How does dune morphology shape coastal EC habitats occurrence? A remote sensing approach using airborne LiDAR on the Mediterranean coast

We examined the relationship between coastal habitats (sensu European Union Habitats Directive) and local dune morphology along a Mediterranean coastal dune system by integrating field collected vegetation data and remotely sensed imagery. Specifically, we described the morphological profile of each EC habitat based on the morphological variables that are most likely to affect their occurrence, including elevation, slope, curvature, northness, eastness and sea distance. In addition, we assessed the role and strength of each morphological variable in determining the occurrence of EC habitats.We used 394 random vegetation plots representative of six EC habitats (Habitat 1210: “Annual vegetation of drift lines”; Habitat 2110: “Embryonic shifting dunes”; Habitat 2120: “Shifting dunes along the shoreline with Ammophila arenaria”; Habitat 2210 and 2230: “Crucianellion maritimae fixed beach dunes” and “Malcolmietalia dune grasslands”; Habitat 2250: “Coastal dunes with Juniperus spp.”; Habitat 2260: “Cisto-Lavanduletalia dune sclerophyllous scrubs”) found along the Tyrrhenian coast of central Italy. We derived each morphological variable from a DTM (Digital Terrain Model) obtained from 2-m resolution LiDAR (Light Detection And Range) images. The mean value of each variable was calculated at different spatial scales using buffer areas of increasing radius (2 m, 4 m, 8 m) around each vegetation plot. Mean morphological values for each EC habitat were compared using Kruskal-Wallis rank test. The role and strength of the relationship between habitat type and the morphological variables were assessed using Generalized Linear Models.EC habitats occur differentially across dune morphology, and the role and strength of each morphological variable define habitat specificity. Dune elevation and sea distance were determined to be the key factors in shaping EC habitat occurrence along this section of the Mediterranean coast. Identification of the close relationship between habitat type and morphological variables deriving from airborne LiDAR imagery points to the high potential of such remote sensing tool for analyzing and monitoring the integrity of coastal dune ecosystems. As airborne LiDAR enables the rapid collection of extremely accurate topographic data over large areas, it also offers useful information for the management of these threatened and fragile ecosystems.     

The influence of rainfall variability on the species composition of a northern California salt marsh plant assemblage

Natural variability in the species composition of salt marsh plant assemblage was studied for 4 years (1986–90) at Bolinas Lagoon, California (USA). The study was conducted during a period in which little or no physical disturbance occurred in the marsh. During the study, Bolinas Lagoon experienced highly variable rainfall, both within and between years. In years with average or below average winter and spring rainfall, the cover of Salicornia virginica increased relative to that of the other species. During the one year with much higher than average spring rainfall, the cover of Salicornia declined and rare species increased in relative abundance. These patterns suggest that under typical marsh conditions, the plant assemblage experiences stress due to low availability of freshwater and high soil salinity. Under such conditions, the stress-tolerant Salicornia dominates the assemblage. If, however, there is abundant rainfall early in the growing season, the other species are released from stress and are able to increase in cover. The marsh of Bolinas Lagoon appears to be resistant to change and able to tolerate stress. Few studies have examined natural variability in species in undisturbed marshes and more of such studies must be made in order to understand whether or not marshes are in general resistant to change caused by rainfall variability.Abbreviations MLLW = mean lower low water     

Floristic affinities of an inselberg archipelago in the southern Namib desert—relic of the past,centre of endemism or nothing special?

The floral composition of an inselberg archipelago in the southern Namib desert was investigated with regard to species diversity, geographic range of the species, habitat niches, seed dispersal abilities and plant herbivore defence. Although no endemic species were found, the archipelago forms an extreme and often isolated outlier for a large number of species in their distribution area. The hypothesis is proposed that the isolated extreme habitat allowed survival of relic populations due to low immigration rate and low competition. The high proportion of species favouring long-range dispersal might explain the lack of endemic species as well as the large contribution of species at their distributional boundary.     

