Summer Mowing Research Articles

Effects of experimental and real land use on seedling recruitment of six fen species

Summary Seedling emergence and early establishment of six fen species differing in seed mass and growth form were investigated under experimental land use with changed vegetation structure and under real land use in a calcareous fen. Seeds of all six species were sown in plots with different experimental land-use treatments: summer and autumn mowing with or without litter removal, trampling and abandonment. Additionally, emergence and survival of experimentally sown seeds was investigated under real land use on adjacent sites managed by mowing, grazing, intense trampling or abandonment. On abandoned plots and on plots without litter removal of the land-use experiment, emergence rates of all species were negatively affected either by high litter and moss cover or by tall canopy. No differences were found between autumn and summer mowing. Gap creation by experimental trampling did not increase germination rate. Under real land use, establishment of seedlings of most species was positively affected by litter cover and tall canopy. Trampling, in contrast, had a severe negative effect on seedling survival. The investigated species differed in their germination ability which was tested in the germination chamber and in their response to land use. Succisa pratensis with the highest seed mass germinated well in the chamber and in the field more or less regardless of land use. The low germination rate of Parnassia palustris in the germination chamber indicated a limitation of viable seeds. In the field, however, seedling emergence was additionally limited by microsite availability. Seeds of Serratula tinctoria and Primula farinosa germinated well in the germination chamber, but seedling recruitment in the field was hampered in the presence of a high litter or moss cover. Seeds of Tofieldia calyculata and Pinguicula vulgaris were strongly dependent on the availability of suitable microsites in the field. They hardly germinated under natural conditions, in spite of a high number of germinable seeds in the germination chamber.

Research: Effects of Summer Burning and Mowing on Central Texas Juniper-Oak Savanna Plant Communities During Drought Conditions

Research: Effects of Summer Burning and Mowing on Central Texas Juniper-Oak Savanna Plant Communities During Drought Conditions

Long‐term compositional responses of a South African mesic grassland to burning and mowing

AbstractQuestion: What is the long‐term compositional response of grass and forb species to various combinations of burning and mowing? Can these responses be predicted from simple plant traits?Location: Ukulinga research and training farm (24°24′E, 30°24′S), Pietermaritzburg, KwaZulu‐Natal, South Africa.Methods: Grass species relative abundance in 1996 in various burning and mowing treatments of a long‐term (> 50 a) experiment was calculated from data obtained using a point sampling method, whereas forb species abundance in 1999 was determined using the importance score method. The experiment consisted of different frequencies (annual, biennial and triennial) of burning and mowing in winter or spring in combination with different frequencies of summer mowing (none, early, late or both).Results: Grasses responded to the type of disturbance (burn or mow) and frequency of burning, whereas forbs responded primarily to the presence or absence of any form of disturbance and secondarily to the timing of burning (spring versus winter). Summer mowing and annual or biennial dormant‐period burning maintained communities dominated by short grasses, whereas tall grasses dominated under annual dormant‐period mowing, triennial burning or protection from disturbance. Grass tillering strategy (below‐ or above‐ground) influenced response to burning frequency. Many erect herbaceous dicot species with aerial meristems were reduced in abundance by summer mowing whereas most small creeping herbaceous dicot species appeared to be dependent upon summer mowing.Conclusions: This long‐term experiment demonstrated that: (1) grasses and forbs responded differently to burning and mowing; (2) simple plant traits, such as height, position of tiller initiation, and position of meristems have potential for predicting the response of species to the timing and frequency of burning and mowing.

Long-term compositional responses of a South African mesic grassland to burning and mowing

