Demography of exploited tree species in the Bolivian Amazon

Tropical forests are threatened world-wide. Therefore, there is a search for ways to use the forests in a sustainable way, as this could assist in the conservation of these special ecosystems. Non-timber products collected from trees in tropical forests are often mentioned as examples of sustainable exploitation. Their collection causes far less disturbance to forest structure and functioning than the felling of trees for timber. This PhD thesis reports on ecological studies on tree species exploited for non-timber products. Three tree species were investigated in the tropical forests of the Bolivian Amazon region. The demography of these species is analysed and the impact of exploitation on population dynamics and future productivity is assessed. Use is made of matrix population models to analyse the population dynamics of the study species. Two of the three investigated species yield products with good prospects for sustainable extraction (Brazil nuts and palm leaves), whereas the palm heart collected from the third species offers little potential for sustained use. Brazil nuts have been collected from the emergent tree Bertholletia excelsa for decades in the region, without a clear negative impact. In spite of the fact that around 90% of the seeds are harvested, seedlings can be found in reasonable densities and demographic models predict a stable size and a continued rejuvenation of exploited populations. The Brazil nut tree may reach an age of over 300 yr, and becomes reproductive only at the age of 120-140 yr. Therefore, if there would be an effect of nut collection on future nut production, this would only become apparent after several decades. Leaves of the small understorey palm Geonoma deversa are cut for high-quality thatching material. The collection of leaves does not infer permanent damage to the plant, and all harvested leaves are replaced by new ones in approximately three years. Reproductive activity (flowering, fruiting and cloning) is strongly reduced after leaf cutting, but defoliation did not cause an elevated mortality risk. Population growth was only moderately reduced after leaf cutting. Model results show that the availability of leaves at population level recovers rapidly after simulated harvests. When harvests are repeated once every 16 years, leaf availability may be sustained at reasonable levels. The third product, palm heart, is collected from the canopy palm Euterpe precatoria. Collecting palm heart - the meristem of the plant - involves the cutting of the entire reproductive individual, and thus causes the death of the individual. As reproductive individuals of this species are approximately 90 yr in age, exploitation has a strongly negative impact on the population. Cut palms have to be replaced from seeds, as the species does not reproduce by clonal propagation. Demographic models show that the survival of adult palms is crucial to sustain population growth, and model simulations show that the availability of palm heart can only be sustained when a low proportion of reproductive individuals is cut and populations are left undisturbed for long periods between harvests. The current harvest practice - cutting around 90% of the adults and repeating this as soon as possible - clearly can not be sustained for longer periods. In addition, the thesis contains two chapters focusing on technical aspects related to the type of demographic models used for the case studies - matrix population models. An additional type of sensitivity analysis for matrix models is presented, which takes into account the inherent variability in demographic rates. Furthermore, the application of matrix models to analyse the demography and sustainable use of woody plants is reviewed

Mobile dune fixation by a fast-growing clonal plant: a full life-cycle analysis

Desertification is a global environmental problem, and arid dunes with sparse vegetation are especially vulnerable to desertification. One way to combat desertification is to increase vegetation cover by planting plant species that can realize fast population expansion, even in harsh environments. To evaluate the success of planted species and provide guidance for selecting proper species to stabilize active dunes, demographic studies in natural habitats are essential. We studied the life history traits and population dynamics of a dominant clonal shrub Hedysarum laeve in Inner-Mongolia, northern China. Vital rates of 19057 ramets were recorded during three annual censuses (2007–2009) and used to parameterize Integral Projection Models to analyse population dynamics. The life history of H. laeve was characterized by high ramet turnover and population recruitment entirely depended on clonal propagation. Stochastic population growth rate was 1.32, suggesting that the populations were experiencing rapid expansion. Elasticity analysis revealed that clonal propagation was the key contributor to population growth. The capacity of high clonal propagation and rapid population expansion in mobile dunes makes H. laeve a suitable species to combat desertification. Species with similar life-history traits to H. laeve are likely to offer good opportunities for stabilizing active dunes in arid inland ecosystems

Planning en controle bij uitkapbeheer met casestudies in Kolkbos, Oude Trekerbos en Boombos

From 1984 to 2012, three studies were carried out in an uneven-aged mixed species forest, two of which were managed as selection forests. Forest development was monitored in terms of tree growth, mortality, ingrowth and harvest. The diameter increment was described as a function of tree type, basal area per hectare of small, medium and large sized trees, and the period of growth. Using a modified IPM the probabilities of moving into a higher diameter class were calculated. With transi-tion matrices with probabilities for moving up, mortality, harvest, and in-growth, were estimated and using eigenvectors the stable state was determined. Notably, the selection cut was redefined. Regen-eration of light demanding tree species proved to be problematic. Selection forest management ap-peared possible in the Kolkbos and Oude Trekerbos; in the Boombos, currently managed without har-vest, a return to selective cutting management appears to be an option. The current selective har-vesting partly meets the conditions of Heyer’s allowable cut

