Resprout Growth Research Articles

Beavers, Bugs and Chemistry: A Mammalian Herbivore Changes Chemistry Composition and Arthropod Communities in Foundation Tree Species

The North American beaver (Castor canadensis Kuhl) and cottonwoods (Populus spp.) are foundation species, the interactions of which define a much larger community and affect a threatened riparian habitat type. Few studies have tested the effect of these interactions on plant chemistry and a diverse arthropod community. We experimentally examined the impact of beaver foraging on riparian communities by first investigating beaver food preferences for one cottonwood species, Fremont cottonwood (P. fremontii S. Watson), compared to other locally available woody species. We next examined the impact of beaver foraging on twig chemistry and arthropod communities in paired samples of felled and unfelled cottonwood species in northern Arizona (P. fremontii) and southwestern Colorado (narrowleaf cottonwood, P. angustifolia James, and Eastern cottonwood, P. deltoides W. Bartram ex Marshall). Four major patterns emerged: (1) In a cafeteria experiment, beavers chose P. fremontii six times more often than other woody native and exotic species. (2) With two cottonwood species, we found that the nitrogen and salicortin concentrations were up to 45% greater and lignin concentration 14% lower in the juvenile resprout growth of felled trees than the juvenile growth on unfelled trees (six of seven analyses were significant for P. fremontii and four of six were significant for P. angustifolia). (3) With two cottonwood species, arthropod community composition on juvenile branches differed significantly between felled and unfelled trees, with up to 38% greater species richness, 114% greater relative abundance and 1282% greater species diversity on felled trees (six of seven analyses with P. fremontii and four of six analyses with P. angustifolia were significant). The above findings indicate that the highest arthropod diversity is achieved in the heterogenous stands of mixed felled and unfelled trees than in stands of cottonwoods, where beavers are not present. These results also indicate that beaver herbivory changes the chemical composition in 10 out of 13 chemical traits in the juvenile growth of two of the three cottonwood species to potentially allow better defense against future beaver herbivory. (4) With P. deltoides, only one of five analyses in chemistry was significant, and none of the four arthropod community analyses were significant, suggesting that this species and its arthropod community responds differently to beaver. Potential reasons for these differences are unknown. Overall, our findings suggest that in addition to their impact on riparian vegetation, other mammals, birds, and aquatic organisms, beavers also may define the arthropod communities of two of three foundation tree species in these riparian ecosystems.

Interspecific variation in post‐disturbance growth responses of a savanna tree community and its implications for escaping the fire trap

AbstractVegetation states in savannas are highly sensitive to tree growth rates, which determine whether individual trees can “escape” periodic disturbances. Resprouting trees have lopsided shoot:root ratios and are often multi‐stemmed, and these variables can modify post‐disturbance growth rates and therefore the probability of escape. To date, few studies have systematically examined the implications of interspecific variation in these factors for escape. We conducted a two‐year field experiment across 16 tree species in a South African lowveld savanna to quantify growth metrics following topkill. We examined the dependence of growth on pre‐disturbance stem size and the relationship between growth rate and the tendency of trees to produce a few large vs. many small resprouts following disturbance. We found that resprout growth was strongly influenced by pre‐disturbance size, but the strength of this relationship did not vary across species. In contrast, our results showed that fast‐growing species tended to allocate resources toward a few dominant stems, while slow‐growing species allocated new biomass towards many smaller stems. Tree species that produced a few large stems also tended to produce individual stems that were tall and thin, further suggesting that the “few large vs. many small” axis is linked to intrinsic species attributes. These findings have implications for understanding how interspecific variation in savanna tree communities may influence their ability to escape disturbance traps.

