Ecological vegetation maps

On ecological vegetation maps, the distribution of vegetation is related to one or more features of the environment. Tolerance, competition, map scales and the environment are discussed with regard to their bearing on the geographical distribution of phytocenoses and their portrayal on maps. There are two types of ecological vegetation maps: those relating the vegetation to one environmental quality, and those with two or more such qualities. The interpretation of ecological vegetation maps is relatively simple when plant communities are related to a single quality of the biotope and difficult but usually more useful when related to several qualities. Perfection is not possible but can be approached asymptotically.     

A vegetation map of The Netherlands,based on the relationship between ecotopes and types of potential natural vegetation

Summary The method of mapping the vegetation on scale 1: 200,000 and the starting points in relation to the potential natural vegetation and ecotopes, are discussed.In view of the planological background of this study, some restrictions have been added to the concept of potential natural vegetation, concerning the period of development and the human influence.The relationship between soil, ground water and vegetation was studied, which resulted in the map of the potential natural vegetation.Each type of potential natural vegetation stands for a series of vegetation types on the same site. Seven main series, with a number of sub-series are distinguished. Within each vegetation series the plant communities have been spread over five groups, according to their structure and naturalness.Ecotopes and ecotope complexes are considered as landscape ecological units. A list of ecotopes was obtained by interpreting topographical maps and by inventory data.The actual vegetation was mapped by estimating the size of the ecotopes within the separate areas. It was expressed in a five figure code for the five groups from the vegetation and ecotopes is combined into the vegetation map of The Netherlands.Interpretation problems, some of them specific for The Netherlands, are discussed and some remarks are made on the necessity of further research.Contribution to the Symposium on Plant Species and Plant Communities, held at Nijmegen, 11–12 November 1976, on the occasion of the 60th birthday of Professor Victor Westhoff.Nomenclature follows Heukels-van Ooststroom, Flora van Nederland, 18e druk, 1975, Wolters-Noordhoff, Groningen; nomenclature of syntaxa follows Westhoff & den Held (1969)     

Late Quaternary vegetation history of the Mexican highland

Results of pollenanalytical investigations in the Highlands of Mexico (area of Puebla — Tlaxcala) are presented together with a survey of the last 35 000 years of vegetation history. After 3 pine periods from 35 000 to about 7 000–8 000 B. P., according to high and late Pleistocene condition, the Holocene vegetation history becomes more diversified: periods of alder, pine, fir and mixed oak forests alternate and end in a period of cultivated landscape.     

Brazilian vegetation on maps

The development and current status of mapping the vegetation of Brazil is discussed. This includes the manner of portraying the vegetation on maps, especially with regard to physiognomy and structure, the floristic composition and ecological relations. A slow beginning has given way to a rapid though uneven development. Recent government efforts tend to correct this.     

Classification of vegetation sequences in Toohey Forest,Queensland

In this paper we consider one method of mapping larger units identified from the spatial pattern of sequences of vegetation types. The basic data were presence/absence data for 6450 stands arranged in 90 transects. A second set of data was derived by averaging the species occurrences in non-overlapping groups of 5 stands. A divisive numerical classification was used to determine the primary vegetation units. In all, 5 different sets of primary types were derived, using different species suites, different sample sizes and different numerical methods. We briefly discuss the types identified and their spatial patterns in the area.Each of these types was then used to define a string of type-codes for every transect so that each transect represents a sample from the landscape containing information on the frequency and spatial distribution of the primary vegetation types. The transects may be classified using a Levenshtein dissimilarity measure and agglomerative hierarchical classification, giving 5 analyses of transects, one for each of the primary types discussed above. We then examine these transect classifications to investigate the stability of the vegetation landspace patterns under changes in species used for the primary classification, in size of sample unit and in method of primary classifications. There is a considerable degree of stability in the results. However it seems with this vegetation that the tree species and non-tree species have considerable independence. We also indicate some problems with this approach and some possible extensions.     

The subalpine vegetation of Mt. Vysokaya, central Sikhote-Alin

The subalpine vegetation structure of Mt. Vysokaya, the Central Sikhote-Alin, is described. This vegetation consists mainly of subalpine spruce-fir forest, a complex of subalpine meadows, shrubs, groves of Betula lanata (B. ermanii s.l.), krummholz of Pinus pumila and alpine tundras. Significant disturbances in the vegetation structure were noted, especially in the forest-tundra ecotone accompanying a sharp reduction of the belts of Betula lanata and Pinus pumila. The altitudinal level of the upper timberline reaches 1600 m a.s.l. which is 250 m less than the expected altitude calculated by Kira's warmth index. An undergrowth of scattered trees of Picea and Betula are growing up to the mountain top. Based on these data and a review of the literature, we concluded that a catastrophic lowering of the timberline and devastation of the subalpine vegetation belt occurred several centuries ago, probably as result of fires.     