Pollen-based reconstructions of Japanese biomes at 0, 6000 and 18,000 14C yr bp

A biomization method, which objectively assigns individual pollen assemblages to biomes ( Prentice et al., 1996 ), was tested using modern pollen data from Japan and applied to fossil pollen data to reconstruct palaeovegetation patterns 6000 and 18,000 ¹⁴C yr bp Biomization started with the assignment of 135 pollen taxa to plant functional types (PFTs), and nine possible biomes were defined by specific combinations of PFTs. Biomes were correctly assigned to 54% of the 94 modern sites. Incorrect assignments occur near the altitudinal limits of individual biomes, where pollen transport from lower altitudes blurs the local pollen signals or continuous changes in species composition characterizes the range limits of biomes. As a result, the reconstructed changes in the altitudinal limits of biomes at 6000 and 18,000 ¹⁴C yr bp are likely to be conservative estimates of the actual changes. The biome distribution at 6000 ¹⁴C yr bp was rather similar to today, suggesting that changes in the bioclimate of Japan have been small since the mid‐Holocene. At 18,000 ¹⁴C yr bp the Japanese lowlands were covered by taiga and cool mixed forests. The southward expansion of these forests and the absence of broadleaved evergreen/warm mixed forests reflect a pronounced year‐round cooling.     

Succession and fluctuation in a wet dune slack in relation to hydrological changes

Vegetation changes in a wet dune slack complex have been studied over a period of 23 yr. The vegetation was recorded in 40 permanent plots: all plots in 1964, 1977, 1983 and 1987 and some also in five other years. There were large fluctuations in annual precipitation during this period, including some extremely dry (1976) and wet (1985) years. Many species of wet calcareous and pioneer habitats declined in cover between 1964 and 1977, when there were prolonged dry summer periods, though few species were lost from the sampled quadrats. Practically all calciphilous and pioneer species disappeared between 1977 and 1983, when there were relatively many wet summers. It is suggested that extremely dry conditions temporarily obscure the impacts of hydrological changes in local hydrological systems, by retarding the vegetation succession. After a period of excessive precipitation the (acidifying) effects of ground-water withdrawal rapidly became evident in the species composition of the dune slack.     

Comparative impacts of dam water level regimes on herbaceous plant growth strategies in cascade reservoirs and downstream reaches of a major river

1. Flow regulation is a prolific and growing influence on rivers world-wide. Nine cascade hydropower dams were constructed along the 1,150-km Wujiang River in China over the past 30 years, disrupting longitudinal continuity. Water level fluctuations in the associated reservoirs range between daily, weekly, seasonal, and annual, depending on the type of regulation, but the comparative impacts of these regimes on plant growth strategies, or the extent of their downstream influence, is unknown.
2. Competitor, stress-tolerator, and ruderal (CSR) plant strategies were used to assess the impact of reservoir regulation type on the riparian herbaceous plant community based on sampling the inundation zone of nine reservoirs and their downstream river reaches during 2017 and 2018.
3. Our results revealed profound differences in CSR plant strategies of the dominant vegetation with respect to water level regime. While ruderal plants dominated (45%–60% of species), irrespective of regulation type, vegetation in reservoirs exhibited a strong shift from stress-tolerators (e.g., Cynodon dactylon, C-11.9:S-41.5:R-46.5%) to competitors (e.g., Reynoutria japonica, C-77.9:S-0:R-22.0%) with increasing intensity of water level fluctuation, reflecting the shift from annual to daily regulation. The width of the inundation zone was the best overall variable in explaining the CSR strategies of riparian vegetation, both in the reservoir inundation zone (r²-adj = 15.4%) and the downstream river (r²-adj = 7.3%). Retention time significantly explained variation in CSR plant strategies in the reservoir inundation zone (r²-adj = 3.7%, p = 0.002) but not downstream (p > 0.01). There was also a clear scale dependency of CSR plant strategies, with an increase in stress tolerators (average slope = 0.7%/km) and decline of competitor (average slope = −0.3%/km) and ruderal plants (average slope = −0.9%/km) with increasing distance downstream from dams.
4. The growth strategies of the dominant riparian vegetation changed with the magnitude and frequency of water level fluctuations caused by differences in regulation type, and local environmental conditions. Clear scale dependency in the CSR plant strategies was observed with distance from the dam, with ruderals dominating closest to the reservoirs and declining gradually downstream as stress tolerators increased.
5. Our study helps to evaluate the impact of river damming on the functional traits of riparian vegetation and to predict the resilience and restoration potential of riparian vegetation under different forms of human disturbance.

