Low street tree survival rates and the resulting short lifespans are frequently discussed but inadequately quantified in urban forestry literature. This study addresses street tree survival rates ...with a meta-analysis of previous literature and a case study assessment of street trees in Philadelphia, USA 2–10 years after planting. Reported survivorship rates from 16 previous studies were compiled. Estimated annual survival rates for individual past studies were mostly above 91.0%. To estimate the annual street tree survival rate across multiple studies, a subset of previous studies was pooled for regression analysis of
ln transformed cumulative survivorship vs. time since planting. Lifespan metrics were estimated using the annual survival rates determined from regression analysis. Based on the meta-analysis, we estimated that street tree annual survival rates ranged from 94.9 to 96.5%, and street tree population half-life ranged from 13 to 20 years. Estimated mean life expectancy ranged from 19 to 28 years, which is considerably longer than the 7- or 13-year street tree average lifespan reported in previous studies. Estimated annual survival rates and lifespan metrics were similar in the Philadelphia case study. Urban forest researchers are encouraged to use demographic concepts and analyses in the study of tree survival and mortality, and to monitor tree survival at repeated time intervals every few years.
Cloud- and rain-water samples collected between 1984 and 2007 in the Luquillo Experimental Forest, Puerto Rico, were analyzed in order to understand the main processes and sources that control their ...chemistry. Three sites were used: El Verde Field Station (380 m asl), Bisley (361 m asl), and East Peak (1051 m asl). Bulk rainwater samples were collected from all sites, and cloud water was also collected on East Peak. All samples were analyzed for pH, conductivity, and concentrations of Cl−, SO42−, NO3−, NH4+, Na+, K+, Ca2+ and Mg2+. Similar patterns in overall chemistry were observed for both cloud- and rain-water samples. The majority of samples had low acidity (average pH of 4.4–5.0), similar to other remote sites. Sea salt (Na+ and Cl−) had a large influence on rain and cloud chemistry and accounted for approximately 70% of the total mass of solutes, followed by SO4=, which controls the acidity of the clouds and rainwater. Calcium accounted for 6–8% of the total cations and dominated neutralization processes. The highest concentrations of Ca2+ and NO3− in both cloud- and rain-water were observed in the summertime when large amounts of dust from the African continent reached the sites. Enrichment Factor and Principal Component Analyses showed that Na+, Cl−, and Mg2+ in the cloud- and rain-water were primarily of marine origin, while most of the Ca2+ was from crustal sources; and NO3− was predominantly anthropogenic, presumably from both local and long-range sources. In general, the results of this study suggested that cloud- and rain-water chemistry in northeastern Puerto Rico is strongly influenced by natural and marine sources rather than local anthropogenic sources. The pollutant species in the samples were mainly derived from long distance transport.
► Results of a long-term of monitoring of rain and cloud water in background sites. ► Few places on the Planet are possible to collect cloud water with natural features. ► The results are important for comparison and evaluation of anthropogenic impacts. ► Concentrations, trends, seasonality and correlations are discussed in the paper. ► It is important to understand the effects of nutrients and pollutants on ecosystems.
Humid tropical forests play a dominant role in many global biogeochemical cycles, yet long-term records of tropical stream chemistry and its response to disturbance events such as severe storms and ...droughts are rare. Here we document the long-term variability in chemistry of two streams in the Luquillo Mountains, Puerto Rico over a period of 27 years. Our two focal study watersheds, the Río Icacos and Quebrada Sonadora, both drain several hundred hectares of tropical wet forests, and each received direct hits from Hurricanes Hugo (1989) and Georges (1998). They differ primarily in lithology (granitic vs. volcaniclastic) and elevation. Changes in major cations, anions, silica, and dissolved organic carbon were minimal over the study period, but the concentrations of nitrate show a strong response to hurricane disturbance and the longest time to recovery. Potassium also showed a large, although less consistent, response to disturbance. In the granitic terrain, nitrate concentrations exceeded long-term pre-hurricane background levels for over a decade, but were elevated in the volcaniclastic terrain for only 1–2 years. Lithology appears to be the primary driver explaining the different response trajectories of the two watersheds. In the granitic terrain, which showed slow recovery to pre-hurricane conditions, the quartz diorite bedrock weathers to produce coarser soils, deeper groundwater flow paths, and riparian zones with sharp spatial variation in redox conditions and very high nitrogen levels immediately adjacent to the stream. Groundwater flow paths are shallow and the levels of N in streamside groundwater are much lower in the volcaniclastic terrain. The recovery of vegetation following hurricane disturbance appears similar in the two watersheds, suggesting that the extent of structural damage to canopy trees determines the magnitude of NO₃ increases, but that the duration of elevated concentrations in stream water is a function of lithology.
