西双版纳热带雨林和哀牢山亚热带常绿阔叶林雾特征研究

以西双版纳热带雨林和哀牢山亚热带常绿阔叶林为研究对象,利用PWS100天气现象仪获取两种森林类型的能见度数据。基于2014年西双版纳热带雨林和哀牢山亚热带常绿阔叶林的能见度数据,对两种森林类型雾的特征进行定量研究。研究结果表明:(1)西双版纳热带雨林全年雾日数为196 d,占全年的53.7%,哀牢山亚热带常绿阔叶林全年雾日数为100 d,占全年的27.4%,热带雨林全年雾日数几乎为亚热带常绿阔叶林雾日数的两倍;(2)热带雨林雨季和干季各占28.06%和71.94%,而亚热带常绿阔叶林雨季和干季各占72%和28%;(3)热带雨林一日内雾持续的最长时间为10.5 h,而亚热带常绿阔叶林雾生成和消散时间不定,一日内雾最长持续时间可达24 h,但雾发生的频率低于西双版纳热带雨林。两种森林类型全年雾日特征有明显的差异性,通过定量评价地处过渡带上的两种多雾森林生态系统雾特征,可为未来气候变化对不同森林生态系统碳水交换影响提供数据支撑。     

哀牢山常绿阔叶林乔木树种的幼苗组成及时空分布特征

哀牢山自然保护区的常绿阔叶林面积达到504 km2,是我国亚热带常绿阔叶林保存面积最大的保护区之一.2008年,中国科学院两双版纳热带植物园在哀牢山自然保护区的中山湿性常绿阔叶林核心区建立了一块6 ha的森林动态监测样地.为了了解哀牢山中山湿性常绿阔叶林树种幼苗组成和分布特征及其存活和死亡的规律,对样地中的幼苗分别进行了定位监测和动态研究.结果表明,重要值居前10位的林下幼苗中,有5种是重要值居前10位的树种.从雨季末期到旱季末期,幼苗的数量和种类都大量减少,因为可能是由于干旱胁迫的影响.在林窗中央和林窗边缘,新增的幼苗数量和种类都较多,死亡率较低,而林冠下新增的幼苗死亡率较高.可见,林窗的出现可能更有利于某些树种幼苗的定居,从而维持了森林树种的多样性.     

云南哀牢山徐家坝中山湿性常绿阔叶林动态和节律的研究

根据多年定位观察资料,包括从组成种的种子萌发、幼苗生长及成年物种的生长规律和物候节律对湿性常绿阔叶林动态和节律的研究,结果表明：林地种子贮量、可萌发种子量和萌发种数,雨季大于旱季。幼苗生长雨季快于旱季。表明雨季是种子萌发、幼苗生长的最佳季节。立木生长是种间竞争、自我调控、自疏的过程。成年物种各物候期长、不明显与温带阔叶林各物候期短、明显不同,而开花、结果、落果终年进行与西双版纳季节雨林物候节律相似。三者的不同在于季节雨林春季（２～３ 月）落叶,常绿阔叶林冬季（１１～１２ 月）落叶,温带阔叶林秋季（９～１０ 月）落叶。依据物种物候节律特点及其对气候环境的反应区分出３ 种生态物候型：１．暖温生态物候型（占总种数（５０）的８２％ ）;２．温性生态物候型（占１２％ ）;３．温凉生态物候型（占０．６％ ）     

