bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in soil characteristics in eucalypt plantations replacing natural broad‐leaved forests
Authors: Bargali S. S. , Singh R. P. , Joshi Mukesh
Published: May 2006

Properties of the top 30 cm of soil under plantations of 1‐yr to 8‐yr old Eucalyptus (the hybrid E. tereticornis) and in adjacent natural mixed broad‐leaved forest were compared in the sub‐tropical zone of the central Himalaya. Various soil‐physical characteristics decreased with increasing age; soil‐chemical properties, notably organic carbon, total N, P and K decreased as a result of reforestation with Eucalyptus and further decreased with increasing age of the plantation.
Vegetation‐environment relationships in a Negev Desert erosion cirque
Authors: Ward David , Olsvig‐Whittaker Linda , Lawes Michael
Published: May 2006

The relationship of desert vegetation to topographic and edaphic factors in Makhtesh Ramon, an erosional cirque in the Negev Desert of Israel, was analyzed using redundancy analysis ordination. Altitude and geological substrate had the most significant correlations with vegetation patterns. In particular, significant and monotonic increases in both total species richness and the percentage of annual species were found with increasing altitude. A comparison was made of the effectiveness of Whittaker's diversity sampling plots (Shmida 1984) versus the log‐series survey method of McAuliffe (1990). We concluded that at small sample sizes, the Mc Auliffe plots were more likely to yield interpretable ordination results, even though they included only the perennial flora.
Tree seedling development in tropical dry abandoned pasture and secondary forest in Costa Rica
Authors: Gerhardt Karin
Published: May 2006

Development of planted seedlings of four canopy tree species in recently abandoned pastures (mown and unmown) and in ca. 40‐yr old secondary dry forest in Guana‐caste National Park, Costa Rica, was studied from July 1989–June 1992. The species were the light‐demanding Cedrela odorata and Swietenia macrophylla, and the shade‐tolerant Hymenaea courbaril and Manilkara chicle. Seedling mortality was high and primarily correlated with dry season drought. After the first dry season, M. chicle and C. odorata showed < 5 % survival in the pasture and 20 % in the forest, but after 3 yr survival had decreased to 3% in all plots. Survival of S. macrophylla was highest in the mown pasture (45 % after 3 yr) and lowest in the forest (10 %). For H. courbaril, survival was 40–55 % under all three conditions.

Growth rates were low, with a height increment of < 15 cm/yr, possibly due to low precipitation in 1990 and 1991. All species grew taller in the pasture than in the forest.

Differences in soil depth, texture and drainage appeared to contribute to variation in the results both within and between plots. Herbivory contributed to the lower survival of C. odorata and S. macrophylla in the forest.
A two thousand year history of a northern Swedish boreal forest stand
Authors: Bradshaw Richard H. W. , Zackrisson Olle
Published: May 2006

Abstract. Successional processes within northern Swedish boreal forest are investigated for the last 2000 years by analysis of pollen, charcoal fragments and insect remains preserved in a deep mor humus layer on a small island in a large lake. Frequent disturbances by fire, blow‐down, insect attack and flood have been the chief influence on vegetation dynamics. The gradual climatically induced replacement of Betula pubescens by Picea abies is superimposed on the disturbance dynamics. Picea first became established during the Little Ice Age, which was the longest period without fire in the record. A thin layer of volcanic ash from Iceland confirms the chronology at the onset of the Little Ice Age. The present importance of Pinus sylvestris and Ericaceae on the island is a product of a recent increase in disturbance frequency. The disturbance regime ensures that the communities stay in equilibrium with prevailing climate.
Fine‐grain pattern in Southern Cape plateau forests
Authors: Midgley J. , Seydack A. , Reynell D. , McKelly D.
Published: May 2006

Abstract. Regeneration levels, size class distributions and a nearest neighbour technique were used to describe apreliminary dynamics frameworkfortheplateauforests. Taken over a large area, most of the canopy dominants have a negative exponential distribution of stems > 10 cm dbh per size class. In small (0.04 ha) plots, if present as more than one stem, most species are present as both canopy (> 25 cm dbh) and understorey (10–15 cm dbh) individuals. The canopy dominants maintain their rank in the bank of advance regeneration (> 5 cm height < 10 cm dbh). However, relative numbers of all regeneration of most canopy individuals are not strongly correlated with canopy closure or local abundance of conspecific adults. The mean area of nearest neighbour polygons of canopy individuals around saplings of the more common species are small.

In conclusion, most species appearto be shade tolerant and locally persistent conferring a fine grain on this forest. We support recent questioning of universality of the gaps/non gaps paradigm.
Nutrient utilization in Quercus leucotrichophora and Pinus roxburghii seedlings at five soil fertility levels
Authors: Singh S. P. , Bisht Kiran
Published: May 2006

Abstract. Nutrient utilization and growth performance of Pinus roxburghii Sarg. and Quercus leucotrichophora A. Camus, the two major forest trees of the Central Himalaya Mountains between 1000 and 2000 m elevation, were analysed at different nutrient levels. The early successional P. roxburghii occurs naturally on nutrient‐poor sites and the late successional Q. leucotrichophora on nutrient‐rich sites. Seedlings of these two species were grown both in monoculture and mixed, in plastic bags containing 1 kg soil and representing five levels of nutrients (NPK) in a 12 : 32 : 16 ratio.

