nena masthead
SENA Home Staff & Editors For Readers For Authors

Instream Woody Debris and Riparian Forest Characteristics in the Sabine River, Texas
Matthew McBroom, Michael Ringer, and Yanli Zhang

Southeastern Naturalist, Volume 13, Special Issue 5 (2014): 1–14

Full-text pdf (Accessible only to subscribers.To subscribe click here.)

 



Access Journal Content

Open access browsing of table of contents and abstract pages. Full text pdfs available for download for subscribers.

Issue-in-Progress: Vol. 23 (1) ... early view

Current Issue: Vol. 22 (3)
SENA 22(3)

Check out SENA's latest Special Issue:

Special Issue 12
SENA 22(special issue 12)

All Regular Issues

Monographs

Special Issues

 

submit

 

subscribe

 

JSTOR logoClarivate logoWeb of science logoBioOne logo EbscoHOST logoProQuest logo


1 Instream Woody Debris and Riparian Forest Characteristics in the Sabine River, Texas Matthew McBroom1,*, Michael Ringer1, and Yanli Zhang1 Abstract - We examined instream large woody debris (LWD) dynamics on the Sabine River, TX. All wood >10 cm in diameter and >2 m long was measured on four river meanders (meander wavelengths) below the dam on Toledo Bend Reservoir. We determined LWD species, degree of decay, bank orientation, jam association, and stage contact. We also measured riparian vegetation characteristics on each meander. LWD volumes were significantly greater at the site immediately below Toledo Bend Dam, due to the relatively steeper channel gradient and higher rates of channel erosion. Based on mass balance estimates, between 11 and 21% of total annual recruitment came from upstream fluvial transport, and the remainder resulted from bank erosion and tree mortality. We estimated average LWD residence time to be 12–14 years. The lower Sabine River is transport-limited for sediment, and the same is true for LWD. Based on these measurements, it is unlikely that Toledo Bend Reservoir is having a significant impact on LWD dynamics at the measurement reaches due to lacustrine wood storage. Of greater concern in the study system are riparian forest degradation and invasive species spread, which may dramatically affect future LWD loadings and residence times, and thus, riverine biota. Introduction Large woody debris (LWD) is an extremely important structural and functional component for aquatic ecosystems (Wallace et al. 1993). While LWD habitat may only be a small part of the total habitat surface in southeastern US rivers (≈4%), it may support over 60% of the total invertebrate biomass for a river stretch (Benke et al. 1985). In addition, fish species obtained at least 60% of their prey biomass from snag habitat (Benke et al. 1984). Ecologically, LWD provides a reservoir for nutrients and energy vital to the detrital food chain, nutrient cycling, plant growth, and productivity (Goodburn and Lorimer 1998, Harmon et al. 1986, Huston 1993, Muller and Liu 1991). Stable debris slows fine organic matter transport and allows greater opportunity for biological processing of fine organic detritus (Swanson et al. 1976). Invertebrates and aquatic insects utilize LWD as direct and indirect food sources, attachment sites for feeding and retreat or concealment, material for larval cases, a substratum for pupation and emergence, and sites for egg deposition (Wallace et al. 1993). Consequently, management practices that alter LWD dynamics may have dramatic effects on aquatic ecosystem productivity. LWD, including trees, snags, and logjams, has been shown to also influence stream morphology (MacDonald et al. 1982, Mutz, 2000, Shields and Nunnally 1984). Nunnally and Keller (1979) found that standing riparian trees play a vital 1Stephen F. Austin State University, Box 6109 SFA Station, Nacogdoches, TX 75962. *Corresponding author - mcbroommatth@sfasu.edu. Manuscript Editor: Jerry Cook Proceedings of the 5th Big Thicket Science Conference: Changing Landscapes and Changing Climate 2014 Southeastern Naturalist 13(Special Issue 5):1–14 Southeastern Naturalist M. McBroom, M. Ringer, and Y. Zhang 2014 2 Vol. 13, Special Issue 5 role in slowing bank erosion. Wood in natural quantities results in complex flow regime patterns (Mutz 2000). Keller and Swanson (1979) add that tree root-wads in a hardwood forest were found to protect a length of bank five times the trunk diameter. The hydraulics of stream river systems are in a perpetual state of dynamic fluctuation as the flow of energy is distributed through the drainage basin, shaping channel morphology. Removing debris from streams increases current velocity and reduces the amount of material that can provide protection to the bank. These changes cause an acceleration of bank erosion and a wider channel (Nunnally 1978). Also, woody debris helps control river gradient. Abbe et al. (2003) reported that clearing wood from the Red River in Louisiana caused portions of the river to incise more than 4 m. LWD provides additional roughness and resistance (Shields and Gippel 1995) as it redirects the flow of water, slows velocity, increases depth, and creates backwaters, local scour, and various types of