Search

High biodiversity of forests is not predicted by traditional models, and evidence for trade-offs those models require is limited. High-dimensional regulation (e.g., N factors to regulate N species) has long been recognized as a possible alternative explanation, but it has not be been seriously pursued, because only a few limiting resources are evident for trees, and analysis of multiple interactions is challenging. We develop a hierarchical model that allows us to synthesize data from long-term, experimental, data sets with processes that control growth, maturation, fecundity, and survival. We allow for uncertainty at all stages and variation among 26000 individuals and over time, including 268000 tree years, for dozens of tree species. We estimate population-level parameters that apply at the species level and the interactions among latent states, i.e., the demographic rates for each individual, every year. The former show that the traditional trade-offs used to explain diversity are not present. Demographic rates overlap among species, and they do not show trends consistent with maintenance of diversity by simple mechanisms (negative correlations and limiting similarity). However, estimates of latent states at the level of individuals and years demonstrate that species partition environmental variation. Correlations between responses to variation in time are high for individuals of the same species, but not for individuals of different species. We demonstrate that these relationships are pervasive, providing strong evidence that high-dimensional regulation is critical for biodiversity regulation. Key words: Bayesian analysis; biodiversity; coexistence; competition; forest dynamics; hierarchical models.

Secondary forests and plantations increasingly dominate the tropical wooded landscape in place of primary forests. The expected reduction of biodiversity and its impact on ecological functions provided by these secondary forests are of major concern to society and ecologists. The potential effect of biodiversity loss on ecosystem functioning depends largely on the associated loss in the functional diversity of animal and plant assemblages, i.e., the degree of functional redundancy among species. However, the relationship between species and functional diversity is still poorly documented for most ecosystems. Here, we analyze how changes in the species diversity of ground-foraging ant assemblages translate into changes of functional diversity along a successional gradient of secondary forests in the Atlantic Forest of Brazil. Our analysis uses continuous measures of functional diversity and is based on four functional traits related to resource use of ants: body size, relative eye size, relative leg length, and trophic position. We find a strong relationship between species and functional diversity, independent of the functional traits used, with no evidence for saturation in this relationship. Recovery of species richness and diversity of ant assemblages in tropical secondary forests was accompanied by a proportional increase of functional richness and diversity of assemblages. Moreover, our results indicate that the increase in functional diversity along the successional gradient of secondary forests is primarily driven by rare species, which are functionally unique. The observed loss of both species and functional diversity in secondary forests offers no reason to believe that the ecological functions provided by secondary forests are buffered against species loss through functional redundancy. Key words: ant assemblages; Atlantic Forest, Brazil; Formicidae; functional diversity; functional redundancy; human impacts; recovery; secondary forests; tropical forests.

In the past, explanations for high species diversity have been sought at the species level. Theory shows that coexistence requires substantial differences between species, but species-level data rarefy provide evidence for such differences. Using data from forests in the southeastern United States, I show here that variation evident at the individual level provides for coexistence of large numbers of competitors. Variation among individuals within populations allows species to differ in their distributions of responses to the environment, despite the fact that the populations to which they belong do not differ, on average. Results are consistent with theory predicting that coexistence depends on competition being stronger within than between species, shown here by analysis of individual-level responses to environmental fluctuation. 10.1126/science.1183506