The P. roxburghii seedlings showed significantly greater nutrient extraction efficiency (nutrient unit extracted by seedlings per nutrient unit in the soil) than the Q. leucotrichophora seedlings, and this difference was increased in interspecific competition, particularly at the higher nutrient levels. In interspecific competition the extraction efficiencies of P. roxburghii for N, P and K were distinctly higher than those of Q. leucotrichophora. This we consider to be the main reason for the replacement of Q. leucotrichophora by P. roxburghii, even on nutrient‐rich soils, after disturbance and subsequent increase in light availability. In both the species, re‐translocation of nutrients from senescing leaves declined with increasing soil fertility. For example, re‐translocation for P. roxburghii was 49% N, 30% P and 32% K at the lowest soil fertility, and 20% N, 8% P and 13% K at the highest soil fertility.
Vegetation and soil seed bank of successional stages in tropical lowland deciduous forest
Authors: Rico‐Gray Victor , García‐Franco José G.
Published: May 2006

Abstract.We studied vegetation structure and soil seed bank composition in different successional stages of secondary lowland tropical deciduous forest in Yucatán, Mexico. The series of study sites includes: slashed (S), slashed‐and‐burned (SB), and regenerating for 1, 6, 10, 15, 30, 40 and 100 yr. Species richness (S= 42 ‐ 65), evenness (E= 0.32 ‐ 0.38), and diversity (H'= 1.2 ‐ 1.6) do not vary much as the forest grows older. 20 species of shrubs and trees were present in at least six of the seven regrowth years studied; 10 of these account for more than 50% of the total density values per regrowth year. These species dominate the vegetation due to their capacity to withstand repeated fire and felling. One third of the individuals sampled had regenerated from coppiced shoots. Species composition little resembles that in earlier accounts. The area is now largely covered by young regrowth stages (1 ‐ 20 yr). Species constituting the original woody structure of the mature forest are rare or absent due to the lack of seed sources and failure of dispersal (which is due to limited dispersal capacities), lack of dispersal agents, or long distances. Herbs were the most important life form in the soil seed banks; only one tree species was found. The number of viable seeds varied between sampled areas: 70/m2in the 40 yr‐old, to 1 815/m2in the slashed‐and‐burned (SB). The vegetation of S‐ and SB‐areas was the same, but the number of viable seeds germinating in SB was twice the number in S; the number of species in the seed bank is the same for both areas. We speculate that fire modifies species dominance early in succession, allowing seeds of some species to germinate in great numbers.
Vegetation changes on formerly overgrazed hill slopes in semi‐arid central Tanzania
Authors: Backéus I. , Rulangaranga Z.K. , Skoglund J.
Published: May 2006

Abstract. Composition of hill slope vegetation was studied in a semi‐arid part of upland Tanzania where all grazing had been banned for 12 yr. The hills had been severely overgrazed previously and suffered from heavy gully and sheet erosion. Eight vegetation types are described. Floristic gradients revealed by numerical ordination techniques were found to be related mainly to degree of erosion, soil type and succession. The more or less bare soil that prevailed after grazing had ceased is now covered by grassland, woodland and immature secondary forest. The grasslands are still characterized by early successional species and they will probably remain open grassland as long as frequent burning continues. Brachystegia woodlands may have developed during earlier periods when the field layer was sparse due to grazing. The grazing had reduced the frequency of fire which in turn promoted the establishment of Brachystegia spp. Secondary forests are believed to have developed mainly where fires were not frequent, particularly at higher altitudes.
Stem growth and canopy dynamics in a world‐wide range of Fagus forests
Authors: Peters Rob , Poulson Thomas L.
Published: May 2006

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.
Elevational distribution of conifer‐broadleaved hardwood forests on South Island, New Zealand
Authors: Allen Robert B. , Reif A. , Hall G. M. J.
Published: May 2006

Constrained canonical correspondence analysis was used to compare the elevational distribution of conifer‐broadleaved hardwood forests at nine localities on South Island, New Zealand. Elevations of individual species were compared using cover‐weighted mean elevations and cover‐weighted standard deviations of mean elevation. Mean elevations of floristically similar stands declined with latitude, but was also lower at a locality with a granite substrate than at an adjacent locality with a schist substrate. The mean elevation breadth of frequent species (those in >5% of stands) was greatest at a locality underlain by schist and least at a locality underlain by granite. This is consistent with wide habitat breadth for species in early successional stages, because forest underlain by schist is more frequently disturbed than forest underlain by granite. Elevation breadth of frequent species was less, and species' turnover greater, in South Island conifer‐broadleaved hardwood forests than in conifer forests at similar latitudes in the Southern Rocky Mountains, USA.
Gap structure, disturbance and regeneration in a primeval Picea abies forest
Authors: Liu Qinghong , Hytteborn Hakan
Published: May 2006

We investigated patterns of disturbance and recovery in Fiby urskog, a primeval spruce (Picea abies) forest, situated south of the border between the Boreo‐nemoral and Boreal regions in East‐central Sweden. The main types of disturbances are storm damage, fungal infection and insect attacks. The response of the different tree species varied and the mode of tree‐fall depended on the different combinations of disturbance agents. The DBH distributions of gap creators and gap‐border trees were almost the same. There was a high age diversity (100–240 yr) among the fallen trees. We concluded that all canopy trees (DBH > 20 cm) had the same probability of being felled by storms, irrespective of their age and DBH.

