Are neighboring trees in tune? Wood formation in Pinus pinaster

Neighboring trees growing under identical environmental conditions can exhibit different dynamics and periods of growth. Despite the recent advances in cambial biology, the exogenous and endogenous factors generating asynchronous xylem growths still remain undetermined. This study investigated timings and duration of xylem formation in maritime pine (Pinus pinaster Ait.) from an even-aged plantation in Portugal growing under Mediterranean climate. Cambial phenology and stem diameter were monitored weekly, from March to December 2010, on two classes of trees divided according to the tree ring widths of the last 15 years, but similar age and size: fast- and slow-growing trees. We tested the hypothesis that differences in tree ring widths result from cell production which in turn affects timings of xylogenesis and that the bimodal growth pattern, typical of the Mediterranean, originates from a double reactivation of the cambium: in spring and autumn. Cambial activity started earlier and ended later in fast-growing trees, confirming that cell production is a key factor determining the duration of xylogenesis. Intra-annual variations in stem diameter recorded by band dendrometers revealed two peaks of increment occurring in spring and late summer. However, the number of cambial cells did not increase in late summer, which suggested that the second peak of increment was caused by stem rehydration, rather than by a reactivation of cell division. These results demonstrated that the variability in the timings of xylem phenology observed among trees of the same age and size and growing under similar environmental conditions was closely related to cell production and not to age or size per se.     

毛白杨形成层的活动周期及其POD同工酶的变化

北京地区生长的毛白杨 (PopulustomentosaCarr .)在春季芽膨大前 ,形成层带已经进入了恢复活动期。在芽展开后一周形成层进入活动期 ,细胞开始分裂 ,细胞层数也有所增加 ,同时分化出未成熟的韧皮部细胞。未成熟韧皮部细胞的数量在形成层活动初期快速增长 ,随后是一个持续而缓慢的连续过程。木质部的产生比韧皮部要晚 3周 ,未成熟的木质部细胞层数在开始变化不大 ,5月底～ 6月底 ,增长速度明显高于初期 ,随后便急剧下降。成熟木质部细胞的出现比成熟的韧皮部细胞要晚约一个月。与其他研究结果不同 ,毛白杨在4月底到 6月底这段时间 ,形成层细胞层数迅速下降 ,未成熟韧皮部细胞也略有减少 ,而未成熟和成熟的木质部细胞则大量增加。木质部在 9月底停止分化 ,较韧皮部要晚约 2 0d。 9月底形成层进入休眠期后 ,形成层细胞层数基本保持不变 ,直到翌年春天恢复活动。毛白杨形成层区域的过氧化物酶 (POD)同工酶在形成层活动期其活性低、酶带少 ,而恢复活动期和休眠期其活性高且酶带多 ,组织化学反应还表明 ,不同时期POD在不同的细胞和组织中的活性不同。本文对POD同工酶在形成层活动周期中的变化与其组织分化的关系进行了讨论。     

The effect of cork removal on the radial growth and phenology of young cork oak trees

The effect of the removal of cork was studied in 11-years old cork oak trees (Quercus suber L.), growing in favorable conditions, in relation to phenology and radial growth during two years. Longevity of leaves was 14–15 months (1996, 1998) and 10 months (1997). Bud burst started in mid-February and leaf flushing in April, extending until June. Neither a distinct two-period flushing nor an autumn bud burst or leaf flushing were observed. Radial growth started in mid-April and continued until the end of November, with the maximum growth in June and July. In trees with the removal of cork, leaf abscission occurred a little earlier and new branches had on average 23% fewer new leaves. The radial growth of the trees and its general seasonal pattern were not affected by cork removal in the year of removal or in the year after. The only observation was a shift of the maximum radial growth rate from June to July for the trees where cork had been removed.     