Forests and their soils contain the majority of the earth's terrestrial carbon stocks. Changes in patterns of tree growth can have a huge impact on atmospheric cycles, biogeochemical cycles, climate change, and biodiversity. Recent studies have shown increases in biomass across many forest types. This increase has been attributed to climate change. However, without knowing the disturbance history of a forest, growth could also be caused by normal recovery from unknown disturbances. Using a unique dataset of tree biomass collected over the past 22 years from 55 temperate forest plots with known land-use histories and stand ages ranging from 5 to 250 years, we found that recent biomass accumulation greatly exceeded the expected growth caused by natural recovery. We have also collected over 100 years of local weather measurements and 17 years of on-site atmospheric C[O.sub.2] measurements that show consistent increases in line with globally observed climate-change patterns. Combined, these observations show that changes in temperature and C[O.sub.2] that have been observed worldwide can fundamentally alter the rate of critical natural processes, which is predicted by biogeochemical models. Identifying this rate change is important to research on the current state of carbon stocks and the fluxes that influence how carbon moves between storage and the atmosphere. These results signal a pressing need to better understand the changes in growth rates in forest systems, which influence current and future states of the atmosphere and biosphere. biomass change | carbon cycle | carbon fertilization | climate change | forest stand dynamics doi/10.1073/pnas.0912376107

Forests both take up C[O.sub.2] and enhance absorption of solar radiation, with contrasting effects on global temperature. Based on a 9-year study in the forests' dry timberline, we show that substantial carbon sequestration (cooling effect) is maintained in the large dry transition zone (precipitation from 200 to 600 millimeters) by shifts in peak photosynthetic activities from summer to early spring, and this is counteracted by longwave radiation (L) suppression (warming effect), doubling the forestation shortwave (S) albedo effect. Several decades of carbon accumulation are required to balance the twofold S + L effect. Desertification over the past several decades, however, contributed negative forcing at Earth's surface equivalent to ~20% of the global anthropogenic C[O.sub.2] effect over the same period, moderating warming trends. 10.1126/science.1179998

Byline: Leonard Ornstein (1) Author Affiliation: (1) Mount Sinai School of Medicine, NYC, 5 Biltom Road, White Plains, 10607, NY, USA Article History: Registration Date: 03/06/2009 Received Date: 17/05/2008 Accepted Date: 28/04/2009 Online Date: 19/08/2009

The Northern Hemisphere has large areas that are forested and seasonally snow covered. Compared with open areas, forest canopies strongly influence interactions between the atmosphere and snow on the ground by sheltering the snow from wind and solar radiation and by intercepting falling snow; these influences have important consequences for the meteorology, hydrology, and ecology of forests. Many of the land surface models used in meteorological and hydrological forecasting now include representations of canopy snow processes, but these have not been widely tested in comparison with observations. Phase 2 of the Snow Model Intercomparison Project (SnowMIP2) was therefore designed as an intercomparison of surface mass and energy balance simulations for snow in forested areas. Model forcing and calibration data for sites with paired forested and open plots were supplied to modeling groups. Participants in 11 countries contributed output from 33 models, and the results are published here for sites in Canada, the United States, and Switzerland. On average, the models perform fairly well in simulating snow accumulation and ablation, although there is a wide intermodal spread and a tendency to underestimate differences in snow mass between open and forested areas. Most models capture the large differences in surface albedos and temperatures between forest canopies and open snow well. There is, however, a strong tendency for models to underestimate soil temperature under snow, particularly for forest sites, and this would have large consequences for simulations of runoff and biological processes in the soil.

Surface application of urea to pine forests may lead to ammonia (N[H.sub.3]) volatilization, which can reduce forest production. The objective of this study was to characterize urea reactions with the forest soil and to determine how various forest floor components interact with weather to affect N[H.sub.3] loss. Three field studies were performed in a midrotation loblolly pine (Pinus taeda L.) plantation with up to three treatments in each study, where N[H.sub.3] volatilization chambers were fertilized with 200 kg N [ha.sup.-1] that contained either (i) intact forest floor, (ii) forest floor removed by hand raking, or (iii) forest floor burned. In a complementary laboratory study, N[H.sub.3] loss was evaluated from cores comprised of: (i) mineral soil only, (ii) mineral soil + humus layer, (iii) mineral soil + humus + old needles, and (iv) mineral soil + humus + old needles + new needles. Loss of N[H.sub.3] in the field was generally greatest when urea was applied to a mineral soil with no forest floor, resulting in a loss of 53 and 59% of the applied N in two 29-d studies. Loss of N[H.sub.3] was intermediate from a complete forest floor (11 and 35% loss), and rates of loss appeared to be most affected by relative humidity. Losses were least from a recently burned forest floor (6 and 7% loss), due partly to slower urea hydrolysis. Loss of N[H.sub.3] in the laboratory study was also greater from the bare soil than from the complete forest floor. Retention of N[H.sub.4.sup.+] in the soil layers was related to the soil pH buffering capacity below pH 7. Because the humus layer was shown to have a large pH buffering capacity to retain N[H.sub.4.sup.+], these results suggest forest management that enhances humus formation should increase N[H.sub.4.sup.+]] sorption and decrease N[H.sub.3] volatilization. Abbreviations: CRH, critical relative humidity; DI, deionized; RH, relative humidity.

