林业科学  2002, Vol. 38 Issue (1): 15-23   PDF    
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文章信息

Wang Guohong
王国宏
PLANT FUNCTIONAL TYPES OF ZONAL WOODY PLANT COMMUNITIES IN RELATION TO HYDROTHERMIC FACTORS
地带性木本植物群落功能型的水热分布格局
Scientia Silvae Sinicae, 2002, 38(1): 15-23.
林业科学, 2002, 38(1): 15-23.

文章历史

Received date: 2001-02-09

作者相关文章

王国宏

地带性木本植物群落功能型的水热分布格局
王国宏     
中国科学院植物研究所植被数量生态学开放研究实验室 北京 100093
摘要:植物功能型是对环境条件做出相似的反应和对关键生态学过程具有相似影响的植物组合。不同功能型植物对生态系统过程的作用不同, 通过植物功能型的分析对揭示生态系统功能至关重要。甘肃省境内5种地带性木本植物群落(亚热带常绿落叶阔叶林、暖温带落叶阔叶林、温带针阔混交林、寒温性针叶林和荒漠旱生灌木群落)依据植物体的高度、叶片的生长对策及果实类型可划分出23种功能型。其分布格局与水热因子的相关分析表明: 1)湿热的生境利于乔木、大灌木、藤木、寄生植物和常绿植物及翅果、坚果、核果、蓇葖果、颖果类植物的发育, 干冷生境利于灌木、小灌木和落叶植物以及蒴果类植物的发育。2)干果类和肉果类的成因可能与植物生长环境中水分供应状况密切相关, 即潮湿的生境利于肉果类植物的发育, 干旱的生境有利于干果类(如胞果)的发育。3)研究区域地带性木本植物群落物种丰富度和功能型的丰富度格局主要受制于水分梯度影响, 而良好的水热组合可孕育木本植物群落最丰富的果实类型。
关键词植物功能型    地带性木本植物群落    水热因子    
PLANT FUNCTIONAL TYPES OF ZONAL WOODY PLANT COMMUNITIES IN RELATION TO HYDROTHERMIC FACTORS
Wang Guohong     
Laboratory of Quantitative Vegetation Ecology, Institute of Botany, Chinese Academy of Sciences Beijing 100093 China
Abstract: Plant functional types can be defined as sets of plants exhibiting similar responses to environmental variations and having similar effects on the dominant processes in ecosystems. In the present paper, 23 plant functional types were identified from five zonal woody plant communities occurred in Gansu province, NW of China. This paper has made some explorations on the relationship between the patterns of zonal woody plant functional types and the hydrothermic factors to which they subjected. Some conclusions are as follows : Environments with warm-humid combinations would result in welldeveloped plant communities characterized by arbor, big shrubs, lianas and parasites as the dominant life forms and key fruit, nut, drupe, follicle, caryopsis as the dominant fruit types, while dry-cold habitats are always correspond to those with shrubs, small shrubs and deciduous trees as well as capsule as the dominant life forms and fruit types. The trade-off of species relative richness between dry fruit and sarcocarp in a given plant community may be strongly influenced by the humidity level in plant' s growing seasons. In addition, plants of cone fruit types are specially favored by wet-cold habitats. A precipitation gradient is one of the decisive factors shaping the patterns of both species richness and richness of plant function types (in terms of plant stature and fruit types)among these five zonal woody plant communities in the study area, while environments with optimal hydrothermic combinations would lead to the highest diversity of fruits types.
Key words: Plant functional types    Zonal woody plant community    Hydrothermic factors    