Question: What is the long-term compositional response of grass and forb species to various combinations of burning and mowing? Can these responses be predicted from simple plant traits? Location: Ukulinga research and training farm (24°24'E, 30°24'S), Pietermaritzburg, KwaZulu-Natal, South Africa. Methods: Grass species relative abundance in 1996 in various burning and mowing treatments of a long-term (> 50 a) experiment was calculated from data obtained using a point sampling method, whereas forb species abundance in 1999 was determined using the importance score method. The experiment consisted of different frequencies (annual, biennial and triennial) of burning and mowing in winter or spring in combination with different frequencies of summer mowing (none, early, late or both). Results: Grasses responded to the type of disturbance (burn or mow) and frequency of burning, whereas forbs responded primarily to the presence or absence of any form of disturbance and secondarily to the timing of burning (spring versus winter). Summer mowing and annual or biennial dormantperiod burning maintained communities dominated by short grasses, whereas tall grasses dominated under annual dormant-period mowing, triennial burning or protection from disturbance. Grass tillering strategy (below- or above-ground) influenced response to burning frequency. Many erect herbaceous dicot species with aerial meristems were reduced in abundance by summer mowing whereas most small creeping herbaceous dicot species appeared to be dependent upon summer mowing. Conclusions: This long-term experiment demonstrated that: (1) grasses and forbs responded differently to burning and mowing; (2) simple plant traits, such as height, position of tiller initiation, and position of meristems have potential for predicting the response of species to the timing and frequency of burning and mowing.

The effects of grassland management on plant performance and demography in the perennial herb Primula veris

Summary Because of changing land‐use practices and abandonment, many European calcareous grasslands are under increasing threat. In order to protect those grasslands that remain, better insights into how plant populations respond to different management scenarios are needed. Using transition matrix models and life‐table response experiment (LTRE) analysis, the effects of different management strategies (grazing, summer and autumn mowing, and no management) on plant performance and population dynamics of the perennial herb Primula veris (Primulaceae) were experimentally studied. Data were collected between 1999 and 2003 in a species‐rich calcareous grassland. Early grazing (May) resulted in low population growth rates (λ < 0·860) and a mean annual population decline of 11%. Under these conditions, both the proportion of flowering individuals and flower and seed production per plant were low, resulting in seed limitation overall. However, when grazing started later in the growing season (early July) flowering probability and overall seed set increased, as did population growth rates (λ > 1). Mowing in autumn (October) was the most favourable management scenario (mean λ= 1·213), resulting in high proportions of flowering individuals and a large seed output. Furthermore, this management yielded optimal conditions for recruitment and seedling establishment during the next growing season. Summer mowing (mid‐July) resulted in a similar increase of flowering and overall seed shed to autumn mowing, but recruitment rates were lower because of a dense and tall vegetation structure at the time of germination. Consequently, population growth rates (mean λ= 1·045) were lower compared with the autumn mowing regime. No management of the grassland resulted in low growth rates (λ < 0·843) and a mean annual population decline of 35%, because of high mortality rates of each life stage and a lack of recruitment. Recruitment rates were strongly reduced by lowered flowering probabilities and limited germination possibilities. Synthesis and applications. This study may enable conservation managers to understand better the effects of time and type of management on population dynamics of P. veris. In order to preserve the remaining populations of this long‐lived species, management interventions can promote flowering and seed shed and reduce productivity of the vegetation by mowing in autumn. Finally, this study has clearly shown that the lack of any management, which is the fate of many abandoned calcareous grassland relicts, will seriously restrict the long‐term survival of P. veris.

Effect of burning and mowing on grass and forb diversity in a long‐term grassland experiment

Abstract. Disturbance may be an important determinant of plant community composition and diversity owing to its effects on competitive interactions, resources, dominance and vigour. The effect of type, timing and frequency of disturbance on grass and forb species richness was examined using data from a long‐term (> 50 yr) grassland burning and mowing experiment in KwaZulu‐Natal, South Africa.Grass species richness declined considerably (> 50%) in the absence of disturbance, whereas forb species richness was unaffected. Annual burning in sites not mown in summer tended to increase grass species richness relative to triennial burning (22% increase) with the reverse being true in sites mown twice in summer (37% decline). Forb species richness declined by 25% in sites mown twice in summer relative to sites mown in early summer only. Disturbance was necessary to achieve maximum grass species richness presumably by removing litter and increasing the availability of light. The interaction of time of mowing in summer (early versus late) and time of burning during the dormant period (spring versus winter) had the most dramatic effect on species richness. Time of burning had no effect on richness in sites mown in early summer, but winter burning resulted in a dramatic decline (27–42%) in richness in sites mown in late summer. This effect may be related to possible greater soil desiccation with this combination of disturbances.

