Atlantic White Cedar Wetlands Research Articles

Influence of environment and substrate quality on root decomposition in naturally regenerating and restored Atlantic white cedar wetlands

Restoration efforts and ecologically based management practices for Atlantic white cedar wetlands have recently focused on organic matter aggradation as an ecosystem function critical to this system’s maintenance. The objective of this study was to evaluate environmental and substrate quality factors influencing root decomposition in naturally recovering (reference) and restored Atlantic white cedar wetlands in southeastern Virginia and northeastern North Carolina. Chamaecyparis thyoides roots were used as a standard substrate to evaluate environmental influences. Roots native to each site were used to evaluate community-level decay dynamics. Standard root mass loss was similar across all sites. Surprisingly, substantial differences in hydrology and soil organic matter among sites did not influence standard root decay. Although regression analysis detected a significant relationship between soil pH and decomposition rates, no significant relationship was found with depth to ground water. Native root decomposition rates were similar among the reference sites, but were substantially faster on the restored sites. This suggests that litter quality exerts a strong controlling influence on decomposition in Atlantic white cedar wetlands. Native root decomposition rates were correlated with lignin concentration and L:N ratios, which were higher in the roots on the reference sites due to greater proportions of woody species. Nitrogen alone did not appear to be a major regulating factor for root decomposition on our sites. Our results imply that as soon as a restored Atlantic white cedar wetland develops a closed canopy of cedar, its decomposition dynamics are likely to equilibrate with natural mature stands.

Root Dynamics in Restored and Naturally Regenerated Atlantic White Cedar Wetlands

Abstract This work addressed the seasonal and successional factors of root dynamics in natural and restoration Atlantic white cedar (AWC) wetlands. Using minirhizotrons and soil root cores, fine root dynamics were measured in a chronosequence of reference and restoration AWC wetlands to compare trends in ecosystem development after canopy harvest. Seasonal fine root abundance, production, and mortality were sampled during a 439‐day period in one restoration and three reference AWC wetlands. Soil cores were collected to measure fine root biomass and to determine allometric relationships between root length and biomass. Significant seasonal variation of root dynamics was observed in the young reference and restoration sites. The mature and intermediate‐aged sites exhibited little seasonal variability in root abundance and mortality. Root production was variable but not seasonally consistent. Results suggest that root dynamics become less seasonal as AWC communities shift from herbaceous to woody vegetation dominance. No trend in fine root abundance along the chronosequence was observed, suggesting that roots rapidly reestablish following tree harvest. Measurements of annual root length production suggest increasing annual production with decreasing stand age. However, a reversal of this trend was observed when using production estimates calculated from minirhizotron measurements and root length–mass relationships. These findings underscore the importance of supplementing minirhizotron data with root allometric relationships when analyzing vegetation gradients. Overall, results indicate substantial differences in the form and quantity of root contributions to soil organic matter in the restoration site compared to that in the reference chronosequence. Higher initial planting densities of AWC are recommended to achieve similar contributions of roots to soil organic matter accumulation in the restoration site.

Fine root dynamics in two atlantic white-cedar wetlands with contrasting hydroperiods

Using minirhizotrons, fine root dynamics were compared in two Atlantic white-cedar swamps with contrasting hydroperiods (intermittently and persistently flooded) in order to evaluate the effects of flooding regime on fine root depth, abundance, production, and longevity. Despite the higher mean watertable depth in the persistently flooded, site, no differences in rooting depth were observed. Root length density, root abundance, and root longevity were generally greater in the persistently flooded site throughout the 439-day study period, although root length production was similar between the two sites. These results suggest that prolonged inundation in Atlantic white-cedar swamps decreases root elongation rates, but due to greater observed root densities, stand-level belowground production remains similar to that of intermittently flooded stands. Significant increases in root mortality were observed in the intermittently flooded side during a period of water-table drawdown, suggesting less than optimal hydrologic conditions at this site.

Nitrogen Retention and Release in Atlantic White Cedar Wetlands

AbstractThe fate of N inputs to freshwater wetlands from enriched runoff, ground water, or atmospheric deposition reflects a variety of processes that determine the net retention of N or its release to downstream ecosystems. The history of N enrichment may affect the relative importance of different pathways. We compared the ability of sediments from Atlantic cedar wetlands in suburban and undisturbed watersheds to remove added inorganic N in laboratory incubations. Three pulses of NH4NO3, at 50 mg N L−1 concentration, were added at consecutive 2‐wk intervals as an analog of pulsed stormwater inputs. After each incubation, soils were leached with CaCl2 and inorganic N concentrations in the leachate were analyzed. The peats retained added N during the first incubation, but after the second and third, all soils released more N than had been added. Nitrate concentrations were always lower than ammonium concentrations. Soils from hollows and most hummocks retained added nitrate throughout the study, but all soils released ammonium. Soil extractable ammonium increased four to 10 times after the 6‐wk incubation, while extractable dissolved organic N (DON) decreased. There also was a net decrease of soil total Kjeldahl N (TKN). The patterns of retention and release of nitrate and ammonium were correlated positively with the N mineralization and nitrification rates of the soils. Our results suggest that wetland peats in suburban drainages may have limited ability to retain frequent, pulsed N inputs from runoff and high intrinsic N mineralization in N‐saturated sediments can become a cause of water quality degradation.