基于地形因子的天童地区常绿树种和落叶树种共存机制研究

位于亚热带的浙江天童和古田山常绿阔叶林大样地分布有较高比例的落叶树种,那么它们与常绿树种的共存机制是什么?常绿树种和落叶树种生态习性差异较大,二者对生境的选择应有所不同,我们推测生境分化可能是两类植物实现共存的主要机制。为检验该假设,我们以天童20ha动态样地调查数据为依托,选择个体数≥20的55个常绿树种和42个落叶树种作为分析对象,用典范对应分析(CCA)研究了地形因子对二者分布的影响差异,用torus转换检验来分析常绿树种和落叶树种与各类地形生境的关联。结果如下:(1)CCA分析表明地形因子对常绿树种分布的解释量为19.2%,对落叶树种分布的解释量为7.0%。(2)torus转换检验结果表明,与沟谷成正关联的常绿树种和落叶树种的比例分别为16.4%和28.6%,成负关联的比例分别为40%和7%;与山脊成正关联的常绿树种和落叶树种的比例分别为41.8%和4.8%,成负关联的比例分别为10.9%和47.6%;与受干扰生境成正关联的常绿树种和落叶树种的比例分别为16.4%和42.9%。上述结果说明地形对常绿树种分布的影响大于落叶树种;两个植物类群对生境的选择多呈现相反格局,尤其是在沟谷生境和山脊生境,这进一步表明生境分化是常绿树种和落叶树种共存的重要机制之一,生态位理论在一定程度上能较好地解释亚热带常绿阔叶林物种多样性的维持。     

哀牢山亚热带常绿阔叶林乔木碳储量及固碳增量

为了解哀牢山亚热带常绿阔叶林的乔木碳储量及其固碳增量,利用2005和2008年的植被调查数据,对哀牢山3种主要常绿阔叶林的乔木碳储量及其固碳增量进行了分析。结果表明:原生的中山湿性常绿阔叶林、滇山杨次生林和旱冬瓜次生林的乔木碳储量分别为257.90、222.95和105.39tC·hm-2;中山湿性常绿阔叶林乔木碳储量主要存储在DBH≥91cm的乔木中(34.68%);而次生林的乔木碳储量主要分布在径级21cm≤DBH41cm的乔木中(滇山杨林77.29%;旱冬瓜林69.28%)。由此可见,哀牢山地区原生的中山湿性常绿阔叶林乔木层在碳蓄积方面占主导优势。哀牢山亚热带常绿阔叶林的3个森林类型乔木层均具有固碳增量,即使是原生的中山湿性常绿阔叶林,其乔木层年平均固碳增量也达2.47tC·hm-2·a-1;次生林乔木层的年平均固碳增量约为原生林的2倍,显示了哀牢山亚热带常绿阔叶林乔木层具有较强的碳汇增量。初步估算,哀牢山亚热带常绿阔叶林林区内每年乔木固碳增量为8.52×104tC·a-1。     

哀牢山中山湿性常绿阔叶林主要树种的物候研究

以哀牢山中山湿性常绿阔叶林的１４个主要树种为材料,研究了树种物候的主要特征,编制了物候谱,考察了树种物候期与温度、光照等环境因子的关系。采用主要万分分析方法,揭示了各物候期平均温度和≥５℃积温地 物候表现最为密切。对于树木开花期的诱导,光和温度具有同等重要的作用;但在萌动－展叶期中,降雨量和光照则起主导作用。     

云南中山湿性常绿阔叶林起源的探讨

云南中山湿性常绿阔叶林广泛分布于海拔1800~3400 m的山地,这类常绿阔叶林在生态外貌上具有亚热带常绿阔叶林特征,但其分布生境却是暖温带-温带气候,且植物区系组成与热带植物区系有古老的渊源。该文以研究得比较深入的哀牢山中山湿性常绿阔叶林为例,对其植物区系与其气候条件的不协调进行剖析。哀牢山的中山湿性常绿阔叶林记录了种子植物110科386属821种。在植物区系科的地理成分上,无论是含种数多的科,还是所有科的分布区类型,都是以热带分布科为主,体现了它的远古热带起源背景。在该种子植物区系中,热带分布属占总属数的47.75%,热带分布种占总种数的33.45%,在近代演化上仍体现出明显的热带亲缘特征。按照哀牢山中山湿性常绿阔叶林分布地区的暖温带-温带气候条件,它相当于中国东部的暖温带落叶阔叶林地区。在中国东部地区类似气候条件的地带性植被的植物区系中,热带分布属通常只占总属数的25%~27%,云南中山湿性常绿阔叶林植物区系的地理成分与所在地的温带气候明显不协调。对这种现象的解释,笔者认为结合哀牢山地区曾经是低海拔夷平面,在第四纪以来才迅速抬升形成的地质历史,可能这里曾经在第四纪以前的热带-亚热带性质的植物区系和常绿阔叶林随着地形的迅速抬升,逐渐适应了因海拔上升而形成的温带气候,成为在云南高海拔山地存在的所谓中山湿性常绿阔叶林,其植物区系和植被的热带-亚热带性质及常绿阔叶生态外貌并未因气候改变而发生改变。     

