Limitations to sustainable frankincense production: blocked regeneration, high adult mortality and declining populations

Abstract

Summary 1.Resins are highly valued non-timber forest products (NTFP). One of the most widely traded resins is frankincense, tapped from several Boswellia tree species (Burseraceae). Exploited Boswellia populations often show poor regeneration, but the demographic consequences of these bottlenecks are unknown. Here we report on the first large-scale demographic study of frankincense-producing trees. 2. We studied 12 populations of Boswellia papyrifera in northern Ethiopia, varying in altitude and productivity. Six of these populations had been tapped before and were tapped during the study. Survival, growth and fecundity were determined for 4370 trees and 2228 seedlings, in 22.8 ha over a 2-year period. We also studied a remote population where no grazing and tapping took place. Matrix models were used to project population growth and frankincense production under four restoration scenarios. 3. Population structures of both tapped and untapped populations showed clear gaps. Small seedlings were abundant in all populations, but none developed into persistent saplings. Such saplings were only present in the remote population. Fire and grazing are the likely causes of this regeneration bottleneck. 4. Adult mortality was high (6-7% per year) in both tapped and untapped populations, probably caused by beetle attacks and fire. Unexpectedly, tapped populations presented higher diameter growth rates and fecundity compared to untapped populations. These differences are probably caused by non-random selection of exploited populations by tappers. 5. Under the 'business as usual' scenario, population models projected a 90% decline in the size of tapped and untapped populations within 50 years and a 50% decline in frankincense yield within 15 years. Model simulations for restoration scenarios revealed that populations and frankincense production could only be sustained with intensive management leading to full sapling recruitment and a 50-75% reduction in adult mortality. 6. Synthesis and applications. Regeneration bottlenecks and high adult mortality are causing rapid decline in frankincense-producing tree populations in Ethiopia. This decline is unlikely to be a consequence of harvesting and is probably driven by fire, grazing and beetle attacks. Fire prevention and the establishment of non-grazing areas are needed. Our results show that other factors than exploitation may seriously threaten populations yielding NTFP.

Fine-scale spatial genetic structure in the frankincense tree Boswellia papyrifera (Del.) Hochst. and implications for conservation

“…The population was characterized by patches of abundant seedlings and saplings and a few small and big-sized adult trees. Unlike Groenendijk et al (2012) in the population in Metema, in the North of Ethiopia, we observed that several small B. papyrifera individuals as tall as only 1.5 m were already flowering in this population.…”

“…The two populations were treated as replications for the FSGS analysis of the species. All four life cycles/size classes described in Groenendijk et al (2012) were present simultaneously in these two populations, although the relative abundance differed between the two populations.…”

“…Populations in Northern (Abergele) and Northwestern (Metema) Ethiopia are suffering from lack of saplings and small trees (Abiyu et al 2010;Eshete et al 2011;Groenendijk et al 2012;Tolera et al 2013). In these Boswellia populations, non-permanent seedlings (seedlings of which the shoots die back during the dry season and reappear in the rainy season) are abundant, but they do not develop to the sapling stage mainly because of the impacts of frequent forest fire and intensive grazing in the area (Groenendijk et al 2012;Tolera et al 2013). A similar situation was reported for Eritrea Rijkers et al 2006) and Sudan (Adam and El Tayeb 2008;Abtew et al 2012).…”

Determination of Growth Rate and Age Structure of <i>Boswellia papyrifera</i> from Tree Ring Analysis: Implications for Sustainable Harvest Scheduling

“…The annual rainfall of Metema ranges from 660-1100 mm with mean annual rainfall of about 884 mm (Groenendijk et al, 2012). Metema has a uni-modal rainfall pattern.…”

DEMOGRAPHY OF Astrocaryum malybo H.Karst. (ARECACEAE) IN COLOMBIA, RECOMMENDATIONS FOR ITS MANAGEMENT AND CONSERVATION

“…Based on this transformation, the population dynamics of A. malybo was described as in standard matrix models: n(t + 1) = K n(t). [ 111 ] population growth rate (λ t ) was calculated as in Groenendijk et al (2012):…”