Untapped Trees Research Articles

DOES RESIN TAPPING AFFECT THE TAPERING AND ACCUMULATION OF MERCHANTABLE TIMBER VOLUME IN PINE TREES?

Form factors and taper functions are used for the quantitative and qualitative description of tree stem shape. In southeastern Mexico, there are plantations of Pinus caribaea var. hondurensis (Sénécl.) W.H. Barrett & Golfari, Pinus elliottii var. elliottii Engelm., and hybrids between these species to simultaneously produce resin and wood. Farmers need to know whether the practice of resin tapping to death has a negative impact on tree shape and volume of the wood produced. To answer these questions, this study compared the shape, taper, and volume of resin-tapped and untapped trees from three P. caribaea origins. A total of 198 trees (99 resin-tapped and 99 untapped) were measured in all diameter categories of the plantation. Total volume models, along with a compatible taper system and variable merchantable timber volume, were fitted using linear and nonlinear regression analyses. To compensate for the lack of initial tree size data prior to tapping, indicator variables (dummies) and an additive structure were used to parameterize volume and taper models. Untapped trees accumulated greater volume than tapped trees. In contrast, the form factor (ff) of resin-tapped trees (ff = 0.51) was greater than that of untapped trees (ff = 0.45). The form factor increased due to tapping between 4 and 7 % depending on the origin, although the hybrid P. caribaea × P. elliottii presented the most desirable stem geometry in tapped and untapped trees. Based on the Demaerschalk model, the variability is estimated at 99 and 97 % of the merchantable and taper volumes, respectively.

CORRELATION BETWEEN CO2 ASSIMILATION RATES AND OTHER GAS EXCHANGE PARAMETERS OF Hevea WITH REFERENCE TO COMMENCEMENT OF TAPPING

The present study was supplement to a longer experiment to determine the feasibility of early commencement of tapping of two Hevea genotypes i.e. RRIC121 and RRISL 211. The main objective of this study was to develop a correlations between CO2 assimilation rates and other leaf gas exchange parameters of Hevea with reference to the commencement of tapping. Tapped and untapped trees of two Hevea genotypes, i.e. RRIC121 and RRISL 211 at the same age were selected for the study. All cultural practices were performed according to the Rubber Research Institute of Sri Lanka. To evaluate the significance of differences between all possible pairs of treatment means, mean separation of treatments was performed with Duncan’s Multiple Range Test (DMRT). The strength of the relationships between yield and photosynthetic gas exchange parameters was estimated by linear correlation analysis. The leaf gas exchange parameters were measured under optimal environmental conditions clearly showed the intercellular CO2 concentration (Ci) gradually decrease with increasing light intensity in both clones. The same trend was observed in the different canopy layers under both tapping treatments. The highest leaf-air vapour pressure deficit (lvpd) was shown in the leaves of the upper canopy and lowest in the bottom canopy layer. Furthermore, the water use efficiency (WUE) of clone RRISL 211 was higher than that of clone RRIC 121 under tapping. This was primarily because of the greater photosynthetic rates of RRISL 211, rather than lower transpiration rates.When considering the correlation analysis of gas exchange parameters of Hevea, CO2 assimilation rate (A) had highly significant correlations with gs, Tr and intensity of PAR. However, the absence of a correlation between PAR and WUE showed that, when PAR increases both A and Tr increase in similar magnitudes. Therefore, WUE remains approximately constant. The presence or absence of correlations in gas exchange parameters of tapped and untapped treatments were broadly similar to the overall correlation analysis. In the tapped treatments, because of tapping, the photosynthetic rate is stimulated relative to the transpiration rate. The positive latex yield response to WUE and lvpd of top leaves indicates that, in top leaves when lvpd increases transpiration also increases accordingly. Hence WUE and ivpd increase latex flow within the tree and finally increase the latex yield with increasing latex volume. On the other hand, latex yield has a negative correlation with gs. The study findings clearly revealed that, in top leaves reduced Ci increases the CO2 gradient and uptake of CO2 for more photosynthesis, which increases the latex yield. Faster utilization of absorbed Ci may enhance the yield potential.