     

Effects of hydropriming treatments on the invigoration of aged Dodonaea viscosa seeds and water‐holding polymer on the improvement of seedling growth in a lava field

Restoration requires techniques similar to those used in agriculture to improve germination and seedling vigor. We treated 6‐year‐old (collected in 2003, S‐2003) and 1‐month‐old (S‐2009) seeds of Dodonaea viscosa with hydropriming (HP). Seeds were made permeable with hot water prior to hydration for 24 or 48 hours (HP‐24 and HP‐48, respectively) followed by dehydration. The resulting seedlings exposed to both HP treatments were sown in a lava field in soil mixed with hydrogel (HG) under the shade projected by five vegetation patches. The effects of these treatments on germination, seedling field survival, and growth were assessed. HP‐24 in S‐2009 and HP‐48 in S‐2003 increased the germination percentage from 22.5 and 31.7% in control seeds (permeable seeds) to 63.3 and 98.3%, respectively. The seedlings‐2009 (from S‐2009) with HG maintained high survival in all vegetation patches. Seedlings‐2003, however, had low survival. The lack of HG was negatively related to the photon flux in each patch. Survival of seedlings‐2009 increased with HG of up to 398.41 µmol m^?2 s^?1; after which survival decreased. During the rainy season, HP enhanced seedling growth, except the basal diameters and number of leaves in the seedlings‐2003 with HP‐24. During the dry season, the effects of HG and HP were similar for all the seedlings. In the following rainy season, the priming effect was lost while HG continued to promote seedling growth. The combined use of HP and HG and the shade projected by the patches resulted in a successful vegetation recovery strategy.     

Long‐term outcomes of forest restoration in an urban park

Creating, restoring, and sustaining forests in urban areas are complicated by habitat fragmentation, invasive species, and degraded soils. Although there is some research on the outcomes of urban reforestation plantings during the first 5 years, there is little research on longer term outcomes. Here, we compare the successional trajectories of restored and unrestored forest sites 20 years after initiating restoration. The sites are located within the Rodman's Neck area of Pelham Bay Park, in the northeast corner of the Bronx in New York City (NYC), U.S.A. Compared with unrestored sites, we saw improvements in species diversity, greater forest structure complexity, and evidence of the regeneration and retention of native tree species in restored sites. In addition, we found differences in restoration outcomes depending on the level of intervention: clearing exotic shrubs and vines and planting native trees and shrubs improved tree diversity and canopy closure to a greater extent than clearing exotics alone, and the mechanical removal of invasive plants after the native plantings further improved some measures of restoration, such as tree species diversity and native tree regeneration. The results of this study suggest that the goal of a sustainable forest ecosystem dominated by native trees and other plant species may not be achievable without continued human intervention on site. In addition, these results indicate that the restoration approach adopted by NYC's reforestation practitioners is moving the site toward a more desirable vegetative community dominated by native species.     

Temperature,precipitation, and insolation effects on autumn vegetation phenology in temperate China

Autumn phenology plays a critical role in regulating climate–biosphere interactions. However, the climatic drivers of autumn phenology remain unclear. In this study, we applied four methods to estimate the date of the end of the growing season (EOS) across China's temperate biomes based on a 30‐year normalized difference vegetation index (NDVI) dataset from Global Inventory Modeling and Mapping Studies (GIMMS). We investigated the relationships of EOS with temperature, precipitation sum, and insolation sum over the preseason periods by computing temporal partial correlation coefficients. The results showed that the EOS date was delayed in temperate China by an average rate at 0.12 ± 0.01 days per year over the time period of 1982–2011. EOS of dry grassland in Inner Mongolia was advanced. Temporal trends of EOS determined across the four methods were similar in sign, but different in magnitude. Consistent with previous studies, we observed positive correlations between temperature and EOS. Interestingly, the sum of precipitation and insolation during the preseason was also associated with EOS, but their effects were biome dependent. For the forest biomes, except for evergreen needle‐leaf forests, the EOS dates were positively associated with insolation sum over the preseason, whereas for dry grassland, the precipitation over the preseason was more dominant. Our results confirmed the importance of temperature on phenological processes in autumn, and further suggested that both precipitation and insolation should be considered to improve the performance of autumn phenology models.