Wild pigs (Sus scrofa) are considered opportunistic omnivores that consume primarily plant matter; vertebrates are thought to constitute only a minor component of their diets, primarily as carrion, but active predation on vertebrates has been suspected. We examined the stomach contents of 104 wild pigs collected during a 7-year period in oak woodlands of the Diablo Range, California, and found that 40.4% contained vertebrate prey comprising 20 species, including 11 mammals, and totaling 167 individuals. Most stomachs with vertebrate prey included multiple individuals (< 18) of >1 species ( Key words: diet, feral pigs, oak woodlands, predation, protein deficiency, Sus scrofa, wild pigs

Changes in land use have been shown to have profound effects on forest plant community structure and diversity. Dispersal limitation has been invoked as a major factor hampering colonization of forest plant species, while seed-sowing experiments and performance observations have provided some evidence for recruitment limitation determining forest plant distribution in post-agricultural forests. However, most of these studies were relatively short-term, and very few studies have investigated long-term growth rates of populations occurring in recent and ancient forests. In this study, matrix models using demographic data collected for four consecutive years were used to study the effect of forest age on population dynamics of the temperate forest herb Primula elatior. A life table response experiment (LTRE) and elasticity analysis were used to analyze the effect of forest age on population growth rate ([lambda]) and to decompose the effect of forest age on [lambda]. into contributions from each matrix element. Population growth increased logarithmically with increasing forest age. Bootstrap analyses showed that populations located in very recent forests ( 150 years old had growth rates that were significantly >1. Summed elasticities for individual growth significantly decreased with increasing forest age, whereas summed elasticities for survival and fertility significantly increased with increasing forest age. The LTRE analysis showed that the increase in [lambda] with increasing forest age was mainly due to increased seedling and juvenile growth and increased juvenile and adult survival. Our results indicate that past agricultural land use has long-lasting effects on the demography of forest herbs and may provide an additional mechanistic explanation for the poor colonization capacity of many forest herbs in post-agricultural forests. Key words: ancient vs. recent forest; forest history; life table response experiment; matrix projection model; population growth rate; Primula elatior.

