Herbivory and habitat association of tree seedlings in lowland evergreen rainforest on white-sand and terra-firme in the upper Rio Negro
Stropp, J. ; Sleen, J.P. van der; Quesada, C.A. ; Steege, H. ter - \ 2014
Plant Ecology & Diversity 7 (2014)1-2. - ISSN 1755-0874 - p. 255 - 265.
amazonian forests - resource availability - growth - patterns - soils - specialization - communities - landscape - diversity - worldwide
Background: It has been proposed that the interaction between herbivory and soil nutrient availability drives habitat association of tree species in Peruvian Amazonia. Nevertheless, there is no empirical evidence that this interaction holds across other Amazonian regions. Aims: We address this knowledge gap by testing whether the interaction between herbivory and soil nutrient contributes to habitat association of tree species in white-sand and terra-firme forests in the upper Rio Negro, Brazil. Methods: We conducted a reciprocal transplanting field experiment in which we controlled for the presence of herbivores. We tested for differences in tree-seedling growth and herbivory among seven white-sand and seven terra-firme habitat-specialist species. Additionally, we assessed whether tree seedlings differed in their functional traits. Results: We found no empirical evidence that an interaction between herbivory and soil nutrients shapes habitat association in white-sand and terra-firme forests of the upper Rio Negro. Tree seedlings showed higher mortality when growing in their non-typical habitat. Growth and herbivory were similar regardless of the presence or absence of herbivore protection and type of soil. Conclusions: We suggest that the overall differences in soil nutrient status between white-sand and terra-firme forests in the upper Rio Negro are insufficient to trigger an interaction between herbivory and soil nutrient availability.
What could have caused pre-industrial biomass burning emissions to exceed current rates?
Werf, G.R. van der; Peters, W. ; Leeuwen, T.T. van; Giglio, L. - \ 2013
Climate of the Past 9 (2013)1. - ISSN 1814-9324 - p. 289 - 306.
rain-forest fires - past 2 millennia - amazonian forests - southern africa - trace gases - model tm5 - land-use - carbon - 20th-century - climate
Recent studies based on trace gas mixing ratios in ice cores and charcoal data indicate that biomass burning emissions over the past millennium exceeded contemporary emissions by up to a factor of 4 for certain time periods. This is surprising because various sources of biomass burning are linked with population density, which has increased over the past centuries. We have analysed how emissions from several landscape biomass burning sources could have fluctuated to yield emissions that are in correspondence with recent results based on ice core mixing ratios of carbon monoxide (CO) and its isotopic signature measured at South Pole station (SPO). Based on estimates of contemporary landscape fire emissions and the TM5 chemical transport model driven by present-day atmospheric transport and OH concentrations, we found that CO mixing ratios at SPO are more sensitive to emissions from South America and Australia than from Africa, and are relatively insensitive to emissions from the Northern Hemisphere. We then explored how various landscape biomass burning sources may have varied over the past centuries and what the resulting emissions and corresponding CO mixing ratio at SPO would be, using population density variations to reconstruct sources driven by humans (e.g., fuelwood burning) and a new model to relate savanna emissions to changes in fire return times. We found that to match the observed ice core CO data, all savannas in the Southern Hemisphere had to burn annually, or bi-annually in combination with deforestation and slash and burn agriculture exceeding current levels, despite much lower population densities and lack of machinery to aid the deforestation process. While possible, these scenarios are unlikely and in conflict with current literature. However, we do show the large potential for increased emissions from savannas in a pre-industrial world. This is mainly because in the past, fuel beds were probably less fragmented compared to the current situation; satellite data indicates that the majority of savannas have not burned in the past 10 yr, even in Africa, which is considered "the burning continent". Although we have not considered increased charcoal burning or changes in OH concentrations as potential causes for the elevated CO concentrations found at SPO, it is unlikely they can explain the large increase found in the CO concentrations in ice core data. Confirmation of the CO ice core data would therefore call for radical new thinking about causes of variable global fire rates over recent centuries
Tree height integrated into pantropical forest biomass estimates
Feldpausch, T.R. ; Lloyd, J. ; Lewis, S.L. ; Brienen, R.J.W. ; Gloor, M. ; Montegudo Mendoza, A. ; Arets, E.J.M.M. - \ 2012
Biogeosciences 9 (2012). - ISSN 1726-4170 - p. 3381 - 3403.
