METHODS OF CONTROLLING BLACK-POD DISEASE (CAUSED BY PHYTOPHTHORA PALMIVORA) OF THEOBROMA CACAO IN NIGERIA

Supplementary methods of controlling black-pod disease ( Phytophthora palmivora ) of cocoa in Nigeria are considered, because fungicide application is not always economic.
There is no evidence that resistance occurs within the local population of Amelonado-type trees.
Although the percentage of diseased pods was greater with trees closely spaced (5 times 5 ft. to 8 times 8 ft.), than with widely spaced trees (10 times 10 ft. to 15 times 15 ft.), the closer spacings often gave more healthy pods per acre.
Loss of pods from black-pod was decreased when trees were inspected frequently (alternate days) and infected pods were removed when showing the earliest symptoms. However, this procedure may not be economic, except when potential yields are relatively small (fewer than twelve pods per tree).
Satisfactory control of black-pod was obtained with copper fungicides, applied with either hand-sprayers or a power-sprayer. The monetary return depends on yield level, rather than on disease incidence or on spraying costs. It is recommended that spraying should be practised when the potential yield is twelve or more pods per tree.     

Maximum Fruit Growth Potential Following Resource Limitation During Peach Growth

To achieve its maximum organ growth potential, an organ mustgrow at its potential relative growth rate (RGR) throughoutdevelopment. When resource availability limits growth, the RGRis reduced below the potential RGR. This study examines whether,following a period of resource-limited growth, the RGR is ableto increase to the potential RGR when sufficient resources areavailable. Fruit RGRs of a late maturing peach cultivar wereexamined following removal of most of the fruits (heavy thinning)from previously unthinned trees in Apr., May, and Jun. The fruitRGRs after imposition of the thinning treatments were higherthan those on unthinned trees during source-limited periodsof the growing season, suggesting that fruit RGR can increasein response to increased resource availability. In general,the RGRs of fruits of trees thinned in Apr., May, and Jun. didnot exceed those of fruits on trees thinned at bloom, suggestingthat heavy thinning at bloom provides a reasonable estimateof the potential RGR. There were times, however, when the effectsof competition with vegetative sinks were apparent, suggestingthat the RGR of fruits on trees that were heavily thinned atbloom may underestimate the potential RGR during these times.The absolute growth rates of fruits on thinned trees were greaterthan those on unthinned trees, but generally were not greaterthan those on trees that were thinned at bloom, suggesting thatpeach fruits are unable to recover potential growth lost duringresource-limited growth periods.Copyright 1995, 1999 AcademicPress Prunus persica (L.) Batsch, peach, maximum fruit growth potential, relative growth rate, absolute growth rate, thinning, fruit-fruit competition, resource availability, resource limitation, growth analysis     

Factors influencing choice of balsam fir twigs from thinned and unthinned stands by moose

Summary Moose were observed to browse preferentially on balsam fir (Abies balsamea) trees in stands where the stem density had been mechanically reduced to about 2000 stems/ha from over 30,000 stems/ha. Twigs from trees in thinned and unthinned stands were analyzed to test the hypotheses that moose were choosing thinned stands to maximize intake of a nutrient, or avoiding plant secondary compounds deliterious to digestion. Analyses included: twig length, weight, diameter, acid detergent fiber, neutral detergent fiber, dry matter digestibility, macroelements, crude fat (resins), crude protein, ash, and volatile secondary metabolites. Significantly higher concentrations of crude protein, P, Ca, Na, and crude fats occurred in trees from thinned compared to unthinned stands. Twigs from thinned stands were more digestible, longer, heavier, and had a greater diameter than those from unthinned stands. Several secondary metabolites were found in highest concentration in thinned stands. We suggest that moose chose thinned stands over unthinned stands for feeding because of high protein levels and large twigs. Trees in unthinned stands had protein levels below reported maintenance levels required by moose. Secondary metabolite concentrations were opposite to the direction predicted and the data do not support plant defence hypotheses for the chemicals analyzed.     