Control mecánico del árbol no nativo Ligustrum lucidum (Oleaceae): supervivencia, regeneración y costos

Introducción y objetivos: Existe una creciente demanda de estudios que evalúen el costo-beneficio de la aplicación de técnicas de control de especies no nativas. Evaluamos la eficiencia de la aplicación de dos tratamientos de control mecánico sobre la especie no nativa Ligustrum lucidum, a través de la regeneración por rebrote y por semilla, integrando costos y esfuerzo.M&M: Asignamos 120 árboles a tres grupos de tratamientos: 1) testigo, sin tala ni aplicación de polietileno; 2) tala, y 3) tala con aplicación de polietileno sobre el tocón. Seleccionamos 60 árboles en fisonomía de bosque y 60 en fisonomía de matorral. Removimos manualmente todos los plantines menores a 50 cm alrededor de cada árbol tratado.Resultados: Transcurridos 12 meses y dos aplicaciones de tratamientos, la supervivencia de los testigos, tala y tala con polietileno fue 100%, 95% y 68%, respectivamente. La altura de los rebrotes en el tratamiento de tala y en el de tala con polietileno fue 78% y 95% menor respectivamente, comparado con los individuos testigos. La fisonomía del sitio solo influyó sobre la densidad de plantines, siendo 300% mayor en bosque que en matorrales. El costo del tratamiento tala con polietileno fue 150% mayor al costo del tratamiento tala, pero fue compensado por la mayor eficacia para reducir la supervivencia y la altura de rebrotes.Conclusiones: Debido a la mayor eficiencia, recomendamos la aplicación del tratamiento de tala con polietileno. Sugerimos remover manualmente los plantines en matorrales o sitos con baja cobertura de adultos de L. lucidum.

Leaf and bark functional traits predict resprouting strategies of understory woody species after prescribed fires

In temperate forests, both deciduous and evergreen species with small or large leaves coexist in the understory and resprout after prescribed burnings. This diversity of traits suggests that there are different strategies operating after the initial resprout growth to re-acquire space, capture resources and resist additional stresses. This study aims to understand resprout vigor 3 years after burning of woody understory species with different leaf traits and bark investment (i.e., the ratio between bark thickness and basal stem diameter).In two temperate forests, we burned one stand in late spring and another in fall. After 3 years, we studied resprout number and resprout basal diameter and length of ten individuals of six species per stand. Three species were common in both forests and three were different. Therefore, species of both forests were grouped in three groups based on leaf traits and in three different groups according to their bark investment. Besides the expected positive effect of pre-fire plant size, resprout number and vigor were higher after burning in spring than in fall. The higher resprout volume in evergreens, with small specific leaf area (SLA), than in deciduous species, with large SLA, may be related to evergreens having a longer possible growing season than deciduous species. In addition, species in different leaf groups differed in the ratio of resprout length to diameter growth, suggesting that it is important for deciduous small-leaved species to grow tall rapidly before they are shaded by large leaved species. In contrast, no direct effect of light availability on resprout vigor was detected. Bark investment did not explain resprout vigor but did affect resprout number in the low bark investment group. In this group, resprout number decreased with increasing maximum fire temperature. Based on our results, burning in the fall is advisable when the management objective is to minimize the recovery of the understory. In addition, to reduce the dominance of understory woody species with low bark investment, our study suggests that understory fires must be performed with moderate to high intensity.

Effects of fire frequency and season on resprouting of woody plants in southeastern US pine-grassland communities

Past studies suggest that rates of woody plant resprouting following a "topkilling" disturbance relate to timing of disturbance because of temporal patterns of below-ground carbohydrate storage. Accordingly, we hypothesized that fire-return interval (1 or 2 years) and season of burn (late dormant or early growing season) would influence the change in resprout growth rate from one fire-free interval to the next (Δ growth rate) for broadleaf woody plants in a pine-grassland in Georgia, USA. Resprout growth rate during one fire-free interval strongly predicted growth rate during the following fire-free interval, presumably reflecting root biomass. Length of fire-free interval did not have a significant effect on mean Δ growth rate. Plants burned in the late dormant season (February-March) had a greater positive Δ growth rate than those burned in the early growing season (April-June), consistent with the presumption that root carbohydrates are depleted and thus limiting during spring growth. Plants with resprout growth rates above a certain level had zero or negative Δ growth rates, indicating an equilibrium of maximum resprout size under a given fire-return interval. This equilibrium, as well as relatively reduced resprout growth rate following growing season fires, provide insight into how historic lightning-initiated fires in the early growing season limited woody plant dominance and maintained the herb-dominated structure of pine-grassland communities. Results also indicate tradeoffs between applying prescribed fire at 1- versus 2-year intervals and in the dormant versus growing seasons with the goal of limiting woody vegetation.