tropical rain-forest - aboveground live biomass - net primary production - land-use change - wood density - amazonian forests - carbon stocks - allometric equations - neotropical forest - secondary forests
Aboveground tropical tree biomass and carbon storage estimates commonly ignore tree height (H). We estimate the effect of incorporating H on tropics-wide forest biomass estimates in 327 plots across four continents using 42 656 H and diameter measurements and harvested trees from 20 sites to answer the following questions: 1. What is the best H-model form and geographic unit to include in biomass models to minimise site-level uncertainty in estimates of destructive biomass? 2. To what extent does including H estimates derived in (1) reduce uncertainty in biomass estimates across all 327 plots? 3. What effect does accounting for H have on plot- and continental-scale forest biomass estimates? The mean relative error in biomass estimates of destructively harvested trees when including H (mean 0.06), was half that when excluding H (mean 0.13). Power- and Weibull-H models provided the greatest reduction in uncertainty, with regional Weibull-H models preferred because they reduce uncertainty in smaller-diameter classes (=40 cm D) that store about one-third of biomass per hectare in most forests. Propagating the relationships from destructively harvested tree biomass to each of the 327 plots from across the tropics shows that including H reduces errors from 41.8 Mg ha-1 (range 6.6 to 112.4) to 8.0 Mg ha-1 (-2.5 to 23.0). For all plots, aboveground live biomass was -52.2 Mg ha-1 (-82.0 to -20.3 bootstrapped 95% CI), or 13%, lower when including H estimates, with the greatest relative reductions in estimated biomass in forests of the Brazilian Shield, east Africa, and Australia, and relatively little change in the Guiana Shield, central Africa and southeast Asia. Appreciably different stand structure was observed among regions across the tropical continents, with some storing significantly more biomass in small diameter stems, which affects selection of the best height models to reduce uncertainty and biomass reductions due to H. After accounting for variation in H, total biomass per hectare is greatest in Australia, the Guiana Shield, Asia, central and east Africa, and lowest in east-central Amazonia, W. Africa, W. Amazonia, and the Brazilian Shield (descending order). Thus, if tropical forests span 1668 million km2 and store 285 Pg C (estimate including H), then applying our regional relationships implies that carbon storage is overestimated by 35 Pg C (31–39 bootstrapped 95% CI) if H is ignored, assuming that the sampled plots are an unbiased statistical representation of all tropical forest in terms of biomass and height factors. Our results show that tree H is an important allometric factor that needs to be included in future forest biomass estimates to reduce error in estimates of tropical carbon stocks and emissions due to deforestation.
Climate is a stronger driver of tree and forest growth rates than soil and disturbance
Toledo, M. ; Poorter, L. ; Peña-Claros, M. ; Alarcón, A. ; Balcázar, J. ; Leaño, C. ; Licona, J.C. ; Llanque, O. ; Vroomans, V. ; Zuidema, P. ; Bongers, F. - \ 2011
Journal of Ecology 99 (2011)1. - ISSN 0022-0477 - p. 254 - 264.
tropical rain-forest - long-term plots - diameter increment - amazonian forests - french-guiana - phosphorus fertilization - silvicultural treatments - nutrient limitation - neotropical forest - carbon dynamics
1. Essential resources such as water, nutrients and light vary over space and time and plant growth rates are expected to vary accordingly. We examined the effects of climate, soil and logging disturbances on diameter growth rates at the tree and stand level, using 165 1-ha permanent sample plots distributed across Bolivian tropical lowland forests. 2. We predicted that growth rates would be higher in humid than in dry forests, higher in nutrient-rich than nutrient-poor forests and higher in logged than non-logged forests. 3. Across the 165 plots we found positive basal area increases at the stand level, which agree with the generally reported biomass increases in tropical forests. 4. Multiple regression analysis demonstrated that climate variables, in particular water availability, were the strongest drivers of tree growth. More rainfall, a shorter and less intense dry period and higher temperatures led to higher tree growth rates. 5. Tree growth increased modestly with soil fertility and basal area growth was greatest at intermediate soil fertility. Surprisingly, tree growth showed little or no relationship with total soil nitrogen or plant available soil phosphorus. 6. Growth rates increased in logged plots just after logging, but this effect disappeared after 6 years. 7. Synthesis. Climate is the strongest driver of spatial variation in tree growth, and climate change may therefore have large consequences for forest productivity and carbon sequestration. The negative impact of decreased rainfall and increased rainfall seasonality on tree growth might be partly offset by the positive impact of increased temperature in these forests.
Tree diversity, composition, forest structure and aboveground biomass dynamics after single and repeated fire in a Bornean rain forest
Slik, J.W.F. ; Bernard, C.S. ; Beek, M. van; Breman, F.C. ; Eichhorn, K.A.O. - \ 2008
Oecologia 158 (2008)3. - ISSN 0029-8549 - p. 579 - 588.