Effect of burning and mowing on grass and forb diversity in a long-term grassland experiment

Disturbance may be an important determinant of plant community composition and diversity owing to its effects on competitive interactions, resources, dominance and vigour. The effect of type, timing and frequency of disturbance on grass and forb species richness was examined using data from a long-term (> 50 yr) grassland burning and mowing experiment in KwaZulu-Natal, South Africa.Grass species richness declined considerably (> 50%) in the absence of disturbance, whereas forb species richness was unaffected. Annual burning in sites not mown in summer tended to increase grass species richness relative to triennial burning (22% increase) with the reverse being true in sites mown twice in summer (37% decline). Forb species richness declined by 25% in sites mown twice in summer relative to sites mown in early summer only. Disturbance was necessary to achieve maximum grass species richness presumably by removing litter and increasing the availability of light. The interaction of time of mowing in summer (early versus late) and time of burning during the dormant period (spring versus winter) had the most dramatic effect on species richness. Time of burning had no effect on richness in sites mown in early summer, but winter burning resulted in a dramatic decline (27–42%) in richness in sites mown in late summer. This effect may be related to possible greater soil desiccation with this combination of disturbances.Nomenclature: Arnold & De Wet (1993).Abbreviation: AGP = Above-ground phytomass production.

Methods of Establishing Annual Ryegrass and Clover into Broomsedge‐Infested Pastures

Establishing cool‐season forages into broomsedge (Andropogon virginicus L.)–infested pastures would increase forage nutritive value and extend the grazing season. Experiments were established in southeastern Oklahoma in late summer at four locations in 1995 and at six locations in 1996 to determine the effects of three forage removal techniques for establishing clovers (Trifolium spp.) and annual ryegrass (Lolium multiflorum Lam.). The main plots used in both years included: (i) mowing plus vegetation removal in late summer, (ii) paraquat (1,1′‐dimethyl‐4,4′‐bipyridinium ion) plus burning 1 wk after treatment (WAT), and (iii) burning after frost. In 1995, two annual ryegrasses (‘Marshall’ and ‘TAM90’) and three clovers [‘Yuchi’ arrowleaf (T. vesiculosum Savi.), ‘Overton R18’ rose (T. hirtum All.), and ‘Ladino’ white (T. repens L.)] were broadcast‐seeded into the three seedbed preparations. In the 1995 planting, dry conditions in the fall resulted in no establishment of annual ryegrass and erratic establishment and production of clovers. In 1996, Marshall annual ryegrass and a clover mix [arrowleaf, red (T. pratense L.), rose, and white] were each broadcast‐seeded into tilled and nontilled subplots in the three seedbed preparations. Clover and annual ryegrass dry matter (DM) production was generally highest in paraquat plus burn treatment and lowest in the burn after frost treatment. Tillage generally did not improve clover or annual ryegrass production. The nontilled paraquat plus burn treatment produced the most forage and had the lowest production cost for both clover and annual ryegrass; therefore, it should be considered when establishing clover and annual ryegrass into permanent pastures.

Broomsedge (Andropogon virginicus) Response to Herbicides and Burning1

Broomsedge control studies were conducted on six broomsedge-infested pastures in southeastern Oklahoma from 1995 to 1997. Glyphosate applied in spring at 2.24 kg ai/ha decreased broomsedge plant density by 58% 3 mo after treatment (MAT), on areas where the previous year's forage was grazed, and by 95% 3 MAT, where spring fire had removed the old top-growth before glyphosate application. Broomsedge plant density was not affected where glyphosate was applied in spring to sites with old-standing top-growth. Paraquat applied in spring at 0.56 kg ai/ha and spring burning without a herbicide treatment had no effect on broomsedge plant density. Glyphosate at 0.56 and 1.12 kg ai/ha applied in late summer reduced the number of broomsedge stems 1 yr after treatment (YAT) by an average of 65 and 80%, respectively. Paraquat at 0.56 kg/ha applied in late summer of 1995, followed by burning 1 wk after treatment (WAT), decreased broomsedge stem density by more than 60% 1 YAT at four of six locations when compared with mowing in late summer. Burning in November after an October frost decreased broomsedge stem density by more than 47% 1 YAT at four locations. Two consecutive years of burning after frost and paraquat applied in late summer followed by burning 1 WAT reduced broomsedge dry matter production by 68 and 96%, respectively, when compared with mowing in late summer. These data suggest that good to excellent control of established broomsedge is possible with herbicides alone, with a combination of herbicides and late-summer burning, and with fall burning after an early frost in a dry fall. However, broomsedge control was short-lived with all the treatments because of the establishment of new broomsedge seedlings. Thus, it will be important to integrate the destruction of broomsedge plants with proper fertility and grazing management in order to provide satisfactory broomsedge control.Nomenclature: Glyphosate; paraquat; broomsedge, Andropogon virginicus L. #3 ANOVI.Additional index words: CYNDA, Cynodon dactylon, mowing, prescribed fire.Abbreviations: DM, dry matter; MAT, months after treatment; WAT, weeks after treatment; YAT, years after treatment.