pools (Robison and Beschta 1990). The number of morphological structures, such as bars, is also increased by the presence of LWD (Harmon et al. 1986, Keller and Tally 1979). Because of the additional flow resistance created by LWD in the stream system, there can be a net increase in sediment storage, changes in bed texture, and changes in sediment transport (Smith et al. 1993). These combined factors can change the local and reach-average hydraulic conditions, which may affect channel bank stability (Bilby 1984, Trimble 1997). While the importance of LWD to ecosystem structure and function in the Southeast is widely accepted, very little empirical information exists to quantify LWD biomass and dynamics in low-gradient rivers in the region (including Texas). However, rapid population growth in recent years coupled with greater demands on limited water resources has generated concern about the health and viability of river systems in the southeastern US. This concern prompted our examination of LWD dynamics in southeastern rivers to quantify possible management effects on LWD dynamics. Because woody debris is critical for proper function of aquatic ecosystems, it is imperative that woody debris budgets be evaluated in order to ensure that adequate habitat for aquatic biota is maintained in lower coastal plain rivers. The purposes of this study were to: 1) measure LWD loadings and riparian vegetation volumes in the lower Sabine River; 2) determine if significant differences exist among sites in measured variables like relative degree of decay, bank orientation, jam association, root-wad presence and likely origin; and 3) conduct a basic massbalance calculation for instream LWD downstream of the largest reservoir in the southeastern US, Toledo Bend. Methods Field-site description This study was conducted on the lower Sabine River downstream of Toledo Bend Reservoir on the boundary between Texas and Louisiana (Fig. 1). The total drainage area of the Sabine River is 25,267 km². Located in the Gulf Coastal Plain physiographic province, the region has a humid subtropical climate (Phillips 2003). The Sabine has the greatest total flow of any river in Texas, with average annual Southeastern Naturalist 3 M. McBroom, M. Ringer, and Y. Zhang 2014 Vol. 13, Special Issue 5 flows ranging from 402 cms in 1975 to 30 cms in 2011, with an overall average flow of 220 cms for the 1961–2011 period of record at the downstream-most US Geological Survey (USGS) gauge at Deweyville, TX. The soils surrounding the lower Sabine River were mostly light-colored, fine, sandy loams with subsoils that were loamy sand to plastic clay in texture, and yellow to red in color. The vegetation was mostly composed of a mixture of Pinus taeda L. (Loblolly Pine) and various hardwoods like Quercus nigra L. (Water Oak), Quercus phellos L. (Willow Oak), and Liquidambar styraciflua L. (Sweetgum). Wet Figure 1. Sampling site locations for large woody debris measurements on the lower Sabine River. Southeastern Naturalist M. McBroom, M. Ringer, and Y. Zhang 2014 4 Vol. 13, Special Issue 5 areas of the floodplain are dominated by Taxodium distichum L. (Baldcypress), Salix nigra Marsh. (Black Willow), Betula nigra L. (River Birch), and the invasive exotic Triadica sebifera (L.) Small (Chinese Tallow). Much of the surrounding land had previously been cultivated and is now used for pasture or has been reforested, either by natural seeding and resprouting or by planting. We chose four meander wavelengths as study reaches that represented the upper, middle, lower, and estuarine sections of the river. Three sites were located near USGS river-gauging stations, and discharge data were obtained from these stations. The Burkeville site (USGS 0802600) was northernmost and closest to the dam, followed by Bon Wier (USGS 08028500), and Deweyville (USGS 08030500). We measured sites once—during fall 2007 for Deweyville and summer 2008 for the other three sites. Following Hurricane Rita in 2005, the Sabine River Authority of Texas removed all bankside woody debris for a few river km above the southeast Texas intake canal to prevent possible water supply disruptions to the region. Our fourth site, denoted as the southern site, was located in the de-snagged zone, and we used it to estimate the amount of time required for woody debris to return to pre-snagging densities. LWD measurement methods To ensure that we had access to our sample sites, we measured instream LWD during the lowest available river stages. Based on seasonal streamflow patterns and hydropower release schedules from Toledo Bend Reservoir, we chose sample dates when the river stage fell to a level low enough to allow access to a maximum number of stems. Minimum LWD size was 10 cm in diameter and 2 m in length. We measured log length and top butt diameter, and identified the logs to species when possible. We determined relative degree of decay based on methods reported by Hyatt and Naiman (2001) and used a scale from 1 to 5, where 1 meant that no sign of decay was visible and all bark and branches were intact, and 5 indicated that the bark