Search

Given the long-term human habitation and prolific land use change trajectories in the eastern United States, few remnants of the pre-European settlement Mid-Atlantic forest remain on the Atlantic Coastal Plain. This study utilized metes and bounds witness tree locations and descriptions produced during colonial land subdivision to understand the relationships between tree types and biogeographic environments for an area on Maryland's Eastern Shore. Using correspondence analysis, we reveal habitat partitioning among witness tree species based on soil drainage characteristics, that enable the visualization of a pre-European settlement reconstructed forest. Our research finds that oak (Quercus), most often white oak (Quercus alba), was the dominant genus for most of the study area underlain by well-drained soils. To a much smaller extent, gums were also associated with these well-drained soils. Areas of poor drainage most often contained pine (Finns) and an assemblage of different oaks (Quercus spp.). Hickory (Carya), also noted in the witness tree record in small numbers, was found across all soil drainages. Key words: witness trees, precolonial forest, soil drainage, Wicomico Co., Maryland, Introduction The eastern forests of the United States have been greatly affected by anthropogenic activity, first by Native Americans and later by European colonists. The impact of Native Americans on [...]

The unsaturated zone is a complex multiphase system, and modelling and prediction of flow and contaminant transport in this zone remain a challenge. In order to understand the mechanisms of fluid flow in unsaturated sands, an accurate and efficient approach to estimate unsaturated hydraulic conductivity (K) is essential. In this study, a power law relationship was derived from a combination of Archie's law and van Genuchten's model to relate bulk (apparent) electrical conductivity (E[C.sub.a]) with unsaturated K. The laboratory sandbox experiments were conducted first to delineate the soil water characteristic curves (SWCCs). Time domain reflectometry was used to simultaneously measure volumetric water content ([theta]) and E[C.sub.a]. Then, the experimental relationships of the effective saturation (S) and E[C.sub.a] and simulated S-K were combined to establish the relationship between E[C.sub.a] and unsaturated K. The developed power law relationships described the relative EC (E[C.sub.r]) and relative K ([K.sub.r]) very well by just using one parameter, exponent [beta]. When fluid EC was low, the [beta] values for the drainage and wetting processes ranged within 2.09-2.74 and 2.50-3.79 respectively. The variations of [beta] values of homogeneous material were smaller that of heterogeneous material and the effect of hysteresis on the E[C.sub.r]-[K.sub.r] relationship was observed. When pore space was filled with the high-EC solution, it easily mimicked the S-[K.sub.r] relationship and resulted in a smaller [beta] value. The [beta] value acted as a lumped factor accounting for pore tortuosity, pore connectivity, shape of pore space, and fluid EC. The power law relationship of E[C.sub.r]-[K.sub.r] developed in this study could lead to a direct estimation of the spatial and temporal variations of unsaturated K, once the measurements of SWCC are available from estimation of saturated K and combination of time-lapse E[C.sub.a] measurements. Accurate and efficient estimation of unsaturated K could improve the prediction of flow in the unsaturated zone and allow a comprehensive understanding of unsaturated zone processes. Keywords: electrical conductivity, heterogeneous, homogeneous, hydraulic conductivity, power law relationship, soil water characteristic curve, time domain reflectometry, unsaturated sands., Introduction Unsaturated hydraulic conductivity (K) is a crucial parameter to evaluate infiltrated water flux in the soil. However, estimation of K is still a challenge because it varies over orders [...]