Management impacts on vegetation dynamics of hyper‐eutrophicated fields at Berlin, Germany

Abstract. This paper reports on vegetation dynamics on terrestrial, temperate grassland sites at the upper range of the productivity scale, i.e. on abandoned sewage fields (fields once used for waste water disposal) at Berlin‐Blankenfelde, Germany. I studied regeneration and the influence of different management practices (removal of top soil and mowing in late summer). Changes in species composition and cover were followed on permanent plots of 2m × 2m size through five years of vegetation development. At the outset of the experiment the abandoned fields were dominated by dense Urtica dioica /Elymus repens stands. Species richness was 7 species/ 4m2, and it remained low on unmanaged plots during the time of observation (7.6 species/plot in year 5). Removal of 20 cm of top soil caused a severe decline of Urtica and a large increase in species richness (21 species in year 1 after disturbance). Mowing was slightly higher compared with unmown plots on both initially excavated and unexcavated plots. Total cover was always near 100 % (except immediately after top soil removal). Colonization of bare soil was very rapid and in late summer of the first year after disturbance cover already increased towards 100%. On all plots the vegetation was mostly dominated by perennial herbs and grasses. Winter season gaps are occupied by Galium aparine, a large‐seeded annual scrambling climber. Monocarpic perennials behaved as winter annuals in most cases. Woody species were inhibited by dense above‐ground biomass and litter cover. The paper questions whether succession on abandoned sewage fields may proceed towards a woodland stage and advises how vegetation of such hyper‐eutrophicated sites can be managed towards higher diversity.

Dynamics of common reed (Phragmites australis Trin.) in Swiss fens with different management.

Dynamics of common reed (Phragmites australisTrin.) in Central Europe have so far mostly been investigated in connection with studies on reed ‘die-back’ along lake shores. However, there has recently been increasing concern about reed expansion at terrestrial sites, such as fens and wet grasslands. In this paper we report on the results of four separate studies which monitored reed dynamics in Swiss fens with various mowing regimes over a period of 4 to 15 years. The first study compared unmown plots with plots mown in winter in a triennial rotation; the second one included unmown plots, plots mown in summer, and plots mown in winter; the third one compared plots mown in June and September with plots only mown in September; the fourth study investigated only plots mown in September. Shoot number and shoot size were recorded in permanent quadrats. In all studies the performance of P. australis fluctuated without trend or tended to decrease during the period investigated. The decreasing tendency concerned shoot size rather than shoot number, and within a given study it was stronger for plots with initially taller shoots. The various mowing regimes did hardly influence these changes. Mowing in winter every three years reduced shoot size in the year after mowing, but not on the long term. Mowing every year in late summer reduced the shoot size compared with unmown plots on the short term, but this effect almost disappeared on the long term, after mowing had become biennial. Mowing in June (in addition to in September) caused no noticeable effects. We conclude that other factors (e.g. weather conditions, competition, or population processes) are more important than management in determining the abundance of P. australis in the fen communities investigated here, although long-term effects of mowing in summer still need more investigation. As a practical consequence it is suggested that at sites which are not strongly dominated by P. australis, as most of those investigated here, reducing the performance of this species should not constitute a major target of nature conservation management, nor can its dynamics be used as an indicator for management success before underlying causes are better understood.