According to an estimate along transect lines, gaps made up 31% of the spruce forest area. Individual gap sizes ranged from 9 m2 to 360 m2, but 83% of the gaps were < 150 m2. The varied age structure of logs in individual gaps indicated that gap enlargements were common. 96 tree‐falls were observed on four days with an hourly mean wind speed > 12.0 m/s; all trees fell in the direction of the wind. However, when we consult the 30‐yrrecord(l 959–1989)ofthemeanhourly wind speed >12.0 m/s, it is clear that the pattern of storm‐directions does not match the pattern of orientation of fallen logs.

The present disturbance regime and the predominance of small gaps were more favourable for the regeneration oí Picea abies than of light‐demanding tree species. In one large, 2900 m2 gap, not crossed by the transects, all the major tree species had established within 7 yr, suggesting that classical succession in the sense of complete species replacement or ‘relay floristics’ didnot occur. Our observations seem rather to fit the ‘initial floristic’ model. Estimates of turnover time ranged from 170 to 228 yr, depending on the method used.
Forest gap formation and closure along an altitudinal gradient in Tongariro National Park, New Zealand
Authors: Ogden J. , Fordham R. A. , Pilkington S. , Serra R. G.
Published: May 2006

24 treefall gaps accumulated over a 10 year period along an altitudinal transectcovering 4.6ha on Mt. Hauhungatahi, Tongariro National Park, New Zealand were described quantitatively in terms of the area of damage (‘expanded gap’), the canopy opening (‘Tight‐gap’) and the size of the root mound. Tree mortality and branch loss following cyclone Bola, 1988, were recorded. In each gap saplings were ranked by species according to their vigour. Pre‐gap and post‐gap vertical and horizontal branch growth rates were calculated. Effects in the subalpine forest (> 1050 m) were compared with those in the montane zone.

Tree mortality was highly episodic, associated with major storms, and patchy. Falling canopy trees destroyed, on average, 1.3 additional trees (> 10 cm diameter at 1 m). About half the trees were uprooted and the remainder broken off. Uprooted angiosperm (canopy) trees frequently resprouted from their bases, gymnosperms rarely. Expanded gap area averaged 56 m2 in the sub‐alpine forest and 88 m2 in the montane zone. Median expanded gap areas were about twice those of light gaps. Gap size frequency distribution was highly skewed. The largest gap was formed by a single Dacrydium cupressinum which destroyed six other trees creating a gap of ca. 0.03 ha.

Expanded gaps, light gaps, and root mounds comprised 4.5, 2.8 and 0.1 % of the forest area in the sub‐alpine zone, and 3.8, 2.5 and 0.06 % in the montane forest. These values represent 10 years of accumulation, and imply light gap ‘return times’ of 360 years for the sub‐alpine and 400 years for the montane forest. These periods are in agreement with the known longevities of the canopy and emergent trees.

Vertical shoot growth rate was about twice that in the horizontal plane, and both increased following gap formation. The relative increase was greatest in the subalpine forest. Using the measured growth rates it is estimated that gaps of median dimensions are filled by lateral extension growth in 31–44 yr. Saplings require longer to reach the mean canopy height and consequently require large (multiple tree) gaps or sequential gap events.
Effects of fern thickets on woodland development on landslides in Puerto Rico
Authors: Walker Lawrence R.
Published: May 2006

Abstract.Thicket‐forming ferns are common colonizers of disturbed habitats in the tropics, but little is known about their ecology. The effects of thickets formed by the fernDicranopteris pectinataon tree seedlings on five landslides in the Luquillo Experimental Forest in northeastern Puerto Rico were both positive and negative. Soil moisture and total soil N were higher under fern thickets than in adjacent open areas and soil bulk density and soil surface temperatures were lower. Germination of seeds of the treeCecropia schreberianawas higher for seeds sown under fern thickets than for those sown into adjacent open areas. Tree seedlings ofTabebuia hetero‐phyllaexhibited a threefold reduction in photosynthesis under ferns, probably resulting from a twelvefold reduction of photosynthetic photon flux density. Growth ofTabebuiaseedlings was reduced under ferns but the distribution of seedlings of naturally occurring woody plants was not strongly correlated with the presence of fern thickets. Although fern thickets on low‐nutrient landslide soils appear to facilitate germination, they inhibit growth of tree seedlings and may, therefore, delay forest development on landslides in Puerto Rico.
A 30000 year record of vegetation dynamics at a semi‐arid locale in the Great Basin
Authors: Nowak Cheryl L. , Nowak Robert S. , Tausch Robin J. , Wigand Peter E.
Published: May 2006