Auxin and ethylene regulation of diameter growth in trees

Recent studies on the phytohormonal regulation of seasonal cell-division activity in the cambium, primary-wall radial expansion of cambial derivatives, differentiation of xylem cells, and growth of the cortex in forest trees of the north temperate zone are reviewed. Indol-3-ylacetic acid (IAA, auxin) has been characterized by combined gas chromatography-mass spectrometry (GC-MS) in the cambial region of Abies balsamea, Pinus densiflora, Pinus sylvestris and Quercus robur. All of the evidence supports the hypothesis that developing leaves and extending shoots are primary sources of IAA. The rate of ethylene emanation varies among conifer species when adjoining phloem and cambial tissues are incubated in vitro. The cambium from young cuttings of Abies balsamea produces more ethylene than that from older cuttings. Ethylene production by seven-year-old Abies balsamea cambium is substantially increased in vitro when the tissue is provided with exogenous 1-aminocyclopropane-1-carboxylic acid and IAA. In response to elevated ethylene concentrations, cortex growth is accelerated in both hardwood and conifer seedlings. Ethrel (2-chloroethylphosphonic acid) increases ray size and ray-cell number and promotes traumatic resin-canal development in xylem. In Ulmus americana, endogenous ethylene concentrations are inversely correlated with cambial activity. Ethylene decreases vessel diameter in Acer negundo, Acer platanoides and Ulmus americana. Several studies suggest that ethylene has a role in regulating reaction-wood formation in both conifers and hardwoods.     

Comparing the intra-annual wood formation of three European species (Fagus sylvatica, Quercus petraea and Pinus sylvestris) as related to leaf phenology and non-structural carbohydrate dynamics

Monitoring cambial phenology and intra-annual growth dynamics is a useful approach for characterizing the tree growth response to climate change. However, there have been few reports concerning intra-annual wood formation in lowland temperate forests with high time resolution, especially for the comparison between deciduous and coniferous species. The main objective of this study was to determine how the timing, duration and rate of radial growth change between species as related to leaf phenology and the dynamics of non-structural carbohydrates (NSC) under the same climatic conditions. We studied two deciduous species, Fagus sylvatica L. and Quercus petraea (Matt.) Liebl., and an evergreen conifer, Pinus sylvestris L. During the 2009 growing season, we weekly monitored (i) the stem radial increment using dendrometers, (ii) the xylem growth using microcoring and (iii) the leaf phenology from direct observations of the tree crowns. The NSC content was also measured in the eight last rings of the stem cores in April, June and August 2009. The leaf phenology, NSC storage and intra-annual growth were clearly different between species, highlighting their contrasting carbon allocation. Beech growth began just after budburst, with a maximal growth rate when the leaves were mature and variations in the NSC content were low. Thus, beech radial growth seemed highly dependent on leaf photosynthesis. For oak, earlywood quickly developed before budburst, which probably led to the starch decrease quantified in the stem from April to June. For pine, growth began before the needles unfolding and the lack of NSC decrease during the growing season suggested that the substrates for radial growth were new assimilates of the needles from the previous year. Only for oak, the pattern determined from the intra-annual growth measured using microcoring differed from the pattern determined from dendrometer data. For all species, the ring width was significantly influenced by growth duration and not by growth rate, which differs from previous studies. The observed between-species difference at the intra-annual scale is key information for anticipating suitability of future species in temperate forests.     

Regular cambial activity and xylem and phloem formation in locally heated and cooled stem portions of Norway spruce

The effect of heating (23–25°C) and cooling (9–11°C) on regular cambial activity and xylem and phloem formation in the stem portion of Norway spruce was investigated. Adult trees were sampled at 21-day intervals during the 2005 vegetation period. Continuously elevated temperatures increased the rate of cell division in the first part of the growing season, but did not significantly prolong cambial activity at the end of the vegetation period in the heated tree. Low-temperature treatments shortened regular cambial activity and slowed down cell production. The xylem growth ring was wider in the heated sample and narrower in the cooled sample compared to the control. The temperature in the cambial region was only negligibly transferred along the stem from the site of its application. In general, the temperature in the cambium was affected by a long-term rise or drop in air temperatures. Both experiments affected the structure and width of phloem growth increments. The tangential band of the axial parenchyma was not continuous in the cooled sample. The number of late phloem cells was reduced in the cool-treated sample and increased in the heat-treated sample. Our experiments confirmed the effect of constantly increased or decreased temperatures on regular cambial activity in Norway spruce.     

Does tree-ring formation follow leaf phenology in Pedunculate oak (<Emphasis Type="Italic">Quercus robur</Emphasis> L.)?