Seed dynamics and seedling establishment in the invading perennialSolidago altissimaunder different experimental treatments

1Population increases inSolidago altissima, an aggressive invader in central Europe, can be due to clonal growth by rhizomes or sexual reproduction by seeds. We studied transitions between different reproductive stages, to assess the potential ofS. altissimato colonize new habitats by seed, and the influence of annual mowing on the dynamics of seeds and juvenile plants.2The dispersal of the numerous achenes, their subsequent fate on and in the soil, and the growth and survival of seedlings and juvenile plants were followed from 1988 to 1990 in an old‐field population.3The seed rain was 49 000 seeds m−2per annum in unmown and 1800 seeds m−2per annum in adjacent mown plots. Survivorship and germinability of seeds in the soil decreased rapidly in the first 3 months after dispersal. Thereafter the declines were much slower. Germination within the established vegetation was very rare: only 12 out of 150 000 experimentally sown seeds (0.008%) became seedlings.4The survival and growth of seedlings transplanted into closed vegetation increased with age and developmental stage. Nevertheless, no transplants flowered during the 24 months over which their fate was followed.5Mowing affected neither seed survival nor germinability, nor did it have any effect on the growth, survival and reproduction of seedlings or juvenile plants.6The creation of 1‐m2openings in the vegetation strongly increased the number of emerging seedlings. Production of achenes was high (c. 20 000 per sexual shoot) and seed rain data suggested that 80–90% of all seeds may have been dispersed outside the study area. The colonization of nearby open sites is therefore quite probable.7Thus, mowing in late summer to control the growth ofS. altissimadoes not provide opportunities for further seedling establishment in existing populations and may prevent the colonization of new sites by reducing seed supply from the source population.

Experimental demography of rhizome populations of establishing clones ofSolidago altissima

1Solidago altissimaforms large compact below‐ground rhizome systems. The rhizome systems of 30 genets in a population that had colonized an old‐field in 1984 were mapped yearlyin situfrom 1988 to 1992. Branching angles, lengths and survival of rhizomes, and production of daughter rhizomes, were calculated from digitized maps.2We hypothesized that genets ofS. altissimawould prevent intraclonal crowding by producing longer but fewer rhizomes as they increased in size. In addition, we tested the effects of environmental factors on rhizome dynamics by (i) mowing in late summer, (ii) cutting of rhizome connections, and (iii) removal of close neighbour plants.3Most rhizomes were initiated at an angle of 60°−65° relative to the parent rhizome. Subsequent growth tended towards the parent axis and towards more centrifugal growth. Rhizome angles were not influenced by any treatment.4In control genets, rhizome density increased 1.3‐fold from March 1988 to March 1992. The number of newly produced rhizomes per genet decreased and their length increased from 1988 to 1992. Longer rhizomes had a higher survival probability than shorter rhizomes did. The number of newly produced rhizomes per parent rhizome was positively correlated with mean rhizome length per genet.5Mowing strongly decreased rhizome density from 1988 to 1992, mainly due to reduced production of new rhizomes.6Rhizome cutting led to a slight decline in the rhizome population and to shorter lengths of rhizomes in their second year compared with controls.7The removal of close neighbour plants led to increased rhizome densities. These rhizomes grew longer than controls in unmown plots and shorter in mown plots and had higher probabilities of surviving into their second year.8Yearly mowing could successfully prevent the further spread ofS. altissimabecause it acts on rhizome and shoot dynamics as well as on seed output.

Effects of experimental fire regimes on the population dynamics of shape Schwalbea americana L.

We studied the effects of experimental fire regimes, (dormant season fire, growing season fire, growing season mowing and control, i.e., no experimental treatment) on populations of the USA federally endangered, Schwalbea americana L. between 1992 and 1996. Although this species occurs in fire-maintained habitat in the Southeastern USA, there is concern about the use of fire for such rare populations. The purpose of the study was to examine how seasonal timing of fire and fire suppression affect population demography, flowering phenology and spatial distribution; to identify modes of persistence associated with fire regimes; and to determine if summer mowing provides a management alternative to fire. Fire-induced flowering was demonstrated in this species. Seasonal timing of burns appears to have relatively little consequence on population structure or spatial extent, but alters flowering phenology. Burning, regardless of season, resulted in increased population density and expansion in areal extent. Two possible mechanisms of persistence between fire events were identified including regression from reproductive stage to vegetative stage in the absence of fire and dormancy of individual plants for one or more seasons. Growing season mowing does not appear to be an adequate substitute for burning.