Invasive on invasive – On the feeding ecology of the Ring-necked Parakeet,Psittacula krameri,in Oman (Aves: Psittacidae)

The Ring-necked Parakeet, Psittacula krameri, an invasive bird species in Oman was found to be feeding on the immature green pods of another invasive tree species, Prosopis juliflora, commonly known as Mesquite. This parakeet strips the pods and consumes the soft seeds within. The green pods collected from the base of trees were a mixture of stripped pods showing various levels of feeding damage and un-stripped pods without any damage. The percentage of stripped pods was significantly higher than that of un-stripped pods. The mean percentage number of pods in the five levels of feeding damage (10, 25, 50, 75 and 100%) significantly differed from each other. The un-stripped and undamaged pods indicate wasteful feeding activity. The comparison of the five levels of feeding damage (10, 25, 50, 75 and 100%) and the undamaged condition (0%) to the mean number of pods as percentages suggests that wasteful feeding is not a random event; the reasons for this relationship are discussed.     

长白落叶松（Larix olgensis）工业人工林的模拟间伐

应用马尔柯夫过程理论,在获得林分直径转移概率的基础上,采用间伐最小径阶林木,最大径阶林木,中间径阶林木三种间伐方式,在保留不同密度情况下对长白落叶松工业人工林进行模拟间伐,提出了适宜的保留密度和相应的抚育间伐对象。结果表明：马尔柯夫过程确能反映长白落叶松工业人工林的直径转移过程,利用马尔可夫过程理论对长白落叶松工业人工林进行模拟间伐实现了依据培育时间来确定间伐方法和措施,提高了长白落叶松工业人工林经营管理的精准性;长白落叶松工业人工林成林后的间伐无论从培育森林方面,还是从取得木材、加大林分收益方面考虑,都应该以间伐小径阶的林木为主,注重培育I、II级木,间伐III, IV级木;20～25 a长白落叶松工业人工林间伐后的保留经营密度以0.7为宜。     

Effects of a Hurricane Disturbance on Aboveground Forest Structure, Arbuscular Mycorrhizae and Belowground Carbon in a Restored Tropical Forest

To better understand how management and restoration practices influence the response of terrestrial ecosystems to large-scale disturbances, it is critical to study above- and belowground effects. In this study, we examined the immediate effect of a major hurricane on aboveground forest structure, arbuscular mycorrhizae (AM) and belowground carbon pools in experimentally thinned plots in a tropical forest. The hurricane occurred five years after a thinning treatment, when thinned plots had similar aboveground carbon stocks but different forest structure compared to control plots. Thinned plots had more large diameter (>10 cm) trees compared to the control plots, which were characterized by a higher density of small diameter (<10 cm) trees. Despite pre-hurricane differences in forest structure, there were no significant differences between treatments in changes of canopy openness or number of affected trees following the hurricane. Thinned plots had larger belowground carbon pools than the controls plots before the hurricane, and these differences remained after the hurricane despite rapid decomposition of organic matter rich in nitrogen. There were no pre-hurricane differences in AM fungal spores or total AM root colonization. The hurricane reduced AM sporulation by nearly 50% in both treatments, yet we observed a significant increase in AM root colonization after the hurricane with greater AM colonization in the thinned plots. Hurricanes have well-known visible aboveground effects, but here we showed that less visible belowground effects are influenced by forest management and may play an important role in forest recovery.     

Vegetation changes in restored semi-natural meadows in the Turku Archipelago of SW Finland

In the Turku Archipelago of SW Finland the traditional animal husbandry dramatically decreased in 1950s after which the unused semi-natural pastures and meadows began to develop into less species rich shrub and tree communities. Restoration of some semi-natural meadows and pastures started in the late 1970s. Removing trees and shrubs, grazing, mowing, and pollarding deciduous trees were used as restoration of practises. Vegetation changes were followed from forty-one permanent sample plots established on restored areas. In this paper the data before restoration and 7–8 years after the first monitoring was analysed with parametric tests. The sample plots were divided into three restoration groups where the main restoration practises were: group 1. grazing, group 2. thinning (clearing plots from shrubs and removing some trees), group 3. thinning, mowing, and grazing (old wooded meadows). The results showed that: (1) The vegetation changed during analysed time. The number of species increased in all restored areas even though the changes were more pronounced in grazed areas and wooded meadows than in thinned areas. During restoration many common herb and grass species immigrated into the sample plots, but very few new indicator species of meadows were recorded. Most of the new species were found in few numbers in a sample plot which led to the significant increase in the number of sparse species (percentage cover < 1) in all restoration groups. The grasses benefited more from the restoration than herbs increasing their percentage cover significantly in grazed areas and in wooded meadows. In thinned areas the total percentage cover of the ten most dominant herb and grass species increased significantly. (2) The different restoration groups changed vegetation quite similarly. In grazed areas and in wooded meadows significant changes were slightly more numerous than in thinned areas. (3) The differences between the islands in vegetation changes were not pronounced. The added variance components among islands increased during restoration which probably indicated that the restoration practises as well as the species pool of the islands influenced the success of restoration.     

