6.6. Resprouting capacity after major disturbance

The capacity of a plant species to resprout after destruction of most of its above-ground biomass is an important attribute for its persistence in ecosystems where recurrent major disturbances are common. Fire (natural or anthropogenic), hurricane-force wind and logging are the most obvious and widespread major disturbances; however, extreme drought or frost events, severe grazing, browsing or trashing by large herbivores, landslides, flooding and other short-term large-scale erosion events also qualify. There appear to be ecological trade-offs between sprouters and non-sprouter plants. Compared with non-sprouters, sprouters tend to show a larger allocation of carbohydrates to below-ground organs (or storage organs at soil-surface level); however, their biomass growth tends to be slower, and their reproductive output lower. The contribution of sprouters to species composition tends to be associated with the likelihood of major biomass-destruction events, as well as to the degree of stress in terms of available resources.

How to assess?

Here, we define resprouting capacity as the relative ability of a plant species to form new shoots after destruction of most of its above-ground biomass, using reserves from basal or below-ground plant parts. The following method is a clear compromise between general applicability and rapid assessment on the one hand and precision on the other. It is particularly relevant for woody plants and graminoids, but may also be applied to forbs. Within the study site, search for spots with clear symptoms of a recent major disturbance event. In general, this event should have been within the same year. However, if only woody species are being considered, the assessment may be carried out up to 5 years after the disturbance (as long as shoots emerging from near the soil surface can still be identified unambiguously as sprouts following biomass destruction). For each species, try to find any number of adult plants between 5 and 50 individuals (depending on time available) from which as much as possible but at least 75% of the live above-ground biomass was destroyed, including the entire green canopy. This is to ensure that regrowth is only supported by reserves from basal or below-ground organs. Note that in the case of trunks and branches of woody plants, old, dead xylem (wood) is not considered as part of the live biomass. Thus, if a tree is still standing after a fire, but all its bark, cambium and young xylem have been killed, it should be recorded as destruction of 100% of the above-ground biomass.

Make sure that enough time has lapsed for possible resprouting. Estimate (crudely) the average percentage of above-ground biomass destroyed among these plants (a measure of disturbance severity) by comparing against average undamaged adult plants of the same species. Multiply this percentage by the percentage of the damaged plant population that has resprouted (i.e. formed new shoots emerging from basal or below-ground parts) and divide by 100 to obtain the ‘resprouting capacity’ (range 0–100, unitless). When data are available from more than one site, take the highest value as the species value, although this ignores the fact that great intraspecific variability in sprouting capacity may occur. In longer-term studies, resprouting may be investigated experimentally by clipping plants to simulate destruction of 75–100% of the above-ground biomass (in which case, the clipped parts can be used for other trait measurements as well). If fewer than five plants with ‘appropriate’ damage can be found, give the species a default value of 50 if any resprouting is observed (50 being halfway between ‘modest’ and ‘substantial’ resprouting, see below). In species where no resprouting is observed merely because no major biomass destruction can be found, it is important to consider this a missing value (not a value of zero).

Broad interspecific comparisons have to take into account an intraspecific error of up to 25 units as a result of the dependence of resprouting capacity on the severity of disturbance encountered for each species. However, within ecosystems where different species suffer the same disturbance regime, direct comparisons should be safe.

Special cases or extras

(1) Data from literature. Useful and legitimate data may be obtained from the literature or by talking to local people (e.g. foresters, farmers, rangers). Make sure that the same conditions of major destruction of above-ground biomass have been met. In such cases, assign subjective numbers for resprouting capacity after major disturbance as follows: 0, never resprouting; 20, very poor resprouting; 40, moderate resprouting; 60, substantial resprouting; 80, abundant resprouting; and 100, very abundant resprouting. The same crude estimates may also be used for species for which the more quantitative assessment is not feasible, e.g. because the non-resprouting individuals are hard to find after disturbance, as is common in some herbs.

(2) Strongly clonal plants. In the case of strongly clonal plants, it is important to assess whether damaged ramets can resprout from below-ground reserves and not from the foliage of a connected ramet. Therefore, in such species, resprouting should be recorded only if most above-ground biomass has been destroyed for all ramets in the vicinity.

(3) Resprouting of young plants. Additional recording of resprouting ability of young plants may reveal important insights into population persistence, although this could also be seen as a component of recruitment. Thus, data on the age or size limits for resprouting ability may reveal important insights into population dynamics. It is known that some resprouting species cannot resprout before a certain age or size, and others may lose their resprouting capacity when they attain a certain age or size.

(4) Resprouting after smaller biomass destruction. Additional recording of resprouting after less severe biomass destruction may provide useful insights into plant response to disturbances. For instance, Quercus suber and many Eucalyptus spp. can resprout from buds located in high positions along the stem, following a fire. Be aware that species highly adapted to fire (such as these examples) may give the false impression that an area has not been exposed to severe fires recently. Other species in the same area, or direct fire observations, should provide the evidence for that. The approach of recording resprouting after less severe biomass destruction could also be applied to the study of resprouting in the face of disturbances other than fire, such as herbivory or trashing by vertebrates.
 
References on theory, significance and large datasets: Noble and Slatyer (1980); Everham and Brokaw (1996); Pausas (1997); Kammesheidt (1999); Bellingham and Sparrow (2000); Bond and Midgley (2001); Higgins et al. (2000); Del Tredici (2001); Burrows (2002); Vesk and Westoby (2004); Pausas and Bradstock (2007); Poorter et al. (2010).