We monitored leaf phenology and xylogenesis of 12 Pedunculate oaks in northern Poland in 2014. We hypothesized that the individual trees, which differed in size, age and habitat (tree stand or gap), also diverged in terms of the seasonal patterns of leaf phenology and xylogenesis. The samples used for wood formation observations were collected most frequently during the early leaf phenophases (from March to end of June). The transverse sections of the cambial region were cut with a sledge microtome. We counted the number of cambial cells, measured the width of xylem increment and assessed the timing of xylogenesis and earlywood-vessel formation. We found significant differences in leaf phenology and timing of xylogenesis among individual trees. The smallest differences in wood formation among the trees were observed at the beginning of the vegetation season when the first earlywood vessels were detected (9 days). The dates of completion of the first tangential row of earlywood vessels varied by up to 30 days, while for the completion of the entire earlywood dates varied by up to 32 days. The highest productivity of cambial cells (13 cell layers) was observed around the time of bud swelling at mid-April. In the last days of April, the number of cambial cell layers decreased and subsequently increased again when the leaves were nearly fully expanded at the end of May. To summarize, we observed a high seasonal variability in the number of cambial cell layers. Differences in the time of cessation of cambial activity and xylogenesis amounted to 1 month. We conclude that: (1) oak tree-ring widths and earlywood-vessel sizes and numbers may not be sensitive indicators for early spring temperature and spring defoliation; (2) the missing association between leaf phenophases and xylogenesis as well as the phenological variability may be the reasons for the lack of a clear climatic effect on the above-mentioned parameters.     

Xylogenesis in black spruce: does soil temperature matter?

In boreal ecosystems, an increase in soil temperature can stimulate plant growth. However, cambium phenology in trees was better explained by air than soil temperature, which suggested that soil temperature is not the main limiting factor affecting xylogenesis. Since soil temperature and snowmelt are correlated to air temperature, the question whether soil temperature directly limits xylogenesis in the stem will remain unresolved without experiments disentangling air and soil temperatures. This study investigated the effects of an increase of 4 °C in soil temperature and a consequent 1-week earlier snowmelt on growth of black spruce [Picea mariana (Mill.) BSP] in the boreal forest of Quebec, Canada. The soil of two natural stands at different altitudes was warmed up with heating cables during 2008-2010 and cambial phenology and xylem production were monitored weekly from April to October. The results showed no significant effect of the treatment on the phenological phases of cell enlargement and wall thickening and lignification. The number of cells produced in the xylem also did not differ between control and heated trees. These findings allowed the hypothesis of a direct influence of soil temperature on stem growth to be rejected and supported the evidence that, in the short term, air temperature is the main limiting factor for xylogenesis in trees of these environments.     

Xylogenesis of Pinus pinaster under a Mediterranean climate

Context

The knowledge on cambial activity in water-limited environments, such as the Mediterranean, is still fragmentary. Dendrochronological studies have determined that spring precipitation plays an important part in determining tree-ring width and the properties of tracheids. However, the complex relation between cambial phenology and climate is still far from understood.

Aims

We studied the influence of climate, especially water stress, on maritime pine wood formation with the aim of determining the influence of drought on cambial activity.

Methods

A plantation of maritime pine (Pinus pinaster) was selected in the west coast of Portugal, to monitor cambial activity and wood formation using anatomical observations and band dendrometers. The trees were monitored weekly over 2 years (2010 and 2011).

Results

Xylem differentiation started earlier when warmer late winter temperatures were observed. Water stress triggered an earlier stop of wood formation and also the formation of tracheids with smaller lumen area. In both years a bimodal pattern of stem radial increment was registered by band dendrometers with two periods of increment: one in spring and another in autumn. The xylem anatomy study suggests that the autumnal increment period corresponded mostly to stem rehydration, since the differentiation of new xylem cells by the cambium was not observed.

Conclusion

Maritime pine cambial activity appears to be under a double climatic control: temperature influences cambial onset and water availability growth cessation.     

The relationship between crown size and ring width in Pinus sylvestris L. stems: dependence on indole-3-acetic acid, carbohydrates and nitrogen in the cambial region