Attributes of deadwood in forests, including quantity, landscape position, and state of decay, influence numerous ecosystem processes such as wildfire behavior, tree regeneration, and nutrient cycling. Attributes of deadwood that vary over subdiurnal time steps, including moisture, have not been routinely measured despite the profound effects they have on ecosystem processes. To improve our understanding of forest deadwood subdiurnal moisture dynamics, we installed an intensive time-domain reflectometry (TDR) sensor network in a log and surrounding soil within a northern hardwood forest in New England, United States. Intensive monitoring during a partial growing season indicated that deadwood moisture was dynamic but similar to that of surrounding soils at 15-min intervals, especially during wetting and drying events. Field results and bench analysis of the sample log revealed numerous challenges when attempting to monitor deadwood moisture with TDR such as heterogeneous and (or) advanced decay confounding TDR moisture measurements in logs. An efficient, high-frequency TDR sensor network was demonstrated to record deadwood and soil moisture fluctuations, which provides an opportunity to refine our understanding of deadwood dynamics in the context of global change such as changing precipitation regimes. Key words: downed deadwood, soil moisture, TDR sensors, wildfire, wood decay. Les caracteristiques du bois mort en foret, telles que la quantite, la position dans le paysage et l'etat de decomposition, influencent plusieurs processus de l'ecosysteme, comme le comportement du feu, la regeneration des arbres et le recyclage des nutriments. Les caracteristiques du bois mort qui varient en fonction d'echelles de temps sous-diurnes telles que l'humidite n'ont pas ete mesurees de facon routiniere malgre les effets importants qu'elles ont sur les processus de l'ecosysteme. Afin d'ameliorer notre comprehension de la dynamique sous-diurne de l'humidite du bois mort en foret, nous avons installe un reseau intensif de capteurs utilisant la reflectometrie a dimension temporelle (TDR) dans une bille et le sol environnant dans une foret de feuillus nordiques en Nouvelle-Angleterre, aux Etats-Unis. Un suivi intensif durant une partie de la saison de croissance a montre que l'humidite du bois mort est dynamique mais semblable a celle du sol environnant a intervalles de 15 min, surtout durant les episodes de mouillage et de sechage. Les resultats sur le terrain et l'analyse en laboratoire de la bille qui a servi d'echantillon ont fait ressortir de nombreux defis lorsqu'on tente de faire le suivi de l'humidite dans le bois mort avec la TDR, tels que l'etat d'avancement et rheterogeneite de la carie qui reduisent la fiabilite des mesures d'humidite par TDR dans les billes. L'efficacite d'un reseau de capteurs qui utilisent la TDR a haute frequence pour enregistrer les fluctuations de l'humidite dans le bois mort et le sol a ete demontree, ce qui fournit une opportunite de raffiner notre comprehension de la dynamique du bois mort dans le contexte du changement global dont le changement des regimes de precipitation. [Traduit par la Redaction] Mots-cles: bois mort au sol, humidite du sol, capteurs TDR, feu de foret, decomposition du bois., Introduction Over the past decades, it has become increasingly evident that deadwood plays a critical role in numerous forest ecosystem functions, including wildfire behavior (Schoennagel et al. 2004), nutrient cycling [...]

Photosynthetic light response curves were parameterized for eight species in two genera, Pinus and Picea, grown in a 2 * 2 factorial of atmospheric C[O.sub.2] and soil moisture treatments. Four of the pines and three of the spruces are native to eastern North America, and the fourth spruce, Norway spruce (Picea abies (L.) Karst.), is native to Europe. There was a significant genus x C[O.sub.2] interaction in apparent quantum efficiency (AQE): spruce AQE was greater under ambient C[O.sub.2] (C[O.sub.2]) than elevated C[O.sub.2] (eC[O.sub.2]), but pine AQE were equal. Under drought treatment (DR), AQE declined for both genera. Assimilation at light saturation (Alsat) was greater for spruces than pines, and for both genera, Alsat decreased under eCO2 and DR. Water-use efficiency was greater for pines than spruces and greater for pines and unchanged for spruces under DR. Examining AQE and Alsat change (%) from aC[O.sub.2] to eC[O.sub.2], there was a significant positive relationship to biomass growth stimulation (%) across species. These relationships support the theory of sink (biomass growth) regulation of assimilation traits and also the importance of needle nitrogen. Our results in response to eC[O.sub.2] and DR suggest a shift toward increased use of pines in forest management for eastern North America. Key words: elevated C[O.sub.2], light efficiency traits, light response curves, pines and spruces, soil moisture stress. Les courbes de reponse photosynthetique a la lumiere ont ete parametrees pour huit especes appartenant a deux genres, Pinus et Picea, cultivees selon un plan factoriel comprenant deux traitements de C[O.sub.2] atmospherique et deux traitements d'humidite du sol. Les quatre especes de pins et trois especes d'epiceas sont des especes indigenes de l'est de l'Amerique du Nord et la quatrieme espece d'epicea, l'epicea commun (Picea abies (L.) Karst.), est originaire de l'Europe. Il y avait une interaction significative entre le genre et le C[O.sub.2] dans le cas du rendement quantique apparent (RQA): le RQA des epiceas etait plus eleve dans le traitement a la concentration ambiante de C[O.sub.2] (aC[O.sub.2]) que s'ils etaient exposes a une plus grande concentration de C[O.sub.2] (eC[O.sub.2]), mais le RQA des pins restait le meme. Dans le traitement emulant une secheresse (SE), le RQA diminuait chez les deux genres. L'assimilation a saturation lumineuse (Alsat) etait plus elevee chez les epiceas que chez les pins et elle diminuait chez les deux genres dans les traitements eC[O.sub.2] et SE. L'efficience de l'utilisation de l'eau etait plus elevee chez les pins que chez les epiceas et plus elevee chez les pins et inchangee chez les epiceas dans le traitement SE. L'examen de la variation (%) du RQA et de l'Alsat entre les traitements aC[O.sub.2] et eC[O.sub.2] suggere une relation positive significative avec la stimulation de la croissance de la biomasse (%) chez l'ensemble des especes. Ces relations supportent la theorie de la regulation par l'effet de puits (croissance de la biomasse) des caracteres associes a l'assimilation et aussi mettent en evidence l'importance de l'azote dans les aiguilles. Nos resultats en reaction aux traitements eC[O.sub.2] et SE suggerent d'evoluer vers une utilisation accrue des pins en amenagement forestier dans l'est de l'Amerique du Nord. [Traduit par la Redaction] Mots-cles : enrichissement en C[O.sub.2], caracteres d'efficacite lumineuse, courbes de reponse a la lumiere, pins et epiceas, stress hydrique dans le sol., Introduction Ecophysiological adaptations in carbon assimilation and growth are important for plant fitness and have significant growth and ecological implications for both intra- and inter-specific competition (Bazzaz 1979). Light utilization [...]