Liparis loeselii (L.) Rich. in eastern England: constraints on distribution and population development

The fenland form of Liparis loeselii is currently known from only three sites in eastern England, having been lost from about 30 former localities since the start of the nineteenth century. The reason for its loss is sometimes uncertain, but in only a small number of instances can it be attributed confidently to drainage. The habitat of the current Liparis populations, all in the Norfolk Broadland, can be summarized as ‘base-rich, wet, low-fertility, herbaceous fen’. Vegetation management, usually summer mowing, helps maintain the relatively low-growing, herbaceous vegetation that the orchid requires. In addition, all localities are in reflooded turbaries, the plant growing on a relatively buoyant mat of vegetation. Many former Liparis localities were apparently of similar character. Demographic studies on tagged plants in ten permanent plots in one population (Sutton Fen) between 1983 and 1990 showed that individuals were mostly short-lived but developed quickly. Small (young) individuals had particularly high mortalities and the majority died without flowering; individuals frequently, but not invariably, increased their leaf dimensions in successive years; flowering was almost entirely restricted to 2-leaved plants, especially robust individuals, and most flowering individuals re-appeared in the next growing season. The main period of emergence was between mid-June and mid-July, though some individuals that emerged in mid-June disappeared by mid-July (apparently due to mollusc grazing). The number of plants in the population showed considerable flux (though not all plots showed the same trends). A peak of numbers in some plots in 1986 and 1987(due to both high rates of recruitment and low mortality) was followed by a crash in 1988 and 1990. This affected the entire population (1990 numbers were about one third of those in 1983) but was particularly evident in plots which had shown an earlier strong increase in numbers. The population peak occurred after a winter burn and may have occurred in response to this. The cause of the subsequent decline is not known with certainty but it was associated with lack of vegetation management, low fen water levels (lack of surface inundation) at the time of emergence of Liparis plants and mollusc grazing damage. The effects of these events are difficult to disentangle, but grazing damage, perhaps facilitated by lack of shallow flooding at the time of shoot emergence, may be the proximate cause of loss. The short-lived character of many Liparis individuals and the quite rapid population turnover suggests that effective conservation management must provide conditions suitable for recruitment of new individuals as well as the maintenance of established plants, but the character of suitable regeneration niches is not well understood. It is possible thatperpetuation of Liparis populations may require some disturbance (perhaps winter burning or light trampling) as well as mowing. Rejuvenation of the hydrosere, by further peat removal, may be another long-term requirement.

Liparis loeselii(L.) Rich. in eastern England: constraints on distribution and population development

The fenland form ofLiparis loeseliiis currently known from only three sites in eastern England, having been lost from about 30 former localities since the start of the nineteenth century. The reason for its loss is sometimes uncertain, but in only a small number of instances can it be attributed confidently to drainage. The habitat of the currentLiparispopulations, all in the Norfolk Broadland, can be summarized as «base-rich, wet, low-fertility, herbaceous fen». Vegetation management, usually summer mowing, helps maintain the relatively low-growing, herbaceous vegetation that the orchid requires. In addition, all localities are in reflooded turbaries, the plant growing on a relatively buoyant mat of vegetation. Many formerLiparislocalities were apparently of similar character. Demographic studies on tagged plants in ten permanent plots in one population (Sutton Fen) between 1983 and 1990 showed that individuals were mostly short-lived but developed quickly. Small (young) individuals had particularly high mortalities and the majority died without flowering; individuals frequently, but not invariably, increased their leaf dimensions in successive years; flowering was almost entirely restricted to 2-leaved plants, especially robust individuals, and most flowering individuals re-appeared in the next growing season. The main period of emergence was between mid-June and mid-July, though some individuals that emerged in mid-June disappeared by mid-July (apparently due to mollusc grazing). The number of plants in the population showed considerable flux (though not all plots showed the same trends). A peak of numbers in some plots in 1986 and 1987 (due to both high rates of recruitment and low mortality) was followed by a crash in 1988 and 1990. This affected the entire population (1990 numbers were about one third of those in 1983) but was particularly evident in plots which had shown an earlier strong increase in numbers. The population peak occurred after a winter burn and may have occurred in response to this. The cause of the subsequent decline is not known with certainty but it was associated with lack of vegetation management, low fen water levels (lack of surface inundation) at the time of emergence ofLiparisplants and mollusc grazing damage. The effects of these events are difficult to disentangle, but grazing damage, perhaps facilitated by lack of shallow flooding at the time of shoot emergence, may be the proximate cause of loss. The short-lived character of manyLiparisindividuals and the quite rapid population turnover suggests that effective conservation management must provide conditions suitable for recruitment of new individuals as well as the maintenance of established plants, but the character of suitable regeneration niches is not well understood. It is possible thatperpetuation ofLiparispopulations may require some disturbance (perhaps winter burning or light trampling) as well as mowing. Rejuvenation of the hydrosere, by further peat removal, may be another long-term requirement.