哀牢山常绿阔叶林树种多样性及空间分布格局

为了探究哀牢山中山湿性常绿阔叶林树种多样性特点及优势种群空间分布特征,2008年,中国科学院西双版纳热带植物园在哀牢山生态站附近的常绿阔叶林建立了一块6 ha的森林动态监测样地,逐一测量并记录了样地中所有胸径(DBH)≥1 cm的树木的胸径,并对其挂牌标记、鉴定和确定坐标位置.应用Ripley's L-Function分析了样地内4个上层优势种的空间分布格局.结果表明,样地内共有DBH≥>1 cm的乔木12,131株,隶属于25科49属68种.样地内硬壳柯(Lithocarpus hancei)的重要值最大,其胸高断面积也最大;其次为变色锥(Castanopsis wattii);排在第三位的为云南连蕊茶(Camellia forrestii),有1,712个个体,是样地内个体数量最多的树种.和同类型森林相比,哀牢山中山湿性常绿阔叶林是多优种类型,物种总数较少,稀有种所占比例也较小.样地内4个上层优势种的小径级个体数量较多,而大径级个体数量较少,而且在空间上呈现互补特征.对样地中符合条件的26个树种(生活史期间的树木株数≥40株)的空间格局进行分析,53个生长时期中有37个表现为集群分布,表明在树种多样性维持方面,密度制约机制町能不是主要因为,生境异质性可能起着重要作用.     

云南哀牢山栎类次生林树种多样性特征研究

在哀牢山徐家坝地区,采用样方调查的方法对中山湿性常绿阔叶林受到人为破坏后形成的栎类次生林的树种多样性特征进行了研究。结果表明,恢复约40a的栎类次生林的乔木树种组成主要以云南越桔(Vacciniumduclouxii)为主。树种的萌生现象非常突出,超过2/3的树种具有萌生现象,在DBH≥3cm的植株中有72.7%是由无性系萌株产生的。栎类次生林乔木的密度随高度级、径级的增加而递减,但树种丰富度却不随树木的密度增加而增加。以Shannon-Wiener指数H、Simpson指数D和Fisher指数α计算了栎类次生林的树种多样性(H=1.42±0.27;D=0.65±0.09;α=2.59±1.16),并与中山湿性常绿阔叶林的树种多样性进行了比较,结果显示处于演替顶级阶段的中山湿性常绿阔叶林具有更高的树种多样性。     

哀牢山常绿阔叶林水源涵养功能及其在应对西南干旱中的作用

为了解云南哀牢山中山湿性常绿阔叶林在2010年初西南地区特大干旱中是否遭遇水分胁迫,及其水源涵养功能在应对干旱中的作用,测定了该森林土壤和主要树种在2010年旱季的水分状况,并对比研究了原生林和森林经砍伐烧垦后形成的毛蕨菜-玉山竹群丛的土壤持水、凋落物持水、水面蒸发和土壤水分季节动态。结果表明:常绿阔叶林主要树种在2010年初西南特大干旱中并未遭受水分胁迫(最旱月叶片凌晨水势高于-0.4 MPa)。虽然常绿阔叶林土壤含水量和地下水位在最旱月都达到了有观测以来的最低点,但主要根系分布区的土壤水势仍不低于-0.5 MPa,并高于毛蕨菜-玉山竹群丛。森林较好的水分状况和原生常绿阔叶林较好的水源涵养功能有关。常绿阔叶林的土壤总持水量尤其是非毛管持水量要显著大于毛蕨菜-玉山竹群丛,同时也大于云南地区的一些次生林和人工林。常绿阔叶林地表丰富的凋落物通过持水和抑制土壤蒸发也对水源涵养有一定作用。哀牢山常绿阔叶林良好的水源涵养功能,充足的土壤地下水储存弥补了旱季和特大干旱中降水的不足。结果指示原生林在水源涵养中不可替代的作用,以及加强原生林保护在提高区域抗干旱能力中的重要意义。     