Short-term resin tapping activities had a minor influence on physiological responses recorded in the tree-ring isotopes of Chinese pine (Pinus tabuliformis)

Resin tapping might affect tree-ring growth, but details on the physiological responses of trees to resin tapping are still lacking, particularly for long-term responses. This study aimed to explore the physiological processes underlying resin-tapping of Chinese pine (Pinus tabuliformis) by using tree-ring stable isotopes. We compared tree-ring earlywood and latewood stable carbon (δ13C) and oxygen (δ18O) isotopes in the pre-resin tapping and post-resin tapping period for tapped trees and compared their values between tapped and untapped trees and their responses to climate variables in a forest stand from 1984 to 2017. Furthermore, we used a dual isotope model to distinguish between the effects of the photosynthetic assimilation rate and stomatal conductance. Results indicated that tapped and untapped trees showed similar inter-annual variation for two isotopes, while the absolute values of tapped trees were slightly (P > 0.05) lower than tapped trees in the two years following resin tapping. Climate response analysis indicated that resin tapping had no significant effect on climatic sensitivity for either stable isotope. Earlywood stable isotopes were mainly influenced by temperature, relative humidity, and Palmer Drought Severity Index (PDSI) from May to July, while latewood isotopes were mainly influence by relative humidity form July to August and PDSI from July to September. The conceptual model results indicated that resin tapping lead to a slight, but not significant, decrease in the intrinsic water-use efficiency caused by increased stomatal conductance for the first two to three years following resin tapping. We conclude that tree-ring physiological responses could be less affected by short-term resin tapping activities.

A predominant isoform of fructokinase, HbFRK2, is involved in Hevea brasiliensis (para rubber tree) latex yield and regeneration

Fructokinase (FRK) mediates fructose phosphorylation to regulate the carbon flow and its assignment to sink tissues. Out of five HbFRKs in the genome of the rubber tree, three (HbFRK1-3) that were highly expressed in latex (cytoplasm of laticifers) were isolated and examined. According to phylogenetic analysis and intracellular location experiment, both HbFRK2 and HbFRK3 were highly possible to be expressed in cytosol, while HbFRK1 was in plastid. As the predominant isoform in laticifers, HbFRK2 had the highest transcripts, followed by HbFRK3 and HbFRK1. In enzymatic function, HbFRK2 also showed the highest affinity for fructose. To examine the roles of FRKs in latex yield and regeneration, changes in HbFRKs were examined when latex outflow from the trees were increased through two experimental interventions. In the first approach, tapping was initiated on previously untapped trees, resulting in latex yield increasing with consecutive tapping at the initial stage before it stabilized. In the second approach, latex yield from trees that were already in regular tapping was stimulated by treatment with the ethylene-based yield stimulant, ethephon. Using either method to induce an increase in latex yield, the abundance of HbFRK2 and HbFRK3 in transcripts, was increased. This development, which was especially marked in HbFRK2, may reflect a strengthening of glycolysis to meet the carbon flux and energy demands for increased rubber biosynthesis to replace rubber lost in the increased latex yield. Our results, therefore, suggest that HbFRK2 plays a critical role in fructose catabolism to facilitate rubber regeneration in the commercially exploited rubber tree.

Does resin tapping affect the tree-ring growth and climate sensitivity of the Chinese pine (Pinus tabuliformis) in the Loess Plateau, China?