was absent and the wood was irregularly shaped and was darkened. We determined bank orientation using the following criteria: 0° meant that the root wad was facing upstream and the LWD was parallel to the bank, a bank orientation of 90° indicated that the log was perpendicular to the channel, and a bank orientation of 180° indicated the LWD was facing downstream. In addition, we noted the presence of a root wad and branches with a yes or no. We categorized LWD origin as local riparian or upstream import and noted whether the LWD was an individual piece, jam-associated, or a fallen tree. We defined a debris jam as a discrete grouping of several pieces. Finally, we classified each LWD by stage contact zone: zone 1 indicated that the piece was sitting in a low-flow contact area, zone 2 indicated that it was within the bank-full channel, zone 3 indicated that it extended over the bank-full channel, and zone 4 indicated that LWD was beyond the bank-full channel. Bankside vegetation data collection We performed an inventory of the bankside vegetation at all four sites to determine the total volume of standing timber. We established 0.04-ha and 0.004-ha Southeastern Naturalist 5 M. McBroom, M. Ringer, and Y. Zhang 2014 Vol. 13, Special Issue 5 circular plots about 20 m from the bank on both the west and east banks at all four sites. This distance was based on predictions by Robison and Beschta (1990) that at least 50% of woody loading comes from within 15 m of the channel edge. In the 0.004-ha plots, we measured top and bottom diameters, length, and distance from the bank for woody debris on the forest floor. In the 0.04-ha plots, we measured and recorded diameter at breast height (DBH), total tree height, and distance from the bank for all trees ≥10 cm DBH. We followed Clark and Souter (1996) to calculate volumes using Girard Form Class 81 for pines and 79 for hardwoo ds. Statistical analysis For categorical data, we used chi-square tests to determine if a category was uniformly distributed, i.e., the same number of individuals in each category. We chose a uniform distribution because there were no a priori assumptions about expected distributions. We used the chi-square tests (α = 0.05) available in the statistical analysis system (SAS) version 9.2 (SAS Institute, Inc. 2008) to examine seven categories within the individual sites: degree of decay, branch presence, origin, bank orientation, root-wad presence, position, and stage contact. The null hypothesis in each case was that there was a uniform LWD distribution in each category. We then developed contingency tables to test these same seven categories between the sites. The null hypothesis was that there was no association between each variable and the four sites. Finally, we used an ANOVA with Tukey’s honest significant difference for multiple comparisons to determine if there were significant differences between sites in riparian forest density and instream LWD volumes. Conceptual models of LWD dynamics Benda and Sias (2003) developed functions that define wood recruitment into a given study reach (Li): Li = Im + If + Ibe + Is + Ie, (1) where Im is the forest mortality, If is the toppling of trees after a fire or during a windstorm, and Ibe is the recruitment due to bank erosion. They go on to define Is as the wood brought into the system because of landslides, debris flows, and snow avalanches, and Ie as the exhumation of buried wood. Benda and Sias (2003) further developed a function that defines wood recruitment based on chronic forest mortality only: Im = [BLMHPm] N, (2) where Im is the annual flux of LWD. They define BL as the volume of standing live biomass per unit area, M as the rate of mortality, H as the average stand height, Pm as the average fraction of stem length that becomes in-channel LWD, and N as the number of banks contributing LWD. One of the biggest contributors of LWD is bank erosion. In many regions, the greatest amount of in-channel debris is found on the cutbank side of the river (Wallace and Benke 1984), and that is one reason why the equation developed by Benda Southeastern Naturalist M. McBroom, M. Ringer, and Y. Zhang 2014 6 Vol. 13, Special Issue 5 and Sias (2003) for bank erosion is appropriate for the Sabine River. The function used for LWD recruitment due to bank erosion is: Ibe = [BLEPbe] N, (3) where BL is the standing biomass, E is the mean bank erosion rate, and Pbe is the expected stem length of the debris that falls into the channel. We applied this model to the lower Sabine River with data collected in the current study. For the four study reaches, we calculated the overall lateral recruitment (Li). We converted the volume of live standing biomass (m3 ha-1) measured to m3 m-2, assumed a mortality rate of 1% based on relative mature forest age for the dominant species present, and measured average stand heights. Number of contributing banks was 2 for mortality input calculations, 1 for bank erosion. The proportion of stem becoming biomass was 0.13 for mortality calculations, and 0.75 for bank erosion. We assumed fall direction for mortality