Long-Term Community Dynamics Reveal Different Trajectories for Two Mid-Atlantic Maritime Forests

Maritime forests are threatened by sea-level rise, storm surge and encroachment of salt-tolerant species. On barrier islands, these forested communities must withstand the full force of tropical storms, hurricanes and nor’easters while the impact is reduced for mainland forests protected by barrier islands. Geographic position may account for differences in maritime forest resilience to disturbance. In this study, we quantify two geographically distinct maritime forests protected by dunes on Virginia’s Eastern Shore (i.e., mainland and barrier island) at two time points (15 and 21 years apart, respectively) to determine whether the trajectory is successional or presenting evidence of disassembly with sea-level rise and storm exposure. We hypothesize that due to position on the landscape, forest disassembly will be higher on the barrier island than mainland as evidenced by reduction in tree basal area and decreased species richness. Rate of relative sea-level rise in the region was 5.9 ± 0.7 mm yr−1 based on monthly mean sea-level data from 1975 to 2017. Savage Neck Dunes Natural Area Preserve maritime forest was surveyed using the point quarter method in 2003 and 2018. Parramore Island maritime forest was surveyed in 1997 using 32 m diameter circular plots. As the island has been eroding over the past two decades, 2016 Landsat imagery was used to identify remaining forested plots prior to resurveying. In 2018, only plots that remained forested were resurveyed. Lidar was used to quantify elevation of each point/plot surveyed in 2018. Plot elevation at Savage Neck was 1.93 ± 0.02 m above sea level, whereas at Parramore Island, elevation was lower at 1.04 ± 0.08 m. Mainland dominant species, Acer rubrum, Pinus taeda, and Liquidambar styraciflua, remained dominant over the study period, with a 14% reduction in the total number of individuals recorded. Basal area increased by 11%. Conversely, on Parramore Island, 33% of the former forested plots converted to grassland and 33% were lost to erosion and occur as ghost forest on the shore or were lost to the ocean. Of the remaining forested plots surveyed in 2018, dominance switched from Persea palustris and Juniperus virginiana to the shrub Morella cerifera. Only 46% of trees/shrubs remained and basal area was reduced by 84%. Shrub basal area accounted for 66% of the total recorded in 2018. There are alternative paths to maritime forest trajectory which differ for barrier island and mainland. Geographic position relative to disturbance and elevation likely explain the changes in forest community composition over the timeframes studied. Protected mainland forest at Savage Neck occurs at higher mean elevation and indicates natural succession to larger and fewer individuals, with little change in mixed hardwood-pine dominance. The fronting barrier island maritime forest on Parramore Island has undergone rapid change in 21 years, with complete loss of forested communities to ocean or conversion to mesic grassland. Of the forests remaining, dominant evergreen trees are now being replaced with the expanding evergreen shrub, Morella cerifera. Loss of biomass and basal area has been documented in other low elevation coastal forests. Our results indicate that an intermediate shrub state may precede complete loss of woody communities in some coastal communities, providing an alternative mechanism of resilience.

Localized Augmentation of Net Precipitation to Shrubs: A Case Study of Stemflow Funneling to Hummocks in a Salinity-Intruded Swamp

The interception of precipitation by plant canopies can alter the amount and spatial distribution of water inputs to ecosystems. We asked whether canopy interception could locally augment water inputs to shrubs by their crowns funneling (freshwater) precipitation as stemflow to their bases, in a wetland where relict overstory trees are dying and persisting shrubs only grow on small hummocks that sit above mesohaline floodwaters. Precipitation, throughfall, and stemflow were measured across 69 events over a 15-months period in a salinity-degraded freshwater swamp in coastal South Carolina, United States. Evaporation of intercepted water from the overstory and shrub canopies reduced net precipitation (stemflow plus throughfall) across the site to 91% of gross (open) precipitation amounts. However, interception by the shrub layer resulted in increased routing of precipitation down the shrub stems to hummocks – this stemflow yielded depths that were over 14 times larger than that of gross precipitation across an area equal to the shrub stem cross-sectional areas. Through dimensional analysis, we inferred that stemflow resulted in local augmentation of net precipitation, with effective precipitation inputs to hummocks equaling 100–135% of gross precipitation. Given that these shrubs (wax myrtle, Morella cerifera) are sensitive to mesohaline salinities, our novel findings prompt the hypothesis that stemflow funneling is an ecophysiologically important mechanism that increases freshwater availability and facilitates shrub persistence in this otherwise stressful environment.

Regeneración natural en sitios impactados por incendios en la Reserva Biológica Uyuca, Honduras.