In the ancient and acidic Ultisol soils of the Southern Piedmont, USA, we studied changes in trace element biogeochemistry over four decades, a period during which formerly cultivated cotton fields were planted with pine seedlings that grew into mature forest stands. In 16 permanent plots, we estimated 40-year accumulations of trace elements in forest biomass and O horizons (between 1957 and 1997), and changes in bioavailable soil fractions indexed by extractions of 0.05 mol/L HCl and 0.2 mol/L acid ammonium oxalate (AAO). Element accumulations in 40-year tree biomass plus O horizons totaled 0.9, 2.9, 4.8, 49.6, and 501.3 kg/ha for Cu, B, Zn, Mn, and Fe, respectively. In response to this forest development, samples of the upper 0.6-m of mineral soil archived in 1962 and 1997 followed one of three patterns. (1) Extractable B and Mn were significantly depleted, by -4.1 and -57.7 kg/ha with AAO, depletions comparable to accumulations in biomass plus O horizons, 2.9 and 49.6 kg/ha, respectively. Tree uptake of B and Mn from mineral soil greatly outpaced resupplies from atmospheric deposition, mineral weathering, and deep-root uptake. (2) Extractable Zn and Cu changed little during forest growth, indicating that nutrient resupplies kept pace with accumulations by the aggrading forest. (3) Oxalate-extractable Fe increased substantially during forest growth, by 275.8 kg/ha, about 10-fold more than accumulations in tree biomass (28.7 kg/ha). The large increases in AAO-extractable Fe in surficial 0.35-m mineral soils were accompanied by substantial accretions of Fe in the forest's O horizon, by 473 kg/ha, amounts that dwarfed inputs via litterfall and canopy throughfall, indicating that forest Fe cycling is qualitatively different from that of other macro- and micronutrients. Bioturbation of surficial forest soil layers cannot account for these fractions and transformations of Fe, and we hypothesize that the secondary forest's large inputs of organic additions over four decades has fundamentally altered soil Fe oxides, potentially altering the bioavailability and retention of macro- and micronutrients, contaminants, and organic matter itself. The wide range of responses among the ecosystem's trace elements illustrates the great dynamics of the soil system over time scales of decades. Key words: ecosystem ecology; Fe; iron oxides; nutrient cycling; reforestation; soil organic matter; Southern Piedmont, USA; trace elements.

The influence of inorganic nitrogen (N) inputs on decomposition is poorly understood. Some prior studies suggest that N may reduce the decomposition of substrates with high concentrations of lignin via inhibitory effects on the activity of lignin-degrading enzymes, although such inhibition has not always been demonstrated. I studied the effects of N addition on decomposition of seven substrates ranging in initial lignin concentrations (from 7.4% to 25.6%) over five years in eight different grassland and forest sites in central Minnesota, USA. I predicted that N would stimulate the decomposition of lignin-poor substrates but retard the decomposition of lignin-rich substrates. Across these sites, N had neutral or negative effects on decomposition rates. However, in contrast to my hypothesis, effects of N on decomposition were independent of substrate initial lignin concentrations, and decomposition of the lignin fraction was unaffected by N fertilization. Rather, substrate-site combinations that exhibited more rapid decomposition rates in the control treatment were affected more negatively by addition of N fertilization. Taken together, these results suggest that decreased decomposition with added N did not result from inhibition of lignin-degrading enzyme activity, but may have resulted from abiotic interactions between N fertilizer and products of microbial degradation or synthesis or from N effects on the decomposer community. Low initial substrate N concentrations and N fertilization both stimulated N immobilization, but the differences among substrates were generally much larger than the effects of fertilization. This study suggests that atmospheric N addition could stimulate ecosystem carbon sequestration in some ecosystems as a result of reduced rates of forest floor decomposition. Key words: decomposition; forest; grassland; immobilization; lignin; Minnesota, USA; nitrogen.

In this paper, a model for prediction of radar backscatter from coniferous forests in the VHF and UHF band is proposed. The model includes the double-bounce scattering originating from vertical stems standing on an undulating ground surface and is based on a physical-optics approach. The model can be used to assess the importance of ground topography in synthetic aperture radar (SAR) imagery of forests, and it is applicable to SAR systems using horizontally transmit and receive polarization (HH). The model was validated against data from the airborne SAR systems CARABAS-II and LORA. Precision measurements of ground topography and forest characterization at a single tree level were used as model input to simulate SAR images. The simulated images were compared to radar data in the frequency bands 22-82 and 225-470 MHz, and it was found that the model could predict much of the variation in backscatter observed in images ([R.sup.2] = 0.44 and 0.65 at best, for the lower and higher frequency band, respectively), which should be compared to [R.sup.2] [approximately equal to] 0.1 if the same model, but assuming a flat ground, was used. The results thus indicate that ground topography must be considered when predicting the variations in backscatter in the SAR images studied. The model did, however, fail to predict the absolute values of the backscattered intensity. The reason for the discrepancy is believed to be the value chosen for stem dielectric constant and unmodeled effects due to wave attenuation, tilting stems, and small-scale surface roughness. Index Terms--Forest, model, physical optics (PO), surface scattering, synthetic aperture radar (SAR), UHF radar, VHF radar.

