© 2006 Heron Publishing—Victoria, Canada
Interspecific variation in vessel size, growth and drought tolerance of broad-leaved trees in semi-arid regions of Kenya
Shoko Kondoh (1, 2, 3), Hisashi Yahata (4), Tohru Nakashizuka (5) and Michio Kondoh (6)
1. Graduate School of Social and Cultural Studies, Ropponmatsu, Chou-ku, Fukuoka, 810-8560, Japan / 2. Center for Ecological Research, Kyoto University, Kamitanakami Hirano-cho, Otsu, Shiga 520-2113, Japan / 3. Corresponding author (tsuji@ecology.kyoto-u.ac.jp) / 4. Institute of Tropical Agriculture, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan / 5. Research Institute for Humanity and Nature, Takashima-cho, Kamigyo-ku, Kyoto 602-0878, Japan / 6. Department of Environmental Solution Technology, Faculty of Science and Technology, Ryukoku University, Yokoya, Seta Oe-cho,
Otsu 520-2194, Japan / Received July 12, 2005; accepted October 5, 2005; published online April 3, 2006
Summary
In semi-arid regions, trees often wither during the dry season. Withering is sometimes manifest as die-back, whereby whithering
results in shoot death, which progresses downward from the uppermost part of the crown. In this study, we measured the relationships
between height growth and diameter at breast height, die-back frequency and severity, vessel size and specific hydraulic conductivity
of four evergreen (Senna siamea (Lamk) H.S. Irwin & Barneby, Jacaranda mimosifolia D. Don, Azadirachta indica A.H.L. Juss and Acacia gerrardii Benth.) and one deciduous (Melia volkensii Gürke) plantation tree species in Kenya, which has a conspicuous dry season. Die-back occurred readily in some species, but
not in others. Senna siamea showed the highest specific hydraulic conductivity and the highest growth rate among the five species and was quite susceptible
to die-back. Among species, height growth and specific hydraulic conductivity were positively correlated with vessel size
and negatively correlated with die-back frequency, suggesting a trade-off between growth rate and drought tolerance. This
implies that an adaptation to rapid growth under humid conditions leads to low drought tolerance. However, the deciduous tree
Melia volkensii showed high specific hydraulic conductivity and growth, with no symptoms of die-back, implying that a mechanism associated
with the deciduous habit results in drought avoidance by reducing the requirement for water during the dry season.
Keywords:
deciduous tree, die-back, drought stress, water transport, xylem architecture.