Soil and vegetation response to thinning White Cypress Pine (Callitris glaucophylla) on the North Western Slopes of New South Wales, Australia

Dense White Cypress Pine (Callitris glaucophylla J. Thompson and L.A.S. Johnson) regrowth occurs frequently across previously cleared landscapes in New South Wales (NSW), and is thought to adversely affect agricultural production and to cause land degradation. The NSW Native Vegetation Act (2003) requires that management of native vegetation including pre-1990 regrowth must ‘improve or maintain’ site condition, yet there is currently limited information regarding techniques for the optimum management of C. glaucophylla in this regard. We conducted a preliminary study to examine floristic composition, soil condition (to 50 cm) and carbon storage under ‘Dense’ (dense regrowth), ‘Thinned’ (dense regrowth thinned 2000/2001) and ‘Un-colonised’ (pasture not yet recolonised by C.␣glaucophylla) plots on private lands in NSW. Reduced tree density from thinning resulted in increased biomass of the remaining individual trees. Un-colonised plots had significantly more groundcover than thinned plots, which had significantly more groundcover than dense plots. Differences in plant diversity however, were explained by site factors rather than land use. Soils in the dense plots were the most acid but soil pH was significantly higher in thinned plots and pH was highest in soil of the un-colonised plots. Mean values for carbon, nitrogen, sulphur and extractable phosphorus varied among sites, although each were significantly more abundant in the mineral soil of dense and thinned plots compared with un-colonised plots, suggesting that thinning had had a minimal effect on the soil parameters assessed. Accounting for all site components, site carbon storage was significantly higher in dense and thinned plots compared with un-colonised plots due to elevated levels of soil and litter carbon as well as the presence of trees. The results indicate that thinning dense C. glaucophylla can maintain and (by some measures) improve site condition. However, given the variability in some of the parameters assessed, further study across a wider range of soil types and rainfall gradients is proposed.     

Seven-Year Results of Thinning and Burning Restoration Treatments on Old Ponderosa Pines at the Gus Pearson Natural Area

Abstract We examined the 7‐year effects of three restoration treatments on leaf physiology and insect‐resistance characteristics of pre‐settlement age ponderosa pines (Pinus ponderosa Dougl. ex Laws.) at the Gus Pearson Natural Area (GPNA) in northern Arizona. Restoration treatments were: (1) thinned in 1993 to approximate pre‐Euro‐American settlement stand structure, (2) thinned plus prescribed burned in 1994 and 1998, and (3) untreated control. Tree physiological and insect‐resistance characteristics were measured in year 2000, 7 years after thinning, using the same procedures as an earlier study performed in 1996. Consistent with the 1996 results, pre‐dawn water potential in 2000 was consistently lower in the control than both thinned treatments. Both thinned treatments continued to have increased foliar nitrogen concentration in leaves 7 years after treatment. However lower leaf nitrogen concentration in the thinned and burned compared with the thinned treatment suggests lower nitrogen availability to trees in repeatedly burned plots. Analysis of leaf gas exchange characteristics and carbon isotope content (δ¹³C) suggests continued stimulation of photosynthesis by both thinning treatments. Differences among treatments in resin volume, a measure of bark beetle resistance, depended on season of measurement. Trees in both thinning treatments continued to have increased leaf toughness, a measure of resistance to insect folivores. Our results show that many beneficial effects of restoration treatments on carbon, water, and nitrogen relations and insect‐resistance characteristics of pre‐settlement ponderosa pines continue to be expressed 7 years after treatment at the GPNA.     