Comparison of climatic effects on radial growth of evergreen broad-leaved trees at their northern distribution limit and co-dominating deciduous broad-leaved trees and evergreen conifers

Using dendrochronological techniques, this study examined whether tree-ring width of two evergreen broad-leaved species (Cleyera japonica, Eurya japonica) at their inland northern distribution limit in central Japan is more limited by low temperature compared with two co-dominating deciduous broad-leaved species (Fagus japonica, Magnolia hypoleuca) and two evergreen conifer species (Chamaecyparis obtusa, Abies firma), whose distribution limits are further north. The two deciduous broad-leaved species and the two evergreen conifers are tall tree species. Evergreen broad-leaved Cleyera japonica is a sub-canopy species and Eurya japonica is a small tree species. The tree-ring widths of four of the six species (except for Eurya japonica and Magnolia hypoleuca) correlated positively with the March temperature just before the start of the growth period. For deciduous broad-leaved Magnolia hypoleuca, the tree-ring width was correlated positively and negatively with July temperature and precipitation, respectively. However, the other deciduous broad-leaved Fagus japonica showed no such relationships. For the evergreen broad-leaved Cleyera japonica and evergreen conifers Chamaecyparis obtusa and Abies firma, tree-ring widths correlated positively with winter temperatures, probably because evergreen species can assimilate during warm winters. The tree-ring width of Cleyera japonica also correlated positively with temperatures of many months of the growth period. By contrast, the tree-ring width of the other evergreen broad-leaved Eurya japonica showed no positive correlation with the temperature in any month. Most Eurya japonica trees were suppressed by tall trees, which might disguise any climate effect. Thus, there were species differences in response to climate for each life form, and the tree-ring width of Cleyera japonica at the northern distribution limit was more limited by low temperatures compared with co-dominating species. It is suggested that growth of Cleyera japonica is increased by global warming at the latitudinal ecotone.     

Cambial growth dynamics and climatic control of different tree life forms in tropical mountain forest in Ethiopia

Munessa Forest is a mountain forest in south-eastern Ethiopia experiencing seasonal rainfall variation. We investigated seasonal cambial activity and dormancy from increment rates of four different tree species belonging to varying life forms, namely, evergreen native conifer (Podocarpus falcatus), evergreen introduced conifer (Pinus patula), evergreen broadleaved tree (Prunus africana) and deciduous broadleaved tree (Celtis africana). Measurements of stem radius fluctuations were registered with the help of high-resolution electronic dendrometers. Daily amplitudes of stem diameter variations and daily and monthly net growth rates were determined and related to climatic variables measured at local climate stations. Thin sections of wood collected with a microcorer every 3–6 weeks allowed a visual control of newly formed wood cells during consecutive time intervals. Lack of water availability during the long dry season induced cambial dormancy of 5–7 months depending on life forms. After the onset of the short rainy season, stem swelling started quite synchronously with a variation of only single days in all studied species. Evergreen tree species were able to initiate wood formation during the short rainy season, whereas growth in the deciduous broadleaved species started in the long rainy season. The acquired data provide a basis for delineating the species-specific growth boundaries and the duration of the cambial growing season.     