Reversion of vegetation following the cessation of fertilizer application

Abstract. Tadham Moor in Somerset, England, is an exceptionally rich wetland site which has been mown for hay for many years, with stock grazing the aftermath, but with no history of any fertilizer use. A randomized blocks field experiment (1986–1989) was used to study the effects of five levels of nitrogen input treatments: 0 = control, 25, 50, 100 and 200 kg of N fertilizer per ha per yr. In Phase II of the experiment (1990–1993), each plot was split into two subplots. The allocated fertilizer treatment for the plot was continued in one, randomly selected, subplot but the treatment was discontinued in the other subplot. The experiment not only identified and quantified the changes occurring in the vegetation of hay meadows under different levels of N input, it also provided valuable insight into the dynamics of the sward upon the discontinuance of the treatments. The data for Phase II were used to estimate the time required by the changed vegetation (under different nitrogen treatments) to revert to a state comparable to that prevailing in the control plots. A method for estimating reversion times is described. The main difficulties in estimating the reversion times are identified, the choice of robust vegetation variables being critical. Reversion time estimation methods are presented and used to obtain working estimates for the four nitrogen treatments, applied for 5 yr. These estimates are 3, 5, 7 and 9 yr respectively. The validity of the estimates of 3 yr for the lowest nitrogen input treatment (25 kg /ha/yr) was checked using the available post cessation data.     

小流域林草植被控制土壤侵蚀机理研究

从坡面水动力学角度研究了坡面乔木林、草本植物和林地枯落物对坡面径流流速和动能的影响机理.结果表明,坡面径流水头损失与坡面坡度、林木密度、净雨强、坡长等有关,水头损失与林木间距(b)和树木地径(D)间的关系为:E^∝(D/b)^4/3;坡面草本植物在水流作用下易弯曲,增大水流底层的阻力,减小床面的切应力;枯枝落叶使径流速度减小,从而大大降低径流挟沙能力.对甘肃省天水市桥子东沟和桥子西沟两个对比小流域的实测单次降雨、径流、泥沙资料分析可见,在相同降水条件下,已治理小流域内的径流量、产沙量、洪峰流量、最大输沙率等指标均小于未治理小流域,说明林草植被在小流域中的涵养水源、保持水土的作用明显.     

Fuzzy systems vegetation theory

Fuzzy systems vegetation theory is a comprehensive framework for the expression of vegetation theory and conceptual models, as well as the development of vegetation analyses. It is applicable to vegetation/environment relations, vegetation dynamics, and the effects of environmental dynamics on vegetation composition. Fuzzy systems vegetation theory is a fuzzy set generalization of dynamical systems theory and incorporates a formal logic and mathematics. This paper presents the elements of fuzzy systems vegetation theory and discusses the relationship of the fuzzy systems theory to the geometric concepts generally employed in vegetation theory.     

Acceleration of vegetation succession on eroded land by reforestation in a subtropical zone

Based on field investigations in the East River basin in Guangdong Province, south China, the processes of vegetation development and vegetation succession on bare slopes with high erosion rates are studied. Different reforestation measures have been applied to the slopes, which have resulted in very different processes of vegetation development and succession. On an experimental plot with burned forest but surviving roots, the vegetation restored naturally and quickly because there was little soil erosion. However, in the plots suffering from long-term severe soil erosion, natural vegetation recovery on these barren slopes is very slow. After 26 years, a barren slope has only been partly colonized by poorly developed vegetation composed of heliophilous herbages and scattered shrubs. On the other hand, plantation of some selected wood species on the slope land has dramatically accelerated the vegetation recovery and succession. The plots were reforested with plantation of Acacia auriculiformis in the early 1980s. Twelve years later, the vegetation cover of the artificial forests reached 90% and an understory vegetation community consisting of local species had naturally developed. Reforestation with suitable strategies may control erosion and greatly accelerate vegetation succession in the eroded slope land in the subtropical zones.     

Objective classification and analysis of vegetation data

A program package is described in which vegetation data can be objectively classified and analysed. Classification is based on minimum entropy. Results show that in a comparison with TWINSPAN, improvements to the relevé sequence, in terms of community variation, can be obtained. Furthermore, TWINSPAN classifications are shown to be dependent on a particular relevé input sequence.     

植被砍伐对土壤养分的影响

研究了不同砍伐频率下,香港、深圳和鹤山研究样地山坡地Ｎ、Ｐ、Ｋ含量的差异．不同采样地之间,养分全量和有效量差异显著．在尚未砍伐的山坡地,土壤养分含量显著高于经常砍伐的山坡地．未伐土壤的Ｎ含量顺序为香港样地＞深圳样地＞鹤山样地．下层土壤Ｐ的含量高于上层土壤．深圳样地常代土壤养分含量高于鹤山．结果建议采用最适砍伐频率和在最适季节砍伐,以便减少砍伐产生的不利影响．     

Patterned vegetation and rainfall intermittency

We study a mathematical model for the dynamics of patterned dryland vegetation in the presence of rainfall intermittency, adopting a spatially explicit approach. We find that most results found for constant precipitation carry over to the case of intermittent rainfall, with a few important novelties. For intermittent precipitation, the functional forms of the water uptake and consequently of the vegetation growth rate play an important role. Nonlinear, concave-up forms of water uptake as a function of soil moisture lead to a beneficial effect of rainfall intermittency, with a stronger effect when vegetation feedbacks are absent. The results obtained with the explicit-space model employed here are in keeping with those provided by simpler, implicit-space approaches, and provide a more complete view of vegetation dynamics in arid ecosystems.     

