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Cornwall-on-Hudson, NY, United States

Falxa-Raymond N.,Columbia University | Falxa-Raymond N.,U.S. Department of Agriculture | Patterson A.E.,Barnard College | Patterson A.E.,Lamont Doherty Earth Observatory | And 3 more authors.
Tree Physiology

Oak forests dominate much of the eastern USA, but their future is uncertain due to a number of threats and widespread failure of oak regeneration. A sudden loss of oaks (Quercus spp.) could be accompanied by major changes in forest nitrogen (N) cycles with important implications for plant nutrient uptake and tree species composition. In this study, we measured the changes in N use and growth rates of black birch trees (Betula lenta L.) following oak girdling at the Black Rock Forest in southeastern New York, USA. Data were collected from nine experimental plots composed of three treatments: 100 oaks girdled (OG), 50 oaks girdled (O50) and control (C). Foliar N concentration and foliar 15N abundance increased significantly in the oak-girdled plots relative to the control, indicating that the loss of oaks significantly altered N cycling dynamics. As mineralization and nitrification rates increase following oak loss, black birch trees increase N absorption as indicated by higher foliar N content and increased growth rates. Foliar N concentration increased by 15.5 in the O50 and 30.6 in the OG plots relative to the control, while O50 and OG plots were enriched in 15N by 1.08‰ and 3.33‰, respectively (P<0.0001). A 641 increase in black birch growth rates in OG plots suggests that this species is able to respond to additional N availability and/or increased light availability. The loss of oaks and subsequent increase in black birch productivity may have a lasting impact on ecosystem form and function. © 2012 The Author. Source

Searle S.Y.,University of Canterbury | Turnbull M.H.,University of Canterbury | Boelman N.T.,Lamont Doherty Earth Observatory | Schuster W.S.F.,Black Rock Forest Consortium | And 3 more authors.
Tree Physiology

Urbanization is accelerating across the globe, elevating the importance of studying urban ecology. Urban environments exhibit several factors affecting plant growth and function, including high temperatures (particularly at night), CO2 concentrations and atmospheric nitrogen deposition. We investigated the effects of urban environments on growth in Quercus rubra L. seedlings. We grew seedlings from acorns for one season at four sites along an urban-rural transect from Central Park in New York City to the Catskill Mountains in upstate New York (difference in average maximum temperatures of 2.4°C; difference in minimum temperatures of 4.6°C). In addition, we grew Q. rubra seedlings in growth cabinets (GCs) mimicking the seasonal differential between the city and rural sites (based on a 5-year average). In the field experiment, we found an eightfold increase in biomass in urban-grown seedlings relative to those grown at rural sites. This difference was primarily related to changes in growth allocation. Urban-grown seedlings and seedlings grown at urban temperatures in the GCs exhibited a lower root: shoot ratio (urban ∼0.8, rural/remote ∼1.5), reducing below-ground carbon costs associated with construction and maintenance. These urban seedlings instead allocated more growth to leaves than did rural-grown seedlings, resulting in 10-fold greater photosynthetic area but no difference in photosynthetic capacity of foliage per unit area. Seedlings grown at urban temperatures in both the field and GC experiments had higher leaf nitrogen concentrations per unit area than those grown at cooler temperatures (increases of 23 in field, 32 in GC). Lastly, we measured threefold greater 13C enrichment of respired CO2 (relative to substrate) in urban-grown leaves than at other sites, which may suggest greater allocation of respiratory function to growth over maintenance. It also shows that lack of differences in total R flux in response to environmental conditions may mask dramatic shifts in respiratory functioning. Overall, our findings indicating greater seedling growth and establishment at a critical regeneration phase of forest development may have important implications for the ecology of urban forests as well as the predicted growth of the terrestrial biosphere in temperate regions in response to climate change. © 2012 The Author. Source

Xu M.,Rockefeller University | Schuster W.S.F.,Black Rock Forest Consortium | Cohen J.E.,Rockefeller University | Cohen J.E.,Columbia University
Population Ecology