Resin tapping could affect water and nutrient transport processes in Chinese pine trees, rendering them more vulnerable to extreme climatic events, such as drought, and affecting the ecological function of forests in semi-arid regions. This study evaluated how resin tapping affects the tree-ring growth and climate sensitivity of Chinese pine in the Loess Plateau. We compared tree-ring growth patterns between the tapped and untapped faces of tapped trees, and investigated tree-ring growth and its response to climate between tapped and untapped trees in a forest stand during the 1967–2017 period. Tapped trees showed asymmetrical growth patterns after resin tapping, with narrower rings near the tapped face and wider ones near the untapped face. Furthermore, tapped trees had inter-annual variations consistent with those of untapped trees except for the years 2000 and 2001, with significantly lower values following resin tapping, and tree-ring growth then returning to normal. The climate response analysis indicated that the tree-ring growth of both tapped and untapped trees was negatively affected by monthly mean temperatures during the early growing season (May to July) in the post-resin-tapping period. Furthermore, tree-ring growth in tapped trees also revealed significant correlation with water vapour deficit and the Palmer drought index, which indicates that tapped trees are more vulnerable to drought. Further studies based on stable isotopes (i.e. δ13C, δ18O, and δ15N) could improve our understanding of the physiological mechanisms that regulate the effects of resin tapping on tree-ring growth.

Effect of tapping for syrup production on sugar maple tree growth in the Quebec Appalachians

Some studies suggest that tapping sugar maple (Acer saccharum Marshall) trees can cause their growth to decline, particularly on poor and acidic soils. We tested this hypothesis in seven sugar bushes located in the Quebec Appalachians by comparing the growth of tapped trees with nearby untapped trees. The sites represented a range of soil fertility, from very good for sugar maple to strongly deficient in calcium. Trees were cored, and individual dendrochronology series were used to analyze trends in basal area growth, from a period of 10 years before, to 8–10 years after tapping began. Basal area growth of sugar maples did not appear to be influenced by tapping (p ≥ 0.134), except at one site (p < 0.001), where the growth of tapped trees decreased by 33% over 10 years. This decline could not be explained only by the poor soil fertility observed at the site. Although a tree biomass distribution budget indicated that maple syrup production represented only 4–6% of the carbon allocated annually to net primary production, the long-term relationship between maple syrup production and tree growth requires further study.

Preliminary Results of Sugar Maple Carbohydrate and Growth Response under Vacuum and Gravity Sap Extraction

Recent technological advancements have increased the amount of sugar-enriched sap that can be extracted from sugar maple (Acer saccharum). This pilot study quantified overall sugar removal and the impacts of vacuum (60 cm Hg) and gravity sap extraction on residual nonstructural carbohydrate (NSC) concentrations and on stem and twig growth. Vacuum sap extraction (VSE) resulted in significantly greater mean sugar removal (1.19 ± 0.46 kg [SE]) than gravity sap extraction (GSE) (0.48 ± 0.14 kg). Residual stem NSC displayed a pattern of increased concentration with increased extraction. Twig residual NSC concentrations were highly variable, perhaps because of the highly dynamic late spring period, and no clear patterns were observed. Mean radial stem growth in the year after sap extraction was greater in untapped trees (2.93 ± 0.58 mm) than with VSE (1.99 ± 0.44 mm) or GSE (1.67 ± 0.12 mm). The results raise the possibility that sap removal shifts sugar maple NSC source-sink relationships toward storage at the expense of growth.

Carbon isotope composition of latex does not reflect temporal variations of photosynthetic carbon isotope discrimination in rubber trees (Hevea brasiliensis).

Latex, the cytoplasm of laticiferous cells localized in the inner bark of rubber trees (Hevea brasiliensis Müll. Arg.), is collected by tapping the bark. Following tapping, latex flows out of the trunk and is regenerated, whereas in untapped trees, there is no natural exudation. It is still unknown whether the carbohydrates used for latex regeneration in tapped trees is coming from recent photosynthates or from stored carbohydrates, and in the former case, it is expected that latex carbon isotope composition of tapped trees will vary seasonally, whereas latex isotope composition of untapped trees will be more stable. Temporal variations of carbon isotope composition of trunk latex (δ(13)C-L), leaf soluble compounds (δ(13)C-S) and bulk leaf material (δ(13)C-B) collected from tapped and untapped 20-year-old trees were compared. A marked difference in δ(13)C-L was observed between tapped and untapped trees whatever the season. Trunk latex from tapped trees was more depleted (1.6‰ on average) with more variable δ(13)C values than those of untapped trees. δ(13)C-L was higher and more stable across seasons than δ(13)C-S and δ(13)C-B, with a maximum seasonal difference of 0.7‰ for tapped trees and 0.3‰ for untapped trees. δ(13)C-B was lower in tapped than in untapped trees, increasing from August (middle of the rainy season) to April (end of the dry season). Differences in δ(13)C-L and δ(13)C-B between tapped and untapped trees indicated that tapping affects the metabolism of both laticiferous cells and leaves. The lack of correlation between δ(13)C-L and δ(13)C-S suggests that recent photosynthates are mixed in the large pool of stored carbohydrates that are involved in latex regeneration after tapping.

