The importance of history in understanding large tree mortality in African savannas

<p>Repeat airborne LiDAR data provides a unique opportunity to study tree mortality at the landscape scale. We use maps of canopy height derived from repeat LiDAR (two or more scans collected a few years apart) to detect changes in forest structure. Visually, the most obvious changes are caused by large treefall events, which are difficult to study using field plots due to their rarity. While repeat LiDAR data provides exciting new possibilities, validation is a challenge, since we cannot easily determine how many trees have died and we may miss trees which are dead but still standing. I will discuss our progress so far, studying large-tree mortality rates across multiple countries and forest types.</p>

Download Full-text

Hybrid Rootstocks for Valencia Sweet Orange in Rainfed Cultivation Under Tropical Savannah Climate

Journal of Agricultural Science ◽

10.5539/jas.v12n11p40 ◽

2020 ◽

Vol 12 (11) ◽

pp. 40

Author(s):

Danilo Pereira Costa ◽

Eduardo Sanches Stuchi ◽

Eduardo Augusto Girardi ◽

Abelmon da Silva Gesteira ◽

Maurício Antonio Coelho Filho ◽

...

Keyword(s):

Drought Tolerance ◽

Production Efficiency ◽

Tree Mortality ◽

Sweet Orange ◽

Fruit Production ◽

Tree Size ◽

Soluble Solids ◽

High Yield ◽

Rangpur Lime ◽

Large Tree

The performance of Valencia sweet orange grafted onto 41 hybrid citrus rootstocks was evaluated for 11 years in rainfed cultivation under tropical savannah climate (Aw type) in Brazil, in addition to three selections of the standard drought-tolerant Rangpur lime and two selections of Sunki mandarin. Drought tolerance, assessed by visual score of leaf wilting, was directly related to the mean fruit yield. Indio and Riverside citrandarins, Tropical Sunki mandarin and the hybrid TSKC × CTSW-028 were grouped with the most productive selections of Rangpur lime, all of them inducing large tree size, intermediate fruit production efficiency, and high drought tolerance. The hybrid TSK × TR English-CO was similar except by inducing a higher mean soluble solids concentration in the orange juice. A third group of rootstocks induced high yield and drought tolerance, and a mean 30% reduction in tree size that led to high production efficiency, which comprised the hybrids HTR-053, TSKC × (LCR × TR)-017 and-059, TSKC × CTSW-041, LCR × TR-001 and San Diego citrandarin. The tree mortality on Rangpur lime selections was as least as 46%, while more than 80% of trees grafted onto the aforementioned rootstocks survived without visual symptoms of citrus sudden death disease or graft incompatibility. The selected hybrids and Tropical Sunki mandarin also induced fruit quality, mainly soluble solids, superior to the Rangpur lime and, therefore, are potential rootstocks for rainfed cultivation of Valencia sweet orange.

Download Full-text