The cocoa yield gap in Ghana: a quantification and an analysis of factors that could narrow the gap

Open Access Article; Published online: 28 Jul 2022CONTEXT Global cocoa production is largely concentrated in West Africa where over 70% of cocoa is produced. Here, cocoa farming is largely a rain-fed, low-input system with low average yields, which are expected to decline with climate change. With increasing demand, there is a need to evaluate opportunities to increase production whilst avoiding deforestation and expansion to croplands. Thus, it is important to know how much additional cocoa can be produced on existing farmland, and what factors determine this potential for increased yield. OBJECTIVE The objective was to quantify the cocoa yield gap in Ghana and identify the factors that can contribute to narrowing the gap. METHODS We calculated the cocoa yield gap as the difference between potential yield (i. water-limited potential(Yw) quantified using a crop model, ii. attainable yield in high-input systems(YE), iii. attainable yield in low-input systems(YF)) and actual farmer yield. Both absolute and relative yield gaps were calculated. We then related each yield gap (absolute & relative) as a function of environment and management variables using mixed-effects models. RESULTS AND CONCLUSIONS There were considerable yield gaps on all cocoa farms. Maximum water-limited yield gaps (YGW) were very large with a mean absolute gap of 4577 kg/ha representing 86% of Yw. Attainable yield gap in high-input (YGE) was lower with mean absolute gap of 1930 kg/ha representing 73% of YE. The yield gap in low-input (YGF) was even lower with mean absolute gap of 469 kg/ha representing 42% of YF. Mixed-effects models showed that, absolute YGW were larger at sites with higher precipitation in the minor wet and minimum temperature in the minor dry season explaining 22% of the variability in YGW. These same factors and cocoa planting density explained 28% of variability in absolute YGE. Regardless of climate, absolute YGF and relative YGW, YGE and YGF were reduced by increasing cocoa planting density and application of fungicide against black pod. The models explained 25% of the variability in absolute YGF, and 33%, 33% and 25% in relative YGW, YGE and YGF respectively. In conclusion, climate determined absolute YGW in Ghana whilst absolute YGE were determined by both climate and management. In contrast, absolute YGF and relative YGW, YGE and YGF can be reduced by agronomic management practices. SIGNIFICANCE Our study is one of the first to quantify cocoa yield gaps in West Africa and shows that these can be closed by improved agronomic practices

Parâmetros fotossintéticos e crescimento em mudas de bertholletia excelsa e carapa guianensis em resposta a pré-aclimatação a pleno sol e estresse hídrico moderado

Light and water are important factors that may limit the growth and development of higher plants. The aim of this study was to evaluate photosynthetic parameters and growth in seedlings of Bertholletia excelsa and Carapa guianensis in response to pre-acclimation to full sunlight and mild water stress. I used six independent pre-acclimation treatments (0, 90 (11h15-12h45), 180 (10h30-13h30), 360 (09h00-15h00), 540 (07h30-16h30) and 720 min (06h00-18h00)) varying the time of exposure to full sunlight (PFS) during 30 days, followed by whole-day outdoor exposure for 120 days. Before PFS, the plants were kept in a greenhouse at low light levels (0.8 mol m-2 day-1). The PFS of 0 min corresponded to plants constantly kept under greenhouse conditions. From the beginning to the end of the experiment, each PFS treatment was submitted to two water regimesmoderate water stress (MWS, pre-dawn leaf water potential (ΨL) of -500 to -700 kPa) and without water stress (WWS, ΨL of -300 kPa, soil kept at field capacity). Plants under MWS received only a fraction of the amount of water applied to the well-watered ones. At the end of the 120-day-period under outdoor conditions, I evaluated light saturated photosynthesis (Amax), stomatal conductance (g s), transpiration (E) and plant growth. Both Amax and g s were higher for all plants under the PFS treatment. Stem diameter growth rate and Amax were higher for C. guianensis subjected to MWS than in well-watered plants. The contrary was true for B. excelsa. The growth of seedlings was enhanced by exposure to full sunlight for 180 minutes in both species. However, plants of B. excelsa were sensitive to moderate water stress. The higher photosynthetic rates and faster growth of C. guianensis under full sun and moderate water stress make this species a promissory candidate to be tested in reforestation programs.A luz e a água são importantes fatores que limitam o crescimento e o desenvolvimento das plantas. O objetivo deste estudo foi avaliar os paâmetros fotossintéticos e o crescimento em mudas de Bertholletia excelsa e Carapa guianensis em resposta a pré-aclimatação à luz solar plena e estresse hídrico moderado. Foram usados seis independentes tratamentos de pré-aclimatação a pleno sol (PFS), sendo estes de (0, 90 (11h15-12h45), 180 (10h30-13h30), 360 (09h00-15h00), 540 (07h30-16h30) e 720 min (06h00-18h00)) durante 30 dias seguidos por um período de exposição a pleno sol de 120 dias durante o dia todo. Antes da PFS, as plantas foram mantidas em casa de vegetação a baixos níveis de luz (0,8 mol m-2 dia-1). O PFS de 0 min correspondeu às plantas mantidas constatemente na casa de vegetação. Cada tratamento de PFS foi submetido desde o início até o final do experimento a dois regimes hídricos, denominado de estresse hídrico moderado (MWS, potencial hidrico da folha medido antes do amanhecer (ΨL) de -500 a -700 kPa) e sem estresse hídrico (WWS , ΨL de -300 kPa, solo mantido na capacidade de campo). As plantas do tratamento MWS receberam apenas uma fração do volume de água fornecido para aquelas do tratamento WWS. No final do período de 120 dias foi avaliada a fotossíntese saturada por luz (Amax), a condutância estomática (g s), transpiração (E) e o crescimento. Amax e g s foram maiores em todas as plantas sob o tratamento de PFS. A taxa de crescimento em diâmetro e Amax foram maiores em plantas de C. guianensis submetidas à MWS. O contrário foi observado em B. excelsa. O crescimento das mudas foi maior nas plantas expostas à luz solar em 180 minutos em ambas as espécies. Entretanto, as plantas de B. excelsa foram mais sensíveis ao estresse hídrico moderado. C. guianensis foi à especie que teve melhor desempenho fotossintético e crescimento sob estresse hídrico moderado e luz solar plena. Portanto, essa espécie tem grande potencialidade para ser testada em programas de reflorestamento