First report of Lasiodiplodia theobromae causing canker on tapped Boswellia papyrifera trees in Ethiopia

Boswellia papyrifera (Burseraceae) is found mainly in the Amhara, Tigray and Benshangul Gumze Regions of Ethiopia (Vollesen, 1989). This economically important tree species is widely used for frankincense (incense) production. Incense is…

Molecular characterization and expression analysis of the small GTPase ROP members expressed in laticifers of the rubber tree (Hevea brasiliensis)

ROP (Rho of plants) proteins are plant-specific Rho-type small GTPases which play important roles in cellular processes and stress responses. This study explores the characteristics and possible functions of ROPs that are expressed primarily in laticifers of the rubber tree (Hevea brasiliensis). The work serves as a preliminary step to determining their involvement in latex flow and regeneration, laticifers formation and tapping panel dryness (TPD, a physiological disorder in rubber trees that result in the stoppage of latex flow). In this connection, we (i) identified five HbROPs (HbROP1–HbROP5) by searching latex transcripts database and the genome databases, (ii) characterized molecular and phylogenic aspects of the HbROPs and examined the cis-regulatory elements in their promoter regions; (iii) analyzed by Real-time Quantitative PCR (QPCR) the tissue specificity of the HbROPs and their expression patterns in response to tapping, bark wounding and growth regulator treatments. All five HbROP genes were strongly expressed in the latex, with HbROP1, 3, 4 and 5 showing the highest expression among the six Hevea tissues examined, viz. latex, bud, mature leaf, bark, male flower and seed. When tapping was initiated on previously untapped trees, HbROP3 transcription was substantially down-regulated whereas HbROP5 expression was markedly up-regulated. Transcripts of HbROP3 rose gradually with the development of TPD. Except for the cytokinin 6-benzyl aminopurine that induced a rise in HbROP5 transcripts by more than 2-fold, the other growth regulators tested had little effect on HbROPs expression. The roles of HbROPs in rubber tree are discussed in relation to the diverse functions of ROP homologs reported in other plant species.

Starch Synthesis and Mobilization in Wood and Bark of Rubber Tree, in Relation with Latex Production, (1) Methodological Approach

In rubber tree, starch reserves are necessary for growth and latex regeneration when the demand exceeds supply from photosynthesis. It tends to accumulate in the wood near the tapping cut [1,2] whereas sucrose remains rather stable in the wood and decreases in the latex vessels where it is used to regenerate the exported latex [3].Thus higher starch ability could sustain higher latex yield. However the enzymatic processes driving the dynamics of starch synthesis and hydrolysis as related to tapping are not known. The objective of the study is to analyze the effects of tapping on the enzymes involved in starch and sucrose metabolism in the wood of rubber trees. The first approach of this study was to set up the most adapted methodology on measurement of total nonstructural carbohydrates (NSC) and related enzymes activities. The experiment was conducted in Heveabrasiliensis (rubber tree), clone RRIM600. Treatments include untapped trees (Control) and yielding trees tapped with Ethephon stimulation (ET). Each treatment includes 6 trees. Samples have been collected along the trunk and separated into 2 parts, wood and bark, from both side of the tree tapped and untapped panel. The activity of acid invertase (AI), amylase (AMY), sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) were assessed in the part of soft bark with amethod of sample preparation recoveringmore protein and concentrated enzyme with acetone precipitation. The method has increased enzyme activities of SuSy and SPS. On another hand, starch, sucrose, fructose and glucose concentrations have been enzymatically measured.The results showed that starch was the major component in wood and sucrose was mostly found in bark. There was no difference between the former drainage area and resting area after 2 untapped years before restarting tapping.