Selective thinning of Arbutus unedo coppices following fire: Effects on growth at the individual and plot level

In recent years, several Mediterranean forests subject to fire are becoming increasingly dominated by the resprouter species Arbutus unedo L. (strawberry tree). However, there is little information available about the management of these areas, and it is not clear if the approaches utilized for other, more abundant Mediterranean resprouter species such as Quercus ilex and Quercus cerrioides would produce similar results for A. unedo. In this study, performed in the NE Iberian Peninsula, we analyzed the effect of two post-fire treatment types, selective thinning and selective thinning plus understory clearing, on the growth of retained A. unedo resprouts and the new resprouting induced by the treatment itself. Treatment effects were analyzed at both the individual and plot level. Our results showed that, in the short term, retained resprouts on treated trees grew more in height and diameter (absolute and relative) than those on control trees, with no differences seen between treatment types. In the intermediate term, all the strawberry trees occurring on treated plots grew longer, and this growth was greater in plots that had been both thinned and cleared. New, induced resprouts were unaffected by the type of treatment applied. In contrast to other studies, we failed to find a negative relationship between the degree of induced resprouting and retained resprout growth We therefore conclude that, irrespective of understory clearing, the selective thinning of A. unedo improves coppice vertical structure. Retained resprouts grow more in diameter and will thus more rapidly become exploitable as firewood and timber. Also, the tree is kept free of dead fuel, reducing the risk of spreading fire.

Exotic deer diminish post-fire resilience of native shrub communities on Santa Catalina Island, southern California

Browsing by exotic mule deer on Santa Catalina Island (SCI) off the coast of southern California may diminish the post-fire resilience of native shrublands. To assess this, deer exclosures were established following a wildfire to monitor post-fire recovery of three dominant, native shrub species (Heteromeles arbutifolia, Rhus integrifolia, and Rhamnus pirifolia). Post-fire resprout growth, mortality, and tissue water status as well as pre- and post-fire shrub density and cover were measured inside and outside of deer exclosures. We found that deer browsing significantly limited post-fire resprout growth and led to increased mortality of resprouting H. arbutifolia shrubs (88 % mortality outside compared to 11 % inside exclosures). Post-fire resprouts maintained favorable water status during the study despite drought conditions, indicating that water stress was not a proximate cause of resprout mortality. Deer browsing resulted in a >93 % reduction in canopy coverage of dominant shrub species. The dramatic reduction of native shrubs at this site may create opportunities for displacement by exotic species, resulting in eventual vegetation-type conversion. The observed link between intense browsing and post-fire shrub mortality provides much needed information concerning the environmental impact of exotic deer on SCI and illustrates the interaction between exotic herbivores and fire on an island system.

Frequency and timing of stem removal influence Corylus americana resprout vigor in oak savanna

Shrubs are an important component of many ecosystems, contributing to spatial and resource heterogeneity and adding to life form and species diversity. Many shrub species have adapted to regular disturbances such as fire by resprouting after stem removal. The relative vigor with which shrubs resprout influences post-disturbance size and density of individuals and thus, can alter community structure. However, little is known about how disturbance frequency and seasonality influence resprouting. We studied resprout vigor of the native shrub American hazel ( Corylus americana Walter) in oak savanna in Minnesota, USA. We measured resprout growth of individual shrubs in response to the frequency and timing of clipping in relatively open and shaded conditions. We hypothesized that resprouting of C. americana would be negatively related to clip frequency, due to more rapid depletion of stored resources necessary for resprouting, and positively related to light availability. In 12 weeks following a single clipping, shrubs recovered 82% of the lost stem biomass in open savanna, but only 17% in shaded forest. In both open and closed sites, shrubs clipped three times or more resprouted only 10–15% as much biomass as those clipped once. Moreover, the timing of clipping had as large an effect on resprout potential as the number of clipping events, and small differences in timing were important. Plants clipped once in mid or late June or in July regrew 57, 17, and 8% as much biomass, respectively in the six weeks following clipping as those clipped in early June. These results illustrate that both the timing and number of disturbance events within a growing season can strongly influence shrub growth, which can have important implications for ecosystem structure, function, and management.