Strong environmental gradient can shape the distribution and functional characteristics of ecosystems (Woodward, 1983; Korner et al., 1989; Karlsson, 1992), e. g., climatic gradients generate variation in species composition (Kadmon et al., 1999).The studies of plant distribution along climatic gradients may aid in predicting the responses of plant communities to global climate change (Brzeziecki et al., 1995; Huntley et al., 1995) and help in identifying areas characterized by a high conservation value and determining priorities for conservational efforts (Kadmon et al., 1999).Plant functional types are ultimately the outcomes of plants respond to environmental conditions (Jiang et al., 1999).Plantswith similar functional types exhibit similar responses to environmental conditions and have similar effects on the dominant ecosystem process (Walker, 1992; Noble et al., 1996). Different Plant functional types are expected to play different roles in terms of matter and energy processes in ecosystems. Their identifications and estimations are highly relevant to the assessment of ecosystem function (Diaz et al., 1997). Zonal plant formations are characterized by the abundance of a specific life form spectrum, irrespective of the taxa, presented in a large region of a continent.Such zones include typical animal life forms and are therefore described as biomes (Galan de Mera et al., 1999). Examples are the rain forest biome, the temperate deciduous forest biome and the evergreen forest biome.Thus, some mechanisms withwhich plants respond to an environmental gradient may also be disclosed by analyzing the patterns of plant functional types in a given biome (Guo et al., 1998;Lieberman et al., 1996;Aiba et al., 1999).

Two of the most readily demonstrated aspects in the physical and biological world are change and diversity, which basically resulted from the vicissitude of earth history (Fuller, 1972). Fruits, the unique plant reproductive organs owned only by angiosperm, were derived from the primitive ancestor in the processes of plant evolution.It is well accepted that angiosperm became the dominant plants on the earth in the Cretaceous mainly because of the occurrence of fruits.Different fruits are expected to reflect different life strategies and with different ways to deal with the environmental variations (Mabry, 2000). The pattern of fruit types in a given plant community may also be a clue to uncover the impacts of environmental changes on plant communities.

Gansu, located along the northeast margin of Qinghai-Tibetan Plateau, northwest of China, is characterized by both diverse forest vegetations and complicated physiognomic climatic types.From the south to the north, four climate types occurred, i.e., northern part of subtropical area, warm-temperate, semiarid temperate and arid area with a span of 10 latitudes and 15 longitudes(93° 25' ~ 108° 42'E, 32° 18' ~ 42° 18' N). Accordingly, subtropical evergreen-deciduous broadleaved forests, warm temperate deciduous broadleaved forests, temperate conifer-broadleaf mixed forests, cold-temperate coniferous forests as well as xeromorphic shrubs occurred respectively (Fig. 1).So, Gansu province is particularly suitable for investigating floristic pattern in relation to climatic gradients.Some information with respect to this study such as the inventory of woody plant flora were well documented in the previous studies (Institute of Northwest Botanical Research CAS, 1983; Liu, 1987; Wang, 1996; Wang et al., 1997), together with the long term accumulation of meteorological observations, which have built a solid foundation for this study.In the present paper, we try to answer two questions :⑴how do hydrothermic factorsinfluence the pattern of plant functional types in zonal woody plant communities and ⑵how do species richness, richness of plant functional types respond to a climatic gradient.

Fig.1 Study area : showing the dominant zonal woody plant communities occurred in the study area. Subregions: 1 Hexi Corridor; 2 Qilianshan; 3 Zhongbu Loess Plateau; 4 Tianshui; 5 Longnan; 6 Gannan
1 Methods

A woody plant floristic study of Gansu province provided subregion-based data sets on the distribution and abundance of wood plant species (Wang, 1995 unpublished data; Wang, 1996;Wang et al., 1997). Six woody plant floristic subregions of Gansu province have been classified, i.e., Hexi corridor, Qilianshan, Zhongbu Loess Plateau, Tianshui, Longnan andGannan.As showed by Fig. 1, woody plant communities occurred in the six subregions are xeromorphic shrubs, cold-temperate coniferous forests, temperate deciduous broadleaved forests, warm temperate deciduous broadleaved forests, subtropical evergreen-deciduous broadleaved forests, cold-temperate coniferous forests and coniferous broadleaf mixed forests respectively.Totally 1291 species of woody plants belonging to 292 genera and 94 families were recorded in the floristic study.Among them, 91 species occurred in Hexi corridor subregion, 193 species in Qilianshan subregion, 173 species in Zhongbu Loess plateau subregion, 586 species in Tianshui subregion, 594 species in Longnan subregion and 495 in Gannan subregion.Species occurred in each subregion were classified into 9 plant functional types in terms of the height of plant, instead of Raunkiaer' s classification, i.e., big arbor (>30 m in height), arbor (5 ~ 30 m), big shrub (3 ~ 5 m), shrub (1.5 ~ 3 m), small shrub (< 1.5 m)as well as lianas and parasites.Deciduous and evergreen species were also identified.