Canopy Photosynthetic Capacity and Light Response Parameters of Rubber Hevea brasiliensis with Reference to Exploitation

The main objective of this study wasto investigate the relationship between canopy photosynthetic capacityand light response parametersof tapped and untapped trees of twoHeveabrasiliensis genotypes, i.e. RRISL 211 and RRIC 121. Moreover, attempts have been made to develop correlations between canopy photosynthesis and light response parameters Heveawith reference to exploitation. The canopy photosynthetic rates measured under optimal environmental conditions clearly showed clonal differences in CO2 assimilation rates. The photosynthetic capacities of leaves from all strata of RRISL 211 were greater than the corresponding strata values in RRIC 121. A greater canopy photosynthetic rate was observed in clone RRISL 211 despite its leaf area index being 2% lower than in RRIC 121. This could be because of the greater photosynthetic capacity of RRISL 211, as indicated by the greater Amax values.In each clone, Amax of the tapped trees was greater than the Amax of untapped trees, and this difference was greater in RRISL 211 than RRIC 121. Another reason for the greater canopy photosynthesis of clone RRISL 211 was the presence of a higher percentage of leaf area in the top canopy layer as compared to clone RRIC 121. Even though, the light saturation point, LSP (i.e. the light intensity at which photosynthetic rate reaches maximum), did not differ significantly between different canopy layers within a clone for both clones, RRIC 121 had greater LSP for corresponding layers than RRISL 211. Moreover, it was evident that, due to the more open canopy architecture of clone RRIC 121, LSP of its middle canopy layer was very close to LSP of the upper canopy layer.In both clones QE of all canopy layers did not show a consistent variation between tapped and untapped treatments The Rd rates of corresponding canopy layers were always slightly greater in RRISL 211 than in RRIC 121. In both clones there was a gradual reduction in Rd rates when moving from upper through middle to bottom layers of the canopy. However, detailed analysis of Rd rates in the different canopy layers between tapped and untapped treatments showed clonal differences. Nevertheless, in both clones Rd of all canopy layers did not show a consistent variation pattern between tapped and untapped treatments. The overall results of both clones clearly showed that tapped trees have a greater photosynthetic capacity as compared to untapped trees because tapping exerts a stimulatory effect on photosynthesis. This trend was more evident in clone RRISL 211.

RESIN YIELD AND TIMBER QUALITY OF Pinus caribaea TREES TAPPED USING RILL METHOD

Experiments to study the oleo-resin yield in different diameter trees, tapping depths andtapping heights were under taken in the wet zone in the Kalutara District. Oleo-resin yieldwas measured in Pinus caribaea trees belonging to two diameter classes (10 em - 20 cmDBH, &gt;20 cm DBH classes), two tapping heights above ground (0.5 m and 1.3 m) andthree tapping depths (I mm, 2 mm and 5 mm).Results showed that oleo-resin yield was higher in larger diameter classes compared withlower diameter classes. Resin yield was also higher at 1.3m tapping height compared with0.5m height. Resin yield also increased as the tapping depth increased from I mm to 5mm. Based on these data it is recommended that the lowest tappable limit may be above20 ern DBH and it can expected to increase the yield of oleo-resin as well as health andvigour of the tree. It is suggested the height of tapping should be increased to yield moreoleo-resin. However the cost of tapping would increase when higher heights are to be used.A 5 mm depth starting from the live bark can be recommended as suitable depth in resintapping. This depth can increase the yield of oleo-resin while maintaining the health andvigour of the tree.Experiments to study the growth rate and timber quality of tapped and untapped P.caribaea trees were also done by measuring density and width of the rings. Log samplesfor this experiment were obtained from plantation at Guruthalawa in the Badulla district.At the time of sampling these trees had been tapped for 5 years.There were three tapped and three untapped trees which belonged to 3 diameter classes(20cm, 28cm, 36.5 ern). Each couple of tapped and untapped tree had the same diameter.For each tree, discs were extracted at 0.5 m height and 1.3 m height. The width of growthrings which is a measure of growth rate, were measured on untapped tree, tapped radiusand untapped radius in tapped tree. The data showed that wood production has not beenaffected considerably by resin tapping.The density which is an indicator for wood quality showed an increasing trend from pithoutwards. Density in the tapped trees was higher due to infiltration of oleo-resin into thewood after resin tapping. Except this variation, no other considerable difference wasobserved in density between tapped and untapped trees.