to be non-preferential, and we chose a proportion of 0.13 based on long term averages compiled by Van Sickle and Gregory (1990). Fall direction for bank erosion was based on values given in Benda and Sias (2003). We derived estimates for mean bank-erosion rates of 0.1341 m yr-1for Burkeville, 0.10 m yr-1 for Bon Wier, and 0.05 m yr-1 for Deweyville and the southern site based on Heitmuller and Greene (2009). We then calculated the total woody debris budget from the basic relationship as summarized by Benda and Sias (2003) as follows: ΔSc = [Li - Lo + Qi / Δx - Qo / Δx - D] Δt, (4) Where: ΔSc = change in woody debris storage Δx = reach length Δt = time interval Li = lateral recruitment of LWD within the reach Lo = wood loss due to overbank depositions in flood events or the abandonment of jams Qi = fluvial transport of wood into the reach Qo = transport of wood out of the reach D = loss of wood due to decay Results LWD mass and volume A total of 374 pieces of LWD were found, with 93, 95, 119, and 67 pieces at the Burkeville, Bon Wier, Deweyville, and southern sites, respectively (Table 1). The total volume of LWD was significantly greater at the Burkeville study site, immediately below Toledo Bend Reservoir. LWD volumes were similar at sites further downstream. Burkeville and the downstream sites had similar LWD counts (number of stems), but because volume was much higher at Burkeville, we inferred that piece size was larger there than at the other sites. Total bankside vegetation volume was not significantly different among the four sites (Table 1). Southeastern Naturalist 7 M. McBroom, M. Ringer, and Y. Zhang 2014 Vol. 13, Special Issue 5 LWD characteristics by site Degree of decay was significantly different at each of the 4 sampling sites. Decay class 3 was the most prevalent at Burkeville, Bon Wier, and Deweyville, while significantly more LWD was found in decay class 4 at the southern site than at the other three sites further upstream. Also, jam-associated LWD pieces were more likely to be decayed at Burkeville, Deweyville, and the southern site. There was not a statistically significant relationship between whether a piece was associated with a jam and degree of decay at Bon Wier. In addition, decayed wood was more likely to be in contact with low flows of the river at Burkeville, Deweyville, and the southern site, while there was no relationship between decay and stage contact at Bon Wier. LWD bank-position category was significantly different at the southern site and at Bon Wier. At the southern site, half the LWD was located in jams. Bank orientation was significantly different among sites. Pieces were more likely to have a 0° orientation (root wad upstream, oriented with the flow) at Burkeville and Bon Wier. However, at Deweyville and the southern site, orientation was more likely to be 180°. Pieces were more likely to have intact root wads at Burkeville, Bon Wier, and Deweyville, while LWD at the southern site was more likely to be without a root wad. Root wads would tend to cause a 0° orientation with the flow, which helps explain why pieces at the southern site have a greater frequency of 180° orientations. However, when contingency tables were analyzed for root wad versus orientation, no significant differences were found at any of the sites. As noted above, pieces at the southern site were more decayed, and pieces with greater decay are less likely to attach to a root wad. In terms of stage contact, a significantly greater proportion of LWD was in the low-flow contact zone or within the bank-full channel at all four sites, as opposed to being beyond the bank-full channel. Pieces in the low-flow contact zone are subject to greater mechanical battering and decay. In addition, very large floods would be required to float and transport larger pieces (particularly if the root wad is still attached) out of the bank-full channel. Branches were more likely to be absent at Bon Wier and the southern site, but frequencies were not significantly different at the other two sites. As expected, when analyzing the contingency table for branch presence and degree of decay, significant differences were found among categories, with more decayed pieces lacking branches. We also conducted contingency-table analysis for bank position Table 1. Total counts, volume, and ANOVA results (using Tukey’s honest significant difference) for LWD and bankside vegetation for each study site along the lower Sabine River, TX. Mean values with the same letter are not significantly different at α = 0.05 Bankside Tukey grouping LWD LWD Reach Volume per volume for LWD for bankside count volume (m3) length (km) length (m3/km) (m3 ha-1) volume vegetation Burkeville 93 98.94 1.16 85.29 349.9 A A Bon Wier 95 29.67 1.00 29.67 248.1 B A Deweyville 119 49.43 1.06 49.63 407.1 B A Southern 67 30.43 2.29 13.29 476.3 B A Southeastern Naturalist M. McBroom, M. Ringer, and Y. Zhang 2014 8 Vol. 13, Special Issue 5 versus branch presence, with frequencies found to be significantly different at all four sites. In general, LWD lacking branches was more likely to be