True bug (Heteroptera) impact on cocoa fruit mortality and productivity

The real impact of true bug damage on cocoa pods has never been assessed precisely. We conducted a 2-yr study on 1,080 cocoa trees on 36 farms in Cameroon to assess the contribution of true bugs to fruit mortality and production loss. The cocoa fruiting cycle, fruit mortality, and damage caused by true bugs as well as other pests and diseases were monitored on a weekly basis. True bug damage also was described on 2,500 ripe pods per year. Pod weight, bean number, and bean weight were measured and compared for different degrees and types of damage on the ripe pods. Our results showed that true bugs were the main external cause of young fruit abortion. They reduced the abundance of young fruit by up to 10%. In contrast, although one-third of the ripe pods sampled had true bug lesions, only 4% were moderately to heavily damaged. The mean weight of ripe pods was reduced by 12% when there was medium to heavy damage. While the mean weight of wet beans was reduced significantly (by 3-10%), the number of beans per pod was not changed by damage. Despite the reduction in mean weight, the overall weight of beans for the pods sampled was reduced by <2%. Therefore, our study confirmed the common assumption that the economic impact of true bug damage on mature pods is negligible on cocoa farms in Cameroon. However, true bugs have a significant impact on young fruit mortality.     

Carbon isotope discrimination and growth response of old Pinus ponderosa trees to stand density reductions

Stand density reductions have been proposed as a method by which old‐growth ponderosa pine (Pinus ponderosa) forests of North America can be converted back to pre‐1900 conditions, thereby reducing the danger of catastrophic forest fires and insect attacks while increasing the productivity of the remaining old‐growth individuals. However, the duration of productivity response of individual trees and the physiological mechanisms underlying such a response remain speculative issues, particularly in old trees. Tree‐ring measurements of carbon isotope ratios (δ¹³C) and basal area increment (BAI) were used to assess the response of intrinsic water‐use efficiency (the ratio of photosynthesis, A to stomatal conductance, g) and growth of individual> 250‐year‐old‐ponderosa pine trees to stand density reductions. It was hypothesized that reductions in stand density would increase soil moisture availability, thus decreasing canopy A/g and increasing carbon isotope discrimination (Δ). Cellulose‐δ¹³C of annual tree rings, soil water availability (estimated from pre‐dawn leaf water potential), photosynthetic capacity, stem basal growth and xylem anatomy were measured in individual trees within three pairs of thinned and un‐thinned stands. The thinned stands were treated 7 to 15 years prior to measurement. The values of δ¹³C and BAI were assessed for 20 consecutive years overlapping the date of thinning in a single intensively studied stand, and was measured for 3 years on either side of the date of thinning for the two other stands to assess the generality of the response. After thinning, Δ increased by 0.89‰ (± 0.15‰). The trees in the un‐thinned stands showed no change in Δ (0.00‰ ± 0.04‰). In the intensively studied trees, significant differences were expressed in the first growing season after the thinning took place but it took 6 years before the full 0.89‰ difference was observed. BAI doubled or tripled after disturbance, depending on the stand, and the increased BAI lasted up to 15 years after thinning. In the intensively studied trees, the BAI response did not begin until 3 years after the Δ response, peaked 1 year after the Δ peak, and then BAI and Δ oscillated in unison. The lag between BAI and Δ was not due to slow changes in anatomical properties of the sapwood, because tracheid dimensions and sapwood‐specific conductivity remained unchanged after disturbance. The Δ response of thinned trees indicated that A/g decreased after thinning. Photosynthetic capacity, as indexed by foliar nitrogen ([N]) and by the relationship between photosynthesis and internal CO₂ (A–C_i curves), was unchanged by thinning, confirming our suspicion that the decline in A/g was due to a relatively greater increase in g in comparison with A. Model estimates agreed with this conclusion, predicting that g increased by nearly 25% after thinning relative to a 15% increase in A. Pre‐dawn leaf water potential averaged 0.11 MPa (± 0.03 MPa) less negative for the thinned compared with the un‐thinned trees in all stands, and was strongly correlated with Δ post‐thinning (R² = 0.91). There was a strong relationship between BAI and modelled A, suggesting that changes in water availability and g have a significant effect on carbon assimilation and growth of these old trees. These results confirm that stand density reductions result in increased growth of individual trees via increased stomatal conductance. Furthermore, they show that a physiological response to stand density reductions can last for up to 15 years in old ponderosa pines if stand leaf area is not fully re‐established.     

