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Species are often controlled by biotic factors such as competition at the warm edge of their distribution range. Disturbances at the treeline, disrupting competitive dominance, may thus enable alpine species to utilize lower altitudes. We searched for evidence for range expansion in grazed, fire-managed Ethiopian subalpine Erica heathlands across a 25-year chronosequence. We examined vascular plant composition in 48 plots (5 × 5 m) across an altitudinal range of 3,465-3,711 m.a.s.l. and analyzed how community composition changed in relation to increasing competition over time (using a Shade index based on Erica shrub height and cover) and altitude. Species' habitats and altitudinal ranges were derived from literature. Time since fire explained more variation (r = .41) in species composition than altitude did (r = .32) in an NMDS analysis. Community-weighted altitudinal optima for species in a plot decreased strongly with increasing shade (GLM, Standardized Regression Coefficient SRC = -.41, p = .003), but increased only weakly with altitude (SRC = .26, p = .054). In other words, young stands were dominated by species with higher altitudinal optima than old stands. Forest species richness increased with Log Shade index (SRC = .12, p = .008), but was unaffected by altitude (SRC = -.07, p = .13). However, richness of alpine and heathland species was not highest in plots with lowest Shade index, but displayed a unimodal pattern with an initial increase, followed by a decrease when shading increased (altitude was not significant). Our results indicate that disturbance from the traditional patch burning increases the available habitat for less competitive high-altitude plants and prevents tree line ascent. Therefore, maintaining, but regulating, the traditional land use increases the Afro-alpine flora's resilience to global warming. However, this system is threatened by a new REDD+ program attempting to increase carbon storage via fire suppression. This study highlights the importance of understanding traditional management regimes for biodiversity conservation in cultural landscapes in an era of global change.

The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRaP URL' above for details on accessing the published version and note that access may require a subscription.

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32Grass pollen is the world's most harmful outdoor aeroallergen and sensitivity varies between 33 species. Different species of grass flower at different times, but it is not known how airborne 34 communities of grass pollen change in time and space. Persistence and high mobility of grass 35 pollen could result in increasingly diverse seasonal pollen communities. Conversely, if grass 36 pollen does not persist for an extended time in the air, shifting pollen communities would be 37 predicted throughout the summer months. Here, using targeted high throughput sequencing, 38we tracked the seasonal progression of airborne Poaceae pollen biodiversity across Britain, 39 throughout the grass allergy season. All grass genera displayed discrete, temporally restricted 40 peaks of pollen incidence which varied with latitude, revealing that the taxonomic composition 41 of grass pollen exposure changes substantially across the allergy season. By developing more 42 refined aeroallergen profiling, we predict that our findings will facilitate the exploration of links 43 between taxon-specific exposure of harmful grass pollen and disease, with concomitant socio-44 economic benefits. 45 46 47