Abstract.Plant macrofossils extracted from fossil woodrat(Neotomaspp.) middens at a single locale in the northwestern Great Basin were used to examine vegetation dynamics during the last 30 000 yr. Although the modern assemblage of xeric species at the study site is a recent occurrence, a large proportion of the modern plant taxa near the study locale were also found 12 000 ‐ 30 000 yr BP. The persistence of extant species through time was likely facilitated by within‐species genetic diversity and the formation of coenospecies. The diverse topographic and microhabitat features in the northwestern Great Basin also allowed different species to coexist during glacial periods. Changes in species composition occurred during two time intervals: 20 000 ‐ 30 000 and 10 000 ‐ 12 000 yr BP. Vegetation changes during 20 000 ‐ 30 000 yr BP were cyclic; community composition oscillated between two groups of taxa. Vegetation changes between 10 000 ‐ 12 000 yr BP occurred during the Pleistocene‐Holocene transition and were largely directional from the Pleistocene assemblages through two transition assemblages to a Holocene assemblage. These changes in species composition generally reflect changes in climate. The presence of relatively mesic species during 10 000 ‐ 30 000 yr BP is consistent with the regional late‐Pleistocene climate, and the gradual loss of relatively mesic species during the Holocene parallels the change to a more xeric climate. Contrasted with other areas of North America and Europe, the magnitude of vegetation changes at our study area were relatively small. Furthermore, the persistence of many species through time at this site in the northwestern Great Basin also differs from results at other study sites in North America and Europe. These differences are probably related to land form characteristics and genetic diversity within species.
Species‐environment patterns of forest vegetation on the uplifted reef limestone of Atiu, Mangaia, Ma'uke and Miti'aro, Cook Islands
Authors: Franklin Janet , Merlin Mark
Published: May 2006

Abstract. We examined woody species composition and its relation to environmental variables in native forest growing on four limestone islands in the southern Cook Islands: Atiu, Mangaia, Ma'uke, and Miti'aro. Relative dominance (percent basal area) of woody species in 74 sites was sampled using the point‐centered quarter method, and the data were analyzed using clustering and ordination techniques. These tropical forests have a relatively low diversity of native woody species (32 native and 10 introduced species occurred in our sites). Four forest types were recognized: Pandanus/Guettarda littoral forest (with several subtypes), Hernandia nymphaeifolia littoral forest, Barringtonia littoral forest, and makatea forest (dominated by Elaeocarpus tonganus and Hernandia moeren‐houtiana). These types were related, using canonical correspondence analysis, to geographical attributes (wind‐wardness, elevation, and proximity to the coast or roads) that served as surrogates for environmental variables (maritime influence, soil variation, and degree of human disturbance). The eigenvalues for this direct ordination were much lower than for indirect ordination (0.32 vs. 0.71 for the first axis), indicating that the measured geographical attributes could explain only a modest portion of the compositional variation.
Effects of fire on forest dynamics in southern Switzerland
Authors: Delarze R. , Caldelari D. , Hainard P.
Published: May 2006

Abstract. We analysed the influence of fire on species composition, floristic diversity and indicator values of the vegetation in forests of the Canton Ticino (South Switzerland). Both frequency of fire and time since last fire were taken into account using variance analysis. Results show a strong interaction of these two parameters, i.e. the reaction of the vegetation after a fire depends on the frequency of past fires. A rapid recovery is generally observed after fire, involving both herbaceous and woody species. However, a long‐term tendency towards floristic and edaphic impoverishment is observed with increasing frequency of fires. This phenomenon appears to be linked to the progressive dominance of a few fire‐tolerant species.
A method for studying dead bole dynamics in Pinus contorta var. latifolia ‐ Picea engelmannii forests
Authors: Johnson E. A. , Greene D. F.
Published: May 2006

Rates of decomposition were determined for the boles of Pinus contorta var. latifolia Engelm. and Picea engelmannii Parry ex. Engelm. in five lower subalpine forest stands in the Southern Canadian Rocky Mountains. Stands ranged in age from 58 to 222 yr since last fire. The date of death of standing dead and fallen boles was determined by cross‐dating their ring‐width patterns to stand master ring‐ width chronologies. Boles could be dated which had been dead for up to 35 years in a 58‐yr old stand and 100 yr in a 222‐yr old stand.

An empirical relationship between mass density and diameter of live trees was used to predict the mass density at death for trees already dead. The falling rate of dead standing boles was estimated from the dead bole's time of death and whether it was standing or on the ground at the time of observation. The falling rates for both Pinus contorta and Picea engelmannii ranged from 0.020 to 0.064/yr falling with most stands in the 0.050 range. No effect of size was found on the falling rate probably as a result of the small size of the boles (< 20 cm). Because of their dry condition standing dead boles do not decompose.

