Climate and vegetation in China V. Effect of climatic factors on the upper limit of distribution of evergreen broadleaf forest

In order to clarify correlations between the upper limit of distribution of evergreen broadleaf forest and climatic factors, 62 stands distributed at the upper limit of the forest were collected from various parts of China, and their thermal and precipitation factors were estimated. Among six thermal climatic indices, i.e., warmth index (WI), coldness index (CI) and annual mean (AMT), January mean (JMT), mean minimum (MMT) and minimum (MT) temperatures, the CI at the stands showed the smallest range of variance, and it was therefore considered to be the most significant for interpreting the upward distribution of the forest. However, the distribution of the forest in mountain areas in southwestern China could not be explained by lower temperatures in winter such as CI but by a cumulative temperature such as WI. The continentality and precipitation factors were also important for delimiting the distribution of the forest. In addition, the relation between the distribution of the forest and the MMT was noted, and it was concluded that the MMT was an effective thermal index for explaining the upper limit of distribution of evergreen broadleaf forest in China.     

Seasonal changes of root hydraulic conductance (KRL) in four forest trees: an ecological interpretation

This paper deals with the possibility of relating root hydraulic parameters to an ecological index describing the continentality/oceanicity of four forest trees. Root hydraulic conductance ($K_R$) of seedlings of Fagus sylvatica L., Quercus ilex L., Quercus suber L. and Quercus pubescens Willd. was measured in May, August and November 1996. $K_R$ was calculated in terms of the relation of the water flow through intact root systems in situ measured with the pressure chamber, and the pressure driving the flow. The sufficiency of the root system to supply the foliage was estimated by dividing $K_R$ by the seedlings leaf surface area ($A_L$) thus obtaining $K_RL$. In the spring, $K_RL$ was largest in F. sylvatica and smallest in Q. pubescens with intermediate values recorded in Q. ilex and Q. suber. All the species studied showed a large decline in $K_RL$ just prior to the winter rest except for Q. suber which mantained $K_RL$ approximately constant through the period of study. In most cases, $K_RL$ changed in accordance with analogous changes in the flow. When the total seedlings' leaf surface area ($A_L$) was plotted versus $K_RL$, it appeared that $K_RL$ of Q. pubescens increased with $A_L$, proportionally, while $K_RL$ of F. sylvatica was inversely related to $A_L$. This, together with the largest $K_RL$ recorded in the summer in Q. pubescens, was interpreted as advantageous to this species (which is adapted to semi-arid environments) in that: (a) roots could supply water to foliage efficiently even during the adverse season and (b) the foliage growth could be sustained even in summer.No statistically significant relation of $K_RL$ to the continentality index calculated for the four species studied on the basis of their European distribution, was found to exist. Nonetheless, our data appear to be encouraging for future research aimed at better interpreting the typical distribution areas of plant species.     

Windchill influence on thermal conditions in North Patagonia

The occurrence of windy conditions in Patagonia is well known. However there has been little attempt made concerning the wind cooling effect in the area. Because of windchill, equivalent temperatures may be quite different to the actual temperature. In Patagonia, constancy and wind strength determine a yet unexplored bioclimatic factor. This paper deals with windchill and the resulting equivalent temperatures in Puerto Madryn, Chubut, North Patagonia. This location may be considered as having the most favourable thermal conditions south of latitude 42°S, being a sheltered place near the sea-shore. Hourly values of windchill were calculated using Steadman's formula, based on records over 11 years. The results show that, even in such favourable conditions, windchill is an important feature of the Patagonian climate, and is perceived as being cooler than it actually is.     

Climatic determinism in phytogeographic regionalization: A test from the Irano-Turanian region,SW and Central Asia

This study investigates the role of climate in determining phytogeographic regions, focusing particularly on the Irano-Turanian floristic region in SW and Central Asia. A set of simple climatic variables and bioclimatic indices were used to prepare climate-space scatter plots and climate diagrams. The climate data were also subjected to multivariate analyses (PCA and Regression tree) in order to develop a bioclimatic characterization of the Irano-Turanian region in comparison with the adjacent Mediterranean, Saharo-Sindian, Euro-Siberian, and Central-Asiatic regions. Phytogeographic regions of SW and Central Asia display distinct bioclimatic spaces with small overlaps. The Irano-Turanian region is differentiated from surrounding regions by continentality, winter temperature, and precipitation seasonality. Continentality is the most important bioclimatic factor in differentiating it from the Mediterranean and Saharo-Sindian regions and is responsible for floristic differences among sub-regions of the Irano-Turanian region. In our case study, the Irano-Turanian region is a nearly independent bioclimatic unit, distinct from its surrounding regions. Hence, it is suggested that the term “Irano-Turanian bioclimate” be used to describe the climate of most of the continental Middle East and Central Asia. Among different sub-regions, the west-central part of this floristic region (“IT2 sub-region”) is a major center of speciation and endemism. Our case study demonstrates that climate is a primary determinant of phytogeographic regionalization. Although modern climate and topography are strong control parameters on the floristic composition and geographical delimitation of the Irano-Turanian region, the complex paleogeographic and paleoclimatic history of SW Asia has also influenced the Tertiary and Quaternary evolution of the Irano-Turanian flora, with additional impacts by the long-lasting historic and present land-use in this region. Many Irano-Turanian montane species are threatened by global warming, and particular conservation measures are needed to protect the Irano-Turanian flora in all sub-regions.     