Indole-3-acetic acid (IAA), carbohydrates, total nitrogen and amino acids in the cambial region and bark were measured at the top (10-year-old internode) and bottom (1.3 m) of the main stem of 50-year-old Pinus sylvestris L. trees, having different rates and longitudinal gradients of annual ring width formation. The trees were sampled during the most active period of wood production (June 23, July 15) and at the end of this period (August 23). Trees with a small crown and relatively slow growth rate (S-trees) were compared with trees in the same stand that had a large crown and fast growth rate (F-trees) as a result of thinning and fertilization. The effect of bottom pruning fast-growing trees (pruned F-trees) was also investigated. The F-trees had greater wood production than the S-trees at both the stem top and bottom. The difference was larger at the stem bottom, thus the relative decrease in ring width down the stem was steeper in the S-trees. The amount of sucrose and IAA per cm(2) in cambial region tissues was higher in F-trees than in S-trees. However, the differences in annual ring width between treatments and within trees were not reflected in the concentrations (expressed per gram fresh weight) of these substances, measured either in differentiating xylem, the cambium plus phloem, or in the cambial region as a whole. The concentrations of total nitrogen and amino acids were slightly higher in the F-trees than in the S-trees. Pruning the F-trees reduced wood production, particularly at the stem bottom, inhibited the springtime increase in starch, and decreased the amounts of sucrose and IAA per cm(2) in the cambial region. However, it was evident that the concentrations of sucrose, IAA, amino acid and nitrogen in the cambial region were not related to ring width. During June and July, the concentrations of these substances were generally higher at the stem bottom in the pruned F-trees than in the F-trees. The results provide evidence that it is the activity of the cambium rather than the availability of carbohydrates that determines the allocation of wood production along the tree stem. The results also indicate that tracheid production is not directly related to the IAA concentration in the cambial region.     

Temporal water deficit and wood formation in Cryptomeria japonica

Cell behavior in the cambium and developing xylem of 3-year-old Japanese cedar (Cryptomeria japonica D. Don.) trees, during and after an 11-day suspension of irrigation, was analyzed. Leaf xylem pressure potential and tangential strain of the stem surface were monitored throughout the experiment. Anatomical features and numbers of developing tracheids and cambial cells were observed in four trees, sampled on Days 0, 4, 8 and 11 after irrigation was suspended. Daytime xylem pressure potential decreased to -1.9 MPa on Day 7 and remained the same until irrigation was resumed on Day 11. The transverse dimensions of the tracheids, which began to form secondary walls, began to decrease on Day 4. The number of cells in the cambial zone and cell expansion zone decreased abruptly on Day 8. Tangentially aligned developing tracheids with collapsed cell walls were observed in samples harvested on Days 8 and 11. Secondary wall formation was recognized in these tracheids. After the resumption of irrigation, xylem pressure potential recovered rapidly to the same value as before the suspension of irrigation. Tangential strain increased within 30 min after the resumption of irrigation, and continued to increase until the onset of light the next day. Eighteen days after the resumption of irrigation, anatomical features of cells in the cambium and cell-expansion zone were similar to those observed before suspension of irrigation.     

Tissue culture responses of explants taken from branch sources with different degrees of juvenility in mature black locust (Robinia pseudoacacia) trees

We studied the in vitro responses of cambial tissue and dormant vegetative buds obtained from top and epicormic branches of three mature black locust (Robinia pseudoacacia L.) trees. Cambial tissues isolated from epicormic branches produced more callus than cambial tissues isolated from top branches, whereas in vitro shoot cultures derived from buds excised from top branches grew faster than those derived from buds excised from epicormic branches. There were no significant differences between the two branch sources in in vitro bud break or shoot multiplication from bud explants or cambial-derived callus tissue, respectively. Furthermore, the top branches, generally considered to be the most mature in a tree, were not recalcitrant in terms of morphogenic capacity compared to epicormic branches.     

Can the structure of dormant cambium and the widths of phloem and xylem increments be used as indicators for tree vitality?

We investigated the structure and width of the dormant cambium and of the increments of phloem and xylem of Quercus robur to estimate their potential as indicators for tree vitality. The samples were taken from three woodlands, two in Slovenia [Krakovo forest (KRA) and Murska Suma (MUS)] and one in Croatia [Kobiljak (KOB)], with reported tree decline. The number of dormant cells seems to reflect the initial capacity of the cambium to accomplish cell division. With the exception of two trees at KRA, cell production was always higher on the xylem side than on the phloem side. The annual phloem increments were narrower, less variable among trees and with clear lower and upper limits. With increased cambial cell productivity, the share of the xylem in the total annual radial increment increased following a curvilinear function. In trees with an annual radial increment >3.5 mm, the xylem size represented more than 90 % of the total radial growth. The anatomical variables analyzed show that the most limiting environmental conditions seem to prevail at KRA, whereas the conditions at MUS seem to be most favorable in terms of radial growth. Analysis of the width and structure of xylem and phloem increments, the number of dormant cambial cells and their inter-relationships can provide additional information on the vitality of oaks.     