jam-associated, and pieces with branches were typically more likely to occur singly or as bank-fall. This finding is consistent with degree of decay and position as noted above. The chi square goodness-of-fit test was also run on volume of LWD by origin. In terms of total volume, frequency of origin was significantly different at all four sites, with about 60–90% of the total volume originating from a local source. Larger keystone pieces tended to be less decayed and less mobile, and accounted for more of the overall volume at each site. All four study sites had large amounts of standing vegetation, and most of the overall LWD volume originated from bankside sources. LWD recruitment rates The southern site was important to the study because all of the LWD had been removed from the site three years prior to sampling, following Hurricane Rita. This knowledge of a confirmed date at which there was no LWD present, enhanced our ability to estimate the time required for LWD recruitment into the Sabine River. When compared to the LWD counts at the other three sites, the southern site had the least LWD within its reach, with 13.29 m3 km-1, about half that found at the next lowest site, Bon Wier, with 29.67 m3 km-1(Table 1). Based on our sampling, we estimated that about 12–14 years would be required for LWD volume at the southern site to be equal what was observed at the Deweyville site. This figure could change dramatically depending on the number and size of catastrophic events (i.e., hurricanes and mass flooding) that impact the area (Phillips and Park 2009). Conceptual models of LWD dynamics Lateral recruitment estimates illustrate differences between the four river segments (Table 2). Burkeville, which has the highest total LWD loading (85.29 m3 km-1) also had the highest recruitment rate, and bank erosion was the primary source for recruitment. At Deweyville and the southern sites, the riparian forest volume was slightly higher with smaller tree sizes and much lower bank erosion rates; mortality was the dominant recruitment source there. We then compared these estimates of lateral recruitment with the overall woody debris budget (Equation 4, above). To accomplish this, an estimate of woody debris decay was needed. While specific estimates were not available, Spies et al. (1988) estimated annual decay rates of between 2 and 7% of live biomass in a forest floor Table 2. Lateral recruitment budget estimates (m3 km-1 yr-1) for the four study reaches on the Lower Sabine River, TX (Benda and Sias 2003). Mortality Bank erosion Total lateral Site recruitment (Im) recruitment (Ibe) recruitment (Li) Burkeville 1.40 3.52 4.92 Bon Wier 0.95 1.86 2.81 Deweyville 1.80 1.53 3.33 Southern 1.92 1.79 3.71 Southeastern Naturalist 9 M. McBroom, M. Ringer, and Y. Zhang 2014 Vol. 13, Special Issue 5 environment. Due to warm temperatures and high humidity, southeastern Texas has one of the highest wood-decay rates in the continental United States (Harmon et al. 1986), so we used the higher end of this range, 7%, for budget calculations. With a 7% decay rate, the average decay-based residence time for an average piece of LWD is 14.29 years. For the Burkeville and Deweyville sites, recruitment volume was a net positive, meaning that fluvial transport of wood into the reach was occurring at a greater rate than fluvial outflow. Recruitment volume was highest at Burkeville, which was expected given the higher rates of bank erosion immediately downstream of Toledo Bend Reservoir reported by Phillips (2003). This finding is consistent with measured source data reported above and is also consistent with the lateral recruitment estimates for Burkeville, where recruitment due to erosion is 2.5 times higher than recruitment due to mortality (Table 3). It is unlikely that the Toledo Bend Dam had a significant effect on reducing LWD loadings due to reservoir interruptions of fluvial LWD at the Burkeville site. Additional measurements immediately below the dam in the scour zone described by Phillips (2003) would be necessary to determine if these LWD reservoir storage effects extend upstream of the Burkeville site. At Deweyville, forest mortality recruitment is greater than bank-erosion recruitment, due to the lower gradients at this site. Also, with lower gradients more LWD accumulations from upstream may be occurring. At Bon Wier, we estimated that more wood is being recruited than stored in the channel, so the loss may be due to offsite transport (0.54 m3 km-1 yr-1) as fluvial outflow or floodplain deposition. At the southern site, LWD accumulation had only occurred for about 3 years since the post-Hurricane Rita de-snagging operation, with a lateral recruitment estimate of 10.47 m3 km-1, meaning that the difference of 2.82 m3 km-1 may have come in as fluvial inflow from further upstream. Discussion Total instream LWD volume was found to be significantly higher at Burkeville (immediately below Toledo Bend Reservoir) than the other four sites likely due to greater bankside erosion rates and geomorphologic differences between sites. This result is supported by Phillips’ (2003) study of the lower Sabine River in which Table 3. Estimated woody debris storage, decay, and recruitment by sampling site for the lower Sabine River, TX. Variable Burkeville Bon Wier Deweyville Southern Total recruitment (Li, m3 km-1 yr-1) 4.92 2.81 3.33 3.71 Volume decayed (D, m3 km-1 yr-1) 0.34 0.20 0.23 0.22 Net recruitment (m3 km-1 yr-1) 4.58 2.61 3.10 3.49 Recruitment in 14.29 Yrs (m3 km-1) 69.29 37.29 44.29 49.86 Volume measured (m3 km-1) 85.29 29.67 49.63 13.29 (Qi - Qo - Lo) Vol. (m3 km-1 yr-1)A 1.05 -0.54 0.38 N/AB AQi = LWD from fluvial inflow, Qo = LWD from fluvial outflow, Lo = floodplain deposition. BEstimates are not available for the southern site since it was de-snagged 3 years prior to measurement. Southeastern Naturalist M. McBroom, M. Ringer, and Y. Zhang 2014 10 Vol. 13, Special Issue 5 he examined the effects of Toledo Bend Reservoir on the river downstream of the dam. In that study, significant bank erosion, sandbar migration, and LWD inputs at the Burkeville site were observed (Phillips 2003). The banks at Burkeville were the steepest of the three study sites, and were heavily eroded, resulting in greater LWD inputs than we observed at the other sites. Phillips (2003) reported that the left bank was characterized by many fallen trees and bank-eroded trees, and that overall, this section of the river was very dynamic, with many migrating sandbars and higher rates of bank erosion. In contrast, lower rates of channel erosion were reported near the Bon Wier section of the river (Phillips 2003). The Deweyville site has a completely different form, with lower banks and fewer sandbars (Phillips 2003). The left bank at Deweyville had large amounts of LWD and numerous tilted trees, and the right bank had former bank scarps with abundant LWD at the bank base and in the channel. The LWD loadings observed in our study were similar to those observed by Phillips (2003) (Table 1). Evaluating local geomorphic features and understanding how river flow was affecting the banks at the local sites were the best ways to explain the LWD loading differences. The Burkeville site was characterized by active erosion and by larger diameter trees standing closer to the channel, which explained the higher volumes of LWD. Total LWD loading was best explained by the combination of bank erosion rates and riparian forest structure. In terms of number of pieces, frequency of LWD origin was significantly different at Bon Wier and Deweyville. Wood at these two sites was more likely to be local in origin. Origin frequencies were evenly distributed at the other two sites. Because the Burkeville site is downstream of Toledo Bend Reservoir where banks are steep and erosion is high, it would be expected that a greater number of wood pieces would originate from stream bank erosion, with less relative upstream contribution. This recruited wood would be deposited below the zone of influence immediately below the dam, at the Burkeville site. At the southern site, more decayed wood indicated more pieces being transported in from elsewhere. The Burkeville and Deweyville sites had a uniform distribution for the position category, meaning that the LWD present had an equal probability of being associated with jams or present as individual pieces. At Bon Wier, a significantly greater portion of LWD occurred as single pieces than as part of debris jams. Jamentrained pieces were also significantly less likely to have intact branches. Large, infrequent floods would be required to mobilize some of the jams that were found on the Sabine, but as jam-entrained LWD decays and fragments over time, smaller and more mobile decayed pieces move downstream to the southern site, where about half of the LWD was located in jams. However, these smaller pieces represent a lower overall contribution to total LWD volume than a comparable number of larger pieces. Because we found no significant differences in total bankside volume among sites, we conclude that recent hurricanes have not resulted in significant overall reduction in quantity of riparian forest vegetation at the sites close to the Gulf Coast. This lack of statistical significance can be attributed in part to the large Southeastern Naturalist 11 M. McBroom, M. Ringer, and Y. Zhang 2014 Vol. 13, Special Issue 5 amount of variation observed among individual plots in each stand. Riverside forest vegetation volumes tend to be rather heterogeneous overall, with much higher volumes on the cut-bank side of the meander than on the deposition side. However, there was a great deal of variation within meander wavelengths, and additional vegetation sampling would be needed to make specific determinations about effects on riparian forest structure and composition along the Sabine River. Also, Hurricane Rita, which made landfall at the Sabine estuary on 24 September 2005 resulted in a significant increase in L WD contributions to the river (Phillips and Park 2009). The northernmost Burkeville site had larger trees overall compared to the more downstream sites. In particular, the invasive exotic Chinese Tallow Tree tended to be