# Carbon Dynamics of _Pinus palustris_ Ecosystems Following Drought
## 1 Introduction  
Limitations in water availability in forested ecosystems can elicit varied responses over contrasting spatial and temporal scales. On short temporal and spatial scales, individual trees or stands can alter their leaf morphology to limit the loss of water from the system and try to reduce the stress that is being imposed on the plant and the ecosystem [1]. Forests may also reduce their physiological activity, on the order of minutes to hours, to reduce water loss when demands are greatest during drought or high afternoon vapor pressure deficits [2]. These reductions in physiological activity are typically associated with stomatal limitations, driven by lack of soil water availability. Individual forests can respond to drought in a variety of ways. During seasonal droughts (several months in length), forests may facultatively reduce their leaf area with a premature dropping of foliage or a reduction in leaf development to reduce evaporative demands on the system [3; 4; 5]. It has been hypothesized that the timing of leaf flush co-occurs with a plant's ability to maximize carbonuptake prior to seasonal drought becoming so severe that respiration dominates the leaf-level carbon balance, which leads to an overall reduction in the plant's carbon stores [6]. This strategy, ultimately, aids in the conservation of water and, at the same time, limits additional carbon losses; however, this also limits the plant's and forest's ability to sequester carbon immediately after the drought is alleviated [4; 6]. Over long time periods and large spatial scales (100 to 1000 years and 100 to 1000 km\({}^{2}\)), the landscape is a mosaic of smaller-scale ecosystems [7]. These mosaics, in many cases, have developed in association with drought, which has also been shown to influence the structure and function of forested ecosystems based on their position within the landscape. The combination of drought, legacy effects, and underlying environmental conditions further drives gene expression, and leads to specific phylogenetic traits that create variations in forest types and their functions [7; 8; 9]. This variation due to environmental pressures and landscape position has led to varying degrees of resilience in forest ecosystems along their distributional gradient [10; 11]. With climate change, questions have arisen regarding the future distribution and survival of several key trees and forest types across the globe [12]. Shifts in climate envelopes are expected to cause changes in tree species' distributional ranges [12; 13; 14], which will lead to greater uncertainty in estimates of future carbon sequestration of these forests. To better understand changing conditions and their roles on forest carbon capacity, the scientific community must undertake additional studies that utilize environmental gradients as \"treatments\" to facilitate the extrapolation of results to larger spatial scales and modeling efforts [15]. Only then will we begin to develop the understanding needed to predict the future structure and function of forests [11; 16; 17]. We began a long-term study using an edaphic moisture gradient as a proxy for climate change in longleaf pine (_Pinus palustris_ Mill. )-dominated forests within the Southeastern United States (SEUS), to better understand their carbon dynamics [18; 19; 20]. The longleaf pine forest is an excellent example of how placement of a stand within the landscape has led to variation in structure and function, particularly when influenced by water limitations [21; 22; 23; 24]. Soil water holding capacity has been shown to be the primary variable that controls net primary production (NPP) within the longleaf ecosystem [21], and was linked to plant rooting zones and access to the water table [23; 25]. Longleaf pine has historically been a significant part of the landscape in the SEUS, but intensive forest management has led to large-scale forest conversion to loblolly pine (_Pinus taeda_ L.) plantation [26], resulting in a fragmented habitat.