Comparative resprouting response of Savanna woody plant species following harvesting: the value of persistence

Understanding the relative ability of favoured fuelwood species to resprout following harvesting is integral to designing strategies for sustainable woodland resource utilisation. Harvester preference for particular woody plant species and plant size was examined in a formerly protected area, severely harvested over a short period of time. The resprouting response of harvested plants was measured five months after harvesting, towards the end of the wet season. Although a large proportion of stems of the dominant species ( Terminalia sericea and Dichrostachys cinerea) had been harvested, certain less common species were particularly targeted (e.g., Pterocarpus rotundifolius and Peltophorum africanum). Harvested plants were mostly larger than 4 cm in stem diameter. Almost all harvested plants of all species resprouted. Species differed in whether resprout growth was channelled into many small resprout shoots or fewer large shoots. The species most highly favoured by harvesters produced relatively large resprout shoots. Plant stem diameter was the most important determinant of resprout output, with both shoot number and their composite diameter increasing with increasing plant size. Cut height, although having no significant effect on resprout output, influenced the location of resprouting, with taller stumps having a higher proportion of resprout shoots originating from the stem than from the root crown. For all species, approximately a third of the resprout shoots of harvested plants died during the five months following harvesting. Shoots originating from the stem had a higher dieback than those growing from the root crown. Resprout biomass production over the five month period was considerable, amounting to 989 kg ha −1 (wet mass). An abundance of seedlings of the most common species may be a consequence of woodland thinning through harvesting.

Effect of fire season, aspect and pre-fire plant size on the growth of Arbutus unedo L. (strawberry tree) resprouts

Resprouting is an important survival strategy for many plant species that allows their survival after fire. The time of fire has been identified as one of the factors affecting the ability and vigor of resprouting in a variety of ways. It is believed that plants recovering after spring fire have a comparative advantage over those recovering after autumn fire due to the larger pool of stored carbohydrates in the beginning of the growing season which can lead in more vigor resprouting. In the current study we present the results of an experiment on the effect of fire season, aspect and pre-fire plant size on the resprout growth of the common Mediterranean shrub Arbutus unedo L. The growth parameters of height and diameter were monitored every 3 months for the total of 3 years after fire. Fire season has no immediate effect on resprout height by the end of the first post-fire growing season. It has however an effect on resprout diameter with plants recovering after spring fire reaching bigger diameter by the end of the first post-fire growing season. Aspect has an important effect on both height and diameter of resprouts. The pre-fire plant size was also found to be affecting growth of resprouts especially after the second post-fire growing season.

The role of disturbance in the co‐existence of the evergreen Quercus ilex and the deciduous Quercus cerrioides

Abstract:Question: Which is the response of the evergreen Quercus ilex and the deciduous Q. cerrioides to repeated disturbances?Location: central Catalonia (northeastern Spain), in the areas affected by two of the largest historically recorded wildfires in NE Spain: the Bages‐Berguedà fire (24 300 ha forested area burned in July 1994), and the Solsonès fire (14 300 ha burned in 1998).Methods: Survival and growth of individuals of Quercus ilex and Q. cerrioides were evaluated in plants subjected to different fire histories and experimental disturbances (burning, cutting or clipping) applied either before or after summer.Results: Survival was high (> 99%), with both species showing a similar high resistance to disturbances. Growth after experimental disturbance was positively related to the size of the individual before the latest forest fire occurred. Fire history had a large effect on resprout growth, as the repeated incidence of disturbances lowered the capacity of individuals to grow. The type and season of experimental disturbance experienced by plants had a large effect. Individuals that experienced total above‐ground loss had lower growth rates than those with partial loss. A similar pattern was observed in individuals disturbed after the summer in relation to those disturbed before summer.Conclusions: The larger growth rates recorded in Q. cerrioides across all fire histories and experimental treatments, and the higher vulnerability of Q. ilex to increased fire frequency, intensity of experimental disturbance, and disturbance season, provide evidence for the relatively high susceptibility of the latter to repeated disturbances. This view disagrees with the larger resilience of this species compared to co‐existing deciduous oaks, as reported.