The release of carbon dioxide (C[O.sub.2]) occurs through soil respiration. However, release of C[O.sub.2] from soil to the atmosphere is subject to interference from agents such as relief, edaphic and climatic conditions. Thus, this research aimed to quantify edaphic respiration related to edaphoclimatic factors in a toposequence area in Caatinga of Delmiro Gouveia, Alagoas, Brazil. The research was conducted from February 2013 to June 2014, with bimonthly collections during day and night. The soil C[O.sub.2] losses, temperature measurements, soil water content and rainfall were quantified. We verified that, independent of the evaluated points, C[O.sub.2] release was higher at night. Half-slope and shoulder were the areas with the highest emissions. Additionally, the C[O.sub.2] emissions presented annual variation, increasing with the availability of soil water and showing peaks of release in the rainy season. Soil and air temperature had no direct influence on soil C[O.sub.2] release; however, the highest C[O.sub.2] emissions occurred when temperatures were moderate and stable. Therefore, the conservation of this unique Brazilian biome is necessary because the impacts of its disturbance can increase the level of C[O.sub.2] released from the soil, increasing the amount of C[O.sub.2]in the atmosphere. Additional keywords: Brazilian semi-arid, rainfall, soil carbon dioxide, soil moisture, soil temperature. Received 12 June 2019, accepted 9 December 2019, published online 3 February 2020, Introduction Caatinga is the predominant vegetation type of the semi-arid region of north-eastern Brazil. Due to its heterogeneity and the significant number of rare and endemic species in the Caatinga, [...]

Soil water repellency (SWR) is a common phenomenon observed throughout the world. It has a significant impact on water infiltration, altering soil hydrology and consequently the soil microbial community and nutrient cycling. Despite the importance of this phenomenon, the processes involved in the development and breakdown of SWR are poorly understood. The importance of the microbial community for SWR is becoming increasingly apparent. In this study, relationships between microbial activities and SWR were investigated by utilising the patchy occurrence of SWR to select both repellent and wettable soils in six locations of the east coast of the North Island of New Zealand. Samples were from directly adjacent locations in mid spring and late summer, and a range of soil physico-chemical properties and enzyme activities were measured. The degree and potential persistence of SWR did not change between the two sampling times, whereas actual persistence of SWR increased. Soil moisture decreased between the two times, and although there was an inverse relationship between moisture and actual persistence of SWR in late summer, unexpectedly, it was a positive relationship in spring. Phosphatase, arylsulfatase and polysaccharide degrading enzyme activities increased with increasing SWR, whereas peroxidase activity decreased. The possible effects of increasing temperature and decreasing water content were modelled, and the observed relationships were strengthened. Arylsulfatase activity was strongly correlated with the degree of SWR, as was extractable organic sulfate, suggesting that the breakdown of sulfate-esters within humic material in soil may be involved in the release and accumulation of SWR-inducing hydrophobic compounds. Additional keywords: humic material, microbial community, peroxidase, phosphatase, soil moisture, sulfatase., Introduction Soil water repellency (SWR) has been observed in a wide range of natural and agricultural environments in over 50 countries (Dekker et al. 2005). SWR is a temporary property [...]

