Fire exclusion changes belowground bud bank and bud-bearing organ composition jeopardizing open savanna resilience

Bud production, dormancy, and mortality patterns differ by growth form and photosynthetic pathway following high-energy fire

Aboveground growth and production of native perennial grasses are determined by vegetative reproduction from belowground bud banks. Despite their importance, the phenology and dynamics of these belowground bud banks are poorly researched, even for dominant grass species. This information becomes even more essential for managers considering the potential use of high-energy fires to reduce encroaching woody shrubs because it might impact herbaceous bud bank dynamics and resultant grass productivity and relative abundance. The objectives of this study were to assess long-term bud bank dynamics of two dominant perennial grasses with different growth forms and physiologies, Nassella leucotricha and Hilaria belangeri, in a Texas semiarid savanna and determine the impact of fire energy on the recovery of their bud bank dynamics. Our experimental treatments were applied in the summer and consisted of replicated and randomized no burn (control), low-energy burn, and high-energy burn plots. For both species, the total bud number peaked in the spring and was lowest in the winter, although N. leucotricha had fewer buds in winter than H. belangeri and greater variability in total buds. For both species, dormant buds increased during the winter and active buds decreased. However, N. leucotricha maintained a smaller dormant bud bank through the winter, with larger fluctuations in total buds. In high-energy burned treatments, N. leucotricha had some bud loss but recovered; 8 months postfire, bud counts were comparable to the low-energy and control treatments. However, H. belangeri did not return to pretreatment bud totals in high-energy burned treatments during the study period. This suggests that grass productivity should not be reduced over the long term following restoration of woody-encroached grasslands with high-energy fire but that managers should consider potential shifts in species dominance from differential responses of grass species within the community.

Short-term fire exclusion affects germination and seed traits in tropical savannas

In fire-prone ecosystems, plant traits are influenced by the fire regime, thus reproduction and establishment can be altered by this disturbance. Changes in fire frequency and history can therefore influence seed and germination traits. We investigated the effects of short-term fire exclusion on seed and germination traits of species from tropical open savannas. Seeds from 27 species were collected from two areas with distinct fire histories: recently and frequently burned (RB) or unburned for 5 to 7 years (E). Seeds from both areas underwent germination trials under optimal conditions for 30 days. Also, 10 species were exposed to high temperature treatments (100 or 200 °C) and seed and germination traits measured. Comparisons were then made for each trait, analysing each species separately, between the two areas. Approximately 85% of species studied had at least one of their germination traits altered in the RB area compared to the E area. Clear differences included lower viability and faster germination in seeds from RB areas. Seed traits of 70% of measured species differed between the two areas. Our results show species-specific trait response to different fire histories. For example, faster germination and lower viability of seeds from RB plots suggest selection for faster maturing individuals and differences in resourcing, respectively, under a regime of frequent fire. This study provides insights into fire effects on regeneration responses of tropical savanna species and also points to the need for more studies evaluating the effects of fire history on seed traits.

Fire facilitates ground layer plant diversity in a Miombo ecosystem

BACKGROUND AND AIMS

Little is known about the response of ground layer plant communities to fire in Miombo ecosystems, which is a global blind spot of ecological understanding. We aimed: (1) to assess the impact of three experimentally imposed fire treatments on ground layer species composition and compare it with patterns observed for trees; and (2) to analyse the effect of fire treatments on species richness to assess how responses differ among plant functional groups.

METHODS

At a 60-year-long fire experiment in Zambia, we quantified the richness and diversity of ground layer plants in terms of taxa and functional groups across three experimental fire treatments of late dry-season fire, early dry-season fire and fire exclusion. Data were collected in five repeat surveys from the onset of the wet season to the early dry season.

KEY RESULTS

Of the 140 ground layer species recorded across the three treatments, fire-maintained treatments contributed most of the richness and diversity, with the least number of unique species found in the no-fire treatment. The early-fire treatment was more similar in composition to the no-fire treatment than to the late-fire treatment. C4 grass and geoxyle richness were highest in the late-fire treatment, and there were no shared sedge species between the late-fire and other treatments. At a plot level, the average richness in the late-fire treatment was twice that of the fire exclusion treatment.

CONCLUSIONS

Heterogeneity in fire seasonality and intensity supports diversity of a unique flora by providing a diversity of local environments. African ecosystems face rapid expansion of land- and fire-management schemes for carbon offsetting and sequestration. We demonstrate that analyses of the impacts of such schemes predicated on the tree flora alone are highly likely to underestimate impacts on biodiversity. A research priority must be a new understanding of the Miombo ground layer flora integrated into policy and land management.

Ancient grasslands guide ambitious goals in grassland restoration

Grasslands, which constitute almost 40% of the terrestrial biosphere, provide habitat for a great diversity of animals and plants and contribute to the livelihoods of more than 1 billion people worldwide. Whereas the destruction and degradation of grasslands can occur rapidly, recent work indicates that complete recovery of biodiversity and essential functions occurs slowly or not at all. Grassland restoration-interventions to speed or guide this recovery-has received less attention than restoration of forested ecosystems, often due to the prevailing assumption that grasslands are recently formed habitats that can reassemble quickly. Viewing grassland restoration as long-term assembly toward old-growth endpoints, with appreciation of feedbacks and threshold shifts, will be crucial for recognizing when and how restoration can guide recovery of this globally important ecosystem.