Determination of biotic aetiology of tapping panel dryness (TPD) syndrome of rubber tree (Hevea brasiliensis) by return-polyacrylamide gel electrophoresis (R-PAGE) technique

Tapping panel dryness (TPD) syndrome affecting rubber tree (Hevea brasiliensis) is known to reduce natural latex production. Its aetiology remains ambiguous despite long years of research. A low molecular weight RNA similar to viroid RNA was isolated from TPD-affected samples of rubber trees. In the present study, a modified return-polyacrylamide gel electrophoresis procedure was standardised. The viroid-like low molecular weight (LMW) RNA was found associated with leaf, bark and root tissues and rubber seedlings. The technique was employed to detect LMW RNA in different clones of rubber planted in different locations and in bud-grafted plants. The LMW RNA isolated from TPD-affected trees was found infectious on seedlings of tomato cv Pusa Ruby. The LMW RNA was reisolated from symptomatic tomato leaves but not from control plants. This is for the first time that a biotic agent, a viroid RNA, is found consistently associated with the syndrome. The technology developed can be useful to demonstrate the onset of TPD in untapped trees in the absence of other methods such as nucleic acid hybridisation.

Effects of resin tapping and tree size on the purity, germination and storage behavior of Boswellia papyrifera (Del.) Hochst. seeds from Metema District, northwestern Ethiopia

Boswellia papyrifera (Del.) Hochst. is one of the tree species in dry woodlands of Ethiopia that provides several goods and services. Despite its wide economic and ecological importance, its area coverage is dwindling from time to time, and its natural regeneration is hampered. Hence, long-term prospect for a sustained supply of the goods and services from the species is becoming questionable. The objectives of this study were to investigate: (i) the effect of resin tapping and tree size (DBH) on seed susceptibility to insect attack and the production of viable seeds; and (ii) seed longevity and germination ecology of the seeds of B. papyrifera. We collected seeds from tapped and untapped B. papyrifera stands at Lemlem Terara in Metema District, northwestern Ethiopia. The result showed that both tapped and untapped stands produced comparable insect attacked seeds (tapped stands=16.6%; untapped stands=15.8%). Untapped trees yielded significantly (P<0.0001) higher viable seeds (59%) than continuously tapped trees (49.3%), and trees with medium size (20cm DBH) provided more viable seeds than bigger (30cm DBH) and younger trees (10cm DBH). Longevity of B. papyrifera seeds indicated significant difference in viability under three different temperature regimes (5, 15 and 21°C), three storage periods (6, 9 and 12months) and two tapping regimes (tapped and untapped populations). Fire that produced temperatures above 100°C was lethal to the seeds as it caused complete loss of germinability regardless of exposure time. However, heat with temperatures less than 100°C did not cause loss of germinability even after an hour of exposure. We also found that light conditions had no significant impact on the germination percentage. In general, viability of the seeds was affected by tapping and tree size but not by storage conditions and period, modest temperature and light conditions.