We revisit a previously published approach, and present a new approach, to calculate the effect of osmotic stress on soil water availability assuming conservation of mass with respect to salt. The two (completely different) approaches allow the water capacity to be attenuated and a plant-sensitivity factor is introduced to enhance flexibility in modelling when new plant-response data arises. The results should be of value in evaluation of different cultivars of important crops being screened in the field for genetic tolerance to salinity in different soils. Additional keywords: Groenevelt-Grant equation, integral water capacity, plant sensitivity to salt, weighting functions. Received 29 November 2018, accepted 11 February 2019, published online 19 March 2019, Introduction Applications of Groenevelt et al.'s (2004) theory have evaluated both plant response and drainage effects on the calculation of plant available water in saline soils (e.g. Shani et al. [...]

Although the terrestrial biosphere absorbs about 25 per cent of anthropogenic carbon dioxide (CO.sub.2) emissions, the rate of land carbon uptake remains highly uncertain, leading to uncertainties in climate projections.sup.1,2. Understanding the factors that limit or drive land carbon storage is therefore important for improving climate predictions. One potential limiting factor for land carbon uptake is soil moisture, which can reduce gross primary production through ecosystem water stress.sup.3,4, cause vegetation mortality.sup.5 and further exacerbate climate extremes due to land-atmosphere feedbacks.sup.6. Previous work has explored the impact of soil-moisture availability on past carbon-flux variability.sup.3,7,8. However, the influence of soil-moisture variability and trends on the long-term carbon sink and the mechanisms responsible for associated carbon losses remain uncertain. Here we use the data output from four Earth system models.sup.9 from a series of experiments to analyse the responses of terrestrial net biome productivity to soil-moisture changes, and find that soil-moisture variability and trends induce large CO.sub.2 fluxes (about two to three gigatons of carbon per year; comparable with the land carbon sink itself.sup.1) throughout the twenty-first century. Subseasonal and interannual soil-moisture variability generate CO.sub.2 as a result of the nonlinear response of photosynthesis and net ecosystem exchange to soil-water availability and of the increased temperature and vapour pressure deficit caused by land-atmosphere interactions. Soil-moisture variability reduces the present land carbon sink, and its increase and drying trends in several regions are expected to reduce it further. Our results emphasize that the capacity of continents to act as a future carbon sink critically depends on the nonlinear response of carbon fluxes to soil moisture and on land-atmosphere interactions. This suggests that the increasing trend in carbon uptake rate may not be sustained past the middle of the century and could result in accelerated atmospheric CO.sub.2 growth.Earth system models suggest that soil-moisture variability and trends will induce large carbon releases throughout the twenty-first century., Author(s): Julia K. Green [sup.1] , Sonia I. Seneviratne [sup.2] , Alexis M. Berg [sup.3] , Kirsten L. Findell [sup.4] , Stefan Hagemann [sup.5] , David M. Lawrence [sup.6] , [...]

Soil surface topography affects fundamental hydrologic processes, such as infiltration and soil water percolation. Topographic variations potentially alter both the magnitude and directions of unsaturated flow The objective of this study is to evaluate the effects of surface topography on wetting front moving patterns under different rainfall and soil conditions through combined experimental and numerical modelling studies. Specifically, laboratory-scale infiltration and unsaturated flow experiments and HYDRUS-2D modelling were conducted for different topographic surfaces, rainfall intensities, and soil types. The simulated and observed wetting front distributions were compared and evaluated. Two different stages were observed: topography-dominated two-dimensional flow and uniform one-dimensional flow. A uniformly distributed wetting front was eventually achieved although soil surfaces had dissimilar topographic characteristics. However, the timing or duration to reach such a uniform flat wetting front varied, mainly depending on surface topography, rainfall characteristics, and soil hydraulic properties. The findings from this study are important to better understand the mechanism of topography-controlled unsaturated flow, wetting front movement, and overland flow generation, and to further improve modelling of soil water flow and transport processes under such complex conditions across different scales. Additional keywords: HYDRUS, surface roughness, unsaturated flow, vadose zone., Introduction Many experimental studies have quantified wetting front movement in unsaturated soils under different conditions. For example, Bernadiner (1998) investigated the capillary microscale structure of wetting fronts, and the mechanism [...]

