Bamboo, climate change and forest use: A critical combination for southwestern Amazonian forests?

Abstract

About 160 000 km² of forests in the border zone between Brazil and Peru are dominated by semi-scandent bamboos (Guadua spp.). We argue that both predicted decreased precipitation during the dry season and widespread anthropogenic disturbances will significantly increase the distribution and biomass of bamboos in the area. Seasonal dryness favours the growth of evergreen bamboos in relation to trees that shed their leaves during the dry season. Disturbance can be beneficial for the bamboo because, as a clonal plant, it is often able to recover more rapidly than trees. It also withstands dry season better than many trees. The bamboo life cycle ends in a mass mortality event every 28 years, producing potential fuel for a forest fire. Presently, natural forest fires hardly exist in the area. However, in the projected future climate with more pronounced dry season and with increased fuel load after bamboo die-off events the forests may start to catch fire that has escaped from inhabited areas or even started naturally. Fires can kill trees, thus further increasing the fuel load of the forest. As a result, the landscape may start to convert to a savanna ecosystem.

Keywords: Deciduous forest; Fire; Forest management; Guadua; Rain forest.

Fig. 1

Average precipitation during the three driest consecutive months in western Amazonia. Precipitation data downloaded from the Chelsa site (Karger et al. 2017). The cities of Rio Branco (RB) and Cruzeiro do Sul (CdS) are marked with a triangle. The bamboo forests, as mapped by de Carvalho et al. (2013), are marked in yellow. The base map is the elevation model of the shuttle radar topography mission

Fig. 2

Walter climate diagrams for the cities of Rio Branco and Cruzeiro do Sul. The diagrams are modified from ClimateCharts.net

Fig. 3

A. Aerial view from the Chandless State Park in central Acre showing abundant deciduous trees during the dry season (photo: E. Ferreira 2008). B. Green and leafless tree canopies in southern Acre (Digital Globe image, 28.9.2012, 9° 58′ S, 70° 37′ W)

Fig. 4

a Bamboo stand occupying a roadside in southeastern Acre (10° 4′ S, 67° 36′ W; photo: R. Kalliola 2017). b Forest dotted by household-sized forest clearings in the Chico Mendes Extractive Reserve (10° 38′ S, 69° 17′ W; image from Google Earth)

Fig. 5

A possible scenario of the future of the bamboo forest area in southwestern Amazonia. The upper diagram depicts tropical vegetation along a natural gradient of increasing dryness without the presence of bamboo. The evergreen forest gives way to deciduous vegetation that turns to savanna by the effect of fire. The lower diagram illustrates the same gradient with the presence of mast flowering semelparous bamboo under a rapid change of climate and extensive anthropogenic disturbance. The bamboo competes especially with deciduous trees. Bamboo die-off events increase the flammability of the vegetation, allowing fire to affect vegetation in wetter climatic conditions than would happen without the bamboo. Fires consuming dead bamboo are so strong that they kill native deciduous trees. Dead trees provide fuel for further fires. The vegetation turns to savanna, consisting of a mixture of introduced weedy species and native savanna species that manage to disperse to the area from existing savannas that lie some two hundred kilometres away in Bolivia