant at Thurston.
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PREFACE TO THE SECOND EDITION LIST OF SYMBOLS 1. SCOPE OF ENVIRONMENTAL PHYSICS 2. GAS LAWS Pressure, volume and temperature Specific heats Lapse rate Water and water vapour Other gases 3. TRANSPORT LAWS General transfer equation Molecular transfer processes Diffusion coefficients Radiation laws 4. RADIATION ENVIRONMENT Solar radiation Terrestrial radiation Net radiation 5. MICROCLIMATOLOGY OF RADIATION (i) Interception Direct solar radiation Diffuse radiation Radiation in crop canopies 6. MICROCLIMATOLOGY OF RADIATION (ii) Absorption and reflection Radiative properties of natural materials Net radiation 7. MOMENTUM TRANSFER Boundary layers Wind profiles and drag on uniform surfaces Lodging and windthrow 8. HEAT TRANSFER Convection Non-dimensional groups Measurements of convection Conduction Insulation of animals 9. MASS TRANSFER (i) Gases and water vapour Non-dimensional groups Measurement of mass transfer Ventilation Mass transfer through pores Coats and clothing 10.MASS TRANSFER (ii) Particles Steady motion 11.STEADY STATE HEAT BALANCE (i) Water surfaces and vegetation Heat balance equation Heat balance of thermometers Heat balance of surfaces Developments from the Penman Equation 12.STEADY STATE HEAT BALANCE (ii) Animals Heat balance components The thermo-neutral diagram Specification of the environment Case studies 13.TRANSIENT HEAT BALANCE Time constant General cases Heat flow in soil 14.CROP MICROMETEOROLOGY (i) Profiles and fluxes Profiles Profile equations and stability Measurement of flux above the canopy 15.CROP MICROMETEOROLOGY (ii) Interpretation of measurements Resistance analogues Case studies: Water vapour and transpiration Carbon dioxide and growth Sulphur dioxide and pollutant fluxes to crops Transport within canopies APPENDIX BIBLIOGRAPHY REFERENCES INDEX
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This paper reviews current knowledge of the effect of forest type, ground cover and climate on rainfall partitioning into throughfall, stemflow and interception. It considers the variety and reliability of measurement techniques that have been used and interprets the results of interception studies in relation to methodological, vegetational and climatic factors. The review illustrates that it is difficult to draw general conclusions about interception losses by particular forest types because they almost always depend on the type of rainfall and other meteorological conditions during the study period. Characteristics of a forest that affect interception are not always easy to identify and quantify. Characteristics such as trees/ha, branch angle, the uniformity or lack of uniformity in crown height, the nature and thickness of the bark layer, leaf shape and inclination, and leaf area index will all influence interception. The major difficulty is reliable estimation of throughfall. It is not unusual for measured throughfall to exceed the rainfall value, causing interception to be negative. The difficulty in estimation of throughfall is discussed, while also addressing the need for accurate measurement of rainfall. In forests where stemflow volumes are large enough to significantly influence the interception values, the methodological approach is even more difficult. Measurement of interception on a periodic basis presents fewer problems than estimation on an individual event basis because the variables that affect the values of throughfall and stemflow can change over very short periods, for example the intensity and angle of rainfall, and wind speed and direction. However, carefully conducted event-based studies can quantify the influence of a number of the variables.
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Rainfall and cloud water interception (CWI) were determined for a mature and a 19-year old secondary lower montane cloud forest in central Veracruz, Mexico. Cloud water was measured using a passive fog gauge, and consisted most likely of a mixture of fog and wind-driven drizzle. CWI by the canopy was derived from the wet canopy water budget as throughfall + stemflow + calculated interception loss minus rainfall. Rainfall interception loss was calculated using the Liu model, parameterized for events with rain-only. Precipitation events with cloud water input occurred exclusively during the dry season (November-April), and were primarily associated with cold fronts. CWI was estimated at 6% of dry season rainfall (640 mm on average) for the secondary forest vs. 8% for the mature forest, whereas annual values were of total rainfall (3180 mm). Infrequent fog occurrence and low wind speeds were the most important reasons for the observed low values of CWI. Total apparent interception loss (i.e. including CWI) was 17% of annual rainfall for the mature forest and 8% for the secondary forest. Post-event evaporation of intercepted water stored in the canopy rather than within-event evaporation dominated interception loss at both forests. Hence, the higher loss observed for the mature forest is considered to reflect a higher canopy storage capacity, related in turn to a higher Leaf Area Index and larger epiphyte biomass.
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A novel design of gauge for measuring net rainfall beneath a forest canopy is described. The advantages of this system, based on the use of a large plastic sheet, over conventional throughfall and stemflow measuring systems is discussed.
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Recent studies of the water balance of tropical rainforests in northern Queensland have revealed that large fractions of rainfall, up to 30%, are intercepted by the canopy and lost as evaporation. These loss rates are much higher than those reported for continental rainforests, for example, in the Amazon basin, where interception is around 9% of rainfall. Higher interception losses have been found in coastal and mountain rainforests and substantial advection of energy during rainfall is proposed to account for these results. This paper uses a process based model of interception to analyse the interception losses at Oliver Creek, a lowland coastal rainforest site in northern Queensland with a mean annual rainfall of 3952 mm. The observed interception loss of 25% of rainfall for the period August 2001 to January 2004 can be reproduced by the model with a suitable choice of the three key controlling variables, the canopy storage capacity, mean rainfall rate and mean wet canopy evaporation rate. Our analyses suggest that the canopy storage capacity of the Oliver Creek rainforest is between 3.0 and 3.5 mm, higher than reported for most other rainforests. Despite the high canopy capacity at our site, the interception losses can only be accounted for with energy advection during rainfall in the range 40 70% of the incident energy.
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Although floristic lists for a large sample of U.S. reserves have 5-25% introduced species, most introductions are confined to drastically disturbed areas and pose little or no threat to native ecosystems. A survey of Biosphere Reserves of the United States suggests that many reserves have only very minor problems or no problems at all with introduced plant species. Problems with invasive introduced species are most severe on oceanic islands, but serious problems occur in some continental areas as well. In some U.S. parks and reserves, the primary concern for introduced plant species is that they pose economic threats to adjacent agricultural lands. In extreme situations, however, introduced plants may inhibit and entirely prevent reproduction of native plant species, degrade habitat for native animal species, and/or alter otherwise natural habitats through changing nutrient, fire, or water regimes. At the highly disruptive end of the spectrum, native ecosystems may become so totally transformed by invaders that they are scarcely recognizable, although this condition is rare within U.S. parks and reserves.