Wetland forests around the world have been reduced to a small proportion of their original expanse due to changing climatic conditions and intensification of human land use activities. As a case in point, the Columbia bottomland hardwood forests along the Brazos–Colorado coastal basin on the Gulf coast of Texas are currently threatened by an increasingly erratic hydroclimate in the form of both extreme floods and droughts and by urban expansion. In this study, we use dendrochronology and tree ring carbon isotopes to understand the effect of changing hydroclimatic conditions on the functional attributes of these forests. We examined the tree rings of Quercus nigra at four sites within the Columbia bottomlands, of which one site experiences frequent and prolonged flooding, while the other three are less flood prone. The objectives of this study were to (i) understand the impact of hydroclimatic variation on radial growth, using tree ring width analysis, (ii) assess the magnitude of physiological stress inflicted by extreme hydroclimatic conditions, using tree ring Δ¹³C measurements as a proxy, and (iii) evaluate the relationship between tree ring width and Δ¹³C values. Radial growth across the landscape was influenced most strongly by the midgrowing season climate, while the early growing season climate had the strongest effect on Δ¹³C. Growth inhibition was minimal, and tree ring Δ¹³C values were not affected in trees at the wetter site under extreme hydrological conditions such as droughts or floods. In addition, trees at the wet site were less sensitive to precipitation and showed no response to higher temperatures. In contrast, trees at the three drier sites experienced growth inhibition and had lower tree ring Δ¹³C values during dry periods. Our results indicate more favorable growing conditions and lower stress in trees growing under wetter hydrological conditions. Management and conservation strategies dependent on site-specific conditions are critical for the health of these wetland forests under a rapidly changing hydroclimate. This study provides the first dendrochronological baseline for this region and a better understanding of favorable conditions for the growth and health of these forests, which can assist in management decisions such as streamflow regulation and conservation plans.

中文翻译：

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滩硬木森林生长和应激反应水文气候变化：从证据和树轮树环Δ ¹³ C值

由于气候条件的变化和人类土地利用活动的加剧，世界各地的湿地森林已减少到原始面积的一小部分。举例来说，德克萨斯州墨西哥湾沿岸的布拉索斯-科罗拉多海岸盆地沿岸的哥伦比亚底层硬木森林目前受到极端洪水和干旱以及城市扩张形式日益不稳定的水文气候的威胁。在这项研究中，我们使用树木年代学和年轮碳同位素来了解改变水文气候条件对这些森林功能属性的影响。我们检查了栎木的年轮在哥伦比亚河谷地带的四个地点，其中一个地点经常遭受洪水和长时间洪灾，而其他三个地点则较不容易发生洪水。本研究的目的是（ⅰ）理解上的径向生长水文气候变化的影响，使用树环宽度分析，（ⅱ）评估由极端水文气候条件造成的生理应力的大小，使用树环Δ ^13个Ç测量作为代理，和（iii）评估年轮宽度之间的关系Δ ¹³ C值。在景观径向生长是由midgrowing季节气候最强烈影响，而早期生长季节气候对作用最强Δ ¹³C.生长抑制是最小的，并且树环Δ ¹³ C值没有在极端水文条件如干旱或洪水下多雨站点树受到影响。此外，湿地的树木对降水的敏感性较低，并且对高温没有反应。与此相反，在三个干燥部位有经验的生长抑制和树木有较低的年轮Δ ¹³干旱时期的C值。我们的结果表明，在潮湿的水文条件下生长的树木具有更好的生长条件和更低的压力。在快速变化的水文气候下，取决于特定地点条件的管理和保护策略对于这些湿地森林的健康至关重要。这项研究提供了该地区的第一个树木年代学基线，并更好地了解了这些森林的生长和健康状况，这可以有助于管理决策，例如流量调节和保护计划。