Detecting changes in tree health and productivity of silver fir in Slovenia

Cambial electrical resistance (CER) was used as an objective measure of vitality of silver fir (Abies alba) in the forests of Slovenia. Trees were rated during the growing season by CER and a subjective crown status index (CSI). Both CER and CSI were inversely correlated to annual ring width increment. Using both CER and CSI, fir were assigned to vitality and vigour categories. Inferences made from these categories and radial growth trends indicated that ring growth decreased prior to the development of canopy symptoms. This decrease in ring growth would have been detected as an increase in CER. This pattern of decline is consistent with the decline of trees due to chronic below-ground stress. Variation in CER was due both to the vascular cambium and to the thickness of the nonconducting phloem.     

Water storage capacitance and xylem tension in isolated branches of temperate and tropical trees

Trees of tropical semi-deciduous forests range from "drought-avoiding" stem-succulent species with low-density wood (< 0.5 g cm(-3)), which maintain high stem water potentials (psi(STEM) > -0.7 MPa) throughout the year, to "drought-tolerant" deciduous hardwood species (wood density > 0.75 g cm(-3)), which dehydrate strongly during seasonal drought (psi(STEM) < -6 MPa). In stem-succulent and other drought-avoiding species, xylem vessels are surrounded by extensive parenchyma providing intracellular water storage, whereas in deciduous species stem water storage is mainly extracellular. Thirteen tropical and two temperate tree species, representing different functional types, were studied. The contribution of stem water storage to these species' water use during water stress was determined by time-series analysis of dehydration and rehydration of excised leaf-bearing branches of these trees. During dehydration, stem water potential slowly declined 1-2 MPa in drought-avoiding species, but in deciduous species it rapidly fell 4-5 MPa, suggesting that water storage capacitance was related to xylem anatomy. After immersion of dehydrated, leafless branches in water, the decline in xylem tension and rate of water uptake during rehydration were linearly related, as predicted by application of Ohm's law to water flux. The decline of xylem tension during rehydration was biphasic, with a phase of rapid water uptake into extracellular spaces being followed by a prolonged phase of slow water uptake into living cells. The rate of water uptake during rehydration and the minima of leaf water potential observed in the field during the dry season were highly correlated with water storage capacitance, indicating that wood anatomy is a major determinant of drought adaptation.     

Coremia formation by Ceratocystis ulmi on elm stem discs

The seasonal fluctuation in the production of coremia by Ceratocystis ulmi (Buis.) was studied on elm stem discs taken from trees felled in April, June, July, September, October and November 1971 at Valcartier, Quebec. More coremia formed on stem discs of trees felled during the growing season. Except for trees felled in October and November, more coremia formed on sapwood than on heartwood. Evidence obtained during the study showed that the compounds, which trigger coremia formation, are not uniformly distributed within and between trees or throughout the period from April to November.     

Photosynthesis and growth of Thujopsis dolabrata var. hondai seedlings in the understory of trees with various phenologies

We have studied the photosynthetic production and growth of Thujopsis dolabrata var. hondai (hiba) seedlings under typical light conditions found in mixed forests, including constant shade, phenological gaps under broad-leaved trees with different lengths of foliation period, and in an open plot. Leaves sampled from the open plot had significantly higher rates of light-saturated gross photosynthesis and dark respiration, and a significantly lower specific leaf area than leaves from the other plots. The relative growth rate of whole plant biomass was significantly higher in plots that received larger amounts of light. The variations in these properties under the various light conditions are considered to reflect the ability of hiba seedlings to adapt to available light. In the late autumn, leaves sampled from the open and from the gap under deciduous trees indicated photoinhibition. However, the estimated value of monthly net photosynthesis of hiba seedlings was greater in these plots, indicating that the benefit of a greater light intensity for photosynthesis seems to be larger than the detriment of photoinhibition. The seasonal pattern of photosynthesis by understory hiba seedlings was affected by the phenology of canopy trees. Light availability under the canopy of deciduous trees associated with phenological gaps helped hiba seedlings to tolerate the relatively dark conditions during the subsequent foliation period. These results for reaction to the light regime and for the phenology of hiba seedlings are practicable for hiba forest management.     

