Exhibit 12

Computation of Ratio of Earnings to Combined Fixed Charges

	Quarter Ended March 31,						Year Ended December 31,
	2007			2006			2006			2005			2004			2003			2002

Income from continuing operations	$	22,738		$	19,871		$	100,292		$	162,555		$	108,133		$	116,027		$	122,664

Interest expense incurred, net	111,660			104,555			426,662			360,984			305,717			289,912			284,316
Amortization of deferred financing costs	2,564			2,738			8,297			6,499			5,810			5,192			5,260

Earnings before combined fixed charges and preferred distributions	136,962			127,164			535,251			530,038			419,660			411,131			412,240

Preference Unit distributions	(7,424		)	(10,095		)	(37,113		)	(49,642		)	(53,746		)	(76,435		)	(76,615		)
Premium on redemption of Preference Units	—			—			(3,965		)	(4,359		)	—			(20,237		)	—
Preference Interest and Junior Preference Unit distributions	(223		)	(1,099		)	(2,002		)	(7,606		)	(19,490		)	(20,536		)	(20,536		)
Premium on redemption of Preference Interests	—			(674		)	(684		)	(4,134		)	(1,117		)	—			—
Earnings before combined fixed charges	$	129,315		$	115,296		$	491,487		$	464,297		$	345,307		$	293,923		$	315,089

Interest expense incurred, net	$	111,660		$	104,555		$	426,662		$	360,984		$	305,717		$	289,912		$	284,316
Amortization of deferred financing costs	2,564			2,738			8,297			6,499			5,810			5,192			5,260
Interest capitalized for real estate and unconsolidated entities under development	7,866			4,016			20,734			13,701			13,969			20,647			27,167

Total combined fixed charges	122,090			111,309			455,693			381,184			325,496			315,751			316,743

Preference Unit distributions	7,424			10,095			37,113			49,642			53,746			76,435			76,615
Premium on redemption of Preference Units	—			—			3,965			4,359			—			20,237			—
Preference Interest and Junior Preference Unit distributions	223			1,099			2,002			7,606			19,490			20,536			20,536
Premium on redemption of Preference Interests	—			674			684			4,134			1,117			—			—
Total combined fixed charges and preferred distributions	$	129,737		$	123,177		$	499,457		$	446,925		$	399,849		$	432,959		$	413,894

Ratio of earnings before combined fixed charges to total combined fixed charges (1)	1.06			1.04			1.08			1.22			1.06			—			—

Ratio of earnings before combined fixed charges and preferred distributions to total combined fixed charges and preferred distributions (1)	1.06			1.03			1.07			1.19			1.05			—			—

(1) For 2003 and 2002, the coverage deficiencies on both ratios approximated $21.8 million and $1.7 million, respectively. All ratios have been reduced due to the disposition of properties which resulted in the inclusion of those properties in discontinued operations for all periods presented. For 2003, the ratios have been further reduced due to the one-time $20.2 million premium on the redemption of the Series G Preference Units.