An equation was developed which estimates the time a dead bole has been on the ground, given that it would have stood for some time before falling over and been subject to little decomposition during this time. Decomposition rates, using a negative exponential model, gave only marginally better r2 than linear models. Pinus contorta had exponential decay rates from 0.0299 and 0.0171 mass density loss/yr for the most recent 15 and 25 yr in stands 58 yr old, to 0.0045 and 0.0035 mass loss/yr for the most recent 65 and 80 yr in stands 215 and 222 yr old. Picea engelmannii had exponential decay rates of 0.0054 and 0.0025 mass loss/yr for the most recent 20 and 65 yr in stands 99 and 215 yr old.
The effect of salinity on the dominance‐diversity relations of experimental coastal macrophyte communities
Authors: Grillas Patrick , van Wijck Carla , Bonis Anne
Published: May 2006

Salinity and water regime have previously been recognised as the main environmental factors controlling the abundance of coastal submerged macrophytes in temporarily‐flooded marshes in the Camargue. The effects of these environmental variables, which are considered interrelated, are tested experimentally by subjecting experimental macrophyte communities from six temporarily flooded marshes to different levels of salinity (from 0 to 6 g/1 Cl−). Communities subjected to high salinity levels (4 and 6 g/1 Cl~) showed a decrease in species richness and in biomass of all species involved. The species that most frequently dominate these communities, Chara áspera and Zannichellia pedunculata, are tolerant of salt and dominate over the entire salinity range. Three species groups can be distinguished based on the distribution of their biomass and centre of gravity of distribution over the salinity range: (1) non‐salt‐tolerant species, ‘glyco‐phytes’, (2) moderately salt‐tolerant species and (3) very tolerant species (‘halophytes’). A species ordination based on the experiments appeared to give results close to those previously obtained from field data.
Small‐scale spatial dynamics of plant species in a grassland community over six years
Authors: Herben T. , Krahulec F. , Hadincová V. , Kováf ova M.
Published: May 2006

Abstract. In a species‐rich mountain grassland in the Krkonosse Mts., Czechoslovakia, data from four permanent plots of 50 cm x 50 cm were recorded annually from 1985 to 1990 to study the spatial dynamics of the species. Plots were divided into 15 x 15 subplots and the number of vegetative units of all plants within each subplot was determined. There was not much net change at the plot level, but the subplots were very dynamic. Two aspects of the spatial dynamics of the species were followed: (1) persistence, i.e. the tendency of the species to remain in the same subplot, and (2) long‐distance spreading, i.e. movement to subplots beyond the immediate neighbourhood. Species differed widely in their persistence and longdistance spreading and were classified into mobility types: long‐range guerrilla, short‐range guerrilla, phalanx and 'sitting’. The mobility types were, to a certain extent, correlated with the growth form of plants, but some species of one growth form showed different types of small‐scale dynamics and some species with different growth forms had the same spatial dynamics.
A vegetation switch as the cause of a forest/mire ecotone in New Zealand
Authors: Agnew A. D. Q. , Wilson J. Bastow , Sykes Martin T.
Published: May 2006

Abstract. Vegetation switches are those processes in which there is positive‐feedback between vegetation and environment, i.e. a vegetation state modifies its environment producing conditions more favourable to itself (Wilson & Agnew 1992). Switches can produce and maintain abrupt ecotones between plant communities.

Such a sharp ecotone exists between beech‐podocarp forest and mire vegetation, both on deep peat, in southwest New Zealand. One such site was examined. There was no apparent explanation for the ecotone in the present topography nor in the substrate.

Levelled transects through the forest demonstrated that most seedling establishment occurred on dead fallen tree boles. These microsites were significantly richer in N, P and K than the wet sump microsites. We argue that this is a mechanism whereby trees can become established in the forest, but not in the open mire. In the forest, the presence of trees ensures the presence of dead‐log microsites on the ground, permitting tree seedlings to grow. In the mire, there are no such micro‐sites, and trees cannot establish.

The ecotone may be sharpened because of the presence of an ecotonal band of the small tree Leptospermum sco‐parium between forest and mire. This species can reproduce vegetatively by root suckers in the mire. Its boles are light, and even if they fall to the mire surface they are not thick enough to form a substrate for tree‐seedling establishment. The larger tree species may be prevented from falling onto the mire by the wind‐sheltering of the forest, and by the zone of Leptospermum.

The postulated process would represent a new kind of water‐/nutrient‐mediated switch, of Type 1 (‘One‐sided’). It may occur in many waterlogged forests worldwide.
Structure and seasonal dynamics of humid tropical grasslands in Meghalaya, India
Authors: Shankar Uma , Tripathi R. S. , Pandey H. N.
Published: May 2006

Abstract. Four humid grassland communities at three different locations in Meghalaya, India were analysed during 1988 and 1989 for species and life‐form composition, diversity and dominance in relation to altitude, soil and prevailing disturbances. Due to the adverse interactive influences of exceptionally high annual rainfall (> 10 000 mm), topography and human interference on soil fertility, the grassland at Cherrapunji, at 1300 m altitude, had a low species diversity (H'= 1.74) and was dominated by three perennial grass species. Similar grasslands, at both higher and lower altitudes on fertile soil and with lower rainfall (ca. 2000 mm), showed higher diversity values (H'= 2.28 at Burnihat and 2.31 at Upper Shillong). The proportion of perennial species and chamaephytes increased with elevation. At the high altitude site a grassland under short‐term protection from fires and grazing had a higher species richness, density and basal cover than an unprotected grassland. All grasslands show a clear seasonality, albeit with different patterns, with a maximum in density and basal cover in August.