much more prevalent at the southern and Deweyville sites than at the two sites further upstream. This would be expected given this tree’s ability to dominate the wet conditions characteristic of these two sites. Also, given the high seed production rate, high primary productivity, and extensive colonization of the lower Gulf Coastal Plain of Texas, continued domination of this species in the riparian forest is likely at these two sites (Bruce et al. 1995). LWD budget estimates are a reasonable approximation of LWD dynamics in the lower Sabine River. One significant conclusion from this budget analysis is that the riparian forest density and volume are the most important factors for LWD recruitment. Fluvial transport into the reach was estimated to be between 11 and 21% of total annual recruitment, with the remainder governed by lateral recruitment, which depends mostly on surrounding forest density and bankside erosion rates. These estimates are consistent with recruitment rates measured upstream. Therefore, the most effective means of enhancing LWD recruitment for the lower Sabine would be to protect and enhance the riparian forest. There does not seem to be much evidence from this analysis that the Toledo Bend Dam had a significant impact on LWD dynamics in the lower Sabine River due to upstream LWD storage in the reservoir. As noted by Phillips (2003), the lower Sabine is transport-limited for sediment, and the same is true for LWD. It is likely that the large volumes of LWD that were historically in the rivers of East Texas were the products of extensive, more contiguous riparian forests composed of relatively decay-resistant species like cypress and oak, and that centuries of riparian forest degradation and spread of less decay-resistant and invasive species like Chinese Tallow has resulted in lower maximum potential LWD loadings. A majority of LWD research has been conducted in higher-gradient streams, where fluvial export is an important factor controlling LWD dynamics. Very little research has been conducted on low-gradient Coastal Plain streams in the Southeast. One exception to this is a study by Beneke and Wallace (1990) in the Ogeechee River in the Coastal Plain of Georgia, in which they found that decomposition and fragmentation of LWD is the most common fate for LWD rather than direct fluvial export. We reached a similar conclusion for the lower Sabine River, TX in this study. In addition, as concluded by Beneke and Wallace (1990) for the Ogeechee River, as the larger, more stable, and persistent LWD pieces in the lower Sabine Southeastern Naturalist M. McBroom, M. Ringer, and Y. Zhang 2014 12 Vol. 13, Special Issue 5 break down over decades, they will provide an important source of organic matter and habitat for aquatic organisms. Additional studies are needed to determine the optimal LWD loading for riverine invertebrate and fish populations in the lower Sabine. Additional research is also needed on LWD loading and dynamics on other southeastern lower Coastal Plain rivers. Acknowledgments This study was funded by the Texas Water Development Board. The assistance of Mark Wentzel and Greg Malstaff is greatly appreciated. The Sabine River Authority of Texas provided invaluable information, river transportation, and much assistance to this project. Special thanks go to Luke Sanders, Brian King, John Payne, Jamie East, Jerry Wiegreffe, and Elizebeth Loomis. Assistance and support was also provided by the Waters of East Texas (WET) Center at the Arthur Temple College of Forestry and Agriculture at Stephen F. Austin State University. Literature Cited Abbe, T.B., A.P. Brooks, and D.R. Montgomery. 2003. Wood in river rehabilitation and management. Pp. 367-389, In S.V. Gregory, K.L. Boyer, and A.M. Gurnell (Eds.). The Ecology and Management of Wood in World Rivers. American Fisheries Society Symposium 37, Bethesda, MD Benda, L.E., and J.C. Sias. 2003. A quantitative framework for evaluating the mass balance of in-stream organic debris. Forest Ecology and Management 172:1–16. Benke, A.C., and J.B. Wallace. 1990. Wood dynamics in coastal plain Blackwater Streams. Canadian Journal of Fisheries and Aquatic Science 47:92–99. Benke, A.C., R.L. Henry III, D.M. Gillespie, and R.J. Hunter. 1985. Importance of snag habitat for animal production in southeastern streams. Fisheries 10(5):8–13. Bilby, R.E. 1984. Post-logging removal of woody debris affects stream channel stability. Journal of Forestry 82:609–613. Bruce, K.A., G.N. Cameron, and P.A. Harcombe. 1995. Initiation of a new woodland type on the Texas coastal prairie by the Chinese Tallow tree (Sapium sebiferum (L.) Roxb.). Bulletin of the Torrey Botanical Club 122:215–225. Clark, A. III, and R.A. Souter. 1996. Stem cubic-foot volume tables for tree species in the Deep South Area. Research Papr SE-293. US Department of Agriculture Forest Service, Southern Research Station, Asheville, NC. 131 pp. Goodburn, J.M., and C.G. Lorimer. 