I checked the Canadian Transportation Safety board website but did not find any studies that split out tree vs water landings. However this report shows some interesting stats for sea plane accidents and could probably be extrapolated for small wheeled aircraft as well. I posted some info but the above link provides much more details.

The Transportation Safety Board (TSB) recently completed an analysis of seaplane accidents that occurred in Canada over the 15-year period from 1976 through 1990. During that period, there were 1,432 such accidents; and 452 people died in 234 of these accidents.

The TSB examined these 1,432 accidents in order to identify underlying safety deficiencies in seaplane operations. Using this database, the Board recently completed a safety study addressing shortcomings in piloting skills, abilities and knowledge.3 This second study deals with occupant survivability in seaplane accidents.

Of the 234 fatal accidents examined, 96 (41%) occurred during the take-off phase, and 87 (37%) occurred during the approach and landing phase.4 In 48% (103) of the 216 fatal accidents where the accident site was described fully in the occurrence records, the aircraft terminated in the water. Less than 10% of the 276 occupants involved in these 103 accidents escaped unhampered from these aircraft.

The circumstances surrounding each of the fatalities were examined to determine the location of the deaths. The fatalities occurred predominantly within the confines of the aircraft cabin.

Of the 168 occupants (including pilots and passengers) who died in the 103 accidents known to have terminated in the water, 118 (70%) were located inside the aircraft, 37 (22%) were located outside the aircraft, and 3 (2%) were found onshore.5 Half of the occupants drowned while trapped in the confines of the cabin. Of the 63 pilots who died, 49 (78%) were located inside the aircraft, 10 (16%) were located outside the aircraft, and one (2%) was found onshore.6

Table 1 indicates that less than 10% of the 276 occupants escaped unhampered from the aircraft cabin.

Table 1 - Occupant Egress (276 occupants)
Number Percentage
Escaped unhampered 23 8
Escaped with difficulty 72 26
Did not escape 121 44
Undetermined 44 16
No information recorded 16 6

The aircraft fuselage often buckled during impact, bending doors and door-opening mechanisms. Aircraft sometimes flipped upside-down, making it difficult to maintain situational awareness. The flaps, which are at least partially lowered on most aircraft during take-offs and landings, may have prevented egress through outward-opening exits. Disoriented occupants may have panicked as icy cold water rushed into the cabin in the seconds following impact. Some of the aircraft involved in water-impact accidents did not have a rear exit, making evacuation for the rear-seat passengers difficult. In these cases, the only egress route for passengers would have been to crawl over the front seats and through the crew door(s). Actuating a simple door-opening mechanism can become an almost impossible task in cold dark water when the aircraft cabin is vertical or upside-down. This may be compounded by the fact that the opening mechanism of some doors is not so simple (with more than one handle or lever to actuate) and few are standard.

Recognizing the difficulties of emergency egress from seaplanes in the water, following a fatal DHC-2 Beaver accident, the TSB recommended in 1992 that "the Department of Transport require that the exits of DHC-2 aircraft be marked clearly."7 In response, Transport Canada (TC) issued an Airworthiness Directive requiring the inspection and rectification of door placards.

A 1988 study conducted by the Canadian Aviation Safety Board (CASB)8 cited eight occurrences in which the occupants exited the aircraft successfully but drowned attempting to swim to shore. The report found evidence that "occupants sometimes drown while attempting to reach life jackets stowed in the rear of the cabin or under seats. Often the aircraft became inverted in the water, suspended by the floats. The occupants then swam to the surface whereupon one would dive back to the aircraft to retrieve the life jackets."