The differences in structure and seasonality are discussed in terms of different levels of stress.
Plant communities of a tussock tundra landscape in the Brooks Range Foothills, Alaska
Authors: Walker Marilyn D. , Walker Donald A. , Auerbach Nancy A.
Published: May 2006

Abstract. We present the first vegetation analysis from the Arctic Foothills of northern Alaska according to the Braun‐Blanquet approach. The data are from the Imnavait Creek and Toolik Lake regions. We focus on associations of dry and mesic upland surfaces and moderate snow accumulation sites; other upland plant communities, i.e. those of blockfields, non‐sorted circles, and water tracks, are briefly described. Summary floristic information is presented in a synoptic table. Five associations and 15 community types are tentatively placed into seven existing syntaxonomical classes. The community descriptions are arranged according to habitat: dry exposed acidic sites, moist acidic shallow snowbeds, moist non‐acidic snowbeds, moist acidic uplands, and moist non‐acidic uplands. Many of the communities are Beringian vicariants of associations previously described from Greenland and the European Arctic. The described communities have a widespread distribution in northern Alaska. The relationship of the associations to complex environmental gradients are analyzed using Detrended Correspondence Analysis. Community composition is controlled primarily by mesotopographic relationships (slope position and soil moisture), microscale disturbances, and factors related to long‐term landscape evolution.
Nitrate reductase activity in vegetation below an arctic bird cliff, Svalbard, Norway
Authors: Odasz Ann Marie
Published: May 2006

Abstract. Vegetated sites below bird‐nesting cliffs are uniquely nutrient‐rich habitats in the otherwise nutrient‐poor arctic environment. Plants from six distinct vegetation zones below such a cliff at 79° N, Svalbard, Norway, were collected for analysis under greenhouse conditions. Leaf nitrate reductase activity (NRA) was analysed in 42 species representing 25 % of the Svalbard vascular flora. The species mean NRA values ranged from 0.37 to 8.34 μmols of nitrite ions formed per gram of plant fresh weight per hour. Species in the vegetated zone growing closest to recent guano deposits had the highest NRA values, (mean = 4.47) whereas plants growing farther below the cliff had significantly lower values (mean = 0.55).

A similar pattern was detected in a duplicate set of plants induced with 15 mM KNO3; vegetation zone means for NRA ranged from 5.08 to 0.98 μmols of nitrite ions formed per gram of plant fresh weight per hour. Maximally induced species NRA values were highest in the first zones below the cliff and decreased downslope. This gradient paralleled the steep soil nitrate gradient, which decreased from 13.84 mg/l at the cliffbase to 1.03 mg/l downslope. Correspondingly, soil ammonium ions in the vegetation zones ranged between 1.96 mg/l at the cliff‐base to 0.03 mg/l downslope. Correlations between NRA and soil nitrate provide a systematic basis for assigning scalar ‘nitrogen figures’ as indicators of habitat preference, here for the first time applied to arctic species.
Lottery coexistence models extended to plants with disjoint generations
Authors: Laurie Henri , Cowling Richard M.
Published: May 2006

Abstract. Neither conventional niche theory nor current lottery models offer a satisfactory theoretical scope for modelling coexistence of species with disjoint generations. South‐African fynbos and Australian kwongan include many species which are killed by, and recruit only after, fire. We propose a density‐dependent lottery model which accommodates the unusual demographics of these species. We show that coexistence requires density dependence in recruitment. The result applies to a wider class of populations than the one considered here. It is applied to non‐resprouting species in fynbos and kwongan. We show that the lottery assumption of recruitment in proportion to propagules is often satisfied, while the production of such propagules is often density‐dependent, and we discuss some evidence of mechanisms whereby this may occur.
Forest dynamics, differential mortality and variable recruitment probabilities
Authors: Lertzman Kenneth P.
Published: May 2006

Abstract. Both spatial and temporal variability in recruitment probabilities can lead to coexistence in gap‐phase regenerating forests which would otherwise tend to be dominated by fewer species. Using modified Markov models, the potential roles were examined of temporal variability and differential mortality rates among species in the dynamics of a forest for which spatial variability has been rejected as a strong factor leading to coexistence. Differential longevity modifies results obtained from a simple Markov model: it exerts a strong influence on the equilibrium species composition, on the rate of community change and on the time a community requires to reach equilibrium. Simulations with varying transition probabilities mimicked a changing climate, producing four main results: 1. Unless the duration of climate states is very long or very short, forest composition is in a continual state of disequilibrium. 2. Species vary in their response times to changing climate. 3. The mean abundance of each species under a varying climate scenario is different from that expected from the mean climate state. 4. The rare, long‐lived species was favored by climatic fluctuations at the expense of more common shorter lived species. Differential mortality rates provide an equilibrium‐based mechanism for coexistence, and temporally fluctuating recruitment probabilities a non‐equilibrium mechanism. Composition could be maintained by differential longevity among species and climatic fluctuations allowing periodic recruitment of the less common species.
Climatic range and distribution of Chinese Fagus species
Authors: Cao Kun‐fang , Peters Rob , Oldeman Roelof A.A.
Published: May 2006