Species of each subregion were re-classified according to their fruit types.Totally 12 plant functional types in terms of fruit types (cone, legumen, capsule, achene, key fruit, nut, berry, pome, drupe, follicle, caryopsis and utricle)were recorded.Furthermore, all fruit types were separated into two types, i.e. dry fruit and sarcocarp.

Hydrothermic factors of the six subregions, including active accumulated temperatures (≥5 ℃, AT5; ≥ 10 ℃, AT10), mean annual precipitation (P), mean annual temperatures (T), were collected from six national standard weather stations of Gansu province.Humidity degree was calculated (K = Mean annual precipitation (0.1 ×≥0 ℃Accumulated temperature))(Ren et al., 1985). STATISTICA software was involved in correlation analysis on the data sets.Taking the relative species richness of functional type (species richness of given functional type total species richness of all functional types within a subregion, in %)as the variables for both regression analysis and illustrations.

2 Results 2.1 Plant functional types in terms of the stature of woody plants 2.1.1 Pattern of plant functional types

The highest richness of plant functional types in terms of the stature of woody plants occurred in Tianshui, Longnan and Gannan with big arbor, arbor, big shrub and shrub as the dominant life forms (Fig. 2). Two subregions, i.e., Zhongbu Loess Plateau and Qilianshan had fairly higher richness of plant functional types with the deciduous arbor trees and shrubs as the dominants.However, Hexi Corridor was poor in plant functional types with deciduous shrubs and small shrubs as the dominants.Lianas and parasites mainly occurred in Tianshui and Longnan and became sparse in Gannan and Zhongbu Loess Plateau.Otherwise, no lianas and parasites occurred in Qilianshan and Hexi Corridor. Deciduous types (arbors and shrubs)were dominant in all the six subregions, however, the relative richness of both deciduous trees and evergreen trees was quite different among the six subregions.The highest relative richness of evergreen species occurred in Tianshui and Longnan, then decreased in Gannan, Qianlianshan, Hexi Corridor and Zhongbu Loess Plateau (Fig. 3).

Fig.2 Patterns of plant functional types in terms of the stature of woody plants
Fig.3 Evergreen and defoliated plant functional types of 6 subregions
2.1.2 Plant functional types in terms of the stature of woody plant in relation to hydrothermic factors

Correlation analysis showed (Tab. 1)that species relative richness of arbors, lianas and parasites were positively correlated with hydrothermic factors, while negatively with that of small shrubs.The species relative richness of shrubs with the height of 1.5 ~ 3 m were negatively correlated with mean annual precipitation and mean annual temperature.

Tab.1 Correlations between the relative richness of plant functional types in terms of the stature of woody plant and hydrothermic factors

Hydrothermic factors were positively correlated with the relative richness of evergreen species while negatively with that of the deciduous species(Tab. 1).

The ratio of evergreen species to deciduous species were higher in Tianshui and Longnan, while declined in Qilianshan, Gannan and Hexi Corridor (Fig. 3). More than one factor may have determined this observed pattern, e.g., the ratio of evergreen species to deciduous species was fairly higher in Hexi Corridor than that in Zhongbu Loess Plateau, the latter, however, had relatively more optimal hydrothermic combinations than the former. In this case, the specific background of floristic origin in Hexi Corridor is expected to be responsible for the observed pattern.Plant flora of Hexi Corridor primarily originated under subtropical paleo-climatic circumstances along the paleoMediterranean shore, and the climatic aridification in the middle Asia might have driven the evolving processes of plant flora.Some evergreen shrubs such as Ephedra sp.Ammopiptanthus mongolica etc. survived the vicissitude of paleo-climate (Liu, 1982), and consequently contributed to relatively higher percentage of evergreen species in Hexi Corridor in spite of the crucial modern environmental conditions.The reasons why Tinashui and Longnan have relatively higher percentage of evergreen species may be quite different from those of Hexi Corridor.Modern environmental conditions in these subregions are fairly similar with the paleo-subtropical climates in the pre-Tertiary, which are intrinsically favorable for the development of evergreen species.