Variation in evergreen and deciduous species leaf phenology in Assam, India

In the present study phenological activities such as leaf and shoot growth, leaf pool size and leaf fall were observed for 3 years (March 2007–March 2010) in 19 tree species (13 evergreen and 6 deciduous species) in a wet tropical forest in Assam, India. The study area receives total annual average rainfall of 2,318 mm of which most rain fall (>70 %) occurs during June–September. Both the plant groups varied significantly on most of the shoot and leaf phenology parameters. In general, growth in deciduous species initiated before the evergreen species and showed a rapid shoot growth, leaf recruitment and leaf expansion compared to evergreen species. Leaf recruitment period was significantly different between evergreen (4.2 months) and deciduous species (6.8 months). Shoot elongation rate was also significantly different for evergreen and deciduous species (0.09 vs. 0.14 cm day^?1 shoot^?1). Leaf number per shoot was greater for deciduous species than for evergreen species (34 vs. 16 leaves). The average leaf life span of evergreen species (328 ± 32 days) was significantly greater than that of deciduous species (205 ± 16 days). The leaf fall in deciduous species was concentrated during the winter season (Nov–Feb), whereas evergreens retained their leaves until the next growing season. Although the climate of the study area supports evergreen forests, the strategies of the deciduous species such as faster leaf recruitment rate, longer leaf recruitment time, faster shoot elongation rate during favorable growing season and short leaf life span perhaps allows them to coexist with evergreen species that have the liberty to photosynthesize round the year. Variations in phenological strategies perhaps help to reduce the competition among evergreen and deciduous species for resources in these forests and enable the coexistence of both the groups.     

Species-Specific Growth Responses to Climate Variations in Understory Trees of a Central African Rain Forest

Basic knowledge of the relationships between tree growth and environmental variables is crucial for understanding forest dynamics and predicting vegetation responses to climate variations. Trees growing in tropical areas with a clear seasonality in rainfall often form annual growth rings. In the understory, however, tree growth is supposed to be mainly affected by interference for access to light and other resources. In the semi-deciduous Mayombe forest of the Democratic Republic of Congo, the evergreen species Aidia ochroleuca, Corynanthe paniculata and Xylopia wilwerthii dominate the understory. We studied their wood to determine whether they form annual growth rings in response to changing climate conditions. Distinct growth rings were proved to be annual and triggered by a common external factor for the three species. Species-specific site chronologies were thus constructed from the cross-dated individual growth-ring series. Correlation analysis with climatic variables revealed that annual radial stem growth is positively related to precipitation during the rainy season but at different months. The growth was found to associate with precipitation during the early rainy season for Aidia but at the end of the rainy season for Corynanthe and Xylopia. Our results suggest that a dendrochronological approach allows the understanding of climate–growth relationships in tropical forests, not only for canopy trees but also for evergreen understory species and thus arguably for the whole tree community. Global climate change influences climatic seasonality in tropical forest areas, which is likely to result in differential responses across species with a possible effect on forest composition over time.     

Stem growth and canopy dynamics in a world-wide range of Fagus forests

Abstract. Forests dominated by Fagus (beech) occur widely in the Northern Hemisphere. Tree species dominant together with beech vary in tolerance of understorey conditions. They are deciduous broad-leaved, evergreen broad-leaved or evergreen coniferous. The frequency and intensity of events that reduce the forest canopy cover are important determinants of the ratio of beech to other species in the canopy. For trees in the understorey and the canopy, stem diameter growth rate is determined by light regime and growing space which in turn are determined by canopy cover. We evaluated increase in stem diameter growth rate as an indicator of sudden reductions in canopy cover and canopy dynamics. We used tree-ring chronologies and calculated an index of growth rate increase (GI) to compare the canopy dynamics of 11 natural beech forests. Per site, the annual average value of GI poorly reflected the effects of dry or cool summers, and it clearly reflected events like tornados and hurricanes that removed substantial canopy cover. Among groups of sites average values of GI were significantly different. In the sites with a lower level of average GI, the establishment of the more shade tolerant tree and shrub species in the understorey was favoured, and subcanopy layers became more dense. On the other hand, higher levels of average GI allowed for more light demanding tree species to reach the canopy.     