Understory responses to restoration in aspen‐conifer forests around the Lake Tahoe Basin: residual stand attributes predict recovery

The removal of conifers from aspen (Populus tremuloides) stands is being undertaken throughout the western United States to restore aspen for local‐ and landscape‐level biodiversity. Current practices include mechanically removing conifers or hand thinning, piling, and burning cut conifers in and adjacent to aspen‐conifer stands. To evaluate the effectiveness of restoration treatments, we examined tree regeneration and herbaceous vegetation cover in thinned, thinned and pile burned, and non‐thinned control stands. Growth rates of small conifer saplings threatening to outcompete and replace aspen were also measured. Two to four years after pile burning, herbaceous vegetation cover within the footprint of burned piles (i.e. burn scars) was 35–73% of that in adjacent areas. Aspen was more likely to regenerate inside burn scars where fewer surrounding trees were true firs. Conifer seedlings were more likely to regenerate in burn scars where more of the surrounding trees were conifers (pine or fir) as opposed to aspen. Fir saplings had much slower growth than did aspen saplings. Overall, our findings show that restoration treatments are promoting desirable outcomes such as enhancing aspen regeneration but that follow‐up treatments will be needed to remove numerous conifer seedlings becoming established after restoration activities. Eliminating conifers, while they are small, growing slowly, and contributing little to fuel loads may be an economical way to prolong restoration treatment effectiveness.     

<Emphasis Type="Italic">Acacia karroo</Emphasis> responses to early dormant season defoliation and debarking by goats in a semi-arid subtropical savanna

Research was conducted to investigate responses of Acacia karroo to severe defoliation, with or without debarking, in a semi-arid, subtropical savanna. A herd of 250 goats reduced available foliage by 87% in a 10.5-ha area of Acacia woodland over 3 weeks during the early dormant season (May). The goats debarked 37% of the trees. On average, bark was stripped less than halfway round a stem and 11% of the bark area was affected. Trees 1.6–2.5 m tall and 11–30 cm in basal circumference were most susceptible to debarking. A year later, there were no detectable effects of defoliation on the number of browseable shoots, internode length, shoot length, spine length, number of seed pods, neutral detergent fibre (NDF) or nitrogen (N). Defoliation tended to increase condensed tannin concentration (CT), but the effect was not significant (p > 0.05). The absence of goats during the growth season following defoliation allowed the trees to recover. Debarking had greater impacts on the trees than defoliation had. Debarking reduced the number of browseable shoots, while ringing at the base reduced CT and increased N. Debarking tended to reduce shoot and spine length, and halve the number of pods, but the effects were not significant (p > 0.05). Responses of basally ringed trees indicated rapid vertical growth when the trees were highly vulnerable to browsers and fires, suggesting strong selection for herbivore/fire tolerance. Among all treatments, excluding basal ringing, there were significant variations in NDF and CT between years. There was a positive relationship between N and NDF, and a negative relationship between N and CT, in 1 year, but not in the other. Among basally ringed trees, CT was negatively related to N, but NDF was not. The strong trade-off between N and CT in basally ringed trees probably indicates that large changes in root:shoot ratio are required to effect definite changes in defence.     

Effect of Fruiting Traits on the Field Resistance of Cocoa (Theobroma cacao L.) Clones to Phytophthora megakarya

The effects of some traits of field resistance (precocity and duration of the fruiting cycle, age of diseased fruit and vertical pod distribution on the tree) to Phytophthora megakarya of four known cocoa clones were studied in an on‐station clonal plot planted in 1982 in the south‐west of Cameroon. Weekly observations of fruit set and development, black pod and rainfall were carried out during three growing seasons (1999, 2000 and 2001). The study confirmed the previous field and laboratory assessments of resistance of these clones based on the mean percentages of rotten pods obtained annually. The present study has permitted the identification of fruit aged 2–3 months as the highly susceptible stage of development in the most susceptible clone. In addition, precocity and pod cycle duration varied significantly among the clones. The earlier the pod cycle began, the more susceptible was the clone: the most resistant clone started flowering 1 month after the most susceptible clone and therefore escaped the peak of disease severity. Rainfall intensity greatly modified the incidence of the disease in 2001, with high yield losses occurring in all four clones (70–93%), but their ranking remained stable over the 3 years. The spatial distribution of pods on the trees showed that pods on the trunk were more likely to become diseased than those on the branches, but its effect as a clone resistance component is variable among the four clones; the resistant clone producing more pods on the trunk and the susceptible clone more in the canopy.     