Trees may migrate northward in response to climate change and become exposed to new photoperiod and soil moisture regimes. This study assessed the impacts of photoperiod and its interaction with soil moisture and carbon dioxide concentration ([C[O.sub.2]]) on the hydraulic conductivity in jack pine (Pinus banksiana Lamb.) and its vulnerability to xylem embolism. Seedlings were exposed to 400 vs. 950 ([micro]molX[mol.sup.-1] [C[O.sub.2], 60%-70% vs. 30%-40% (of field capacity) soil moisture, and photoperiods of seed origin and 5[degrees] and 10[degrees] north of seed origin in greenhouses. Cavitation vulnerability curves were measured for determining the xylem pressure at which 50% hydraulic conductivity was lost ([[PSI].sub.PLC50]). It was found that elevated [C[O.sub.2]] significantly increased hydraulic conductivity, whereas low soil moisture decreased it. Under elevated [C[O.sub.2]], the xylem became progressively more vulnerable to embolism with changes in photoperiod regime from the seed origin to 10[degrees] north of the seed origin, as indicated by the progressively less negative [[PSI].sub.PLC50]. However, no such a trend was detected under the ambient [C[O.sub.2]]. The results suggest that the species may become less resistant to drought as the atmospheric [C[O.sub.2]] increases, hindering the northward migration or seed transfers. Even within its current natural distribution range, trees near its northern boundary of the range may be more vulnerable to embolism as the atmospheric [C[O.sub.2]] increases even without any change in moisture conditions. Keywords: climate change, tree migration, jack pine, hydraulic conductivity, embolism. Les arbres peuvent migrer vers le nord en reponse aux changements climatiques et devenir exposes a de nouveaux regimes de photoperiode et d'humidite du sol. Cette etude a evalue les impacts de la photoperiode et ses interactions avec l'humidite du sol et la concentration de dioxyde de carbone ([C[O.sub.2]]) sur la conductivite hydraulique du pin gris (Pinus banksiana Lamb.) et sa vulnerabilite a l'embolie du xyleme. Des plants ont ete exposes a 400 vs. 950 ([micro]molX[mol.sup.-1] [C[O.sub.2]], 60-70 % vs. 30-40 % (de la capacite du champ) d'humidite du sol et a des photoperiodes correspondant a l'origine des semences, et a 5[degrees] et 10[degrees] au nord de l'origine des semences lors d'experiences en serres. Les courbes de vulnerabilite a la cavitation ont ete mesurees pour determiner la pression du xyleme a laquelle 50 % de la conductivite hydraulique etait perdue ([[PSI].sub.PLC50]). Les auteurs ont trouve qu'une [C[O.sub.2]] elevee accroissait significativement la conductivite hydraulique alors que l'humidite du sol la diminuait. Dans des conditions de [C[O.sub.2]] elevee, le xyleme devenait progressivement plus vulnerable a l'embolie avec les changements de regime de photoperiode correspondant a l'origine des semences vers 10[degrees] au nord de l'origine des semences, comme indique par la [[PSI].sub.PLC50] progressivement moins negative. Cependant, une telle tendance n'etait pas detectee dans des [C[O.sub.2]] ambiantes. Les resultats suggerent que l'espece peut devenir moins resistante a la secheresse en fur et a mesure de l'augmentation de la [C[O.sub.2]], genant la migration boreale ou le transfert des semences. Meme a l'interieur de leur distribution naturelle actuelle, les arbres situes pres de la frontiere nord de leur etendue peuvent etre plus vulnerables a l'embolie en fonction de l'augmentation de la [C[O.sub.2]] atmospherique meme sans changement des conditions d'humidite. [Traduit par la Redaction] Mots-cles : changements climatiques, migration des arbres, pin gris, conductivite hydraulique, embolie., Introduction Global warming will increase the frequency and severity of droughts by altering the amount, intensity, frequency, and type of precipitation (Christensen et al. 2007). Rainfalls are likely to increase [...]