issues with triggers

[Juanito Juanito]

Hi,
I have the following (recursive) table, and I want to apply a triger on it.
Please note that area_pai is the portuguese translation of area_father, and nivel the translation of level.

CREATE TABLE `area` (

`area_id` int(11) unsigned NOT NULL AUTO_INCREMENT,

`area_pai` int(10) unsigned DEFAULT '0',

`nome` varchar(45) NOT NULL,

`nivel` mediumint(8) unsigned DEFAULT '0',

PRIMARY KEY (`area_id`),

UNIQUE KEY `unique` (`area_pai`,`nome`),

KEY `area-area_fk_idx` (`area_pai`),

CONSTRAINT `area-area_fk` FOREIGN KEY (`area_pai`) REFERENCES `area` (`area_id`) ON DELETE CASCADE ON UPDATE CASCADE

) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8


The after insert trigger finds the level of the parent area and increases the value by 1; this new value is seat as the level of the inserted row.

USE `parque_novo_indice`;
DELIMITER $$
CREATE DEFINER=`root`@`localhost` TRIGGER `area_AUPD` AFTER UPDATE ON `area` FOR EACH ROW

begin
declare nivelvar mediumint unsigned;
select nivel into @nivelvar from area where area.area_id = New.area_pai;


set @nivelvar = @nivelvar + 1;

update area
set nivel=@nivelvar;

end

The problem, is that when I run the statement:

UPDATE `parque_novo_indice`.`area` SET `area_pai`='1' WHERE `area_id`='1';

I get the erro message:

ERROR 1442: 1442: Can't update table 'area' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.

SQL Statement:

UPDATE `parque_novo_indice`.`area` SET `area_pai`='1' WHERE `area_id`='1'


This is not the first time I have this type of issues on the area table since I also tried to create others triggers to control the hierarchy of the recursive table area.
Any help would be much appreciated!!
Juanito