亚热带常绿阔叶林和暖温带落叶阔叶林叶片热值比较研究

植物干重热值(GCV)是衡量植物生命活动及组成成分的重要指标之一,反映了植物光合作用中固定太阳辐射的能力。利用氧弹量热仪测定了亚热带和暖温带两个典型森林生态系统常见的276种常见植物叶片的干重热值,探讨了亚热带和暖温带植物热值分布特征,以及不同生活型、乔木类型间植物热值的变化规律。实验结果发现:亚热带常绿阔叶林和暖温带落叶阔叶林叶片热值的平均值分别为17.83 k J/g(n=191)和17.21k J/g(n=85),整体表现为亚热带植物暖温带植物。不同地带性植被的植物叶片热值在不同生活型间表现出相似的规律,其中亚热带常绿阔叶林表现为:乔木(19.09 k J/g)灌木(17.87 k J/g)草本(16.65 k J/g);暖温带落叶阔叶林表现为:乔木(18.41 k J/g)灌木(17.94 k J/g)草本(16.53 k J/g);不同乔木类型间均呈现常绿乔木落叶乔木、针叶乔木阔叶乔木的趋势。落叶阔叶乔木表现为亚热带暖温带,而常绿针叶乔木则呈现亚热带暖温带的趋势。此外,我们对于两个分布区域内的4种针叶树种叶片热值进行了比较,发现华北落叶松(19.32 k J/g,暖温带)杉木(19.40 k J/g,亚热带)马尾松(19.82 k J/g,亚热带)油松(20.95 k J/g,暖温带)。亚热带常绿阔叶林和暖温带落叶阔叶林植物热值的特征及其变化规律,为森林生态系统的能量流动提供了理论基础。     

Annual growth rings, rainfall-dependent growth and long-term growth patterns of tropical trees from the Caparo Forest Reserve in Venezuela

1 Tree-ring analyses and dendrometer measurements were carried out on 37 tree species in a semi-deciduous forest of the Reserva Forestal de Caparo, Venezuela, where the mean annual rainfall is about 1700 mm and there is a dry season from December to March. The main purposes of the investigation were to show the seasonality of cambial growth, and the connection between precipitation patterns and tree-ring curves. Long-term rates of wood increment were also estimated.
2 Cambial markings in consecutive years showed that annual rings were formed by many species.
3 The distinctiveness of growth zones was usually greater in deciduous species than in evergreen species, although not all deciduous species had distinct rings.
4 Dendrometer measurements showed that the annual growth rhythm was related to precipitation patterns. Evergreen species tended to show only a short interruption of wood growth (during the later part of the dry season), whereas deciduous species stopped growth completely at the end of the rainy season.
5 For deciduous species, regression analyses showed close relations between tree-ring width and the sum of precipitation outside the rainy seasons (i.e. November to April). Evergreen species reacted to the total annual amount of precipitation.
6 Variation in longest available ring chronology (for Terminalia guianensis ) showed little correlation with the El Niño–Southern Oscillation effect.
7 On average trees from natural forests showed relatively constant growth over the entire life span. Plantation trees grew fast up to an age of 15–20 years, but annual increments then decreased to values seen in natural forest trees.     

Shoot growth phenology of co-existing evergreen and deciduous species in an oak forest

Shoot growth phenology was compared for the saplings of evergreen and deciduous woody species sharing the same microsite. Growth initiation occurred earlier in evergreens (among co-stratal species) while deciduous species completed their growth earlier. Shoot growth rate was significantly greater (P<0.01) for deciduous trees than evergreen trees. The amount of shoot elongations and shoot diameter was also significantly greater (P<0.01) for deciduous trees than evergreens. On the other hand, among shrubs the amount of shoot elongation and shoot diameter was greater for evergreens but the rate of elongation and diameter was more or less similar for both. The duration of shoot elongation and shoot diameter was significantly longer in evergreens than the deciduous species. Leaf packing (number of leaves per shoot) was significantly more dense in evergreen trees (P<0.01) than in deciduous tree species. Leaf packing was more dense in evergreen than deciduous shrubs but the difference was not significant. Leaf area (per individual leaf) at full expansion was significantly greater (P<0.01) in deciduous species. Leaf dry mass and specific leaf mass in the initial stage was significantly greater for evergreen species than for deciduous species. The number of buds/10 cm of shoot was higher in evergreens. However, the per cent mortality was also higher in them.     