Abstract. The distribution of five Chinese Fagus species was mapped, and their geographical range clarified. Their climate range was characterized following Thornthwaite (1948) for moisture and temperature (Thornthwaite's moisture index ranging from 26 to 320), and Kira (1945) for temperature (mean annual temperature from 5 to 17 °C), and compared with the range of other beeches. Chinese beeches occur only in S. China, mainly between 700 m and 2500 m altitude. They grow abundantly only in perhumid climates. The Northern Hemisphere beeches occur mainly in temperate climates; however, they reach warmer extremes in North America and China than in Europe and Japan. Beech habitats in montane China are more humid than in lowland Europe and North America. Chinese beeches are limited by a moisture deficit in the north, and by high temperatures plus relatively low moisture levels in the south. However, they tolerate a certain water deficit in the growing season. The southern geographical and low altitudinal limits of Chinese Fagus species are probably largely determined by the lack of competition with evergreen dicotyledonous trees, together with human influences.
Community dynamics of desert grasslands: influences of climate, landforms, and soils
Authors: Wondzell Steve , Ludwig John A.
Published: May 2006

Abstract. Permanently marked vegetation transects in Big Bend National Park, Texas, USA were monitored to follow temporal dynamics of desert grassland communities on a variety of landforms and soil types over a 26‐yr period after the removal of domestic livestock. Historic records indicate that the park area was severely overgrazed prior to its establishment, and our results show that the species present increased in both cover and density after the removal of livestock. However, the timing of recovery corresponded to multiyear periods of above‐average precipitation. Little change was observed in between 1955 and 1960, a period dominated by several consecutive years of drought. The cover of two large shrubs common to the Chihuahuan Desert, Larrea tridentata and Flourensia cernua, increased from 1960 to 1967, a period dominated by summer drought and frequent wet winters. The cover and density of forbs, perennial grasses, and most shrubs increased on nearly all landforms between 1967 and 1981, when summers were wetter than average. In contrast, the cover of Larrea tridentata decreased during this period. Comparisons among the plant communities on each landform showed that they diverged through time after domestic livestock were removed. Presumably, differences in topographic position and soil texture influence water availability which was reflected in the species composition on each soil series.

Unfortunately, we cannot isolate the effects of recovery from grazing from the effects of climate because the study design did not include control plots located within grazed pastures. Certainly, the directional trajectory of change and the regrowth of grasses into inter‐shrub spaces, must, at least in part, be the result of recovery from grazing. However, our data also indicate that the desert grassland communities are sensitive to multi‐year periods of above‐ or below‐average precipitation. Clearly, the dynamics between shrubs and grasses cannot be explained by a simple successional paradigm that views increased shrub dominance as retrogression from a climax grassland. Many alternate hypotheses have been forwarded to explain the dynamics that control the vegetation composition in the desert and desert grassland region of North America. Experimental tests of these hypotheses are needed to indentify the interactions between biotic and abiotic factors that control dominance by shrubs or grasses.
Vicinism and mass effect in a historical perspective
Authors: van der Maarel Eddy
Published: May 2006

Abstract. The term vicinism, usually ascribed to R. Nordhagen, was probably first coined in 1903 by Hugo de Vries as a genetical term — in the framework of his mutation theory — and only two years later as an ecological concept by F.E. Clements. Since both terms are clearly defined and concern different phenomena it is better to distinguish between genetical and ecological vicinism, while the latter concept can be further subdivided in rhizome and seed vicinism.
The vertical distribution of below‐ground biomass in grassland communities in relation to grazing regime and habitat characteristics
Authors: Rodríguez Miguel A. , Brown Valerie K. , Gómez‐Sal Antonio
Published: May 2006

Abstract. 40 sites, representing different pasture types in Northwest Spain, were sampled in respect of their floristic composition, distribution of above and below‐ground biomass and environmental and physical variables. Five plant community types were identified by classification techniques of plant species composition. These communities were then characterized in terms of the percentage of ground covered by herbaceous and shrub vegetation, stones, rocks and gaps as well as their topographic location and characteristics of the shallow soil (pH, organic matter, nitrogen and calcium content). Bio‐mass was assessed in terms of above‐ground structures, surface crowns and three below‐ground layers to a depth of 10 cm. Three types of grazing regime were distinguished: Concentrated Intense Grazing in early spring (CIG), Extended Intense Grazing throughout the spring (EIG), and Non‐Intense Grazing (NIG). Grazing regime showed the highest association with plant community type and three broad categories were identified: xeric stressed pastures, which nevertheless received CIG, mesic pastures with EIG, and three kinds of NIG mesic pastures.