Testing how well Taylor’s law (TL) describes spatial variation of the population density of a species requires grouping sampling areas (patches of habitat) into blocks so that a mean and a variance of the population density can be calculated over the patches in each block. The relationship between specific groupings and TL remains largely unknown. Here, using tree counts from a deciduous forest, we studied the effect of four biological methods of grouping sampling areas into blocks on the form and parameters of TL. Regardless of the method of grouping, the species-specific basal area densities obeyed TL, and the estimated slopes were not significantly different from one grouping method to another. Surprisingly, TL remained valid when four kinds of randomizations were performed to the biological groupings and tree census. These randomizations randomly assigned sampling areas to blocks, and/or randomized the species composition within or across sampling areas. We found that the form of TL was robust to different grouping methods and species randomizations, but its parameter values depended significantly on species compositions at sampling areas. © 2014, The Society of Population Ecology and Springer Japan. Source

Levy-Varon J.H.,Lamont Doherty Earth Observatory | Levy-Varon J.H.,Princeton Environmental Institute | Schuster W.S.F.,Black Rock Forest Consortium | Griffin K.L.,Lamont Doherty Earth Observatory

Forests serve an essential role in climate change mitigation by removing CO2 from the atmosphere. Within a forest, disturbance events can greatly impact C cycling and subsequently influence the exchange of CO2 between forests and the atmosphere. This connection makes understanding the forest C cycle response to disturbance imperative for climate change research. The goal of this study was to examine the temporal response of soil respiration after differing levels of stand disturbance for 3 years at the Black Rock Forest (southeastern NY, USA; oaks comprise 67 % of the stand). Tree girdling was used to mimic pathogen attack and create the following treatments: control, girdling all non-oaks (NOG), girdling half of the oak trees (O50), and girdling all the oaks (OG). Soil respiratory rates on OG plots declined for 2 years following girdling before attaining a full rebound of belowground activity in the third year. Soil respiration on NOG and O50 were statistically similar to the control for the duration of the study although a trend for a stronger decline in respiration on O50 relative to NOG occurred in the first 2 years. Respiratory responses among the various treatments were not proportional to the degree of disturbance and varied over time. The short-lived respiratory response on O50 and OG suggests that belowground activity is resilient to disturbance; however, sources of the recovered respiratory flux on these plots are likely different than they were pre-treatment. The differential taxon response between oaks and non-oaks suggests that after a defoliation or girdling event, the temporal response of the soil respiratory flux may be related to the C allocation pattern of the affected plant group. © 2013 Springer-Verlag Berlin Heidelberg. Source

Levy-Varon J.H.,Lamont Doherty Earth Observatory | Schuster W.S.F.,Black Rock Forest Consortium | Griffin K.L.,Lamont Doherty Earth Observatory

The goal of this study was to evaluate the contribution of oak trees (Quercus spp.) and their associated mycorrhizal fungi to total community soil respiration in a deciduous forest (Black Rock Forest) and to explore the partitioning of autotrophic and heterotrophic respiration. Trees on twelve 75 × 75-m plots were girdled according to four treatments: girdling all the oaks on the plot (OG), girdling half of the oak trees on a plot (O50), girdling all non-oaks on a plot (NO), and a control (C). In addition, one circular plot (diameter 50 m) was created where all trees were girdled (ALL). Soil respiration was measured before and after tree girdling. A conservative estimate of the total autotrophic contribution is approximately 50%, as indicated by results on the ALL and OG plots. Rapid declines in carbon dioxide (CO 2) flux from both the ALL and OG plots, 37 and 33%, respectively, were observed within 2 weeks following the treatment, demonstrating a fast turnover of recently fixed carbon. Responses from the NO and O50 treatments were statistically similar to the control. A non-proportional decline in respiration rates along the gradient of change in live aboveground biomass complicated partitioning of the overall rate of soil respiration and indicates that belowground carbon flux is not linearly related to aboveground disturbance. Our findings suggest that in this system there is a threshold disturbance level between 35 and 74% of live aboveground biomass loss, beyond which belowground dynamics change dramatically. © 2011 Springer-Verlag. Source

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