Stable annual pattern of water use by Acacia tortilis in Sahelian Africa

Water use by mature trees of Acacia tortilis (Forsk.) Hayne ssp. raddiana (Savi) Brenan var. raddiana growing in the northern Sahel was continuously recorded over 4 years. Water use was estimated from xylem sap flow measured by transient heat dissipation. Concurrently, cambial growth, canopy phenology, leaf water potential, climatic conditions and soil water availability (SWA) were monitored. In addition to the variation attributable to interannual variation in rainfall, SWA was increased by irrigation during one wet season. The wet season lasted from July to September, and annual rainfall ranged between 146 and 367 mm. The annual amount and pattern of tree water use were stable from year-to-year despite interannual and seasonal variations in SWA in the upper soil layers. Acacia tortilis transpired readily throughout the year, except for one month during the dry season when defoliation was at a maximum. Maximum water use of about 23 l (dm sapwood area)(-2) day(-1) was recorded at the end of the wet season. While trees retained foliage in the dry season, the decline in water use was modest at around 30%. Variation in predawn leaf water potential indicated that the trees were subject to soil water constraint. The rapid depletion of water in the uppermost soil layers after the wet season implies that there was extensive use of water from deep soil layers. The deep soil profile revealed (1) the existence of living roots at 25 m and (2) that the availability of soil water was low (-1.6 MPa) down to the water table at a depth of 31 m. However, transpiration was recorded at a predawn leaf water potential of -2.0 MPa, indicating that the trees used water from both intermediary soil layers and the water table. During the full canopy stage, mean values of whole-tree hydraulic conductance were similar in the wet and dry seasons. We propose that the stability of water use at the seasonal and annual scales resulted from a combination of features, including an extensive rooting habit related to deep water availability and an effective regulation of canopy conductance. Despite a limited effect on tree water use, irrigation during the wet season sharply increased predawn leaf water potential and cambial growth of trunks and branches.     

Physiological process of the symptom development and resistance mechanism in pine wilt disease

Pathophysiological changes during the symptom development of pine wilt disease are reconsidered from recent investigations. The symptom development is divided into two stages: the early and the advanced stages. In the early stage, small number of nematodes migrate in cortex, then in xylem of the stem, and induce denaturation and necrosis of parenchyma cells. These changes in parenchyma are regarded as defense reactions of pines which result in terpene synthesis in xylem cells and embolism in tracheids. Such changes in the early stage can be induced in both susceptible and resistant pine species by either virulent or avirulent isolates of pinewood nematode (Bursaphelenchus xylophilus), or byB. mucronatus. No change occur in physiological status of leaves, and nematode reproduction is suppressed during this stage. Pine trees can survive if symptom does not progress from this stage. The symptoms of the advanced stage usually occur only in susceptible pines infected by virulent nematode isolates. At the beginning of the advanced stage, enhanced ethylene production by stem which coincides with cambial destruction occurs, and results in embolism of the outermost xylem in the portion. The embolism causes decrease in leaf water potential and cessation of photosynthesis. After cessation of photosynthesis, symptoms develop drastically with a burst of nematode population. There seems to be some unknown mechanism which suppress nematode reproduction and invasion to the cambial zone. This mechanism is thought to be photosynthesis-dependent, so that in photosynthesis-decrased conditions, even avirulent nematodes can multiply and invade cambium to induce tree death. Water stress in hot and dry summer should accelerates symptom development from the early to the advanced stage through such decrease of photosynthesis-dependent “cambial resistance”.     

Effect of prevailing monsoons on the distribution of beeches in continental East Asia

Beech trees occur in significantly lower latitudes in continental East Asia than in Europe and North America. They are common deciduous trees in the deciduous forests of the temperate zone in Europe, the eastern part of North America and Japan. In continental East Asia, however, they are absent in the deciduous forests of the temperate zone, but occur in the forests of mountains in the moist subtropical zone, south of 34° Northern Latitude. The lower limits of their distribution in these mountains show a significantly different pattern from the usual distribution pattern of plants and vegetation: it declines as the latitude decreases. The altitudinal belts of beech species lie higher in the northern than in the southern parts of their distribution areas in China. Based on an analysis of the climate and the phenology of these deciduous trees, we show that the prevailing monsoon conditions are the main factor affecting the distribution of the Chinese beech species.