Resprouting in the Mediterranean‐type shrub Erica australis afffected by soil resource availability

Abstract. Soil resource availability may affect plant regeneration by resprouting in disturbed environments directly, by affecting plant growth rates, or indirectly by determining allocation to storage in the resprouting organs. Allocation to storage may be higher in stressful, low resource‐supply soils, but under such conditions plant growth rates may be lower. These factors could act in opposite directions leading to poorly known effects on resprouting. This paper analyses the role played by soil resources in the production and growth of resprouts after removal of above‐ground plant tissues in the Mediterranean shrub Erica australis. At 13 sites, differing in substrate, we cut the base of the stems of six plants of E. australis and allowed them to resprout and grow for two years. Soils were chemically analysed and plant water potential measured during the summer at all sites to characterize soil resource availability. We used stepwise regression analysis to determine the relationships between the resprouting response [mean site values of the number of resprouts (RN), maximum length (RML) and biomass (RB)] and soil nutrient content and plant water potential at each site. During the first two years of resprouting there were statistically significant differences among sites in the variables characterizing the resprouting response. RML was always different among sites and had little relationship with lignotuber area. RN was less different among sites and was always positively correlated with lignotuber area. RB was different among sites after the two years of growth. During the first months of resprouting, RN and RML were highly and positively related to the water status of the plant during summer. At later dates soil fertility variables came into play, explaining significant amounts of variance of the resprouting variables. Soil extractable cations content was the main variable accounting for RML and RB. Our results indicate that resprout growth of E. australis is positively affected by high water availability at the beginning of the resprouting response and negatively so by high soil extractable cation content at later periods. Some of these factors had previously shown to be related, with an opposite sign, to the development of a relatively larger lignotuber. Indeed, RML and RB measured in the second year of resprouting were significantly and negatively correlated with some indices of biomass allocation to the lignotuber at each site. This indicates that sites favouring allocation to the resprouting organ may not favour resprout growth.     

Phosphorus nutrition of jarrah (Eucalyptus marginata) seedlings

Summary Effects of calcium phosphate supply on plant dry matter and phosphorus concentrations of parts of jarrah (Eucalyptus marginata) seedlings grown in a lateritic topsoil from the jarrah forest were examined in two glasshouse trials. Phosphorus deficiency depressed root and shoot dry weights and severely deficient leaves were smal and purple with prominent red major veins. Phosphorus deficiency severely reduced stem phosphorus levels (0.5% to 0.02%, experiment 1). Phosphorus concentrations were higher in bark than wood and the amount of phosphorus in the bark was sensitive to stem age and phosphate supply. Phosphorus adequate plants had bark phosphorus concentrations in the range 0.2–0.9% compared to <0.1% in deficient plants (experiment 2). Jarrah leaves accumulated dry matter up to 80 days after expansion and some leaves exported phosphorus during this period. Bark analysis may therefore be preferable to leaf analysis for detecting phosphorus deficiency in this species.     

Fitness implications of late bud break and time of burning in Lannea edulis (Sond.) Engl. (Anacardiaceae)

Many woody plants of savannas have massive underground parts (“lignotubers”) and diminutive aboveground parts with phenologies that are triggered by fire. Lannea edulis (Anacardiaceae) represents this life form and is widely distributed in south central Africa. The phenology of L. edulis was monitored on 42 permanently marked shoots over a 3-year period, from 2002 to 2004, and under three fire treatments (early and middle dry season burning, and fire protection) to determine whether (i) fire affected time of bud break and (ii) time of fruit ripening affected seed germination. Statistical analyses revealed that shoot reproductive status and fire treatments significantly affected time of bud break and the lag between bud break and leaf production. Shoot reproductive status explained 27% (P<0.001) while the interaction between reproductive status and fire treatments explained 34% (P<0.0001) of the variation in time at bud break. The appearance of the first leaf was delayed by 4 weeks in reproductive shoots compared with vegetative shoots. Shoot reproductive status explained 28% (P<0.0001) of the variation in the lag between bud break and appearance of the first leaf suggesting the existence of resource competition between reproduction and vegetative growth. However, reproductive status and fire treatments did not affect shoot size and leaves produced because replacement shoots after dieback due to fire were as long as shoots surviving from previous years due to insignificant annual shoot extension among the latter. There was high autocorrelation in the germination rate of seed-lots with seeds from fruits ripening early having a significantly higher germination rate (47% in 2002 and 89% in 2004) than those from fruits ripening later (3% in 2002 and 53% in 2004). Since time at bud break and fruit ripening were linked, it is proposed that late bud break results in reduced fitness in L. edulis because of reduced seed germination rate. Early and late dry season fires that delay bud break and destroy reproductive structures, respectively, also reduce this measure of fitness.     