On the dynamics of vegetation: Succession in model communities

Summary Successional change is thought to be at least partially driven by forees originating from within the community, namely by reaction and competition. Both processes operate through changes in the environment, but from the literature on the subject it is not clear how they differ.To clarify these issues successiens of model communities are studied. This leads us to conclude that competition represent an instantaneous interaction, whereas reaction has historical aspects since it relies on cumulative changes in the environment. The three models considered-one relying on reaction to cause vegetational change, one relying on competition and differential growth rates, and a hybrid third one-yield very similar predictions: roughly bell-shaped curves displaced along the time axis. This shows that the mere fit of a certain model to successional data may easily be spurious (recently some workers have empirically fitted models identical to one derived here from first principles). The three models do behave radically different under perturbation, however: any model relying completely or partially on historical interactions cannot account for the well known possibility of artificially arresting succession. Even if the importance of historical interactions in succession (i.e. the Markovian character of succession) cannot easily be ascertained, one can nevertheless ask whether historical interactions are at all necessary for the explanation of successional change. It is argued here that succession can be entirely understood in terms of instantaneous interactions, notably competition. The argument rests upon the well known relationship between colonizing and competitive ability, and on the fact, proven here, that stress, defined as expressing itself in severe random fluctuations in the growth parameters, is negatively correlated with competition intensity.The author gratefully acknowledges the critical support be received from Professor László Orlóci. This paper forms part of a wider research program supported by a NCR grant to Proc. Orlóci.     

Linking habitat modification to catastrophic shifts and vegetation patterns in bogs

Paleoecological studies indicate that peatland ecosystems may exhibit bistability. This would mean that these systems are resilient to gradual changes in climate, until environmental thresholds are passed. Then, ecosystem stability is lost and rapid shifts in surface and vegetation structure at landscape scale occur. Another remarkable feature is the commonly observed self-organized spatial vegetation patterning, such as string-flark and maze patterns. Bistability and spatial self-organization may be mechanistically linked, the crucial mechanism being scale-dependent (locally positive and longer-range negative) feedback between vegetation and the peatland environment. Focusing on bogs, a previous model study shows that nutrient accumulation by vascular plants can induce such scale-dependent feedback driving pattern formation. However, stability of bog microforms such as hummocks and hollows has been attributed to different local interactions between Sphagnum, vascular plants, and the bog environment. Here we analyze both local and longer-range interactions in bogs to investigate the possible contribution of these different interactions to vegetation patterning and stability. This is done by a literature review, and subsequently these findings are incorporated in the original model. When Sphagnum and encompassing local interactions are included in this model, the boundaries between vegetation types become sharper and also the parameter region of bistability drastically increases. These results imply that vegetation patterning and stability of bogs could be synergistically governed by local and longer-range interactions. Studying the relative effect of these interactions is therefore suggested to be an important component of future predictions on the response of peatland ecosystems to climatic changes.     

GEMI: a non-linear index to monitor global vegetation from satellites

Knowledge about the state, spatial distribution and temporal evolution of the vegetation cover is of great scientific and economic value. Satellite platforms provide a most convenient tool to observe the biosphere globally and repetitively, but the quantitative interpretation of the observations may be difficult. Reflectance measurements in the visible and near-infrared regions have been analyzed with simple but powerful indices designed to enhance the contrast between the vegetation and other surface types, however, these indices are rather sensitive to atmospheric effects. The correction of satellite data for atmospheric effects is possible but requires large data sets on the composition of the atmosphere. Instead, we propose a new vegetation index which has been designed specifically to reduce the relative effects of these undesirable atmospheric perturbations, while maintaining the information about the vegetation cover.     

秦岭石瓮山地植被研究

石瓮山地共有野生种子植物113科,421属,813种。其植物区系具有地理成分复杂、分布类型多样、温带性质强烈、区系起源古老、特有现象明显的特点。植被类型多样,有3个植被型组、9个植被型、10个植被亚型、16个群系组和41个群系。     

广州城市绿地系统景观异质性分析

选用景观多样性等7个指数对广州城市绿地景观异性质进行了分析.结果表明,广州绿地斑块密度和绿廓道密度分别为118和187km·km-2,在老城区绿地具有斑块小,破碎度大,多样性高,以随机分布为主的高异质性空间结构;在新城区,绿地斑块大,以均匀分布为主,因此,在同等大小的区域内,这类绿地空间结构更能提高景观的异质性,更有效地发挥绿地的生态功能