Maximum Fruit Growth Potential and Seasonal Patterns of Resource Dynamics During Peach Growth

Maximum fruit growth potential, the growth attained by fruitswhen they are grown under optimal environmental conditions inthe presence of a non-limiting supply of resources, was estimatedfor two peach [Prunus persica (L.) Batsch] cultivars that differin the timing of resource demand for reproductive growth. Maximumpotential fruit growth was estimated on trees that were heavilythinned at bloom. On these trees, resource availability exceededresource demand for fruit growth. For both cultivars, the mean dry weights of fruits grown onunthinned trees were approximately half the mean dry weightsof fruits grown on trees that were heavily thinned at bloom,indicating that fruit growth was source-limited on unthinnedtrees. Comparison of the seasonal patterns of relative growthrate of fruits on unthinned and heavily thinned trees indicatedthe source-limited fruit growth occurred during distinct periodsof the growing season. On the early maturing cultivar, source-limitedfruit growth occurred from 300 degree-days after bloom untilharvest (4·5-10 weeks after bloom). On the late maturingcultivar, source-limited fruit growth occurred from 200-900and 1600-1900 degree-days (3·5-12 and 18-20 weeks) afterbloom. Although the final dry weight of fruits on the early maturingcultivar was only half that of fruits on the late maturing cultivar,the potential net sink strength of fruits was significantlyhigher on the early than the late maturing cultivar throughoutthe entire growth period of the early maturing cultivar. Resourceavailability for fruit growth was similar on the early and latematuring cultivars, indicating that selection for early maturingfruits has not changed the patterns of resource availabilityfor fruit growth.Copyright 1995, 1999 Academic Press Maximum fruit growth potential, carbon economy, partitioning, resource availability, resource limitation, source-limited growth, sink activity, sink strength, growth analysis, relative growth rate, Prunus persica (L.) Batsch, peach     

Secondary succession in two subtropical forests

We studied secondary succession in two subtropical evergreen broad-leaved forests near Shanghai, China that had been harvested 2–60 years earlier. Shrubs were thinned in one of the forests to about 60% of their original density for the first 20 years after harvesting. The other was not disturbed after harvesting. Five stands were sampled in each forest. Species composition and richness varied little during succession. Biomass, soil organic matter, total soil nitrogen, and soil water all increased with time. Soil organic matter and total nitrogen were significantly less in thinned forest than in undisturbed forests, but soil moisture did not vary with shrub thinning. Total tree density did not change over time, suggesting that species replacements were not driven by self-thinning. The eventual replacement of shrubs by trees occurred because shrub density decreased whereas tree density remained constant and tree mass increased.     

Thinning improves growth and resilience after severe droughts in Quercus subpyrenaica coppice forests in the Spanish Pre-Pyrenees

During the past years, growth and productivity of different oak species have been constrained by water shortage in seasonally dry regions such as the Mediterranean Basin. Thinning could improve oak radial growth in these drought-prone regions through the reduction of tree competition for soil water in summer. However, we still lack adequate, long-term assessments on how lasting are thinning treatments effects and to what extent they contribute to oak growth recovery after drought. Here we aim: (i) to study the radial growth sensitivity to drought of Quercus subpyrenaica in the Spanish Pre-Pyrenees, and (ii) to verify if thinning represents a suitable option to enhance growth resistance to drought and post-drought growth recovery. We analysed basal area increment (BAI) trends in the period 1960–2020 of formerly coppiced oak stands thinned in 1984 and compared them with unthinned plots and also with coexisting Scots pine (Pinus sylvestris) growing in thinned plots. We used the Standardized Precipitation Evapotranspiration Index (SPEI) to estimate the severity of droughts and we also assessed climate-growth relationships. Oaks in thinned plots showed higher BAI (369 mm²) than those in unthinned plots (221 mm²). Growth rates remained higher in thinned than in unthinned plots also under severe drought stress. A severe summer drought in 1986 caused abrupt BAI reductions in both oaks (- 40.5%) and pines (- 40.1%). The positive effect of thinning on growth lasted for over 20 years and slightly declined as canopies closed. In the thinned plots, trees with smaller diameter showed the greatest growth release. Oaks in unthinned plots and Scots pine were more sensitive to short-term droughts in terms of growth reduction than oaks in thinned plots, while long term droughts have similar effects on oaks from both thinned and unthinned plots. Oaks were resilient to drought, showing recovery periods lasting from 1 to 2 years in both thinned and unthinned plots. However, intense and prolonged droughts could strongly reverse the expected growth enhancement of thinned plots, and a greater frequency of droughts would limit coppice growth and productivity thus lengthening the rotation periods.     