2.2 Plant functional types in terms of fruit types 2.2.1 Pattern of plant functional types

Of the 12 fruit types(Fig. 4), only 5 fruit types occurred in Hexi Corridor with capsule and utricle being the dominant fruit types.However, more than 11 fruit types were recorded in each of the other 5 subregions with little difference in the composition of fruit types (Gannan 12; Longnan and Tianshui 11, lack of utricle; Zhongbu Loess Plateau 11, lack of caryopsis; Qilianshan 11, lack of follicle). Furthermore, capsule, drupe and berry were three dominant fruit types in all subregions except Hexi Corridor. The percentage of dry fruits to sarcocarp was as high as 93 % in Hexi Corridor, declining to about 50 %(ranging from 49 % to 59 %) in the other 5 subregions (Fig. 5).

Fig.4 Patterns of plant functional types in terms of fruit types. (Only showing those fruit types with their relative richness more than 10%)
Fig.5 Variation of dry and sarcocarp fruit types in six subregions
2.2.2 Correlations between functional types in terms of fruit types and hydrothermic factors

Correlation analysis showed that (Tab. 2): humidity degree was correlated negatively with the relative richness of dry fruit species(P < 0.05), while positively with that of sarcocarp species(P < 0.05), indicating that the tradeoff between dry fruit and sarcocarp in a given woody plant communities may be strongly influenced by the availability of moisture in growing seasons.The relative richness of cone species was correlated negatively with heat factors while positively with moisture and significantly with humidity degree(P < 0.05), suggesting that cold-moist environments would be preferable for the development of cone species.The relative species richness of key fruit, nut, drupe, follicle, caryopsis were positively correlated with hydrothermic factors, among them, that of nut and drupe were significantly correlated with precipitation (P < 0.05). The relative species richness of berry was significantly correlated with humidity degree(P < 0.05), while that of capsule was negatively correlated with hydrothermic factors, indicating that capsule might have derived under cold-dry climatic conditions.In addition, the relative species richness of utricle was negatively correlated with precipitation(P < 0.05). Thus it can be seen that the micro-environmental conditions to which species with specific fruit type subjected in the long-term evolutionary processes varied markedly from one to another. The strangeness of biological evolution was well demonstrated in this case.

Tab.2 Correlations between the relative richness of functional types in terms of fruit types and hydrothermic factors
2.3 Species richness and richness of plant functional types

Both species richness and richness of plant functional types, though all increasing with increased precipitation, temperature and degree of humidity (Fig. 6), were strongly influenced by the precipitation gradient.In detail, significant regression curves were observed between species richness, richness of plant functional types (in terms of both fruit types and plant stature) and mean annual precipitation (Fig. 6a, b, c), while no significant relations existed between species richness, richness of plant functional types and mean annual temperature (Fig. 6d, e, f). The degree of humidity was also less important than precipitation except it' s significant impact on the richness of fruit types (Fig. 6g, h, i). In summary, the dynamics of precipitation was a decisive factor shaping the pattern of both species richness and richness of plant functional types of a give zonal woody plant community in the study area.

Fig.6 Regressions of species richness, richness of plant functional types in relation to the hydrothermic factors
3 Discussion 3.1 Classification of woody plant functional types

Community structures influence ecosystem function strongly, and the role of particular species in ecosystems depends largely on their density and individual size (Diaz et al., 1997). In the present paper, we classify plant function types in terms of both the average height (stature)of species as well as the life history strategy of leaf (evergreen and deciduous) and fruit types, which is different from Raunkiaer' s classification.Obviously, this classification with respect to the plant function types conducted in the present paper mainly reflects the structure traits of a given zonal woody plant community.