Nature management experiments in a derelict reedmarsh. II: Effects of summer mowing

Lowering of the summer water table, eutrophication and dereliction have caused severe ruderalisation of the marsh vegetation of the Belgian wetland site, The Blankaart. Management experiments, based on an annual summer mowing regime, have shown that the ruderalised mixed-fen vegetation with dominance of competitive species such as Calamagrostis canescens and Glyceria maxima, which has completely lost its reedland character, can develop into a more diverse hayfield vegetation. However, the high nutrient status of the marsh and difficulties with the invasion of seed of hayfield species, due to the changed environment, discourages further distinct changes of the vegetation.

Seasonal Burning and Mowing Impacts on Sporobolus wrightii Grasslands

Land managers have recommended burning or mowing big sacaton (Sporobolus wrightii) grassland in either fall or winter for 100 years. The greatest potential for natural flre would have occurred when lightning strike frequency peaked in summer. The objective of this study was to determine how burning and mowing in fall (October), summer (July) and winter (February) influences big sacaton forage quantity and quality. Plants defoliated in fall produced leaves within 215 to 245 days, those defoliated in summer within 3 days, and those in winter within 20 days. Green and dead forage that accumulated after the burning and mowing in the same seasons were similar, but differences occurred among seasons. Green and dead forage following summer treatments were similar to that on untreated areas within 2 or 3 summer growing seasons, but were reduced on fall and winter treatments. Crude protein in green forage was 3 to 5% greater in treated plants than in untreated plants for 6 weeks after treatment, but forage quality increases were temporary. Burning or mowing at any season removes green forage available to livestock and reduces the amount of green forage that may accumulate for at least 2 summer growing seasons.

Shoot Growth and Development of Alamo Switchgrass as Influenced by Mowing and Fertilization

The response of shoot development and forage yield of a 2-year old 'Alamo' switchgrass stand to mowing and fertilization was evaluated to provide information needed for effective management of this variety. Mowing to a 20-cm stubble height in mid-spring removed only a few apical me&ems and had little impact on shoot development. Late spring and early summer mowing were done when apical meristems of primary compound shoots were elevated to near the 20-cm cutting height in May and over 20 cm in June. Secondary nonrooted shoot and aerial shoot numbers were increased and plant vigor, measured by spring growth in 1980, was decreased slightly the following spring. Mowing in mid-summer removed apical meristems from essentially all primary compound shoots and many secondary compound shoots. Regrowth was slight during the remainder of the summer, but the number of secondary and tertiary nonroqted shoots and aerial shoots in- creased. The number of proaxis buds decreased, and plant vigor was severely decreased the following spring. Mowing twice includ- ing early fall, removed apical me&ems from secondary com- pound shoots and some primary and secondary nonrooted shoots. Numbers of secondary, tertiary, and quarternary nonrooted shoots increased, but proaxis bud numbers were reduced. Plant vigor was very low the following spring, possibly due to exposure of mowed plants to cold winter temperatures. Fertilization increas- ed the rate of development of compound and nonrooted shoots, the number of secondary and compound shoots in spring, the number of proaxis buds in fall and the weight of primary and secondary compound shoots. Fertilized stands mowed during summer and early fall were more productive than all other mowed stands. Fertilized plants mowed in mid-summer were vigorous and productive the following spring. However, fertilization did not overcome the loss of vigor caused by fall mowing.

Birds on roadside verges and the effect of mowing on frequency and distribution

The study, which was carried out both in the eastern and western parts of Denmark, describes the use made of roadside verges by birds, and makes a quantitative assessment of their importance. In addition, the influence of summer mowing on the birds was studied. The results show that different parts of the road verges are used for foraging and that the skylark Alauda arvensis more often forages on road sides than on the adjacent fields. The verges are also important as a nesting site for some species, for example the skylark, which prefers to nest in this habitat rather than in adjacent fields. Mowing in summer has no decisive effect on the number of birds or their distribution on road verges.