The Luquillo Mountains of northeastern Puerto Rico harbours important fractions of tropical montane cloud forests. Although it is well known that the frequent occurrence of dense fog is a common ...climatic characteristic of cloud forests around the world, it is poorly understood how fog processes shape and influence these ecosystems. Our study focuses on the physical characteristics of fog and quantifies the fogwater input to elfin cloud forest using direct eddy covariance net flux measurements during a 43-day period in 2002. We used an ultrasonic anemometer–thermometer in combination with a size-resolving cloud droplet spectrometer capable of providing number counts in 40 droplet size classes at a rate of 12.5 times per second. Fog occurred during 85% of the time, and dense fog with a visibility
<
200 m persisted during 74% of the period. Fog droplet size depended linearly on liquid water content (
r
2
=
0.89
) with a volume-weighted mean diameter of 13.8
μ
m. Due to the high frequency of occurrence of fog the total fogwater deposition measured with the eddy covariance method and corrected for condensation and advection effects in the persistent up-slope air flow, averaged 4.36 mm day
−1, rainfall during the same period was 28 mm day
−1. Thus, our estimates of the contribution of fogwater to the hydrological budget of elfin cloud forests is considerable and higher than in any other location for which comparable data exist but still not a very large component in the hydrological budget. For estimating fogwater fluxes for locations without detailed information about fog droplet distributions we provide simple empirical relationships using visibility data.
The long-term response of total soil organic carbon pools (‘total SOC’, i.e. soil and dead wood) to different harvesting scenarios in even-aged northern hardwood forest stands was evaluated using two ...soil carbon models, CENTURY and YASSO, that were calibrated with forest plot empirical data in the Green Mountains of Vermont. Overall, 13 different harvesting scenarios that included four levels of aboveground biomass removal (20%, 40%, 60% and 90%) and four different rotation lengths (60 year, 90 year, 120 year, and No Rotation (NR)) were simulated for a 360 year period. Simulations indicate that following an initial post-harvest increase, total SOC decreases for several decades until carbon inputs into the soil pool from the re-growth are greater than losses due to decomposition. At this point total SOC begins to gradually increase until the next harvest. One consequence of this recovery pattern is that between harvests, the size of the SOC pool in a stand may change from −7 to 18% of the pre-harvest pool, depending on the soil pool considered. Over 360 years, the average annual decrease in total SOC depends on the amount of biomass removed, the rotation length, and the soil pool considered. After 360 years a stand undergoing the 90yr-40% scenario will have 15% less total SOC than a non-harvested stand. Long-term declines in total SOC greater than 10% were observed in the 60yr-60%, 60yr-90%, and 90yr-90% scenarios. Long-term declines less than 5% were observed in scenarios with 120 year rotations that remove 60% or less of the aboveground biomass. The long-term decreases simulated here for common management scenarios in this region would require intensive sampling procedures to be detectable.
The combination of human population growth, increased water usage, and limited groundwater resources often leads to extensive damming of rivers and streams on tropical islands. Ecological effects of ...dams on tropical islands can be dramatic, because the vast majority of native stream faunas (fishes, shrimps, and snails) migrate between freshwater and saltwater during their lives. Dams and associated water withdrawals have been shown to extirpate native faunas from upstream reaches and increase mortality of downstream-drifting larvae. A better understanding of the effects of dams and the behavior of tropical island stream faunas is providing insights into how managers can mitigate the negative effects of existing dams and develop alternatives to dam construction while still providing freshwater for human use. We review the ecological effects of dams on tropical island streams, explore means to mitigate some of these effects, describe alternatives to dam construction, and recommend research priorities.
•Soil C and N content was comparatively greater in riparian zone soils sampled here.•Soil C content in forested and non-forested riparian soils was not different.•MRT analysis was able to explain ...>50% of the variability in soil C and N content.•This approach can identify those riparian areas with potential to sequester soil C.
This study investigated the landscape characteristics that influence C and N in unsaturated surface soils of riparian zones along 1st to 3rd order streams in the Atlantic Coastal Plain of the Delaware River Basin. Unsaturated surface soils (0–30cm) were sampled in forested and non-forested sites at 29 locations throughout S New Jersey and SE Pennsylvania. Overall, the soil %C and %N in forested and non-forested riparian sites studied in this investigation were comparable to similar riparian zone soils in eastern North America. However, the soil C and N contents of these Atlantic Coastal Plain soils were 3 to 8-fold greater which underscores the value of these riparian soils as C pools. Soil C content (100.3±15.0Mgha−1) in forested riparian sites was consistently higher but not statistically different (P>0.05) from soil C content (90.6±12.1Mgha−1) in non-forested riparian sites. Likewise, neither soil N storage or the C:N ratio were different between the contrasting land covers but forested sites with forest floor organic horizons had significantly greater (82%, P=0.004) soil C storage than the non-forested sites. Of the forested sites, 70% did not have organic horizons. All of the forested sites without organic horizons had abundant earthworms and comparisons of sites with and without forest floor suggests that earthworms and the removal of native forest cover may be responsible for a loss of 75–93Mgha−1 of soil C from these riparian zones. Multivariate regression tree analysis was able to explain ⩾50% of the variability in soil C and N and as much as 68% of the variability in the C:N ratio. The analysis indicated that watershed-scale land cover, local soil series, and elevation above the active channel had the greatest influence on C and N storage. Moreover, this analysis indicated that a combination of easily measured, reach-scale characteristics and GIS-based watershed-scale variables can be used to estimate regional riparian soil C pools and identify restoration sites with the potential to store soil C.
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