The role of disturbance in the co-existence of the evergreen Quercus ilex and the deciduous Quercus cerrioides

Question: Which is the response of the evergreen Quercus ilex and the deciduous Q. cerrioides to repeated disturbances? Location: central Catalonia (northeastern Spain), in the areas affected by two of the largest historically recorded wildfires in NE Spain: the Bages-Bergueda fire (24 300 ha forested area burned in July 1994), and the Solsones fire (14 300 ha burned in 1998). Methods: Survival and growth of individuals of Quercus ilex and Q. cerrioides were evaluated in plants subjected to different fire histories and experimental disturbances (burning, cutting or clipping) applied either before or after summer. Results: Survival was high (> 99%), with both species showing a similar high resistance to disturbances. Growth after experimental disturbance was positively related to the size of the individual before the latest forest fire occurred. Fire history had a large effect on resprout growth, as the repeated incidence of disturbances lowered the capacity of individuals to grow. The type and season of experimental disturbance experienced by plants had a large effect. Individuals that experienced total above-ground loss had lower growth rates than those with partial loss. A similar pattern was observed in individuals disturbed after the summer in relation to those disturbed before summer. Conclusions: The larger growth rates recorded in Q. cerrioides across all fire histories and experimental treatments, and the higher vulnerability of Q. ilex to increased fire frequency, intensity of experimental disturbance, and disturbance season, provide evidence for the relatively high susceptibility of the latter to repeated disturbances. This view disagrees with the larger resilience of this species compared to co-existing deciduous oaks, as reported.

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.

No allocation trade-offs between flowering and sproutingin the lignotuberous, Mediterranean shrub

Trade-offs between allocation to sexual or vegetative regeneration capacity are well established as a driving force in the life history patterns of plants in fire-prone environments. However, it is not known whether such trade-offs exist in plants which after aboveground removing disturbances, such as fire, may regenerate by sexual (seeding) or asexual (sprouting) mechanisms. We evaluated whether in the fire-recruiting resprouter Erica australis, which after fire can regenerate by seedling establishment or resprouting, a larger investment in flowers and seeds prior to being disturbed by clipping its aboveground parts would decrease subsequent sprouting, that is, its vegetative regeneration capacity. We analysed the relationships between flower and seed production and the ensuing production and growth of sprouts of six plants from thirteen different sites in central-western Spain. We found no significant relationships between measures of sexual reproductive effort and resprout production and growth 6 months after clipping the aboveground parts of the plants. No evidence of trade-offs between sexual and asexual efforts was found. Furthermore, no significant relationship was found between lignotuber total non-structural carbohydrates and sexual reproductive effort. In addition, 2 years after the disturbance, resprout biomass was positively and significantly correlated with sexual reproductive effort prior to the disturbance. This indicates that growth of resprouts was higher at the sites where plants made a greater reproductive effort. The sites that were more favourable to producing flowers and seeds could also be more favourable to resprouting.

INDIRECT INTERACTIONS MEDIATED BY CHANGING PLANT CHEMISTRY: BEAVER BROWSING BENEFITS BEETLES

We documented an indirect interaction between beavers (Castor canadensis) and leaf beetles (Chrysomela confluens), mediated by changing plant chemistry of their cottonwood hosts (Populus fremontii × P. angustifolia). Resprout growth arising from the stumps and roots of beaver-cut trees contained twice the level of defensive chemicals as normal juvenile growth. However, rather than being repelled by these defenses, leaf beetles were attracted to resprout growth, resulting in a strong positive association between beavers and beetles. Why? Cottonwoods contain phenolic glycosides, chemicals that are defensive against mammalian herbivores, but are sequestered and used by the beetles for their own defense. Experiments showed that beetles fed resprout growth were better defended against their predators than those fed nonresprout growth. There also may have been a nutritional benefit, because the conversion of the plant’s defense, salicin and other phenolic glycosides, to salicylaldehyde releases glucose. Also, resprout growth contained more total nitrogen than did nonresprout growth. Transfer experiments showed that, in apparent response to these increased nutritional benefits, beetles fed resprout growth developed faster and weighed more at maturity. Although indirect interactions are much less studied than direct interactions, our work suggests that the indirect interactions resulting from beaver cutting of cottonwoods have important consequences for other organisms and could represent an important component of community structure. The habitat mosaics created by beaver herbivory increase arthropod biodiversity and may benefit other organisms such as birds and mammals. Furthermore, by stimulating the production of resprout growth, beavers may play an important role in the regeneration of a habitat type that is rapidly vanishing in the West.