1998. Cavity trees and coarse woody debris in oldgrowth and managed northern hardwood forests in Wisconsin and Michigan. Canadian Journal of Forest Research 29:427–438. Harmon, M.E., J.F. Franklin, F.J. Swanson, P. Collins, S.V. Gregory, J.D. Lattin, N.H. Anderson, S.P. Cline, N.G. Aumen, J.R. Sedell, G.W. Lienkaemper, K. Cromack, Jr., and K.W. Cummins. 1986. Ecology of coarse woody debris in temperate ecosystems. Advances in Ecological Research 15:133–302. Heitmuller, F.R., and L.E. Greene. 2009. Historic channel adjustment and estimates of selected hydraulic values in the lower Sabine River and Lower Brazos River Basins, Texas and Louisiana. US Geological Survey Scientific Investigations Report 2009-5174. Washington, DC. 143 pp. Southeastern Naturalist 13 M. McBroom, M. Ringer, and Y. Zhang 2014 Vol. 13, Special Issue 5 Huston, M.A. 1993. Models and management implications of coarse woody debris impacts on biodiversity. Pp. 139–143, In J.W. McMinn and D.A. Crossley, Jr. (Eds.). Biodiversity and coarse woody debris in southern forests, proceedings of the workshop on coarse woody debris in southern forests: Effects on biodiversity. USDA Forest Service Gen. Tech. Rep. SE-94. Asheville, NC. Hyatt, T.L., and R.J. Naiman. 2001. The residence time of large woody debris in the Queets River, Washington, USA. Ecological Applications 11:191–202. Keller, E.A., and F.J. Swanson. 1979. Effects of large organic material on channel form and fluvial processes. Earth Surface Processes. 4:361–380. Keller, E.A., and T. Tally. 1979. Effects of large organic debris on channel form and fluvial processes in the costal redwood environment. Pp. 169–197, In D.D. Rhodes and P.G. Williams (Eds.). Adjustment of the Fluvial System. Proceedings of the Tenth Annual Geomorphology Symposium.. State University of New York, Binghamton, NY. MacDonald, A., E.A. Keller, and T. Talley. 1982. The role of large organic debris in stream channels draining Redwood forests in northwestern California. Pp. 226–245, In D.K. Harden, D.C. Marran, and A. MacDonald (Eds.). Late Cenzoic History and Forest Geomorphology of Humbold County, California. Friends of the Pleistocene, Pacific Cell Field Trip Guidebook, San Fransisco, CA. Muller, R.N., and Y. Liu. 1991. Coarse woody debris in old-growth deciduous forest on the Cumberland Plateau, Southeastern Kentucky. Canadian Journal of Forest Research 21:1567–1572. Mutz, M. 2000. Influences of woody debris on flow patterns and channel morphology in a low-energy, sand-bed stream reach. International Review of Hydrobiology 85(1):107–121. Nunnally, N.R. 1978. Stream renovation: An alternative to channelization. Environmental Management 2(5):403–410. Nunnally, N.R., and E. Keller. 1979. Use of fluvial processes to minimize adverse effects on stream channelization. Report No. 144, Water Resources Research Institute of the University of North Carolina, Raleigh, N.C. Phillips, J.D. 2003. Toledo Bend Reservoir and geomorphic response in the lower Sabine River. River Resources Applications 19:137–159. Phillips, J.D., and L. Park. 2009. Forest-blown impacts of Hurricane Rita on fluvial systems. Earth Surface Processes and Landforms 34:1069–1081. Robison, E.G., and R.L. Beschta. 1990. Coarse woody debris and channel morphology interactions for undisturbed streams in southeast Alaska. US Earth Surface Processes and Landforms 15:149–156. SAS Institute, Inc. 2008. Version 9.2 Cary, NC Shields, F.D., and C.J. Gippel. 1995. Prediction of effects of woody debris removal on flow resistance. Journal of Hydrologic Engineering 121:341–354. Shields, F.D., and N.R. Nunnally. 1984. Environmental aspects of clearing and snagging. Journal of Environmental Engineering 110(1):152–154. Smith, R.D., R.C. Sidle, P.E. Porter, and J.R. Noel. 1993. Effects of experimental removal of woody debris on the channel morphology of a forest, gravel-bed stream. Journal of Hydrology 152:153–178. Spies, T.A., J.F. Franklin, and T.B. Thomas. 1988. Coarse woody debris in Douglas-fir forests of western Oregon and Washington. Ecology 696:1689–1702. Southeastern Naturalist M. McBroom, M. Ringer, and Y. Zhang 2014 14 Vol. 13, Special Issue 5 Swanson, F.J., G.W. Lienkaemper, and J.R. Sedell. 1976. History, physical effects, and management implications of large organic debris in western Oregon streams. Pacific Northwest Forest and Range Experiment Station US Department of Agriculture, Portland, OR. Trimble, S.W. 1997. Stream-channel erosion and change resulting from riparian forests. Geology 25:467–469. Van Sickle, J., S.V. Gregory. 1990. Modeling inputs of large woody debris to streams from falling trees. Canadian Journal of Forest Research 20:1593–1601. Wallace, J.B., and A.C. Benke. 1984. Quantification of wood habitat in subtropical Coastal Plain streams. Canadian Journal of Fisheries and Aquatic Sciences. 41:1643–1652. Wallace, J.B., J.W. Grubaugh, and M.R. Wiles. 1993. Influences of coarse woody debris on stream habitats and invertebrate biodiversity. Pp. 119–129, In J.W. McMinn, and D.A. Crossley, Jr. (Eds.). Biodiversity and Coarse Woody Debris in Southern Streams: Proceedings of the Workshop on Coarse Woody Debris in Southern Forests: Effects on Biodiversity. Athens, GA, USDA Forest Service Southern Research Station, Asheville, NC.