Se estudió la riqueza y dominancia de la vegetación producto de la regeneración natural en el bosque de coníferas de la Reserva Biológica Uyuca (Francisco Morazán, Honduras) con uno (T1), siete (T7) y más de 15 años (T15) de haber sido perturbado por incendios. Se establecieron 22 parcelas por tratamiento, 11 parcelas de 1×1 m para muestreo de herbáceas y plántulas de árboles y 11 parcelas de 5×5 m para muestreo de arbustos y bejucos. Se analizaron 3,073 individuos de 79 especies en 36 familias. Las familias con más géneros fueron Fabaceae y Asteraceae. La especie más común en herbáceas y plántulas fue Lysiloma auritum (Schltdl.) Benth. (97 individuos) y estuvo presente solo en T1. Morella cerifera (L.) Small fue la segunda especie de herbáceas y plántulas más común, presente en los tres tratamientos. La mayor abundancia se obtuvo en la categoría de arbustos y bejucos, representada por el helecho Pteridium caudatum (L.) Maxon con 484 individuos y Phyla strigulosa (M. Martens & Galeotti) Moldenke con 287 individuos. Mimosa albida Willd. estuvo presente en los tres tratamientos; Calliandra houstoniana (Mill.) Standl., no se encontró en T15. En las parcelas de 5×5 m también fueron comunes las asteráceas Verbesina agricolarum Standl. & Steyerm. y dos especies de Calea L. La riqueza de especies de herbáceas y plántulas fue diferente entre los tres tratamientos (χ2= 6.4, P= 0.04) con una diferencia mayor entre T1 y T7 (t= -2.37, p= 0.02). Las herbáceas y las plántulas de árboles tuvieron una mayor diversidad en T1 (H΄ Shannon-Weaver = 2.48), mientras que los arbustos y los bejucos fueron más diversos en T15 (H΄= 3.10). La diversidad de arbustos y bejucos fue similar en todos los tratamientos (χ2=1.9, P=0.37). Quizá más importante que las similitudes o diferencias entre los tratamientos, son las especies que allí existen. Varias de las especies encontradas son importantes ecológicamente o para las comunidades cercanas a la reserva.

Wax Myrtle, Morella cerifera Synonym: Myrica cerifera

Wax myrtle is one the most widespread plants in Florida, and it is found in coastal states west to Texas and north to New Jersey. The wax found around seeds can be melted down to make candles. The fruits of wax myrtle are important for birds and other wildlife, and the plant is a larval host for the banded hairstreak and redbanded hairstreak butterflies (Satyrium calanus and Calycopis cecrops, respectively) (Lotts and Naberhaus 2017). Wax myrtle has been shown to contribute substantial nitrogen addition to soils via symbiotic relationships with nitrogen-fixing microorganisms residing in soils (Permar and Fisher 1983).https://edis.ifas.ufl.edu/sg176 This publication is derived from information in SGEB-75/SG156, Dune Restoration and Enhancement for the Florida Panhandle, by Debbie Miller, Mack Thetford, Christina Verlinde, Gabriel Campbell, and Ashlynn Smith. https://edis.ifas.ufl.edu/sg156.

Above-grade Planting with Organic Matter Improves Post-transplant Growth of Two Native Shrub Species

Planting shrubs above-grade with organic matter has shown potential for improving landscape establishment. To further investigate this technique, wax myrtle [Morella cerifera (syn. Myrica cerifera)] (3 gal) and mountain laurel (Kalmia latifolia ‘Olympic Wedding’) (5 gal) were planted on 30 Oct. 2006 (fall planting) and 12 Apr. 2007 (spring planting) in the ground in a shade house in Auburn, AL. At each planting date, plants of each species were assigned one of four treatments. Three of four treatments used a modified above-grade planting technique in which shrubs were planted such that the top 3 inches of the root ball remained above soil grade. Organic matter, either pine bark (PB), peat (PT), or cotton gin compost (CGC), was applied around the above-grade portion of the root ball, tapering down from the top of the root ball to the ground. In the fourth treatment, plants were planted at-grade with no organic matter (NOM). In general, both species had higher shoot dry weight (SDW) and root spread (RS) when planted in the fall than when planted in spring. Among all treatments, plants also typically had larger RS when planted above-grade with PB or PT. For easy-to-transplant species (such as wax myrtle) and especially for difficult-to-transplant species like mountain laurel, fall planting using this modified above-grade planting technique with PB or PT may improve post-transplant root growth and speed establishment in the first growing season.