Climatic gradients within temperate Europe and small-scale species composition of lichen-rich dry acidophilous Scots pine forests

We investigated patterns in community composition in Central-European lichen-rich pine forests along a macroclimatic gradient, using two plot sizes. Diversity of lichens, especially the number of boreal and subatlantic taxa per plot increased from southern Slovakia to northern Poland (Baltic Sea). The ecological indicator value for continentality was highest in two inland regions which were characterised by low winter temperatures. Principal coordinates analysis sorted the regions along two major compositional gradients of similar importance, one mirroring the south-to-north gradient and correlating with the Gorczyński index of thermal continentality, and a second correlating with lowest winter temperature. Regional differences driven by macroclimate were the most important determinant of species composition even in small plots. Continentality was of primary importance in assembling terrestrial lichen communities, but its particular components acted differently. Lowest winter temperature appeared to be well connected with ecological meaning of continentality, which is expressed among others in ecological indicator values.     

Linking Forest Fire Regimes and Climate—A Historical Analysis in a Dry Inner Alpine Valley

Forest fire regimes are likely to experience considerable changes in the European Alps due to climatic changes. However, little is known about the recent regional fire history and the impact of local climate on the fire regime during the 20th century. We therefore reconstructed the fire history in a dry continental valley of the Swiss Alps (Valais) over the past 100 years based on documentary evidence, and investigated the relationship between the reconstructed fire regime and the local climatic variability. We compared the impact of temperature, precipitation, drought and dry foehn winds on fire frequency, extent of burnt area, and fire seasonality on various spatial and temporal scales. In the subalpine zone, the fire regime appears to have been mainly driven by temperature and precipitation, whereas these variables seem to have played only a secondary role in the colline–montane zones. Here, foehn winds and, probably, non-climatic factors seem to have been more important. Temperature and precipitation played a major role in shaping fire frequency and burnt area in the first half of the 20th century, but lost their importance during the second half. Our case study illustrates the occurrence of different fire regime patterns and their driving forces on small spatial scales (a few hundred square kilometers). We conclude that the strong rise in temperature over the past century has not profoundly changed the fire regime in Valais, but in the second half of the 20th century temperature was no longer a strong determinant for forest fires as compared to human activities or biomass availability in forests. Author contributions: T.Z., H.B., M.C., and M.B. conceived of or designed study; T.Z. performed research and analyzed data; T.Z., H.B., M.C., and M.B. wrote the paper.     

Gradient analysis of dry grassland vegetation in Denmark

Abstract. We present a gradient analysis of 620 vegetation samples covering most of the floristic and environmental variation in semi‐natural grassland vegetation on well‐drained soils in Denmark. Vegetation was sampled using frequency in subplots. Explanatory variables were surface inclination, aspect, pH, geographical co‐ordinates together with indications of soil type. Detrended Correspondence Analysis revealed four floristic gradients that could be interpreted in ecological terms by measured variables supplemented with site calibrations based on weighted averaging of Ellenberg's indicator values. All four axes were interpreted using rank correlation statistics, and linear and non‐linear multiple regression of sample scores on explanatory variables. The first gradient was from dry calcareous to humid acidic grasslands; the second reflected an underlying gradient in fertility; the third reflected regional differentiation and the fourth was associated with variation in intensity of competition as indicated by association with calibrated Grime‐CSR values for the plots. We applied subset ordination to the data as a supplement to traditional permutation and correlation statistics to assess the consistency of ordination results. DCA axes 1 and 2 were consistent in space and time. This gradient analysis is discussed in a context of plant strategy theory and species diversity models. Ecocline patterns lend support to the view that grazing not only favours the ruderal strategy but also the stress‐tolerant strategy. The low rank of competition as an explanatory variable for the floristical gradients supports the notion that competitive effects play a subordinate role for species composition compared to microclimate and soil conditions in infertile semi‐natural grasslands.     

Climatic discrimination of Mediterranean broad-leaved sclerophyllous and deciduous forests in central Spain

Abstract. Climatic differences between three types of deciduous (Quercus pyrenaica) and three types of sclerophyllous (Quercus rotundifolia) Mediterranean forests in the Spanish Sistema Central were analyzed by means of Canonical Discriminant Analysis and Jancey's Discriminant Analysis, applied in successive steps to data from 252 meteorological stations. Climatic data included temperature and precipitation records as well as bioclimatic indices. Discriminant analysis was applied to broad-leaved sclerophyllous and deciduous forest communities sampled at each meteorological station using phytosociological methods. Annual and seasonal (summer, spring) water availability are the most important factor controlling the distribution of the two physiognomic forest types; southwestern associations of Quercus pyrenaica and Q. rotundifolia differ from their colder homologues by annual and monthly temperatures; western associations were separated from eastern ones in terms of annual and seasonal precipitation gradients. Discriminant analysis was a good technique to explore climatic gradients not shown by other general ordination or classification methods.     

Ellenberg indicator values for macromycetes – a methodological approach and first applications

Ellenberg indicator values (EIVs) describe the realized niche of species and habitat parameters, and are commonly used for vascular plants, bryophytes, and lichens. We provide a methodology for EIVs and an EIV list for nearly 650 species of macromycetes. We propose a new EIV scale, namely substrate openness (O). We also give the results of two applications and compare EIV values related to the Red List classification with those related to lifestyle classification. Mycorrhizal species on average have higher demands on substrate openness and are less tolerant of high nutrient levels than saprotrophic or parasitic species. Critically endangered species have on average distinctly higher demands on openness of habitat and substrate than not threatened or less strongly threatened species, which in turn have higher demands for nutrient availability. This pattern clearly highlights the points of threat for many macromycete species.