THE WATER RELATIONS OF RUBBER (HEVEA BRASILIENSIS): A REVIEW

SUMMARYThe results of research done on water relations of rubber are collated and summarised in an attempt to link fundamental studies on crop physiology to crop management practices. Background information is given on the centres of origin (Amazon Basin) and production of rubber (humid tropics; south-east Asia), but the crop is now being grown in drier regions. The effects of water stress on the development processes of the crop are summarised, followed by reviews of its water relations, water requirements and water productivity. The majority of the recent research published in the international literature has been conducted in south-east Asia. The rubber tree has a single straight trunk, the growth of which is restricted by ‘tapping’ for latex. Increase in stem height is discontinuous, a period of elongation being followed by a ‘rest’ period during which emergence of leaves takes place. Leaves are produced in tiers separated by lengths of bare stem. Trees older than three to four years shed senescent leaves (a process known as ‘wintering’). ‘Wintering’ is induced by dry, or less wet, weather; trees may remain (nearly) leafless for up to four weeks. The more pronounced the dry season the shorter the period of defoliation. Re-foliation begins before the rains start. The supply of latex is dependent on the pressure potential in the latex vessels, whereas the rate of flow is negatively correlated with the saturation deficit of the air. Radial growth of the stem declines in tapped trees relative to untapped trees within two weeks of the start of tapping. Roots can extend in depth to more than 4 m and laterally more than 9 m from the trunk. The majority of roots are found within 0.3 m of the soil surface. Root elongation is depressed during leaf growth, while root branching is enhanced. Stomata are only found on the lower surface of the leaf, at densities from 280 to 700 mm−2. The xylem vessels of rubber trees under drought stress are vulnerable to cavitation, particularly in the leaf petiole. By closing, the stomata play an essential role in limiting cavitation. Clones differ in their susceptibility to cavitation, which occurs at xylem water potentials in the range of −1.8 to −2.0 MPa. Clone RRII 105 is capable of maintaining higher leaf water potentials than other clones because of stomatal closure, supporting its reputation for drought tolerance. Clones differ in their photosynthetic rates. Light inhibition of photosynthesis can occur, particularly in young plants, when shade can be beneficial. Girth measurements have been used to identify drought-tolerant clones. Very little research on the water requirements of rubber has been reported, and it is difficult to judge the validity of the assumptions made in some of the methodologies described. The actual evapotranspiration rates reported are generally lower than might be expected for a tree crop growing in the tropics (&lt;3 mm d−1). Virtually no research on the yield responses to water has been reported and, with the crop now being grown in drier regions, this is surprising. In these areas, irrigation can reduce the immaturity period from more than 10 years to six years. The important role that rubber plays in the livelihoods of smallholders, and in the integrated farming systems practised in south-east Asia, is summarized.

Effect of tapping tools and date of tapping on Acacia polyacantha gum yield in South Kordofan State, Sudan

A study was conducted in South Kordofan, Sudan to determine the effect of tapping, tapping tools and date of tapping on the gum yield of Acacia polyacantha. A two-factor experiment was conducted for two seasons in 2008–2009. One location was used for two seasons and two locations for one season. The first factor (4 levels) was the tools of tapping: Makmak, Farrar, and Sonki, and the control which was not tapped. The second factor (2 levels) was the date of tapping that comprises mid October and mid November. These treatments were arranged in Randomaized Complete Block Design and replicated three times. Gum yield (g/tree and g/ picking) was recorded for five pickings. Economic analysis was done using the partial budget technique. The results showed highly significant (p < 0.01) differences on gum yield (g/picking and g/tree). The results indicated that the process of tapping increases gum production by 88.4% and 79.8% compared with un-tapped trees, respectively. The date of tapping has no significant effect on gum yield (g/tree and g/picking) of A. polyacantha. Tapping of the tree with Makmak in mid-November was found to be economically beneficial compared to using the other tools and the control. These results could identify a new source of income for the poor farmers in South Kordofan mainly because of the wild occurrence of Kakamut as a potential gum producing tree species grown naturally in the area.