tropical forests - species composition - amazonian forests - east kalimantan - wood density - indonesia - restoration - vegetation - responses
Forest fires remain a devastating phenomenon in the tropics that not only affect forest structure and biodiversity, but also contribute significantly to atmospheric CO2. Fire used to be extremely rare in tropical forests, leaving ample time for forests to regenerate to pre-fire conditions. In recent decades, however, tropical forest fires occur more frequently and at larger spatial scales than they used to. We studied forest structure, tree species diversity, tree species composition, and aboveground biomass during the first 7 years since fire in unburned, once burned and twice burned forest of eastern Borneo to determine the rate of recovery of these forests. We paid special attention to changes in the tree species composition during burned forest regeneration because we expect the long-term recovery of aboveground biomass and ecosystem functions in burned forests to largely depend on the successful regeneration of the pre-fire, heavy-wood, species composition. We found that forest structure (canopy openness, leaf area index, herb cover, and stem density) is strongly affected by fire but shows quick recovery. However, species composition shows no or limited recovery and aboveground biomass, which is greatly reduced by fire, continues to be low or decline up to 7 years after fire. Consequently, large amounts of the C released to the atmosphere by fire will not be recaptured by the burned forest ecosystem in the near future. We also observed that repeated fire, with an inter-fire interval of 15 years, does not necessarily lead to a huge deterioration in the regeneration potential of tropical forest. We conclude that burned forests are valuable and should be conserved and that long-term monitoring programs in secondary forests are necessary to determine their recovery rates, especially in relation to aboveground biomass accumulation.
Hunting increases dispersal limitation in the tree Carapa procera, a nontimber forest product
Forget, P.M. ; Jansen, P.A. - \ 2007
Conservation Biology 21 (2007)1. - ISSN 0888-8892 - p. 106 - 113.
orange-rumped agouti - seed dispersal - tropical forest - french-guiana - rain-forest - bertholletia-excelsa - dasyprocta-leporina - amazonian forests - recruitment - fate
The sustainability of seed extraction from natural populations has been questioned recently. Increased recruitment failure under intense seed harvesting suggests that seed extraction intensifies source limitation. Nevertheless, areas where more seeds are collected tend to also have more intense hunting of seed-dispersing animals. We studied whether such hunting, by limiting disperser activity, could cause quantitative dispersal limitation, especially for large crops and for crops in years of high seed abundance. In each of four Carapa procera (Meliaceae) populations in French Guiana and Surinam, two with hunting and two without, we compared seed fate for individual trees varying in crop size in years of high and low population-level seed abundance. Carapa seeds are a nontimber forest product and depend on dispersal by scatter-hoarding rodents for survival and seedling establishment. Hunting negatively affected the proportion of seeds dispersed and caused greater numbers of seeds to germinate or be infested by moths below parent trees, where they would likely die. Hunting of seed-dispersing animals disproportionally affected large seed crops, but we found no additional effect of population-level seed abundance on dispersal rates. Consistently lower rates of seed dispersal, especially for large seed crops, may translate to lower levels of seedling recruitment under hunting. Our results therefore suggest that the subsistence hunting that usually accompanies seed collection is at the cost of seed dispersal and may contribute to recruitment failure of these nontimber forest products. Seed extraction from natural populations may affect seedling recruitment less if accompanied by measures adequately incorporating and protecting seed dispersers
Disentangling above- and below-ground competition between lianas and trees in a tropical forest
Schnitzer, S.A. ; Kuzee, M.E. ; Bongers, F.J.J.M. - \ 2005
Journal of Ecology 93 (2005)6. - ISSN 0022-0477 - p. 1115 - 1125.
host liquidambar-styraciflua - fine root biomass - rain-forest - canopy gaps - wet forest - species-diversity - amazonian forests - vine competition - eastern amazonia - seedling growth
1 Light is thought to be the most limiting resource in tropical forests, and thus aboveground competition is commonly accepted as the mechanism that structures these communities. In many tropical forests, trees compete not only with other trees, but also with lianas, which compete aggressively for below-ground resources and thus may limit tree growth and regeneration. 2 Using a replicated experiment, we tested the relative strengths of above- and belowground competition from lianas on tree saplings in a disturbed forest in Côte d¿Ivoire with a heterogeneous canopy and relatively high light penetration. We planted seedlings of three tree species and subjected them to below-ground competition with lianas (BGC), above- and below-ground competition with lianas (ABGC), or a liana-free control treatment. After 2 years, we harvested the saplings and compared the amount of above-ground biomass and its relative allocation among the three experimental treatments and different tree species. 3 Lianas competed intensely with saplings in this tropical forest, substantially limiting sapling growth. Saplings grown in the ABGC and BGC treatments had only 18.5% and 16.8% of the above-ground dry biomass of those grown in the liana-free control treatment. 4 Sapling biomass did not differ significantly among the ABGC and BGC treatments, suggesting that below-ground competition was the driving force behind liana vs. tree competition in this forest. Above-ground competition with lianas, however, did affect the allocation of biomass in saplings, resulting in shorter, thicker stems and a poorly developed crown. 5 Collectively, our findings suggest that below-ground competition with lianas plays a substantial role in limiting the growth of saplings in disturbed and secondary tropical forests, and above-ground effects may be due to a combination of above-ground competition and mechanical stress. 6 Disentangling above- and below-ground competition between lianas and trees is critical for a comprehensive understanding of the dynamics of naturally regenerating tropical forests, as well as formulating successful management plans for sustainable timber harvest. Key-words: above-ground, below-ground, competition, Côte d¿Ivoire, forest regeneration, lianas, trees, tropical forest