Dendrochronology in the dry tropics: the Ethiopian case

Abstract

Dendrochronology is developing outside temperate and boreal regions. Over the past decade substantial progress has been made in Mediterranean and wet tropical regions. However, research in dry tropical regions, notably those of sub-Saharan Africa, has remained fragmentary. Here, we try to identify the unique challenges and opportunities of dendrochronology in the dry tropics. First, we briefly review the status of dendrochronology outside temperate and boreal regions with an emphasis on subSaharan Africa. Subsequently, we focus upon one of those areas where dendrochronology in the dry tropics is at the forefront of scientific advance: Ethiopia. A detailed review of tree ring studies in the lowlands and highlands highlights the complexity of ring formation and made us identify four major types of growth ring expression: anatomically not Trees DOI 10.1007/s00468-010-0521-y distinct rings, multiple rings per year, annual rings and multiple missing rings. This complex tree growth behaviour is associated with large-scale variations in precipitation regime (unimodal to multimodal) and relatively small-scale variations in tree sensitivity to water availability. Literature results are used to develop a scheme that can be used to predict differences in growth ring formation along gradients in these two factors. Because of the exceptional growth sensitivity of and the importance of local site conditions (topography, biological factors, etc.) for most trees sampled, those growing at the limits of their ecological amplitude are prone to possess multiple rings per year or multiple missing rings. In such circumstances, site selection should not always take place at the limits of the ecological amplitude of a species, but may sometimes have to be diverted to more mesic environments. Successful studies are now appearing, such as those reporting correlations between tree ring chronologies and Blue Nile river flows.

CLIMATE-TREE GROWTH RELATIONSHIPS OF Mimosa tenuiflora IN SEASONALLY DRY TROPICAL FOREST, BRAZIL

“…Even for the year 2005 with the lowest rainfall, distinct growth rings were formed, although with the lowest radial growth. Rainfall correlated positively with growth of M. tenuiflora, a similar result obtained in other tropical forest regions (WILS et al, 2011). However, in Limoeiro do Norte, this correlation was low.…”

“…Annual rings allow recovery of information on growth with precision and help to understand the dynamics of growth in relation to seasonality. In dry tropical regions several studies show a positive correlation between growth and precipitation (BRIENEN et al, 2011;ENQUIST;LEFFLER, 2001;FICHTLER et al, 2004;SEITZ, 2008;SCHONGART et al, 2006;VOLLAND-VOIGT et al, 2011;WILS et al, 2011;WORBES et al, 2003). Many researchers also apply the ring-width data to calculate the intervals of cutting cycles of natural forest in the tropics (BRIENEN; ZUIDEMA, 2006;COURALET et al, 2005;MATTOS et al, 2010;SCHONGART, 2008).…”

Early assessment of seasonal forage availability for mitigating the impact of drought on East African pastoralists

“…4) Alternative drought measurements such as long-term rainfall measurements from weather stations (Tapiador et al 2012) and dendrochronological data (Gebrekirstos et al 2014;Wils et al 2011).…”

Temperature modulates intra-plant growth of Salix polaris from a high Arctic site (Svalbard)

“…The comparison of growth patterns was based on the presence of pointer years (Schweingruber et al 1990), generally represented by well-developed wide rings, which could be easily distinguished in most of the sections. Ringwidth matching was complemented by the method applied to tropical species (Wils et al 2009(Wils et al , 2011, which uses other visual features, such as vessel size and density. A ring was defined to be partially missing rings (PMR) if missing from at least one radius of a particular cross-section, but still observed along other radii of the same section.…”