Unthinned slow-growing ponderosa pine (Pinus ponderosa) trees contain muted isotopic signals in tree rings as compared to thinned trees

Key message

The muted wood isotopic signal in slow-growing trees of unthinned stands indicates lower responsiveness to changing environmental conditions compared to fast-growing trees in thinned stands.

Abstract

To examine the physiological processes associated with higher growth rates after thinning, we analyzed the oxygen isotopic values in wood (δ¹⁸O_w) of 12 ponderosa pine (Pinus ponderosa) trees from control, moderately, and heavily thinned stands and compared them with wood-based estimates of carbon isotope discrimination (?¹³C), basal area increment (BAI), and gas exchange. We found that (heavy) thinning led to shifts and increased inter-annual variability of both stable carbon and oxygen isotope ratios relative to the control throughout the first post-thinning decade. Results of a sensitivity analysis suggested that both an increase in stomatal conductance (g _s) and differences in source water among treatments are equally probable causes of the δ¹⁸O_w shift in heavily thinned stands. We modeled inter-annual changes in δ¹⁸O_w of trees from all treatments using environmental and physiological data and found that the significant increase in δ¹⁸O_w inter-annual variance was related to greater δ¹⁸O_w responsiveness to changing environmental conditions for trees in thinned stands when compared to control stands. Based on model results, the more muted climatic response of wood isotopes in slow-growing control trees is likely to be the consequence of reduced carbon sink strength causing a higher degree of mixing of previously stored and fresh assimilates when compared to faster-growing trees in thinned stands. Alternatively, the muted response of δ¹⁸O_w to climatic variation of trees in the control stand may result from little variation in the control stand in physiological processes (photosynthesis, transpiration) that are known to affect δ¹⁸O_w.     

Economic potential of the huizache,Acacia Pennatula (Mimosoideae) in central veracruz, Mexico

Acacia pennatula is a native tree found commonly on cattle pastures and other disturbed sites in the mid-elevation zone of Veracruz, Mexico. The pods are a favorite food source for free ranging cattle. Pod collection and production has been commercialized at a small scale. The results of this study strongly suggest that the management of acacia trees for pod production has the potential for providing an environmentally sound, locally derived food source for cattle while maintaining tree cover on pasture lands. Soil type has a strong influence on stand structure and pod production; the largest pod crops with the largest and most nutritious pods are found on Andosols and Acrisols, as opposed to the unproductive Regosols. We suggest that the current system could be expanded by promotion and marketing of the pods and improved management of the acacia stands.     

Patterns of fruit and seed production inBauhinia ungulata (Leguminosae)

Patterns of seed and fruit production ofBauhinia ungulata, a small tree legume indigenous in tropical America, were studied in Costa Rica. Only about 8% of flowers produced fruits. The average pod had 19 ovules and about two thirds of these began seed development, with mature pods containing an average of 9.7 mature undamaged seeds. About half of the mature pods were damaged by herbivores and within these, 27% of ovules or seeds had been eaten. Among trees there was no significant variation in pod production, but the number of ovules per pod and seed production per pod varied significantly. Within infructescences most pods were retained at middle positions. Within pods, the probability of an ovule developing into a seed increased toward the distal end. The pattern of seed and fruit production in this species agrees well in general with that reported for other neotropical legumes. The abortion of seeds and fruits can be regarded as a way of controlling maternal investment, and as a response to herbivory.