Soil C and N were measured from a chronosequence of adjacent riparian forest sites located along the floodplain terrace of the San Antonio River. The communities were 25, 39, 45, 47, 49, and 53 yr past long-term farmland use. Four of these sites (25, 45, 49, and 53 yr old) were also sampled 20 yr ago. Soil C was significantly greater after 20 yr of community development; however, the increase was dependent on the community age. Soil C increased by 38 g [kg.sup.-1] in the 49-yr-old community during the 20-yr period, but only 11 to 15 g [kg.sup.-1] in the 25-, 45-, and 53-yr-old communities. Soil N was significantly greater (1.7-2.5 g [kg.sup.-1]) after 20 yr of development for communities 25, 45, and 49 yr old. In the oldest community (53 yr old), no significant increase was seen in soil N after 20 yr. No significant spatial differences [underneath the canopy of Acacia farnesiana (L.) Willd. vs. intercanopy grassland] were found in soil C and N in the 25-yr-old community. The late successional dominant Cehis laevigata Willd., total woody plant density, and total woody plant basal area could be explained by soil C or N. Changes in soil C and N through time parallel other studies, increasing through the early- and mid-successional stages and decreasing from the mid- to late-successional stages. Spatial differences in soil C and N that existed in the 15-yr-old community disappeared in the 25-yr-old community as A. farnesiana basal area increased from 0.7 to 13 [m.sup.2] [ha.sup.-1].

This article explores the significance of childhood experience of woodlands and other green or natural places in relation to adult patterns of use and attitudes to such places. It draws on data collected in different parts of Britain. Questionnaires were used to explore the frequency of adults' visits to green places, the frequency with which they reported visiting such places as children, and their attitudes to different attributes of the places they visited. The data show a strong relationship between frequent childhood visits and being prepared to visit woodlands or green spaces alone as an adult. By contrast, not visiting as a child was associated with a very low likelihood of later adult visits. The data also suggest that the physical and the emotional benefits of access to green space are strongly reflected in childhood experience. The significance of these findings for today's children, as they become adults, is discussed. Keywords: childhood; green places; woodlands; green space; access

The long-term ecological response to recurrent deforestation associated with shifting cultivation remains poorly investigated, especially in the dry tropics. We present a study of phosphorus (P) dynamics in the southern Yucatan, highlighting the possibility of abrupt shifts in biogeochemical cycling resulting from positive feedbacks between vegetation and its limiting resources. After three cultivation-fallow cycles, available soil P declines by 44%, and one-time P inputs from biomass burning decline by 76% from mature forest levels. Interception of dust-borne P ('canopy trapping') declines with lower plant biomass and leaf area, limiting deposition in secondary forest. Potential leaching losses are greater in secondary than in mature forest, but the difference is very small compared with the difference in P inputs. The decline in new P from atmospheric deposition creates a long-term negative ecosystem balance for phosphorus. The reduction in soil P availability will feed back to further limit biomass recovery and may induce a shift to sparser vegetation. Degradation induced by hydrological and biogeochemical feedbacks on P cycling under shifting cultivation will affect farmers in the near future. Without financial support to encourage the use of fertilizer, farmers could increase the fallow period, clear new land, or abandon agriculture for off-farm employment. Their response will determine the regional balance between forest loss and forest regrowth, as well as the frequency of use and rate of recovery at a local scale, further feeding back on ecological processes at multiple scales. atmospheric deposition | phosphorus | positive feedback | shifting cultivation | soil degradation