Nitrogen Mineralization and Nitrification in Suburban and Undeveloped Atlantic White Cedar Wetlands

AbstractThe presence of urban and suburban lands adjacent to wetlands may cause changes in nutrient‐cycling processes, due to changes in the quality of the ground‐ and surface waters that drain from the developed uplands into the wetland. We studied N‐cycling processes in Atlantic white cedar [Chamaecyparis thyoides (L.)] swamps in the New Jersey Pinelands to determine their sensitivity to the development of adjoining uplands. We conducted a 19‐wk aerobic incubation to measure N mineralization and nitrification potentials in wetland soils from both developed and undeveloped watersheds. The cumulative inorganic N mineralized during the incubation was two to three times higher in soils from developed sites than from the undeveloped sites. There was virtually no nitrification in undeveloped wetlands, while in developed wetlands, most N mineralized was further nitrified. In developed sites, there was also more nitrification in hollow soils than in hummock soils. Both nitrification and the fraction of soil organic matter mineralized were highly correlated with pH and with soil ash content. These results suggest that increases in ash content of peats attributable to sediment transported and deposited in urban runoff, causes increases in pH, which in turn allows large populations of nitrifiers to develop. Excess mineral N generated within the wetlands through changes in microbial function thus may be as important as N inputs in drainage water in affecting plant community composition, and may cause wetlands to become sources of N to downstream ecosystems rather than serving as regional sinks.

Landscape changes in Atlantic white cedar (Chamaecyparis thyoides) wetlands of the New Jersey Pinelands

Assessing the long-term sustainability of Atlantic white cedar (Chamaecyparis thyoides) wetlands in the New Jersey Pinelands is an important management concern. We used aerial photography dating from 1930 through 1991 and recent satellite imagery to quantify successional trends in these wetlands within the 1,473 km2 Mullica River basin. Over the 61-yr period the composition of individual cedar patches in the study area changed in response to varying disturbance regimes but total cedar cover remained relatively stable. The dominant transitions were conversion of cedar to shrub cover and succession from shrub to cedar. Cedar harvesting, which was the dominant disturbance, was most intense during the early part of the study period. A decline in successful regeneration of more recent cedar cuts maybe related to an increase in the Pinelands deer herd. Other major disturbances included wildfires and flooding. Most flooding was associated with beaver activity. Although the long-term effects of changing disturbance regimes are unknown, our results suggest a positive outlook for sustainability of Atlantic white cedar wetlands within the Mullica River basin. Important management considerations that can affect cedar sustainability include effective post-harvest management of cut swamps and restoration of cedar in shrub or emergent dominated areas that historically contained cedar. Because hardwood conversion of undisturbed cedar patches was not a major transition, cedar harvesting to rejuvenate stands does not seem necessary to maintain Atlantic white cedar wetlands.

Microsite differences in surface substrate characteristics inChamaecyparis swamps of the New Jersey Pinelands

Atlantic white cedar wetlands have pronounced hummock-hollow microtopography, in which the hummocks may be covered bySphagnum spp. or may have only a layer of needle and leaf litter present. I tested the hypotheses that characteristics of the hummock peat, including moisture content, bulk density, redox potential and fiber content, would vary linearly with elevation above the water table, and that these relationships would not vary between moss- and litter-covered surfaces. These hypotheses underlie the frequent use of microsite elevation as an indicator of habitat differentiation in wetlands. I found that moisture and redox potential varied with elevation, but bulk density and fiber content were independent of elevation. Furthermore, moisture and redox status onSphagnum-covered microsites had a weaker relationship to elevation (lower slope coefficient and lower r2) than on litter-covered microsites. Principal components analyses showed thatSphagnum-covered microsites were differentiated primarily on the basis of the relative content of undecomposed and decomposed fibers, while litter-covered sites were differentiated primarily on the basis of moisture and elevation. These results suggest that environmental gradients on hummock-hollow systems are complex and not a simple reflection of elevation. Environmental disturbances that reduceSphagnum cover may affect vegetation by creating more drought-prone microsites on the tops of the hummocks, and this may be important for management of cedar regeneration.

The response of Atlantic white cedar wetlands to varying levels of disturbance from suburban development in the New Jersey Pinelands: J. G. Ehrenfeld & J. P. Schneider, in: Wetland ecology and management, ed D.F. Whigham & others, (Kluwer; Tasks for Vegetation Science, 25), 1990, pp 63–78

The response of Atlantic white cedar wetlands to varying levels of disturbance from suburban development in the New Jersey Pinelands: J. G. Ehrenfeld & J. P. Schneider, in: Wetland ecology and management, ed D.F. Whigham & others, (Kluwer; Tasks for Vegetation Science, 25), 1990, pp 63–78