The xeric communities had the highest proportion of aboveground biomass, as a consequence of their greater proportion of woody perennials. These xeric communities displayed a more gradual reduction in below‐ground biomass with depth than mesic pastures, a likely consequence of the low water content in the upper soil layers. The mesic communities had a high concentration of below‐ground biomass in the upper layers when they were intensely grazed. However, when grazing was low (i.e. NIG situations), these communities had greater variability in biomass profiles than any of the other pasture types. Possible causes of the patterns in biomass distribution of the intensely grazed pastures are discussed.
Vegetation zonation in a former tidal area: A vegetation‐type response model based on DCA and logistic regression using GIS
Authors: van de Rijt C.W.C.J. , Hazelhoff L. , Blom C.W.P.M.
Published: May 2006

Abstract. We studied the effect of flooding frequency on the vegetation of the northern part of the Delta region in the southwestern Netherlands under different grazing and soil conditions using Detrended Correspondence Analysis. We found grazing and frequency of flooding to be the most important environmental factors that determine zonation of vegetation types in the area. We used logistic regression to describe the probability of occurrence of 25 vegetation types in relation to the frequency of flooding under grazed and ungrazed conditions. We implemented the vegetation response model in a Geographical Information System so as to calculate new vegetation maps of outer dike areas under different flooding regimes. The model will be used for evaluation of the effects of different sluice management schemes on outer dike plant zonation in the research area.
Spatial patterns in a two‐tiered semi‐arid shrubland in southeastern Spain
Authors: Haase Peter , Pugnaire Francisco I. , Clark S.C. , Incoll L.D.
Published: May 2006

Abstract. Single species and bivariate distribution patterns in a semi‐arid shrubland in southeastern Spain, dominated by the tall leguminous shrub Retama sphaerocarpa, were investigated by second‐order spatial analysis based on Ripley's K‐function. Shrubs were significantly clumped because of a strong association of dwarf shrubs, mostly Artemisia barrelieri, under the canopy of Retama. Retama shrubs were randomly distributed, but when different size‐classes were analysed separately, the pattern changed from significantly clumped to random and then to regular with increasing canopy diameter, suggesting increasing intraspecific competition with shrub size. Artemisia was significantly clumped at all scales because of aggregation under the canopy of large Retama shrubs. The association between the species became stronger with increasing canopy diameter of Retama shrubs, suggesting that facilitation prevailed over interspecific competition because of niche separation in different tiers, both above and below ground. Retama shrub size thus determined both the type of pattern for its own size class and tier, and the scale and intensity of the association with its understorey shrubs.
On randomization testing in vegetation science: multifactor comparisons of relevé groups
Authors: Pillar Valério De Patta , Orlóci László
Published: May 2006

Abstract.Hypothesis testing in phytocoenological applications is likely to be hindered when based on conventional statistical methods. The problem created by unrealistic assumptions can, however, be overcome by randomization. This paper discusses the general idea of randomization testing, describes a method and interprets its application in group comparisons. Two sets of variables are involved, the vegetation set on the basis of which the groups are compared and the environmental factors which delimit the groups under different analytical designs. Although simple partitioning of sum of squares is at the core of the test, the method has versatility of testing uni‐ or multifactor designs, which is novel in phytocoenological applications. The algorithm has been implemented in programs SYNCSA and MULTIV by V.P. Data from the Campos of southern Brazil are used for illustration.
Why do we need permanent plots in the study of long‐term vegetation dynamics?
Authors: Bakker J.P , Olff H , Willems J.H , Zobel M
Published: May 2006

Abstract. This paper presents a survey of vegetation studies on permanent plots, with an emphasis on the long‐term character of these studies. It makes remarks on the external and internal causes of succession, pays attention to the pathways of succession, links up permanent plots studies and chronosequences, discusses internal causes and mechanisms of succession, and finally mentions the significance of long‐term vegetation dynamics for nature conservation.
Soil seed bank composition along a gradient from dry alvar grassland to Juniperus shrubland
Authors: Bakker J.P , Bakker E.S , Rosén E , Verweij G.L , Bekker R.M
Published: May 2006

Abstract. Dry alvar grasslands on limestone on the Baltic island of Öland, SE Sweden, are very species‐rich as long as the traditional agricultural exploitation of grazing and fire wood collection continues. After abandonment, encroachment of Juniperus communis starts and a closed woodland can develop within 100 yr. A chronosequence, representing a successional series, was used for the comparison of sites still grazed, and sites ungrazed for about 20, 55 and 80 yr, respectively. Out of the 58 characteristic dry alvar grassland species 55 % disappeared from the established vegetation after 80 yr of abandoning, and 80 % also vanished from the seed bank. Arenaria serpyllifolia, Trifolium repens, Agrostis vinealis, Linum catharticum, Polygala vulgaris, Cerastium fontanum, Luzula campestris, Achillea millefolium and Potentilla tabernaemontani were the only species left in the seed bank. More than 75 % of the dry alvar grassland species were classified as having a transient or short‐term persistent seed bank. It is concluded that restoration management, by cutting junipers, of overgrown dry alvar grassland cannot rely on the longevity of seeds in the soil. Seeds have to be dispersed by wind or grazing animals.