Carbohydrate reserves as a competing sink: evidence from tapping rubber trees

Carbohydrate reserve storage in trees is usually considered a passive function, essentially buffering temporary discrepancies between carbon availability and demand in the annual cycle. Recently, however, the concept has emerged that storage might be a process that competes with other active sinks for assimilate. We tested the validity of this concept in Hevea brasiliensis Müll. Arg. (rubber) trees, a species in which carbon availability can be manipulated by tapping, which induces latex regeneration, a high carbon-cost activity. The annual dynamics of carbohydrate reserves were followed during three situations of decreasing carbon availability: control (no tapping), tapped and tapped with Ethephon stimulation. In untapped control trees, starch and sucrose were the main carbohydrate compounds. Total nonstructural carbohydrates (TNC), particularly starch, were depleted following bud break and re-foliation, resulting in an acropetal gradient of decreasing starch concentration in the stem wood. During the vegetative season, TNC concentration increased. At the end of the vegetative season, there were almost no differences in TNC concentration along the trunk. In tapped trees, the vertical gradient of starch concentration was locally disturbed by the presence of the tapping cut. However, the main effect of tapping was a dramatic increase in TNC concentration, particularly starch, throughout the trunk and in the root. The difference in TNC concentration between tapped and untapped trees was highest when latex production was highest (October); the difference was noticeable even in areas of the trees that are unlikely to be directly involved in latex regeneration, and it was enhanced by Ethephon stimulation, which is known to increase latex metabolism and flow duration. Thus, contrary to what could be expected if reserves serve as a passive buffer, a decrease in carbohydrate availability resulted in a net increase in carbohydrate reserves at the trunk scale. Such behavior supports the view that trees tend to adjust the amount of carbohydrate reserves stored to the level of metabolic demand, at the possible expense of growth.

Effect of tapping activity on the dynamics of radial growth of Hevea brasiliensis trees

Rubber tree (Hevea brasiliensis Müll. Arg.) radial growth dynamics were monitored with displacement sensors, together with latex production, to investigate three aspects of the dual production of latex and wood: (1) the usefulness of fine-scale dendrometric measurements as a physiological tool to detect water shortage through radial growth; (2) the dynamic aspects, both at the seasonal and at the multi-year scale, of the competition between latex and wood production; and (3) the spatial distribution of radial growth rates around the tapping cut. Radial growth of untapped control trees started with the onset of the rainy season and lasted until the onset of the dry season, ceasing completely during the driest period. Displacement sensors provided a sensitive means of detecting water shortage, with a clear correlation between diameter variations and changes in water availability (both daily evapotranspiration and monthly rainfall) over the whole annual cycle. However, the correlation was significantly disturbed in tapped trees. After resumption of tapping, the radial growth rate dropped sharply within two weeks and the effect persisted throughout the whole season, so that the cumulative growth of tapped trees was about half that of untapped trees, with the cumulative growth deficit reaching 80% for the period from mid-June to November. This long-known negative impact of tapping on growth was much stronger in the second year of tapping than in the first, whereas latex production increased significantly between the first and second year of tapping. The increased latex production, which could not be ascribed to climatic conditions, shows that the establishment of an artificial latex sink is a progressive, long-term process likely involving many aspects of metabolism. As expected, ethylene significantly increased latex production in both years; however, ethylene had no effect on the growth rates of tapped trees. Radial growth was differentially affected at different locations around the tapping cut, with growth rates significantly lower in the tapped panel than in the untapped panel, and higher above the cut than below the cut. Thus, caution is needed when deriving whole stem wood production from girth measurements at one location on the stem, especially from girth measurements made close to the tapping cut. This also provides new evidence for the location of the latex regeneration area in the tapped panel, below the cut.

Traditional and chemical techniques for stimulation of shorea javanica (Dipterocarpaceae) resin exudation in Sumatra

Resin tappers in Sumatra induce resin flow in Shorea javanica by first opening vertical rows of small (3 cm) holes in the tree trunk. After 6–12 mo, larger (10–15 cm) holes are opened between the rows of small holes for resin harvest. Informants reported that opium applied to trees increased resin yields. Application of 10% 2-chloroethylphosphonic acid to artificial trunk wounds ofS. javanica production trees increased resin yields by 110% relative to controls in 72-h trials. Wounds of previously untapped trees exuded no resin in response to the same treatment.