Demography of exploited tree species in the Bolivian Amazon

Tropical forests are threatened world-wide. Therefore, there is a search for ways to use the forests in a sustainable way, as this could assist in the conservation of these special ecosystems. Non-timber products collected from trees in tropical forests are often mentioned as examples of sustainable exploitation. Their collection causes far less disturbance to forest structure and functioning than the felling of trees for timber. This PhD thesis reports on ecological studies on tree species exploited for non-timber products. Three tree species were investigated in the tropical forests of the Bolivian Amazon region. The demography of these species is analysed and the impact of exploitation on population dynamics and future productivity is assessed. Use is made of matrix population models to analyse the population dynamics of the study species. Two of the three investigated species yield products with good prospects for sustainable extraction (Brazil nuts and palm leaves), whereas the palm heart collected from the third species offers little potential for sustained use. Brazil nuts have been collected from the emergent tree Bertholletia excelsa for decades in the region, without a clear negative impact. In spite of the fact that around 90% of the seeds are harvested, seedlings can be found in reasonable densities and demographic models predict a stable size and a continued rejuvenation of exploited populations. The Brazil nut tree may reach an age of over 300 yr, and becomes reproductive only at the age of 120-140 yr. Therefore, if there would be an effect of nut collection on future nut production, this would only become apparent after several decades. Leaves of the small understorey palm Geonoma deversa are cut for high-quality thatching material. The collection of leaves does not infer permanent damage to the plant, and all harvested leaves are replaced by new ones in approximately three years. Reproductive activity (flowering, fruiting and cloning) is strongly reduced after leaf cutting, but defoliation did not cause an elevated mortality risk. Population growth was only moderately reduced after leaf cutting. Model results show that the availability of leaves at population level recovers rapidly after simulated harvests. When harvests are repeated once every 16 years, leaf availability may be sustained at reasonable levels. The third product, palm heart, is collected from the canopy palm Euterpe precatoria. Collecting palm heart - the meristem of the plant - involves the cutting of the entire reproductive individual, and thus causes the death of the individual. As reproductive individuals of this species are approximately 90 yr in age, exploitation has a strongly negative impact on the population. Cut palms have to be replaced from seeds, as the species does not reproduce by clonal propagation. Demographic models show that the survival of adult palms is crucial to sustain population growth, and model simulations show that the availability of palm heart can only be sustained when a low proportion of reproductive individuals is cut and populations are left undisturbed for long periods between harvests. The current harvest practice - cutting around 90% of the adults and repeating this as soon as possible - clearly can not be sustained for longer periods. In addition, the thesis contains two chapters focusing on technical aspects related to the type of demographic models used for the case studies - matrix population models. An additional type of sensitivity analysis for matrix models is presented, which takes into account the inherent variability in demographic rates. Furthermore, the application of matrix models to analyse the demography and sustainable use of woody plants is reviewed

A physiological production model for cacao : results of model simulations

CASE2 is a physiological model for cocoa (Theobroma cacao L.) growth and yield. This report introduces the CAcao Simulation Engine for water-limited production in a non-technical way and presents simulation results obtained with the model

A physiological production model for cacao : user's manual for CASE2 version 2.2 under FSE Windows

CASE2 is a physiological model for cocoa (Theobroma cacao L.) growth and yield. This report contains a user’s manual for the CASE2 model version 2.2 running in a FSE Windows environment