Plant functional types in terms of fruit types in this study were classified basically according to their morphologic characteristics.Different fruit types were expected to present different evolutional stages with respect to the plant' s systematic origination and under went different environmental vicissitude.Therefore, the analysis of fruit types may be a very important way to probe the relationship between structure and function of ecosystems.In the present paper, due to the lack of detailed and specific classifications of fruits, only 12 fruit types were identified.In fact, the magnitude and shape of a given fruit type may vary remarkably under different environments.Further study is needed on this issue.

3.2 Woody plant community structure trait under shifting climatic conditions

Species richness, richness of plant functional types changed correlatively (Fig. 6). Of the six subregions, Longnan, Tianshui and Gannan were abundant in both species richness and richness of plant functional types.Furthermore, the relative richness of arbor and big shrubs were also higher than that of the other subregions.This pattern coincided with the relatively optimal hydrothermic combinations in the three subregions.By contrary, in response to the crucial ecological conditions, Hexi Corridor was characterized by stunted stature of woody plant, lower species richness, poor assemblage of plant functional types.It can be seen that the height of woody plant species, species richness as well as the richness of plant functional types all increased with the improvement of hydrothermic factors in the studies area, agreeing with the related conclusions drawn from the studies on tropical rain forests (Lieberman et al., 1996; Duivenvoorden, 1996; Aiba et al., 1999). Therefore, we proposed that response of plant community to environmental gradient might show the same trend no matter what plant communities were involved.

It is well documented that species diversity of natural communities is often strongly related to productivity. However, the pattern of this relationship seems to vary, i.e., diversity increases or decreases monotonically with productivity or peaks at intermediate levels of productivity (Abrams, 1995). Temperature and precipitation is expected to be two key factors influencing the distribution and growth of plants.However, their relative contributions may vary with different plant communities in different area. As for the case presented by this paper, precipitation is a dominant factor shaping the magnitudes of both species richness and richness of plant functional types.If productivity refers to precipitation, the results reported here support the resource productivity-species diversity monotonic hypothesis.It is worth notice that the connotation of diversity involved in this study included not only woody plant species richness but also richness of plant functional types.So, a notion with respect to the relationship between plants and their environments is expected, i.e., the responses of plants to environmental gradients may occur in all levels of plant communities.

3.3 Plant functional types in terms of fruit types and climatic gradient

The pattern of fruit type in Hexi Corridor was quite different from those of the five other subregions, the latter, however, shared much similarity in the composition of fruit types. The cause behind these patterns was still unknown based on the present data.One of the possible explanations may be the differentiation in moisture level between them, e.g., the humidity degree in Hexi Corridor was 0.371, however, those in the other five subregions were more than 1.3 (ranging from 1.367 to 2.105). Utricle was a dominant fruit type in Hexi Corridor and it' s origination might be likely associated with the extreme dry environmental conditions in the growing seasons.

The occurrence of fruit was a very important event in plant evolution history.Fruits with different morphological or structural attributes may stand at different evolutionary levels, i.e., one might be evolved from another.Therefore, there surely exists a evolutionary sequence from the primary to derivation among all the fruit types, e.g., cone, follicle and capsule were expected to be primary fruits owned by some old families such as Magnoliaceae, Cercidiphyllaceae, Tentrocentraceae, Salicaceae etc.; achene and caryopsis were thought to be the derived fruit types owned by relative younger families such as Poaceae and Asteraceae.To clarify the evolutionary sequence of fruit would be helpful for the analyses of the pattern of fruit type of plant community and to further the study of the impacts imposed by climatic gradient on plants.Therefore, the evolutionary features of fruit types as well as the mechanism with which they respond to the environmental changes should be taken into account or emphasized in the future studies.

4 Conclusion

As for a given zonal woody plant community, the pattern of plant functional types in terms of both stature of plants and fruit types was strongly influenced by hydrothermic factors, i.e., different hydrothermic combination would lead to different patterns of plant functional types in zonal woody plant communities.

On the other hand, for the variations of both species richness and richness of plant functional types, a precipitation gradient might play a key role for the formation of the observed pattern, while mean annual temperature was less important.In addition, environments with optimal hydrothermic combinations would lead to the highest diversity of fruits types in a zonal woody plant community.

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