Recent studies have demonstrated that natural abundance 15N can be a useful tool for assessing nitrogen saturation, because as nitrification and nitrate loss increase, δ15N of foliage and soil also increases. We measured foliar δ15N at 11 high-elevation spruce-fir stands along an N deposition gradient in 1987-1988 and at seven paired northern hardwood and spruce-fir stands in 1999. In 1999, foliar δ15N increased from -5.2 to -0.7[per thousand] with increasing N deposition from Maine to NY. Foliar δ15N decreased between 1987-1988 and 1999, while foliar %N increased and foliar C:N decreased at most sites. Foliar δ15N was strongly correlated with N deposition, and was also positively correlated with net nitrification potential and negatively correlated with soil C:N ratio. Although the increase in foliar %N is consistent with a progression towards N saturation, other results of this study suggest that, in 1999, these stands were further from N saturation than in 1987-1988. Foliar δ15N increased with increasing N deposition from Maine to NY, but decreased between 1987-1988 and 1999

The first report on oxidant-induced plant damage in the Valley of Mexico was presented over 30 years ago. Ozone is known to occur in the Mexico City Metropolitan Area and elsewhere as the cause of chlorotic mottling on pine needles that are 2 years old or older as observed in 1976 on Pinus hartwegii and Pinus leiophylla. Visible evidences for the negative effects of ozone on the vegetation of central Mexico include foliar injury expressed as chlorotic mottling and premature defoliation on pines, a general decline of sacred fir, visible symptoms on native forest broadleaved species (e.g. Mexican black cherry). Recent investigations have also indicated that indirect effects are occurring such as limited root colonization by symbiotic fungi on ozone-damaged P. hartwegii trees and a negative influence of the pollutant on the natural regeneration of this species. The negative ozone-induced effects on the vegetation will most likely continue to increase. Ozone induced symptoms, poor tree regeneration and limited root colonization by mycorrhiza fungi observed in the valley of Mexico.

This study aimed to investigate the diversity and distribution pattern of tree in different altitudes in a protected area of Churdhar Wildlife Sanctuary (CWS), situated in Himachal Pradesh, Western Himalaya, India. CWS is one of the famous sanctuaries and rich in biodiversity. The tree species analysis was done with the stratified sampling technique by performing a random sampling using the quadrats method. The study area was divided into four different altitudes: (i) Chhogtali (CT; 1900–2200 masl), (ii) Churas (CH; 1900–2200 masl), (iii) Nohra 1 (NH1; 2800–3200 masl), and (iv) Nohra 2 (NH2; 2800–3200 masl). Among the studied sites, results revealed that tree species richness decreases with an increase in altitude. Quercus leucotrichophora was dominant in CT and CH sites, whereas Q. semecarpifolia was dominant in NH1 and Abies spectabilis in NH2 sites. Picea smithiana reported to be dominant species in the studied sites. Compared to CT and CH sites, the dominance-diversity (d-d) curve showed a decrease in species richness on HN1 and NH2 at higher altitudes, whereas tree total basal cover (TBC) increases with altitude. The maximum similarity was between CT and CH sites and reduced between CT and NH2 sites with higher altitudes. Almost all tree species exhibited contagious distribution patterns which are common in natural forests; however, a few species showed random distribution, and no species were found distributed regularly. This study provides fruitful information to the policy-makers, environmentalists, and foresters to understand species diversity and distribution with species composition and structure with altitude. Thus, conservation and sustainable management strategies of the forest could be design in better ways to conserve diversity on a regional and/or global scale.

The recovery potential of stream acidification from years of acidic deposition is dependent on biogeochemical processes and varies among different acid-sensitive regions. Studies that investigate long-term trends and seasonal variability of stream chemistry in the context of atmospheric deposition and watershed setting provide crucial assessments on governing biogeochemical processes. In this study, water chemistries were investigated in Noland Divide watershed (NDW), a high-elevation watershed in the Great Smoky Mountains National Park (GRSM) of the southern Appalachian region. Monitoring data from 1991 to 2007 for deposition and stream water chemistries were statistically analyzed for long-term trends and seasonal patterns by using Seasonal Kendall Tau tests. Precipitation declined over this study period, where throughfall (TF) declined significantly by 5.76 cm year−1. Precipitation patterns play a key role in the fate and transport of acid pollutants. On a monthly volume-weighted basis, pH of TF and wet deposition, and stream water did not significantly change over time remaining around 4.3, 4.7, and 5.8, respectively. Per NDW area, TF SO4 2- flux declined 356.16 eq year−1 and SO4 2- concentrations did not change significantly over time. Stream SO4 2- remained about 30 μeq L−1 exhibiting no long-term trends or seasonal patterns. SO4 2- retention was generally greater during drier months. TF monthly volume-weighted NH4 + and NO3 - concentrations significantly increased by 0.80 μeq L−1 year−1 and 1.24 μeq L−1 year−1, respectively. TF NH4 + fluxes increased by 95.76 eq year−1. Most of NH4 + was retained in the watershed, and NO3 - retention was much lower than NH4 +. Stream monthly volume-weighted NO3 - concentrations and fluxes significantly declined by 0.56 μeq L−1 year−1 and 139.56 eq year−1, respectively. Overall, in NDW, inorganic nitrogen was exported before 1999 and retained since then, presumably from forest regrowth after Frazer fir die-off in the 1970s from balsam wooly adelgid infestation. Stream export of NO3 - was greater during winter than summer months. During the period from 1999 to 2007, stream base cations did not exhibit significant changes, apparently regulated by soil supply. Statistical models predicting stream pH, ANC, SO4 2-, and NO3 - concentrations were largely correlated with stream discharge and number of dry days between precipitation events and SO4 2- deposition. Dependent on precipitation, governing biogeochemical processes in NDW appear to be SO4 2- adsorption, nitrification, and NO3 - forest uptake. This study provided essential information to aid the GRSM management for developing predictive models of the future water quality and potential impacts from climate change.