Persistence of resprouting species after fire in natural and post‐mine restored shrublands in southwestern Australia

Questions: Is post‐fire persistence of resprouting species lower in restored sites, and is survival related to lignotuber size? Location: Southwestern Australia, Eneabba, 300 km north of Perth. Methods: Post‐fire persistence of 10 lignotuberous shrub species was compared between three sites restored 8–24 years ago after mineral‐sand mining and three surrounding natural shrubland sites (8–24 years since previous fire). Results: Overall persistence of species was 11–93% in restored sites (mean 52%) and 79–100% in natural sites (mean 96%). Persistence increased with time since rehabilitation for five species with <25% of individuals in three species surviving in the youngest stand. For equivalent crown size, average lignotuber circumferences were 50% smaller at restored sites and this probably accounted for their higher post‐fire mortality. Apart from differences in the age of plants, restored sites had lower soil penetrability than natural sites, which may have restricted rootstock development. A tradeoff favoring a higher crown volume to lignotuber size ratio was apparent in nine of the ten species with greater crown volumes (by 37%) and smaller lignotubers (by 36%) in restored sites. Two resprouting species for which crown seed store was quantified had much higher fecundity in restored sites. Conclusions: Fires reduced resprouter persistence in restored sites owing to poor development/insufficient size of lignotubers. Further management after fires is required, including application of resprouter seeds/seedlings on restored topsoil, transplanting adult resprouters (where viable) from natural areas ahead of the mining front. Low intensity/patchy fires are recommended on long unburnt sites. Resprouter survival would have likely been much greater in the first place if a deeper sandy soil profile was rehabilitated, thereby providing a more suitable medium for lignotuber development.     

Effects of cutting and rainfall pattern on resprouting vigour and growth of Erica arborea L.

Abstract. This study analyses the effects of recurrent cutting and rainfall pattern on sprout and genet growth in the resprouting shrub Erica arborea. Three different intervals between consecutive clear-cutting events were applied: 30, 5 and 2 yr. Above-ground genet biomass after 2 yr of treatment application was correlated with burl size and decreased with increasing recurrence of cutting, indicating that more than 5 yr were needed to re-establish the resprouting potential of genets. The effect of rainfall on growth was evaluated through the correlations between sprout RGR and several variables related to the rainfall pattern at different regeneration stages. The effect of the rainfall pattern on sprout RGR was dependent on the regeneration age, suggesting that water availability becomes more limiting after two years of regrowth.     

Comparative physiology of burned and unburned Rhus laurina after chaparral wildfire

Summary Laurel Sumac (Rhus laurina) is a dominant member of the coastal chaparral community of southern California that survives periodic burning by wildfires by resprouting from a lignotuber (root crown). We investigated the physiological basis for resprouting by comparing shoot elongation, leaf nitrogen content, tissue water status, leaf conductance to water vapor diffusion, and photosynthetic rates of post-fire R. laurina to those of adjacent unburned shrubs. Resprouts had higher rates of shoot elongation, leaf conductance, and photosynthesis than mature, unburned shrubs. Leaf nitrogen contents were elevated in burned shrubs even though their leaves developed interveinal chlorosis. A comparison of soil water potential to predawn water potential indicated that roots of R. laurina remain active below 2 m during the first summer drought after wildfire. Our results support the hypothesis that lignotubers not only contain dormant buds that develop into aerial shoots after wildfire but they also supply nutrient resources that enhance shoot elongation. Because R. laurina is relatively sensitive to drought, yet very successful in its rapid recovery after fire, maintaining an active root system after shoot removal may be the primary function of the massive lignotuber formed by this species.     

Continuous basal sprouting from a lignotuber:Arbutus unedo L. andErica arborea L., as woody Mediterranean examples

Summary The two dominant species of the Corsican mattoral,Arbutus unedo L. andErica arborea L., can produce abundant sprouts from the lignotuber not only immediately after fire but also more or less continuously in the absence of major disturbance. The lignotuber appears to be more important during the early stages of development; the result is an increase in the number of sprouts during the 25 years following the establishment of the individuals. Later the lignotuber seems to lose the ability to ensure the development of new basal sprouts. A hypothesis is that the presence of a lignotuber is related to the growth form.Arbutus unedo andErica arborea show behaviour intermediate between acrotony and basitony, as the shoots show acrotony, and continuous sprouting is characteristic of basitonic species. The fact that sprouting from the lignotuber is not necessarily a result of fire suggests that the relation between fire and vegetation in the Mediterranean region should be reconsidered.     

Phosphorus accumulation by lignotubers of jarrah (Eucalyptus marginata Donn ex Sm.) seedlings grown in a range of soils

Summary Jarrah seedlings were grown in six virgin Western Australian soils for up to 27 months. Lignotubers were produced in all soils and formed 10–16% of plant dry weight. The phosphorus concentration in the lignotuber (250–800 g g^–1) was nearly twice that in the stem and roots. The lignotuber contained 10–30% of total plant phosphorus and like the leaves was a sink for phosphorus. In one lateritic soil the phosphorus concentrations of lignotuber and stem barks were similar. However, in the same plants the concentration of phosphorus in the lignotuber wood was five times the phosphorus concentration in stem wood. Hence both lignotuber bark and sap wood in young jarrah seedlings are storage sites for phosphorus. X-ray probe analysis showed that wood phosphorus was associated with the ray parenchyma. Unlike phosphorus, nitrogen did not accumulate in the lignotuber and the concentrations of nitrogen were similar for roots, lignotubers and stems.