Radial growth response of trees to seasonal soil humidity in a subtropical forest

Tree growth is the most important factor in determining the carbon sequestration processes of forest ecosystems. However, the growth phenology (seasonal growth pattern) and responses of tree growth to climatic variables vary considerably among different species, especially between deciduous and evergreen species. Thus, it is crucial to explore the seasonal growth patterns of different tree species in relation to climate to better understand the responses of tree physiology to climate changes, especially in mixed-species forest stands. In this study, we monitored the daily basal area increments of 220 individuals belonging to 15 common broadleaved tree species, nine deciduous and six evergreen species, in mixed-species experimental stands in subtropical China and analysed the relationships between radial stem growth and seasonal climate at a high-temporal resolution. We fitted daily increments of stem diameters with four frequently used nonlinear models and chose the best model for each species. The results showed that the evergreen trees grew faster than the deciduous trees, both annually and within the growing season. The tested nonlinear models (Korf, Weibull, logistic and Gompertz) produced good fits for the growth patterns of all species. Overall, the evergreen species began stem growth earlier and finished later during the growing season than that of the deciduous species. Within the growing season, the radial growth of trees in mixed stands containing both types of species was strongly positively correlated with humidity. In spring, increases in both temperature and moisture increased the daily relative basal area increment of all species. Maximum growth rates occurred when the soil water content reached its highest level and gradually decreased when the soil water content decreased. In summer, high temperatures combined with low amounts of precipitation led to heat-induced summer drought, to which the evergreen trees appeared to be more tolerant than the deciduous trees, which was reflected in the reduced stem growth of the latter. These results indicate the different climate-dependent seasonal growth strategies of evergreen and deciduous trees related to the trade-off described by the leaf economics spectrum, i.e., short-lived leaves with higher assimilation rates in deciduous and longer-lived leaves with a greater drought tolerance in evergreen species.     

Effects of climate on the growth of exotic and indigenous trees in central Zambia

Aim Climate change has far‐reaching effects on species and ecosystems. The aims of this study were to determine how climate factors affect the growth pattern of indigenous and exotic trees in Zambia and to predict tree growth responses to a warmer climate with the use of mathematical models. Location Two savanna sites in central Zambia. Methods Diameter at breast height (1.3 m above ground, d.b.h.) of 91 permanently marked trees belonging to three indigenous and four exotic species was measured fortnightly for periods of 1–2 years from 1998 to 2003. Correlation and regression analysis was used to determine the effect of climate factors (minimum, maximum and average temperature and rainfall) on monthly daily d.b.h. increment of each species. Regression models were used to predict the growth behaviour of trees under a 0.5 °C warmer climate. Results Interactions between temperature and rainfall explained 60–98% of the variation in d.b.h. increment in all the tree species, except the exotic Eucalyptus grandis. For deciduous species, stem expansion was delayed by 2–12 weeks following leaf‐flush and d.b.h. increment peaked during the rainy season. Evergreen and deciduous species could not be separated on the basis of annual d.b.h. increment because the higher growth rates of deciduous species compensated for the shorter growing period. Mathematical models predicted slight changes in d.b.h. growth pattern under a 0.5 °C warmer climate in five of the seven species. Significant changes in d.b.h. growth patterns were predicted in the indigenous Bridelia micrantha and exotic Gmelina arborea under a warmer climate. However, models failed to adequately represent potential soil water stress that might result from changes in tree growth patterns and a warmer climate. Main conclusions Climate factors explained a large proportion of the variation in diameter growth of both indigenous and exotic trees, rendering it possible to model tree growth patterns from climate data. Tree growth models suggest that a rise in temperature of 0.5 °C is unlikely to induce significant changes in the growth behaviour of the majority of the studied species. However, because the growth behaviour of some species may be substantially affected by climate change, it is recommended that strategies for the future production of such climate‐sensitive trees should incorporate aspects of climate change.